andywalter

Not yet. Building my large printer has been on hold, my fault for being too busy & having too many projects on the go.

Thanks, I'll give it a go. I might also remove that "safety" lock preventing you extruding unless the nozzle is up to temp; my extruder uses smooth pinch-wheels which cannot grind the filament, so that's another (much smaller) annoyance to be fixed!

Why not simply buy one? What level of design are you looking for - sub-millimetre drawings of all the parts, including the complex splined-gear which grips the filament? Details of what wire thickness is used to make the spring? (too weak won't feed, too strong will damage the filament). If so you won't find anyone giving you that - there's a lot of work even in these small items! Why should anyone simply dish that out for free? You might find ideas in thingiverse, but if you want the design, it's up to you to reverse-engineer it, if that's what you want. Or simply design your own, why not? People here can help you with design questions & ideas, if you ask precisely. I'm perfectly capable of designing any small spring like that one, but would need to know the outside dimensions & what forces you want at what spring-length. I also cut gears. What tooth-shape did you want? How much are you prepared to pay, if you want someone else to design (a clone of) this for you? Simply asking "I want a design" is much too vague.

Ever since I've had the excellent Ultimaker Controller, I've found it easy to use - except that bl**dy timeout of 15 seconds is driving me spare. I'm perfectly capable of navigating up & down the menus, and can always power of/on if it got stuck. When you're carefully levelling the bed, moving the motors around, tha last thing you need is being pushed back up to the top level, then needing 2 or 3 button-presses & 2 knob-twiddles to get back to where you were 16 seconds ago. Can someone tell me where to get the source code for this - I'll very gladly rebuild it in I assume the standarf Arduino IDE & reflash it. I have this revision, acc to "Control" menu: Ultimaker: _2.6.2 250000_single Jul 4 2017 16:32:03 Anyone else driven to madness by this damn stupid minuscule timeout? I could understand 5 minutes, but the current value is bonkers.

Construction of the first Extruder Carriage is complete, I've made the heat-block down-pipe, brackets, heater block, and a couple of semicircular grippers which will hold the bowden tube firmly to the top of the downpipe in such a way that I can unscrew it easily from thare and not have to pull it out from the extruder-end of the tube. I've made the 4 sets of bearing-blocks & clamps which hold the helical plastic nuts & the 8mm linear bearings. So here are some pics! Front view showing the Bowden-tube gripper pieces. The two semicircular grippers fit inside the thin-walled steel cup, and that lot is held down onto the heater-block downpipe. With bowden tube pieces screwed onto downpipe View from above, gripper pieces sitting inside aluminium screw-cap Finally! First sight of the whole thing assembled. Everything moves freely and feels fine so far. The outer plastic pieces locate the helical nuts, the smaller pieces just inside sit on the standard 8mm rails. This assembly weighs 317 grams.

Lars, any rotation about a vertical axis, as seen from above, should be prevented by the X and Y "flat" rulers. Any rotation as seen from front of UMO about Y axis should be prevented by "vertical" ruler going in X direction. Similarly rotation about X axis prevented by the other vertical ruler.

I have a UMO not UM2, but didn't find anything I much liked either. So I've 3D printed my own in ABS, in 2 bits. It uses the original single fan mounted in the original position. Aim is to get uniform air flow from all sides, trying to miss the tip of the nozzle but hit the hot plastic just below it!!! The flattened torus is hollow, and couldn't have internal supports, so the model is sliced horizontally through the mid-plane of the torus. Then the sheared-hollow-cone bit is printed the other way up with full supports, and the tiny "cap" which is the bottom half of the torus is also printed upside-down with supports. Clean the supports out, Swiss-file the air-holes to clean them and Acetone-weld the bits together & it's ready to go. I made the air holes to be angled-in, and the holes furthest from the main conical supply are slightly larger in diameter, as the air pressure will be slightly lower at the "far" end of the torus. It seems to work fine so far, ABS hasn't sagged or anything like that. Top view. It's a bit tricky getting the nut onto thread through bottom-right hole. Next one I do will have a suitable cutaway-recess in the large sheared-cone section.

Am not familiar with Marlin code, but as far as I can see, the AD597A uses a K-type thermocouple, and gives a reading of 1V at 100C, 2V at 200C etc up to 4V at 400C should be no problem, even up to 1200C providing the input supply voltage is at least 12V plus a bit. Farnell.com has a datasheet on the chip. This extract says Since the output can only swing to within 2 V of the positive supply, the usable measurement temperature range will be restricted when positive supplies less than 15 V for the AD597... . So if you give the chip a 5V supply, ti can only output at most a 3V signal corresponding to 300C. Suggest you check what voltage it's getting, and maybe give it 7V or even a bit more. Also make sure you're using a K-type thermocouple, not some thermistor or other J-ytpe or whatever TC. I replaced a defective AD597A on my UMO, and in the process found that mine gets a 5V supply voltage. Enough for my ABS at 260C.

We can do a very approximate ballpark capacitance figure as follows: C = K x E0 x A / D (e.g. see http://www.daycounter.com/Calculators/Plate-Capacitor-Calculator.phtml so put in an area of 100 mm2, a distance of 1 mm, K=1 for air is accurate enough, and yo get a capacitance of 0.885 pF. This is pretty d*m small. Supposing you print 2x20x20x20 cubes, I'll take it that's 1x20x20x20 = 8000 cubes for one plate of the cap, so the maximum surface area you can get is 8000 x 6 cm**2 for each "plate". 1mm is my assumed distance between one plate & the nearest bit of the opposite polarity plate. so that's an area of 4800000 mm**2. Stick that in the calculator and you get 425 pF, or about 0.4 nF. But a lot of your cubes won't be able to expose 6 faces to another cube, as they will need a face to attch to the next one. End cubes will be able to expose 5 faces. So multiply than guesstimate by 5/6. This formula reveals that what matters is the area exposed to the other plate, not the volume. Also halving the air gap doubles the capacitance. So cubes are the wrong thing to be printing, you want flat sheets. And you may as well try to use both sides of any sheet you print. So what you want to aim for is rather like the tuning capacitors found on 1930s valve radios, I've knocked up a quick pic here. Yellow bits are fixed, red bit rotates, and the more red plate gets sandwiched between yellow ones, the greater the capacitance, so you can alter the frequency of a tuned circuit. You could do something similar by printing tall thin flat plates interleaved, something like this: The narrower the air-gap (d) is from one plate to another, the greater the capacitance. But get it too small, a higher voltage could arc-over (say 10,000 volts/cm in air maybe might arc) and it's toast. And maybe dust accumulating might short it out a bit.

I'm building up a small collection of these, hoping some project will come up that needs them. But maybe I should just take them down to my local recycling centre when I take other stuff there, and put them in the energy recovery bin?

Ok, some of you may have seen my other appends in this thread https://community.ultimaker.com/topic/1114-throw-away-your-short-belts-direct-drive/?page=9&_fromLogin=1 , but it's time I had my own thread & stopped hijacking that one! I want the best quality I can get from my UMO, by which I mean round things really should be round, and there should be no ringing/overshoot at sharp corners etc. This requires 3 things; zero backlash in the X & Y drives, the highest possible rigidity, and the lowest friction. Backlash means you get flat-spots in round objects where the step motor reverses direction but the print head fails to move until the backlash distance has been moved. Ringing, or overshoot, is a symptom of the drive system being flexible, e.g. press lightly on the side of the print-head with your finger, and watch the ( hopefully cold! Don't want Elfin Safety complaining...) nozzle move. So if you decelerate hard at a corner, the printhead's momentum can carry it beyond the desired stopping distance. Then it bounces back towards where it should be, etc. Any friction there might be in linear bearings in the printhead can make things worse, as it may help the slowdown, but it hinders the accelerate-away at the next corner causing increased forces on the drive system so less positional accuracy. Friction, a.k.a. stiction, creates a kind of backlash-like effect, where the final resting place can be offset from the desired one. The more rigid the drives are, the less positional offset error we'll get due to some small unavoidable friction that we're bound to get. I've already eliminated the rubber belt drive, replacing this with a helical rolled steel shaft which drives a pair of plastic nuts. These nuts are tightened very slightly against each other to eliminate backlash; I will be altering this slightly so the tightening will be done by a small tension spring as the nuts move, rather than being clamped as now. Details to follow when I get round to that. Others have noted that the 6mm dia rods going through the printhead are rather flexible. There's a suggestion to replace with 8mm rods which would be 3.16 times stiffer, but would weigh 1.78 times as much. So to improve that, hollow 8mm shafts can be used which keeps the mass down, but presumably cost a bit more. I looked at getting Misumi hollow rods in UK, but they don't sell to you unless you're a company, and I'm not going down that path of complication just for 2 rods. I couldn't find anyone else in UK making these at anything under 16mm diameter. So I've made my own system, using 4 cheap-but-accurately-made steel rulers, and 24 flanged ball-bearings. One drive axis uses 2 rulers; one ruler is laid flat and controls the horizontal positioning, the other is laid on edge and holds the printhead at the correct height at all times. Each ruler is supported by 2 flanged bearings along one top edge, spaced about 30mm apart with the flange on the far side of the edge, and two more similarly placed with flange on the near edge. In the middle of the opposite edge are 2 more flanged bearings. So the flanges stop the ruler flexing sideways & falling out. The two bearings on their own are mounted on a sprung slider, this eliminates backlash in this part of the drive. The greatest forces will be on the 2 flat rulers, as these do the X & Y acceleration, and this acceleration must not be enough to overcome the tension springs. I've measured my X & Y tension springs at about 250 Grams weight, call it 2.4 Newtons. The rulers on-edge simply take the weight of the printhead, so these won't really need backlash removal, and these tension springs are 150 gr weight so about 1.4 N. The force needed to push the flat ruler through the bearing-clamps is tiny, about 10 gr weight, or 0.1N . The force needed for the on-edge rulers is about 1/2 this, so 0.05N. The mass of the print head so far is 63 gr, this is the plastic shown in pics below plus all 24 bearings. The 4 rulers weigh 70 gr, they're original length of 330 mm, and will be cut down to about 270mm so should reduce to nearer 60 gr finally. Rulers are 13mm wide x 0.6mm thick, very flexy! Given a max tension of 1.4N as we accelerate the printhead, one axis , say the X axis, has to accelerate 2 rulers printhead, so about 100 gr so far. If that was the total final mass, 1.4N could accelerate the 100 gr at 14 m/sec**2, or 14000 mm/sec**2. I'm currently running Cura at 750 mm/sec**2, so there's plenty of tension and I won't be in danger of overcoming the tensioners, even when the heater block & tube & fan & support plates etc are fitted. I might even be able to fit low tension springs to the X & Y flat rulers and reduce the friction by another 5 gr weight per axis! Here's the rigidity & mass calculation to justify this design as potentially "better" than 6mm circular rods: (I don't yet know if this works!) Stiffness (I) of 6mm dia Rod is Pi * (r**4) /4 = 3.14 * (3**4) /4 = 63.6 Stiffness (I) of 13 * 0.58 mm Bar is b * (h**3)/12 = 0.58 * (13**3)/12 = 106 so it's nearly twice as stiff as the rod (but only in 1 plane). Mass of Rod is proportional to X-sectional area = Pi * (r**2) = 28.27 Mass of Bar is proportional to X-sectional area = b * h = 0.58 * 13 = 7.54 but I need 2 Bars to replace 1 Rod, so total Rod X-sectional area = 7.54 * 2 = 15.1 So my stiffness increases from 64 to 106, nearly double, and my mass reduces from 28 to 15, almost half. There's some added weight from the bearings, washers and retaining screws, but these are small, 3mm i.d. x 7mm o.d. flanged FR683ZZ, 6 per ruler. I save weight by removing the 6mm linear bearings in the original head, so I think bearing masses will cancel out. Cost looks cheap so far. Plastic bits printed in ABS on my UMO. Springs from my recycled scrap bin. Bearings cost me £13 for 30 on eBay. 4 Rulers from kinexmeasuring.com cost me £15 which included shipping & £0.37 bank cost converting £ to Euros. So under £30. Problems so far are slight. 1: The rulers have engraved markings, so I've used a very fine Arkansas oilstone (my ArkanStone! )to remove any burrs and get the marked face really smooth & polished. The bearings are from China, and have some tiny remaining swarf sitting in the grooves of the seals, so these need cleaning out. 2: The bearings have a groove where the flange meets the outer race, and this is wide enough for the edge of the thin ruler to fall into. So I've made 0.6mm thick washers to fill this groove. 3: The inner race on these bearings doesn't stick out further than the flange, so either you need to add small spacer washers, or you can do as I did which is machine 0.2mm off the 0.8mm thick flange to provide clearance to stop rubbing & friction. Only 13 of my 26 bearings needed this doing. 4: Each bearing has at least one 3mm i.d. washer transferring the clamping force to the plastic, and these are stamped out 0.5mm thick, so are very slightly dished. I've been careful to assemble these with the sharp, burred edge against the plastic, and they do not appear to rub against the outer race when put this way. Now for some pics! I'm finding it very hard to put these where I want them in the text, and can't see how to rearrange them in an edit, so apologies for the mess following. Two design schematics showing the basic idea. Flanged bearing FR683ZZ as supplied. Bearing with 0.2mm skimmed off outer race. Plastic washer fitted. Original bearing is 3mm wide. Flange is 0.8mm wide. Ruler edge falling into the outer race groove. You can also see the raised surface of the ruler where the 1mm markings are. 0.6mm washer fitted to hide groove. 0.6mm washer fitted to hide the groove. This bearing has been skimmed. Slider parts before assembly, top & underside views Slider parts fitted together, top & underside views Schematic view of how bearings & rulers will go... ... final assembly. Some washers later got trimmed a bit more as too large outer diameter. Reverse side of slider. This is X or Y axis, stronger springs out of my recycle store. You can see a small snake-shaped S-piece forming a loop for the spring. This has half a halved-torus to reinforce the contact point and make it easy to print flat with no supports. Front side. Bearing screws at the bottom are loose. Edeg on view shows where ruler will go. Note thinner flanges where flange is close to plastic. Smaller of the 2 ABS printed chassis parts. Final assembly without rulers in. The item just above fits at the left side, dropping downwards. With rulers fitted. You can just see a tiny 1/2 mm gap opening up where the flat ruler in the middle at the bottom has gone through the slider.

Yes the filament will rotate between the driving wheels & melt zone, and you've got a good point there. I would hope that ABS would survive this, as usually it will be molten at hot end when moving like this, so with luck the colder & solid section will rotate freely inside the PTFE section, and the hot gooey rest of it is fine. Some day I want to try out metallic filament which can be fired in a furnace (& yes I've made my own mini-furnace, 1"x1"x2" high! some years back), and I think that stuff might be brittle, so I really like your idea of a rotating hot end! It hadn't occurred to me, so thank you for it! I read that these metallic filaments don't like bowden tube feeders - maybe there's too much push & pull reversal going on? Hmmm... Another advantage is it eliminates the (small) torque trying to bend the rectangular drive-rods. And if they're Carbon Fibre, with rollers running on them, I have no idea whether CF likes little wheels running up & down it, so it's best to minimise all those loads on it! I have some miniature ball-races in front of me for another project, they're 15mm i.d. & 21mm o.d., 4mm high, so these would be perfect to have a pair holding the downshaft.( Planned downshaft is 10mm o.d., I could reduce this to 8mm, just, using extra-fine thread, or I could go up to 12mm o.d. with tons of metal to play with - I want minimum metal for low weight, maximum diameter for rigidity as nozzle is a few cms away from bearings, but the metal wall must not be too thin. I have space to play with these values). 10mm o.d. downshaft looks ok; I will use 0.75mm pitch thread, that cuts 0.46mm radially call it .5mm, so 4.5mm radius is outer radius of solid bit; allow 1mm wall thickness leaves 3.5mm down to 1.5mm filament for the PTFE sleeve, so the PTFE sleeve has wall thickness 2mm. I think this will work nicely. If the hot end rotates, you must be sure the nozzle tip is concentric with the bearings. So I would have a circular ring sitting inside the bearings, lets say 1mm i.d & 15 o.d. to fit mine, and I'd put 3 grub screws through that at 120 degrees, so by adjusting these 3 & clamping the down tube, I can adjust the eccentricity down to zero. The test would be to disengage the rectanguler drive rods, and print straight lines in X & Y directions while waggling the rotation by hand, and looking to see if any waves appear. Or simpler may just be a dial gauge on the cone of the nozzle. I can clamp the downtube in the bottom bearing with 2 thin washers and locknuts, this bearing can take the main vertical forces. The top bearing can have the 0.5mm gap all round with the 3 grub-screws, and that's enough adjustment to correct for any slight errors in runout at bottom bearing & the nozzle+heater block. I really like this idea; it does mean I need to find a bit more space around the heater block to let it swing +- 30 degrees or so, but the axis of the downshaft will still be inside my 50x50mm "box" carriage, so it will be fine I'm sure. I'll see if I can add all this to the current design, should be able to. ================== Update to design pics above: just realised I stacked my layers wrong - oops! The brown ruler should be mounted above the blue one, similarly the flat pair below. I want to get the end-points of these rulers as close as poss to their 8mm rods. Just a small editing job, swap the X & Y positioning coords, and negate them.

Bevel gears etc are a complete no-no, I'm sorry to say. The last thing I want is any more backlash, = rattle, noise & unpredictable inaccuracies. Mounting 2 step motors on gimbals in one corner means all you're doing is using a long lever to turn them a small angle, about a pivot that runs through the centre of gravity of the motors+gearbox. This is actually a tiny force that's required, far less than the force required to accelerate & decelerate the "ideally" placed MakerBot Replicator motors on top of the nozzle carriage, and probably less than the force required to accelerate the mass of the transfer shaft + 2 bevel gears that you suggest. The gimbal vertical axis doesn't have to be close to the corner of the HBP either; you can hang it as far outside the UMO corner as you like; the further out you place it, the lower the rotational acceleration when nozzle is v close to that corner (the worst case for forces, but the best for extrusion control!). My steppers are already well outside the UMO case; I'm happy to hang the extruder steppers maybe 10 to 15 cm out from the UMO corner. My extruder gearbox alreads reaches 17 cm out from the back. You can't get much simpler than a shaft going straight from extruder motor through middle of the actual wheel driving the filament; if it needs a reduction gearbox stage, the fewer of those I have, the better. And I would make that backlash-free by using one large dia cylinder clamped against the stepper shaft, rather than using gear teeth. The forces are low enough to do that, as the tangential force will be maybe 3x less than the tangential force where the clamp-cylinder forces the filament into the nozzle. And in fact putting the gimbal out from one corner isn't ideal, it means the longest transfer shaft. Putting it out from 1/2 way along one axis make better sense, by a tiny amount. Reduces the distance to the (2) far corners opposite; you increase the angular sweep a bit, but you also reduce the max acceleration, as the mid-point of the near axis is further away from you, than it would be by putting the gimbal diagonally out from one corner. That max acceleration is the thing you want to minimise. My nozzle is at the front of my nozzle-carriage, so ideally gimbals+extruder go at back of m/c, which is already where my gearbox sticks out a long way, so this fits nicely.

Hopefully this is my final layout for the 4-Ruler-Guide replacement fo 6mm rods project. Guides are now single-sided = slimmer & lighter, and by juggling the widths & exactly where in the middle I put the anti-backlash tensioner wheels, I've managed to overlap things nicely while still keeping decent clearances. It's 6mm less high than the prev design shown above, much neater layout leaving front-right corner completely clear, and the X/Y motion-control rulers are level with top of nozzle & top of heater block, so I'm really happy so far. Various views:

Yes indeed, I remember someone doing that! But my extruder mechanism is built on a substantial piece of aluminium plate, it's rather large & heavy as it uses dual geared clamp wheels. Besides, I'm thinking about eliminating the bowden tube using that neat ?ZeroG? idea where the extruder motor(s) are placed in a gimbal at one corner, with splined shaft reaching across top of UMO, and all you have then is a clamp-wheel-gripper thing on rotary mount directly above nozzle shaft. I'm going to have a strong 10mm dia threaded shaft, easily enough to take something added to the top of it. I've been impressed by the ability of Replicator 2G to retract very cleanly, thanks to having extruder wheel mounted immediately above the nozzle, not at far end of elastic rod & tube. So I'm thinking of having 2 step motors counter-rotating (maybe geared down as my present extruder is), in gimbal at one corner, 2 carbon-fibre square tubes reaching across UMO and passing through centres of my 2 grooved aluminium clamp-wheels. These wheels will have 4 small but wide roller bearings in the middle, running on the 4 faces of the tubing. Should be torsionally very stiff indeed.

Having slept on it (I do all my best work in my sleep! ) the above layout needs to be improved, and simplified. I tried to minimise overall height & keep it compact at all costs. Tesult is a spaghetti mess of internal support beams, and it's difficult to route the heater & thermocouple wires to where they won't touch some sliding item. Latest thoughts: 1) It's desirable to get the plane of the 2 X-Y horizontal-motion Guides as close as possible to the height of the tip of the nozzle; this will minimise twisting torques trying to get nozzle out of vertical. So the above layout will be inverted, to put the flat sliders at the bottom. The lower one will be level with the top of the nozzle's thread. 2) Height doesn't matter so much; we have plenty of vertical space above. 3) Want to keep the vertical Guides close to the horizontal Guides, esecially in X-Y directions, so the attachment to the blocks running on 8mm rods isn't huge. Not a problem for these blocks to get a bit taller than now. So I will stack vertical Guides above the related horizontal Guides. By interleaving the X-axis Guides & the Y axis Guides, this will keep the design more regular, and the 8-mm rod blocks more similar. So I will have an L-shaped design, looking from above, with one corner of the Carriage completely empty. I can then route wires up that corner, well away from the moving parts. 4) Want the nozzle at the front of the Carriage, I like to see what's happening & have access to remove plastic build-up with tweezers etc. So one branch of the L-shape goes at the back, the other will be at one side, but which? 5) My bowden tube gets a bit stretched when nozzle is at front-left of UMO, so want the nozzle as far right & back as poss to reduce stretch. Won't put at back as visibility more important, but can put it at the right side. So the Y-axis sliders will go at the left side of the new Carriage. From bottom to top, I can choose whether to stack the guides X-horiz, Y-horiz, X-vert, Y-vert , or Y-horiz, X-horiz, Y-vert, X-vert. As UMO 8mm X-rods are above the Y-rods, it makes sense to choose X-axis Guides above Y-axis. Decision made. I already have my X-axis spiral-screws above my Y-axis screws, for that same reason. It all fits. New design pics later today I hope.

Yes. Almost completed the initial layout design, here's a piccy. Uses 4 Ruler-guide-mechanisms, these are T shaped and fairly thin. Top Ruler-Guide is the yellow plates + orangy slider + 6 grey bearings + 6 M3 capscrews+nuts&washers. (Just spotted 2 nuts need raising!). It's the X-axis direction guide controlling the Y-axis motion. Ruler-Guides have pairs of flanged bearings, 3mm thick, 7mm dia on the running face, 8mm dia at the flanges. Two flanged bearings go side-by-side, with flanges reversed to give me a sort of double-flanged bearing. 3 of these pairs per ruler. The central pair is mounted on a slider which has a short tension spring. So will need to measure strength of that spring & calculate what acceleration it will take without introducing backlash-due-to-acceleration-forces. So zero backlash. Big yellow rod is M10 stainless steel shaft, drilled 6 dia, filled with PTFE plug then drill that 3mm dia to make my thermal block. Locknut at very top stops rotation, and the top aluminium square chassis has 6mm thick threaded hole for the locknut to clamp. Bottom end is simply screwed very tight into the heater block. Might put a clamp as well. Orangy thing at top is the slider plate, with bent thin yellow strip with hole in for tension spring (cylinder). Haven't put in retainer screw at far end of spring yet. Yellow plates at back are rigidly bolted to the pale cyan aluminium top chassis plate. The other 3 T-assemplies are brown at left, the UMO Y axis direction vertical-load slider. Blue is the X axis direction vertical load, Green is the Y axis horizontal motion controller. Pale pink square is visual guide, 50mm square so same area as standard UMO. A bit more ro add yet, needs support for Extruder Column at the bottom to stop it shaking around. I don't think need cooling fins on that, but there's space if I do. Not sure how to fit my cooling fan in yet!

Pointer to append I made, planning to replace 6mm rods by a construction of thin-but-long steel rulers! Almost twice the stiffness & half the mass of the 6mm rod, that's my target. Details here: https://community.ultimaker.com/topic/1114-throw-away-your-short-belts-direct-drive/?do=findComment&comment=197722

latest update. I've now repaired the temp controller, turned out that the AD597A chip was giving out incorrect voltage, telling the Arduino that the head was hotter than it was. I've also re-made the fan-shroud so the cooling air in now directed more downwards than before, hopefully it's not cooling the brass 0.4mm nozzle at all. I'm still not happy with the way my laminations stick together, so am experimenting with 260C extrusion, and may have to slow down to less than 50mm/sec. On the rigidity side of things, I'm going to replace the original UMO printhead with a new design which will try to get the nozzle much closer to the same level as the present rods. I looked at getting hollow 8mm shaft, all I could find was Misumi, and as far as I can see (in UK anyway) they only sell to companies, not individuals. So I'm going to do it very differently. I've ordered 4 steel rulers, 300mm x 13mm x 0.58mm thick, from Kinexmeasuring.com. I hope these are hardened steel - the company looks decent quality judging by what they sell. 2 of these will replace one circular 6mm rod; one will be laid "flat", and one "on edge" or vertically. So it's a sort-of L-shaped angle-iron going across the UMO. The ends will be clamped to the plastic helical-nuts on my direct-drive shafts. Small ball-bearings will be wheels & guides, so the ruler mounted edge-on will provide stiffness in the vertical plane, keeping the height of the extruder nozzle correct. The ruler mounted "flat" will have similar bearings, and this one will keep the horizontal movement of the extruder-head the same as the 2 helical nuts. Here are the calculations about stiffness & weight: Stiffness (I) of 6mm dia Rod is Pi * (r**4) /4 = 3.14 * (3**4) /4 = 63.6 Stiffness (I) of 13 * 0.58 Bar is b * (h**3)/12 = 0.58 * (13**3)/12 = 106 so it's nearly twice as stiff as the rod (but only in 1 plane). Mass of Rod is proportional to X-sectional area = Pi * (r**2) = 28.27 Mass of Bar is proportional to X-sectional area = b * h = 0.58 * 13 = 7.54 but I need 2 Bars to replace 1 Rod, so total Rod X-sectional area = 7.54 * 2 = 15.1 So my stiffness increases from 64 to 106, nearly double, and my mass reduces from 28 to 15, almost half. There's some added weight from the bearings, but these will be as small as I can find, something like 4mm i.d. x 7mm o.d. flanged, probably need 7 or 8 per ruler. I'll save weight by removing the 6mm linear bearings in the original head, so I think bearing masses will cancel out. Now my head is reaching proper temperatures again, I'll re-do the box-tests above. I've discovered, as Torgeir said, that the "dodgy corner" is where Cura makes a 180-degree U-turn and goes back the opposite way it approached the corner; I had a minimum 5 seconds/layer time, and the gcode had a time-delay inserted at this corner, so I think that was messing my prints up. I've reduced this to about 2 secs/layer, so the delay has gone, and the corners now look much better. Pictures later when I've got the UMO as good as I can.

Torgeir, my 6mm shafts are the originals, as is my UMO head. I think I've pretty-much eliminated any resonance in my m/c from the belts, as I don't use them! The spiral shaft+plastic nuts is a very rigid system. I suspect hollow 6mm shafts would be too flexible. Hollow 8mm shafts does sound interesting though. Very interesting about the head C og G being so low; I'm starting to think about redesigning this lot using 8 mm shafts placed really low, as close to the table as possible. Then the nozzle+block could sit in the corner of the 2 shafts, rather than dangling vertically below the intersection area. My HBP can easily go 40mm higher. Maybe it's time to think about making one of those extruded-aluminium frames, and also about keeping the heat in the print-area like MakerBot does with the lid & enclosed sides. Sometimes I've wrapped a towel carefully round my UMO on large prints to try to keep everything warm, and it's not the ideal solution! In Cura I've reduced all the accelerations to 750 mm/sec**2. This may be the biggest factor in reducing my ripples. But I do need to improve my positional accuracy, and the flexy head you've discovered won't be helping my accuracy.

Torgeir, a few thoughts: Wider belts would be nice to try, but the increases the effective mass of the printhead! And the wider pulleys add inertia. I have my original UMO belts, just weighed these on my calibrated lab scales, all belts are 6.5mm wide: Long belt B300MXL weighs 5.900 gr Short belt "B100 MXL" weighs 1.744 gr lets call it 1.75 gr. Each axis has 2 x Long + 1 Short so that's =13.55gr mass. Call it 13.6 gr. I also have the aluminium pulleys, so could do an accurate inertia calculation on those. But it's probably good enough to simply weigh them; as most of the inertia comes from the outer dia where the speed is close to the belt speed, and that's also where most of the mass is, this will give a good estimate of the equivalent mass, after converting rotational moment of inertia to linear. Each axis has 6 pulleys, these weigh 35.004 gr, so approximate this to 35 gr linear-equivalent mass. 13.6 + 35 = 48.6 gr so call it =49 gr for belts+pulleys. So a double-width set of pulleys & belts would add about another 45 gr to this. (screw-hub & grubscrew not duplicated) I've weighed the plywood blocks plus bolts & nuts + oilite bearings which clamp drive-belt to the 6mm rods, 2 of these per axis. 6 blocks + bits weigh 54 gr. This mass only affects the belt-resonance deflection, not the 6mm shaft deflection. So we're now up to 49+54 = 103 gr for the belt load. Next we need mass of the central printhead thing, plus equivalent mass (inertia) of the long 8mm rods, mass of 6mm rods, and inertia of the stepper rotor. Anything I've missed? I need to calc the elasticity of the 6mm shaft under bending; knowing this, and the printhead mass, we can calculate the out-of-straight deflection distance of the middle of the 6mm shaft when the stepper is accelerating at whatever mm/sec**2 we set in Cura's speed controls. That should be the max deflection we get from resonance due to a 90 degree sharp corner, no? Should we measure the belt-stretch & tooth-deflection elasticities as well, because those have to accelerate the mass of the 6mm shaft + blocks, as well as the printhead, so I think the drive belts might be as springy as the 6mm shaft maybe? If we measure the peak-to-peak distance of the resonance ripples after a sharp corner, and we know the travel speed, we can calculate he resonant frequency. That should line up with some combination of masses and elasticities form the above bits. There could be several things happening: 1) Suppose the step-motor has a large inertia, and a smallish stationary holding torque, and everything after that (belts, oilites, 6 & 8mm shafts, printhead) are of negligible mass and infinitely stiff in comparison; then we should see a resonant frequency & amplitude matching a step-motor oscillation. 2) Suppose the step-motor is perfect (doesn't oscillate & stops perfectly at the sharp corner with zero overshoot and has infinite stationary holding torque). Also suppose the drivebelts & pulleys are perfectly rigid & zero mass; then we are left with the 6mm shaft bending acc to the mass of some of the 6mm shaft itself ?half? plus mass of printhead. Hopefully would have different freq & amplitute to case 1) above. 3) Suppose step motor is perfect, 6mm shaft is perfectly rigid, and it's the belts that are flexy. We should see a different frequency, I hope, based on mass-equivalent of 2x8mm shaft + 5 pulleys + 2.5 belts, then the added mass of 6mm shaft + blocks + printhead, all oscillating, depending of stiffness of these belts. (Motor pulley is perfectly stationary, and we should probably halve the short-belt mass, as one end is locked motionless!). 4) Real life will be some superimposed combination of the above, or maybe the belts are flexy-but-well-damped, so it's all a bit too complicated to calculate. What I can do is print the testcase on my UMO, and use identical feeds & speeds as you use on your m/c; maybe if we crank the speeds up high we can get the ripples really high amplitude; then if I have ripples with stiff drive & 6mm shafts, and you have none with belts & stiff 8mm shafts, that might really prove what's the wobbly bit. I think we need to agree a set of speeds & accelerations & get matching Cura profiles as far as possible. It might be possible to design a test-shape that deliberately provokes the worst accuracy & maximum rippling, once we know some frequencies & stiffnesses! Sounds like a lot of fun!!

Hi, Torgeir (& Lars86), Nice to see your 50mm square box. The "bubbly corner" is interesting, as you're only seeing that effect for half the way up the corner. I get a similar defect on my UMO, Cura 3.1.0. Background digression, hopefully useful info for someone: I've just discovered that my printhead isn't actually getting anything like hot enough. Thinks it's 250C but actual is 175C. That's why my prints are weak, and not glossy. So the above pics and tests will need re-doing when I've repaired it. Spent a couple of days analysing it & studying the heating controls, and my temp sensor chip AD597A is defective, replacement chip + spare on order (RadioSpares 230646). I'll make a better thermocouple & relocate the tiny preamplifier board holding the AD597A & put it near the motherboard, it has a built-in standard-temperature generator so "knows" what the room-temperature is; surely it can't be good to have it sitting above the heated nozzle head gently roasting if you leave m/c on preheat for any length of time, plus that board, wires, connectors, led, is all adding mass to printhead. I will now make a super-short, super-light thermocouple & take wires & preamp elsewhere. I prefer thermocouples, rather than thermistors. AD597 calibration accuracy is +- 4C at 60C, and it's meant to be laser-trimmed to be accurate to within 1C over range -20C to +350C (seems to be a bit of conflict in the docs as I read them) so, whatever, should be within +- 5C at the very worst. At any room temperature the machine is in. New thermocouple will be super-short bit of stainless steel tube maybe 4mm long, drilled, RadioSpares 6212158 K-type welded bead thermocouple wrapped in a tiny bit of Kapton tape to insulate, crimp the end up & poke it in the heater block 3mm dia hole. The Existing thermocuple is perfect, but I htink I can reduce mass with a new one. Arduino Mega 2560 is doing a perfect job, converts the preamp's output of, say, 2.40 Volts to temp=240C. Couldn't be a simpler conversion, and the Arduino screen temp-display exactly matches my digital voltmeter measuring that voltage signal from preamp. Back to the test-shape. I wonder if the bubbly corner only extending 1/2 way up the wall is connected with whether the print at the zig-zag bit fills in the hole (lower half), or leaves a groove (top half). It seems too much of a coincidence that both our prints have rather different top & bottom halves! The top half of all our prints looks better than the bottom half; there's no infill to be done at the zigzag place. So top half is just printing continuous walls sections, immediately before, and after, a Z-step. If, like me, you have Cura's Z-step Place set to Nearest, then the printer hardly needs to stop moving as it Z-steps. Even if you have a fixed place set, the nozzle is going to be in the right place after printing 2 walls, inner & outer. On the bottom half, there's an infill to do. My print-sequence is infill-before-walls, inner-wall, outer wall, Z-step, infill, inner-wall, outer-wall, Z-step, ... so I'm wondering if on the bottom half of the print, a side-effect of the extra extrude, & maybe a retract, to do the infill, means your PLA feed gets slowed-down a bit compared to the top half, and the hotter PLA is outgassing/boiling/oozing a bit/whatever at that corner? Maybe my UMO does my inner wall, outer wall, gets to a uter corner, then traverses across to the other side of box to to the infill, and it's that traverse which is tearing/pulling my almost-solid too-cool filament with it? I will know more once m/c is fixed & I'll watch the print sequence like a hawk next time !!! Info about a MakerBot 2X Replicator making the same box resonance-test-shape using default 0.2mm settings: I'm fixing one for a school nearby, just used default ABS at 250C. That's sliced with MakerBot Desktop, and has a lower-half wall section immediately after the filled-in zig-zag bit, where the inner & outer walls look as if someone has touched the wall with sticky tape & dragged the surface a bit, leaving it a rough & a bit like sandpaper. A sort of "torn" roughness. I think this m/c is set too hot, and during the slower zig-zag infill maybe the plastic is oozing out a bit, or overheating a bit more as the tip stays in that place for maybe a second more, and immediately after that, when it does the inner wall, the plastic temp is a bit wrong, maybe too runny, and it's tearing rather than melting & blending in nicely. But the print on this m/c comes out really strong, and nice & glossy, as it should. My UMO obviously is nothing like that, and that's what made me realise my nozzle temps have been slowly falling over time without me realising what the problem was! So I now have a few reels of other ABS which weren't working at all, while the Voltivo ExcelFil I have been managing with (very high quality stuff, no nasty phthalates etc in it by the way!) presumably has a slightly lower melting point; Voltivo Black ABS is recommended to print between 211C & 219C; I've been forcing it out at 176C or close to that !!!

Ok, so I think you have the 4x4 shaft going through the bondtech extruder, and that bit has some gearing which drives 2 clamp wheels, or something like that. I think I'd want to roll my own, using 2 separate parallel drive shafts, so avoiding having any gearing in the printhead. My 2x10 rods would just go straight hrough tthe middle of my pinch wheels, and if they have to grow a bit in diameter to make everything fit, they can.

I love your idea! But do you have to use 4mm square section? What about maybe 2x10mm section. https://www.cromwell.co.uk/shop/materials-and-maintenance/ground-flat-stock/precision-ground-flat-stock-2mm-x-500mm-gauge-plate-01-tool-steel/f/63500 supply 2x10mm in 500mm length. Ok this is annealed, not yet hardened, but could be hardened after being machined to size. Hardening won't alter the torsional stiffness, all it will do is increase the max torque possible, and reduce wear from the wheels running up & down it. But I don't hink that extruder loads & torques will be very high at all, so personally I could live with annealed. I've done some torsional stiffness calcs, 4x4mm square rod J' = 36, 2x10mm rod J'=23.3 so it's 2/3 the stiffness of 4x4. The weight is also greater, as 2x10 20 is > 16, but not hugely heavier, especially if you can counterbalance the whole thing. My own homebuilt UMO extruder uses 2 smooth aluminium wheels 30mm dia with grooves in to stop filament sliding out sideways, these wheels are sprung together as well as both being geared to give drive. Advantage is I don't grind the filament if anything slips. But the bowden tube is not ideal and I have to retract about 4mm to avoid oozing, and I'd like to reduce that & get better flow. I'm now wondering if I can get 4 small outside-diameter roller bearings 10mm long, 2 per wheel, and these would clamp each side of the 2x10 rod & be located in the middle of the wheel. FWIW stiffness of 3x3 rod has J' = 11.4 . Formula for square rod is 2.25 x r**4 courtesy of roymech.co.uk

It usually pretty easy to reverse the motor direction. If it's like my UMO, you have 2 pairs of wires out of the motor. Take one pair (leave the other alone) and swap the 2 wires over. May need some delicate poking a tiny, tiny screwdriver into a plug to get the pins out, whatever. Or snip the 2 wires a few cms from the plug, swap them over & resolder, having put a length it heatshrink sleeving on first to cover the joins & seal with hot air gun.