Jump to content

Fixing Pulley Innacuracy


Recommended Posts

Posted · Fixing Pulley Innacuracy

Im going to buy some new belts and pulleys, although my print quaility is now much improved generally

its still not as good as it could be.

When I move the printhead around by hand, it makes a sounds like "vvvvvvVVVVVvvvvvvvVVVVVvvvvvVVVV"

Its movement is not even across the bed XY area. This can be traced to the pulleys being eccentric, which is

parcially because they are cheap in general but mostly because of the grub screw attachemnt method. Which is unreliable, damages the shafts and causes the pulley to rotated off centre (see attached image).

Anyway, im going to buy some of these pulleys, which look much more sensibly designed to attach concentrically to a shaft. Of course they will cost way more than the standard ones...but Im happy to pay.

http://www.cmtco.com/pdf/cmt_primer.pdf

Anyway, I will get back with some results in a while, but in the mean-time perhaps someone has had similar ideas or tried something like this and can share the results ?

C.

EDIT, I tried to align the pulleys so that they are all eccentric at the same angle together..which did help a little bit. But clearly its also the tolerances of the pulleys as well as the grub screw cause thats the issue.

  • Link to post
    Share on other sites

    • Replies 281
    • Created
    • Last Reply

    Top Posters In This Topic

    Posted · Fixing Pulley Innacuracy

    Hi,

    I only just emailed them to ask for a quote !

    Will post prices as soon as I get a response. Its in the USA unfortunately, but I cannot believe

    that a similar product is not available in the European union...somewhere.

    C.

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Good question !

    No I have not tried will all the belts off...its such a pain to take apart to that leve I dont know if I can face testing your idea ! :lol:

    I suppose I should test that before I spend out on new parts though.

    I did spend a while to align the XY rods because certainly if there is any misalignment the linear ball bearings

    in the printhead they sound like very unhappy fellows. But that was more a constant grumbling sound than a varying one.

    C.

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Pffff !!!!!

    "Unfortunately the largest bore size for that bushing size would be 6mm or .250”. To move up to an 8mm bore size the smallest standard pulley/bushing combination would be CMT36-2MR09-0909.8, if that item would work in your application it is priced as follows:

    1-9 pieces @ $49.75

    10-24 @ $32.34

    25-49 @ $22.39

    50+ @ $19.90

    Thank you for your interest in CMT’s products and services, please feel free to call or reply with any questions"

    Thats THAT plan down the drain !

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    I guess 1/5th the value of the original machine is a bit of a steep price to pay.

    One of the issues surrounding eccentricity is that for these types of couplings normally the fit needs to be a interference fit, which on the ultimaker (as I remember it during assembly anyway) it's not.

    This is a bit difficult to achieve when the shaft is shared with the bushing, but in any case you would need to have the shafts modified. Probably the most straightforward way would be to have the ends of the ground shaft linear knurled and press the pulleys on that way. Obviously your bronze bushing is never going to come out ever again if you choose this route though. Probably not an issue unless you want to upgrade the bushing.

    ED- mind you this also means your linear blocks are never going to come out again, too.

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Holy, that's expensive. Normal pulleys are around $2 in large quantities I think. (As you can buy them for $4 for single pieces) So that's about 10x as expensive.

    I can see the pulleys 'wobble' on some of the machines. But want to argue that it won't effect printing quality much. Possibly it causes some a-linear movements, which you could test by printing square boxes at different locations and measure them. But my gut feeling says the effect is very limited. Maybe someone could do some simulations or math to figure out the effect?

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    I think this really illustrates a big gap in the market here:

    For people like me, alot of the time we are keen to upgrade parts whenever its possible to do so, however

    at the moment we have only 2 kinds of parts-

    1) Stuff from china which functions, but is not exactly prescision engineering

    2) Industrial grade automation components, which are way overkill for 3D printer loads and duty cycles.

    Hopefully someone will come to fill the gap.....

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy
    I think this really illustrates a big gap in the market here:

    For people like me, alot of the time we are keen to upgrade parts whenever its possible to do so, however

    at the moment we have only 2 kinds of parts-

    1) Stuff from china which functions, but is not exactly prescision engineering

    2) Industrial grade automation components, which are way overkill for 3D printer loads and duty cycles.

    Hopefully someone will come to fill the gap.....

    http://www.sdp-si.com has plenty of pulleys to choose from ($5-20), and even the polycarbonate ones should be a great replacement... in regards to the axle diameter, finding the perfect one is probably the most difficult, and simply getting a smaller ID and drilling them out to spec shouldn't be so hard.

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Please keep us updated. I noticed the same 'problem' with mine after assembly, it's hard to tell if it's just due to the whole in the stock pulleys being too large or if they become distorted when you try to tighten the grub screw. It can be made better by aligning the offset like you mentioned (reducing the tight spots in the x or y motion), but it also adds a cam-effect to the motion. If I was buying new pulleys, it might be a good time to upgrade the belt as well, or at least install one that's ~2 teeth shorter so I could eliminate the extra tensioners.

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    can I suggest we make a test calibration piece so we can both see and quantify the effect

    I don't have any smart ideas what it would look like but perhaps Someone could Suggest?

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Hi Nik,

    Can you explain a bit more, are you proposing to test the before and after effects of changing the pulleys ?

    Or just a test piece to show the effect of the eccentricity of the current ones ?

    Anyway here are some measurements:

    Original Pulley bore diameters = Ø8.10mm

    Original Shaft Diameters= Ø7.94 > Ø7.99mm (maybe mine have worn down a bit in places)

    So we have a total clearance of up to 0.16mm

    When I assemble a pulley to a shaft (a replacement shaft which is Ø7.99mm )

    then tighten the grub-screw, then measure from the edge of the pulley to the shaft on both sides I get:

    4.42mm

    4.62mm

    So the pulley is eccentric on the shaft by 0.1mm. This is matching up pretty well to the numbers suggested by measuring the bits separately.

    It doesnt SOUND much, but this is with a tighter tolerance shaft than the original printer. So I would think that on

    an original ultimaker maybe 0.15mm eccentricity per pulley is possible.

    If the belts are tensioned up tight, this would be enough to generate noticable force variations in tension as the printhead moves.

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    I tried pulling the print head across it's range of motion using a spring-type fish scale. Where the cams/gears are out of phase (tightening the belt), the force more than doubles (jumps off the little scale).

    I liked the previous version of Cura (pre 12.12) because it let me select the center of the machine to start the parts at so I could try to avoid spending too much time in the overly tight area (the rest of the updates to 12.12a are very nice). The little stepper motors are more than strong enough to power through the tension variations, but when printing a big part, overheating the motors can lead to some missed steps. If we can lower the stress on the motors, that should reduce the heat build up which should reduce those glitches.

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Hi Kristen,

    A big improvement for me (one of those really obvious ones that I just never thought of) was replacing

    the shaft end caps.

    http://www.thingiverse.com/thing:23835

    The wooden ones, when tightened down can really rub on the end of the bearings and shaft ends.

    I recommend printing these ASAP, and replacing. This will not fix everything, but its a very noticable

    reduction in overall drive system friction.

    C.

    EDIT: For reference some printhead force friction measurements for you from my printer.

    Force to start printhead moving from static = 0.9kg = 9 Newtons = 2lbf

    Average force to move printhead full 200mm in 4 seconds = 0.7Kg = 7N = 1.5lbf

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    really good discussion going here -

    SG - I was being a bit vague-sorry

    I think the latter -quantify the error by observing its effect on a simple print

    0.1mm should be easy to see- perhaps a simple octagon vase would show it on the faces that align with the axes?

    just thinking aloud here really...

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    I noticed the same problem with my new UM. I measured one of my pulleys was wobbling by 0.38mm, very noticeable. Which means the hole is 0.19mm off from centre. The other pulleys seem ok. I don't think it is caused by the deformation pressure from the grub screw. I think the bore hole is drilled off centre.

    I will definitely need to replace it, as this will cause my models to be in error up to +/-0.19mm at the point closest to the bad pulley.

     

    http://www.sdp-si.com

    has plenty of pulleys to choose from ($5-20), and even the polycarbonate ones should be a great replacement... in regards to the axle diameter, finding the perfect one is probably the most difficult, and simply getting a smaller ID and drilling them out to spec shouldn't be so hard.

    I've looked around for a stock replacement pulley (in the US) and cannot find any 20 tooth MXL pulleys with a 8mm bore. It makes me think an off the shelf replacement is not available. The nearest I can find is a 20 tooth MXL with 6mm bore (or 0.25"). I agree drilling it out to 8mm accurately should not be too difficult.

    I would not be surprised if the UM supplied pulleys are in fact 6mm pulleys specially drilled out to 8mm. Does anyone know?

    Anyway if anyone is interested I found these 6mm/0.25" bore pulleys (in the US):

    http://www.mcmaster.com/#timing-belt-pulleys/=lagn79

    part# 1375K39 $10.77ea

    https://sdp-si.com/eStore/Direct.asp?GroupID=346

    part# A6A16-020DF2508 $9.17ea (out of stock)

    https://sdp-si.com/eStore/Direct.asp?GroupID=346

    part# A6A16M020DF6006 $9.17ea (out of stock)

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Finally they arrived.

    A nearby CNC turning shop produces some thousand gas burner jets for my wok burners each year. So I asked them, if they see a way to produce tailored pulleys for a reasonable price. For this reason it had to be a one-part-pulley instead of the three-part-pulleys, which are commonly available - and fall into pieces when drilled to 8mm, as I had to learn...

    Production samples arrived today.

    From left to right: Ulimaker pulley, standard pulley with pilot borehole, "new" pulley

    ulitmaker-pulley-vs-standard-pulley-vs-lathe-pulley.jpg

    Ultimaker pulley, new pulley

    ulitmaker-pulley-vs-lathe-pulley.jpg

    We tested the fitting by hand with an Ultimaker short belt, which I don't need anymore (thanks Calum). You can feel no play, whereas the original pulleys slightly move with a belt wound tightly around them.

    The pulleys feature a 8h7 center bore and two M3 threads. The small gap between the cogging and the flange is a trade-off of the one-pice design. I'm not sure whether this will increase belt wearing (if so, it should be possible to design and mount some split spacers to fill the gap). But compared to the wobbling original pulleys (hey, really ugly in closeup), which even seem to feature a slightly contorted cogging, it is definitely worth a try.

    I will be mounting the new pulleys the next days and keep you informed.

    Markus

     

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Looks like hopefully an improvement, looking forward to seeing results.

    I dont think the standard ones have a particuarly well cut toothform...so might be a good jump

    in removing play in the system.

     

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    So if I understand correctly you went to some machine shop and asked them to machine it for you. Do you have a cad file? And what did you pay?

     

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Well, not just some machine shop but the one where I am already placing orders for several thousands € a year.

    I had nothing but the original pulley and a belt. But the master craftsman and owner, who is approaching his 70s I think, is well versed and very cooperative. So he did me a favor. They make a lot of miniaturized stuff for the medical device industry and are used to deliver utmost precision.

    I have no exact price tag yet. But if I will manage to place an order of at least 100 pieces, they will be less expensive as anything else, mentioned in this thread (except Chinese bulk ware). My intention was just this:

     

    Hopefully someone will come to fill the gap.....

     

    Markus

     

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Ahh, I see :)

    Have you contacted Ultimaker about switching to these pulleys? Seems like a nice improvement. Either way I'd be interested in buying a few if they turn out nicely :)

     

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Markus, this is really cool!

    I just got my UM a few days ago, and the pulley runout has been bothering the hell out of me!

    Please keep us updated, and I would definitely be interested in purchasing a set.

    Thanks,

    Lars

     

    Finally they arrived.

    A nearby CNC turning shop produces some thousand gas burner jets for my wok burners each year. So I asked them, if they see a way to produce tailored pulleys for a reasonable price. For this reason it had to be a one-part-pulley instead of the three-part-pulleys, which are commonly available - and fall into pieces when drilled to 8mm, as I had to learn...

    Production samples arrived today.

    From left to right: Ulimaker pulley, standard pulley with pilot borehole, "new" pulley

    ulitmaker-pulley-vs-standard-pulley-vs-lathe-pulley.jpg

    Ultimaker pulley, new pulley

    ulitmaker-pulley-vs-lathe-pulley.jpg

    We tested the fitting by hand with an Ultimaker short belt, which I don't need anymore (thanks Calum). You can feel no play, whereas the original pulleys slightly move with a belt wound tightly around them.

    The pulleys feature a 8h7 center bore and two M3 threads. The small gap between the cogging and the flange is a trade-off of the one-pice design. I'm not sure whether this will increase belt wearing (if so, it should be possible to design and mount some split spacers to fill the gap). But compared to the wobbling original pulleys (hey, really ugly in closeup), which even seem to feature a slightly contorted cogging, it is definitely worth a try.

    I will be mounting the new pulleys the next days and keep you informed.

    Markus

     

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Same here, the wobbling of the pulleys is irritating.

    and sign me up for the list for a set :)

     

  • Link to post
    Share on other sites

    Posted · Fixing Pulley Innacuracy

    Why not switch to GT2 belts and pulleys, when puting so much time and money into an upgrade?

    Johan

  • Link to post
    Share on other sites

    Create an account or sign in to comment

    You need to be a member in order to leave a comment

    Create an account

    Sign up for a new account in our community. It's easy!

    Register a new account

    Sign in

    Already have an account? Sign in here.

    Sign In Now

    • Our picks

      • Introducing Universal Cura Projects in the UltiMaker Cura 5.7 beta
        Strap in for the first Cura release of 2024! This 5.7 beta release brings new material profiles as well as cloud printing for Method series printers, and introduces a powerful new way of sharing print settings using printer-agnostic project files! Also, if you want to download the cute dinosaur card holder featured below, it was specially designed for this release and can be found on Thingiverse! 
          • Like
        • 10 replies
      • S-Line Firmware 8.3.0 was released Nov. 20th on the "Latest" firmware branch.
        (Sorry, was out of office when this released)

        This update is for...
        All UltiMaker S series  
        New features
         
        Temperature status. During print preparation, the temperatures of the print cores and build plate will be shown on the display. This gives a better indication of the progress and remaining wait time. Save log files in paused state. It is now possible to save the printer's log files to USB if the currently active print job is paused. Previously, the Dump logs to USB option was only enabled if the printer was in idle state. Confirm print removal via Digital Factory. If the printer is connected to the Digital Factory, it is now possible to confirm the removal of a previous print job via the Digital Factory interface. This is useful in situations where the build plate is clear, but the operator forgot to select Confirm removal on the printer’s display. Visit this page for more information about this feature.
          • Like
        • 0 replies
    ×
    ×
    • Create New...