Axis Steppers

[msurunner 2]

Is there a reason why the axis steppers don't have a flat spot on the output shaft to help prevent pulley slippage? I understand it's easier to access that grub screw than the top ones if the belt tension needs adjusted but it seems to me that the grub "fails" like once every other week causing the infamous sideways print.

[joergen 2]

Is there a reason why the axis steppers don't have a flat spot on the output shaft to help prevent pulley slippage? I understand it's easier to access that grub screw than the top ones if the belt tension needs adjusted but it seems to me that the grub "fails" like once every other week causing the infamous sideways print.

the setscrew is quite sufficient to hold the pulley on the round shaft. the flat surface is an obstacle to some users, causing the pulley to wobble on the shaft if the setscrew is not perpendicular and tight. round is more foolproof.

[Daid 306]

We've had 1 machine with flat motors installed by mistake. It caused more problems then it solved, as having the pulleys slightly mis-aligned with the flat will cause the pulleys to shake lose and shift.

[msurunner 2]

the setscrew is quite sufficient to hold the pulley on the round shaft.

I would generally beg to differ as the short belt tension seems to have to be high enough that the one grub screw on a smooth round surface causes slippage. I can see that it may cause more issues with some users not being able to correctly align the flat.

I guess I'm just noting that if the wall placement and infill touching errors are related to tension, as you increase that tension you do increase the strain on a small grub screw. Factor in a lot of small movements for infills and what not, and it can easily work itself out. I was just wondering aloud if a flat spot would help prevent that.

[joergen 2]

the setscrew is quite sufficient to hold the pulley on the round shaft.

I would generally beg to differ as the short belt tension seems to have to be high enough that the one grub screw on a smooth round surface causes slippage. I can see that it may cause more issues with some users not being able to correctly align the flat.

the short belts don't need to be crazy tight, if you take a ruler, you can deflect the belt in the center easily by 2-3mm, and this is quite OK in regards to tension. too much tension is causing too much wear on the belt. in addition, too much tension is hard on the bearings in the stepper. also, you are mixing up the directional forces; the setscrew handles the torque forces of the shaft-pulley assembly, while the belt tension affects the torsion of the shaft-stepperbearing-woodmount system.

the flat on the shaft is nice, when installed properly, but if that is causing too much problems for too many users, it's not worth the extra benefit, when a round shaft will achieve almost the same without installation problems.

[msurunner 2]

If you increase the tension on the belts, the torque necessary to spin those is bound to increase as well. This is the simple way of limiting backlash. The by product of this, however, is the torque threshold of the frictional force from the grub screw to the stepper shaft is closer to the torque necessary to spin the assembly. A flat spot would require the grub screw to raise in the assembly to slip, not simply having a torque greater than the friction of the grub. Maybe I'm asking too much of the machine to run at high speed on some prints, I was just thinking that a flat spot would allow us to increase that point. As far as the tension goes, I can not count how many times I've been told/seen others told they have a tension issue for infill not matching walls or wall placement being off. Either quite a few people have gotten lazy with assuming it's a tension issue or there's something else at work. Now, I'm inclined to believe it's a combination of things, including, but certainly not limited to, belt tension. Regardless, I've been steadily trying to monitor tension, and have upped it a couple of the small belt tensioners http://www.thingiverse.com/thing:34785 to try to keep a constant tension. Problem is, there's not really a sound way of determining "correct" tension aside from everyone's twang method (talk about unreliability in reproduction...). I have got to assume that it couldn't be that difficult to get a screw on the flat spot, but if it is, that's fine. I'm also fine with an answer of that's the mechanical limitation of the machine. But, if everyone wants to keep saying tension tension tension, I'm not too happy if the by product is producing a failure elsewhere.

IMHO... the max jerk values in the firmware are too high. I've been trying to take a more scientific approach to problem solving this by following a "solution" to fruition and as such have been with belt tension right now. BUT, I think the increases in our speeds over other RepRap type machines introduces a problem with high speed prints. When we are doing the vase type of prints, it's not nearly as apparent. But if you start doing pieces with sharp corners, that's when I've noticed the problems. I know I'm not alone as several others have noticed this too. Now, I haven't tested that, so I have no idea, but I would be interested in seeing if someone has lowered their max jerk and if it's helped. I don't think it would slow the prints down incredibly, but I could also be wrong their too.

[msurunner 2]

I know that Daid's spoken of placing "marker dots" on the pulleys and shafts in the machines AT Ultimaker to determine if slippage has occurred over time. That means that the grub screw cannot indefinitely provide enough friction to prevent slippage. All I'm wondering is if there's one spot that could definitely use a flat, I would see it as on the axis steppers. I understand why you wouldn't want it on the axis itself, but I'm just thinking there ought to be some sort of mechanical solution available. Some companies utilize a second grub on their pulleys. Perhaps something to consider if the round shaft is superior to one with a flat.

[joergen 2]

my steppers have flats, and the pulleys and grub screws are properly installed.

one way to be more scientific, measuring the deflection in the center of the belt with a fixed pressure (i.e. 1 newton), would be way to go.

I would venture that my belts have the perfect tension, not crazy tight to damage the belts, but tight enough to allow printing infill (solid) at 200mm/s, even after increasing the XY jerk from the default 20 to 26 (I tested up to 40, while was still printing nice, it sounded a bit unhealthy/unpleasant). so lowering it below 20, as you suggest, will make printing on the ultimaker only slower and more boring, which is not my cup of tea.

I think after you exhausted the belt tensioning options, and you still see infill not connecting on one side only, I would look how the X or Y rod are held in the sliding block. I'll bet the side where you see the disconnect, the rod has play in the sliding block, probably the one on the back, since it is the hardest to reach during maintenance. If you eliminate that play, the infill problem should go away.

[Daid 306]

 

I know that Daid's spoken of placing "marker dots" on the pulleys and shafts in the machines AT Ultimaker to determine if slippage has occurred over time. That means that the grub screw cannot indefinitely provide enough friction to prevent slippage. All I'm wondering is if there's one spot that could definitely use a flat, I would see it as on the axis steppers. I understand why you wouldn't want it on the axis itself, but I'm just thinking there ought to be some sort of mechanical solution available. Some companies utilize a second grub on their pulleys. Perhaps something to consider if the round shaft is superior to one with a flat.

The marker dots method actually allowed me to establish that the flat side shafts where causing problem. But we had some bad grub screw that are causing the slipping problems. The pulleys on my machine are still in place after a year of operation and dragging it around everywhere.