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Step-Motor Shafts & Pully Adjustments.

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just going off the build notes for Version 3, of the Ultimaker.

Regarding the removal of pulleys from the Step-Motor Shafts.

There is talk of filing a flat, on these shafts ... to make it easier to either adjust or remove the pulleys later on. (one flat or four? ... 4 would drasticaly reduce the size of shaft?)

Has anyone done this? How many flats and how deep a flat did you grind?

I would rather "NOT" have to do this.

Can someone explain to me ... is there a way to adjust the pulleys without having to go to these extremes?

If I must grind or file a flat ... what are the "risks" involved and how do I go about it? I am unacustomed to filing flats.

PS ... how many more modifications, (like this) of the existing gear must be made. I'm hoping not many. :(


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I have a set of very small files. They are useful for many purposes including cleaning up some parts after printing. I used one of these to file flats on the 3 motor shafts and I think the Z screw maybe but nothing else. The 8 gears with the long belts - you can't file flats on these because you will have to adjust them *after* assembly. Or maybe someone knows how to do it but I certainly don't. Just tighten these extra tight once you have things square (perpendicular).

As far as other cusomizations or modifications - well there are several. I had to adjust the positions of washers for the extruder (and manufacture my own extra washer). I had to cut some bolts for the fan cover. I can't remember what else.

This is a kit. UM tries to do a good job on the kit but there are mistakes, issues, things that don't quite fit - oh yes, I had to do tons of filing of the plywood to get everything to fit. The bed was probably the worst.

Anyway, since you can't file the 8 pulleys flat then there is no definite need to file flat the rest either. I just removed about a half a millimeter of material. It's easier than you may think but optional.


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I mean no disrepect. Yes ofcourse, I should expect to do some modding with any kit. I am just trying to avoid doing too much is all. I guess I am not as confident as I should be. I was like this before building my own computer and messing around with telescopes. Looking back after giving these things a go, I often wonder what it is that I was ever worried about.

I am a slow learner and whilst lack confidence, I do love the challenge and reward of building things myself. I just hope I don’t become too much of a nesiaince, as I am bound to ask a million quesitons … and sometimes the same ones different ways.

Thanks for the welcome Owen … Very happy to have a response in good time. I have been around and check out the different forums at different manufacting sites and this one looks more active when compared to those others.

Here is a Link to when I first had my panic attack on the build note … LOL … I just have to ussually know more than what these good willing people describe well enough:

Mechanics build guide - Ultimaker Wiki

Thank you to the guy from Boston ... See, I can't even find your name ... If I can build this thing I will be impressed :)

Its in the MOTOR Section:

It's about the forth comment down at the bottom of page ... there is a small discussion about it.


I think I wll get a set of little files for tidying up as well ... sandpaper and even check out what solutiion some people are using.

I am happy to at least some eactivity going on here!

Perhaps If I get stuck ... I can upload some photos to describe what I am baffled by. I am kind of a picture guy. ;)

Thanks again for you help ... untill I understand this process much, I think will skip the filling of flats and just be careful if and when it comes time to adjusting (if needed) for the fine tuning process.

Now ... where to make a post asking for adivce on all the extras I should buy as well, to avoid ongoing international post? I'm looking to use ABS for parts as well as playing with the LPA ... looked into the CubeX but MAN oh Man ... the price of those rolls ... Sigh ... off to make another post.





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I highly recommend AGAINST filing flats on the steppers for the pulleys. We've build 1 machine which had the wrong motors by mistake, and it kept having backlash issues. This was because even while the pulley screws can get better grip, unless you perfectly align the screw with the flat, you will introduce some play. One we secured the pulleys on the rounded part of the axes the problem was gone.

This is one of those "sounds like a good idea but really isn't" things. It's in the same group as "using WD40" and "securing the Z-screw at the top", both things you also should NOT do.


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The shaft of the motor is round (cylindrical). When you slide the pulley over the motor shaft there is a set-screw that you tighten to attach the pulley to the cylinder. But the cylinder is super strong hard. Stainless steel maybe? So you have to really tighten the heck out of that set-screw. However some people take a file and rub it carefully back and forth on one spot on the shaft to make a flat spot on the curved shaft. This is called "filing a flat".

That way if you center the set-screw on that spot it's less likely to slip.

The problem is if the screw is a tiny bit loose, everything will seem like it is working fine except you will have this extra play and when you print, your circles will be ellipses and you will think it's a loose belt and might not occur to you to check for this.


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Thanks for this explications, you could describe a new issue on my ultimaker...

Yesterday, I have to dissassembly some axis to install the Dioder, but after manipulate the printer and reassembly all, when I move quickly the head on X or Y, some time the head really slow down (some time stop) and I can heard a really bad noise like something is sliding. I will check that, but I think the motor shaft and the pulley are not tighten then they slides together...


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Those symptoms may be the motors missing steps, due to excessive friction in the mechanics, rather than anything slipping (but there could be some of that too!).

Power the printer off and try moving the head by hand, by finger pressure on the sliding blocks. Make sure both X & Y move easily and smoothly. If they do not, check that the axes are square; the cross rods are properly seated in the sliding blocks; the pulleys are properly aligned so top and bottom sides of the belts are directly above one another and not catching on anything; and also check that the end caps on the axis rods aren't so tight that they restrict the rotation of the axes. Once everything is square, make sure that the pulleys are all tight, including the ones on motor shafts. Then add a little light oil (I use sewing machine oil) to the axes and cross rods to help things slide smoothly.


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If something is slipping, tighten all the set screws very very tight. To the point where you are afraid you might break something.

There are 5 set screws for each axis. Not 4. The 5th is at the motor. Tighten all 5 for the slipping axis!


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I have filed flats onto shafts quite often on my RC model helicopters. I use a Dremel with a cutting disc at high speeds. And a small file for the fine work.

On the Ultimaker I have used LocTite Blue on the set screws for the motor pulleys. This is the only place in the machine where I have done so since I do not want any hassles with grubscrews on the belt pulleys. Using LocTite can backfire on you if you want to disassemble the machine and cant get the screws to move.

To check for slippage I draw a line across the axes and the pulleys with a felt tip pen. I also did this on the heads of the motor screws. This way you can quickly check if a screw has vibrated out of position and become loose.

The xy pulleys used could be of better quality. They tend to deform when the screws are tightened. I would prefer a pulley without grub screws on the xy axes. There are pulleys with a clamp type system where the tightening screw is 90 degrees to the axis. The grub screws bite into the metal on the axes and I do not look forward to disassemble my machine if I ever have to change belts or things like that. To pull the steel shafts out thru the ball bearings when they are deformed can be a chore.

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