RepRapPro Mendel Y rail binding

I've just finished building my machine and am working on tuning it.

I am having an issue with the Y rail binding. The rail has been cleaned and lubricated with a lithium grease yet the issue still exists. After moving the platform back and forth many many times, the Y axis no longer appears to skip when moved an max speed (G1 Y180 F12000). Yet, if I turn power off and manually move the platform back and forth, I still feel a binding at a couple of places along the middle of the Y rods. My concern is that at some time this will cause a hiccup during printing.

It's interesting that the binding only occurs for movement in one direction, away from the Y home. Movement in the other direction is fine. While moving the platform by hand, I have carefully observed the movement of all parts. The belt is not hitting the mud washers or anything else. Everything looks fine - I don't see anything that could be causing the friction.

Has anyone observed this? Any suggestions?

Note, my machine has two LM8UU bearings on the left side and one on the right.

Thanks.

Watch what the belt does on the idler and pulley when moving the y axis back a forth. Is the belt rubbing on the big washers that eare each side of the bearing? If your frame is not exactly square the the belt will travel between the big washers. This can be more of a problem with the x axis, in my experience. There are plastic guides on thingiverse.

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Using ABSPrusa Mendel Zaphod with Pronterface and slic3r 1.3.0. Printing well with 3mm PLA and ABS through 2 x J Head Mk IV b and Wade Geared Exruders. Controlled using RAMPS1.4 board running Marlin_v1.1.9

@MotoBarsteward
Thanks, but as noted above, the belt is not touching the washers or rubbing on anything else. The frame is square so, there just a little travel in the belt between the washers.

It's possible you might have a bent on mis-lined rail. Try loosening off the nuts that clamp one of the rails and moving the stage back and forth. See if the rail is moving in the clamp sideways. Another guy I helped had a similar problem and it turned out that his rails were not parallel. Not sure what motors or electronics you are using but check that the driver is supplying the correct current.

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Using ABSPrusa Mendel Zaphod with Pronterface and slic3r 1.3.0. Printing well with 3mm PLA and ABS through 2 x J Head Mk IV b and Wade Geared Exruders. Controlled using RAMPS1.4 board running Marlin_v1.1.9

Just a tip. Lubricating your smooth rods does not get much grease into the bearing itself. You need to lubricate the bearings. Take them off and put the lithium grease inside the bearing. Make sure you get some grease into all 4 races for every bearing.

Edited 1 time(s). Last edit at 10/28/2012 06:46PM by tosjduenfs.

@MotoBarsteward
I don't think the issue is a mis-lined rail. If that were the case, I would expect the binding issue to be worse at one rail end or possibly both. On my machine travel at the ends are fine, the binding occurs in the middle of the rail. I think that must mean the rail is slightly warped (or not lubricated well enough).

@tosjduenfs
An interesting idea. I will try that. Thanks.

Thurdy,

You can try taking the rods out and rolling them on a flat surface to see if there is an issue with their straightness.

Or try rotating the rods 90 degrees in their clamps.

Are you using O1, A2 or hardened steel rods specifically made for linear motion? In any case, run your fingers over them to ensure there are no obvious deviations or burrs on the rod. Also you could try swapping the positions of the bearings, try swapping your right side bearing with one of your left bearings.

Thanks (I was off line for a while after Hurricane Sandy).

I don't know what type of rods I have, it's whatever came with my RepRapPro Mendel kit.

At this point the binding is fairly minimal. The machine does not appear to miss any steps. Motor current is still set at 1 amp, I could turn that up a little if needed. The binding is only observable when the motors are off and I manually move the platform. The binding only occurs for movement in one direction. This rules out any rod issues.