Backlash on y axis?

With motors on, if I lightly push on the platform, i can feel movement fore and aft on the y axis ( much more than if I push the spindle carriage left / right or up /down. This appears to allow the platform bto move due to force from the cutter. I get long thin walls within my parts that are parallel to the x axis despite the stepover being about 0.015 less than the diameter of my cutter. This does not seem normal but then again, I am a noob. So, Is there a way to make this not happen?

I have also had this occur, and can second this observation of backlash. My Nomad does the same thing.

The Y-axis is directly driven by the motor on a (GT2?) belt, so my guess is it could be insufficient tension in the belt. I’ve looked at the undercarriage to see if I could tighten the belt any, but my machine is already under as much tension as the adjustment screws would allow—tension is supplied by screws which push against the Y-motor, which is mounted on screws in slots for that purpose. My y-motor is “fully-extended” and I have no further travel in the slot, even if I had longer screws to push on it with.

Unfortunately what I think this means is that to get the play out I’ll need to loosen the y-motor mounting screws and the tension screws that push against the y-motor, release the belt clamp block and shorten the belt slightly, then re-clamp the belt and re-tension it up.

Before I do that though I was going to ask the same question you did, and see if there’s another fix! It may be something that can be partially or completely dealt with through internal hysteresis calculations in software that can be adjusted.

As far as longer-term mechanical improvements/solutions, I’m thinking it may also be possible to add a secondary means of adding tension to the belt, such as putting a very heavy spring loaded belt-following bearing on the undercarriage, since the carriages are machined symmetrically and have mount-holes that are un-used on one side:

This may be detrimental for some people’s use as it would introduce some hysteresis when the y-axis loading is significant enough, so for anyone trying to do hard materials (aluminum/brass) it would require that they slow their feeds on the y-axis down to ensure that the carriage “suspension” isn’t overloaded and that the carriage has fully reached the desired position before they move on to the next move.

My other initial thought for a work-around is to put a shim in under the belt and affix it using the threaded holes… that could also easily increase the tension, but the question then would be how tall of a shim is appropriate?. Rob & co, what do you guys think?

Upon inspection, the connection between the belt and the platform appears to be the issue. The plate that clamps the belt to the platform was not pinching the belt securely and was allowing the previously mentioned play. It was tightened down snugly so either the toothed pattern in the small plate is too deep or the belt too thin. I placed a small aluminium shim between the back of the belt and the platform ( effective making the belt thicker in that spot) and this appears to have sorted the issue for now. The play is gone anyway.

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this seems to have worked. same part, no gills.

Hi Mark- there was a batch of belts that came in thinner than what the plate was machined for. We thought we caught them before they got shipped out but I guess one batch made it through. (Sorry about that)

You can either sand down the face of the belt grip or, like you did, shim the belt from behind to make it grip tighter and it should be fine. I would expect a thin strip of aluminum foil or two would be enough. If you have any problems with that approach, we can ship you a new clamp.

I would be very careful about retensioning the belts. It is very easy to bend the motor shaft if you’re not careful.


Thanks, it is all good now.

Mark I’m glad you did that extra observation work there, a little styrene shim-stock in there and I’m tightened up as well. Good call.

This seems to have also solved my issues with aluminum. I can machine it now, slowly.