[mjohnsonsa]

I am not sure how the answer to this question can be relayed verbally but I am not sure where else to turn at this point... I am at my wits end and do not know anyone locally who can come check for me if what I am experiencing is within acceptable tolerance... My question is how can I tell if my X-Axis has too much resistance when moving the spindle plate back and forth on the X-Axis? I am building a new machine from a kit and I have spent no less than 8 hours building, rebuilding, tweaking, etc, the extrusions and linear slides for the X-Axis and no matter what I do I cannot get it so it is smooth and consistent as I slide the linear bearing blocks with the spindle mount attached back and forth over the range of the X-Axis (4 feet). I have not installed the ball screw or anything yet, I just wanted to make sure it was smooth and consistent on the rails with the X-Axis motion before moving any further along in the build. I have used my calipers many times, tried different methods of tightening the linear rails to the extrusions, etc.... I am so frustrated. It does not bind to the point where I cannot move it or anything, it just has two points of various resistance along its range of motion that are "tighter" than the rest. For example, I can move the plate with my fingers and it feels smooth, then it comes to a point where it requires a little more pressure to move past and then it gets easier again. I need to know if what I am feeling is acceptable or if it is too tight and requires more tweaking.

If anyone knows a way to answer this question without having to feel it in person I would appreciate it. Thanks.

Matt Johnson

[ger21]

Not sure if anyone can answer that question.

What kind of machine is this, and what type of rails?

How tight is too tight may also depend on your motor and drive system's capabilities. A ballscrew can exert a lot of force. You may find that it's more important that the ballscrew turns freely in all areas than the carriage movement.

[mjohnsonsa]

Thank you for your response. It is this kit here: Cnc Router Kit 4 x 4 x 7 - Cnc

I am using NEMA 34 motors. The ball screw and rails are mentioned on that page.

- Matt

Not sure if anyone can answer that question.

What kind of machine is this, and what type of rails?

How tight is too tight may also depend on your motor and drive system's capabilities. A ballscrew can exert a lot of force. You may find that it's more important that the ballscrew turns freely in all areas than the carriage movement.

[Devastator]

Tight spots will create increased wear of components in those areas even if the finished machine operates normally. I'd do my best to minimize them even if it takes some time to do.

[ger21]

It looks like they are profile linear rails?

You really want them to slide consistently over their entire length. Profile rails are not very tolerant of misalignment. Maybe contact the manufacturer for recommendations on how to align them. If your bolting them to an extrusion, your best bet is to probably mount a dial indicator to a bearing block and use that to align the rail to the block.

Extrusions are not really a good mounting surface for linear rails, because by design, they flex when bolts are tightened into their slots. THis can make alignment rather difficult.

[wizard]

It looks like they are profile linear rails?

You really want them to slide consistently over their entire length. Profile rails are not very tolerant of misalignment. Maybe contact the manufacturer for recommendations on how to align them. If your bolting them to an extrusion, your best bet is to probably mount a dial indicator to a bearing block and use that to align the rail to the block.

The other approach I've had is to use precisely machined parallels. Of couture this really only works with rails that are relatively close together. In general though you make one rail the master rail and strive to make the slave rail parallel to the master rail.

You can also use a precisely machined saddle that has the linear bearings mounted on it to align the rails.

Extrusions are not really a good mounting surface for linear rails, because by design, they flex when bolts are tightened into their slots. THis can make alignment rather difficult.

This needs to be highlighted, unless designed for the purpose and suitably machined it can be very tough to get good alignment with run of the mill extrusions. Beyond getting the rails parallel you also need them in the same plane which can be an issue with extrusions.

As for the original poster his question is very hard to answer over the phone so to speak. Maybe a video might help.

[wizard]

One thing that can be an issue is extrusion flatness. If you can change the amount of drag by loosening the rail mounting screws in the area where the problem is that might indicate a flatness problem. It takes very little to cause binding with profile rails. By the way binding can be the result of interaction with the parallel rail but also with the two bearing blocks on the same rail. Flatness issues can be caused by dips, highs points or twists in the beam.

[ggprasad_92]

It looks like they are profile linear rails?

You really want them to slide consistently over their entire length. Profile rails are not very tolerant of misalignment. Maybe contact the manufacturer for recommendations on how to align them. If your bolting them to an extrusion, your best bet is to probably mount a dial indicator to a bearing block and use that to align the rail to the block.

Extrusions are not really a good mounting surface for linear rails, because by design, they flex when bolts are tightened into their slots. THis can make alignment rather difficult.

Yes this is true.

LM rails (that's how we call it here) have to be dialed in properly, and if they are, they are awesome when performing.

The proper way to do it is to mount a rail on an extrusion and dial the side of that extrusion. Then use this mounted rail to dial the other one to a parallel.

You can also try dialing the top of the rail to check if it sits flat with the first rail. The possibility for misalignment on extrusions is very high.

[trailerparkboys]

It looks like they are profile linear rails?

You really want them to slide consistently over their entire length. Profile rails are not very tolerant of misalignment. Maybe contact the manufacturer for recommendations on how to align them. If your bolting them to an extrusion, your best bet is to probably mount a dial indicator to a bearing block and use that to align the rail to the block.

Extrusions are not really a good mounting surface for linear rails, because by design, they flex when bolts are tightened into their slots. THis can make alignment rather difficult.

As an example, for light pre-load 20mm rails Hiwin recommend the rails be mounted parallel to no worse than 25um (0.00098 inches) and coplanar to no worse than 130um (0.00512 inches). Practically I wouldn't think many DIY machines are within these tolerances, meaning the name of the game is designing for an acceptable increase in friction due to the misalignment of the rails.