[Nathan P]

Hello!

I'm working on a hand guided linear motion project (similar to a duplicator) and I'm curious what type of tolerance I would need to hold for my linear rail alignment if I wanted to use hiwin profile rails? Accuracy is fine if it's anywhere under .050 so we're not talking super tight here, I'm mostly concerned with the ease of which the system can be pushed around by hand.

Also, would you have any suggestions for a linear rail substitute that can span 12' in one shot if the profile rails require too tight a tolerance?

Thanks,
Nathan

[mactec54]

Nathan P

The tolerance the linear rail can have, depends on the clearance in the bearing block, they have different grades & different loading of the bearings

But the general purposes Linear rails & bearings sets you would get away with around .0015 for straightness of the rail & flatness of the rail mount, anymore than this the linear bearing will bind

Round linear rails are more forgiving, & the tolerance is not so critical, But still would have to be a lot better than (.050) More like .005 to .010 these may work better for what you want to do

Next would be V-rollers

[Nathan P]

So have the people doing profile rail mounted directly to aluminum extrusion gotten very lucky as far as alignment goes or are their machines flexing enough that it makes up for misalignment? I wouldn't think the extruded surfaces would be anywhere near .0015 flatness.

Thanks,
Nathan

[louieatienza]

So have the people doing profile rail mounted directly to aluminum extrusion gotten very lucky as far as alignment goes or are their machines flexing enough that it makes up for misalignment? I wouldn't think the extruded surfaces would be anywhere near .0015 flatness.

Thanks,
Nathan

As mactec mentions, just check the specs; some rails are more tolerant of misalignment than others. I'd also agree that round rail may be the best way to go. Some profile rail are designed specifically to accomodate planar misalignment, THK (I believe GSR rails and blocks), ROLLON (TK and U rails) make such rails/blocks. Also if you need flatness, you can purchase MISUMI GSR series extrusions milled flat on two faces specificaly for bolting on linear railing.

[mactec54]

So have the people doing profile rail mounted directly to aluminum extrusion gotten very lucky as far as alignment goes or are their machines flexing enough that it makes up for misalignment? I wouldn't think the extruded surfaces would be anywhere near .0015 flatness.

Yes that's about how it works when they are mounted on unmachined extrusions, although some have machined the extrusions were the rails are mounted, you also can buy it already machined for the rail mounting

[Spk64]

So have the people doing profile rail mounted directly to aluminum extrusion gotten very lucky as far as alignment goes or are their machines flexing enough that it makes up for misalignment? I wouldn't think the extruded surfaces would be anywhere near .0015 flatness.

Thanks,
Nathan

Bolting to extrusions is not out of the question and depends on the design. I used a spacer plate between the extrusions and the rails to give them a flatter surface. Then during assembly I bolted things together loosely and moved my carriage down as I tightened the bolts. Once all tightened up there were no tight spots and everything moved smoothly. My X and Y axis are both assembled this way and the z axis is on MIC6 plates.
If my gantry is not squared up properly it binds quickly. This tells me the rails are doing their job and things are rigid.


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