Usual silly questions

[lgalla]

Thanks Zoners for all the help.
I have purchased a bunch of items from E-bay just for the sake of checking out linear stuff.I need it in my hands to better understand it.
Question#1 just got ballscrew 20mm dia.5mmlead 220 long , it turns silky smooth.I thought from what I read on the zone it would be stiffer.Also the smaller bearing end has play. Is this normal?
Question #2 Have 2 rails&4 blocks THK HRW21.From the thk site[ All moment loads handled by single rail]. What does this mean?Are these rails a good choice for a heavy duty Z axis?
Question#3 After looking at belt drive in detail , R&P looks like a better choice.Is it less costly and simpler to implement?The belt drive seems to require huge gear reductions.
Answers Yes I have the CNC bug with side effects of E-Bayitus.Does anybody know the cure?Got to go check E-bay, bye Larry

[Mat-C]

#2: The 'HRW21 is a wider track than usual. The idea is that twist (moment) loads are handled by a single rail rather than a pair. To help with this, the track is wider than usual (better handling of twist or moment, that would otherwise be spread across 2 tracks). How heavy duty or not it is I don't know, I figure you use wide tracks where there isn't room for 2 tracks side by side.
I can't tell you if this is strong enough for your application, read the specs I guess.
Easiest cure for the CNC bug is to actually try and build something

[mike hide]

Originally Posted by Mat-C #2: The 'HRW21 is a wider track than usual. The idea is that twist (moment) loads are handled by a single rail rather than a pair. To help with this, the track is wider than usual (better handling of twist or moment, that would otherwise be spread across 2 tracks). How heavy duty or not it is I don't know, I figure you use wide tracks where there isn't room for 2 tracks side by side. I can't tell you if this is strong enough for your application, read the specs I guess. Easiest cure for the CNC bug is to actually try and build something

Another silly question, rather than the skate bearings running on the black iron pipes has anyone tried solid hex stock ? That would change it from point contact to line contact, which in turn should lower the contact loads reduce wear, and reduce drive forces

[Mat-C]

the tricky thing about hex stock is keeping the alignment... any twist as you move along it is very bad, because the diameter effectively changes.

[mike hide]

Originally Posted by Mat-C the tricky thing about hex stock is keeping the alignment... any twist as you move along it is very bad, because the diameter effectively changes.

I do not understand how torsional loads are generated normal to the length of the hex bar length

[synthetiklone]

Hello,
I have seen a professional router machine built using the hex steel lengths for the complete linear mechanism here in NZ. (professionally homemade!) It works perfectly, and an X-axis span of 2.4 meters plus, and y-axis is over 1.2 meters. (built to route a complete 1200x2400 sheet in one go) He even uses it on the z-axis One thing I noticed is that it is only about 25mm diameter steel, so every 100mm he has a bolt and spacer on the bottom flat part tying it to the more substantial steel frame. One bearing rides on top, with an offset cam type pivot for adjusting a mm or so. The lower 2 bearings are held on each underside via an aluminium block. (there is the standard gap for the mounting bolts on the bottom).
As another note of interest, he is also using a linear cam cog drive, with the steppers geared down. The linear cog isn't one 2400mm long piece either, it is roughly 300mm sections end to end, with the joins having no effect on the transition of the cog.
I have seen it running smooth as. I even saw small chips & wood dust sitting on the top flat of the rail, as the bearing rode over it, there was no visable effect on the routering design!
Hope this helps

Tony

[synthetiklone]

Heres a you tube video link to the machine in action, with a rotary on the z and a rotary on the table.
You can see the hex rails on the Y-axis. It is the same for the X as well.


http://www.youtube.com/watch?v=O3d0fueNr30

If link no go, let me know, and ill find another way of getting it to you, if interested.

ch33r5.
tony