The age old lead screw question...

[CNC Darren]

hi guys,
I remember seeing a chart on here a while back that said how fast a ACME screw could be turned without whipping, I belive it was off a manufactures web site but cant seem to find the post here on the zone. Anyone know where i can find it? I'm starting on a new larger router that will be servo driven and i would like to get around 200ipm rapids. I remember seeing in the charts that 1/2-10 should only be used up to 100 ipm. I have been looking at either a 5/8-6 or a 3/4-6 to avoid it whipping but could always use opinions!

Darren

[ger21]

http://www.nookind.com
The speed depends on how you mount the screw, and how long it is. You might want to look at 1/2-8 2 start (1/2-4). It's only $23 for 6 feet at MSC.

[CNC Darren]

the longest span will be 6' for the X Axis, the Y will be 5' long. they will be surported on both ends by dual bearings as i heard this helps reduce whipping.
Darren

[jeffs555]

Here is a link to the Nook Industries acme calculators page. The critical speed calculator is about halfway down the page.
http://www.nookindustries.com/acme/AcmeCalculators.cfm

[WoodSnarfer]

What RPM do you guys run ACME screws at? I thought I read somewhere that above 350 RPM the screws tend to get very hot (and wear out quicker) due to the inherent friction of their design.

True, or nasty rumour?

-Chris

[chuckknigh]

Actually, ACME threads have a lower loss in their transmission of power. I haven't seen a breakdown of the various types of friction involved, but their higher transfer efficiency than 60 degree (allthread) screws would lead me to believe that, all else being equal, they'd run *cooler.*

Of course, if you're comparing them to ballscrews, that's a whole 'nuther matter. Those things have almost *no* friction involved!

-- Chuck Knight

[ger21]

It also depends on whether you use a plastic nut, or bronze? Lubrication? An anti backlash nut will cause a little more friction. The sample plastic nut I tapped myself seems to get looser the warmer it gets.(expansion?) Just by holding it in my hand for a few minutes. I haven't actually used it, though.

[WoodSnarfer]

I guess I was comparing to ballscrews. I found the site where I read the info originally:

http://www.roton.com/web/application.2.jsp#13

Maybe they are talking about a continuous duty situation.

-Chris