A source for 1/4 - 4 acme leadscrew? cheap of course!

[fyffe555]

Any sources for a 1/4-4 ( 1/4 od 0.25 lead single start) 36" leadscrew in stainless? I've tried a few, (msc, roton, techno isel) and Nook has one on the books but its $78 or $601 with machining..... This is stainless but if pushed I could use 4140 or something similar.

Here's the problem; I've a large format plotter, 36" wide pen type from Mutoh that has a wear problem on a leadscrew. I've had it for about 14 years, heavy, built like a tank but recently has been stalling the x stepper and screwing up the plot. Now can't reliably plot at 50ipm, it used to do 800ipm with pencil on vellum... The leadscrew is stainless and the nut is Bronze and it's galled in the most used area, on the left by the pen carousel. It's machined such that I can't swap ends.

I want to replace/repair it but the arrangement is a little different from most. It uses a fixed, non rotating 1/4-4 acme profile leadscrew and a linear stepper which has the shaft replaced by an internal rotating nut in bearing bronze. I've sourced a replacement motor or two from ebay, cheap, and thought that would be the problem. Now I just need to find the leadscrew and off we go. Nook's machined price is worth more than the plotter is..

So, any ideas?

thks

Andrew

[ger21]

Spend the $78 and have someone else machine it? Or a 4140 for about $46 from McMaster Carr. Part # 98940A7

[fyffe555]

Thanks Gerry, but that's 1/4-4 four start, I need 1/4-4 one start.. I guess I'll have to buy the $78 special and see if i can get it machined somewhere. Or maybe its a good excuse to buy a lathe! Three fet of 1/4" woobling out the back would be a bit scary though .

[ger21]

Sorry, I just assumed 4 start because I don't think I've ever seen such a small diameter single start screw with such high lead.

[ger21]

Make sure that Nook screw is not 4 start, because the Nook Catalog I downloaded shows their 1/4-4 screw as being 1/4-16, 4 start. Nook labels there screws by diameter and lead, not diameter and threads/inch.

[fyffe555]

Gerry, Thanks! you're right. Even though they specified single start in thier email quote the part number lists it as four start in the catalog.

Back to the drawing board. Looked at the motor last night and the bronze integral nut appears to be pressed in. I think I'll try pressing out the old motor nut and see whats what and maybe switch it for something more readily available. Have to keep the mechanical gearing though as the logic is all on one big board..

The small diameter single start screw is needed to move the plotter head at high speed and accuracy (0.0006" supposedly) with very little load. The motor is a bit wierd, it's wired eight wire bipolar parallel, 0.8 degree 400 step, 1.2v 4A 4.2kg-m (about 44oz-in?) but rated to 3600rpm! That ties up with the 800ipm rated speed of the plotter.

off to dig out that arbor press...

[cbcnc]

I came across this link for Acme rod. I think they are manufacturers.
http://www.dependableacme.com/

Chris