1/2-8 8 start ACME for 8' axis?

[Rhodan]

Do you guys think 1/2" 8 start (1 inch per rev) running at a max of 300 RPM would work ok for an 8' long axis?

[Oldmanandhistoy]

Hi,

Go here http://www.nookindustries.com/acme/AcmeCalculators.cfm and look for the “critical speed” section. Click on the link to a calculator and punch in your numbers.

John

[Geof]

Originally Posted by Rhodan .... 1/2" 8 start (1 inch per rev)....

That is one heck of a helix angle, something like 35 degrees I think. Have you found a source? I would expect cutting a thread like this would be a challenge and its driving efficnecy would be very low.

[ger21]

Actually, the efficiency is much higher, probably near 80%

[Rhodan]

McMaster Carr sells the 8 start and Joe of Joe's CNC has them installed on his 4'x4' hybrid. They seem to work quite well and he's exceeding 300IPM on it.

Of course with that 1 inch per rev the torque is lower and step size is up to .0005 but just what wood really needs .0005 precision? As long as no steps are lost the results should be indistinguishable from 1/2-10 single start.

[Rhodan]

Originally Posted by Oldmanandhistoy Hi, Go here http://www.nookindustries.com/acme/AcmeCalculators.cfm and look for the “critical speed” section. Click on the link to a calculator and punch in your numbers. John

Awesome! Thanks for that link - it takes the mystery out of acme sizes vs length and speed.

1/2 inch acme with double bearings on each end can do 311 RPM max (106" between bearings to allow for a 10" traveller) which probably means the DIY guy should look at the dual single bearing speed of 212 RPM when using double bearings. So I should probably be looking at a 3/4" leadscrew if I want a reliable 300 RPM.