New Machine Build- What size threads should I use?

[thebuggman]

I'm starting to gather parts for my first build & I'm wondering what thread size/pitch I should use.

I have some 5/16x18 now, but I think it might be a little too flimsy over a 4' span and from what I gather, it will take 18 rotations of the motor to move 1 inch.
I found some 1/2x13 threaded rod that seems much stiffer and the 13 threads should speed things up a bit.

From reading through several threads, the ACME thread seems to be what everyone is using, but I'd rather use something I can find locally.

[DonFrambach]

Since you're talking about a 4 foot span, I think you'll be much happier with multistart lead screws. When I order from McMaster-Carr, I usually get delivery in one day.

If you're interested, here's a link: http://www.mcmaster.com
Then search for "acme precision lead screw"

Many people are using 1/2 by 10 five start ACME lead screws. You can get the delrin nuts from CNCRouterParts.com or DumpsterCNC.com.

[thebuggman]

Wow!
Those acme screws are expensive. $57.50 for a 6', 1/2 x 10 1:5 ratio rod.

I may have to start out with the 1/2 x 13 regular threaded rod & see how well that works.
At $10 v/s almost $60, I can probably live with a slower feed rate.

I haven't dug into the design details yet, but is a bearing used at the carriage mounting location to make things run smoother along the screw or would a bearing eventually jam up the threads?

[CarveOne]

Originally Posted by thebuggman Wow! Those acme screws are expensive. $57.50 for a 6', 1/2 x 10 1:5 ratio rod. I may have to start out with the 1/2 x 13 regular threaded rod & see how well that works. At $10 v/s almost $60, I can probably live with a slower feed rate. I haven't dug into the design details yet, but is a bearing used at the carriage mounting location to make things run smoother along the screw or would a bearing eventually jam up the threads?

You can, but you won't be happy with the results. After seeing your projects cutting at 30 IPM for hours you will wish you paid for the 1/2-10 5 start ACME rods. Initially we tell ourselves that speed is not very important, but that mindset quickly changes and we spend more money and time on the rods and anti-backlash nuts twice. Been there and done that.

If you go with regular all-thread rods the performance will be even worse.

You want a feed rate of around 75 IPM minimum to create anything useful. Cutting feed rates are dependent on the material you are cutting and the type of cutter you are using. Going too slow in some materials can cause burning or melting of the material. The cutters get dull sooner too.

You need a bearing support at each end of the rod, and an anti-backlash nut to connect the carriage to the rod(s).

CarveOne

[johnmac]

I agree with CarveOne. My first router used threaded rod. Bad mistake! For stepper driven systems, try for 3-5 motor RPMs per inch of travel in the X and Y directions. Steppers have best power at slow speed. Design with that in mind.

John