1,2, or 5?

[jimmyzwoodworks]

I am building a CNC Router for woodworking. Basically 24 wide by 30 deep, with a Bosch Colt router. First attempt at buildiing a machine from scratch. I want to use an Acme threaded rod, 1/2 - 10, but don't know how many starts to select. What number of starts for the screw would you recommend?

[louieatienza]

I am building a CNC Router for woodworking. Basically 24 wide by 30 deep, with a Bosch Colt router. First attempt at buildiing a machine from scratch. I want to use an Acme threaded rod, 1/2 - 10, but don't know how many starts to select. What number of starts for the screw would you recommend?

With steppers, you'll generally have high torque at lower speeds and vice versa. If you use a 1 start (.1" lead) you may not have enough torque at the speed you may need to cut.
Too coarse a lead and you lose the mechanical advantage that a fine pitch screw gives. That said, I've used 1" lead ACME on my router for 8 years and still able to resolve fine detail. I won't be doing wax jewelry molds but been happy with my results...

I'd say, under 2' get 2 start, and over, 5 start... Smaller motors, 2 start. Larger motors, 5 start...

[ger21]

How big is the machine? As Louie said, either 2 or 5 start, depending on what motors you're using.

[jimmyzwoodworks]

The machine is about 24" wide and 30" deep. I plan to use Nema 23 motors (> 300 oz). The first response, if I understand it, says he has used a 1" (single start?) screw for 8 years and hasn't had any problems. Then he gives some dimensions and recommended starts. You say 2 or 5. I've tried to look at free plans for CNC routers, to see what size linear motion rods and drive screws they use. Some use threaded rod from the hardware store. I don't want to do that. Some use pipe for the linear motion rods. I want to use solid steel rods. I see where Dave Gatton uses a 5 start acme screw in his kit. Haven't been able to verify what others do. Just looking for some solid recommendations. My plan is use whatever I build until I quit woodworking. Can't justify buying a machine, but would like to build a solid machine to help me. Appreciate any help I can get.

[steve323]

Are you able to find cheap acme screws in anything other than 1 start? All I have ever seen are 1 start. If you are going to buy custom screws, then it would certainly seem worthwhile to consider ballscrews. I swapped my acme screws with Ebay ballscrews on my wood router and am much happier. Backlash is much smaller and speeds have more than doubled.

Steve

[louieatienza]

Are you able to find cheap acme screws in anything other than 1 start? All I have ever seen are 1 start. If you are going to buy custom screws, then it would certainly seem worthwhile to consider ballscrews. I swapped my acme screws with Ebay ballscrews on my wood router and am much happier. Backlash is much smaller and speeds have more than doubled.

Steve

The precision ACME screws, which are slightly different than cheap ACME, aren't that expensive, maybe under $12/ft for multi start.

There are some advantages to ACME, such as tolerance to dust and debris, inexpensive, ease of making home brew end fixity assemblies, AB nuts are cheap and easy to replace, and the friction or ineffiency can actually help damp stepper resonance and prevent the vertical axis from dropping when off.

[ger21]

The first response, if I understand it, says he has used a 1" (single start?) screw for 8 years and hasn't had any problems.

No, he used a 1/2-8 8 start screw, which is 1" per turn.

1/2-10 5 start is really the best way to go, and it's not expensive at all.
304035 1/2-10 x 72 inch (6 foot) 5 start RH Acme threaded rod for lead screw CNC | eBay