acme lead screw

[helpmeout]

Has any one have single start acme lead screws on there home built cnc,are they working out OK.That is is backlash,and do they work OK. When I built mine I bought Three lead screws with two anti-backlash nuts,7/16 two start acme leadscrew.At the time I bought them I had never heard the term 2-start,5 start,ect and still not sure what its for,I think for....Thinking of extinding the x-axis out a foot or so and was thinking of getting some,but dont know if I can mix single start with 2-start leadscrew.......

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[ger21]

You didn't say what length the axis is, but single start would not be the best choice, as it will be quite slow.

All things being equal, a 2 start screw will move twice as far per revolution as a single startscrew, and a 5 start will move 5x farther. That makes the machine much faster, and because the screw will spin slower, the chance of whipping is reduced.

[helpmeout]

The length is about 6 foot,im thinking it needs to be at least 1/2 inch or better.Im thinking I should keep the spped because of whipping...

[ger21]

My 1/2-8 2 start acme screws are about 54" long, and whip a lot over 500rpm.

[helpmeout]

thats the only reason I have considered going to a chain and pulley system on my longest axis,using a #25 chain.Im thinking of connections on both sides of the gantry so that it will reduce binding on the sides.

[ger21]

Imo, chain is a terrible choice.

[skrubol]

Has any one have single start acme lead screws on there home built cnc,are they working out OK.That is is backlash,and do they work OK. When I built mine I bought Three lead screws with two anti-backlash nuts,7/16 two start acme leadscrew.At the time I bought them I had never heard the term 2-start,5 start,ect and still not sure what its for,I think for....Thinking of extinding the x-axis out a foot or so and was thinking of getting some,but dont know if I can mix single start with 2-start leadscrew.......

No, definitely can't put a single start nut with 2-start lead screw or vise versa.

By using a chain do you mean to connect the screw(s) to the motor, or to replace the screws? If it's to connect the screws to the motor you would be best off with a timing belt. There are many profiles out there, so best to post more details if you'd like advice on what to go with.

[wizard]

thats the only reason I have considered going to a chain and pulley system on my longest axis,using a #25 chain.Im thinking of connections on both sides of the gantry so that it will reduce binding on the sides.

I have to agree chain is a terrible choice here. If your longest axis is only 6 feet that isn't really that long of an axis, leadscrew solutions are still viable and may even be preferred. There are ways to deal with the whipping including larger screws and as noted already faster leadscrews.

If you are dead set against leadscrews other options are possible including rack and pinion, and even timing belt drive. Rack and pinion can be a good choice but it does involve the purchase of gear boxes and is another precision alignment issue. Timing belts can also be good but again to do it right is expensive and you still don't get the performance of a lead screw.

The reality is you have lots of options, I would not however automatically dismiss a leadscrew for this short distance. Log on to a good web site for a lead screw manufacture and look for their engineering charts and calculators. You can get a surprisng amount of design work done right at your finger tips helping you to zero in on the right components.

[helpmeout]

I will Use Acme lead screw, whipping was why I was considering it.thinking about putting one on each side where they both act as one to help with racking. When I first built this I made both X,Y, axis stationary and the table moved between the two sides that the Z axis was mounted on.This time Im thinking of making The X axis where the Zaxis is mounted on move and the Table will be stationary,The way it is now the part moves below the router.That method works very good,and I might stay with that method because I only about half of my acme leadscrew that is on it now.

I think if I just extend the sides about a foot,keep the acme leadscrew that I have that should make the routing size about 15 1/2 by 22 inches.

[skrubol]

So right now the spindle moves only in Z, and the table moves in X and Y? Like a normal mill?

[helpmeout]

Yes that is correct,and it has worked out very good for me.If I need too,I can loosen the bolts thats holding the Z axis up over the table,and slide it where I need too,tighten an square up the legs with the table and start routing again.