1/2-10 5 Start on Z axis

[finishlinewrx]

I currently have Z axis mocked up with a section of 5 start acme that got trimmed off my X axis.

I guess what i am wondering is, will a 387ozin motor dead lift a +/- 25 lbs axis?
Or should i drop to single start screw?

I still need one more anti backlash nut anyway and i have both pieces of screw for either way available. So it is just a matter of what to go with single or 5 start.

Thanks Nick

[BobF]

I think it will.
Of course this advice is worth exactly what you paid for it.

[ger21]

If you look at Nook's acme catalog
http://www.nookindustries.com/pdf/NookInchAcmeScrew.pdf

You'll see that with those screws, it takes 1.7oz of torque to lift 1 lb, so about 43oz to lift 25 lbs. Now, keep in mind that this would be slowly lifting. I don't know how to calculate what torque you'll need to accelerate quickly, but it seems like it would work fine.

[grahamshere]

It works fine with mine, have no problems. Im using 4 start 8 tpi witch is basically the same. Graham

[finishlinewrx]

So there is no need to add a couter balance or spring then?

Just turning it by hand it goes down very easy and up and quite a bit harder but i can still rotate the screw with a few fingers compared to the X and Y that are pretty much balanced both ways.

I know it is due to weight, i was just woried about it being to much.

[johnmac]

When the machine is shut off the Z will drop. Its called backdriving. Yes, you can use a spring to counterbalance it.

I have a ball screw on my Z and it dies the same thing. Try a long spring, like the kind used on screen doors.

Set the spring tension so the Z motor has to push the router down and the spring lifts it up. Then you don't have to worry about backlash!

John

[BobF]

My machine has a Milwaukee 5625 router on the Z. This is one of the heaviest routers I think you will find. My screws are 1/2 -8 2 starts or 4 tpi. I have no back driving or issues lifting. Motors are 305 oz in.

[johnmac]

The 8 TIP 2 start is about the limit for screws that don't back drive. It would be my choice for the Z axis.

John

[grahamshere]

I don't think there is a problem there, when the motors are on its not going to drop as long as the couplings are tight, I have yet to have any problems.

Graham

[sweckard]

I have the same screw and approx. +25 lbs for the z-axis with a 420 oz-in stepper. The motor handles the weight with ease and I don't see any need for a counter balance or spring. Also I have none to hardly any drop when the motors are shutdown.

Sweck

[finishlinewrx]

Alright thanks! I'll just leave the one I have in there and give it a shot.
It will be easier with all the same tpi everywhere anyway.