Ballscrew Thickness!

**AdCNC** · 18-08-2009

ok. goin for a thiner screw would drastically reduce starting and stopping inertia and rotational mass! meaning that i dont have to go overboard with the motors! do you think a small 430oz-in NEMA23 gear say to 5:1 would move a Y axis of a 6ft (5ft effective) long table with say 16mm OD screw? this got me wondering because having studied joe's 4x4 CNC videos and pics, it look to me like he's using NEMA23 motors with a long screw, more friction than ball screw and his machine has a inch lead, and its surprising to see thats it flys!

**AdCNC** · 18-08-2009

oh btw i would be using 2 motors and 2 ball screws one either side of the x axis

**Gary** · 18-08-2009

If you are set on a smaller screw, and by the looks of it, you could get away with it, then it may work, but you also need to take into account the mass you are moving.
the heavier the Y axis the more mass the X has to move, and if you want it to move quick, that is a lot of inertia it has to overcome and that requires power.
You allready have the motor, so you can allway try them, but i dont think you will get the speed you want, especially with the current drivers.
The voltage of the drivers is the killer, so i suspect you will need to change them to a higher voltage driver.

What are you making the frame out of? if it is quite large it needs to be as ridgid as possible, or any small amount of flex will be seen.

We are starting to develope a Y and Z axis combined but it is made from steel, so is quite heavy.
The attached pictures shows a large Z axis (400mm stroke and a 34 frame motor) and this weighs about 15 KG, so i suspect our Y axis would be about 50KG.

**AdCNC** · 18-08-2009

iim not set on the smaller motors but as i have them now i may as well give them ago the machine does not have to work mega fast! its being made out of aluminium. ill give anything ago (within reason) if it works ok and saves abit of money! if not then ill have to go for some " muchas maracas ". that Z axis you got there gary looks a fair bit of kit what OD and pitch is that ball screw?

**Gary** · 18-08-2009

This version has a 20mm ball screw with a 5MM lead, but can go up to 25mm diameter with any lead.
We are also working on a smaller version that uses a 16mm ball screw, so will be a lot smaller, but i wnat to keed the width to keep the ridgidity.
I only use profiled rail, so no round or supported round rail.
If you have a more details specification, email it over to me and i can work out what you need.

Originally Posted by AdCNC

iim not set on the smaller motors but as i have them now i may as well give them ago the machine does not have to work mega fast! its being made out of aluminium. ill give anything ago (within reason) if it works ok and saves abit of money! if not then ill have to go for some " muchas maracas ". that Z axis you got there gary looks a fair bit of kit what OD and pitch is that ball screw?

**AdCNC** · 18-08-2009

Thanks Gary ill have to go over a few things then once ive got all the axis up and running then ill drop you a mail with some photos and details. see what you think!

**ptjw7uk** · 19-08-2009

If the problem with long ballscrews is whip why not fit traveling intermediate bearings as in travelling steady would only need a bearing in which the ballscrew would slide and then some sliding mechanism to pull the steady back into place when the axis moved to the other end. t least 2 steadies would be needed each side (if double ballscrews) plus space at each end to park the steady.

Just an idea!

Peter

**Gary** · 19-08-2009

You would still have a bit of chatter and vibration and i think the cost of this would also be more than the cost of a larger ball screw.

Originally Posted by ptjw7uk

If the problem with long ballscrews is whip why not fit traveling intermediate bearings as in travelling steady would only need a bearing in which the ballscrew would slide and then some sliding mechanism to pull the steady back into place when the axis moved to the other end. t least 2 steadies would be needed each side (if double ballscrews) plus space at each end to park the steady.

Just an idea!

Peter

**John S** · 19-08-2009

Originally Posted by ptjw7uk

If the problem with long ballscrews is whip why not fit traveling intermediate bearings as in travelling steady would only need a bearing in which the ballscrew would slide and then some sliding mechanism to pull the steady back into place when the axis moved to the other end. t least 2 steadies would be needed each side (if double ballscrews) plus space at each end to park the steady.

Just an idea!

Peter

It's only circumventing a bad design.

.

**vre** · 02-02-2014

I want to retrofit a lathe with servo 1.8kw 3000 rpm.
lathe between center is 1.6m and the leadscrew for z axis is 1.8m diameter 30mm 4TPI
i will replace the leadscrew with ballscrew.
What diameter-pitch ballscrew will be optimal for this situation ?
Also what is better to drive the ballscrew with coupler directly from servo or drive it with pulleys & timing belts ?
What pulleys & timing twill be strong enough and without backlash ?