[mocnc]

Ok sorry about the title, its kinda misleading.........I am not here to offer a simple 4th axis but was wondering if anyone knew of one. One that is able to hold round stock, like a pool cue. I want to be able to cut out a pool cue (or parts of one) as well as be able to do inlaying on a pool cue. So I guess I am looking at a 4th axis(tail and headstock) design. I perfer something home made, to keep the cost down. But I will not turn down any idea even if it has be purchasing something to help make my 4th axis

[kentavv]

It would be easy to add a stepper onto an existing import rotary table and have an inexpensive 4th axis. However, it seems the killer for this idea is the backlash and holding power. I've read that some of the expensive 4th axis have pneumatic locks for the additional holding power. I wonder how well useful the "inexpensive" 4th axis sold by Tormach and others work.

[walter]

One way to eliminate backlash is to use Harmonic Drive. Ingenious device with 1:100 or higher reduction and virtually zero backlash. Google "harmonic drive" to find out how it works.

You can find them on Ebay, sometimes with the motor.

picture#1 shows your complete 4th axis (motor, housing with harmonic drive & output bearing)

picture#2 shows housing with harmonic drive & output bearing

picture#3 shows only harmonic drive, no housing, no output bearing

[DareBee]

You could be REALLY simple.
Use a headstock/tailstock (or clamp your lathe to the table).
Put on an indexing plate.
Program it using 3 axis programming and index it 3-4 times by hand running a 3 axis program on it.

Maybe this is too DIY - but it is inexpensive.

[kentavv]

Walter - I assume you would couple this drive directly to the rotary table and thus not go through the gear reduction in the rotary table. Is that right?

FWIW: This page provides a nice description. http://www.powertransmission.com/iss...6/harmonic.htm

One way to eliminate backlash is to use Harmonic Drive. Ingenious device with 1:100 or higher reduction and virtually zero backlash. Google "harmonic drive" to find out how it works.

[SORCHEROR]

i have a small indexer that you might be able to use for pool cues,it has a 2:1 gear raito,a nema 23 stepper motor,the motor is small but you can put your own nema 23 motor on it,what diameter stock you using,i have two indexers,one has a .750 cup the other 1.00 cup,the other side of the indexer has a face plate with four screw holes,i could make up a tail stock for it,ive sold 6 of them on ebay already,i have pics but not sure how to post it on here
ill try to figure it out later,or i could email you a pic if interested
steve

[walter]

Walter - I assume you would couple this drive directly to the rotary table and thus not go through the gear reduction in the rotary table. Is that right?

FWIW: This page provides a nice description. http://www.powertransmission.com/iss...6/harmonic.htm

I wouldn't use rotary table at all. Harmonic drive is the 1:100 reductor, it's housing has a massive cross roller bearing on the output side- all you need is a chuck.

Keep in mind that not every harmonic drive is sold as a comlete package. One of the pictures shows the 3 piece device with no housing and no output bearing. Pretty hard to build one...

There is only one firm making those drives and they charge a lor of money. Quote on 5" gearhead was $2000. That should easily roll over a car. Check out NASA robotic arms..

You can find small 2" ones on Ebay for $50- $100.

[walter]

Here's another one, listed 'used' for $50.

Pretty small, only 2" in dia but there's no better 4th axis if you have a mini stepper with 6mm shaft. All you need is a mini chuck!

[SCHootie]

I don't what router you have, but I'm currently building the Solsylva. I'm not concerned with adding a 4th right now, but I had already considered the idea of adding exactly what your are talking about to mine. I think it would be pretty simple adding one to the table I'm building. If you just wanted to turn the cues, I believe it wouldn't be too difficult to just set up the router directly over a normal lathe and just let the lathe do the spinning and the router do the cutting.

[JW Peters]

How about direct drive? No measurable backlash? JP

[Bowman]

I intend to try my wood lathe with a stepper attached by belt to the lathes belt pulley as a 4th axis. Seems like an easy mod to make to the lathe and I can still use it as a wood lathe as well when not on the router table. Already has the headstock with spindle and bearings pre-aligned with the adjustable tailstock and live center. Just get it located and make some location pins to put it back each time. Still long way to go on axis 1,2 and 3 for now but these thoughts crossed my mind about a 4th looking at my lathe.

Bo