low cost indexer

[Ernie Balch]

on Youtube I saw an ingenious rotary modification for a laser and wondered if a similar modification could be made to my shopbot prs alpha. No motors or controllers needed.

http://youtu.be/ksnVMXjrR1s
I would mount a rack on the inside wall of the router then mount a rotary indexer on the carriage under the spindle such that any piece of wood would rotate as the gantry carriage moves in the X-axis.

All I would have to do is scale the X-axis drawing by multiplying the diameter by Pi.

[Ernie Balch]

I made a sketch of what I had in mind.
15044

[Brady Watson]

Ernie,
It is a neat concept, and it has been done before on applications that have little or no cutting forces applied to the part and where the feedstock is perfectly round to begin with. It is rare that the feedstock is ever round, unless you are working with very small dowels. This setup may be OK for just engraving on a cylinder, but it would be awfully sloppy with the feedstock just laying there & not chucked in.

I wouldn't recommend this setup for a ShopBot...because I know it would only end in disappointment. My advice would be to find a used lathe and adapt a stepper to it. It does not have to be an Alpha motor & drive to work with your Alpha control board.

-B

[Ernie Balch]

Brady, You are correct in pointing out the design problems. I posted it as an interesting concept more than anything else.

.... I gave away a bench top wood lathe last fall that would have been good as an indexer.

I have steppers and controllers from previous home built routers, what would be the best way to interface to the alpha?

[Brady Watson]

You will need to make up your own 'rainbow' cable that will hook up to your stepper driver. You will also need a separate power supply for just that one stepper. It takes a little ingenuity and research, but it isn't hard to do.

-B

[ken_rychlik]

Actually with a few pinion gears on the shaft like ernie has and a few pieces of track bolted to each side of the main rails, this would probably work fine on a bot. Don't rely on the table deck at all. Holders on the gantry could have spring tension to hold the gears in the track and with a little experimenting you would know exactly how much x travel one full revolution is.

The issue would then be attaching the shaft to your workpiece.

Idea revision:
Ok,, assume.. the tail stock would be mounted to the gantry on one side and only the other side had the gear and track.

On a prs you could attach the tailstock bracket to the back side of the gantry with some of those t nuts and have it arch under the center of the spindle. The other end would be rotated with the gear by moving the x gantry. This way you would have an adjustable tail stock for different width parts.

[Brady Watson]

I don't know...seems awfully Rube Goldberg. I've never seen a commercial 'indexer' or 4th axis used in that orientation. Seems like a lot of work just to save cash on an extra motor + trimmings...but I could be wrong. Make one & see how it works out for you.

-B

[ken_rychlik]

Thats kind of funny. My son has been on the A&M rube goldberg team for the last several years. He graduates next month. I don't think the engineer is gonna work for dad anymore. lol

I can't try it on mine. I went to a different flat bed cnc that doesn't have the side rails like a bot.

[Brady Watson]

Hey Ken - Is that Peter Griffin in your avatar? :D

-B