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Author Topic: Cheap but sturdy 4th axis  (Read 4902 times)

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Cheap but sturdy 4th axis
« on: November 14, 2013, 08:22:12 AM »
I've been looking for a 4th axis for my Bridgeport interact for a while.  There are the  cheap Chinese ones on ebay, but nothing very substantial. Does anyone know where I can find a sturdy 4th axis, I have my own servo’s I can use with it.

Failing this, has anyone got any drawings of a 4th axis so I can try and make one.

Thanks
Jim
Re: Cheap but sturdy 4th axis
« Reply #1 on: January 07, 2014, 10:47:41 PM »
I reviewed the drawings in my Owner's Manual, and realized that there just isn't much detail (or focus) on the 4th axis that I added to my machine. (See the attached file MyCNCV2Design.pdf)
But if you look on pages 9-10 you can see the jist of the 4th axis construction. It's basically just a 2" diameter shaft which I turned on the metal lathe down to 1" diameter on each end, and mounted thru 2 self-aligning bearings (surface mount type) driven directly with a toothed belt and stepper motor. The turned-down ends created a shoulder on each end, which I seated against the bearings (to prevent end-to-end sliding movement of the "Headstock" assembly).
It had the end result of converting my 3 axis router table into a combination mill/lathe. I toyed with it only briefly after building it, but rarely use it these days. I have a 6" diameter 3 jaw chuck mounted on the 4th axis, but usually just use a wood lathe center plate on both the headstock end, and the tailstock end (since wood is all I do on this machine, most of the time). The stepper motor I am using to drive the 4th axis is a 1200 oz in NEMA 34 model (after learning that the 900 oz in model just wasn't up to the task). The orientation (parallel to the X axis of the table) will allow pieces up to 8" diameter x 36" length to be mounted. (Assuming the material is something light weight, such as foam or something when working with something 8 inches in diameter). All that I have actually tried has been 4" diameter, or smaller pine or oak. As for "Cheap", I probably have about $400 invested in the large stepper motor, and the self-aligning bearing assemblies, as well as the toothed belt pulleys and belt. It would probably be about the same investment to make one using a horizontal/vertical rotary table and motor with lovejoy couplings on each. Such a design would have the advantage of being able to switch the orientation from horizontal to vertical without a complete rebuild of the machine. However, the trade-off would be the speed reduction (of the worm gear driven rotary table vs direct belt driven shaft). Anyway, take a look at the PDF, it should give you some ideas.