[perfcomp]

Here's a screen shot of the design sans the CNC driving aspect: http://www.airgunstocks.com/images/m...duplicator.png

A few notes:
The machine is designed for carving gunstocks. It is meant to be used both in manual and in CNC mode. In manual mode a stylus is in the first hole for copying an original (master), with two 3 1/4 hp Milwaukee routers in the other two holes. With the CNC driving aspect added, the stylus hole is a 3rd router.

It is my 3rd manual 3d pantograph type machine I've made. The other two were 'tilt box' machines though, so this is a departure from my previous experience by using slide rails for x and y. On a tilt box machine when moving in x one is moving the counterweights back and forth. This machine moves the counter weight to the y axis only, making x axis carving motions ever so much easier. As well, tilt box machines moves y axis (and x of course) in an arc, preventing the drilling of holes.

The cable for the counter weight is not drawn, but goes up from the y axis plate, over a pulley down around a few more pulleys, and up to the counterweight lever arm. The counterweight may not be necessary when the axis is driven by CNC, but is required when in manual mode.

The chain driven rotational axis has an idler to adjust chain tension. The handle drawn for the z axis is not actually necessary. I took it off my current machine a year ago.

The tilt axis has relatively minimal movement compared to rotating the routers about their middle, but is adequate for the intended use (primarily drilling holes along the plane of the y axis), and provides good torque holding.

To add CNC, my idea is to add steppers and b board from https://buildyourcnc.com and ball screws for driving x, y, z, and tilt. The rotational aspect would remove the crank handle and replace with a gear drive to a stepper.

I was about to start buying components but thought I'd reach out for some peer input first. Thank you.
Michael McKeown
www.airgunstocks.com

[perfcomp]

I'm wondering if the poor tension capability of open bearings on supported rail might be worse than the flex of 20mm unsupported shaft. The furthest a bearing goes away from a rail end mount on my design is about 9". Seems like the flex should be quite small and the closed bearing would provide equal tension and compression loads, and maybe be better at dust rejection.
Michael