[shermama96]

I'm a second year mechanical engineering student, and as a summer project I've designed and plan to build a small lathe from bar stock. I am doing this a learning experience and plan to validate all the design aspects with hand calculations and FEA/Modal analysis. The entire machine will only be 15 inches in length. I plan to start machining the bed next week I figured I would try and resolve some questions regarding the bed material and the E/G fill. I was having trouble attaching a PDF and had to instead post a pixelated screenshots of the machine.

The bed is to be constructed from a 2"x 2" square thick walled tube. A piece of cast iron Durabar will be bonded to the tubing with machine epoxy and countersunk machine screws will be used to hold it in place. The flat head screws will pass into the center of the tubing and act as anchor points for the E/G. I'll then machine a dovetail into the CI bar and surface grind the profile.

Bed material:
- I was using other small machines as a reference, and noticed the Taig lathe was made from an aluminum extrusion and also filled with E/G. For the longest time I planned to use aluminum for the bed, and now I can't seem the understand why, considering steel will have a significantly higher young's modulus and damping coefficient. The only fighting chance extruded aluminum has is it has a much tighter tolerance on straightness and twist from the distributor, and I'm worried grinding the CRS tubing straight will be difficult as it flatten out of the magnet and then return to it's original bowed state.

E/G Mix:
-I have read several threads on this site about different epoxy granite mixes. Most are either for bulking up very large machines, or casting machines totally out of E/G. Because my machine is so small and the cutting forces won't be as extreme as most of the machines on here, I was hoping the follow a post by Taz on this site where he sieves locally sourced decomposed granite to obtain different grain sizes. Does anyone have a rule of thumb on aggregate sizes and ratios to use for a slightly more simplistic E/G fill for such a tight cavity.

-The inside dimension of the tubing is going to be around 1.5" square. Since the machine will only be 15 inches long, and only 8-10% of the volume taken up will be epoxy, I was hoping to avoid buying the expensive West Systems epoxy, most of which will go unused. I have some cheap general epoxy resin from ebay that I planned to use, but I am worried the performance of the E/G will suffer dramatically due to the poor quality of epoxy. At the same time I'm assuming the epoxy acts purely as a binder and might not have such a huge effect. I was hoping someone could speak on the effects on the mechanical properties of the E/G they might have done tests on that didn't use the west systems and maybe used the generic cheapo stuff.

Anyway, any help would be greatly appreciated.

Thank you in advance.