Some Ideas on A machine I'm designing

[clovenedhoof]

Hello,
I would like some critiques of a cnc lathe I'm going to attempt to build.

The general idea is:
I take the head stock from a hardinge lathe, then mount a Taig cross slide for a mill and then gang tool the whole thing.

What it's for making:
Body jewelry out of stainless steel and titanium. The work area on this machine needs only be 2x2 inches. I'm not expecting to take really heavy cuts. I hand make everything now on a manual 9 inch south bend and it takes me about an hour to make 2-3 pieces. So if I can improve that I'm happy!

What I expect:
Medium to light cuts in difficult metals, a 5-7 piece gang tooling setup up (probably a copy of an omni turn gang holder) very good finish quality on light cuts and accuracy around .005 would be fine.

What I have:
hardinge headstock
the Taig cross slide with 400 once stepper motors
a lot of carbide tooling
As much steel box tubing as I want.
Access to a friend that is really good with a TIG welder, and owes me

Some pictures of what I'm thinking about doing.
Basically I want to take a 6x2x.3125 thick piece of steel box tubing, and weld the headstock directly to it. Then down further screw a piece of steel to hold the Taig in place. I want to weld some posts in place in the tube to keep the steel from separating and twisting. Then most likely fill it with concrete or epoxy. The last step will be mounting pieces of ground tool steel to the table of the Taig and setting my tooling up on it.

http://s133.photobucket.com/albums/q...t=DSCF4896.jpg
http://s133.photobucket.com/albums/q...t=DSCF4898.jpg
http://s133.photobucket.com/albums/q...t=DSCF4901.jpg

This last picture just shows the factory mount for the Taig.

http://s133.photobucket.com/albums/q...t=DSCF4899.jpg


My questions,
Do you think this is possible? Such as to obtain my goals
Do you think that welding is the best way to hold the head stock in place?
Would I be better served to somehow put pins in the bottom of the headstock and screw it to some sort of granite base?
Do you think this machine will twist or vibrate too much?

[LeftCoastCNC]

Intuitively it looks like the tube base is on the light side and would allow for a vibration you would notice, especially with the materials you will be machining. I would avoid welding the head stock at all cost. Welding cast iron is usually a last resort. So yes pinning and bolting to a plate would be much better. Another problem with the tube is it is not very flat in machine terms. A structural frame out of the tubing with a heavy (1"+) ground plate would serve much better.
If the head stock is pinned in place, it would be a good idea to have adjustability in the slides so you can get everything square to the spindle axis, unless the ground plate has precision dowel holes for the head stock and slide.

Looks like a fun project. Good luck!

[clovenedhoof]

My real problem is how to drill the underside of the head stock. It's an uneven round part.

[LeftCoastCNC]

How did Hardinge hold it down?

[BobWarfield]

Definitely don't weld the headstock!

For the size you're looking at, you could buy a piece of Durabar cast iron the same size as the tubing and it would be a lot more rigid.

Think about mounting the Taig assembly first. Now how do you align the headstock so that the rotation is parallel to the Taig axis? You'll need to be able to pivot your headstock to adjust for that parallelism. In theory, you want to pivot along 2 dimensions:

- viewed from above, you need to rotate an axis straight down to align for parallelism. This is the same as azimuth on a transit.

- viewed from the side, you need to rotate in elevation for parallelism.

Focus on deciding how to mount that headstock so you can make those adjustments. Note that you may not literally be rotating. Rather, you may machine the base so it is pretty close and then shim into alignment.

To measure how you're doing, you'll want a precision rod in the headstock and a DTI on the Taig carriage.

Cheers,

BW

[clovenedhoof]

wow guys! thanks for the feedback! I think that piece of steel will be replaced by a pieces of iron, and I have an idea of how to mount the headstock more like it was originally.
do you know the best kind of cast iron to use?
and where is the best place to buy it?
-Chris

[BobWarfield]

I use SpeedyMetals. They have a web site. Gray cast iron. If you want really nice cast iron, look for Durabar, but it will be more expensive.

[clovenedhoof]

I'm thinking at this point that my best bet would be to go and buy the carriage casting that this headstock came off of and then figure out how to mount my taig set-up to that. then i have a very solid cast iron base with the whole mounting the headstock thing taken care of, and all i need to do is mount the crossslides.
-Chris,
I will be back later with pictures! and thanks for your ideas!