I've been snooping around this forum for a while now and i thought i would share one of my progects with you guys.
It started out as a taig micro lathe that i bought 3 years ago and an xy table that i bought for my drill press. Soon after trying to convert my drill press into a milling machine, I realized it was not goign to work well. so i began to think of another way. About 4 months ago i purchased a 10x18" lathe from busy bee, and i no longer had a use for the taig lathe. so i decided to use it as the z axis for my mill. i figuured i would just attach the head stock/spindle assembly to the carriage, but i would only have like 3 1/2" between the colum and spindle. for this problem i made a riser block. i milled the carriage flat and screwed the riser block to it with nine 10-24 screws.
I didnt like the lack of sensitivity in the z axis handle to i geared it down with a steel gear i found in a printer, luckily i found a matching pinion from another dismantled thing. After about 2 hours on the millpress lol, i had a gear train to reduce the force and increase the accuracy.
I went the the local scrap dealer (abc traders) and picked up a bunch of t6 for the base and the lower half of the colum.
This lower part have gave me another inch from the spindle to the colum so now it has a distance of 6 1/2".
The xy table need a little bit of work, so i took out the acme lead screws and replaced them with bearing supported 1/2-20 rods, and the lead nuts were made from brass with slots to adjust for backlash.
just the other night i was able to assemble it all together and get a final look at it. I still have a few problems to work out, like what kind of motor to use,

I got a hold of a 36v permanent dc motor, but im unsure about the power. what would you guys recomend for a motor?

I have been looking at 190oz/in stepper motors would these have enough torque?

and of course any suggestions to improve the machine?

thanks for your time,
Mike G

I would be interested to see how this progresses. Please keep posting updates as you continue with your project. If you have any quesitons ask them here as there are many here with great knowedge of this stuff.

As for your z axis. I am not sure how well it will hold position or hold up to movement over time as that is a small gear on the rack and pinion setup. You will have a lot of weight hanging on it and I think this will speed up the wear that you encounter. You might consider using Nook screws as they are cheaper than ball screws but better than threaded rod. By using a screw you will lower the force needed to raise and lower the headstock on the mill and this will allow you to run a smaller motor and also to reduce wear. To get it started on the cheap you could use threaded rod and I feel it might work better for you even than the rack and pinion you have. I could be wrong with about the rack and pinion but time will let you know.

Best of luck and keep us posted.

AC

After doing a little bit of research, decided to go back to the original 1/2-10 tpi acme leadscrews. My only doubt was how to make an accurate and smooth leadnut. with the help of acetal (delrin) and a few pieces of 1/8" angle alum I put together a fairly smooth system. it's not quite done yet, still have to cut the slots and taper the thin end , then put a ring to hold a spring. This will hopfully eliminate the backlash i got the idea from a pdf file.
anyways here are some pictures of what it looks like so far.
Mike