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Inspiration

When I started considering this project, I poked around the usual places.
I looked into various plans, commercial kits, etc. I'm surprised at just how much people are charging just for motor mounts. Finally I ran across an open design on CNC-zone.
Hoss now has a site on his conversion here. I used his mechanical design - but I made a few modifications as I went along.
Once I update things with my changes, I'll mirror the DXF files here. Make sure you check out Hoss's build - he did a fantastic job.

I'm Lazy

I decided to keep a bit of my sanity during the project.
These ball-nut stops replace the original brass acme nuts.
Rather than spend $20 on a 15/16-16 tap from wholesale tool,
I paid Hoss to make me a set of ball nut stops and to modify the Z-axis pully.
He did a great job, and I've got no regrets there.

Motor couplings

Hoss made some aluminum couplers.
I wanted some flexible couplers that would avoid binding
I got the idea to use lovejoy couplers from this conversion
I ordered my lovejoy spider couplings
from Enco. OD=1.08", OAL=1.72"
I bought 1/4" hole hubs, and Buna-n spiders
Part numbers:
990-4044 (hubs) x4
990-4042 (spiders) x 2

Ballscrews

After using my mill manually for a few tasks, I began to despise the play in the ACME ball screws. I bit the bullet and converted my mill to use ballscrews like Hoss did.
I ordered three lengths of ball screws and three ballnuts from homeshopcnc.com.
I turned the screws on my mini-lathe using tungsten carbide bits. --once I used a decent cutting angle, it went along nicely.
The steel is hardened, but only on the surface.
I used his spec, but made a couple of changes.
I didn't use a 1.1" y spacer - I used a 1.0" y spacer.
It was easier to buy and needed less machine work.
I compensated for the thinner spacer when I turned the Y ballscrew in my lathe.
I also turned down 1/4" the opposite end of the ballscrew to fit inside
the carboard spacer that comes inside the Nook ballnuts - allowing me to remove
the Y ballscrew without pulling the saddle to make some adjustments later on.
Finally, I turned the ends of the ballscrews down to 1/4" to match the lovejoy couplings.
(I wanted to keep parts homogenous)

The z-axis is mostly just like Hoss's build.
I didn't cut off the corners, and I made everything from 6061 aluminum instead of cold rolled steel
I turned the bearing spacer and retainer on my mini lathe with carbide brazed toold.
I had hoss drill and tap the pulley for me. I used nearly the same pulley, but mine
lacks flanges. The bearing spacer acts as a lower flange, so it's not an issue.
To align the pulley, I chucked the bearing spacer, put slow CA adhesive on the pulley
Then used the tailstock of the mill to press the two together and provide alignment.
Once it set, I drilled and tapped the four screw holes that secure the pulley
See the updated Z axis below
I redesigned the Z axis ballscrew mount out of neccesity.
I haven't gotten around to picking up a drill chuck for the tailstock
Until I get it, I have no way of accurately drilling and tapping a hole
in the end of the ballscrew.
Instead, I turned the screw down to .5", then cut a .5" hole in a 3/8" plate.
Then I milled a flat notch into the part I turned down.
I added a 1/4" set screw to hold the ballscrew in. So far it's good.
I'm getting the chuck ASAP, but I'll probably wait until it fails before I rebuild it.
Once the last motor came in, I started thorougly testing the Z axis.
It had alot of flex in it. I added a stiffener to the side (not really neccesary
The main improvement was the addition of the two small brackets on either side of the bearing. I cut the inset too much, so the bearing was sliding around too much. Now it stays pu.
The play in the large bearing was causing funky slack in the belt drive.
Additionally, I had to put the inner bearing spacer that the pulley is mounted
to on the lathe and true it up a bit. Somehow I managed to leave an uneven surface before.
I added some lock-tite to the two main hold down screws, and plan to add another side bracket to the stiffener.
The bracket will connect the stiffener to the column for extra stiffness.
Until I trued up the spacer, the assembly had a tight spot as it turned.
Last Modified 10/6/12 01:21