Since I’m just a hobbyist, I couldn’t see purchasing a 4th axis for my 1994 Fadal VMC20 for much more than $1000. Since these things seem to go on eBay for more like $3500 and up, I jumped at the chance when one came up for $999. After the bidding was over, it cost several hundred bucks more, but still pretty reasonable.
Since this was an eBay purchase, I had my expectations in check when it arrived. I’ve learned with eBay you get what you pay for, so I figured it would be a good idea to disassemble the easy stuff apart to see what the condition was. Good thing too - it turned out it was a mess. Right off the bat, I noticed the motor cover had a nice dent in the top and several of the screws that held it to the motor mount end plate were cross threaded. This cover had been off before. I wondered what was lurked inside.
BTW - The part numbers I’m referencing come from the Fadal Options Parts Manual, pages 16 - 18.
I pulled the motor cover off and found the first issue. The motor wasn’t actually bolted to the mount plate - it was just sort of rattling around in there. I then removed the bolts on the motor mount end plate removed the motor and plate. Two things became obvious - The four screws meant to fasten the motor to the plate were just missing altogether and there was no gear oil at all. On the plus side, the motor looks like a fresh replacement/rebuilt unit (also the wires had labels on them, like you might do when replacing a motor). I hope the previous owner was in the middle of a motor replacement when they lost interest.
Once the motor was out, I tried to turn the worm by hand. Got about a 1/16 of a turn and that was pretty stiff. What little I could find by searching the web indicated it should be pretty easy to turn by hand, which it was not. Time to dig deeper, so I decided I better take whole thing apart. Whoever worked on this last was an ape - all the fasteners were REALLY tight - way too tight.
My first problem was the Higgins nuts (HDW-0230). The hold the worm in place and they were on really tight. I didn’t want to chew them up removing them, so I made a tool. (In hindsight, this was probably overkill, but when you have a mill…)
If you want the STEP 214 file - HigginsTool.stp
I made two and they really made it easy to get the nuts off (it also helped setting things up on reassembly). Once I had the nuts off and slipped the drive shaft gear (ROT-0280) off, it’s easy to remove the worm by pushing it out toward the motor end. I left the motor end worm pivot plate (ROT-0043) along with gear key as I didn’t need to take it apart any further.
With the worm out, the chuck should be able to spin relatively easily. Not in my case. So I now needed to remove the preload adjusting ring (ROT-0035). It took a while to figure out how this worked, but I finally got it. There are two small set screws that deform a thinner section to create a locking feature (Note: There are two small pins located under set screws, so you only need to loosen - not remove - the screws. In my case, however, the gorilla that worked on this last managed to bend the locking section of the ring so much I couldn’t release it. Time for another tool…
STEP 214 file - preloadnuttool.stp
In my case, I had to resort to an impact driver to get this off. One removed, it became obvious the previous person had way overtightened the set screws and overbent the thin middle sections enough to damage the threads. I managed to bend it back enough and clean up the threads so I could hand thread it back on. (Note set screws partially exposed in the picture. You can also just make out one of the pins just touching the thin section.)
Once the ring was off, I needed to pull the back cover/bearing race (ROT-0033). There were 6 screws holding it on, and once removed, I realized the thing wasn’t going anywhere. I noticed 4 threaded holes around the periphery and decided they were there for pulling. Those holes are 4.75″ apart. I guess I needed another tool…
Although crude looking, it worked. Basically I used 4 screws ( I think they’re 8x32) to mount it to the back cover, and placed a small block of aluminum between the central cap head screw and the end of the chuck shaft. By screwing down on the cap screw, it jacked the cover up. After about a half an inch, it came free. You’re pulling against larger perimeter o-rings, so it’s supposed to be tight.
Once that’s off you can gain access to the 12 screws (HDW-0303) the hold the brake plates (ROT-0036) to the chuck (ROT-0000).
After removing the screws, you can extract the chuck out the front. Before you do that, you’ll need to pull the large front seal (HDW-0224). I drilled a small hole in it, then mounted a slide puller with a screw in the end. It didn’t take much to get it out. You can then push the brake plate and brake piston out the back. There are 3 large o-rings (HDW-0176) you need push them past. Note, the brake plates are dished! I didn’t notice that when I removed them and had to guess as to the way they went back to together.
At this point, it should be disassembled!