As most folks probably do I wanted to get a little better quality out of my cheap lathe. I bought a 4" 4 Jaw chuck from Little Machine Shop and an adaptor plate. They claim all kinds of wonderfulness and accuracy.
It arrived Saturday, but I had a fishing tournament to go out and donate some money to on Saturday, and I didn't get around to playing with it until today. Actually this afternoon. I always sleep late the day after a tournament. LOL.
Anyway, I check the plate to the plate on the lathe. Perfectly snug fit. I mean if there was oil on it, and there wasn't a hole in the middle it would pull a vacuum taking it off perfect. Cool I thought. Then I checked the plate to the chuck. Same fit. I was excited. Man oh man this was going to be awesome.
I bolted the plate to the chuck and retrieved the studs from the old chuck. After lining up and assembling snugly I picked up the assembly to put it on the lathe.
CLUNK!
No I didn't drop it. The bolt holes in the chuck where not tapped deep enough to mount the plate solidly. The came up nearly a 1/16 short. Ok, disassemble it again. Tap out the holes after I find the right tap, and re-assemble.
Now to mount it on the lathe. I could feel that perfect fit slide together. Oooh! Nice! Carefully I torque the holding nuts on the studs. Loose all the way around, then snug all the way around, then tight all the way around. I felt like a surgeon performing a delicate arterial graft.
Click, and watch expectantly for that butter smooth rotation to begin.... What, its wobbling like a drunken sailor. No kidding. It was bad. No offense to any drunken sailors who might be reading this.
I took it apart, checked to make sure all my bolts cleared, and everything was snugged and then torqued nicely. Everything was fine so I put it back together just "knowing" that I most have been hallucinating the first time. Nope. :^(
Wobble wobble wobble.
Then I thought maybe my lathe was just that crappy that it couldn't handle a heavier chuck. While I watched it wallow its way around in a slow circles I grabbed a scale and set up up next to the assembly to see if I could spot the first place it was out of true. It was the adaptor plate. I had to look three times and then I still didn't believe it. The adaptor plate that was such a perfect fit to everything else was a full 1/32 out of true. I could see the edge of the adaptor plate going back and forth on the front and back side in relationship to everything else. The only other thing visibly out of true was the chuck that was mounted on it.
I took everything back apart again and thought about it for a while. Then I figured what the heck. I'll turn one side flat. As I was getting it mounted back up with out the chuck so I could turn it I noticed a tiny dent or flat spot on one edge of adaptor plate. I wonder if it could have been dropped hard enough to bend it, and I wonder if it will try to find its old shape over time? I guess only time will tell.
Turning it went ok except the hand ground left hand HSS cutter I ground wouldn't touch it. I'm not kidding. It made a bunch of noise, but didn't do anything. I reground the lathe bit three or four times and nothing. Since it was the first HSS bit I have ground I was thinking it must be something I was doing. Sharp point, rounded point, square point. Nothing. Oh some metal came off, but is was mostly the bit. Ok. Break out a brand new carbide cutter. Nothing. WHAT!? Oh, what an idiot. I was running the lathe in reverse.
I resharpened the HSS bit again to a nice point and started removing material. It made a whapping sound as the adaptor plate turned under it for the first couple passes until it got close to true. By then I needed to resharpen the bit again. A radius tip did a nice job of smoothing the surface, and then resharpen to a point again to clean out the corners.
I dismounted the plate, and marked it with a file next to one of the studs. I marked the matching stud hole with a file on the spindle mounted lathe plate as well. That way it will go back on exactly the same way every time.
I carefully torqued the chuck onto the plate, and then I carefully torqued the plate onto the lathe. Gently tighten all the way around, then snug around, then tight around.
I flipped the switch expecting who knows what all kind of catastrophic failure.
It looks good. I don't have a piece of precision rod to check it, but it looks really good.
I suppose for an old hack machinist checking this sort of thing and machining it true is routine, but for me it was quite an adventure.