Finally a replacement chuck

[fixerup]

I have been wanting to replace my 3 jaws 8" chuck for quite a while because it only had inside jaws. I started looking for an LO 8' chuck adapter plate and a 8" chuck on the used market and never found a decent one in my budget range, So I bought an adapter plate from CME for about $125, a chuck from Vevor $205 and hope with a little TLC I can make a good chuck for my hobby lathe.
The chuck looked nice, the jaws felt tight in the gibs, it has a grease nipple on the body, the pinion drive were really loose in the housing and the scroll movement had some tight spots. I took it all apart except the scroll plate. There was lots of sharp edges. Spent about 1:30hrs deburring all the edges with a stone and then a cleanup which followed with a grease job. A major improvement but still some minor binds which seem to be caused by the one of pinion drive moving in and out and not synchronized with the other two. I had some o-ring gasket, maybe from a storm door screen, with a .150" dia cross section. With that material I made some o-ring to fit in the pinion gear retaining groove and screw it back together. That made each pinion drive much more snug in the housing and they all tracked better now. I could use a single finger on the T wrench to get it to move smoothly.
Now closing the jaws together I could see some light in between the jaws, with a feeler gauge I measured a gap of .009". on one jaw. The other two jaws had .002". I might need to grind the jaws, but for now I proceeded to get it mounted. The CME cast iron adapter plate was easy to machine, a got a good interference fit between the two, I used the mounting screws to draw them together.

Now the drum roll .........

Using a 10 mm dowel pin I measured a runout of .006" ouch!!!
But found out if I pull the dowel out and only used 5 of 7 teeth on the jaws I get .002" repeatedly . Those inner 2 teeth on the jaws are probably the reason the jaws won't close together and the cause of the .006" runout. At some point I will get my tool post grinder out and make it better.
I also check that the jaws faces were perpendicular to the lathe and the came out within .002" .

Over all I am really happy with my purchase, the final results and the good time spent in the shop.

 

[Susquatch]

Using a 10 mm dowel pin I measured a runout of .006" ouch!!!
But found out if I pull the dowel out and only used 5 of 7 teeth on the jaws I get .002" repeatedly .

This is probably caused by jaws that are not slightly tighter at the nose than at the base. This is necessary to stop this exact result.

There is another thread ongoing right now where this is being discussed in great detail. Do yourself a favour and read the whole thread. There is a lot of detail in there and it's easy to jump to the wrong conclusions.

Thread 'Mr Crispin grinds his jaws' https://canadianhobbymetalworkers.com/threads/mr-crispin-grinds-his-jaws.8537/

For now, your solution will work just fine.

You might also want to make a base spacer to keep that spacing and also maintain square. Here are some commercial ones:




You can also use parallels, but it's fiddly and you run the risk of launching a parallel through a window or worse. I confess I've done it, but only at low rpm.

 

[fixerup]

Yes those two post " Mr. Crispin grind his jaws " and " A tale of two 3" chucks" gave me the courage to buy a cheaper quality chuck, now knowing there was a possibility to make them better. Lots of good information in those post, which I will be reviewing when come times to do the jaws re-grind.

My jaws are skewed the other way, loose at the nose and tight inside. The two inside teeth of the jaws are the problem ones. Using a thin base spacer is a great idea, thanks. It would prevent me from clamping on those bad inside teeth and keeping the part on the remaining good 5 teeth.

The second picture shows the o-ring spacer I made for the pinion gear. I didn't bother to glue the ends together, once it was wrapped around the pinion groove and shoved in the chuck body and lock in with the screw, it had just a bit of resistance and the pinion no longer shifted in and out of the chuck body.

 

[Susquatch]

My jaws are skewed the other way, loose at the nose and tight inside. The two inside teeth of the jaws are the problem ones.

This is normally what happens. I'd bet a good third of chucks out there are like that. It is so common that I assumed mine was like that too. It wasn't.