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Re: 4" 4-jaw Union Mfg. chuck

 

Sounds like a good plan.

The registration recess is the important bit; that's what sets the chuck concentric to the spindle. That said, if the chuck is an independent 4-jaw, the work will need to be set concentric to the spindle axis using a dial indicator. Thus, absolute concentricity of the recess isn't as essential as with a self-centering chuck, but eccentricity could cause imbalance and vibration.

According to this drawing:
< > the registration recess should be 55mm diameter, and the PCD of the bolts is 66mm PCD. You may find that the holes on your spindle flange are somewhat oversized, which may allow you a bit of leeway when setting out for the threaded holes in your backplate/adapter plate.

I suppose you might get really lucky and find that your existing 4 1/4-20 holes are at a PCD of 66mm, and that 1/4" (6.35mm) studs will go through the holes in your spindle flange.

Andy

--- In 7x12minilathe@..., "paul.consolini" <consolinipj@...> wrote:

Looks like I'll probably go with the adapter plate. I took the chuck apart and what looked to be a blank back on the chuck was actually an adapter plate fitted to the recess in the back of the chuck.

The plate has 4 5/16-18 holes that the chuck was screwed to with socket heads and 4 1/4-20 holes slightly inboard and in line with the larger holes. Looks like all I need to do is drill and tap 4 holes on the 45 degree radials (the other holes are on the 90's, if you can visualize that, turn a registration recess and install studs and be good to go. The OD of the adapter is already a good snug fit to the chuck.

Any hints for a novice on accurately locating those holes?

--- In 7x12minilathe@..., "Roy" <roylowenthal@> wrote:

There's no problem with the lathe being able to handle a 4" chuck, it's a common upgrade. Some folks have fitted 5" chucks with no problems.

I'd go with an adapter plate; it lets you pass long stock thru & it avoids the risk of the chuck unscrewing itself from its mounting if you slow/stop the spindle too quickly.
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