Lathe Material Holding? Odd Size

[Wreck™Wreck]

Something like so?
With no through holes permissible using an 8" 4 Jaw chuck with the feature as far off center as the sample shown will require one jaw to be extended well beyond the body, a soft top jaw would be used for this purpose. If a chuck with 2 piece jaws is not available then tapped blind construction holes may be required for bolting to a face plate or other fixture.

I realize that many hobbyists loathe unused holes or other features they are sometimes needed during manufacturing, many products have construction features such a holes used for handling during plating/anodizing or painting much as the center in one or both ends of a round part serve no purpose in use, they are only there for machining.

This is a 5" X 8" X3" rectangle with an off center 3.500" +.005/-.000 bore in a 20" 4 jaw chuck that I did several weeks ago (3 of them), one would find it difficult to place a part this size in an 8" chuck with 1 piece jaws. The hold down clamps are counter weights as this beasty was well unbalanced, I placed 3/8 round bar stock between the part and chuck face as the boring tool would have hit the chuck at that diameter. Drilled a 5/8ths" hole through then a 3" hole with twist drills then finished with a boring bar.

 

[Scott P]

Yeah Wreck thats the part for sure, thanks for this! And thanks to everyone who took the time to help out. I forgot I even had a faceplate duh!! guess I will use it. I spoke to the person this is going to be made for and sees no problem with 1 or 2 additional holes being made if need be...but I will try to use the ones that will mate up to the trans/bellhousing.

Thanks, Scott.

 

[Wreck™Wreck]

I also use strips of common steel banding as used in shipping between the hard jaws and part to help eliminate the tooling marks produced by the hard jaws if the chucked surfaces have already undergone a finishing operation, all bets are off with finished aluminum or 300 whatever alloy soft stainless. This also works well in a scroll chuck as the banding produced during one production run is rather uniform in thickness.

In order to make chucking such a part easier, lay out by hand the center of the bore and use a center drill to make a hole, use a live center held in the tailstock to push the part against the chuck then close the jaws on it and indicate from there. This will get you very close to where you want to be.