[nmcdairmant]

Im needing info on how to bore a hole that is .75 off center. How do I go about putting the hole that is of center on center in a three jaw chuck four jaw is not an option. I also have to hold a parallel tol. to the O.D. at .001 what type of fixturing is available this is a new one for me

[Geof]

If the chuck has serrated jaw mounts you can offset the jaws to get close then exeperiment with different thicknesses of packing under one jaw.

If it is a manual scroll chuck displace one jaw a turn outwards on the scroll and then use the packing.

[djr76]

One of my jobs is to make aluminum flywheels for an assembly for the machine I manufacture. It has an .800 offset stem turned on it, achieved by purchasing pie jaws and boring the offset in the mill. Would require removing the chuck and clamping it in you mill, find the center, then make your offset, and then bore the what ever diameter the part is. Or if is feasible, and part length and rigidity permits, do it in the mill. If I saw a print or picture, it would be easier to determine how to go about it.

[nmcdairmant]

I have attached print

[JWB_Machining]

Hey,

I would go with that I think djr76 is saying. That is take the piece off the lathe, drill out your hole then bore it on the mill. You can either clamp your lathe chuck to the mill table or use a super spacer if you got it. That's probably easiest.

[little bubba]

That looks like a pain in the ass. I hope you don't have a lot of them to do.

I'm with the others, get it off the lathe, after the turning is done anyways.

What I would do and have done on similar parts, get(make) some long jaws 12"+ for your 6" vise. Bore/mill/some how put a hole in each end(spacer between the jaws of course) so that the part is being grabbed on the top and can sit flat on the table. One on each end.

Now if your ends are nice and square, and your table is clean and flat, since you are only going in 1.25" on each end, the parallelism should be easy. Location might be a little trickier, and each one may have to be indicated in since jaws do flex when hanging out the side of a vise. If you could back up the fixed jaw with something significant, and use a torque wrench on the vise, you might be able to just let it rip.

[dertsap]

take the jaws out of the chuck and try using the scroll to your advantage by trying different combinations of turns per jaw if you catch my drift , then you will probably only need to shim one jaw slightly

[Donkey Hotey]

• How many do you have to make?
• What shape do you start with? Is this a cast part that comes to you rough or are the outer features done and you're just doing the center?
• Are you doing the broaching?
• How big is the chuck you're putting this in? Outside diameter? Bore? Type of jaws (serrated, step, pie)?

I'm a little lost. The print calls out the interior bore finish "As Cast" which implies to me that you're finish machining their cast parts. If that's the case, you need an offset arbor to hold the part by the center bore and it needs to be 0.750 offset. Or are you making them from bar stock instead of the castings?

My thoughts are that at almost 5" long, it's ain't going to fit inside any 8" or even 10" chuck. If you're holding the outside, you'll need a 4.5" center bore on the chuck to accommodate that thing (do the math: 1.5" outside radius of the part, plus the 0.75 offset= 2.25" radius or 4.5" diameter). If your chuck has a smaller bore, then the whole job has to be held outside the face of the chuck (not as rigid or true).