[HELP] Concentric Turning To A Bore

[EdK]

I'm working on a power feed for the X axis on my mill. I have to make an adapter that fits onto the lead screw shaft and gets pinned to it. The power feed is made for a Bridgeport mill but my mill has a 17mm lead screw size so the adapter connects my lead screw to the power feed which is dimensioned for a 5/8" shaft.
My question is what's the best way to turn this so the OD is concentric with the ID of the bore for the lead screw? I'll be drilling close to the 17mm size and then using a 17mm reamer for the ID.

Ed

   

[Mayhem]

If it were me, I would do the large diameter and bore first. Next I would turn the part around and indicate it off of the turned diameter and then finish it off. Obviously, this assumes that you have a 4-jaw chuck.

[f350ca]

Pretty much what Mayhem said but I'd be tempted to use a boring bar instead of a reamer, thats a pretty deep hole to rely on the drill staying straight.
Or drill and ream then turn a shaft to fit the reamed hole and use it as an arbour to do the rest of the machining.

[DaveH]

Here's my lazy way
In the 3 jaw chuck turn all the od's and the thread - using a center support.

Hack it off about 1/4" longer turn it around and place it back in the 3 jaw chuck. Use some brass shim as to not mark the od. "Clock" it, if I can get it to be less than a thou off I go. Sometimes by rotating it in the chuck it can help.
Now if it is not cooperating I swear at it, go and talk to the dog have a cup of tea and a fag. On returning I swear a bit more at it and put the 4 jaw chuck on.

DaveH

[PixMan]

Do you have a 4-jaw chuck, Ed?

I'd make it complete on the O.D.'s as Dave H suggests, then turn it around and true it up in a -4-jaw independent chuck to make the bore. And I too would use a (solid carbide, in my case) boring bar to finish the I.D. as Greg suggested.

[TomG]

Ed,

I would face the stock to length and drill and ream the 17mm hole. Then I would chuck a piece of stock and turn a stub arbor with a shoulder with a snug fit in the the reamed hole. Then you can slip the part on the stub arbor, center drill the opposite end and support it with a center to finish the O.D. This way there is no indicating to be done and the I.D. and O.D. will be perfectly concentric.

Tom

[PixMan]

That's a good way too Tom, though it does depend heavily upon the fit of the bore to the stub arbor. Even if pretty good, there's a risk of chatter in the finishes on the O.D. being turned afterward.

[TomG]

I use that technique quite a lot Ken and it works well. You are correct though, it does require a close fit on the bore, which is pretty easy with the reamed part as a gauge. I would personally bore and turn that end in the same set-up and then flip and indicate for the other end, but Ed stated that he wanted to use a reamer it so making a stub arbor or pressing a mandrel in the bore would be the best option.

Tom

[Sunset Machine]

I'm making something similar myself using a chuck table. The table is threaded 3/8" x 16 clear though, it's a 2" dia chunk of CRS just a tad shorter (1/4") than the chuck jaws. One end is bored out a little to clear the hole in the adapter I'm making. It'll come within .002" pretty easily using a 3-jaw (I just checked - faces parallel within a few tenths, diameters concentric within .0015". No dial indicator was used in the setup).

The details:
There's a bit of allthread though the headstock. A nut & washer on the outboard end, the table is loosely secured by the chuck jaws and the allthread drawbar tightened up good. Now you have a flat surface just shy of the jaw tips. Open up the chuck and in goes my adapter-to-be with its pre-drilled bore. A short bolt through the adapter secures it flat to the chuck table and the jaws snugged up. Remove the bolt.

The part is faced, flipped, bolted, mounted, unbolted, faced again and bored. The bolt re-inserted, tightened, chuck jaws loosened and drawbar removed. The chuck table with the adapter attached is pulled out of the jaws until the part is clear, and then the jaws are wound down around the body of the chuck table. The part OD is then turned. Done.

Handy for making precision washers/spacers/etc.

[EdK]

(04-16-2014, 07:23 PM)f350ca Wrote: ...
Or drill and ream then turn a shaft to fit the reamed hole and use it as an arbour to do the rest of the machining.

This was my thought also.

Ed