[HELP] Oops ... Now It's Too Small

[arvidj]

I was turning down a back plate ... this one to be exact ... https://www.grizzly.com/products/6-Pre-Machined-Back-Plate-D1-5/T25218 ... to allow the protrusion to fit into the recess of a 5C collet chuck ... http://www.cdcotools.com/item.php?itemid=404 ...

Things were going along nicely. I was sneaking up on the required 3.74 inch protrusion diameter. I had gone thru several iterations of warming the chuck up in the oven, testing the fit, then taking "just a smidgen" off the back plate. Wash, rinse, repeat.

I'm sure you know how this story ends. The protrusion is now "just a smidgen" too small as the chuck fits without any issues and "just feels loose". I'm guessing the back plate protusion is about .001 - .002 too small. Even thought I knew it was too small I mounted the chuck anyway just to see how bad it was and indeed, there is an unacceptable amount of run out in the mounting.

What are the options to build the protrusion back up 'just a smidgen" so I can take another shot at getting it right?

Thanks,
Arvid

[EdK]

Arvid,

Just remove the existing protrusion and make a new one. You may not even have to remove the existing one if the collet chuck has a deep enough recess.

Ed

[f350ca]

I expect its cast iron, welding would warp it. Could you make the protrusion smaller and put set screws in the side of the chuck to centre it like a set through.
Ed probably has the best plan.

[Mayhem]

What Ed said.

Also, when getting close I would take a spring pass (i.e. don't advance the tool, just take another pass).

[ieezitin]

Leave it... its going to work to your advantage.. you may have slight runout on the new chuck you will be able to cancel it out ny playing with the draw bolts.

Anthony.

[EdK]

http://www.metalworkingfun.com/showthrea...9#pid18879

Ed

[Dr Stan]

1)  Make dimples on the face of the protrusion very close to the edge with a center punch.  I recommend 8 dimples fairly equally spaced.  You'll probably have to "turn" the diameter again to avoid a excessively tight press fit.

2) Use .0005" thick shim stock about 1/2" wide and place 3 pieces equally spaced to "tighten up" the diameter.

3)  Try some Loctite for bearings to improve the fit.

4)  Build it up with silver solder as that should not be hot enough to warp the plate, then turn to size.  You'd need to pre-heat the plate.

BTW, I second the idea of cutting off the existing protrusion and repeat the process.  Personally I've had the best results simply making sure the spindle nose and the back of the plate are as clean as possible.  Then rough it in 050" or so oversize.  Leave it on the lathe until it has cooled down to room temp then take the finish cuts.

I also typically make an undercut in the corner using a grooving/parting tool with the compound set at 45 degrees and the same for the cutting tool before making the final cuts.

[pepi]

(11-25-2016, 07:15 PM)Mayhem Wrote: What Ed said.

Also, when getting close I would take a spring pass (i.e. don't advance the tool, just take another pass).

Good tip regarding close and spring pass, makes sense ..............thanks

greg

[Hopefuldave]

Not just a spring pass - leave it to cool between the last two passes, if you've taken much off the heat form cutting will have expanded it and a perfect fit will be sloppy once it cools... DAMHIK, OK?

Dave H. (the other one)

[arvidj]

Thanks for all the suggestions, especially the spring pass. This may have been the ultimate mess up point. When I got "really close" I would actually move the tool what I thought was "just a little" while just using the same setting and another pass might have done it.

Also waiting for the adapter to cool between passes is another 'must do next time'.

I'll ponder the solutions and let you know how it turns out.