Putting thin parts in 3-Jaw

[jtrout13]

I have a question about putting small parts in the 3-jaw chuck. For instance, I am trying to make a flywheel which is 1.25" diameter, 0.44" thick. (For now it is just a disc of metal, the rest of the work will be done on the mill.)

I do fine turning the OD and facing off one side, then part off the flywheel from the bar stock. Now, I want to flip the part around and face the other side and bring the thickness to size. I can't seem to get the part chucked in such a manner that the axis of the flywheel is exactly coaxial with the axis of the spindle. It seems the part is a bit crooked. So, after I face the other side and mount the flywheel on a shaft and spin it at high speed, it has a 'runout'. (If you looked at the flywheel from the side view, the sides seem to wobble instead of being straight up and down.) I hope what I'm saying is making sense.

Anyway, is there any trick to chucking up a part this thin and keeping it coaxial with the machine spindle?

 

[steamer]

You might want to try turning it on an arbor made up in place., or "in Situ".

Turn it to a diameter that matches the bore of the flywheel and thread the end, but DO NOT take it out of the chuck!. Now mount up the flywheel and turn the OD and both faces in one setting, thereby assuring concentricity and true faces.

The other way would be to clamp it to a face plate, but that may depend on the flywheel.

Do you have a picture?

Dave

 

[maverick]

Try using parallels between the chuck face and work piece, you may have to remove the chuck and place it on it back while doing this. Remember to take out the parallels before turning thr lathe on.
Or you can make a chuck spider, basically a round disc of the right thickness and diameter to space
the work piece to just past the jaws. It will have 3 radial slots to clear the jaws.

 

[Maryak]

The best and easiest way I know for this is to make a tapered mandrel.

The taper should be no more than 0.0005"/inch around your bore diameter. Your disk is pushed on until it jambs on the taper. The parted off side can now be machined. You'd be amazed at how this arrangement grips however it still relies on friction so light cuts are the order of the day.

You can only machine in such a way as to keep up the pressure on the taper. Any attempt to machine the back face will result in a mess as the part slides down the taper and starts to flang about.

Hope this helps

Best Regards
Bob

 

[jonesie]

i have done it by making a mandrel with a shoulder and a tapped hole in the end to hole flywheel on and i have also done it like maverick said which also works good and is fast and easy like was said make real sure you remove the parallels. good luck jonesie

 

[Spurry]

Just mount a piece of 1 1/2" scrap metal in the chuck, and face the end. Stick your flywheel to that face with double-sided tape, cyno, shellac or any other wonder material. It does not have to be precisely concentric as you are only machining the back face of the flywheel.

When the gentle facing cuts have been completed, just warm up the pieces with a hot-air gun, and the flywheel with fall off with little persuasion.

Pete

 

[steamer]

Just mount a piece of 1 1/2" scrap metal in the chuck, and face the end. Stick your flywheel to that face with double-sided tape, cyno, shellac or any other wonder material. It does not have to be precisely concentric as you are only machining the back face of the flywheel.

When the gentle facing cuts have been completed, just warm up the pieces with a hot-air gun, and the flywheel with fall off with little persuasion.

Pete

Yes, I had forgotten about that one ...goodonya Pete.

Dave

 

[DICKEYBIRD]

A "pot chuck" works very nicely. Made from scrap aluminum or mild steel.

John Moran shows how: http://www.gadgetbuilder.com/MiniMods.html#PotChuck

 

[peatoluser]

Here's a nifty trick for getting parts to run true in the 3 jaw I found on you tube

[ame]http://www.youtube.com/watch?v=tn7A9PqNftY&playnext=1&list=PL6BF22BF816080F47[/ame]

peter

 

[jtrout13]

Thanks for the tips! I see there are many ways to do the same thing, but I really like the ball bearing idea on youtube. Thanks again!

 

[Ken I]

Applause to Peatlouser for going to the trouble.

The butt end of a toolshank works (but not as well) and may mark the work.

When truing a cylindrical part - if you push it too far it tends to come out of the chuck - same principal as a wobbly pin edge finder - so be careful.

Ken

 

[Swede]

I am a fan of the inexpensive expanding mandrels for such work... like these:

They can be purchased or made. Very handy, but not as accurate nore as firm a mount as a true tapered mandrel.

 

[Ken I]

I was once turning a taper mounting (as suggested by Maryak) but went that fraction of a thou too far (small) - an old toolmaker said "no problem" coated it in black Koki marker - lo and behold as tight as a Duck's A..

Surprised me.

I have also used Loctite - just heat it to break the bond.

Plenty of ways to skin a cat.

Ken