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Three Jaw Chuck - Backplate and Beyond

K

Kevin T

Stainless
Joined
Jan 26, 2019
My other thread was not very specific but I did make it through the backplate fab and assembly. I really didnt want to mess up the attach holes so I went as methodical as I could. Latheman helped me with an old back he had that was pre threaded 2 3/8-6 but the hole pattern was not right. I faced the part and reduced the OD so it would fit in the recess on the chuck.

Layed out the holes and some witness marks this helped since my eyes are getting old.

P1050437.jpg

I wasn't sure how to approach the hole but I did some searching in here and I saw that at least one guy goes straight to full size so I did too.

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I am using an early 70's Rockwell 11" drill press that I refurbished but havent used a lot. It did great!

P1050458.jpg

I didn't see a bottom tap in my box at first glance so I ran the depth a little farther down than needed. This is one of the things that will bug me everytime I look at this part!

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cont...
 
I like to use a hand tapper on critical holes.

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Here's those peek-a-boo blind holes when all assembled! About .25 deeper than I needed.

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Mounted...I really like the size of this chuck but as many of you have pointed out, it's a 3 Jaw!

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cont...
 
I dont really have a good test bar but I do have a fat piece of steel bar I chucked up to see how much runout this 3 jaw has.

Best I could manage was about .005 at 10 inches from chuck face but it's just a piece of raw stock 1018 Steel so maybe it's not too bad.

P1050465.jpg

I have some more check outs to do to see where my machine is but I "should" be able to use the three jaw to make the collet closer assembly so I can hold some things more precise and check tailstock alignment!
 
2 things : 1 I hope that chuck has the other set of jaws with it? And 2 ,to hide those offensive holes turn up a counter bored sleeve to press over the hub of the mounting plate.
 
Just curious why you reduced the OD of the mount plate to match the step in the back of the chuck. I would have just machined a step on the mount plate to match the chuck but left the step shy of bottoming in the chuck. That would have given the full diameter of the mount plate to support the chuck against bending loads and given you a stiffer assembly.
 
Dobermann said:
Just curious why you reduced the OD of the mount plate to match the step in the back of the chuck. I would have just machined a step on the mount plate to match the chuck but left the step shy of bottoming in the chuck. That would have given the full diameter of the mount plate to support the chuck against bending loads and given you a stiffer assembly.
Click to expand...

That would have been a good way to go but I was just copying the original one that I took off.
 
SLK001 said:
Why don't you just plug it, then turn the plug down to size?
Click to expand...

You guys are awesome! I like that when a guy says, "This is gonna bug me..." You guys have a bag of solutions!

You propose a solid offering here! I should re-phrase, It's gonna bug me everytime I look at it but "if it's functional" I can let it slide. I am so busy that I won't "really" look at it for a couple years!
 
I dicked around with the setup a bit and with two .001 shim stock spacers I can get that 3 jaw pretty accurate. .001 runout at 10 inches from chuck face! Not too shabby. So with the new found accuracy I embarked on making my collet closer handwheel. I'm turning the indexing shoulder portion out of 1018 Steel. I "may" be getting ahead of myself since I haven't spec'd the thrust washer yet and I dont have that big of a dia of steel but I just had to make some chips and make sure I am set up for the next time I get some shop time. Really nice with a .020 cut at .0093 per turn on the second cone. ~270 RPM? HSS bit.

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If you have to mess around shimming jaws to get the concentricity you need for the job, you'd be time and money ahead with a 4-jaw (independent) chuck don't you think? The supposed advantage of the 3-jaw is that you plop the round stock in, close the jaws and go to work--accepting whatever runout you get. With a 4-jaw you do have to center the piece but you can center it absolutely if necessary. And a 4-jaw gives more support against bending of the piece from cutting forces.
 
Dobermann said:
If you have to mess around shimming jaws to get the concentricity you need for the job, you'd be time and money ahead with a 4-jaw (independent) chuck don't you think? The supposed advantage of the 3-jaw is that you plop the round stock in, close the jaws and go to work--accepting whatever runout you get. With a 4-jaw you do have to center the piece but you can center it absolutely if necessary. And a 4-jaw gives more support against bending of the piece from cutting forces.
Click to expand...

You're not wrong, but I don't have a four jaw that is useable right now. I have a Skinner 10" that came with the machine but one of the jaws is bad. I am now functional and can take my time to find a 4 jaw that works for me. Win Win!
 
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