Arrg, fit back plate loose

M

Makintrax73

H-M Supporter - Silver Member
H-M Supporter - Silver Member
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Jun 20, 2022
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I bought a cheap 4 jaw 6" for my 9B Logan and tried fitting a back plate as my first real project. Ouch kinda screwed up!

Facing the front and rear surfaces went fine. I tightened up everything I wasn't using and sharpened the tool. No real issue except too high speed on outer edge. Put it in back gear and it cut ok. Little too rough finish but hey.

Of course the register of the nose is the only thing that counts....I read you gotta sneak up on it. I was sure I was .010" over so I took a couple spring passes and brought it over to the chuck. At first it look to be still oversize but before I took it back I gave a little twist......It dropped right on. Gulp!

So if I put it on my machine and keep the cap screws loose best I can tell with an indicator is it will bump up .001" if I lift up by hand. My bearings pretty tight so im pretty sure thats all in the chuck. So the nose is. 002" ish undersized. Is the going to cause me unending issues or did I get lucky? Maybe the cap screws tight will keep it rigid enough?
Should I peen some center punch holes around the outside of the nose to raise a burr and keep it tighter?

Anyway the runout across the face is less than .001" by my measurements so I got one thing right.
 
I would bolt it up and use it, 4 jaw is always going to be adjusted with an indicator anyway.

As long as you're not seeing any balance issues I can't figure what the problem would be.

John
 
matthewsx said:
I would bolt it up and use it, 4 jaw is always going to be adjusted with an indicator anyway.

As long as you're not seeing any balance issues I can't figure what the problem would be.

John
Click to expand...

OK thanks that's encouraging. I know you dial in a 4 jaw so I was hoping it will be OK.

I just checked by putting some English on it with a foot long oak piece.



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Then with the cap screws barely tight I get +/- .001"

With the cap screws 1/8 turn loose I get .002" when I lean on it with the oak board.
 

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Seems legit, go make some chips....

Don't think the deflection would have anything to do with the backplate though if it's bolted on tight.
 
matthewsx said:
Seems legit, go make some chips....

Don't think the deflection would have anything to do with the backplate though if it's bolted on tight.
Click to expand...

I measure it with my cheapo calipers as .001" (maybe a hair more) undersize. I'm getting .001" at the chuck with the bolts snug (bearings I assume), and .002" at the chuck with the bolts just barely cracked loose (bearings + undersize backplate). So I think my measurement of .001" undersize on my register is where it is. I was just worried it might move around and cause chatter or un-center my parts if it moves while I'm running the machine.
 
Shouldn't if the bolts are tight. Also you could use a rubber mallet to tap it as close to zero as you can then snug them down.
I really don't think it's going to make any difference, if I get my part within .001 when I chuck it into my 4 jaw I think I'm a rock star....

John
 
I think you can use it as is.
But if want a true fit you can smack the locating edge with a hammer in about 4 places then recut the needed size where it is swelled up.
 
I know this will have mixed reviews, but when I skimmed my backplate for a 6" Shars self centering chuck, I got it perfect, but it had .0045 run out. That did cause issues as I would like the repeatability of taking something out and putting it back in and be damn near good enough where a skim cut wouldn't require taking it down to center it again. I went and cut my register down a little on the loose side, and centered it like a tru-set chuck. I got it at .001" and tightened the hell out of it and it has been a blessing. I don't think you'll have any problems, I know I have had nothing but great results.
 
If you made one cut too many and it is now under, knurl it.

A knurl will cause the diameter to get larger.

You only need to fill in the tiny space that allows the chuck to move.

Before knurling place a dial indicator in tool post and make sure it is true.

Make sure the tool is square to the work and give it a light pass.

Test fit and repeat until snug fit.

Leave backplate on lathe until done.

When snug fit install and tighten the screws carefully.

If you want a better fit you can go past fit then with sharp cutter take skim cut to fit.

Sent from my SM-G781V using Tapatalk
 
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