What the heck?

[middle.road]

Like my pictures above, 1st one that's on the lathe presently.
Else put a large chamfer on it.
I vote for the former.


Pull that screw out and get us some dimensions in SAE and Metric.
Something isn't right here. and the head Dia. of 14.85mm doesn't match anything that I can find.
That's too large of a counter-bore for that screw. - Shars is going to need to see that.

 

[higgite]

I'm thinking maybe what you got from Shars is a truly 6" chuck paired with a nominal 6" (160mm) backplate. I've seen so called 6" chucks and backplates that are actually 160mm (6.3"). They sometimes round off whole mm sizes to the nearest inch. My 4 jaw is actually 100mm but masquerades as a 4". It can get confusing. But, with that said, it does sound like you got a backplate intended for use with M10 capscrews and a chuck with M8 holes. That's not a cheap backplate, pushing $70 if I remember right. I think I would call Shars again. Everybody has a boss, ask to speak him. Or her.

Tom

 

[DavidR8]

It is an M10 cap screw.
The head of the cap screw is 14.75 mm or .58"
The counterbore is 17.75 mm or .70"

 

[Flyinfool]

Since we are hobbyists we are always looking for something to make.
How about making A cup washer that will be a very close fit to the bolts you have, and the OD a press fit into the back plate. Make the bottom thin enough so that the bolt head will not stick out the back. Once you press these into place and tighten a bolt down on it they will not move. You can then turn down the OD of the face plate. And no one will ever see what you did.

 

[DavidR8]

I'm thinking maybe what you got from Shars is a truly 6" chuck paired with a nominal 6" (160mm) backplate. I've seen so called 6" chucks and backplates that are actually 160mm (6.3"). They sometimes round off whole mm sizes to the nearest inch. My 4 jaw is actually 100mm but masquerades as a 4". It can get confusing. But, with that said, it does sound like you got a backplate intended for use with M10 capscrews and a chuck with M8 holes. That's not a cheap backplate, pushing $70 if I remember right. I think I would call Shars again. Everybody has a boss, ask to speak him. Or her.

Tom

Indeed the backplate is advertised as 6.3" listed for $67.95.

So something is up. I bought them as a package:

6" 4 Jaw Independent Lathe Chuck With 1-1/2 x 8 Threaded Mounting Plate

<!-- <ul><li>Chuck diameter: 6"</li><li>Thickness: 2.559"</li><li>Center hole: 1.575"</li><li>Back mounting: Plain back</li><li>Bolt Circle Diameter: 5.709"</li><li>Internal Jaw Clamping Range: 0.315" - 3.149"</li><li>External Jaw Clamping Range: 1.969" -

www.shars.com

The included parts are:
Chuck (202-6579) which has an advertised diameter of 6.299". The specs as displayed are for a front mounting chuck but they are still the advertised specs

6" 4 Jaw Independent Chuck

Shars Tool

www.shars.com

Back plate (202-6600) which has an advertised diameter of 6.3"

6.3" Fully Machined Threaded Back Plate with 1-1/2" - 8 TPI for 6“ 4 Jaw Independent Lathe Chuck

www.shars.com

So according to the advertised specs I should have had a .001" difference in diameter when they mated up which is completely fine. In fact the difference was more like .25"

Shars will be getting a call tomorrow.

 

[DavidR8]

Since we are hobbyists we are always looking for something to make.
How about making A cup washer that will be a very close fit to the bolts you have, and the OD a press fit into the back plate. Make the bottom thin enough so that the bolt head will not stick out the back. Once you press these into place and tighten a bolt down on it they will not move. You can then turn down the OD of the face plate. And no one will ever see what you did.

Hold the phone! I thought this was about tool acquisition...

 

[extropic]

When I read the Shars info on the 202-6579 chuck, the drawing does not agree with the pictures. The pictures show chuck mounting holes (tapped) in the back of the chuck. The drawing shows mounting screws with heads on the face side of the chuck, (BC=5.709") indicating the backing plate is tapped. David's experience reinforces the proverb "Let the buyer beware". Good luck with that phone call.

 

[savarin]

Its an interesting exercise making the backplate yourself and isnt really difficult.
This is the first part in making mine, mostly down the end.

9x20 chuck backplate

I am considering making a new backplate for a 5" 4 jaw chuck santa has ordered for me. I have available some 2" round bar and 1" plate. (free, my price) What I would like to know is if the following process would work and be strong enough. Turn a 45 degree taper on the 2" bar, set the end of the...

www.hobby-machinist.com

and these posts are how I finished it.

aligning the holes in the back of a chuck.

My new 4 jaw chuck has 4 8mm fixing bolts on the back but the holes do not go all the way through so I cannot use a transfer punch. I need to transfer the hole centres on the chuck to the back plate so I can drill them. 1) How can I do this accurately? My first thought (only one actually) is...

www.hobby-machinist.com

I had only had a lathe and experience for 2 years when I did this which is why I say it wasnt difficult.
Some questions on here with really excellent answers and anything is possible.

 

[DavidR8]

When I read the Shars info on the 202-6579 chuck, the drawing does not agree with the pictures. The pictures show chuck mounting holes (tapped) in the back of the chuck. The drawing shows mounting screws with heads on the face side of the chuck, (BC=5.709") indicating the backing plate is tapped. David's experience reinforces the proverb "Let the buyer beware". Good luck with that phone call.

I agree that the picture and drawing don't match. That said, they do sell them as a set and when I called to place the order (I can't place a web order because I'm in Canada) I asked specifically about the backplate and the chuck being 6.3" when the advertised size is 6".
The phone person said they matched and were designed to go together.

We shall see

 

[extropic]

I agree that the picture and drawing don't match. That said, they do sell them as a set and when I called to place the order (I can't place a web order because I'm in Canada) I asked specifically about the backplate and the chuck being 6.3" when the advertised size is 6".
The phone person said they matched and were designed to go together.

We shall see

I understand (and agree). The set you ordered specifies that it includes a 202-6579 chuck. The dimension table, in the 202-6579 info, specifies the chuck is 6.299" OD. What is the measured OD of the chuck you received?