What the heck?

DavidR8

DavidR8

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I sent an email to Shars telling them that the backplate in the 4-jaw chuck & backplate package is not well matched.

The counterbores for the mounting bolts are too large which means that when you turn down the outside diameter to match the chuck, the edges of the counterbores are exposed.

Below is their response:

“David
The OD of the backplate is not designed to be turned down due to the bolt circle pattern. The bolt circle is a set dimension that can not be changed on the chuck and the relationship between the chuck and back plate requires the OD of the back plate to be larger than the chuck.”

The backplate is advertised as being 6.3” in diameter. Naturally I assumed that was to allow for finishing the outside diameter to exactly match the chuck.

Apparently I was wrong. Now I wonder if I have weakened the backplate.



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I've never seen a mounted chuck that didn't have a backplate turned to match -- that's just goofy. Not saying it could not occur, but I don't think anybody could look at it and think 'oh yeah, you're supposed to leave the back plate larger like that...' .

As for weakening it, I doubt that you did although I suppose technically the lack of integrity on a contiguous perimeter would weaken something like that. Significantly weaken it, I'm doubting it but I am by no means an expert. I really didn't like the fact that you ended up with the open-sided holes though (dubbed "cheese grater" in another post) -- that didn't sit right with me for the reason given.

Scenarios like this are far from uncommon these days with parts made to fit multiple variants of the same piece. You end up with a one-size-fits-all mentality that cuts costs in manufacture but leaves the consumer holding a less than ideal product at the end.

-frank
 
My 3-jaw that was on my lathe when I bought it has a 6.3" backplate on a 6" chuck. I wouldn't worry about weakening it but if you don't like the finish, just replace the back plate. Shouldn't be expensive.

Typically you only need to finish the front face and pilot diameter.

Sorry that happened to you. I've found Shars to be very responsive to issues whenever I've talked with them.
 
My response to them was this:
“I have never seen a backplate that did not to match the chuck diameter.

My point is that the counterbores are too large. Were they smaller there wouldn’t be a problem.
I suggest that the item description be changed so that it explicitly says not to turn down the outer diameter.”

I’ll fill them with some JB weld and call it good. Or I might fill the holes completely and turn the backplate 90 degrees and drill new holes with smaller counterbores.



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You can see the backplate protrudes from the edges of the chuck in this picture. Never found it annoying. Import chuck made in 93'

image013.jpg
 
macardoso said:
You can see the backplate protrudes from the edges of the chuck in this picture. Never found it annoying. Import chuck made in 93'

View attachment 311433
Click to expand...

That much I could deal with but this was 3 tenths of an inch bigger.
I wish I’d taken a picture.


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I think that you are correct about the not ideal matchup. Please make sure that there aren't any sharp edges left on the exposed counterbores. Bumping your hand on that part of the chuck would be no different than touching a live cutting tool.
 
The only problem I see with cutting into the counterbore is now you have little knife edges around the chuck. If you run your hand on the chuck to slow it down when turned off you can now get caught by one of those pieces which could be ugly.
 
Thanks @Cadillac that's also my concern. When I get a bit of time I think my plan will be:

  • Use the backplate to make a hole pattern
  • Fill the existing holes
  • Drill new holes 90 degrees using the pattern
  • Drill new small counterbores
 
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