Marking holes in backplate

[DavidR8]

In looking at 4-jaw chucks and backplates I see some chucks have mounting holes that pass through on the body while others only have holes on the back.

How do I mark the holes on the backplate in the latter situation?


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[benmychree]

With transfer screws, they screw into tapped holes, the parts are assembled and set together with a hammer blow; I make them as needed out of Allen bolts, cut a teat on one end and use a hacksaw to make a screwdriver slot a bit off center from the teat to install and remove them.

 

[pdentrem]

I used a drafting program to print out a sheet with the proper layout and used it to mark the hole centers.

Making a couple of threaded spindle backing plates for my lathe

When I sold my Atlas 10F24, I held on to my Bison 5” 3J, as it was fairly new. Naturally I needed to make a new backing plate to mount it onto the new lathe. The old plate was 1 1/2” X 8 while the new spindle is 2 1/4” X 8, so I needed new metal to do this. I recently purchased 2 backing plates...

www.hobby-machinist.com

 

[BtoVin83]

The important question is what resources do you have? The way I do it is to take a sharp threading tool pointed in to the work face and scribe a line on the circular disk. Using a center head mark the first hole and if even number of holes mark the opposite hole. As best you can center punch those and use dividers to lay the rest of the holes, work both ways from the center punched holes to half the error is setting the dividers to the chord length

 

[BtoVin83]

"The way I do it is to take a sharp threading tool pointed in to the work face and scribe a line on the circular disk" Sorry, this becomes your BC

 

[pontiac428]

Most of the machining reference books have a chapter on layout. Bolt circles can be layed out accurately using a number of tricks with dividers and/or a square. You can convert bcd and number of holes to coordinates using simple trig for drilling with a DRO. You can skip the layout and do it with a rotary table. This cat can be skinned so many ways.

 

[RobertB]

Transfer screws are easy, fast and accurate and if you don't want to make your own are pretty reasonably priced.

Transfer Screw Sets, Single Size 3109

Layout Tools 3109 Includes 6 transfer screws in a wrench/holder; Transfer exact location of threaded holes; Works with blind holes;

littlemachineshop.com

 

[benmychree]

Transfer screws are easy, fast and accurate and if you don't want to make your own are pretty reasonably priced.

Transfer Screw Sets, Single Size 3109

Layout Tools 3109 Includes 6 transfer screws in a wrench/holder; Transfer exact location of threaded holes; Works with blind holes;

littlemachineshop.com

I think that transfer screws are possibly the most foolproof way of locating holes to mount chucks in the situation mentioned, and possibly the fastest method, as well. The ones shown in the LMS site are the Heimann type, and work quite well, and there are other types also, those shown would be my first choice for the job.