Thread: Source of chuck back plates?

If you divide 180 by the number of holes you wish to drill ,then find the Sin of this number,( Reduce to four decimal places).Then multiply the answer by the Pitch Circle Diameter.
This will give you the size to set your dividers to,to mark your holes.
You wont usually get an even number so there will still be a small error.
Cant help you with using a Pin to find centre for a drill,I either use a Centre Pop mark or if its Critical do it on the Mill.

I have purchased 2 back plates from Little Machine shop in the US http://littlemachineshop.com/ do a search under back plate. You need 1 1/2 x 8 tpi. The registration on the plate is always turned down to accurately fit the chuck you're using. It's easiest to use a transfer punch off an existing back plate, however if you have neither, spot the holes by finding suitable bolts to fit your chuck. Cut or part the head off the bolt so you have 3 threads and face them off but leave a pointed pip in the end, and thread them in to the chuck so just the tip of the pip is proud. Ideally you would harden them, but for a one off like this just put some layout or marker pen roughly where the holes will fall on the back plate. Open the jaws right up and place the chuck face down on a bench and fit the now machined back plate to the chuck, give it a tap with a deadblow to spot the holes. Remove and drill.

It takes almost as long to type as do it and if you're careful the holes will be absolutely spot on, though that is unnecessary as they serve no purpose in the accuracy of the mounting, they are clearance holes and simply stop the chuck falling on your newly renovated bed

Pete

PS Here's a way of doing it if you don't have a drill press http://www.arceurotrade.co.uk/review...0MEW%20141.pdf

Several places in the US sell suitable threaded backplates. Check out CDCO for example

http://www.cdcotools.com/

It's under Machine Tool Tooling -> Lathe Tooling

There are three different sizes of 1-1/2 x 8 backplates available there. Presumably the biggest market for these is for the 9" and 10k Southbends.

The spigot behind the thread is a few thou bigger on the Southbend than the Hercus. That doesn't matter though, the Southbend (and Hercus) design was such that the tiny spigot was not used for location like on some other lathes.


(Edit: Didn't see Pete F's post before typing that)

Thanks Pipeclay,

That explains it.

Thanks also Pete F - all these little tricks!

The blue tack and pin idea is to avoid the need for a center punch for drilling, and hence some inherent inaccuracy.

If you put some blue tack on the end of your drill chuck and insert the pin in the center of the blue tack.

Scribe your work making a cross where you want to drill.

The run the drill, and by hand you center the pin in the blue tack, working from the base to the tip until it is true. It therefore is dead true in the center of the chuck. Similar theory to an item in lathe chuck.

Now you can position your work, locating the scribed cross under the pin. When the pin is dead over the scribe marks you are positioned. Raise the drill, insert the required drill bit and drill your hole.

I was assured it is much more precise than a center punch - but try it and form your own opinions...

Just another pearl of wisdom from the era of the legends - what I'd give to have just a tenth of that.

Cheers

Ian

Have you tried this method of finding the centre of something you want to drill.
I am having trouble trying to understand how the pin helps if its not allready on centre with the Spindle of the Drill.
I thought that the Pin would just Centre its self to the job.
What method after using the Pin and Bluetak or other Wax or Plastercene do you use to stop your drill bit wandering,if you dont have a Pop mark for it to locate or do you use a Centre drill.

Hi Pipeclay

Yes I used it on the w/end and it worked.

You don't touch the work, only lower the drill chuck/pin to just above the work so you can accurately locate it over the work then lift the drill and fit the bit without moving the work - we had it in a vice.

By adjusting the end of the pin so it is not "wobbling" for want of a better term it has to be dead center of the chuck, which I guess is assumed where the center of your drill tip will be.

I tend to agree about the moving before but using a center drill we had no issues with movement. High speed, slow introduction and it worked like a charm. And that was on a round edge.

My "instructor" claimed that with a center punch you could always be a few thou out! His claim - but it worked!

I'll see if I can take a photo.

Now I go to find my slide rule and dividers.

Cheers

This is how I marked the drill holes in the back plates of both 3 & 4 jaw chucks.
Chalk the face of the back plate then place it on the back of the (facedown) chuck and tap lightly, the edge of the bolt holes will mark there location.
Holes should be 1/16" dia larger than the bolt size.
This method worked OK for myself.
See page 112 of How To RUN A LATHE, for full details.