# How do you mount a new lathe chuck?



## bmannell (Dec 25, 2011)

I have a new 5" chuck with a backing plate and I understand how to face the backing plate and turn the boss to fit the back of the chuck but how do you mark the holes for the mounting screws? I'm very new to this machining business and I'm sure that a real machinist knows the answer. I'm just learning as I go along and I must say I have a lot of respect for people of this trade, there is so much to know and learn in this field, you certainly don't learn it in a week or two. Would appreciate any help someone could give me.

Thanks,
Burt


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## steamer (Dec 25, 2011)

Hi Burt

Well there are several ways of putting in holes that line up with your chuck. Probably the easiest is to transfer the hole locations with a transfer punch.

If you don't have a commercial set of transfer punches, you can make one on your lathe that will work fine....of coarse you have to have a way to mount the stock, which if this is you only chuck could be problematic!
I would probably use a transfer punch to locate the holes from the chuck into the backing plate.  Remove the plate, and drill and tap for the bolts using the pips as a start for the holes.

What kind of work holding do you have? You could turn up a transfer punch to match your holes pretty quickly.


Dave


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## bmannell (Dec 25, 2011)

Here is my problem, I have a back plate that has to be drilled for the mounting screws. The back plate is solid and when I fit it on to the chuck it covers the threaded mounting screw holes up so they can't be seen. How can I mark these with the back plate covering the holes? The screws will go through the back plate and screw into the chuck which is drilled and threaded.

Burt


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## johnmcc69 (Dec 25, 2011)

An alternative to Daves suggestion of the transfer punch would be a "blind hole" transfer
punch. You may also be able to measure the "bolt circle" with dial calipers to determine
Measurements. Try Googleing "Bolt circle measurement".

John


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## Tin Falcon (Dec 25, 2011)

burt :
 look at page 757 of the current enco catalog for what you need . Made in usa blind spotters for a buck or two a piece depending on size or transfer screw sets for less than $ 10 for import sets less that $20 for USA made. 
you can make your own spotters if the lathe is working. 

http://www.use-enco.com/CGI/INPDFF?PMPAGE=757&PMITEM=317-6931
hope this helps 
Tin


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## Metal Butcher (Dec 25, 2011)

Last year I faced the dilemma of mounting two chucks on two new backing plates for the first time. I made transfer screws from metric bolts. I cut off the heads and machined points similar to the ones shown in the link below. I milled two flats below the points to facilitate their installation and removal. Take your time, its not as hard as it seems. If your off a tiny bit you can shift the hole with a rat-tail file, after all its the register that locates the chuck on its backing plate not the mounting bolts.

http://www.cnccookbook.com/CCTransferScrews.htm

-MB


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## bmannell (Dec 25, 2011)

Thanks everyone for your help, this answers my question. This is such a helpful site especially for an idiot like me. I appreciate all your help, thanks so much!

Burt


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## Springbok (Dec 25, 2011)

Thanks everyone for your help, this answers my question. This is such a helpful site especially for an idiot like me. I appreciate all your help, thanks so much!

Burt

Hi Burt firstly anyone who asks question is not an idiot but has an equireing mind and that is what is needed in ME and
is all about could you let me know your lathe type as this would help in giving advice as there are many different types of backplates. In this case I must stress accuracy rules. 

Regards and a prosperious new year

Bob


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## Ken I (Dec 26, 2011)

Place bolts in the threads - measure the chord distances (average them) - via Trig work out the PCD - normally going to be an exact imperial or metic value. (obviously for even number bolts you can measure the PCD dircetly).
Pitch drill on a mill.

Use spotting points as suggested.

Quick and dirty method - smear a film of engineers blue (or ballpoint ink) around holes - carefully tap faceplate into position being carefull not to smear the impression - centre pop - drill undersize holes and finish file to get them lined up - since these are not locational they would be clearance anyway.

2c - Ken


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## my65pan (Dec 26, 2011)

When I did mine I put the backing plate on the mill, indicated center, and then drilled the bolt circle pattern. If you can give us the diameter of the bolt circle and the number of holes one of us can give you the cooridinates.


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## Tin Falcon (Dec 26, 2011)

> This is such a helpful site especially for an idiot like me. I appreciate all your help, thanks so much!



No one here was born with micrometer in hand or any lathe manuals memorized. We all had to learn what we know bit by bit. 
Some of us are pros and imersed in this stuff. I have th good fortune of training from uncle sam. 
Ask away bro. 
Tin


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## steamer (Dec 26, 2011)

What everyone else said! ;D  NO ONE KNOWS EVERYTHING! We all have to start down this road.  I'm glad there is this and other forums for the student.  They were'nt around in years past.  This is a good time to be a student!

No dumb questions here...just ask.

Dave


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## Blogwitch (Dec 26, 2011)

What I always tended to do when I had that job without the aid of my rotary table, was like most others, use blind transfer punches, but because they are not always as accurate as they should be, I used to open up the holes by an extra 1/2mm, so if for 8mm bolts, make the holes 8.5mm diameter, to make sure that the holes lined up with the threaded holes in the chuck.

Having the holes and thus the bolts going in too tight, due to slight misalignment, could cause the backplate not to sit down correctly against the chuck. It is the turned register that is the critical bit, if that is done well, you should be within a thou of being perfect, the hold down bolts are just there to keep things together. Also, make sure you give the holes a good countersink either side, especially where the backplate sits against the chuck.


John


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