drilling holes in chuck backplate.

[T0rnado69]

hi all, has anyone had the privilege of drilling the holes in a lathe chuck backplate.

i have skimmed the backplate down and stepped it for the 5" chuck thats on my lathe.
a while ago now.
but then i thought maybe best to get another chuck for it.
so ive left it alone until i get a 3jaw chuck for it.
this will save me keep taking the chuck of the lathe and
also if im using the backplate and chuck in the rotary table
then i cant use the lathe,

i know the three holes need to be 120* apart.
but how do you know how far out from the centre they need to be.

 

[piman]

Hello Stuart,

accurate measurement of the pitch of the three holes then geometry. Alternatively, a Zeus tables gives co ordinates for holes on a circle and from that you can work out the circle diameter.

Alec

 

[MattF]

The other ways are just a piece of paper and a grubby/greasy/oily finger rub, else some engineers blue and mate the chuck and backplate for an impression.

 

[DanielW]

Put three short stub studs in chuck that you can screw in enough so that they can be adjusted to come into contact with the backplate.

Put the chuck on the table face down and adjust those studs till you're comfortable that they're just touching the backplate as it sits on the back of the chuck centrally,after being satisfied with that put some engineers blue on the end of the studs and lower the backplate back of the chuck with trying to keep it central with the chuck.

the end result you should have three blue marks on the backplate for drilling the chuck holes.

Ideally the studs would have a taper near enough to a point for precise hole drilling and a dowl of tolerance fit that would fit through the backplate center hole and the chucks center hole..

 

[m1ecy]

Find someone with a mill and a dividing head - the mounting holes will all be centred on a specific diameter - easy to measure. then set the backplate in the dividing head, measure off and set the diameter, then use the dividing head to set the 120deg rotation.

Paper and that sort of thing is a sure fire way of getting the chuck to run off centre.

for the best accuracy you should be mounting the chuck on it's own dedicated backplate - you turn the backplate to size on the lathe it is being used with - there is usually a locating recess in the chuck that the backplate fits into, then drilling the locating positions is much easier.

HTH
Sean

 

[DanielW]

Find someone with a mill and a dividing head - the mounting holes will all be centred on a specific diameter - easy to measure. then set the backplate in the dividing head, measure off and set the diameter, then use the dividing head to set the 120deg rotation.

HTH
Sean

Great if you lived in an ideal world of knowing someone with a mill and dividing head but thats not always possible.

 

[CRB]

As long as the register is spot on, it matters not a jot about how accurate the fixing holes are.

I am sure we all would love to drill holes which are accurate in position to two decimal places in millimeters. In this case a 12dia hole for a 10dia bolt would be acceptable, surely.

 

[waddycall]

It's not that clear what you're trying to do.
Are you trying to get a backplate which has been machined to suit your existing chuck drilled to match the fixings on a chuck you haven't got yet??

 

[outofthefire]

I'm not an engineer and my maths is appalling so I fitted the backplate on to the lathe then held the chuck in place with a revolving centre, I checked it was true with my dti then just used a centre punch i'd made to fit the holes snuggly. Might not be the proper way but it worked for me.

 

[doubleboost]

The bit you want starts at 2.40

 

[T0rnado69]

cheers everyone with your replys.
i think i will source another 5" 3 jaw chuck to fit the backplate before i carry on with it.
it is to fit the rotary table, and if i use the chuck from the lathe
then i can see me having to keep swapping it between the lathe and rotary table.
and that will get annoying after a while.

 

[DanielW]

Don't like three jaw chucks on a lathe,you can't turn square stock.

 

[Pete.]

You can if you make a simple split collar. Turn a short tubular collar that the stock just fits nicely into then cut a small slot in one side to let it spring a bit. Put the stock in the collar and the collar in the chuck.

For backplate holes just drill them over-sized by a couple of mm. You don't want the bolts tight on the side of the holes anyway.

 

[T0rnado69]

Don't like three jaw chucks on a lathe,you can't turn square stock.

i have both 3 and 4 jaw chucks for the lathe.
but want to make more use of the rotary table on the mill.
by adding a chuck to the back plate that fits the RT.

 

[DanielW]

You can if you make a simple split collar. Turn a short tubular collar that the stock just fits nicely into then cut a small slot in one side to let it spring a bit. Put the stock in the collar and the collar in the chuck

Are you saying put a square peg in a round hole sorta thing?

Nah man,think I'd rather buy a 4jaw chuck at least then I can turn round,square,hex stock,saves messing around with a collar.

 

[ukracer]

Are you saying put a square peg in a round hole sorta thing?

Nah man,think I'd rather buy a 4jaw chuck at least then I can turn round,square,hex stock,saves messing around with a collar.

Thats fine but who finds the £860 quid for the chuck I would like to buy??

 

[DanielW]

So whats the lathe then? surely you can source a secondhand effort? mine was £30 and the spindle change was the dearest at £45

 

[ukracer]

So whats the lathe then? surely you can source a secondhand effort? mine was £30 and the spindle change was the dearest at £45

Colchester Master 2500 10 inch chuck...

I have actually got a 4 jaw chuck but my 3 jaw needs truing up so I priced up the best of both worlds and looked at a 6 jaw.

 

[zzr1200]

I just simply purchased a chuck where the bolts go in from the front of the chuck, machine the backplate with a tight fitting boss carefully remove the backplate/chuck from the lathe, then drilled through the chuck mounting holes from the front then turn it over and tapped the threads from the back...

 

[zzr1200]

I purchased my 4 jaw s.c. chuck from RDG Tools maybe not the best quality, but it runs true after following the instructions below:


http://www.lathes.co.uk/latheparts/page7.html

hth.