Burnerd chuck backplate screws

Can anyone advise as to what the screws used to hold a Burnerd 4-jaw chuck to a backplate are? I have purchased a 6" chuck for my Myford/Drummond M and will need to machine and attach a backplate. I had a look on the usual suspect websites (Chronos, RDG, Ebay etc) but can't see any specifically listed which struck me as a bit odd as alternative backplates for different machines is common practice and they are readily available, and the screws are an obvious part to need to replace if the slot gets chewed up when doing so, but I could be searching under the wrong term.

It will matter what they are as the shank will need to fit the hole and the head will need to fit the rebate. If that corresponds to a standard size cheese head machine screw then that would be excellent as I can just buy them off the shelf, but if not then I will have to make them. I would be grateful if someone could point me at dimensions and/or a source.

Thanks

Alec

Depends on what the thread is in your chuck body where the screws fit, which depends on how old it is and what lathe it was originally made for. From memory, my Drummond M backplate is held on by studs and nuts that would be, I think, 5/16" BSF.

The chuck I have picked up has rebated holes in the front to take screw heads. It is labelled 'The Burnerd' on the front so is before the merger with Pratt. The holes are plain through the chuck so I am anticipating cutting threads in the backplate holes. This suggests that the correct screw would have a plain shank the depth of the chuck body and a threaded section into the backplate. It would seem logical for Burnerd to have made the chuck with a standard depth for different machines so that the body and screws were common to a range of machines and only the backplate needed to be varied, but just because that seems logical doesn't mean that's how it works. I am hoping that this is the case and the screws follow a standard form, rather than being Burnerd specials, but it would be handy if that was the case.

All of my chucks, which are mostly Burnard and include two 6" four-jaw, are held by socket headed screws, not cheese-head. The counterbores in the chuck screw-holes seem sized for that type of fastener.

In my collection, the older chucks which are fastened from the back have imperial threads, I'd expect newer ones to be metric but if it's front fastening then it's your choice.

And it depends on the thickness of the backplate. You might drill right through and put nuts on the back, high tensile/grade 8 to match the Allen head cap screws.

The chuck I have obtained is one of these - https://www.ebay.co.uk/itm/314060769553 - the pictures on the link show the slotted screws on the front which screw into tapped holes in the backplate. It should be fairly simple (within my abilities anyway) to make the screws if I have to, but if they are a standard form or available from a specific supplier I can save considerable time and effort, and have the chuck operational sooner which would be useful.

Alec,

Please forgive me if I'm 'teaching Grannie how to suck eggs'!

Starting from the lathe mandrel:

The chuck back-plate should be located radially by the register on the lathe mandrel nose.

The chuck should be located radially on the back-plate by the male register you machine onto the face of the back-plate so that it is a precise fit into the female register on the rear face of the actual chuck.

The fixing screws are responsible for securing the chuck to the back-plate to prevent relative rotation or axial play: they should play no part in radial location and so can be a comfortable clearance fit in the holes in the chuck.

5/16" BSF or M8 sound about right to me for an M-type or an ML7 machine. Choice of thread depends upon what size cap-heads you can most easily obtain and what taps you have.

Machining of the face of the back-plate should include a face skim (outboard of the central register ) so that the chuck will seat so its axis and the lathe mandrel axis are parallel, i.e. no relative squint. The register on the back-plate should almost, but not quite, fill the female register in the back of the chuck, it should not bottom-out.

Best regards,

Swarf, Mostly!

P.S.: you don't need to make your own fixing screws - eBay is full of sellers offering all sizes and lengths and thread types of cap-head screws.

Swarf, Mostly!

P.P.S.:  when I wrote the above, I was assuming we were discussing a three-jaw self-centring chuck.  I have now tried Alec's link and see we're actually discussing ain independent four-jaw chuck.  I think virtually all I wrote is still valid.

Swarf, Mostly!

 

Edited By Swarf, Mostly! on 09/07/2022 13:03:02

Edited By Swarf, Mostly! on 09/07/2022 13:08:38

My chuck looks identical with purpose-made screws you'd need to turn yourself.

The screws are 3/8" BSF, thread length 1.7/8" and the head is 0.556" diameter by 0.278" high.

Andrew

Oh ok. That looks pretty ancient. And kind of familiar from my M Type. Those look like they might be countersunk screws, about 5/16" diameter. If you are machining your own backplate. You might be able to buy standard countersunk screws that fit, or can be modded. probably with a BSW or BSF thread, or even metric perhaps. Or if they are cheeshead, could possibly be modded from hex bolts.

There is a good page on lathes.co.uk on the procedure for machining your own back plate in situ to get it all nice and true etc. Well worth a look.

Edited By Hopper on 09/07/2022 13:05:04

A wee bit late but here is a photo of one of my chucks as supplied originals from Myfors, the screw is 3/8" x 20 BSF underhand its 1.75" long

Thanks Swarf, Mostly

That is really useful information. I was aware of the role the backplate plays in achieving location through the register on the mandrel nose and the squareness of the face (ie the need to skim), and was aware that it achieved radial location through the male register, but I didn't know it should not bottom out and it hadn't occurred to me that the holding screws did not therefore play a critical role in location. I had considered them as actively preventing axial rotation through being a close fit in the holes but in practice I can see that this could be achieved instead by friction between the outboard front face of the back plate and the rear face of the chuck body, so the screws will not be critical.

The only limitation will then be something neatly fits both the main bore through the body and bears on the lower surface of the counter-bore as that will be load-bearing face. I therefore wondered whether Burnerd had employed a screw with an enlarged head diameter to increase the contact area, or used a standard size to keep costs down. It appears from comments so far that it is the latter so anything which fits should be fine.

Alec

Thanks All for the further replies - that gives me exactly the information I needed. Still slightly surprising that these do not appear to be available as a part, but I can now see what I need and they are easy enough to make from a bit of bar.

Alec

Alec

I think you missed the point made about using HT bolts/setscrews, this is to provide a secure fixing of the chuck to the backplate, better to be safe than sorry.

Emgee

I have drawing of a back plate if it helps.

David