Is it possible (or worthwhile!) to adapt an old 4" Burnerd 3 jaw for use on a Sieg SC4?

[LittleRestraint]

Hi all, first post so be gentle!

I have (and am learning on) a Sieg SC4 lathe which runs 100mm chucks. I do already have a 3 jaw and a 4 jaw, so I am fully operational in that respect, but I was given an old Burnerd No.30 chuck which is really nicely made and in great condition. The Burnerd is a 4" 3 jaw. Can this chuck be adapted to work on the SC4? More to the point; would it be a worthwhile exercise?

For the sake of clarity I will list a few points for consideration....

• The SC4 uses a 1-piece spindle and chuck backplate, which is 100mm diameter with holes to suit a 3 or 4 jaw chuck (8mm), and a 72mm register.
• My existing 3 & 4 jaw chucks use a 72mm register with M8 fixing bolts so obviously work as they should.
• The Burnerd uses a 76mm register/recess and different fixing holes (I'm guessing 1/4" something or other, can't measure the thread).
• The fixing holes on the Burnerd, aside from being smaller, are not quite the same hole centre as the backplate.

I messed about with making a template for an adaptor plate and successfully machined a steel plate with a 76mm register to fit the Burnerd chuck perfectly but I'm struggling past that point. I would love to use the chuck but I'm starting to doubt its feasibility. Obviously with it being 3 jaw I am aware of the need for absolute concentricity in anything I come up with.

Am I fighting a losing battle, or am I missing an easy solution to this?

It isn't anything I can't live without, I just like to try/learn if I can!

Thanks for any help you can give

 

[Eddyde]

I sounds feasible, some photos would help us to fully understand the problem. But going with what you described, I would first machine to fit and mount the adapter plate on the existing backplate, then machine it to fit the new chuck and then remove it and drill, counter sink hols to mount the new chuck with flat head screws, then mount the adapter with the new chuck to the backplate. Put witness marks on the all parts so they will go back in the same place when reassembled.

 

[LittleRestraint]

I sounds feasible, some photos would help us to fully understand the problem. But going with what you described, I would first machine to fit and mount the adapter plate on the existing backplate, then machine it to fit the new chuck and then remove it and drill, counter sink hols to mount the new chuck with flat head screws, then mount the adapter with the new chuck to the backplate. Put witness marks on the all parts so they will go back in the same place when reassembled.

Thanks for your response.

I will try and get some photos up later if I get chance.

That is pretty much how I would like to do it, but the issue I am struggling to visualise is the hole placement, i.e. the backplate on the chuck (fixed) has 8mm holes (non threaded), so when attaching a standard chuck the bolts pass through the back of the plate and fasten into the chuck, whereas the Burnerd has smaller holes with a different thread, and the centres aren't in the same place so I doubt it would be straightforward to enlarge them and tap them to M8. Presumably this would mean making new holes in the backplate (which already has a number of 8mm holes in it to accommodate 3 & 4 jaw chucks).

The other issue is that I'm not 100% confident in transferring the holes to a new adaptor whilst keeping the register lined up. The way I understand it is that the register is what gives concentricity so I'm guessing the two main priorities are the two registers on the new adaptor plate (72mm female facing the headstock, and 76mm male facing the new chuck).

As I don't yet have the knowledge for machining and problem solving I am just wondering if I have missed an easy (or easier!) solution

Again, thanks, I will see if I can get some photos sorted as it is tricky to explain (and I'm sure to visualise!).

It isn't an urgent rush anyway, as I have chucks that fit currently, more of a problem that is intriguing me!

J

 

[mksj]

Looking at mounting for this lathe, the current chuck system uses what appears to be either 3 or 4 bolts through the back of the mounting plate into the chuck body. The length of the bolts are such that there is about 3/4" threads into the chuck.



It should be straight forward to use an adapter plate between the current spindle mounting plate and the PBA chuck. What is unclear is on the PBA chuck if the mounting bolts are through the rear (which is uncommon) or mount through the front of the chuck into the back plate which is more common. Procedure wise, I would get a blank backing plate which most likely you will need to get a 6" (not sure if you can find them smaller), alternatively you could get round steel rod remnant which is less expensive.

6" Blank Back Plate

<h1>SB1384 6" Blank Back Plate</h1> <h2>For chucks with uncommon mounts, these 6" blank plates allow you to make modifications to suit your needs.</h2> <p>The unthreaded SB1384 6" Blank Back Plate allows you mount plain back chucks to uncommon lathe spindles, rotary tables or equipment that can...

www.grizzly.com

D-2 TOOL STEEL ROD machine mold die shop round bar stock D2 4 1/4" OD x 1 1/4" | eBay

1 piece of Tool Steel - D2. approx 4 1/4" OD x 1 1/4" OAL.

www.ebay.com

Flip the jaws on your current chuck to hold the blank round plate and surface cut the surface and cut the registration step the fit on your current lathe spindle mount to check fit. You can then drill and tap either 3 or 4 holes to mount to your lathe spindle. Should not be difficult to layout a bolt circle and make sure the holes are equal distant from each other to check position. You want to stagger the mounting holes and those of the PBA chuck so they will not overlap or be close to each other. So if the PBA has 3 mounting bolts, then use 3 mounting holes to the spindle mount which would have a 60 degree stagger from those which will be drilled for the PBA.

Mount the backing plate to your spindle, turn the mating surface to the thickness you need along with the registration step for the PBA chuck (assume ~1" thickness at the mounting holes, a little more than the depth of the mounting bolts thread depth). Then turn down the OD of the plate down to your current lathe spindle mounting plate or slightly larger to the diameter of the PBA chuck. then cut the registration step for the new chuck. I would also drill and center bore the ID to around 1.5" so you can pass stock through.

Remove the plate and drill/tap the mounting holes for the chuck. These should not be too critical as the registration step is what aligns the chuck. If the PBA chuck mounting bolts are through the front of the chuck then you are done. If they mount from the back, then you can use some grade 8 cap screws, or button heads and countersink them into the backing plate. Given the small diameter of the plate/chuck, and the registration step securing the lateral movement this should be plenty secure. Mount the backing plate to the chuck and then mount that to your lathe.

 

[LittleRestraint]

Looking at mounting for this lathe, the current chuck system uses what appears to be either 3 or 4 bolts through the back of the mounting plate into the chuck body. The length of the bolts are such that there is about 3/4" threads into the chuck.

View attachment 323304View attachment 323305

It should be straight forward to use an adapter plate between the current spindle mounting plate and the PBA chuck. What is unclear is on the PBA chuck if the mounting bolts are through the rear (which is uncommon) or mount through the front of the chuck into the back plate which is more common. Procedure wise, I would get a blank backing plate which most likely you will need to get a 6" (not sure if you can find them smaller), alternatively you could get round steel rod remnant which is less expensive.

6" Blank Back Plate

<h1>SB1384 6" Blank Back Plate</h1> <h2>For chucks with uncommon mounts, these 6" blank plates allow you to make modifications to suit your needs.</h2> <p>The unthreaded SB1384 6" Blank Back Plate allows you mount plain back chucks to uncommon lathe spindles, rotary tables or equipment that can...

www.grizzly.com

D-2 TOOL STEEL ROD machine mold die shop round bar stock D2 4 1/4" OD x 1 1/4" | eBay

1 piece of Tool Steel - D2. approx 4 1/4" OD x 1 1/4" OAL.

www.ebay.com

Flip the jaws on your current chuck to hold the blank round plate and surface cut the surface and cut the registration step the fit on your current lathe spindle mount to check fit. You can then drill and tap either 3 or 4 holes to mount to your lathe spindle. Should not be difficult to layout a bolt circle and make sure the holes are equal distant from each other to check position. You want to stagger the mounting holes and those of the PBA chuck so they will not overlap or be close to each other. So if the PBA has 3 mounting bolts, then use 3 mounting holes to the spindle mount which would have a 60 degree stagger from those which will be drilled for the PBA.

Mount the backing plate to your spindle, turn the mating surface to the thickness you need along with the registration step for the PBA chuck (assume ~1" thickness at the mounting holes, a little more than the depth of the mounting bolts thread depth). Then turn down the OD of the plate down to your current lathe spindle mounting plate or slightly larger to the diameter of the PBA chuck. then cut the registration step for the new chuck. I would also drill and center bore the ID to around 1.5" so you can pass stock through.

Remove the plate and drill/tap the mounting holes for the chuck. These should not be too critical as the registration step is what aligns the chuck. If the PBA chuck mounting bolts are through the front of the chuck then you are done. If they mount from the back, then you can use some grade 8 cap screws, or button heads and countersink them into the backing plate. Given the small diameter of the plate/chuck, and the registration step securing the lateral movement this should be plenty secure. Mount the backing plate to the chuck and then mount that to your lathe.

This is fantastic, thank you so much for your time! You have cleared up the sequence in my head and I think I can do it now. Brilliant.

You are correct, that is the mounting on my lathe. Also, you mention the PB.... It is rear mount the same as the existing chucks.

Material isn't a problem as I work at a heavy fabrication shop and get to use what I like

Thanks again for the brilliant write up, hopefully this will help others in my position.