SB9 Collet Chuck & Backplate fit.

[graham-xrf]

We go several steps chasing this one. My SB9s are about 1940 and 1947.
First is a minor confusion about the Morse taper. In all the old catalogues I can find, the spindle taper is listed as MT 2. On both my lathes, the (about 1938 - 1943) SB9C and the 1947 SB9A, the Morse taper is very definitely MT3. The MT3 test bar fits right up it, as does the MT3 reamer. I don't understand that.
Do we know definitely that the Morse taper in SB9 spindles is always MT3?

The more important question is about the 1.5" diameter threaded end of the spindle.
5 turns takes up just short of 15.9mm, so looking like 0.625". So 0.125" per turn, which makes it 1.5" 8TPI.

The motivation is to get a ER32 collet chuck, and there are several seen of various diameters from 80mm to 125mm with 3 bolt holes and a recess to fit over the raised part of a backplate. The picture is of one with 125mm (about 5") diameter



So far - so good. I go after the backplate. Oh boy! I see all manner of rough stuff, from un-machined castings to some with the 8TPI thread in it?
Is the first job to try an cut 8TPI internal threads to make up a backplate?

Confirm - the raised part on it is called the "register"?
Is that what is also known as the "reticule"

I found a couple of backplates with the 1.5" 8TPI thread. In a gorgeous mix of metric and imperial, they are listed sized 100mm and 125mm.
Like this



I am guessing here, but it seems the method is to find a ER32 thingy with a recess smaller than the lump on the backplate, then turn the "register" down until it goes down the hole. If that chuck is to end up with acceptable run-out, that would have to be a very accurate tight fit.

If there is any experience going on how to get this right without purchasing several backplates, it would be much appreciated.

 

[Jim F]

You buy a back plate with your thread, then machine to fit on the chuck, using your spindle, so everything is cocentric to your spindle.
Lots of good youtube videos about it.

 

[silverhawk]

My SB9 "Junior" (sold January of 1930) is an MT3. Around 1938, they introduced the "toolroom" lathes, which were not the same thing as the previous 9" lathes. I agree with Jim - do the back plate. It will be more accurate in regards to repeatability than using a morse taper adapter (the MT collet adapter is what I use on my Junior, and I'm finally upgrading to a true backplate).

On a backplate, This Old Tony on youtube did a video on machining them. Get one in your thread size, then machine the chuck surface to flat and create the register to match the chuck. If your back plate doesn't have holes to bolt the chuck to, you will then need to mark and drill them (some need to have those threaded, depending on the chuck), and then simply put it all together.

You really want a semi-machined plate, because it will be as concentric to your spindle turning when you are done, and the only other variables that will make it less reliable would be how precise the collet chuck itself was ground and the collets (which are issues you'd run into with the MT chuck, too, plus the accuracy of the MT grind).

 

[silverhawk]

The This Old Tony video is over at

if you are interested.

 

[tobnpr]

What amount of runout is acceptable for your use?
First ops? Second ops?

Like a 3-jaw, fine for most first ops. But, you'll never get acceptable runout for second ops- "collet" accuracy with that method of workholding.

I used my 9A first with a MT3 collet adapter (mine is ER40). For my use- never needed to "feed" stock through the spindle.
Later picked up a Jacobs collet chuck, which provides excellent accuracy, and the ability to feed stock through the spindle.

 

[Manual Mac]

I’m pretty sure your ‘40 & ‘47 SB9 would be the *workshop* style. They will have a 3MT inside the spindle, they were supplied with MT3-2 sleeves from the factory.
I have a reprint of a SB Lathes catalog No. 94 from Feb, 1934, 72 pages listing everything they sold at the time.
There was no mention of A,B, or C configuration. Just the Basic workshop 9” lathe (I suppose this would be called the C model in a couple years of years).
The 9” junior was still listed & sold then, was a more heavy lathe.
I agree with posts 2 & 3.
I made #3MT arbors so I can use my 2-1/4” 3&4 jaw chucks on my SB9C for very small stuff.
But for my 5” chucks machined backplates on the lathe 1-1/2”-8 spindle.
I just finished a back plate for a new 4jaw chuck.
Even with magnets & shop vac while machining it was very messy. Cast Iron.
But very accurate.
I do not have a collet chuck, i wish I did.
YMMV, cheers

 

[Jim F]

I’m pretty sure your ‘40 & ‘47 SB9 would be the *workshop* style. They will have a 3MT inside the spindle, they were supplied with MT3-2 sleeves from the factory.
I have a reprint of a SB Lathes catalog No. 94 from Feb, 1934, 72 pages listing everything they sold at the time.
There was no mention of A,B, or C configuration. Just the Basic workshop 9” lathe (I suppose this would be called the C model in a couple years of years).
The 9” junior was still listed & sold then, was a more heavy lathe.
I agree with posts 2 & 3.
I made #3MT arbors so I can use my 2-1/4” 3&4 jaw chucks on my SB9C for very small stuff.
But for my 5” chucks machined backplates on the lathe 1-1/2”-8 spindle.
I just finished a back plate for a new 4jaw chuck.
Even with magnets & shop vac while machining it was very messy. Cast Iron.
But very accurate.
I do not have a collet chuck, i wish I did.
YMMV, cheers

I made a collet holder and drawbar for 3C collets, pretty easy.

 

[Manual Mac]

Jim, i have a 3/8-16 drawbar for my SB9 to use with the #3MT endmill holders & tiny chuck arbors i made.
I would like to make 3C collet holder.
Any link to plans?
Are we hijacking this thread?
Cheers, Steve

 

[Jim F]

Jim, i have a 3/8-16 drawbar for my SB9 to use with the #3MT endmill holders & tiny chuck arbors i made.
I would like to make 3C collet holder.
Any link to plans?
Are we hijacking this thread?
Cheers, Steve

I used 3/4" OD. .095 wall tubing for the drawbar, I used a 12" piece, it was too short for a handwheel, I drilled 4 holes for a pin spanner for my 5C collet blocks.
Hardest part was setting the compound to turn the 3MT.
I used a 4-40 set screw to fit the groovr in the collets.
I used a 1 1/2- 8 nut from Fastenal for the thread protector.

 

[Manual Mac]

Thanks for the write up Jim.
Definitely put this in my “to build” project pile (that’s starting to stack up like cordwood).
Not to mention a couple projects for She Who Must Be Obeyed.
Then there is the windstorm last 2 nights, limbs brought some of the fence down, need to get the sheep back in main pasture...but I digress....