# ER collet chuck mod for South Bend mill



## pmerritt (Jan 21, 2012)

Hi Everyone,

I haven't posted much of what I do in the shop, so I decided to show you guys how I'm going about modifying an ER collet chuck for my South Bend vertical mill. While it is a nice machine, there is a terrible design flaw. The motor sits over the spindle preventing the use of a drawbar to hold the NMTB 30 tooling. 







Their brilliant solution was to use setscrews to hold tooling in from the front. 






The toolholders are modified with pockets for the setscrews. I think they call this a 30mm taper.






While I have the three original holders (collet chuck, shell mill holder and boring head) the collet chuck has only four sizes and is in pretty rough shape so I want to replace it. The solution? Modify an ER-40 chuck with setscrew pockets. I got an MT-3 ER-40 collet chuck set from Tools4Cheap for the lathe. (Its pretty nice stuff for cheap import). So I ordered an NMTB 30 chuck from Shars for the mill.






So the trick is going to be holding the new chuck at the correct angle to mill the pockets. I will do this by boring a 5C emergency collet to match the NMTB 30 taper. This will then be held on an angle plate for milling the pockets. I was worried that the taper would be hardened and therefore a bear to machine, but a file seems to indicate that it is quite soft.

More to come

Peter


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## steamer (Jan 22, 2012)

Cool! keep up stocked up with pictures.

You'd a thunk SB would know better than to do that... ???

Good luck

Dave


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## pmerritt (Jan 22, 2012)

Hi Dave,

You're right, South Bend should have done better. Since these machines were made in the 50's and early 60's I think this design must have been to work around patents held by Bridgeport. This is also probably why you don't see many of these mills around. Amazingly enough there is another one here in Bloomington, I know of a couple of people on the practical machinist board who have them and there is one on eBay right now. I've had the setscrews work lose while making cuts. Let me tell you, BAD things can happen when your end mill holder is lose!! This has actually put me in a bit of a pickle. The last time I put the screws in, I used a little loctite. I now have a stripped out head! Oops!! Once we get the car out of its cocoon of ice I'll head into town for a screw extractor.

Anyway, I have the chuck mounted up and ready for pocket cutting. More pics later.

Peter


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## pmerritt (Jan 23, 2012)

Hello again,

Before I move on to so you how I did this, I must admit that none of these ideas are my own. There is a post on the practicalmachinist board that describes how to modify chucks for the South Bend mill. 

So time to make some chips. The first step was to bore out a 5C emergency collet to fit the nmtb 30 taper. I used my Elgin second op lathe for this. I picked it up last spring but haven't used it all that much. The 5C spindle and variable speed are very, but setting up the cross-slide is a real PITA.






Here is a staged shot showing the setup after the bore was finished. Machining the collet wasn't much fun. Drilling out the pilot hole resulted in something that only remotely resembled a round hole. Since the only boring bars I have on hand that can fit the bore are carbide, I was worried about chipping. The carbide held up nicely until I carelessly retracted the cutter into the hardened pins that hold the emergency collet open 






Now for the setup on the mill. I will mount the new chuck in the 5C collet in a collet block. The bore in the collet serves as a nest for the taper and a drawbar will be used to hold the chuck tightly in the collet.






Finally all is bolted to an angle plate on the mill table and awaits a visit from a carbide end mill...











Off to the real world  More later...

Peter


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