Bridgeport M head Purchase Questions

[techymechy]

I finally found a Bridgeport M head. It seems to be a newer head with a serial number of M26107. I (unfortunately) have the B3 collet but have accumulated a set of collets: 3/16", 1/4", 3/8", and 1/2". I would like to get a 1/8" collet but I feel that I'm probably pretty set up with what I have (although I'm still looking for collets). I know that Bridgeport didn't track the head numbers, but does anyone know when Bridgeport quick making the M heads?


I'm taking some measurements on the head and I think it is OK. I placed a 3/8" pin gage in a collet and drew it tight. I am reading about .0008" TIR when the spindle is turned by hand (spinning the belt sheave). This isn't as good as my Hardinge TM vertical head which has like .0003(-)" TIR - but I wasn't expecting it to be as good.

My intent is to use this on my Hardinge TM mill. The head came with a 2" overarm that fits my Hardinge mill well. The overarm has a tapered slot machined in it. My mill has a threaded 1/2"-20 hole in the casting that could be used to locate the slot in the overarm. The overarm slot is too narrow for a 1/2" dog point set screw. Does anyone have the proper set screw which was used to locate the overarm? I was thinking of machining the proper taper on the end of a mild steel bolt but was hoping that someone had the real part so I could copy it.

Thanks for your help.

Dave

 

[IrbyJones]

You can use a 1/4" to 1/8" collet adapter or reducer instead of an 1/8" collet. I have one for my router and end up using it in my mill all the time when I don't want to switch out a 1/4" collet.

Irby

 

[L Vanice]

"The overarm slot is too narrow for a 1/2" dog point set screw. Does anyone have the proper set screw which was used to locate the overarm?"

It is quite easy to turn a dog point of whatever size you need on the end of a standard set screw. It helps to have a high speed lathe and carbide cutter, of course.

Many die grinders with 1/4" collets come with or have available accessory 1/8" reducer bushings.

Larry

 

[Ohio Mike]

I finally found a Bridgeport M head. It seems to be a newer head with a serial number of M26107. I (unfortunately) have the B3 collet but have accumulated a set of collets: 3/16", 1/4", 3/8", and 1/2". I would like to get a 1/8" collet but I feel that I'm probably pretty set up with what I have (although I'm still looking for collets). I know that Bridgeport didn't track the head numbers, but does anyone know when Bridgeport quick making the M heads?

There is no good source of info on build dates for heads but mine is M16543 and is on a 1951 serial Round Ram mill with serial of 14xxx. I believe this to be the original head because the head, motor several mill body components have the same asset number from DoD on them. And of course how close the two numbers are. Things would have gone wonky when the J head was introduced. Those first J heads were round ram machines, and a few years back I saw a round ram mill sell with a 3 digit J head number. I know the M head was available in catalogs in to the 1980s. I would assume your number is still early 1950s.

 

[techymechy]

Thanks for the idea about the 1/8-1/4" reducer. This is a great idea!

I think that I'll machining a Gr2 1/2"x20TPIx2" bolt so that the end is tapered and fits the overarm slot well. That way, I can tighten the bolt and wedge the taper into the slot. I am thinking Gr2 would be the right material since the shear modulus is the same as the harder materials yet it is not as brittle. Are the set screws case hardened (like Gr5 bolts) are are they through hardened? I have a Logan 400 that I use HSS tooling but I may have a few brazed carbide tools to tackle the hard set screws. I'm thinking a Gr2 bolt may be much easier to machine than a set screw.

Thanks for the information that dates my head to the early 1950's. I thought it might have been newer than that for it's in pretty good shape.

Thanks again for the response.

 

[IrbyJones]

"<snip>

Many die grinders with 1/4" collets come with or have available accessory 1/8" reducer bushings.

Larry

I typed router, but the reducer I have actually came with my old 1960's Sears (you didn't hear me say that word here!) hand - or it could be called a die - grinder.

Irby