Bridgeport M Head Drawbar

[comstock-friend]

Anyone have a drawing with dimensions for a BP M head draw bar??? Right now mine is just all-thread with a nut welded on top. From the exploded view it appears there is flanged piece held by a Woodruff key that goes under the spindle cap (left handed thread). The exploded view has a knurled knob on top.

Looks like you hold the spindle top cap with the wrench and turn the top knob. As the drawbar comes out, the flange hits the cap and applies ejection forces on the tool holder or collet (B&S #7 in my case, BP says the B&S #7 and MT #2 use the same draw bar). BP does have them, but they are $ 144 each, so that probably explains why I got the mill with the all-thread and welded nut in the first place!

Thanks if you can help!

John Friend

 

[bjmh46]

John,
I'm not near my machine right now, but I made my own self ejecting drawbar for my M-head. I used 7/16 cold rolled stock turned and threaded 3/8-16. My flange is made from HT 4140 and pinned it to 7/16 drawbar. I elected to use a 3/4 hex and not a knurled knob. No way I trust a knurled knob to sufficiently tighten the collet. Ever have an endmill pull out, or an adapter spin and scar the inside of your spindle? BTW, the spindle cap that holds the drawbar captive is left hand threaded, 7/8 fine IIRC. Actually when loosening the collet, you hold the spindle against rotation by holding the large hex on the splined pulley carrier. It's a good idea not to overtighten, or leave adapters, chucks, collets in the spindle for extended periods of time. I got my M-head free, it had a collet and broken endmill shank stuck in the spindle, and sat that way in an unheated garage for years. It was a project to remove it.

Bob

 

[comstock-friend]

Thanks, Bob, good comment about not trusting the knurled knob to get a collet tight. If using the pulley nut, doesn't that wear the splines more than if the (rather small) spindle nut flats are used? Answering myself, I guess that using the spindle brakes on the J heads are doing the same thing, so I guess it's not an issue on the splines! I caught the fact that the spindle cap is left handed, the flat is I assume to get it tight on the spindle threads so that it doesn't back off when the ejection flange on the drawbar bears on it.

Thanks again!

John

 

[waynesworld]

Good Morning, I have a BP mill and I am having some brain gas this morning and can't remember which head is on mine. But I got several new draw bars with mine at an auction. Your welcome to one if you pay the postage. The thread on the end fits the threads in the R-8 collets. There is the standard long nut on the end and it's pinned so if it's a different length you could shorten it. I have no use for all these drawbars so the price is right shipping only. Just let me know, cordially wayne

 

[comstock-friend]

Good Morning, I have a BP mill and I am having some brain gas this morning and can't remember which head is on mine. But I got several new draw bars with mine at an auction. Your welcome to one if you pay the postage. The thread on the end fits the threads in the R-8 collets. There is the standard long nut on the end and it's pinned so if it's a different length you could shorten it. I have no use for all these drawbars so the price is right shipping only. Just let me know, cordially wayne

Thanks Wayne, but I need the B&S #7 drawbar, 3/8"-16 thread

John

 

[comstock-friend]

Good Morning, I have a BP mill and I am having some brain gas this morning and can't remember which head is on mine. But I got several new draw bars with mine at an auction. Your welcome to one if you pay the postage. The thread on the end fits the threads in the R-8 collets. There is the standard long nut on the end and it's pinned so if it's a different length you could shorten it. I have no use for all these drawbars so the price is right shipping only. Just let me know, cordially wayne

Thanks Wayne, but I need the B&S #7 drawbar, 3/8"-16 thread

John

 

[comstock-friend]

Except for the crosspins, my new self ejecting M-head drawbar is done. Good thing I don't have to do this for a living, I think I saved about $ 2.50 an hour, but think of the fun!

Here are the parts, the, the second from the left is the Bridgeport spindle nut that came with the machine; Wrenching hex to its left, sleeve/pilot with the ejecting flange next, finally the draw bar itself.

All assembled here:

 

[comstock-friend]

My M-head activity was stirred up by reading Kay Fisher's rebuild notes. Mine isn't going to look like his, but we'll get her working again after about 20 idle years. Found my serial number, she's BH-663 (column door), born in 1941, 10 years older than me.

John

 

[amuller]

John,
It's a good idea not to overtighten, or leave adapters, chucks, collets in the spindle for extended periods of time. I got my M-head free, it had a collet and broken endmill shank stuck in the spindle, and sat that way in an unheated garage for years. It was a project to remove it.

Bob

I'm working on the same project, and so far not having much luck. How did you get it out?

 

[bjmh46]

I'm working on the same project, and so far not having much luck. How did you get it out?

Gentle heat on the spindle nose combined with babbit hammer on the temporary allthread drawbar. I was replacing the spindle bearings in mine so the hammering wasn't a concern. If you want to isolate the bearings from the hammering, make a tube that will support the spindle nose end by raising the knee--one end of the tube on the table, one end under the spindle nose. Preload slightly with the knee. Good luck!

Bob