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Thread: Bridgeport High Speed "M" head
09-13-2006, 07:41 PM #1
I'm kind of curious if anyone else has seen or used one of these high speed heads? It's flat belt driven with six speeds. They are,950rpm,1350,2200,3250,6500,and 12000rpm. I haven't seen any info about them and have never seen one for sale, even on Ebay. Is anyone else familiar with them?
09-13-2006, 10:54 PM #2
The M head was the original offering when the BP round-ram knee mill was introduced in 1938. It had six speeds from 275 to 4250 rpm. Speeds up to 12,750 rpm were available on request.
It's a basic head, smaller than the J, with no power downfeed. I've never used one.
Some comparisons with the J head:
Motor power: (M) 0.5 hp (J) 1 hp
Quill travel: (M) 3.5" (J) 5.0"
Spindle dia: (M) 1.437" (J) 1.875"
Spindle taper: (M) #2MT, #7B&S, & others (J) R-8
Max tool shank: (M) 0.50" (J) 0.875"
Drilling cap: (M) 0.50" (J) 0.75" (in mild steel)
Boring cap: (M) 1.5" (J) 6.0"
Milling cap: (M) 1.0 in^3/min (J) 1.5 in^3/min
09-14-2006, 08:32 AM #3
At one time, Dave Sobel had a couple of those
high speed, flat belt M heads. I think
the model designation is more complicated
than just "M" but I'm not sure on that.
09-14-2006, 06:36 PM #4
Thanks Leigh and Jim! I have one of these and am thinking strongly of selling it. It's an interesting piece but surplus to my needs. I've been a machinist for 30+ years and I don't remember seeing another one. I'll probably put it on Ebay along with it's knuckle and collets, hopefully someone will want it.
01-07-2012, 03:30 PM #5
Picking up on this rather old thread - Just bought a circa 1971 BP with high-speed M head. Apparently it has sealed bearings as the nameplate says "SPINDLE BEARINGS GREASED FOR LIFE". Has a 1hp motor & flat belt / pulleys for 6 speeds, ranging 950 - 12000rpm. My guess is that maybe it was geared toward precision woodworking / pattern making. My question is, what are the pros / cons of the high-speed vs "standard" M head? (I realize there are big differences between any M head vs J / 2J heads etc.). My plan is to use this mill for gunsmithing, mostly pistols. I do plan to install a VFD for better speed control. BTW does anybody know, how rare are these high-speed M heads? Also wondering what the value might be, as I saw somebody's asking $1495 (head only) for one like mine on eBay - that's $295 more than I paid for entire mill w / AcuRite DRO & Kurt vise - anyway thanks in advance for any feedback to this post!
01-07-2012, 04:51 PM #6
I wish I had some help for you. I have been looking at these with interest lately. I have a small Johansson mill all apart and waiting to get scraped with some minor head issues and have been thinking about mounting the hi speed m head instead and using it in my guitar shop. I can think of a ton of stuff I could use it for, mostly in wood and bone/ivory.
I would love to hear how you like yours when you get it running, there are a few heads I know of available and I am on the fence over the money. FWIW I usually see them for definitely less than that one that has been on ebay for a while.
10-29-2015, 08:15 PM #7
Picking up again on this old post. Bridgeport also hade a high speed J-Head, just a 3600 RPM motor and get double the speeds of a normal J. At 5400 RPM spindle speed, it approaches the correct SFM for aluminum or using tiny end mills. I have been told it was marketed to the "hand router" crowd for doing ornamental work, lettering and the like. Parts are easier to find than for an M-Head, and it has power feed quill.
10-30-2015, 05:56 AM #8
It's all there on Tony's site. Never heard of the "hand router" thing. All of the high speed heads that I've seen or run have been in mold shops. Even then they weren't fast enough for drilling 0.030" gates.
Bridgeport Vertical Heads