Bridgeport Model 2 Boring Head Marked NFG
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  1. #1
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    Default Bridgeport Model 2 Boring Head Marked NFG

    Maybe belonged to Norman F. Grossmeyer? Nah, somebody declared it no f. good, but after examining it, I’m not positive why. The ram lock screw was in so tight it took us a while to free up, wonder if former owner couldn’t un-stick it? Drawbar threads are excellent, slide moves 3/4 inch total range (is that enough?). Only real defect I noted was 0.006 in. lost motion in the ram advance screw, assuming each tick mark is 0.001 in. Presumably this would manifest itself in 0.006 in. Uncertainty about the radius of cutter , but I’ve never used one of these. If that’s a fatal flaw, are repair parts available? Photo link:

    Flickr: Page Not Found

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    Quote Originally Posted by Cannonmn View Post
    Maybe belonged to Norman F. Grossmeyer? Nah, somebody declared it no f. good, but after examining it, I’m not positive why. The ram lock screw was in so tight it took us a while to free up, wonder if former owner couldn’t un-stick it? Drawbar threads are excellent, slide moves 3/4 inch total range (is that enough?). Only real defect I noted was 0.006 in. lost motion in the ram advance screw, assuming each tick mark is 0.001 in. Presumably this would manifest itself in 0.006 in. Uncertainty about the radius of cutter , but I’ve never used one of these. If that’s a fatal flaw, are repair parts available? Photo link:

    Flickr: Page Not Found
    Yeah that thing is junk I think you need to send it to me!

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    Do you mean that there is slop in the lead screw going from one direction to the other or there is a dead spot like stripped threads? The only reason I ask is that like every type of lead screw (except maybe ball screws) there is going to be some take up slop. My Kaiser has at least that much play but not in one direction if that makes sense.

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    Quote Originally Posted by crossthread View Post
    Do you mean that there is slop in the lead screw going from one direction to the other or there is a dead spot like stripped threads? The only reason I ask is that like every type of lead screw (except maybe ball screws) there is going to be some take up slop. My Kaiser has at least that much play but not in one direction if that makes sense.
    Now that I think about it more what I’m seeing may just be “knob slop” but I’m not sure. I haven’t tried to bore with it yet. When I adjust the Allen screw in middle of the setting dial, I can turn it past six tic marks with no resistance, ram not moving, then the ram becomes engaged and it gets much harder to turn, but does move the ram. Maybe that’s why they had the ram lock screw tightened so hard?

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    Quote Originally Posted by Cannonmn View Post
    Now that I think about it more what I’m seeing may just be “knob slop” but I’m not sure. I haven’t tried to bore with it yet. When I adjust the Allen screw in middle of the setting dial, I can turn it past six tic marks with no resistance, ram not moving, then the ram becomes engaged and it gets much harder to turn, but does move the ram. Maybe that’s why they had the ram lock screw tightened so hard?
    This sounds like a used Bridgeport boring head that I got for small dollars. It turned out that the very fine-pitch hardened threaded screw that the diameter adjustment dial turns was slightly corroded or worn, and so male and female threads did not quite mesh reliably. I have no way to fix that, so I binned the boring head.

    Perhaps relevant is another used boring head where the slide was almost impossible to move. Turns out that it had been dropped, probably when the slide was absent, bending one jaw or the other slightly, pinching the cross-slide dovetail. This was easily fixed, using HiSpot Blue and some very fine wet-dry sandpaper on a metal block to scrape the offending high spot down just enough, a matter of perhaps 0.0001".

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    Quote Originally Posted by Joe Gwinn View Post
    This sounds like a used Bridgeport boring head that I got for small dollars. It turned out that the very fine-pitch hardened threaded screw that the diameter adjustment dial turns was slightly corroded or worn, and so male and female threads did not quite mesh reliably. I have no way to fix that, so I binned the boring head.

    Perhaps relevant is another used boring head where the slide was almost impossible to move. Turns out that it had been dropped, probably when the slide was absent, bending one jaw or the other slightly, pinching the cross-slide dovetail. This was easily fixed, using HiSpot Blue and some very fine wet-dry sandpaper on a metal block to scrape the offending high spot down just enough, a matter of perhaps 0.0001".
    Thx, I’m guessing I can get it apart by removing the slide locking screw then turning the adjust screw until the slide comes all the way out one end?

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    Quote Originally Posted by Cannonmn View Post
    Thx, I’m guessing I can get it apart by removing the slide locking screw then turning the adjust screw until the slide comes all the way out one end?
    Yes, something like that. I don't recall having any problem figuring it out or getting it apart.

    With hand pressure, the screw threaded into the cross-slide block OK, but in real use, it would slip. Now that I think about it, what may have happened is that when the head got old and dirty and stiff, people just kept on using it, and wore the tips of the threads out. A little grinding dust would help. That would explain why it did not look corroded, and yet failed.

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    Easy disassembly, we cleaned it and put in some light oil. Ram drive screw is like 5/8-20, with some stubby thread profile I don’t know. All looked new inside but the lost motion could only come from the quarter-sized disc rotating in a slot just behind the “thousandths” graduated disc. It functions as a thrust bearing. There must be a few thou. of wear on the disc. Since there’s a locking screw to clamp the body’s dovetail around the ram, hopefully the ram won’t slide in the dovetail once the locking screw is tightened. I’ll have to see how it performs while boring.

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    You know what the NFG stands for!

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    Since last post I watched a couple of videos on boring heads, done by the old guys who know quite a bit. What I called a locking screw is apparently just to snug up the gibs leaving the ram free to slide to various settings set on the dial or tweaked on the dial to close-in on a desired diameter on the work.


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