So, lug 1 is engaged, and #2 is very close, but #3 is about .003 away, and I would like to get all 3 engaged, or at least #1 engaged, and the other 2 very, very close (verified by CMM). I have two very old lathes without DROs, a small mill/drill, a surface grinder, pin gauges, and a lug file. Given this equipment, what would you use to cut the .003 off of #2 and #3? I recall seeing something about using a lathe, but this doesn't make sense to me, as you'd also be cutting the underside of the barrel. Then I read something about using a mill, then the file. Seems like a bunch of ways to go. I'm terrified of screwing this up, because there's no fixing this.
Best way to cut upper lugs to equalize engagement
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4 jaw chuck in a lathe.
Not terribly difficult for a machinist.
Not terribly difficult for a machinist.
Trying to learn, what exactly needs to be 'cut'? The top of lugs 2&3? Or is it the bottoms to allow them, (the barrel), to ride higher into the slide? If #1 is engaged, 2, (and to a greater extent, 3), are not, the angle of the barrel relative to the slide is wrong? Will a longer link be needed? Just got my Kuhnhausen book a couple of weeks ago, MAN there's a lot going on in these!
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You would ruin the barrel, not the slide.
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This is getting into some pretty advanced stuff. You would need to off set the bbl in a 4 jaw like Chuck said.
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If you were to take 100 ea. 1911s and measure them.. I seriously doubt that you would find one that had equalized upper lug contact. The only reason, I and a few other obsessed bullseye smiths bother with it, is to gain rigid, stabilizing support for the barrel in lock up..for enhanced accuracy...
From my observations over the years of major crashes of bullseye guns, I have never seen a lug shear..which tells me that if the pressure reaches high enough to threaten shearing a lug(s) something else will fail before the lug comes close to breaking..Remember, bullseye guns have hard contact between the hood and first lug. No running starts..
Never the less, here's a few photos of how the lugs are machined to make equal contact..
There are a number of ways to do this.. Mapping out the dimensions, and being able to transfer those dimensions is critical..Grinding, or turning work equally well..The scope and DRO is an excellent way to get accurate dimensions.. Can also be done with an indicator and DRO.. You can chuck up the slide in the lathe and use the DRO or in the mill..This also affords the opportunity to match the inner slide radius to the barrel locking lug radius to gain as much extra contact as possible.. The 10/2 spot contact is less than ideal.. As PWrench stated.. "It's a piece of cake." or something like that...
From my observations over the years of major crashes of bullseye guns, I have never seen a lug shear..which tells me that if the pressure reaches high enough to threaten shearing a lug(s) something else will fail before the lug comes close to breaking..Remember, bullseye guns have hard contact between the hood and first lug. No running starts..
Never the less, here's a few photos of how the lugs are machined to make equal contact..
There are a number of ways to do this.. Mapping out the dimensions, and being able to transfer those dimensions is critical..Grinding, or turning work equally well..The scope and DRO is an excellent way to get accurate dimensions.. Can also be done with an indicator and DRO.. You can chuck up the slide in the lathe and use the DRO or in the mill..This also affords the opportunity to match the inner slide radius to the barrel locking lug radius to gain as much extra contact as possible.. The 10/2 spot contact is less than ideal.. As PWrench stated.. "It's a piece of cake." or something like that...
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Not if it's set up properly. As P'wrench said, use a 4 jaw. A three jaw will absolutely not work. That's one clue (difference in the way a 4 jaw and 3 jaw work). Go study the GI blueprints or the barrel drawings in Kuhnhausen very carefully. That might turn on the lightbulb for you in a way that posts on this forum will not.
Okay, the light just turned on. Believe it or not, I'm a certified machinist, but way out of practice due to years of medical school. I really appreciate you guys holding my hand through this. I do have a 4 independent jaw chuck in my old Dalton. Its a little small, but there's a good inch and a quarter or so of jaw, so it should work. There's no hole in the middle going back into the spindle, but shouldn't be a problem. No DRO on the lathe or surface grinder (of course), but one on the mill. I would have to rely on gauge pins if I used the lathe, but I get the feeling that wouldn't be good enough.
Once again, Jerry blows my mind with some seriously esoteric gear. Sometimes I think he works at CERN, or is communicating with aliens��. I'm not as concerned with accuracy as I am with safety with this .460 Rowland build. Are you saying that if I get solid vertical and horizontal contact on lug #1, with zero end shake and head-on headspace, I should be okay? That would be a relief, actually.
Once again, Jerry blows my mind with some seriously esoteric gear. Sometimes I think he works at CERN, or is communicating with aliens��. I'm not as concerned with accuracy as I am with safety with this .460 Rowland build. Are you saying that if I get solid vertical and horizontal contact on lug #1, with zero end shake and head-on headspace, I should be okay? That would be a relief, actually.
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The .460 Rowland is not gonna rip the lugs off the barrel or anything. It operates under 9x23 and some 10mm pressures, and hundreds of those have been sold with not quite ideal barrel fit. No horror stories have appeared yet.
As mentioned before, a good understanding of the basics will see you in good stead, but trying to accomplish online, what Jerry and others are doing, and have spent years developing, may result in a very long session of tailchasing.
Jerry and PW have Some of the best, and most informative pictures on the net, but its useless until the full workings are understood....
CW
.....Which is why I would work for these guys for free if they'd have me, just to learn as much as I could from them, if I didn't have bills to pay. Okay, that's good to know. I'm not going to try to equalize the lugs then. I might just experiment with an old barrel, though, and possibly check with a DTI to see how out-of-round the lugs are just for the hell of it. Why do they usually only contact at 10 and 2, BTW? Also, I think I'm going to finish up the hood on the surface grinder this time, rather than the mill.
I'm very happy with the slide-to-frame fit I got this time. I measured the slide rails with the Starrett slide rail mic, then had a keyseat cutter ground to a half a thousandth over that dimension. I cut the rails so that there would be about a half a thousandth gap on all sides, then went through a 2-day process of applying Dykem, tapping the slide back and forth, fine-filing high spots, washing off and re-applying Dykem, repeat about 60-70 times, until I had smooth movement, but absolutely no play up, down, left, right, twisting, nothing, zero slop. Same with the ramp cuts.
Wow! I just measured the lugs in the slide, and there's about .002 variation on each lug, depending on where you measure it. It starts out small on one end (let's say 10 O'clock) and ends up .002 wider at 2 O'clock. Yeah, I think I'm done playing with that. I wish this wasn't beyond my skill and tooling, though; it's going to drive the perfectionist in me a little crazy! I totally "get" people like Jerry, with their relentless pursuit of perfection. It's almost pathological in me. I got straight A's in pre-med, not because I'm particularly bright, but because I needed to understand everything as near-perfectly as I possibly could. I can see that I'd be suited to this line of work, if I'd taken a different path.
Joe,
Are you measuring the distances from the lug engagement surfaces to the breechface? Or from one engagement surface to the same spot on another engagement surface?
Remember, the slide lugs and breechface are machined at the barrel lockup angle. Furthermore, the cutter that's used is not the same diameter as the barrel lugs, so the slide lugs aren't machined via a simple plunge cut. It's a horizontal cut. As far as measuring goes, that means that if you're simply holding the slide upside down and measuring the distance across the engaging and non-engaging surfaces at various points on each lug, those measurements won't be very useful. On the other hand, if you carefully measure the distance from the breechface to each lug engagement face, you'll be able to fit your barrel lugs to that map.
Hope that helps.
David
Are you measuring the distances from the lug engagement surfaces to the breechface? Or from one engagement surface to the same spot on another engagement surface?
Remember, the slide lugs and breechface are machined at the barrel lockup angle. Furthermore, the cutter that's used is not the same diameter as the barrel lugs, so the slide lugs aren't machined via a simple plunge cut. It's a horizontal cut. As far as measuring goes, that means that if you're simply holding the slide upside down and measuring the distance across the engaging and non-engaging surfaces at various points on each lug, those measurements won't be very useful. On the other hand, if you carefully measure the distance from the breechface to each lug engagement face, you'll be able to fit your barrel lugs to that map.
Hope that helps.
David
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