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recoil rod drillings

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Category: Auto Mag Pistol
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URL: http://www.amtguns.info/forum_posts.asp?TID=2335
Printed Date: 28 Mar 2024 at 1:41pm
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Topic: recoil rod drillings
Posted By: TRX302
Subject: recoil rod drillings
Date Posted: 09 Sep 2018 at 8:53pm
My "scratchbuilt frame" project creeps slowly along... I'm getting ready to do the recoil rod holes.

I have a big flame-cut disc of steel to build a "pallet" to hold the frame, which I'll bolt to the lathe faceplate. I'm sort of jumping the gun on this, because I need to get the pallet done so I can balance it before I sell my engine balancing machine. I can do a dynamic balance with the machine, as opposed to a static balance on knife edges or bearings.

Anyway, I'd always figured on drilling the holes from the front. The production frames were obviously done that way; drilled blind to make the spring abutment, then a smaller hole drilled through for the rod to go through. My production frame is like that.

The Auto Mag patent application, and the prototype frame I got from Walter Sanford, are drilled all the way through, with fine-thread plugs screwed in the back to make the spring abutments.

Obviously, blind drilling saves making, threading, and installing the plugs... but I was remembering Bob B's complaints about crooked drillings in The Book, and there are plenty of comments about recoil rods binding in threads here. Could be that the drills wandered a bit, but not quite enough to bind things up when the cocking piece was all the way forward.

To guarantee cocking piece alignment, you'd want to drill from the back, where you could guarantee the position of the holes. And if they wandered a bit at the front, you could do a little "hand work" reprofiling the outside of the frame to visually center the holes. And Even if they were off-center a lot, it wouldn't matter, since any binding would be at the end of a long rod.

Then I realized that this might also be a reason why the factory moved from .200" recoil rods to .187"; more clearance to save frames where the drillings wandered too far to the side. And that would also explain why there was considerable overlap between large and small rod guns; they probably tried .200 rods from inventory in each frame; if things were OK, it went on to the next station. Otherwise, they put in new .187 rods and tried again. If those failed, the frame went into one of those scrap barrels so many "successor" companies kept buying...

Before I do the pallet I should probably chuck up a piece of round stock and see how much the drill wanders. Even gun drills don't go perfectly straight, and the lathe probably won't work as well as a real gun drilling machine.

Fortunately, I have no problem with drilling from the back and using plugs if I have to.






Replies:
Posted By: USA 1776
Date Posted: 10 Sep 2018 at 12:29am
I'm no machinist, so there may be a laugh to be had here, but I always wondered why you couldn't weld an appropriately sized tube to both sides and go from there. Wouldn't look quite as cool, but seems it would save time and scrapped frames.

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'It has been said that politics is the second oldest profession. I have learned that it bears a striking resemblance to the first.' Ronald Reagan


Posted By: richie_b
Date Posted: 10 Sep 2018 at 1:35am
Originally posted by USA 1776 USA 1776 wrote:

I'm no machinist, so there may be a laugh to be had here, but I always wondered why you couldn't weld an appropriately sized tube to both sides and go from there. Wouldn't look quite as cool, but seems it would save time and scrapped frames.


Welding a thin tube to a thick frame would almost certainly warp the tube. Worse than an off-center through-hole.   Unhappy


Posted By: TRX302
Date Posted: 10 Sep 2018 at 1:35am
You could, and I thought about it, but to do it right would require a TIG welder and I don't have one, and don't know of any welding shops around here I'd trust with welding thinwall tubing like that. Farm implements and trailer hitches are about their skill limits.

I did take a long look at brazing the tubes on, though. There are some German-made brazing compounds with absurd tensile and shear strength ratings. Should my gun drilling go awry, brazing is Plan B.

Max said he intended for the recoil rod holes to be cast and then reamed smooth, which is theoretically within reasonable limits for investment casting stainless, but Bob B.'s description of the grief they were having with other dimensions might account for them sending frames out to be gun drilled.


Posted By: Luvz2Shoot
Date Posted: 10 Sep 2018 at 2:41am
I remember seeing a video post, fairly recently, of an Auto Mag frame that appeared to be getting the recoil rod holes drilled.  Almost looks like it was posted by the new Auto Mag company.  For the life of me I cannot find the link or video.
 
I have a little "project" that needs the holes drilled too.  I was thinking that the only way I (personally, with my "limited" machines) can keep drift to a minimum would be to drill in stages with various length bits.  Start with a short one and progress an inch or so at a time.  I figure it would be better than trying to go all at once with an 8" (?) bit and having it drift.  Shorter bits are stiffer and the longer bits would have a predrilled hole to follow so drift may be reduced.
 
Please keep us posted on what you come up with.  One of these days I'll get to my "project" and I just might copy you instead of going with my hair-brained idea.  I've seen your work and am a fan.  I would trust your method more than what I envision in my head.
 
 


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If you were happy and you knew it, would you clap your hands?


Posted By: TRX302
Date Posted: 10 Sep 2018 at 5:21am
A twist drill needs to be dead nuts on centerline to cut straight. You want a name-brand, split-point, American-made drill; stepped lengths as you suggested is a good idea. I've heard that parabolic point drills run straighter than common geometries, but I've never actually used any; it would be worth your time to talk to one of the places that actually make drills.

Sometmes a twist drill runs straight, sometimes there's a hard or soft spot in the stock and the drill will wander off to the side. A gun drill deals with that a bit better than a twist drill, but even gun drills will sometimes wander.

The sure-fire method would be to EDM the holes; you could guarantee they'd run straight. But that's not in my budget...


Posted By: Luvz2Shoot
Date Posted: 11 Sep 2018 at 1:21am

Do you know of any companies that would EDM pop holes?  Would you trust anyone other than yourself to do something like that?



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If you were happy and you knew it, would you clap your hands?


Posted By: Dances with AutoMags
Date Posted: 11 Sep 2018 at 3:38am
Originally posted by Luvz2Shoot Luvz2Shoot wrote:

Do you know of any companies that would EDM pop holes?  Would you trust anyone other than yourself to do something like that?

 
Caltron Co. EDM Specialist 2121 Floyd Street, Burbank, CA  91504 (818) 846-7000
 
They have cut the recoil rod holes in many Auto Mag frames and probably still have the prints.
 
A through hole is much easier and  cheaper to do.  To cut the step, in the end of the recoil rod hole to retain the spring, is a time consuming task to do correctly.  I have suggested that a through hole could be made and a screw-in spring-stop could be installed.  This is how the XP Auto Mag's were made.  The thinking is that the screw-in spring-stop would be made of a silicon bronze which would be self-lubricating on the stainless-steel recoil rods.   
 
There was talk at one time (by Auto Mag LLC) of casting the recoil rod holes when the frame is cast.  This was done by the factory for the number two and three guns. 
 
You are welcome John. 
 


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An armed society is a polite society.


Posted By: Luvz2Shoot
Date Posted: 11 Sep 2018 at 4:00am

Bruce,

 
Thank you very much for passing along this info.
 
I will contact them when I get around to my project.
 
I believe I read in your book, Auto Mag the Pasadena Days, where you mentioned they started casting the recoil rod holes when the frames were cast?  Or am I imagining that?  haha
 
Thanks again!
 
 


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If you were happy and you knew it, would you clap your hands?


Posted By: AndyC
Date Posted: 11 Sep 2018 at 4:37pm
Originally posted by Luvz2Shoot Luvz2Shoot wrote:

I remember seeing a video post, fairly recently, of an Auto Mag frame that appeared to be getting the recoil rod holes drilled.  Almost looks like it was posted by the new Auto Mag company.  For the life of me I cannot find the link or video.
This one, perhaps:

https://www.youtube.com/watch?v=nrt4Q0LRvcM" rel="nofollow - https://www.youtube.com/watch?v=nrt4Q0LRvcM




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Posted By: Luvz2Shoot
Date Posted: 13 Sep 2018 at 3:20am
Originally posted by AndyC AndyC wrote:

Originally posted by Luvz2Shoot Luvz2Shoot wrote:

I remember seeing a video post, fairly recently, of an Auto Mag frame that appeared to be getting the recoil rod holes drilled.  Almost looks like it was posted by the new Auto Mag company.  For the life of me I cannot find the link or video.
This one, perhaps:

https://www.youtube.com/watch?v=nrt4Q0LRvcM" rel="nofollow - https://www.youtube.com/watch?v=nrt4Q0LRvcM


 
 
Yes, that was it.  Thank you!


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If you were happy and you knew it, would you clap your hands?


Posted By: KMP
Date Posted: 13 Sep 2018 at 3:47pm
I bet Harry S. would have loved to have a modern CNC, back in the early 70's. He told me horror stories about gun drilling those holes. 

Eric


Originally posted by AndyC AndyC wrote:

Originally posted by Luvz2Shoot Luvz2Shoot wrote:

I remember seeing a video post, fairly recently, of an Auto Mag frame that appeared to be getting the recoil rod holes drilled.  Almost looks like it was posted by the new Auto Mag company.  For the life of me I cannot find the link or video.
This one, perhaps:

https://www.youtube.com/watch?v=nrt4Q0LRvcM" rel="nofollow - https://www.youtube.com/watch?v=nrt4Q0LRvcM




Posted By: TRX302
Date Posted: 14 Sep 2018 at 2:38pm
Quote
https://www.youtube.com/watch?v=nrt4Q0LRvcM" rel="nofollow - https://www.youtube.com/watch?v=nrt4Q0LRvcM


Whooo! And that's the difference between pecking a hole out in your home workshop and having the right tool for the job!


Posted By: tgt40
Date Posted: 14 Sep 2018 at 11:27pm
Lol... "pecking"....




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