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General Black Powder => Shop Series: Gun Tuning => Topic started by: Captainkirk on June 17, 2022, 09:17:16 AM
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One of the most FAQ regarding BP revolver tuning on Open Top Colts is regarding the infamous Uberti (and other makes) Short Arbor issue, in which driving the wedge in further closes up the cylinder gap to the point where it locks up the cylinder. This does not seem to affect late model CAM/CAD Pietta revolvers; it seems Pietta addressed and corrected this issue when they switched to CAM/CAD production in 2003.
There are many fixes for this, all, which seem to work if you understand the concept that the arbor should bottom out in the arbor bore of the barrel with the wedge driven in firmly and having a resultant .002-.005 gap between the cylinder face and barrel forcing cone.
Here are some techniques that the pros use.
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I am definitely not a professional. But this is how I do it. I know there are several ways to do it, and hopefully one of the real pros will come along and show their methods. Until then, here's my way.
There is one amendment to this article I'd like to make. Instead of a .006" cylinder gap, I am now going for .003" after many discussions with Mike Brackett. .003" is much better for keeping the cylinder face cleaned of fouling.
First thing I do, is disassemble the gun. Pull the wedge and remove the barrel and cylinder. Now clean all the oil off the arbor and down in the arbor hole on the barrel assembly. Set them aside.
All you need to accomplish this modification is, a piece of round stock, the same or nearly the same diameter as the arbor. You can get it at a lot of hardware stores, or metal supply houses. I get mine from an odd place. I have an old rammer plunger off a gun I cut the barrel down on. The plunger is no longer needed, so I use it to slice pieces off to fix short arbors. It's steel and it works just fine. I hate to waste stuff!
So now you need a slice of the steel round stock, to use as a shim. You can cut it however you like, I just do it this way so it comes out square and flat. I use a clamp that is designed to hold round stock for drilling. It's just a block with a "V" in it to support the metal, and a clamp to hold it in place. It looks like this with the round stock clamped in.
(https://live.staticflickr.com/65535/49324790711_cfb8a5b7c3_z.jpg)
Once the metal is clamped in, as long as you keep your saw blade flat against the clamp, the shim will be flat and square.
(https://live.staticflickr.com/65535/49324790696_19584800cc_z.jpg)
(https://live.staticflickr.com/65535/49324790646_16d9eab504_z.jpg)
So how do I know how thick of a shim I need? I don't really. I just cut a piece off around .008" and test fit it. Just take your newly cut shim, place it down the arbor hole in the barrel, and reassemble the gun. You'll be able to tell right away it it's too thick or thin. If it's too thick, you can cut another one a little thinner, or use a file and thin it out. If it's too thin, you'll obviously have to cut another one that's thicker.
When you assemble the gun for test fitting, put a feeler gauge in the barrel to cylinder gap. See how big it is. The feeler gauges are just automotive type, available at any auto parts store for cheap. Here's how I do mine.
I'm shooting for a cylinder/barrel clearance of about .006"
(https://live.staticflickr.com/65535/49324790621_dbd87b58d5_z.jpg)
Once I'm in the ballpark, I get ready to solder the shim to the end of the arbor. I start by dressing the end of the arbor with a file. Some arbors have a little "teat" sticking up in the center. You need to remove that so the shim will sit flat. You also need to prep the metal for the solder to grab onto.
(https://live.staticflickr.com/65535/49325006927_a2f0503ac2_z.jpg)
Once you've done that, it's time to solder. First I warm the arbor up with a torch. Just warm it up. If you get it glowing red, you got it WAY too hot! Just warm it up.
(https://live.staticflickr.com/65535/49325006862_3654aa279c_z.jpg)
Next, I put a little dab of paste flux on the end of the warm arbor.
(https://live.staticflickr.com/65535/49325006837_94cc25fb95_z.jpg)
Then I cut a little piece of solder off the roll, and set it on the end of the arbor in the flux.
(https://live.staticflickr.com/65535/49324308408_61c372093e_z.jpg)
Now I have to get a little creative. I need a way to place and hold the shim, on top of the arbor so I can heat it and have it stay in the proper position. What I do is, I use the handle off one of my old Exacto knives. It does transfer the heat a little, so wear a glove if you think you might burn your fingers. I don't, because the solder melts so fast that the handle barely gets warm.
I just put a little dab of paste flux on the end of the Exacto handle. it acts as a kind of glue. Then I place the shim on top of that, and another dab of flux on the shim.
(https://live.staticflickr.com/65535/49324308403_04c99f7884_k.jpg)
Now just turn it up on end, and place the shim on the end of the arbor, covering the solder, and hold it there while you heat the shim up with your torch.
(https://live.staticflickr.com/65535/49324790466_8a693821bd_k.jpg)
It only takes a few seconds for the solder to melt. Just remove the heat and let it cool a few seconds. You'll know it worked when you see the shim settle down onto the arbor, and you'll see a thin layer of solder around the edge of the shim.
(https://live.staticflickr.com/65535/49324790401_361e3f257f_k.jpg)
That's it!! It's on there and it ain't going anywhere! Now take the gun in the house, and run some warm water on the end of the arbor to rinse the flux off. Flux is acid, and unless you want your gun to rust in short order, clean it off! Then dry it and oil it up good.
Once you have the gun cleaned and oiled, you'll want to reassemble it again. Once it's back together, check the cylinder/barrel clearance again with the feeler gauges. If it's where you want it, You're done! Go shoot the thing! If it's too loose, which it may be now, because the solder will add a small amount to the end of the arbor, just dress the shim with a file and re-check the fit.
(https://live.staticflickr.com/65535/49324308313_1bbe4103ca_z.jpg)
Now, you can set the cylinder/barrel clearance to whatever you like. Some guys like it a bit on the bigger side, to account for fouling. Some like a bit smaller. I've seen anywhere from .003 to .006 being touted as optimal. If I get mine to around .005 I'm a happy camper.
Here she is, all back together and ready for action!
(https://live.staticflickr.com/65535/49324308323_6e8f7338c3_z.jpg)
Hopefully I didn't bore you with all the pictures and descriptions. I just wanted to be as thorough as I could be, to hopefully help someone. It took me longer to put this post together than it took me to fix the gun. It really isn't hard, just about anyone can do it. I hope it encourages some to give it a try.
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Awesome tutorial Dave. The pictures and text on pictures in tandem with you explanations are spot on and very easy to understand. Nice!
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I do it the same way Dave does. That's because he told me how to do it. I would like to point out a couple things I do. Instead of cutting a shim, I find a steel washer that's a few thousandths thicker than I'll need and solder that on. The solder will squish up through the center but that isn't important because the arbor hole in the barrel has a concave bottom and the outside of the shim is what contacts the barrel. To get a washer thick enough, it's always a little bigger than the arbor but it's easy to dress down. I always make sure to taper the washer so it's smaller than the arbor to allow it to bottom all the way. Once it's on, I dress down the washer to give the gap I want.
(https://i.imgur.com/G8zhK9N.jpg)
For solder I use Brownells Hi-Force 44 (https://www.brownells.com/gunsmith-tools-supplies/general-gunsmith-tools/solders-flux/hi-force-44-solder-prod709.aspx) which melts at about half the temperature of conventional silver solder.
Edit: you may have to shave down the side of the wedge if it doesn't go all the way in after adding the shim to the arbor.
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Interesting Marshal👍👍
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Thanks guys!! That's great stuff!! Because of the "time" element, here's how I accomplish this task - this is a #12 S.S. sheet metal screw. I use it for Army's /Navy's and a #14 screw for Walkers /Dragoons.
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Step 1. Cut off the threaded shaft.
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The "cut off" side will be the "flat side".
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It will look like this when installed - flat side up, round side down.
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Step 2. using a drill motor with a Philips head bit, I reduce the spacer thickness by turning the spacer against a bench belt sander (don't forget to turn the sander on!!).
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Check the gap at the frame / barrel lug. You want this to close first before you "dial in" the endshake or barrel /cyl clearance.
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Getting close
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Success!! Notice the wedge is in place and is driven in until it won't go further.
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Make sure you drive the wedge in solidly when you're checking for the frame /barrel contact. If you wait until there is contact, the spacer may already be too thin!! You can see a witness mark on the spacer when youve made contact at the frame/lug.
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Step 3. I start a hole in two places (one each side). This gives the epoxy an "anchor" so that if the spacer came loose (not ever likely) the "anchors" would still retain the spacer. (Redundancy)
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Step 4. Mounting the spacer. Degrease the arbor hole and the spacer with some alcohol.
Mix a small amount of 5 minute JB Weld. A little grease will hold the flat side of the spacer onto the end of the arbor (don't get any grease on the rounded part of the spacer!!).
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Dabb a little JB on the spacer and install the spacer by assembling the revolver.
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After about 7/8 minutes, remove the barrel and clean up the grease and any flecks of JB.
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Hi, no pro here. I used to do the method described by Dave, but used brass attached to the arbor end by JB-Weld. After having a couple of JB-Weld failures and not wanting to use soft solder, I redid my 17 Uberti and other short arbor revolvers by adding an adjusting setscrew to the arbor end. I drill and tap a 10-32 into the end of each gun arbor. Then an appropriate length 10-32 steel set screw is inserted in the arbor end. After adjusting the set screw for a BP gap (0.008", my choice to minimize fouling) some loctite is applied to the setscrew thread to prevent movement. If the cylinder gap ever needs to change (i.e. using conversion cylinder) it's easy to readjust the arbor length. If using red loctite, heat the arbor end, if blue loctite just make the adjustment.
I'm just an old wannabe amateur gunsmith so take my method with a grain of salt. (7&
Regards,
Richard
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Thank you guys, for eminent tutorials. Seems there are several ways to skin a flea
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Thanks for posting your tutorial Mike. Your way is much simpler, and doesn't involve a torch. I like it! I also like that you use the rounded end of the screw to bottom out in the hole. As we know, that hole isn't square at the bottom. It's concave. Using the round end of the screw head gives you much more contact area.
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I agree Dave. Thanks for posting this Mike!
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Thanks for posting your tutorial Mike. Your way is much simpler, and doesn't involve a torch. I like it! I also like that you use the rounded end of the screw to bottom out in the hole. As we know, that hole isn't square at the bottom. It's concave. Using the round end of the screw head gives you much more contact area.
I agree Dave. Thanks for posting this Mike!
Thanks guys!!
I've never had a problem with JB Weld but I have drilled out a SS spacer before and it surprised me at how tough it was !
You are right Dave and that is exactly why I use those screw heads.
Tomorrow I'll show how I "fine tune" the endshake to get my final spec.
Mike
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Nice ideas, fellers!
I have just been doing it the "Simple Simon" method...stacking AN aircraft hardware washers and half (thickness) washers on the end of the arbor until I get an .002-.003 gap with a tight wedge. This method is quick and dirty but is totally reversible and takes only a minute or two to accomplish.
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After about 7/8 minutes, remove the barrel and clean up the grease and any flecks of JB.
Mike Thanks. I have an overthinking mind here :nocomment:. I think I followed you correctly in that the "flat side" of the screwhead is what makes contact with the arbor? rounded side bottoms out in the hole. So what I don't understand is why in the finished picture I see looks like the head of a Phillip's screw? Is it because as you grind the flat side it begins to reveal or show the slot markings from the head of the screw on the opposite side? :icon_scratch: I told you I overthink :-[ Thank you, Z
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(7+"
Yessir!!! The thickness gets thin enough so that the Philips's bit access shows more and more . . . but, you can easily see the circular "witness mark" of the arbor on the spacer in the pic.
Good observation!!!
Mike
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(7+"
Yessir!!! The thickness gets thin enough so that the Philips's bit access shows more and more . . . but, you can easily see the circular "witness mark" of the arbor on the spacer in the pic.
Good observation!!!
Mike
Can I get a witness??!!!! (7+" I finally see the witness!! Will miracles never cease?!!
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(7+" (7+"
Mike
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Tomorrow I'll show how I "fine tune" the endshake to get my final spec.
Mike
I can't wait to see that Mike!
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Thanks for posting your tutorial Mike. Your way is much simpler, and doesn't involve a torch. I like it! I also like that you use the rounded end of the screw to bottom out in the hole. As we know, that hole isn't square at the bottom. It's concave. Using the round end of the screw head gives you much more contact area.
I agree Dave. Thanks for posting this Mike!
Thanks guys!!
I've never had a problem with JB Weld but I have drilled out a SS spacer before and it surprised me at how tough it was !
You are right Dave and that is exactly why I use those screw heads.
Tomorrow I'll show how I "fine tune" the endshake to get my final spec.
Mike
MIKE???. When is tomorrow? I just noticed that you did not post about the "fine tune endshake" :icon_scratch: Rip Van Winkle?? (7+"
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Thanks for posting your tutorial Mike. Your way is much simpler, and doesn't involve a torch. I like it! I also like that you use the rounded end of the screw to bottom out in the hole. As we know, that hole isn't square at the bottom. It's concave. Using the round end of the screw head gives you much more contact area.
I agree Dave. Thanks for posting this Mike!
Thanks guys!!
I've never had a problem with JB Weld but I have drilled out a SS spacer before and it surprised me at how tough it was !
You are right Dave and that is exactly why I use those screw heads.
Tomorrow I'll show how I "fine tune" the endshake to get my final spec.
Mike
MIKE???. When is
tomorrow? I just noticed that you did not post about the "fine tune endshake" :icon_scratch: Rip Van Winkle?? (7+"
Yeah when is tomorrow Bubba? You got things to see, places to go and people to do? (7+" (7+" (7+"
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(7+" (7+"
I hear ya (Y'ALL !!!)
Ok, after you've got the spacer installed, you should have a slightly larger endshake than you want to end up with. It's easy if you have a sacrificial cylinder to use as a tool. I use an ASM Walker cylinder for Dragoons/ Walkers and an ASM Navy for all belt pistols. With 220 grit sandpaper, I stand the arbor in the appropriate cyl and sand the arbor down by moving the cylinder on the paper ( and checking often) until I get to my specific endshake - .002" max for cartridge, .0025" - .003" for cap guns.
Doing it that way (shortening the arbor a little more) will lengthen the wedge slot overall. That is where the set screw in the end of the arbor comes into play. Being able to "adjust" the slot length will allow you to keep your wedge and not have to buy an oversized wedge or make or have one made.
One thing I'll add is I would never use a set screw to be the correction of the arbor length. What you're doing is reducing the "connection" for the transmission of force to the diameter of the set screw. I'm not saying it's wrong if that's what you want to do, it just doesn't make any sense to me to do it that way.
I'll add some pictures. ( hopefully after this. They tend to go to the top of the post which takes them out of "context ".
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Just hit your enter key a couple of times after your text and they will show up below it.
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Ahhh .
Thanks Hawg!!
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(7+" (7+"
I hear ya (Y'ALL !!!)
Ok, after you've got the spacer installed, you should have a slightly larger endshake than you want to end up with. It's easy if you have a sacrificial cylinder to use as a tool. I use an ASM Walker cylinder for Dragoons/ Walkers and an ASM Navy for all belt pistols. With 220 grit sandpaper, I stand the arbor in the appropriate cyl and sand the arbor down by moving the cylinder on the paper ( and checking often) until I get to my specific endshake - .002" max for cartridge, .0025" - .003" for cap guns.
Doing it that way (shortening the arbor a little more) will lengthen the wedge slot overall. That is where the set screw in the end of the arbor comes into play. Being able to "adjust" the slot length will allow you to keep your wedge and not have to buy an oversized wedge or make or have one made.
One thing I'll add is I would never use a set screw to be the correction of the arbor length. What you're doing is reducing the "connection" for the transmission of force to the diameter of the set screw. I'm not saying it's wrong if that's what you want to do, it just doesn't make any sense to me to do it that way.
I'll add some pictures. ( hopefully after this. They tend to go to the top of the post which takes them out of "context ".
Thank you Mike. The pictures will certainly help tell the story.
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Well :icon_scratch: ….. we’re waiting.
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Here ya go!! 2012 technology at it's finest!!!
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Thank you Mike. Would you mind hanging a few photos of an arbor with the adjustable set screw in place? I know I’m being a pain. I appreciate you Mike. Thanks Z
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Absolutely! Thanks Z!
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Absolutely! Thanks Z!
Howdy Mike, Anxious to see the set screw in place in/on the arbor. Do you dress the set screw? phillips head? grind the head slightly flat but still able to practically adjust with a screwdriver? etc. Thanks, Tim
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I thought I'd make some new pics today. So in the mean time, here's a drawing showing WHY you don't want the set screw to be the "fix" for the length.
The top arbor gets reduced to just the size of the screw to transmit forces. The bottom arbor contacts the spacer with its full diameter.
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Here's the end view of the set screw.
And the second pic is the Bearing side of the screw.
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Thank you Mike👍👍