Cylinder Indexing

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borne2fly

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In all my revolvers there is a small amount of rotational "wiggle" that is considered normal. This has been explained as a consequence of some necessary clearance between the bolt and the corresponding notches in the cylinder. Makes sense if the sides of the bolt and notches are all parallel. Just like a bolt through a hole, some clearance is needed.
So I wonder ... has anyone ever made the sides of the bolt and notches tapered? This is a typical design feature found in many precision tools (spin jigs, index heads, spacer heads, etc.), and is used to eliminate ALL rotational wiggle because positional accuracy is top priority. It's a bit like a tapered dowel pin, except the angle is steeper to permit an easy release.
 

45D

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The "locking" side ( tall side) needs to stay straight with no taper. It has to enter a locking notch of a sometimes rather fast moving cylinder and needs no "ramp" (taper) that will promote "unlocking". The short side likewise needs to have no taper but can have a slight angle to facilitate insertion. Too much angle and the bolt will unlock under recoil, especially with notches that are very shallow on the short side or have material moved into the notch from late bolt drop ( most factory settings).

There are instances of "taper fitting " from the factory as some inexperienced assemblers use it as a "cheat" or "fast" way to fit the bolt and move on to the next piece.

Personally, I put a negative angle on the high side leaving only the very top of the bolt head the "correct" width ( that actually fits inside the notch). This leaves no chance for the side of the bolt to "hammer" on the edge of the notch and wear it out. This works perfectly when used in conjunction with a bolt block.

Mike
 
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borne2fly

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Good info! I enjoy learning these sorts of nitty-gritty details.
So you're cutting a slight dovetail into the high side of the bolt? Do you need to cut a matching dove into the cylinder or just leave it straight?
It sounds a bit like the mild dovetails cut into synchros and dogs to keep transmissions from popping out of gear.

>> "The short side likewise needs to have no taper but can have a slight angle ..."
"Slight angle" ... are you referring to the top face of the bolt?

-Don
 

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Good info! I enjoy learning these sorts of nitty-gritty details.
So you're cutting a slight dovetail into the high side of the bolt? Do you need to cut a matching dove into the cylinder or just leave it straight?
It sounds a bit like the mild dovetails cut into synchros and dogs to keep transmissions from popping out of gear.

>> "The short side likewise needs to have no taper but can have a slight angle ..."
"Slight angle" ... are you referring to the top face of the bolt?

-Don


Here's a pic.
Screenshot_20221202-165945_Gallery.jpg


( about the "short side" - yes, just the top surface edge.)
Mike
 
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45D

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They typically look like this from the factory minus the obvious "flake outs" which is what this pic was about.
Screenshot_20221203-181928_Gallery.jpg


Mike
 

45D

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What is the undercut on the bolt lobe about ?

It's the negative angle that I put below the " full width" (top) section on the tall side of the bolt head ( last paragraph in response #2 above). It keeps bolt material away from the edge of the locking notch when the revolvers are ran hard.

Mike
 

borne2fly

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>> "It keeps bolt material away from the edge of the locking notch when the revolvers are ran hard."

Is this in anticipation of a burr possibly developing on the edge of the locking notch, and the undercut "steps over" any such burr?
 

M. De Land

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>> "It keeps bolt material away from the edge of the locking notch when the revolvers are ran hard."

Is this in anticipation of a burr possibly developing on the edge of the locking notch, and the undercut "steps over" any such burr?
That part of the bolt head never touches the notch wall any way. Most of it is still in the window at full drop.
 

45D

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>> "It keeps bolt material away from the edge of the locking notch when the revolvers are ran hard."

Is this in anticipation of a burr possibly developing on the edge of the locking notch, and the undercut "steps over" any such burr?

No sir. It is purely done to allow the FULL bolt width of the bolt head to be completely inside the locking notch. That removes the ability for any contact with the EDGE of the notch (since they are parallel) where damage can happen and progress.

Mike
 

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That part of the bolt head never touches the notch wall any way. Most of it is still in the window at full drop.

Sure it will, they are parallel surfaces.

Or you're not seeing what's in the picture. The side of the bolt head diminishes as you go down to the more prominent looking cut line.

Mike
 
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borne2fly

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No sir. It is purely done to allow the FULL bolt width of the bolt head to be completely inside the locking notch. That removes the ability for any contact with the EDGE of the notch (since they are parallel) where damage can happen and progress.

Mike
Ahh, ok. I can see this when the bolt is fully engaged in the notch. But until then, before the cylinder spins to a stop, wouldn’t the bolt slam against the side of the notch anyway?
-Don
 

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Ahh, ok. I can see this when the bolt is fully engaged in the notch. But until then, before the cylinder spins to a stop, wouldn’t the bolt slam against the side of the notch anyway?
-Don

No. My profile of the top of the bolt head is shown in my crude diagram. There is usually an "approach" leading to the notch which would automatically introduce the bolt face to the tall side of the notch. On cylinders without an "approach" the slight rake of the face proper ( before the major reduction in the side) still ensures the bolt will encounter the tall side when fully in the confines of the notch.

20221204_141301.jpg


Bob Munden put his "step" (a drop off) in his bolt heads but it can cause peening of the notch. Mine allows it to slide in with no step.

Mike
 
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