Correct Arbor Assessment?

[99whip]

Happy 4th to you guys for starters.

I have an 1849 pocket model (Uberti) that I've been doing a little tune up on.  As all Uberti's it has the short arbor which I wanted to fix.  So I worked up a washer shim stack to correct that but I have a question.  Prior to the using a shim stack, when the wedge was tapped in you'd get a feeler gauge measurement of .004 of clearance.  If you tapped it in a little farther you could get some forcing cone/cylinder binding.  With my shim stack in place, I get a feeler gauge measurement of .008 and of course the wedge doesn't go in quite as far.  I figured if my stack was a little big I'd just dress it back down to the clearance I want. 

But here's my question - even with the shim in place and the wedge tapped in, the barrel lug perfectly mates with the frame/frame pins, I don't see any gap in there.  I know .004 isn't much but I was thinking with the shim stack having increased the clearance up to .008 I thought I'd see a tiny gap between the barrel lug and frame?  If I want to end up at a .003-.004 clearance I was figuring I'd now need to dress the shim stack down a little but also take the same amount off the barrel lugs. 

Is my assessment all wrong?

Thanks,

Whip

 

[Hawg]

I'm sure Mike can explain it but it's probably because the arbor and hole aren't a machine fit. There's probably a little play there. The only one I have experience with is my Dragoon and until I got the shims down to where they needed to be I had a tiny gap at the pins and couldn't install the wedge.

[ssb73q]

Hi Whip, if there isn't any space between the bottom of the frame and the lower section of the barrel, you're good to go. Don't remove any metal there, but only dress the arbor extension part until you get the desire gap. I have run my barrel/cylinder gaps 0.002-0.003". That's fine for conversion cylinders with smokeless powder, but I'm finding that I am getting binding with BP and subs. IMO target for ~0.005" gap for a good compromise.

Regards,
Richard

[Hawg]

Used to be .006-.008 was considered the optimum gap for bp.

[45 Dragoon]

Whip,
  Hawg is right, there's enough slop in the arbor hole to keep the lug /frame in contact as you adjust the barrel/cylinder clearance. I routinely set the clearance at .002"- .0025" with no binding with blk powder. My Dragoons are cartridge with smokless only and run all day with .0015" clearance.

You are on the right track. The bigger the gap, the quicker the binding. A .005" clearance would be twice the "leak" as far as I see it. Of course, that's my opinion.

Mike
www.goonsgunworks.com
Follow me on Instagram @ goonsgunworks

[99whip]

Ok, thanks for the replies.  I will try and finish it up today.  Guess I was just surprised that I didn't see a difference in the lug/frame fit since the shim opened up the bbl/cylinder clearance.

[45 Dragoon]

That's great.
 Just keep in mind, the benefit of a close bbl/cyl clearance is realized the most as you get closest to "0" clearance or a true cylinder. The biggest difference between our open top revolvers and revolvers with a gas ring or bushing is that the O.T. kisses the barrel each time it is cycled and is thus, "self cleaning". If the cylinder isn't allowed to "self clean" (as with a bushing), the face of the cyl can collect fouling and lead and lead to a binding situation. Therefore, O.T.'s can function with a "tighter"  bbl/cyl clearance than the dedicated "gap" guns and receive all the benefits (benefits being more energy and fps., not to mention a much cleaner revolver while you shoot). The benefits are even better with a smokless/cartridge setup.

Keep us posted on how it goes!


Mike
www.goonsgunworks.com
Follow me on Instagram @ goonsgunworks

[99whip]

That makes sense Mike, thanks. 

I'm still somewhat stuck on why I don't see a change in the lug/frame fit.  Since the shim has increased the cyl/Brl clearance that makes me think the arbor is bottomed in the barrel, but I don't see that same change reflected in the lug/frame fit.  Both you and Hawg mentioned some slop in the arbor fit could still be impacting that, would that be more lateral movement than fore/aft? 

Don't have as much experience with it as everyone so will trust the opinions here, just can't seem to get my head around that one.  But it's fun learning.

Thanks all,

Whip

[Hawg]

It is lateral movement. When the arbor bottoms out the barrel will drop down enough to close the gap as long as the gap is pretty small. You can probably pull up on the barrel without the wedge installed and see a gap.

[99whip]

That makes sense.  I guess that's where a bedding procedure would suck up the rest of that slop in there.   

[45 Dragoon]

The space between the arbor and the arbor hole is the space that allows "adjustment " of the clearance while the frame and lug have contact.  If you think of the lug/frame as the fulcrum  or main point of contact,  the arbor length is what adjusts the clearance. So, a small amount of material removed/ added (from the arbor or to the hole) will make a much bigger difference in the bbl/cyl  clearance.  For instance,  to close the clearance  .002" you may only need to remove  .001" from the end of the arbor.

After you get the clearance done you can use a small amount of JB Weld in the bottom of the arbor hole to "bed" the end of the arbor and maintain  the same and unique fit.

Mike
www.goonsgunworks.com
Follow me on Instagram @ goonsgunworks