Heat treating a tumbler? (And other dumb questions)

[Rolf Steiner]

 As all well laid plans do, my intention for the order of my projects has gone awry. Recently I discovered that my Carolina Gun's half-cock is not working correctly, the notch in the tumbler is now too shallow and the sear slips out with very little pressure on the trigger. A bad state for my lock to be in, to be sure.

 So, far earlier than I intended, I am in need of learning that sorcery from which locks are made. I was advised that I can file the notch to a depth that will make the half-cock safely engage but that I will need to re-heat treat the tumbler. I have searched a bit and read several things that make me believe I need some advice about where to even start learning this arcane subject.

 With that said (and yes, I know I'm a bit overly verbose) - can someone be so kind as to suggest a thread/book/graffiti that I can study to learn how to do this? Preferably with warnings for someone heretofore  ignorant of the techniques involved. This lock was probably made in the back of a curry shop in Jodhpur so I am not working with the best quality materials but it is what I have at the moment so I must make do.

 I have a standard oven and a MAPP gas torch as heat sources, hopefully one of those will suffice?

TL;DR : School me on heat-treating a tumbler

Many thanks in advance,

Rolf Steiner

[Bob Roller]

As all well laid plans do, my intention for the order of my projects has gone awry. Recently I discovered that my Carolina Gun's half-cock is not working correctly, the notch in the tumbler is now too shallow and the sear slips out with very little pressure on the trigger. A bad state for my lock to be in, to be sure.

 So, far earlier than I intended, I am in need of learning that sorcery from which locks are made. I was advised that I can file the notch to a depth that will make the half-cock safely engage but that I will need to re-heat treat the tumbler. I have searched a bit and read several things that make me believe I need some advice about where to even start learning this arcane subject.

 With that said (and yes, I know I'm a bit overly verbose) - can someone be so kind as to suggest a thread/book/graffiti that I can study to learn how to do this? Preferably with warnings for someone heretofore  ignorant of the techniques involved. This lock was probably made in the back of a curry shop in Jodhpur so I am not working with the best quality materials but it is what I have at the moment so I must make do.

 I have a standard oven and a MAPP gas torch as heat sources, hopefully one of those will suffice?

TL;DR : School me on heat-treating a tumbler

Many thanks in advance,

Rolf Steiner

Rolf,
I have seen some of these locks from India in past years that had superb workmanship and
were soft as lead(almost). You might heat it bright orange with the Mapp gas and drop it into
a can of oil. After it cools,bring it out,wipe it off and check it with a file to see if it's hard.
If it's not hard after this it will have to be case hardened with Kasenit if you have any or the
easy to get Cherry Red.Use the same heat source and same bright orange color and dip the tumbler into the
carbon powder and hold there for about 10 minutes and quench in room temperature water.
This will surface harden it back to the point of being useful again,at least for a while.
This may be a leaded steel like 12L14 or Ledloy.These steels machine like butter and are easily shaped
into whatever in wanted but frequently they wear out much faster.

Bob Roller

[rich pierce]

So your first challenge is not knowing what steel you have. The finished tumbler should be too hard to file. If you can deepen the notch now with a file, it is not hard.

It is also possible or likely that the angle of the nose of the sear and/or the half cock notch are wrong and deeening the notch won’t help and is not the right corrective action.

I’d first examine the engagement of the sear nose and half cock notch under magnification. The nose of the sear should have a narrow flat surface on a radius to the tumbler axle. I’d correct that angle first.

Then the half cock notch should gently “trap” the nose of the sear so that regardless of trigger pressure, the sear nose will not slip out without such a force that the cock moves toward the full cock position.

Once it functions properly you can think about hardening.

[D. Taylor Sapergia]

Be sure to cut your half and full cock notches to your liking prior to heat treating.  They will function fine while the tumbler is soft, for a couple of cycles.

If the tumbler is mild steel or iron, it will require pack (case) hardening.  Again, if you are using a powder compound like Kasenit, or Cherry Red, heat the soft tumbler bright red, emerse in the compound and reheat, holding it at bright red/orange for at least a minute.  Dip it into the powder again, and continue to heat.  After the second heat, drop it into a gallon pail of room temperature water.  Now, file test a corner of the tumbler...the file should not cut at all.  Now, place the hardened tumbler in a toaster oven set at 375 for an hour.  A oven thermometer in the over is a better indicator of temperature than the dial on the oven.
If the tumbler is tool steel, or high carbon steel, having finalized the notches, heat it bright red, hold it there for 30 seconds, and emerse it into a gallon can of motor oil or better yet, Canola vegetable oil, heated to about 130 F.  File test.  If not hard, it is likely mild steel or low carbon content steel, and will require case hardening.  Draw the temper as with the case hardening process.
Others will hopefully chime in...there's lots of opinions on how to do this simple task.

[Ky-Flinter]

Above are all good advice from experts.  But first I would suggest making sure there's no dirt or debris in the notch, parts aren't binding etc.  If the tumbler is hard now and the notch doesn't need too much work, you could try deepening it with  an appropriately sized stone.  If that doesn't work, see above replies ;-)

-Ron

[D. Taylor Sapergia]

To further Ron's comment, the slot of the half cock notch can sometimes be deepened with a new hacksaw blade.  It doesn't take much.  But if it is worn, it is soft, and will need heat treatment.

[JCKelly]

Heat treating is a wonderful way to ruin something, if this is your first experience with heat treating. I'm a metallurgist & tend to describe things like you have a fully equiped heat treat shop at your disposal.
For more practical information suited to us'ns with basement shops I would suggest reading one or more of the books by the late Kit Ravenshear: 

Simplified V-Springs A Guncraftmanship Manual, Kit Ravenshear   

Metalwork - Part 1 Cleaning, Hardening, Ageing  Colouring, Kit Ravenshear

Woodwork - Part 1 Stockmaking, Inletting, Shaping,  Kit Ravenshear
Woodwork - Part 2 Decoration, Finishing & Repairs, Kit Ravenshear

Craft and Practice - Part 1 Re-conversion, Screw threads, Assembling locks, Kit Ravenshear
   
Craft and Practice - Part 2 Ramrods, Pipes, Sheetmetal Work, Top-Jaw Screws, Etc. 
   
Tubes and Tools Barrels. Barrel Work: the Workshop and Tools, Kit Ravenshear
Kit Bits Professional Gunsmithing, Miscellania, Index, Kit Ravenshear

If you cannot find them at your favorite dealer, consider www.abebooks.com

[Scota4570]

Before we get into hear treating, how deep is the full cock notch?  IF it is really shallow you have a problem. If It is deep but the angle is wrong that needs to be addressed.  It the sear nose is rounded, fix that. 

Any of you lock makers have a figure on how deep a sear notch should be?  I'm thinking 40 thousands minimum. 

[Bob Roller]

It should be deep enough that the tip of the sear or half cock notch would have
to be broken to render it useless.That kind of abuse is not common and the big
job the first position on the tumbler really has to do is to be able to withstand
the torque or thrust of a strong mainspring.

Bob Roller

[mtlonghunter]

Also before you start filing on the tumbler , Check to see what lowering the hammer will do to your flint capacity.  If you cannot put a nice flint in the jaws on halfcock you maybe frustrated at best and hit the jaws on the frizzen at worst .

[Scota4570]

Looks like some are writing about 1/2 cock notches and some full cock.

My question is about the full cock notch depth.   The depth of the sear notch is important to safe operation.  If the notch is to shallow or at the wrong angle that would cause the problem described by the OP.
 
Also, I see most sears made with a sharp point on common locks.  I think that is not good.  I make them so the sear has a flat that matches the full cocks notch in depth and angle.  Having a sharp point invites breakage and fast wear because the force is concentrated on a single edge.   A full depth full cock notch is defeated with the sharp nose sear. 

[Rolf Steiner]

Lots of excellent knowledge imparted so far, you gents do not disappoint!

 I tore the lock completely down this morning which was a learning experience (and a good one at that). Things I discovered -

The tumbler is not hardened, I was able to easily file on it. I took the opportunity to polish all the bearing surfaces inside the lock while I had it apart. So case hardening is in my future.

The notch will indeed need to be cut deeper. The lower edge wore down due to the softness of the steel.

The sear is not sharpened to a sharp point, thankfully, so that's one less thing to fix.

I do have the Ravenshear series...though I had not thought to consult them prior to posting for some unknown reason. As an aside - the set I bought seems like a copy of a copy of a copy and is pretty tough to read in some spots. Are there any editions that are crisp and readable?

Also while I had it all apart I finally managed to get the sideplate off, so I can add a faux third screw at long last.

Now, to order the appropriate materials and get to work. Hopefully I can put all of the good advise above to use and not completely render the lock useless. Many thanks to all of you.

Cheers,

Rolf Steiner

[Scota4570]

"The notch will indeed need to be cut deeper."

Be sure that the sear nose does not catch on the half cock notch when the cock falls.   

[JCKelly]

http://kitravenshear.com/Books.html   or abebooks.com

[Rolf Steiner]

http://kitravenshear.com/Books.html   or abebooks.com

JC, the ones they offer appear to be the same ones I have. I was hoping someone might have a sort of "remastered". I'll soldier on with the ones I have, they aren't unreadable, just a challenge. Amazing how time causes gravity to distort things like print....or sights...and makes them more difficult to see. 

 Got my container of Cherry Red in the mail the other day, now to go acquire some fire bricks and get to work.

Cheers,

Rolf Steiner