Short-throw lock, and "corrections" thereof.

[WadePatton]

After a quick search and reading:

http://americanlongrifles.org/forum/index.php?topic=5979.0 (Book on Lock Geometry?)
http://americanlongrifles.org/forum/index.php?topic=15527.0 (lock geometry)
http://americanlongrifles.org/forum/index.php?topic=29895.0 (Mechanical Properties...)
http://americanlongrifles.org/forum/index.php?topic=20733.15 (lock physics/engineering)
http://americanlongrifles.org/forum/index.php?topic=19492.25 (Getting the lock to ...)

Because my lock had a few issues today I've begun to examine it much more closely.  To be completely honest and fair, the first problem was my overtightening of the rear lock pin which drove it (being overly long since the wood has compressed as there is no washer yet ) against the cock.  Slightly.  The lock was mounted last Fall and has launched only 73 shots, probably been sparked at least twice that, testing/flashing/klatching.  Had one flint go 30-ish shots and thought all was right with the world. Then today.

John thought the mainspring was binding, but there are no marks to indicate that-then i saw the screw marks.  

But my examination and comparison of this lock against the other three i have on hand clearly shows that this is a "short-travel" lock.  I was told when i bought it some ~8 years ago, that it's styled/copied from a Henry Nock lock, although I haven't studied any Nock originals myself.

I compared it to two L&R's (as received, not cleaned up) and one Bob Roller Ketland (as received-ready to rock and Roller ).  The Nock has been cleaned up and polished as per normal, plus i added brass (brazed) to the cover-at pivot, to take a lot of slop out of that joint back when i first got it.

Noticing the shorter travel and less compression of the mainspring (and less spring tension), I measured the travel of the mainspring at tumbler end and found travels to be: .332, .343, .340, and .235".  I then measured center of tumbler to spring attachment and got practically the same measurement on the first three locks and something shorter on the Nock.  

I haven't studied the catalog with all those scale photos yet.  (Learning is much more interesting when the critter can bite you.) But now that I've done this much, I can tell a lot more about a lock with a glance.

I also took in the complexities of the geometric relationships and how each thing affects the other...you know the foot bone is connected to the anklebone.

Probably will start by reworking the mainspring for more tension, but i did check to see if the Egg would fit the mortise!  It will, but I'd have to move the flash-hole and tweak the triggerbar to make it work.  Methinks reworking the mechanism much further is a job best reserved for the gunlocksmiths, or avoided altogether.

Interested to hear from others on this.  Are there other "short throw" locks?  

Photos showing cock positions, spring compression/travel, etc.

[WadePatton]

The first comment about the Nock was "You need a bigger flint, that's a big lock".  

Then I showed how you can barely wrestle a 5/8 into the jaws such that the pan isn't held open at half cock.  But yes after a just a  little shooting/knapping action the flint is too short to be effectively held in the cock.

I am beginning to be of the opinion that a short-action lock is probably not the best thing for a beginner.  If you've not picked up on the easiest way to tell, simply compare locks at half-cock and full.  The shorter action will look like it's not fully cocked, compared to the long/standard action.  Or compare gaps between the top of the plate and the stop on the cock.  

Also do note those lock photos are of two "raw" locks and two finished locks, one finished by a master, the other by me.  

Bob tells me that "Ashmore" was similar and could be troublesome.  I can see the resemblance here in the picturebook catalog.  

From the book I can see that the John Bailes (small Manton) lock has the same travel*, but also appears to have better spring action (it's much higher in the lock at half-cock, need to see at rest and cocked to measure/eyeball if it moves any further than mine.  Maybe some folks have experience with them?  This may be a replacement option either in parts or complete in order to "save the mortise".

I'm going to dig around for a spare/alternate spring for when I screw this one up.  But do think that putting a bit more pressure on things will help.

*correction, I have that lock in hand, and the cock on this one has a bigger gap to plate (than the one in the book) and yes the spring action is far better (longer and stronger) than the Nock.

[Acer Saccharum]

I have a Bailes that is a rocket.

That little stirrup thingie can be put in backwards and cause binding.

For a short throw, you need a kick-butt main spring, and a stiff frizzen spring to balance it.

[WadePatton]

Yes Tom.  I corrected above. I do believe I'm going to love the little one.  I had mis-judged by the gap and had forgotten that i had a John Bailes in-hand.  (in box by my feet).  It shares the same spring-tip travel as the Roller and the Egg.  This is _fine_ by me.

The stirrup thingy is secured by a pin in the Nock, i doubt I've had it out.  I'll paint/mark the Manton one for easy orientations.

Bailes/Manton I have is going on my 30 (nearly have the wood paid for!).  hoorah!

I'm going to rework the mainspring or make another to EMpower this Nock, but alas the travel limitations will take major surgery.  I may do that later by using Bailes internals and such.  


Also some basic beginner gold in this one:
http://americanlongrifles.org/forum/index.php?topic=765.0 (Lock tuning)

And I just remembered that I went to the shop (those ~8 years ago to buy my first bbl and lock and such) with intentions of buying a Durs Egg type lock, but that it wasn't in stock and I chose to pick from what was available and really had no clue what i was looking at/for.  My how things change. 

[Bob Roller]

A properly shaped,forged mainspring will help a lot.I had a fine original lock that was
loaned to me by Lynton McKenzie for study when he found out I had traded TOW out
of the moulds for the Cock,plate and frizzen for the Bailes locks. The two locks were
99% identical in size and I remember the Nock had a good full and half cock position
and plenty of clearance on half cock. I am now wondering if the moulds for the Nock you have
were reproducing a replacement tumbler that was barely workable when it was installed or
perhaps the cock was a replacement that had the square hole a few degrees out of orientation
with the tumbler.I wonder how many of these locks were made and sold and were they all troubled
like yours.My knowledge of production locks is very limited so other than the replacing of the mainspring,
I can't be of much help.

Bob Roller

[WadePatton]

Thanks Bob, I just found your "two-thumb test" for mainspring strength in a thread of 2008.  I can indeed remove tension from the assembly (at rest) with my thumbs. 

I see what you are saying and, will strip both locks to see what may or may not cross-over to make things better or worster.  If anything does, I can order some parts.  But the mainspring is job #1.

Dan gave some cast spring re-working ideas in that other thread i quoted last post.  I'm going to the shop now, enough reading/ritin'/research-time to do some actual doings.  But mainly i have to finish up a scratch-built flat spring for another (not mine) gun of the miniature suppository type.

[WadePatton]

I did as Dan had suggested in another thread, sorta.  I wedged a small chunk of scrap into the mainspring after cleaning it up properly (something I failed to do initially), then heated it very slow and evenly to get a light straw with a couple of hot spots beginning to get blue.

Allowed to cool, checked to find 1/16 increased spread.  re-installed and she's working MUCH better now.

Flipped the rock too, as with BD the flint doesn't even clear the bottom of the steel. 

It was strongly suggested to bend the cock (to point it more to the pan) but I haven't gone that far yet and don't want to decrease my clearance at halfcock.

guns dun for today.