Question on Large Siler flintlock-Mechanical Advantage

[whetrock]

Hugh Toenjes (Blacksmoke) asked the question quoted below in a For Sale ad for a Large Siler flintlock and Whetrock posted a question about Hugh's question.  Since replies that are not related to the sale or purchase of an item are not allowed in the For Sale Forum, I have moved it here. -Ron (Moderator)

When you pull the cock to full cock notch does the poundage increase? or decrease? or remain the same ?  In other words when you pull the cock off full forward rest to "full cock" does the pressure to do so get stronger or does it feel like it gets weaker?  H.T.

Please forgive my ignorance, and I know we are not supposed to be chatting in a classified, but, Hugh, could you briefly explain what you are trying to differentiate here? I know Jim Chambers redesigned his tumblers at some point, but I thought the contrast was just in whether or not the sear returned to the same position. Are there other differences between older and newer Siler tumblers?

[Blacksmoke]

The reason for my question about the large Siler lock is to find out if the assembler of said lock new about the Mechanical Advantage Physics needed for correct and optimum lock performance. So many on this forum do not quite understand the relationship between the mainspring and the tumbler which is critical for best lock operation.  I am constantly having to move the mainspring back towards the tumbler axel to increase MA which lessons the pressure on the nose of the sear as well. This in turn gives you a smoother and lighter trigger pull! At this point I need to pay Bob Roller a compliment because he has understood this principle from dat one!  When you cock a flintlock it should start out hard and get easier towards the full cock notch. Example: full forward is 15 lbs. to start the pull back.  At full cock: 5 lbs. to hold the cock back before it slips into full cock notch!  Hope this makes some sense!?  H.T.

[Ky-Flinter]

Thanks Hugh.

Ron

[oldtravler61]

  This is always an issue when you have more than one person assembling your product.

[Gaeckle]

It would be super if there were a drawing of this.

[whetrock]

Thanks, Hugh.

Yeah, pictures would be nice.

Dan Phariss wrote about this on here some years ago. (Maybe 10. I searched for it but can’t find it.) It wasn't in a discussion about Siler kits. It was just in a discussion about the benefit of preload (downward bend) on mainsprings. If I remember correctly, he used the term “heavy first lifting” (or something similar) to describe how the downward bend of the spring interacts with the cam of the tumbler. As Dan explained it (or as I remember it, anyway), as the spring straightens, the contact point on the end of the spring moves toward the tumbler axle, which is the fulcrum of a lever (formed by the cock and the cam of the tumbler). The maximum pressure at the tip of the spring is when the spring is compressed, with the sear in the full cock notch, but mechanical advantage is gained by the tip of the spring having moved closer to the axle of the tumbler, thus reducing the length of the lever (by sliding up the cam toward the axle), and thus reducing the felt load as the cock is pulled back. It also reduces pressure and (potentially) wear on the nose of the sear and the full cock notch. And (as you point out, Hugh) in a well-tuned and well-timed lock it contributes to reduced pressure required to move the sear, which can in turn translate to reduced trigger pull.

NOTE: Revised 1/4/25 to read "heavy first lifting".
If you want to see a post where Dan talks about this, see:
https://americanlongrifles.org/forum/index.php?topic=79568.0

[Blacksmoke]

 With respect to Dan Pharis,   I will disagree in regards to the preload on main springs.  The MAIN criteria for gaining mechanical advantage on tumbler/cock is positioning the "hook" of the mainspring as close as is physically possible to the axel of the lock plate/tumbler bushing!  as this "hook" rides up the tumbler shoe towards the axel the cock pressure should lesson because of the Physics known as MA. H.T.

[Steeltrap]

H.T. explained how this MA worked when I was attempting to tune a new lock that I acquired. After I read his post a few times, the "light bulb" went off and I had a much better understanding of the mechanics of a lock.

[Bob Roller]

About 1970 I gave up on the slip and slide mechanisms in a flintlock in favor of the linked style.Tom Dawson had a fine Manton flintlock rifle and it went off like a modern bolt action.I made my own version on the next lock I made using the Chet Shoults externals and never went back to the original mechanisms.Once the tumbler was finished it was placed in the lock with the sear in place and at full cock.The mainspring was finished to the point before it was heated and opened and placed on the link and then the hole located for the pin on the upper limb of the spring and then drilled.I used the #44 drill for this.THEN the tumbler was rotated so the link was straight down and then I heated the spring and opened it up to a point where it was about 1/2 inch below the link.The spring was then hardened and tempered and installed and tested by flexing it and then assembled and tested as a finished lock.These locks are alll over the world and so far so good.
the now deceased Helmut Mohr used over 100 of the L&R/Roller Mantons on replica Boutet pistols plus percussion Schuetzen locks with an English styled 3 screw mechanism.L&R made it possible for me to make these locks and I publicly thank them again on this forum.
Bob Roller

[whetrock]

With to Dan Pharis,   I will disagree in regards to the preload on main springs.  The MAIN criteria for gaining mechanical advantage on tumbler/cock is positioning the "hook" of the mainspring as close as is physically possible to the axel of the lock plate/tumbler bushing!  as this "hook" rides up the tumbler shoe towards the axel the cock pressure should lesson because of the Physics known as MA. H.T.

Thanks for the reply, Hugh. I'm sorry if my earlier reply sounded like I was disagreeing with you. Not my intention. I agree completely that the main reason the felt load decreases is that the tip of the spring goes toward the axle as the hook rides up the cam of the shoe. Yes, that's how it gains mechanical advantage.

I know you understand this, Hugh. But for the benefit of anyone reading this who doesn't understand it, it's just like when we used to move up and sit closer to the fulcrum on the seesaw so that we could ride with someone lighter than ourselves. In terms of physics, we were shortening the lever on our side of the see saw. The spring does the same as it moves closer and closer to the axle, as the cock is drawn back. It's just like us moving closer and closer to the fulcrum on the seesaw.

Back to Dan. Dan's post was about making springs, and more specifically, about the benefits of the preload (downward) bend. If I remember correctly, his point was that preload not only adds a little strength to the spring (and, as some suggest, it looks nice for the spring to be straight when at full cock). It also helps the spring work at its best for mechanical advantage. Springs will drive a lock whether or not they are made perfectly or mounted perfectly. But in concept, when a spring is straight, it will at that point be its longest, from bend to tip. So if the spring is made in such a way that the lower limb is straight when compressed, then when it is compressed (in a spring vise) it's near to its longest and it's easy to position it so as to have the tip as close as possible to the tumbler axle at full cock (as we agree it should be for optimum mechanical advantage). (I say "near to it's longest", because a mainspring vise only compresses a spring opposite the top leaf. So the profile of a spring compressed in a vise is still slightly different from a spring in a lock pulled to full cock.) A spring that is straight at its compressed, full-cock position will naturally move away from the tumbler axle as it relaxes.

For anyone unfamiliar with this, I should point out that the Siler springs do have a preload.

Also, this is not suggesting that springs that have an upward bend at full cock are inferior. They work fine, and some antique locks and modern locks were and are made that way.

 

[whetrock]

About 1970 I gave up on the slip and slide mechanisms in a flintlock in favor of the linked style.Tom Dawson had a fine Manton flintlock rifle and it went off like a modern bolt action.I made my own version on the next lock I made using the Chet Shoults externals and never went back to the original mechanisms.Once the tumbler was finished it was placed in the lock with the sear in place and at full cock.The mainspring was finished to the point before it was heated and opened and placed on the link and then the hole located for the pin on the upper limb of the spring and then drilled.I used the #44 drill for this.THEN the tumbler was rotated so the link was straight down and then I heated the spring and opened it up to a point where it was about 1/2 inch below the link.The spring was then hardened and tempered and installed and tested by flexing it and then assembled and tested as a finished lock.These locks are alll over the world and so far so good.
the now deceased Helmut Mohr used over 100 of the L&R/Roller Mantons on replica Boutet pistols plus percussion Schuetzen locks with an English styled 3 screw mechanism.L&R made it possible for me to make these locks and I publicly thank them again on this forum.
Bob Roller

Thanks for telling us how you built these locks, Bob. I really appreciate you taking time to explain your processes.

[rich pierce]

It was interesting that the mechanical advantage or let-off of tension on the cock on a Siler lock as it was pulled to full cock, was questioned. I can’t see how this depends on who assembled it. The tumbler foot and mainspring hook are going to determine this, regardless of who assembles it. Are there any cases of locks which do not drop off in pull poundage as the mainspring moves closer to the tumbler axle at full cock?

[whetrock]

Any Siler ought to show some decrease in felt load at the cock as pulled back.  I interpret Hugh's point to just mean that it could drop off more if the spring was positioned the way he likes it.

[Blacksmoke]

Most of the locks made by a number of manufacturers which are sent to me for tuning have the mainspring anchoring pin inserted into the lockplate too far to the nose of the lock by about 1/8"!  I have to close that hole and drill another hole farther back towards the tumbler!  This is not just "my" thing , you will find this arrangement on most if not ALL historic locks that are still in good working order. Most of my work these days is "restoration" so the first thing I observe is the soundness of the lock and the principle that we are discussing.  No! not all Siler locks are assembled correctly. Some need adjustment. H.T.

[rich pierce]

Hugh, I understand that tolerances are very close to optimize function. I also think that if the hook does not approach the end of the tumbler foot at rest, some power to finish the flint strike can be lost.

[Daryl]

This is a John Blissett lock. It has considerable preload as you can see by the relaxed spring and also relaxes as it goes from 1/2 bent to full.
This is a well made lock.

[Bob Roller]

That one looks like my standard mechanism for my caplocks.These are not hard to do and I used it in the flintlocks I made using the Shoults and L&R external [arts.I made 14 Twigg locks with R.E.Davis externals and a bridle with 3 support posts and the sear on an axle.10 were planned and 4 more were added when the buyers sent the parts.The last one went to South Africa.This picture is a really good example of a simple,quality lock.
Bob Roller

[whetrock]

I found a post where Dan P. mentioned "heavy first lifting".
https://americanlongrifles.org/forum/index.php?topic=79568.0

This is not the really old post I had mentioned earlier, but this one at least helps me quote his term correctly. Here's the quote:

A properly made lock should have what is called a “heavy first lifting” on a percussion lock this helps keep the hammer on the nipple at firing. In a flintlock this means as the frizzen is scraped the geometry of the tumbler increases the force applied to the work so the cock is less likely to slow down. Also as the end of the mainspring gets closer to the tumbler shaft as the lock is cocked the reduced (leverage) force at full cock reduces pressure on the sear nose so it can move easier. The good British locks did not have weak springs. Flint or percussion.

[Blacksmoke]

whetrock: Thanks for finding that posting! "Good stuff" H.T.

[Bob Roller]

That "heavy"first lift is why I put a good pattern of checkering on the hammer spur.I was told at the 2023 CLA show that the Hawken makers didn't like the checkering because the old ones didn't have it.I suppose some prefer the possibility of an unwanted discharge but they could do it without my help.
Bob Roller