Author Topic: Shaping a mainsping  (Read 11022 times)

4ster

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Shaping a mainsping
« on: January 05, 2014, 10:53:33 AM »
I replaced a broken mainspring in a friend's lock, partly because I wanted to learn how to make a spring.  I followed Kit Ravenshear's method, using 1075 annealed spring stock and followed his directions to the best of my ability.  I was very pleased that I created a working spring on my first try.  My friend came over yesterday to shoot his now functioning pistol. 

On the whole I am pleased, but there is room for improvement.  tried as best as I could to copy the geometry of the original broken spring.  The shape pretty much matches the original, except I had difficulty getting a good 90 degree bend at the beginning of the arc that accommodates the tumbler cam arm.

I either missed how to do it or it is not in in Ravenshear's book.

Offline James Wilson Everett

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Re: Shaping a mainsping
« Reply #1 on: January 05, 2014, 03:36:51 PM »
Guys,

This looks like a good job for the first try of spring making.  And, indeed, the right angle of the hook on a mainspring can be difficult.  I guess that sometime soon in the making a gunlock thread I will get a round tuit and show a photo series on forging the spring.  If you look at the tutorial of making a frizzen spring, you will note that the process seems backwards a bit from just installing a ready made spring in that the major bend is one of the last things done, not one of the first.

This is true, also, of the main spring in that the right angle bend for the hook is done very early in the process, long before the major bend.  I make the right angle bend by hot bending the end of the spring back double on itself, a 180 degree bend and hammer it flat and then open it back up to the right angle.  Now the end of the spring looks like a capital "L".  Then I complete the hook.  Sometime later I do the major bend.  If you do the major bend first, it is difficult to get the right angle bend at the hook as the upper limb of the spring is in the way.  Does this make sense?

Anyway, here is a hand made gunlock with the main spring forged this way.

Jim



« Last Edit: December 03, 2019, 06:16:20 AM by James Wilson Everett »

Offline Bob Roller

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Re: Shaping a mainsping
« Reply #2 on: January 05, 2014, 04:08:01 PM »
That's a good looking mainspring.I made all of mine like that until 1970
and then changed to the later link style.I made a die to form the steep
radius that bears on the tumbler and used annealed 1075 because it
can be swaged cold up to a certain point.
That's a good looking lock and work to show with the pride that comes with a well done job.

Bob Roller

Offline David R. Pennington

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Re: Shaping a mainsping
« Reply #3 on: January 05, 2014, 05:04:07 PM »
Forge very hot and bend over a 90 degree corner. Upset a little after the bend to put some metal back in that bend for strength. It is easier to do than to describe. You hit it alternately from opposite directions on the outside of the bend then form the curl. I learned the hard way like Everett said to do this part first. I made one out of old hay rake tooth. I don't know what number it is but it works ok. Trouble is I made it too close to original spring dimensions. Original was too wimpy and mine is better but still needs to be heavier. I need to make another and leave it thicker in the lower arm.
Good job and probably a better spring than was originally on that lock.
VITA BREVIS- ARS LONGA

4ster

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Re: Shaping a mainsping
« Reply #4 on: January 05, 2014, 08:30:29 PM »
Thanks for the tips.  I did indeed form the hook last, which is why I had so much trouble with the proper shape.

Offline Mark Elliott

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Re: Shaping a mainsping
« Reply #5 on: January 05, 2014, 08:49:08 PM »
I made a mandrel/swage to form the bends on my springs.   I will try to find it and photograph it.   It was basically copied from one of the JHAT books. 

Offline Hungry Horse

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Re: Shaping a mainsping
« Reply #6 on: January 05, 2014, 09:09:49 PM »
4ster;

 That little pistol lock you picture, I used one just like it to build my sons miniature trade gun, about twenty years ago. I recently discovered it in the back of a storage closet. The lock plate was worn to the point that the mainspring wouldn't stay on the toe of the tumbler any longer, and I had taken it apart intending to fix it. While it was apart the kid outgrew it. When I found the lock stashed away in a ziplock bag, there was a CVA mountain pistol lock in the bag with it. I remembered that the parts from the mountain pistol lock fit the little flintlocks plate perfectly. The little pistol plate even has a cast in mark for drilling and tapping to use the mountain pistol bridle. I'm rebuilding it now so my gun club can use it to introduce kids to flintlocks. The point is that any of the CVA Maslin copies that have bridles, flies, and the tumbler that fits them, works in this lock. Its a great upgrade.

                      Hungry Horse

Offline satwel

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Re: Shaping a mainsping
« Reply #7 on: January 06, 2014, 12:27:10 AM »
4ster,
Good job! I'm glad to see that you had success following Kit Ravenshear's instructions. I have been studying his V spring book and am about to attempt my first forged spring. Can you please share the source of the 1075 spring stock you used.

Thanks for sharing your experience. I will forge the tumbler hook while the stock is still flat, before I make the 180 degree bend.

4ster

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Re: Shaping a mainsping
« Reply #8 on: January 06, 2014, 12:37:52 AM »
I purchased the stock in 1ft sections from Dixie Gun Works a year or so ago.  I think Ravenshear recommended them.  Since then I heard that Brownells sells spring stock.

Offline Mark Elliott

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Re: Shaping a mainsping
« Reply #9 on: January 06, 2014, 01:00:46 AM »
You can buy 1095  or 1085 much cheaper from Admiral Steel through their online store.  The only drawback is that they offer less thicknesses than Dixie or Brownels and they come in 6' lengths. 

Offline Mark Elliott

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Re: Shaping a mainsping
« Reply #10 on: January 06, 2014, 02:04:48 AM »
Here are the pics of my main spring forming tool.   The flat end is for making the bend.   It really helps to make sure the bend is in the right place when making a replacement.   I make the foot first and them clamp the tool in a vise where the distance from the flat end of the tool to the top of the vise jaw is the desired length from the foot to the bend.   The other end of the tool is for forming the foot.   You use it like you use a hinge former.   You make the 90 degree bend for the foot, then clamp the hot metal in the vise behind the forming tool and bend the foot over former with some pliers.   It takes some practice and some coordination to use it, but it is the only way I have figured out thus far to reproduce those nice tight little feet in late English flintlocks.    Suggestions for improvements are welcomed.   :)




Offline John Archer

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Re: Shaping a mainsping
« Reply #11 on: January 06, 2014, 02:28:22 AM »
Mark

Are those faint lines in the background of your images an inch apart? I'm trying to get a sense of scale.

Thanx,
John.
I cannot be left unsupervised.
(Sent from my immobile dial-operated telephone)

Offline Mark Elliott

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Re: Shaping a mainsping
« Reply #12 on: January 06, 2014, 02:44:51 AM »
Yep,  I photographed it on my cutting table with 1" squares behind it.    This tool was made for making mainsprings for small late English locks.   I believe I have another one in my box of stuff for making early English locks that has a cutout for the foot while making the last bend.   It is also larger.
« Last Edit: January 06, 2014, 02:47:09 AM by Mark Elliott »

4ster

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Re: Shaping a mainsping
« Reply #13 on: January 06, 2014, 03:09:38 AM »
The other deficiency in the spring I made was the decrease in thickness at the major bend.  Compare the difference in James Wilson Everett's thicker cross section to mine.  What is the trick there? 

I don't have a forge so my spring was done with an acetylene torch with a fine tip to concentrate heat at the bend areas while I was shaping the spring.   A radical bend tends to thin the metal in the bend area so I should have compensated by upsetting the stock in the bend somehow.  I'm not clear on how to do that.

Offline Mark Elliott

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Re: Shaping a mainsping
« Reply #14 on: January 06, 2014, 04:25:30 AM »
I should say that the next version of the tool pictured above would be considerably wider.  It would make it much easier to use.    

As to using a torch to make a spring, sometimes that makes it easier.   There are many ways to do this.  You just need to know what the end result needs to be.   If you are going to upset the major bend, then you need to have left some extra width to the spring there.   You are hitting the red hot metal  on either side of the bend as the spring is laying with both arms/legs of the spring touching the face of the anvil.   That is, the spring forms a "V" on the face of the anvil.  You are making the spring narrower and thicker at that point if that makes any sense.   This is very hard to describe.   A picture would help a lot here.  

The only drawback to using a torch to make a spring as opposed to using a forge is that with the torch, you will have to do more filing.  With a forge,  you can do all your thinning and tapering on the anvil.   You will just file to clean it up. 
« Last Edit: January 06, 2014, 04:28:41 AM by Mark Elliott »

Kenny

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Re: Shaping a mainsping
« Reply #15 on: January 06, 2014, 07:41:46 AM »
Guys,

This looks like a good job for the first try of spring making.  And, indeed, the right angle of the hook on a mainspring can be difficult.  I guess that sometime soon in the making a gunlock thread I will get a round tuit and show a photo series on forging the spring.  If you look at the tutorial of making a frizzen spring, you will note that the process seems backwards a bit from just installing a ready made spring in that the major bend is one of the last things done, not one of the first.

This is true, also, of the main spring in that the right angle bend for the hook is done very early in the process, long before the major bend.  I make the right angle bend by hot bending the end of the spring back double on itself, a 180 degree bend and hammer it flat and then open it back up to the right angle.  Now the end of the spring looks like a capital "L".  Then I complete the hook.  Sometime later I do the major bend.  If you do the major bend first, it is difficult to get the right angle bend at the hook as the upper limb of the spring is in the way.  Does this make sense?

Anyway, here is a hand made gunlock with the main spring forged this way.

Jim






jim, I really like this main spring hook. it seems it would work better than the little ones you see. is the big hook as efficient as a little one? work better maybe?  my understanding is you make a big L   and bend the short section that's 90 degrees to the long into the hook?? is this right?
best, Kenny

J.D.

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Re: Shaping a mainsping
« Reply #16 on: January 07, 2014, 04:19:41 AM »
I'm not Mr Everett, nor am I an expert at making springs, however, I did stay at the Holiday Inn Express, last night  ;D

Someone who is more knowledgeable than I can correct me if I'm wrong, but the shape of the hook shouldn't have a profound effect on efficiency, other than limiting the bearing surface on the ramp of the tumbler, in addition to being the correct length to just remain on the end of the ramp, in the full down position. However, the hook needs to be large enough to allow the nose of the ramp to clear the inside of the hook, at full bent, especially on those tumblers with a concave radius to the ramp. That said, the hook still needs to be small enough to clear the bolster, near the top of the lock, as is well illustrated in the photos of Mr Everett's lock.

Just kinda thinkin'...typin' out loud, so to speak...type.
« Last Edit: January 07, 2014, 06:56:42 AM by J.D. »

whetrock

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Re: Shaping a mainsping
« Reply #17 on: January 07, 2014, 06:20:14 PM »
There also seem to be some theoretical issues, affecting how stress is distributed in the spring. It seems to me that there are three main issues. And, if I understand these correctly, they seem to imply that there is some minor mechanical advantage to the keeping the hook small.

In essence, the hook shape is designed so as to allow interaction with the cam foot of the tumbler, but there are some disadvantages and problems with it’s being there.

First, the hook changes the angle of pressure. As a result, a tremendous amount of torque is applied at the “L” bend and along the early part of the curve in the hook. Keeping the hook short is one way to keep that torque to a minimum. Making the hook longer is like adding a cheater bar to a wrench. With a wrench, adding length multiplies the amount of torque that “can” be applied. With the hook, adding length similarly multiplies the amount of torque that is applied at the “L”.

Note that it is not practical to simply make the hook a lot thicker and heavier than the neighboring leaf, in hopes of overcoming such stresses. If you make the back of the leaf (that is, the main bend area) of the spring thick, as it should be, and you make the hook overly thick, as you might do if trying to over-engineer the “L” and the hook, then you have put a weak spot in the spring just behind the “L”. In principle, the strength of the spring needs to taper consistently from the back toward the front. This helps distribute the load across its length evenly, without overstressing any particular point. And that’s why, from a theoretical perspective, the majority of better old locks have the thickness and width of the spring taper fairly consistently all the way down the leaf and continue to follow the same angle of taper on through the “L” and the curve of the hook. (As many of you have heard Hershel House say on his video, “Always taper when making a spring”.)

Second, the space available for the lower arm is a fixed variable in the geometry of any particular lock. The lower arm can’t be any longer than the space available between the forward lock nail and the tumbler. Total length of the lower arm is a combination of leaf plus hook. So a wide, open hook will in turn mean a shorter leaf section. The leaf section is the section best designed to flex, so it’s advantageous for it to be a long as possible. The longer it is, the more length there is over which to distribute the stress. Correspondingly, when working in conjunction with a long, well made leaf, a short tight hook is not required to carry so much of the load.

Third, the bend in the hook does not flex very well. Indeed, with such a bend, if it flexes much at all, it will break. So it is best if the majority of the flexing is done by the long, flat section of the lower arm, and as little as possible by the hook. For the reasons described above, keeping the hook as small as possible helps with this. A wide, open hook bears a lot of stress along its length.

Now, a final comment: In actual practice, the quality of the metal and temper may be more important than anything else in determining how well it actually functions and how long it lasts. What I’ve suggested above is all a matter of mechanical logic. The old guys who came up with superior lock designs did not have micrometers, high speed photography, etc., but they were talented engineers. Some of the details of the best locks show a very clear understanding of mechanical logic. We should not assume that it was all just trial and error.
« Last Edit: May 16, 2014, 07:17:09 AM by Whetrock (PLB) »

whetrock

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Re: Shaping a mainsping
« Reply #18 on: January 07, 2014, 06:29:02 PM »
This same kind of mechanical logic is involved in the principle that the lower arm needs to be straight at full cock. This principle is directly related to the cam action of the tumbler. It is advantageous for the spring to bear upon the cam foot as far as possible from the axle at full release, and as close as possible to the axle at full cock. That arrangement yields heavy pressure when the cock is down (that is, striking the frizzen), but lighter pressure when the cock is fully drawn back. And that in turn, means less pressure between the full cock notch and the nose of the sear, and ultimately a lesser trigger pull weight. (A similar cam principle is used when building compound bows, so that as the bow is drawn, the pull weight decreases, allowing us to hold it at full draw more easily.)

A spring is shortest when it is bent, and longest when it is straight. And so the pressure point of the hook will move away from the axle of the tumbler as the leaf bends. The pressure point will correspondingly move toward the axle of the tumbler as the leaf straightens. This is the reason for the pre-load, which bends the spring before loading. The pre-load bend allows the spring to be straight when it is at its maximum load. It’s a matter of mechanical logic, all designed to move the pressure point back along the cam as the tumbler swings up. (If you want to read more about this, see Dan Phariss' explanations about “heavy first lifting”: http://americanlongrifles.org/forum/index.php?topic=16801.msg157764#msg157764 )

So, in principle, a straight leaf at full cock yields a minor mechanical advantage (in trigger pull weight, etc.). It’s something that the old guys apparently thought through, and decided to do. But, again, in actual practice the spring will work perfectly fine even if it bends back a bit a full cock. There are many other variables at play in how the lock works as a whole. Whether or not the spring straightens out perfectly at full cock becomes a minor issue.
« Last Edit: January 08, 2014, 05:46:55 PM by Whetrock (PLB) »

Offline James Wilson Everett

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Re: Shaping a mainsping
« Reply #19 on: January 07, 2014, 08:11:18 PM »
Guys,

Here is another lock mainspring that is not as nice as the one above, I do hand make the locks, but I don't claim to be very good at it.
This mainspring does have a bit of a backwards bend at full cock, which is not desirable, blame it on the crummy spring maker!
Foe a more detailed look at hand made gunlocks, check out  http://americanlongrifles.org/forum/index.php?topic=18929.msg226830#msg226830







When I forge the spring the overall shape of the spring is just about what it would be with the lock at half cock.  This makes it a lot easier to install/remove the spring as you do the shaping.  You can install/remove the spring with just your fingers, no spring vise to fiddle with.  The last bend before heat treat is to bend the longer limb of the spring to position the spring end about 1/4 below the lip of the tumbler (the preload).  Then heat treat.  I find that fiddling with mainsprings that are already heat treated and have the preload bend already done is a real chore.
« Last Edit: December 03, 2019, 06:13:57 AM by James Wilson Everett »

Offline Bob Roller

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Re: Shaping a mainsping
« Reply #20 on: January 07, 2014, 08:53:57 PM »
The back bend in the lower limb hurts nothing.I have made more than
one that did that but of removed from the link it will recurve in the opposite
direction. Several in the group of Twigg locks I made have a back curve to
the mainspring and they work fine.
That is a good looking lock and I am glad to know someone else is still trying
to make these peculiar mechanisms.

Bob Roller


whetrock

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Re: Shaping a mainsping
« Reply #21 on: January 07, 2014, 09:35:06 PM »
This mainspring does have a bit of a backwards bend at full cock, which is not desirable, blame it on the crummy spring maker!

Jim,
I hope you don’t think of my earlier posts as critical. I greatly appreciate your skill, and your excellent posts and tutorials! All excellent work and a real help to all of us who are eager to learn.
Whet

Offline Curtis

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Re: Shaping a mainsping
« Reply #22 on: January 07, 2014, 11:38:49 PM »
I want to say thanks to everyone who has contributed to this thread, I have learned a lot following the posts!

Curtis
Curtis Allinson
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Sometimes, late at night when I am alone in the inner sanctum of my workshop and no one else can see, I sand things using only my fingers for backing

whetrock

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Re: Shaping a mainsping
« Reply #23 on: January 08, 2014, 05:46:24 PM »
In my post above “heavy first loading” should have been “heavy first lifting”. I’ve edited it above.

Dan Phariss has discuss that topic in several old posts, including posts about the importance heavy first lifting plays in the design of a percussion lock. You can find those posts by key word search.
« Last Edit: January 08, 2014, 06:44:34 PM by Whetrock (PLB) »

whetrock

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Re: Shaping a mainsping
« Reply #24 on: January 08, 2014, 06:57:09 PM »
As Bob Roller mentioned, a slight upward curve is not a problem. “Straight at full cock” is a design feature conceived as an ideal based on the logic of the mechanical relationships, but it isn’t a problem if the spring has a slight upward curve.

That said, while were talking about general principles, I think it’s worth mentioning that whether or not the lower leaf ends up straight or ends up curved seems to be determined by three main issues:
(1) Overall design and consistent taper of the spring
(2) Consistent quality and temper of the steel
(3) The angle of the main bend

If we assume these first two issues to be good, then the bulk of the problem rests on the third. In essence, if you want to adjust a spring so as to get rid of an upward bend, then you need to close the gap in the main bend just a bit. That lifts the thick end of the lower leaf, so that the leaf can point where you want it to when it straightens out.

If you have a spring that already sits straight at full cock, but for which you want to add some additional preload bend (so as to strengthen the spring a tad), then you need to be careful not to change the angles of the main bend while you are adjusting that preload. If you just pull the lower limb down without first putting the main bend in a carefully adjusted vise, then you may also accidentally open up the main bend. And that will change where the spring “aims”, and thus whether or not it comes straight at full cock or must go past straight and into an upward bend. (We are talking about making springs, so I hope it’s clear to everyone that I’m talking about doing this hot.)

Also note that if you have closed the gap so much as to have the upper and lower leaf touching, then you do not have any room left for adjustment in the bend. If the two leaves touch and you have an upward bend in the lower leaf, then (obviously) you can't hope to correct that upward bend by closing the gap. It is possible, however, to change the angle of the entire main bend slightly by adjusting the angle of the upper leaf. (This involves adding curvature or removing curvature from the upper leaf.  For example, some old English style locks have a slight upward curve to the upper leaf. If that curve is straightened slightly, the adjustment in turn lifts the point-of-aim of the lower leaf.) If you decide to make such an adjustment to the upper leaf, then note that any adjustments there can affect whether or not the upper leaf fits its pin hole, etc.

Jim Chambers and Barbie Chambers have posted some helpful notes on ideals for what makes a good lock. http://americanlongrifles.org/forum/index.php?topic=6913.msg65109#msg65109
« Last Edit: January 08, 2014, 07:21:25 PM by Whetrock (PLB) »