Cast versus machined versus forged mainsprings: does it make any difference?

[rich pierce]

Or is design, steel used, and heat treat the decider?

My vote: steel, design, and heat treat.

Nobody has ever made identical mainsprings using these 3 techniques and tested them to failure, so all your responses will be educated guesses - am I wrong?

[whetrock]

 

[JTR]

I agree with whetrock! 

Actually, it could/should be a good discussion. With modern steel I'm not sure how it could be proved one way or another without some serious testing.
John

[Jim Kibler]

Casting is an inferior process simply due to the propensity for defects, internal voids etc.  After well over 10000 locks with machined springs and not one mainspring or frizzen spring breakage it has proven itself to be a wonderful process. 

As far as the potential for a spring to take a set, this is universal with springs made from all processes if the material is too soft such that the yield strength is exceeded during lock function.

Grain direction at the bend makes ablsolutely no difference in this application.  There is slight anisotropy in mechanical properties relative to grain direction but it is so small that it isn't significant. 

I am a degreed metallurgist as well as a respected gunbuilder, but at times others think they know better about subjects such as this.  Makes one wonder...

I'd be happy to debate any of these facts presented.

[Jim Kibler]

Further, if you were to suggest using cast springs to any metallurgist or knowledgeable mechanical engineer they would become uncomfortable very quickly.  The fact that they work as well as they do is really amazing in itself.  If one has any education in this field the debate really is nonsensical.

To be perfectly honest, I don't think a machined or forged spring has any better properties in terms of lock function.  I don't subscribe to the idea of the manufacture method contributing to "whippiness" etc.  From a materials standpoint it doesn't make any sense.  What determines the "feel" of the spring is the geometry.  I would suggest that you could put a cast spring of the same size next to a machined and forged spring and probably feel no difference.

The advantages of machined springs are as follows:
Low chance of defects.  Defects cause failure
High dimensional control, resulting in consistent strength, positioning in the lock etc.

One might also argue that a spring bent is a step up.  I would counter that during the process of bending the spring the chance of introducing defects from overheating, bending too cold etc far outweigh the miniscule to nonexistent benefit of having grain flow wrap around the bend.

[rich pierce]

I like data from experiments where only one variable changes - and it does change. Then outcomes are measured and compared statistically. I’m a published scientist with over 90 peer reviewed papers in medical journals. That’s how things are really tested.

Do I think machined springs are superior or inferior to cast or forged springs? No, because nobody has tested them head to head - same design, same steel, same heat treat, different ways of forming them - within the parameters needed for good flintlock function and flint life. Do I think forged springs are inferior or superior to machined or cast mainsprings? No, for the same reasons.

I’m betting many lock makers could share data on the reliability of their process. I’ve never had a mainspring break but that is simply anecdotal with many variables.

I don’t think that how they are formed - cast, forged, machined - is an issue.

[rich pierce]

Further, if you were to suggest using cast springs to any metallurgist or knowledgeable mechanical engineer they would become uncomfortable very quickly.  The fact that they work as well as they do is really amazing in itself.  If one has any education in this field the debate really is nonsensical.

That’s what we call a hypothesis on their part.

They would probably also say that Bob Roller forging them essentially by hand from flat spring stock and quenching by eye and tempering by burning off in motor oil is a recipe for disaster. Don’t care what they say, who have not done the tests as I outline.

[Jim Kibler]

I like data from experiments where only one variable changes - and it does change. Then outcomes are measured and compared statistically. I’m a published scientist with over 90 peer reviewed papers in medical journals. That’s how things are really tested.

Do I think machined springs are superior or inferior to cast or forged springs? No, because nobody has tested them head to head - same design, same steel, same heat treat, different ways of forming them - within the parameters needed for good flintlock function and flint life. Do I think forged springs are inferior or superior to machined or cast mainsprings? No, for the same reasons.

I’m betting many lock makers could share data on the reliability of their process. I’ve never had a mainspring break but that is simply anecdotal with many variables.

I don’t think that how they are formed - cast, forged, machined - is an issue.

Yes, it's always nice to test things head to head, but there also is proven widespread adopted positions in any field.  In metallurgy and engineering one is that cast material is less reliable than forged material as a whole.  The reason for this is the chance for defects.  Defects cause failures.  For example, would someone question and require testing to conclude that a forged or billet crankshaft is better than a cast one?  This is accepted by everyone with half a brain.  How about a lifting hook?  Would anyone but a fool prefer a cast one?  It really is this simple...

The debate between the benefits and weaknesses of casting versus forging, machining has been settled more than a century ago. 

[Jim Kibler]

For you motorheads, you think anyone building a performance engine would prefer cast connecting rods over billet machined ones?  Ha!  Guess the manufactures should do a side by side test to determine the truth .    Silliness....

[Jim Kibler]

Rich,

You might say this is "hypothesis", but as mentioned all of this has been sorted out LONG ago.  You don't have to re-prove these principals based on every new part design or application.  Just do a google search of properties of castings verses forgings.  This should lead to some research articles.  I'll dig into things and find references if necessary.

[rich pierce]

4140 and others are better barrel steels than some being used today and superior to wrought iron forged barrels. That’s been settled since the invention of high pressure smokeless powder. Yet, somehow our fore bearers managed without it. So 4140 is “superior” - who cares?  It’s irrelevant to me. It’s not going to make the gun shoot better with me behind it. Something can be factually sound and well-reasoned, and practically irrelevant. You’ve obviously made a good and well-reasoned choice that both fits your fabrication philosophy and practice and yields very reliable springs. That’s great! Nothing to prove to me until I own one. I handled one once. Very nice action. Love that “snick, snick” sound and feel when a cock is drawn to half then full cock. Love a frizzen that snaps open and snaps shut decisively, not sorta “well, guess I’ll go that way now.”


Oops I trolled the barrel steel devotees!

[Jim Kibler]

Yeah, I've used lots of cast springs.  I have no problem with them.  I just find machined springs to work extremely well, have no breakage issues and can be manufactured to high tolerances.  I'm in no way saying that cast springs aren't good or okay to use.  I just find it laughable to suggest they are better than those machined from a billet, or to suggest that machined springs have issues and are not suitable (which was done in the other post).  And if someone suggests this, I'd at least like to hear their reasoning why.  Just saying something is meaningless.  I try to have information to defend a position I take. 

[Chris Evrard]

Hey Rich thank you for starting this thread. I look forward to hearing what everyone has to say. Especially those who have been making these springs for decades.

We all know what Jim K thinks.  Anyone else out there care to share? Thanks in advance.

CE

[Jim Kibler]

Chris,

I am asking for your reasoning to believe cast springs are superior to those machined from billet material.  Could you provide this information?  I have defended my position, I'm still waiting for you to do the same.  Otherwise they are just words, which have little value.

If you disagree with anything I've said, please express what this is and why. 

Jim

[Chris Evrard]

Jim,
I never said that cast springs are superior. I did say that I like forged springs better than cast springs.

In fact in my Ditchburn post I said that I'd never say no to machined springs either.

CE

[Jim Kibler]

Here is your comment:


Right now the only thing I lack on the Ditchburn/Beck lock is the mainspring. I've been working on a few ways of going about making them but haven't settled on which option to use yet.

I don't want to do a milled mainspring as there are problems with these types of springs taking a "set" and losing strength.

So I've been working on several different ways of producing a cost effective forged spring. So far I have some good springs, but the "cost effective" element has eluded me. There are still a few things left to try so as time permits in the shop I'll be continuing to work this all out.




In this comment you make the assertation that milled mainsprings have problems taking a "set" and losing strength.  I assume you don't believe cast springs have this perceived issue.  Is this correct?  Isn't it therefore reasonalble to conclude that you believe cast springs are superior?  If this is too big of a step, I retract my statement.

[JTR]

I see an unsetting attitude here, that somebody feels he always needs to be right.....
John

[Jim Kibler]

John,

Are you directing this towards me?  If so, should I interpret this as a personal attack? 

Let me remind you, I've taken a great deal of time defending my statements.  I welcome honest well intended debate.  Actually I hope it happens!  If I end up being wrong, I probably won't like it, but will certainly accept it.  Those who know me well will agree.

Here's the truth...  I am careful what I say and I absolutely HATE when people make comments related to our business that have no basis.

I don't think anyone who "thinks they are always right" could have successfully built a business like our in such a short amount of time.  We are constantly asking ourselves if there are better ways or what we can do better, whether that is manufacturing, customer service, how we treat our employees etc. 

Another example, I was designing the Germanic lock a while back.  I sent it to a very knowledgeable friend and mentor.  He said it sucked it a number of ways and described why.  I didn't like it but took it and made the changes.

[JTR]

Jim, I don't see where I mentioned your name, or your business! Period!
If you think I aimed it at you, consider why you might think such a thing.

[Jim Kibler]

Jim, I don't see where I mentioned your name, or your business! Period!
If you think I aimed it at you, consider why you might think such a thing.

Well, I stand corrected

[rich pierce]

It was possibly aimed at me hahahaha. Not the first time, if so. And probably well-deserved! No sweat.

[Jakob]

I would assume that the biggest reason for casting springs is ease of manufacturing, especially if you're selling on un-finished springs.
Not everyone has access to a CNC mill, but almost anyone can cast a piece.
The question is then if a cast spring is 'good enough'.

[Jim Kibler]

Yeah they are good enough!  The tens of thousands produced has answered this question. 

Are there options I think are better.  Yes!  This is why we machine them.

[Jakob]

Yeah they are good enough!  The tens of thousands produced has answered this question. 

Are there options I think are better.  Yes!  This is why we machine them.

I asked if a cast spring were 'good enough'....

[Jim Kibler]

I answered the following:

Yes they are good enough.  Read my post above again.  In case it was ambiguous, I was referring to cast springs.

In case you or anyone else has missed my point, I have no issue with cast springs.  I have an issue with the suggestion that machined springs don’t work well or that cast springs are better.  Does this make sense?  If you care to, read my posts and you’ll find this has been my consistent message.