# Ordering a new mainspring

#### disciple_dan

NAWCC Member
Donor
I just got this little time only Junghans in with a broken main. Just for thought, If a spring close to the arbor, is it likely to do less damage than if it breaks on the other end?
Ok, to the question, I'm ordering a new spring. the original one measures 12 mm wide x 0.38 thick x 40 1/4" long. The closest match at timesavers is made for a Hermle barrel #32 and it measures 12 mm x 0.42 x 43.3" Is that a good match? It's just a touch longer and thicker.
I know there's a calculator for that but I can't seem to find it.
Thanks, Danny

#### wow

NAWCC Member
Should work, Dan. If it is too long for the barrel, you can cut it anneal the end and punch a new hole.

#### disciple_dan

NAWCC Member
Donor
Yeah, If it's too long will it be strong enough to run the clock? It is a little thicker. How can I tell the days it will run? Is anybody familiar with this movement?

#### Willie X

##### Registered User
If you could find a slightly thinner spring, that would be ideal. But If you can't, I would just give the one you found a try and see how it goes. The power is determined by the springs thickness, the width is a given, and the length is chosen to get the most turns in the limited space of the barrel.

So the spring, of which you speak, will likely make your clock run slightly stronger but possibly for a slightly shorter time.

Good luck, Willie X

NEW65

#### disciple_dan

NAWCC Member
Donor
Ok, my barrel is 1.192" the arbor is .300". So I found a spring that is 472" x .011" x 45.3" According to the NAWCC calculator that spring will fill my barrel. Does that make it the right strength? I've got to learn this.
Thanks, Danny

#### Willie X

##### Registered User
Got some mixing of measurement systems here but the first replacement mentioned is about 10% thicker
(16.5 thou) that's a lot stronger. And, the last pick at 11 thou (.28mm) is way way weaker, probably to weak to run the clock. So, of the two, the first one would be the better choice but not a good choice. It's much thicker/stronger than the original.

BTW, the strength/thickness of the mainspring CAN NOT be calculated. It has to be determined experimentally. So, you are on your own when you stray from the original .38mm (15 thou) thickness.

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#### shutterbug

##### Moderator
Staff member
NAWCC Member
To answer your other question: When the spring breaks on the arbor end, the power is released uncontrolled, and often causes damage to the barrel, the second wheel or both. When it breaks at the other end it tries to unwind and the loose end acts like a sort of brake. That is a much slower and milder release of the energy, and is less likely to cause damage.

disciple_dan

#### disciple_dan

NAWCC Member
Donor
Got some mixing of measurement systems
Yeah, the reason for the switch is the NAWCC calculator uses Inches. I like MM. Timesavers mention both. It seems like I remember a system where you could calculate the different lengths and thicknesses. Like if you make it this much longer then make it this much thicker and vice versa. Was I dreaming that?
Ok, so I'll find one the right thickness and if too long then I'll do as Will says and shorten it. What do you think about that?
Have a great day, Danny

#### Willie X

##### Registered User
The calculator is for calculating spring length, or ideal spring length for a certain size barrel, that's pretty much it. The width is a given and the thickness was figured out at the factory by experiment. For your clock I would be looking for a .015", or a .0145". Good luck, Willie X

#### disciple_dan

NAWCC Member
Donor
So, at any given thickness, isn't the longer the spring is the lesser strength and at the same thickness and shorter, it would be stronger? So, if you get a spring that is shorter than the original could it be a little thinner and have similar power? I'm just trying to learn something now.
Thanks for all your good help, Danny

#### Willie X

##### Registered User
You may be thinking about a suspension spring? If it is longer it becomes more flexible. If it's very short it has to be thin in order to work.

A spring in a barrel needs to be a certain length, only to utilize the amount of space available.

If the length is ideal, the spring will supply the maximum number of turns to the movement. Being longer, or shorter, does not change the power at all. Only the number of turns that the spring will supply.

Willie X

#### disciple_dan

NAWCC Member
Donor
Is that true for open springs also? I guess I must have dreamed that and thought I had read it somewhere. Thanks, WillieX

#### shutterbug

##### Moderator
Staff member
NAWCC Member
There is a calculator that helps you determine how any one change will affect the other. In other words, you can play with the thickness of the spring, and the calculator will re-figure the length needed. It's handy if you know the original thickness and just need to find something close if the original dimensions are not available. But if you don't have a starting place, it's kinda guess work. You do have to know the barrel dimensions and the arbor thickness.

#### disciple_dan

NAWCC Member
Donor
Shutterbug, it wasn't a dream? Do you know where I can find that calculator? I remember it being able to get you a different length by changing the thickness and still not be under or overpowered. I think that's what I remember.
Thanks

#### Willie X

##### Registered User
Again, the formula won't give you the thickness needed to run your clock. That was done back when the clock was designed. You can go slightly thinner but I don't like to go over the original thickness. Using the metric system, .36mm to .38mm would do it. I think I'm remembering the posted original thickness correctly. Willie X

#### disciple_dan

NAWCC Member
Donor
I think I'm remembering the posted original thickness correctly.
Yes, that was it. I actually ordered the only exact thickness one I could find. However, The calculator suggested 37.3" at that thickness (.038MM) and the spring that came in the clock (broken) was 40". The one I ordered is 55". I'll just have to make it 40" long. I ran out of patients trying to get any closer. So, the spring I ordered is 12MM wide x .038MM thick x 55" long. I'll need some help with cutting and making a hole so when I get to that you will be hearing from me again.
Thanks for all the help, Danny

#### Willie X

##### Registered User
That'll do it. I usually leave the new spring about 2 or 3 inch's on the plus side. That way a future repair or two will still leave you a useable spring. Good luck, Willie X

Staff member
NAWCC Member

#### disciple_dan

NAWCC Member
Donor
Thanks, shutterbug. I had been using that one. I must a was think-in wrong. Willie got me straightened out.
So, I got the same thickness and width. the length of the original was 40" the calculator said to use 37.3 " and the one you see in this post is 43' and it will fit in the barrel, howbeit, it will be full.
Will this spring work? Will it just make the clock run a bit longer? If not, then I will need help heating it and punching the hole.
Thanks, Danny

#### shutterbug

##### Moderator
Staff member
NAWCC Member
You'll have to try it to see what kind of run you get from it. It does fill the barrel a bit more than optimal. The good news is that you can easily shorten it if you need to.

#### disciple_dan

NAWCC Member
Donor
It does fill the barrel a bit more than optimal.
Do you think it may cause the spring to want to bind on its self?

#### Willie X

##### Registered User
You will get a short run time. To little space left in the barrel.

First, did you check the actual thickness of the new spring and also the actual length? If it is correct, I would cut off about two turns and do an all up test on just the time train.

Calculations are often wrong but it shouldn't be off this much. Might be an error there somewhere, or your new spring might be thicker than .038mm?

Keep at it, us listers see stuff like this all the time. Sometimes it takes a while to get things figured out.

Willie X

#### disciple_dan

NAWCC Member
Donor
Thanks, Willie X. I'll check all the specs on the new spring. I have trouble getting a good length. What do you use?

#### Willie X

##### Registered User
I place the spring center on a big nail and clamp the nail in a big vise. Use a washer, if necessary, to keep the spring from slipping off your nail. Pull the spring out, measure and add about 6 inches for the inner 4 turns. You can mark the point where you measured to and use a string to measure those inner coils, if you like. Within a few inches is all you need but with all you've been through, might as well take a few extra minutes to get a close measurement. Willie X

#### disciple_dan

NAWCC Member
Donor
Ok, the spring is just as described. 43.3 " and the same as the original on the width and thickness.
So, I'm going to cut 3.5 " off.
Can someone direct me to the best thread for that procedure?

I found it. Thanks, Bangster.

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#### Willie X

##### Registered User
Just went back and looked at the photos.

Looks like your spring is still in the letdown cuff! Thar's yet problem ...

It needs to be wound back into the barrel (where it lives) before making any determination on the length.

Willie X

#### disciple_dan

NAWCC Member
Donor
OOPS too late. I have already taken 3.5" off the length. It is now the exact detentions of the spring I am replacing. I hope it will be fine. I'll let you know.
Thanks, Willie X

#### fbicknel

##### Registered User
"You can make it shorter. But you can't make it longer." -- old mainspring proverb

#### disciple_dan

NAWCC Member
Donor
Ok, I finally got the spring cut and the hole. I heated it to very cherry red and cooled it slowly. How do I make it strong again? do I heat it again just not as hot? Thanks

#### Willie X

##### Registered User
dd,
You leave it as is. Both ends need to be left soft for about 1 1/8" on a small spring like that. Also, there should be a sharp inward bend of about 45° at the back of the outer hole and, from the hole to the tip the spring, should be shaped to have the same curve as the inside of the barrel. You can copy the original, or look at a new spring, it should look like I just described.

Note, some newer springs are left tempered and just punched, with no shaping or clean up ... not good.

Willie X

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#### disciple_dan

NAWCC Member
Donor
Thanks, Willie, I figured out the bend but wasn't sure about the temper in the spring. I'll put it in and give it a spin. Thanks, again, Danny

#### shutterbug

##### Moderator
Staff member
NAWCC Member
Match the shape of the original hole. It usually requires a little filing and smoothing.

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