Making Springs

Doug MacQueen

Making springs has always been an area in metal work that I have found interesting. There is a great deal to learn, however you certainly can make a workable spring without knowing all the physics involved. Generally speaking, steel springs are made of high carbon steel. However, I know a couple blacksmiths who are making workable springs from low or medium carbon steel. These are relying on the work hardening that occurs in many metals. For example, some lever locks use work hardened brass springs. Phosphor bronze has long been a favorite spring material both in lever and pin tumbler locks. This thread will deal primarily with making high carbon steel springs, because of the amount of information needed to successfully to make one. Also I am intensely interested in studying the springs used in pre-Industrial Revolution locks. I encourage involvement in the thread and maybe it will be made a sticky. But please do not, as is all too often done on many threads in this forum, hijack the thread. I am guilty of that offense myself. There is way too much info on this forum that gets buried because of that practice.

Doug MacQueen

Ok to kick this off here are some pictures I took when a made my first and so only black powder gun mainspring. It was made from 1075 carbon steel flat plate, probably from Brownell’s. This is a high carbon steel suitable for spring making. It is supplied in an annealed state, meaning it is soft enough to file and bend into shape. Not shown is how I hardened it it the metal furnace. I used this because the heating was more uniform than using a torch. I brought the steel spring up to a red hot and then quenched it in oil. How hot is hot enough? It is difficult for a beginner to determine by eye the proper redness to bring to the steel. So we cheat by using a magnet. There are 2 pictures of a pencil magnet mounted in a piece of tubing. Quenching the steel should occur at what is called the “critical” temperature. Identifying this temperature is easily done with a magnet, as the steel loses its magnetic property at this temperature. Going far above this temperature is detrimental to proper hardening. Not reaching critical temp is equally bad. Since the springs are small they lose heat quickly, slightly overheating is required so when the steel hits the quench its at the right temp. The problem with using the magnet is that both the magnet and the spring must be securely held so the magnet can be easily swiped against the spring and not stick together. Also the weaker the magnet the better.

Doug MacQueen

Two sources for spring steel are Brownell’s 800-741-0015 and Dixie Gun Works 800-238-6785

Doug MacQueen

Lock springs are usually small and thin. Propane, Mapp gas and Oxy-Acetylene can all be used to harden and temper these springs but the difficulty is getting an even temperature on the spring. And they lose the heat so quickly. The rosebud tips that spread the flame more work best when using a torch. Another method I have never tried is to heat a much larger mass of metal up a bit beyond the temp you want the spring to be and laying the spring on this larger piece until it is reached.

Doug MacQueen

And I should add that it all too easy to overheat small springs when using a torch, so you definitely want to practice on some similarly sized scrap pieces first. Steel will start to burn once it gets into the white hot. This happens quickly especially with the oxy-acetylene torch. Also bright red hot steel in a low light situation will look considerably different in sunlight.

Huw Eastwood

Great subject and a great thread Doug.

Two tips I’ve always used which might help are:

1- Gauging red heat for hardening/tempering- do it in the workshop with lights off and windows covered so as dark as possible- it gives the best visible indication of what level of heat the metals at.
2- To heat multiple small parts equally for same process, fold up a rectangular tray from 16 gauge mild steel, sized to suit parts, and fill with fine, dry sand. Equally space the parts embedded in the sand and then heat from below. Works well for hardening and tempering, but no good if following afterwards with with chemical processes as the sand grains can stick. Fine for quenching though.

wylk

Another resource on making springs – http://route60garage.blogspot.com/2014/11/howto-make-springs.html

Doug MacQueen

Hey Max, you are so right about being able gauge the temp in a darkened room. Unfortunately, I see poorly enough in daylight. In a darkened room you can see the steel start to glow at least 500 deg. F earlier than than the way I am doing it outside. Maybe even a 1,000 deg. earlier. For a beginner though, IDing the correct glow of the critical quenching temperature is difficult. From what I have read, staying within 25 deg F of the critical temperature is fairly important to having best chance of success in making workable springs. And this 25 deg range is after the steel has lost it’s magnetism. IIRC the critical temp for high carbon steels is somewhere around 1600 deg F. And if I am not mistaken, this same critical temp is also used to anneal the steel. The difficulty in using a magnet is, as mentioned, the need to keep the spring from sticking to the magnet.

Doug MacQueen

Wylk, that is one of the better spring making descriptions I have seen. I just quickly glanced through and it seems dedicated to wire springs though. I thought I would focus first on making flat springs such as is being discussed in the Norwalk lock thread. For years in the shop I worked at, flat springs ,and wire springs for that matter, were made from cold pre-tempered spring stock, but never went through the process of heat treatment. For the most part they seemed to be okay as I don’t remember any complaints. However, making springs with sharp bends was out of the question. As time went on and I learned a little about spring making, I came to find out that stresses are induced in bending the pre-tempered spring stock. This lead me into investigating the processes of heat treatment. Now very sharp bends can be achieved. In the lock trade, very little has been written about spring making. You probably have to go back to the 1950’s or earlier to find any real discussion. In the mortise locks of the latter 1800’s, flat springs are commonly used, wire springs not so much, with the exception on the spring latch bolt. In the earlier locks of the 1400-1700’s, some very interesting springs are found.

fuzzymaster

I found this site because my front door latch is broken. I need to make a flat spring to repair it. Would it be possible to use this thread to help me through the process of making the spring that I need?

Doug MacQueen

Would it be possible? Yes. Is it the most practical way? Not necessarily. Depending on the spring shape, it could possibly be made from pre-tempered spring steel without going through the heat treatment process. However it is not likely to work as long and as well as one that is properly made. What kind of equipment do you have? Mapp torch? Fire bricks? If you don’t have this type stuff, then it would likely be cheaper to have it made. And do you have the broken spring parts or is it missing?

fuzzymaster

I do have the torches required, and with some guidance believe I could do this. Here is the thread that has a photo of where the spring is missing.
http://www.antique-locks.com/showthread.php/4048-need-some-help-with-old-door-lock

Doug MacQueen

That spring could be made from pre-tempered spring stock such as what the locksmith suppliers sell. In fact that is what you should get first even if you are determined to make a heat treated spring. Getting the proper thickness stock is a critical factor. Too thick and the bolt will be too hard to push in as the door is shut. Too thin and it will struggle to extend. If you remove that part and flip it over you will see the thin slot the spring has to fit into. This opening will give you a very good idea of what thickness is needed. Flat steel thickness gauges available at auto parts store. Once you have determined what the slot thickness is in thousandths of an inch, post it and I’ll see what I have.

Doug MacQueen

Someone mentioned using the steel banding for making springs. It turns out that some banding might work while others might not. If you are not skilled at IDing high carbon steel by the spark test, another way is to take a sample piece and full harden it. That is, bring it up to the critical temp (somewhere in the cherry red area depending on the lighting) and quench it in oil. If a file skates on the metal, it should work out for springs. Also at full hardness, the steel is extremely brittle and will shatter like glass. It is because of this brittleness full hard high carbon steel is not useful for tools, knives, springs, etc. Therefore this brittleness needs to be tempered down to make it useful.

Doug MacQueen

This lock of Fuzzymaster is a perfect one to look at since it is, when installed takes a smooth curve with no sharp bends needed to be made. And why the pre-tempered spring stock that locksmiths use might work perfectly well. There are 3 states that a spring sees, unloaded, pre-loaded and fully loaded. Unloaded is prior to installation, pre-load is installed and under some stress, and fully loaded is at its full travel and under the greatest stress. If you compare the shape of the unloaded spring, to the shape of the spring after it has been installed, fully stressed and then removed, ideally you see should no change. If you do see a change then the steel has undergone plastic deformation. The greater the deformation or change in shape, the greater the need to stress relieve and re-heat treat the spring. So as long as Fuzzymaster will take pictures of his spring before and after testing it in the lock, we will see if plastic deformation has occurred and if it is enough to warrant further heat treatment.