DOLEP LOCK ASSEMBLY TUTORIAL #5
Back again! Today I’ll go over positioning the mainspring, hardening and tempering.
Before going into that, I thought I should post some pictures of the outside of the original Dolep lock, for those who may not have them, since I posted a picture of the inside last time.
SPRINGING INTO ACTION:
Now that the tumbler is firmly installed, you can use the toe of the tumbler to establish the position of the mainspring. Mainspring position is critical. If it’s too close to the tumbler, the claw of the spring will collide with the tumbler at full cock. It it’s too far forward, it will fall off the end of the tumbler at full rest and take the wood out of your lock mortise when inletted.
Mainspring position is established by drilling a blind hole into the lock plate. This position can be established by mounting the cock on the tumbler, placed in the plate, and positioning the cock at full rest, meaning the flat inner stop surface of the cock lies flush against the top of the lock plate. At full rest, the tip of the mainspring claw should contact the tumbler a very short distance (but not scary close) behind the front tip of the tumbler.
I marked the mainspring stud hole by painting the front inner surface of the plate with Dykem machinist’s blue. I then placed the back tip of the mainspring claw firmly against the front bearing surface of the tumbler toe (at full rest!), and scored a line in an arc across the blue with the tip of the spring stud, the center of the arc being the contact point of the spring and tumbler toe.
The blind hole for the spring stud lies midway between the upper and lower edges of the plate. Center punch this spot. It looks like a 7/64 drill bit is about right for this hole, after cleaning up the lock with files and dressing the stud smooth and cylindrical. (As with the other springs, the surface lying against the lock should be filed smooth and straight right up to the edge of the stud. Later on, you can file off a little from the contact surface of the lower spring arm if you see it scraping on the lock plate.)
Drill a blind hole with tapered and bottoming bits at this site, setting your drill press stop so it doesn’t penetrate the outer surface of the plate. Try placing the stud in the hole. If it doesn’t go all the way in, you can carefully file off some of the tip of the stud until the spring lies flat against the plate. A little rapping with a rawhide or plastic mallet here wouldn’t hurt to get it firmly seated.
The actual measurements for the location of the mainspring stud hole are 2.720” in front of the center of the tumbler hole, 0.720” back from the front rounded tip of the lock plate (assuming you haven’t filed any or much off the front of the plate during cleanup), and about 0.230” up from the lower edge of plate (again allowing a little fudge factor if you have filed some draft into the plate edge.)
The mainspring is held in place by another blind screw measuring 5-40. File the surface of the upper mainspring screw site flat and punch a center hole in what looks like the center of this flat area. Position of this hole is not really critical as long as the upper arm tip of the spring is in contact with the lock plate bolster. Drill a clearance hole through the spring with a #29 drill. Position the spring stud in its hole and center punch for the spring screw through this clearance hole, again with the tip of the upper spring arm up against the bolster. Mainspring screw hole is drilled with #38 tapered and bottoming bits, then tapped to 5-40 with tapered and bottoming taps.
You can try out the fit now, but of course don’t try to flex and mount the spring onto the tumbler until it’s hardened and tempered! Onto this topic next:
The frizzen, tumbler, sear, and all springs need to be hardened, followed by tempering to various temperatures depending on the part. These temperatures are listed in Tutorial #1.
After these parts are hardened, it’s going to be very difficult to do any more engraving or shaping, so you should clean up and finish these parts as close to final finish as you can now. This particularly applies to the frizzen, which will (should?) come out very hard after heat treating. You need to decide now how much decoration/engraving you want on the frizzen and do it.
On the casting, you can see a sharp decorative molding line around the front side of the frizzen and some raised floral designs in the middle. The edges of the moldings and inner details can be sharpened up with curved riffler files, gravers, and stones. The curvy edges around the front stem of the frizzen can also be cleaned up nice and crisp.
If you look closely at the casting you can see the faint impression of a very fine engraved double line outlining the shape of the frizzen between the outer edge molding and the inner raised floral detail. I’m sure there are guys out there who can engrave perfectly parallel fine curved beauty lines exactly 1/16 inch apart going smoothly around an arc with no variations in depth or width, and no wobbles. Unfortunately, I’m not one of those guys. I decided I could engrave a credible single line at this site, but there’s no way I could make a perfect double line. I engraved this line with a small tapered graver (not a square) a little deeper than necessary, trying to keep at least the bottom of my line in one nice uniform arc. This took many repeat cuts and adjustments. There were plenty of bobbles and wobbles at the surface. I filed, sanded, and stoned the surfaces down below the level of the irregularities, leaving a fairly uniform single shallow line. (Sometimes perfect is the enemy of good enough.)
All these parts call for initial heating to 1525F followed by an immediate oil quench. If you have a high temp oven /kiln you can use this, but following the advice of other gurus, I decided to do the initial heat treat just using MAPP gas.
I put together this little temporary heat treating furnace using plain bricks. I plugged up some holes between the edges of bricks with Brownell’s Heat Stop mud, just to keep more heat in the central cavity. I made a little coiled soft steel wire support to raise the parts above the floor of the cavity to be able to get underneath them with a torch. On a hot plate, I warmed up some pure Canola oil to 140F for quenching, using a kitchen thermometer to follow the oil temperature. I didn’t need a huge container for the oil since the parts are generally small and will be quenched one at a time. I put this all together outside, anticipating great eruptions of smoke and flaming oil, and had a fire extinguisher at the ready. In fact, there was only a little smoke and a tiny bit of flame on the larger parts. You could probably do this indoors if you have very good ventilation and a sympathetic spouse.
I heated up the parts with a MAPP torch inside the little brick chamber until they were uniformly glowing bright orange, then quickly grabbed them with tongs and immersed them into the warm canola oil bath, swirling them back and forth in the oil for ten or twenty seconds.
Another thing that may help you determine appropriate heat is the use of a small magnet. When the steel is hot enough for quenching, a magnet will no longer be attracted to its surface. I happen to have a little magnet on the non-pointy end of a scriber, and tried this technique on a couple of parts. It does show you when the metal gets to quench temp, but I found it very cumbersome to use a torch in one hand and a magnet in the other on a loose part inside a small cavity. At the end of the day, I just heated everything bright orange and quenched.
(That big round thing in the picture is a wheel for a wheel lock, not part of the Dolep set.)
Dry the oil off the parts and test for hardness now. If the parts are hard, a file should skate over the surface of the part without cutting into the metal. There will be some burnt oil residue on the parts, and the file will take this off, but should otherwise not show an inclination to cut any grooves into your parts. These parts are very brittle at this stage, so be careful not to drop or strike them.
My results were mixed. I appeared to have nice hard surfaces on my springs, sear, and tumbler, but my frizzen could still be easily cut with a file, and striking the frizzen face with a piece of flint resulted in a dent but no sparks. I repeated the whole process on the frizzen without much more success. (I posted this whole experience on the ALR forum under this topic: “Frizzen not hardening?” http://americanlongrifles.org/forum/index.php?topic=41457.0
Lots of people had input on this).
To make a long saga short, I ended up cleaning up the face of the frizzen with the curved end of a belt sander and case hardened the frizzen using Cherry Red carbonizing compound. This is similar to the old Kasenit and used in the same way. Brownell’s also sells a similar product called “surface hardening compound”.
The Cherry Red comes as a gray powder in a can. I poured a liberal little pile into about a 4” diameter metal lid and heated up the cleaned-up frizzen in my little brick furnace to bright orange again, focusing the heat on the frizzen face. The hot frizzen face was then immediately pushed into the pile of carbonizing compound and allowed to cool. Some of the compound went onto the front (decorated) surface of the frizzen as well, but this is okay. I didn’t try to case harden the stem, toe, or pivot hole of the frizzen. These areas are small and a little fragile and should not be made too brittle, risking fractures.
After the carbonizing compound is cooled it looks like a bubbly cake of gray cooled lava. It will be firm to touch and adherent to the metal. Take the frizzen and caked up carbonizing compound back to the oven and heat it all bright orange again with the torch. The compound should glow as brightly as the steel. Keep it orange-hot for a bit to allow the carbon to soak into the steel. The Cherry Red compound calls for a quench in water rather than oil. The bright orange mass of frizzen and Cherry Red was plunged into lukewarm water, accompanied by a sickening “crack” sound. It was okay, that snapping sound was just the Cherry Red exploding off the surface of the frizzen.
In order to get good deep even penetration of carbon into the frizzen face, I repeated this process three times in a row. After allowing the frizzen to cool off, the frizzen face appeared hard, couldn’t be cut with a file, and striking it with a flint produced some pretty sparks and no big dents!
This process could be repeated at a later date if the frizzen face becomes worn.
All the hardened parts are tempered at specific temperatures to draw out a varying degree of hardness. I did this in my digitally controlled oven/kiln. The frizzen needs the least tempering, heating to 375F and holding that temperature for twenty or thirty minutes, then air-cooling. The tumbler and sear are tempered to 575F for the same period of time, and again air-cooled. (They came out of the cooker a very pretty royal blue color. I was sort of sad to polish them back to the white.) You could probably do the frizzen tempering in your kitchen oven, and possibly also the tumbler and sear, if your kitchen stove can accurately heat up to 575F.
The springs need to be tempered to 750F, and your kitchen stove probably won’t handle this. Some people temper springs with a torch, heating the polished spring to the aforementioned royal blue color, but no further. The recommended 750F is probably much hotter than this, but you could give it a try. Other folks describe placing the hardened spring in a can under a covering of light motor oil, heating the can until the oil ignites and burns and eventually burns itself out. I’ve never tried this myself, but go for it if you like!
These temperatures I quoted above came from Jim Kibler and I believe are the recommendations of his foundry, based on the steels they use.
After tempering the springs, they might look a little black and crusty. This can be polished off to a smooth bright surface.
We’re getting close to final assembly now! In my next installment:
SNAP! SPRING DISASTERS AND FIXES