Lock bridle

[P.W.Berkuta]

I am a bit perplexed with a bridle for a lock I am assembling. The lock is a left hand percussion Mountian Siler about 12 years old and I finally got a reason to use it. I started the assembly with the plate, tumbler, then started on the bridle. I started to file off the flashing and my file went skidding off the part. I picked up another file and made two strokes and again it dulled my file but I knocked off the flashing. Now I chuck up a body drill for the # 8 screw and start to drill on the indicated mark for the first mounting screw - not too fast -just right speed - nothing - drill would not cut the part. Got a new drill bit - again nothing. So I got the torch out and a container of sand - heated the part up let it "soak" for a few min. then into the sand to cool. Two hours later I tried to drill again - still nothing - back with the torch, this time not as hot maybe 1400 degrees - back into the sand - two more hours - back to the drill - no good. Now I get the solid carbide drill bit (.140" dia) out, I figure I got a hard spot and I can drill it out then open it up with the .166" bit. Well that carbide bit was having a devil of a time going through - but it went through. I now chucked up the .166" bit and tried to open the hole up - no good trashed another bit. I gave up on that bridle and now am making one out of a block of 1020 -  Have any of you run into this type of problem - this is the first time for me and I don't know why

[Stophel]

Heeyah!  I've sure run into parts with hard spots, but I've never had one I couldn't anneal down.  Now I have had some that were hard to anneal down.  Siler tumblers and sears (O1) I sometimes have to anneal 2 or 3 times before I get it right.  (Heat to dull red, and put in a sack of lime to cool slowly)

Bridles shouldn't be anything more than 8620, and shouldn't get hard anyway.  You just got a wierd one with some $#@* in it.

[smart dog]

Hi P. W.,
Did you use a welding torch to heat the part?  Did you heat it to bright orange or bright red?  On a couple of occasions, I have overheated parts with my welding torch and they seem to simply cool too quickly from the maximum temperature to anneal properly. If the part is small, I usually use a Mapp gas or propane torch and heat to bright red color.  The other thing that I have noticed is that some parts need to be soaked at the annealing temperature for quite a long time. In one case, I had to heat the part in my burn-out oven at 1500 degrees F for 1 hour and then let it cool in the oven over night before it annealed sufficiently to be filed.

dave

[Sam Everly]

I ran into that one time installing the tumbler bearings in a lock. I always keep a supply of extra parts, i just got another and figured i was way ahead of the game . Man that thing was HARD!!! It to was a older Siler, i guess there may have been some made out of some odd ball material at one time many years ago .   

[LRB]

  Any time you are dealing with steel that has more carbon than .80, it needs a sphereroidized anneal to be soft enough to easily drill. I don't remember the details, but basicly it is ramped down from a high heat in stages before letting to cool all the way. When slow cooling the carbon forms layers which can be nearly as tough as before the common anneal. When the steel is sphereroidized annealed, the carbon goes into sphererical micro balls. These carbon balls will give way to cutting tools and the steel will cut like butter to a drill bit, or any other similar tool. If anyone is interested, I can find the details and post them, but this has to be done with strict temp controls such as an oven, or similar arrangement. When you buy precision ground 01, it is sphereroidized. That's why it is easy to work before HT. If you heat 01 to even a low red, the carbon balls will start forming layers again, and it will cool to hard, to semi-hard, as far as cutting with a drill bit.

[P.W.Berkuta]

Yep, them sphereroidized "balls" will get ya every time, I remember one time I was playing in little league -- OH - sorry wrong balls !
I did my heating with a propane Turbo-torch, I did not want to use the acetylene on it for fear of inducing carbon to the part. You all have good advise - I will make a new part but I think I will play a bit more with this "hard as Hades" bridle and see if it will come around - Thanks - Paul.

[LRB]

  One thing you might try. Do a series of sub critical normalizing heats. Stay below non-magnetic, try to hold a fairly even heat for a minute or so, then let cool to room temp. Repeat 4 or 5 times and see what you get.

[Rolf]

LBR, could you post the details on sphereroidized annealing? I've got a programable heat treating ovn I use for knives and such. I'd like to try this process-

Best regards

Rolfkt

[LRB]

  From what I found so far. I am going to dig deeper as I am curious also. The steel is cycled at 1250° to 1300° several times. You would pre-heat your oven, leave the part in only long enough to reach temp, remove and air cool to well below 400° or room temp. It would seem that you could even quench it, but I would try air cooling first, until I get more info. Sphereroiding begins above 900°, but if slow cooled, such as in normal annealing, will revert back to a layered structure. Air cooling is fast enough to abort this if done in cycles. Sphereroiding takes place between 900° and 1414°. 1414° is the curie point, or non-magnetic, where the carbon will begin forming solution.  The idea is to lock in the sphereroidized carbon condition by cooling it fast enough to avoid it going back into layers. If you were to go to non-magnetic, or higher, you would have to start the process over again because the carbon has started dissolving. Found some more info. If you were to soak at 1250° to 1300°, then air cool, the carbon spheres will be larger and spread apart more, and make the steel even softer to work, but then you will have to soak the part at quench heat longer when you are ready to harden. The first method forms small spheres closer together  which may not be ideal for your purposes. I would still cycle a couple of times though using method 2. This latter method seems the best for making parts softer to work, but you will want decarb protection for a longer soak time for the hardening quench. I would say 20 minutes at 1475°.  The reason for the longer soak time is that the larger spheres take longer to dissolve into solution. All this is based on 01 steel. If 1095, you would only need a few minutes of soak for the quench. Carbon itself dissolves pretty fast, but the alloy carbides in 01 do not. Hope this helps. I'll give more info if I run across any.
   Brownell's carrys two decarb protection products. One is PBC powder, which I have used for a long time, but also have a liquid that is applied with a brush. I am experimenting with the liquid, and so far it seems to work well, and is easier and cheaper to use.

[P.W.Berkuta]

LRB, I will try the series of lower heat with a small firebrick "oven pile" and see what happens. I know this is overkill for a bridle that would cost ~ $4.00 to replace but I got to do it, also I got some 1084 "as rolled" -not annealed - and it need to be soften up so I can work it with normal cutting tools. Maybe even fire up the gas forge - naw - too much house work today - not enough play time.