View Full Version : Leaded steel Mold material
06-01-2005, 08:07 AM
I have seen some people use 12L17 and 11L17 leaded steel for molds. Do you have any idea if it clears out the chips when boring?In don't want to use a material that produces long chips and may roughen the finish in the cavity. I know it machines like butter, and it very stable once stress relieved. Cast iron works, but can be brittle, I am thinking of other materials to use. The biggest problem might be the fact that leaded steel is often Cold rolled and full of stress. Greg
06-01-2005, 09:59 AM
They use the stuff because it machines like butter, it is a material specifically made to machine nicely. I have worked with 41L40 and it was darn nice stuff too (not for molds tho) . 12L14 is the old standard screw machine stock, It is going to be readily avail mostly in rounds, squares, and hex's.
stress relief is not difficult, and I never considered cold rolled material to be full of stress any more so than any other steel.
The only thing a leaded steel should not be used for is items that need to be welded together.
I have been a machinest/toolmaker/cnc/etc. for over 20 years and picked up a few things along the way.
I think my first mold(s) will be aluminum and have dowel pins about like a Lee 6 cav.
06-01-2005, 07:58 PM
I know the stress relief process is not difficult, it just adds a step, and additional cost. I have worked in my Grandfather's machine shop a little bit, and noticed that Cold rolled 1018 often bows after machining if it is not sent out for stress relief. Hot roll has less stress in general, and is more stable without additional heat treatment. For cutting or wear applications, I only us Hot rolled tool steel to lessen warping during heat treatment. I think I will us Hot roll 6150 for the Sprue plates in .375" to machine up at .250" finished dimension. It is cheaper than O-1, and I don't need to pay for Precision ground.
I figured the leaded steel might be easier to machine for some of the people trying to make their own molds. I already made some in Aluminum, and they are a bit soft. I want the mold to last a long time, once it wears in. Aluminum is cheap, and heats up quickly, with no corrosion problems, but not very durable. Thanks for the input on the mold block material. Greg
06-01-2005, 10:20 PM
A lot of the stress in cold drawn steel is from the skin formed by the drawing process. For example 1 1/4" thick 1018 will have about .020" skin on the surface.
I too am thinking of making molds from 12L14.
Have used it in square, rectangle, hex, round stock for over 20 years.
Currently have some 1 1/2" hex stock and will bandsaw the two edges off the hex to make rectangle bar stock. This will get rid of most of the stress and then can surface one side to lay in the cnc mill to final surface and groove face, and ream pin holes.
I am not worried about making the mold blocks, it is the shinkage factor of the poured material that is making me do all the thinking. What is the ratio of shinkage??? I know this will change do to the diameter of the bullet.
06-02-2005, 03:46 AM
I know I have seen the stress in the skin you talk of, in machining 4" square steel bars some 3' long, I inherited the job when the guy that started it quit, they looked lika banannas because instead of cutting opposing sides first to allow the steel to come back he simply flipped them 90 degrees after each cut, we got them squared up tho, that stuff was a burnout.
Most of the cold roll I have worked with is round stock.
On the shrink issue, I was going to measure a mold of similar size to get a starting point.
Inconel would be heck to machine but it has almost the same strength at 1000 degrees as it does at room temp. I think one could pull off sprue plates made from that material but I wouldnt want to make a mold from it. I have not worked with it in thin cross sections enough to know if it would warp when heated.
I have made sprue plates from A2 and left them un heat treated, they turn a pretty plum color, and so far do not seem to warp...the critical temp. of the air hardening steels is much higher than straight carbon tool steels so I assume they would not harden from casting...and they have quite a bit of chrome in them which I thought would make them less likely to oxidise while hot.
also 12L14 I would think to be more of a "dead" material than 1018 and less likely to have stress in the bars, it rolls much nicer.
if you put a 12L14 shaft in a 100 ton press to press it into a hole it acts like lead.........much more so that 1018 (much lower yield strength, higher ductility)
06-02-2005, 07:45 AM
The hex bar idea seems like a good idea. Perhaps you can use the hex shape to your advantage, and cut the handle slots across the opposing flats. The shrinkage is variable. I contacted Dan Lynch at Mountain molds for the shrink factor. On a .730" diamter bullet he told me the shrink was 1-2.5% of the diameter. He said the different casting alloys and bullet diameter all have different shrink rates. Antimony bearing alloys such as WW and Linotype Shrink less.
The sprue plates don't really need to be hardened. I could use A-2, but it is a little more expensive. It also would resist corroion more dur the the 5% Chrome in it. It won't harden , during casting, as the critical temp is 1950F if I remember correctly. O-1 and 6150, whicha re simple carbon and alloy steels are critical at 1370-1550F. The sprue plates will be drawn back during casting . I would harden my plates to 54-56 Rockwell C, and if they get a little softer during casting it won't matter. I think they would have to reach a temp of 650F to get much softer than 50-52C. Some places don't even harden the sprue plates, or give them a nice sharp shearing edge.
I was looking around, and the metals industry is taking heat for the manufacture of Leaded steel. The have come up with Tin steel to replace the lead. I am unsure of the grades available. The reasoning behind the lead and tin in the steel is that the metal chips fracture at machining temperature. This makes the chips clear easier, and gives a good surface finish. Greg
06-02-2005, 08:51 AM
"Inconel would be heck to machine but it has almost the same strength at 1000 degrees as it does at room temp. I think one could pull off sprue plates made from that material but I wouldnt want to make a mold from it. I have not worked with it in thin cross sections enough to know if it would warp when heated."
For a brief while around 1925, Belding & Mull offered mould blocks made in "pure nickel", at about doublt the price of their iron ones. I have an early "Rifleman" writeup on these which made them sound pretty good, but they were said to be quite difficult to machine. One collector friend has a set, and said they cast about like any other mould - thr great adavtage being that the material is not subject to rusting or corrosion in normal use, and lead does not "wet" the nickel.
We used Inconel-800 (or was it Incoloy?) tubing in the boiler in the solar power plant I worked at in Barstow back in the '80's, but I never tried playing with a sample. This alloy was originally developed for housing the heating coils in electric cookstoves; that flat gray stuff wound into a spiral on the "burners".
06-03-2005, 11:43 PM
............I know that the early smokless steels were a nickel bearing steel and it was a cast iron puppy mother to work with, as many tools then were merely forged high carbon. Now forged and correctly heat treated high carbon steel is harder then the hubs of hell and can be brought to a super sharpness. The downside is heat which anneals the edge and then you might as well be trying to cut with a banana.
Before putting a round M36 Marlin 30-30 barrel on an old 1893, I investigated haveing the original "Special Smokless Steel" octagon barrel rebored and rifled 38-55. This was a nickel alloy steel and the word form folks doing this work is, "Yup we can, but the new bore while accurate and good, will be somewhat rough". I wonder if the barrels as they originally left the factory were considered, "Good but rough"? Maybe one of the old machinists at Marlin had found a meteorite in his back yard and brought it in to make tools out of?
Personally I think that certain grades of cast iron is very possibly the best mould material. It doesn't produce clog prone chips, but rather dust when machined. It's stable and doesn't have a grain. It's much more sturdy and long lasting then any aluminum and it's melting point, unlike aluminum is nowhere near the common casting temps of lead. But in it's favor aluminum is certainly a joy to machine :-).
I would think that fully annealed and normalized steel would make a fine mould material. Lyman blocks are steel but I don't know what type of steel it is.
Many years ago I made an adjustable bullet mould to make slugs for paper patching, out of a piece of 1-1/8" HR bar stock. The nose was a SWC type as the bullet was pushed out of the cavity via pushing on the nose plug. The base was flat as that was the sprueplate end, and the nose forming plug was adjustable up and down. Worked lke a champ.
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