Does anyone have any idea of how much oversize to cut mould cavities for various alloys? I can't give up on this 17 twist barrel yet without a fight. The information must be available somewhere out there but if so I sure can't find it.
Thanks In Advance,
Pat
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I've cherry cut about 40 molds, so far. Everytime I think I have a good handle on it, I'm wrong. It is dependent on many factors including mold block material, venting style, bullet design, casting temp., pouring style, and alloy. Deep grooved Keith-style bullets seem to shrink more than shallow grooved bullets. The shrink factor is a percentage of bullet diameter. Bigger the bullet, the more oversize you make it. Because I'm still pretty green on it, I play it safe. I usually go 0.0015 over on 38 caliber and up to 0.002-0.003 over on bullets as large as 475 caliber. That usually allows the mold to drop a bullet either right on to 0.001” over my desired size. It's much easier to size down a little than wish it were bigger. I will also sometimes cheat on gas check shanks by making them a tad small, then use a boring bar to open them up to perfection. Better to cheat, than repeat. That's said, I'm starting to get the “gut feel” as to what it will need.
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BABore summed it up nicely.:P
Let's dispel the “shrinkage” myth. People talk about “shrinkage” as if it were a scientific constant.
Let's consider the other variables.
An “x” diameter reamer will not cut an “x” diameter hole. Instead, the hole will be slightly larger than the reamer. How much larger varies with things like reamer run out and RPM and dwell time.
Then, the cavity expands with temperature. Different metals have different coefficients of thermal expansion. Even if you know the cavity diameter at room temperature, that doesn't tell you the diameter at casting temperature.
Then, the liquid metal has to fill the cavity. Common alloys like WW almost never fill 100% using a gravity pour. It's not like we pressurize the metal to 10,000 psi. So even if you can verify the diameter at casting temperature, you still don't know how completely the metal will fill the cavity.
Even a gravity pour creates slight pressure, and this pressure varies at different points on the bullet. Generally, the bottom band and/or gas check shank sees the least pressure (on a base-pour mold).
Air and dross rise to the top of the cavity, causing more fill problems at this spot.
The liquid metal has to zig zag around the lube grooves. Metal doesn't like to zig zag, so deep, steeply angled lube grooves will impede fill more than shallow, gently angled lube grooves. A smooth paper patch design will fill out much easier than a loverin design.
Likewise, itty bitty bands don't fill out as easily as big bands.
It is very common to see as-cast diameter vary 0.002” just by minor changes in temperature and casting style. Centerfire alloys generally drop smaller as temperature increases. BP alloys generally drop larger as temperature increases. As always, it's not just a question of pot temperature. It's the MOLD temperature that is critical.
Then there is the heat shrink problem which is a whole 'nuther mystery.
So, at the risk of being a smartass, there is no cut and dry answer to your question.
In general, if you cut each band of the cavity exactly the same diameter, the bullet will be tapered, with the base band smaller than the top band (for a base-pour bullet), for the reasons discussed above. Hence, if you want all bands to drop equal diameter, you have to cut a slightly tapered cavity. This is especially true of smokeless alloys, and not-so-true for BP alloys.
I have a database of cavity diameter vs. bullet diameter for a variety of alloys and mold materials. If you specify your alloy and mold material, I might be able to throw you a number. Bear in mind that any such number should be treated as a rough rule of thumb, not a scientific certainty.
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Thank both of you for replying. I lathe bore my moulds using RCBS blocks. For my personal use I use WW with a bit of tin for an alloy but would also be interested in your ideas about lino.
You both have more experience than I do so nothing you write will be taken as being a smart a$$ answer. If there's no cut and dried system then I'll just continue to cut big and size down. The moulds I make are just for my own use anyway so there's no complaints about the finished product.
Pat
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The following numbers are for the bottom band on a base pour mold. Upper bands will have less “shrinkage.” My practice is to cut the mold with a slight taper to compensate for the uneven “shrinkage."
WW&2% tin in iron block: average “shrinkage” 0.80%, low 0.36%, hi 1.27%.
Lino in iron block: average “shrinkage” 0.17%, low 0.00%, hi 0.32%.
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Hello folks:
I have been lurking for a bit and have recently started back casting my own. One area that has always interested me is in producing my own moulds.
With that being said I do not have a machinist background (but liek to think I am a quick study) but am handy in the tool shed. I doubt I could cut cherry's for moulds but lathe boring the mould seems an attaiinable goal.
I have seen several folks mention they “cut thier own” but have not been able to find a consise writeup or howto. Do you folks have any pointers to publications or postings that outline what I would need to be capable of performing?
Besides, I have been looking for an excuse to get me a lathe for a while now. This might just push me over the edge :D
Been eyeing this one for a bit...
Steven
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Steve,
I don't have a machinist background either but after taking a couple of beginners classes at a community college and buying a used lathe I've managed to cobble together a couple of moulds and fit a few barrels for my own use. My advise on a lathe is while the one you're looking at is nice and good enough for mould work you'll find it's the tooling that's going to kill you. I think a better idea would be to look around for a used model with an 1 3/8 or so hole through the headstock that includes a bunch of tooling if you can find one. It took me a while to find what I wanted and my lathe would be said to have seen better days by most folks but it's good enough for what I do and didn't put me in the poor house trying to get all the stuff I wanted to make it useful. I got into this to fit barrels and eventually turned to playing with moulds, you're thinking about getting into it to cut moulds and might eventually want to fit barrels. Having a big enough hole to do the work with the barrel through the headstock seems a lot easier to me and you only buy once.
Boring a mould isn't that hard but does require certain tools and you'll have to make a jig to hold the blocks themselves. I'm no expert but since there's really no good place, or bad place come to think of it, that gives any information on the various ways to cut a mould I might write a little something for the FS and include a bunch of pictures.
Pat
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Pat:
Thanks for the response. Yeah I know the tooling is going to be a big part of the purchase. Like you I have been looking for a good used one but when one comes up I look and it is basically scrap. Government liquidators leave them (even CNC) out in the weather for 6 months or so before selling them.
Add to that I live in a relatively non-industrialized area nd pickings are slim. Out of frustration I have about decided to just buy a new one and be done with it. I
To show you the level of frustration I am thinking of selling one of my pistols to finance the aquisition.:shock:
I think a good write up/tutorial would be a great addition. Especially with pictures and tooling reccomendations etc. If you decide to take it on I one be but one of many that would be grateful.
Steven
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Standles That is a pretty nice lathe in the link. I have been considering one myself, and I looked at ll of their offerings at Grizzley and found the one I would like.
http://www.grizzly.com/catalog/2007/Main/531
I was considering a 3 in one machine, but the through head stock opening on a shosmith is too small to allow a full 1.5 inch barrel.. I guess I just have to wait to get the darn mill.
Pat- Yeah, lot's of pictures on that! I want to see how you constructed the jig. I have an idea on the boring bar, it would be similar to the hobby lathe I have now.
One of my projects for this winter is to revamp the block alignment pins on my LBT moulds. I hate those spring pins he uses. I think the pressure you need to get the darn things to close properly is one of those inconsistant varibles that result in lousy bullets.
I want to be ready for Mike if he comes down to Charlotte in the spring.
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Standles
One of my projects for this winter is to revamp the block alignment pins on my LBT moulds. I hate those spring pins he uses. I think the pressure you need to get the darn things to close properly is one of those inconsistant varibles that result in lousy bullets.
Jeff,
What do you find wrong with the pins on LBT moulds? I've been using Verals moulds for years and as long as you keep them lubricated they work just fine. It might take a little longer to get everything to seat itself in but I think that's one of the reasons they cast so well.
I'd be willing to bet that if people are having problems with an LBT mould it's because they're afraid of dirtying the thing up with the mould lube. Every one mine looks like something left over from an oil change but they cast great.
For boring bars I use Micro 100 carbide internal threading tools, they come in various sizes and work great plus they already have a 60 degree taper built in so there's no sharp corners. I have an Armstrong boring bar holder that came with the lathe and just had to make tool holders out of 3/4 in drill rod to hold them. Naturally you have to make your own nose and ogive cutters and to keep things simple my moulds all have truncated noses. I jerry rigged a couple of cheap micrometers thimbles and small hole gauges into sort of comparator tools to measure the nose diameter when I'm cutting them and don't remove the blocks from the holder until I'm done. I don't trust myself enough to be taking the blocks in and out of the jig. After that a couple of good indicators and an internal micrometer is about all you'll need along with some drill its and possibly a small mill cutter to get the nose meplat flat.
I'm sure there's a few other things I use that I can't think of right now but all the tools fit in a small box. I use RCBS 22 moulds for blocks.
Just remembered I bought a spring loaded center from Brownells years ago that's supposed to be used to indicate barrels in for recrowning and it works great for indicating the cavities in, never used it on a barrel though.
Pat
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I didnt get any mould lube with any of the 8 or so moulds I got from him. George gave me some of the graphite/beeswax stuff eariler this year. I still dont like those pins, of course mine are galled up from not having any lube on them.
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With the condition of the nation, I think it wise for everyone with a real strong interest in making molds to give it a whirl.
My simple suggestion for starters, based on 27 years of making a living cutting molds, by lathe boring, are:
Pick up RCBS or Saeco used blocks with small enough cavities to cut what you want, or even buy them new. they aren't expensive. It is far easier to tune them up than to make a complete set of blocks and sprue plate. Both are cast iron, and Saeco is the finest easiest to cut iron I've ever worked with. To make that statement REAL clear, it is the highest quality iron I've ever worked with anywhere, not just with mold blocks. (I prefer high quality aircraft aluminum for mold blocks, but for beginners iron will cut easiest, and even new mold costs, to get the blanks is the most ecconomical way to get started.) The reason for recommending iron is that when cutting in a lathe it can be scraped slowly and very smoothly by feeding in slow, using NO cutting compound of any kind. Keep it dry and the chips will be fine dust only. If one uses a boring bar with narrow flat faced cutting surface the least cutting pressure will be required. For example, put a bevel on the leading and trailing edges and maybe no more than a 1/32 flat on the tip. The leading bevel should be shallow, with a flat front to cut flatnoses. This one boring bar, with one setup, using a long travel dial indicator, can cut an entire flatnose mold suitable for handguns and larger bore rifles. When boring, turn the boring bar to cut on the back side of the cavity, which will minimuze the tendency to chatter on infeed cuts, and make the mental work exactly like cutting outside, or normal turning. (Most machinest bore with the boring bar toward them, which increases chatter and demands thinking everything in reverse.)
The simplest way to hold the blocks for lathe boring is in a fixture, but a four jaw chuck will work fine. If you want to make a real quick and adaquate fixture to help setting the molds in squarely, machine up a flat plate with shoulder at the back to slide the blocks along, and glue this to one of the jaws with J-B weld epoxy. It won't be a permanent bond but will be strong enough that it won't come off if handled gently. To make that more clear, picture a flat piece of cold rolled bar stock, maybe 2 inches deep and viewed in the lathe, 1/2 inch thickness is enough and short enough that the mold cavities can be centered without an end holding jaw contacting the support piece. To make the shoulder, mill the piece 1/8 inch thinner with a surface wide enough to hold the blocks, leaving a shoulder at the back. Just be sure to grip only one half by three jaws, this by placing a small shim at each end so the teeth on one edge of the end clamping jaws grip just one block. Very little pressure is required, so tighten the jaws quite lightly, We can afford NO side pressure on the alignment pins, which should only be asked to locate the 'loose' block, which will be held in place with just one jaw. When you set up the mold blocks, align them with a dial indicator in the cavities.
To find correct diameter, make your cuts full length of the mold, being certain that you are at least .010 to .020 undersize. Remove the blocks and cast a bullet or three in the cold mold. The diameter you get while the mold is cold will be about .001 smaller than when the mold is hot if casting with tin lead or ww alloy, and .002 smaller if using lino. Commercial casting alloy will come somewhere between, but those are very precise measurements for sizing. Just add a little to be sure the sizer touches your bearing surfaces. Put the mold back in the lathe and open it up as required, going through the steps with your dial indicator. i.e. Say the flat cutting face of your boring bar is .030 wide and you want a bearing band of .1. Plunge the bar in very slowly to the diameter required, hand feed forward .070, back the bar off to yield the depth you want for the lube grooves, feed forward far enough to leave the desired lube groove width, feed in again for the next bearing band, etc,etc.
Cutting the ogive of a rifle bullet is best done with a drill shaped by hand to the form your want. Feed it in to the length you want to rough out the initial cavity, then do your bearing/lube groove bore, and bore ride nose or whatever. A taper from the bored area to ogive can be nicely done by setting the compound at a shallow angle, which will allow feeding the boring bar out to make a nice transition.
With a bit of care and a lot of time, planning on screwing up a few blocks while learning, it doesn't take a super machinest to make very accurate and servicable molds. This will scratch the itch to make your own, and perhaps keep the nation shooting if ammo gets scarce and moldmakers like me finally cave in a quit per government demands, or are killed. (I'm serious hear, my friends. That is my ONLY offence with Big brother, and their off the record stated purpose for attacking me. But they took on a pretty hard headed old goat that ain't gonna quit! Maybe stopped, but I'll never quit!) I wouldn't have wasted my precious time writing this to all of you if I didn't know what I'm saying to be true, in that it won't be long we'll be needing skills that aren't available now.
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George gave me some of the graphite/beeswax stuff eariler this year. I still dont like those pins, of course mine are galled up from not having any lube on them.
Shoulda read the directions!!!:)
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Veral:
I agree with you 100%. I think the next few years we are going to come under increasing levels of attacks. It is easier to regulate and ban the components that outright ban the firearms themselves. The recent trial balloon from the transportation dept shows that components are the weak link.
Also thank you for your insight on the mold making. I find it refreshing that a person that makes their living in that businesses is willing to help others that want to tinker. Putting the continuation of the craft and RKBA above normal business desires.
Having never met you or knowing anything about you that post says alot about the man and his values.
Steven
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After pondering it a bit, I decided to add a few more pointers about cutting molds, for beginners. It took me 8 hours each to cut new cavities in the first two molds I made, by cutting cavities in smaller molds. What I'm telling you will save you hours of time and turn out far higher quality.
The reason I reccomend recuting existing molds is two fold. 1. One only needs to obtain a lathe to recut existing molds, with a drill press also being nice. 2. Complete mold blocks are very time consuming to make and difficult to match the quality of commercial molds, which makes the price of new ones as recommended above a good value.
Before I start though. Jeff! Don't modify the alignment pins on LBT molds. They are the most accurate and long lived in the industry if you'll only lubricate them. If they have gotten sloppy from running dry they can be tightened by prick punching around the cavity on the most worn side till all slop is gone and the bullets are round again. The longest life I've heard of from one of my molds was 400,000 bullets before the customer sent it to me to have a look at how well it had stood up. It still cast within .0002 of round on all 4 cavities! There was NO play at all. The reason I decided to use spring pins for alignment, when I first started making molds was to avoid any chance of loosening. To get high quality pins, when I need to restock, I get samples from several suppliers who have large numbered lots, setting a sample of half a dozen from each lot. I choose the best available and order 35 pounds or so out of it. Probably 20,000 pins. Then I modify them, and to insure a high precision fit, hand scrape the female cavity to a snug fit, then mill the top face of the blocks. No other kind of alignment pin can match the long life of LBT molds.
Pat stated that he used Micro 100 carbide boring bars. - I have them custom grind mine, at about $100 each if I order a minimum of 12 at a time. But they have exactly what I recommended above for only $25 or so, and most hobby mold makers will never have to sharpen it. They are called solid carbide 60 deg internal threading tools and have a .002 radius at the point, which will minimize cutting force to prevent chatter better than anything else one can do. Just hand feed it real slow, with not over 800 rpm, and it will produce a bright smooth chatter free finish, even with a fairly light lathe. Two suitable bars for 30 cal and up are IT-23000 which will bore up to 1 inch deep, and IT-2301500 which will bore up to 1.5 inches deep, but isn't quite as strong and chatter free, so get the short one if it will handle all the bullets your dreaming of making. -- If you have a stout lathe, like a 12 inch or larger with 1 1/2 inch hole through the spindle, you might choose an acme thread boring bar, which has about a .0025 flat in similar sizes. Order a tool catalog by finding Micro 100 on the web and you are home free.
Chatter locks bullets into molds worse than any other flaw. Solid carbide boring bars eliminate it better than any other thing. Don't use a brazed bar.
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Veral,
Thanks for taking the time to reply. I don't feel I have enough experience to be giving out advice but trying to find any information about cutting your own moulds is about next to impossible so felt I could at least offer something.
As long as people know it's a learning experience and with learning comes mistakes they should be able to do it. Don't give up and even crappy looking bullets might shoot alright is the only real advice I can give.
Pat
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Veral is right on target. His moulds work great, but you DO need to lubricate the sprue plate pivot and the alignment pins. I have no idea now many .38 Special and .32 S&W Long flatnosed bullets I've cast in the two mould I use the most, but probably close to 1000 pounds over the years.
If you have any of the old nasty black Lyman Ideal lube, that is what I use to lube the moulds. EVERY time you fire up the mould, once it gets up to temperature, just take a toothpick, poke it into the lube block and just touch it to the pin or pivot. That's all it takes, just do it religiously.
Veral may improve on these instructions, but it works for me.
P.S. - similar lubing is necessary for ALL alluminum moulds of whatever make they are, and it doesn't hurt the meehanite blocks either!
73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia
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Pat,
This is long overdue, but found this in the Metals Handbook, Properties and Selection, 8th edition. Please note their terminology for various alloys may not agree with our notion of them.
Electrotype: 92-4-4. Shrinkage: 2.6%. Stereotype: 83.7-4-11.3. Shrinkage: 2.0%. Linotype: 79-5-16. Shrinkage: 2.0%. Monotype: 76-8-16. Shinkage: 2.0%. Lead: 3.4%. 92 lead, 8 antimony: 2.88%.
These were listed in the type metal section where there would be an interest in shrinkage for the intended use. My calculations show a .314 cavity would produce a .308 bullet.
Your 30x47 may be a thing of the past by now!
Paul Pollard
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