Project update and request for help

[theperfessor]

I'll try to keep this short, but I need to provide some background information concerning the goal of a long term project I have been working on. Then I'm going to ask for some help from 3 or 4 of you so I can finish and document the current phase of the project. It will only require a few minutes of your time, and the end result will (hopefully) be of benefit to many of the people who frequent this site. If you're interested, read on.

I'm a machinist by training and a mechanical engineer by degree. I teach manufacturing courses at a state university, do some consulting and material testing, and have a small machine shop for doing subcontract work and building prototype machines.

A few years ago my interest was rekindled in bullet casting and reloading. I found this site, and gained an appreciation for the technical aspects of the process of casting bullets. I got a real education after reading many posts concerning the quality problems of various molds, and seeing some really innovative ideas on mold modifications and alterations. I also participated in several group buys until the wait time became unreasonable.

I decided that I could make multi-cavity bullet molds at least as good as any of the commercial vendors, and that making small lots of a custom product of the best quality might be a good way to supplement my income and keep me active when I retire in a few years. I laid out a rough plan for this, dividing it up into stages:

Stage 1: Determine the processes necessary to make a mold, develop the tooling, and cut a sample mold. Test the end result, and keep track of all the problems encountered throughout. I did this, and posted a link to the following article:

http://www.usi.edu/science/engineering/moldfixture/MakingBulletMolds.doc

Since publishing the article above I have made many changes and improvements. While not yet perfect, I can now manufacture the mold blanks accurately and relatively efficiently. I felt like I got things 90% right the first time, and now I've got things about 98% right. But I'm always looking for better ways to do things, so I'm still keeping track of problem areas.

Stage 2: Determine a testing process to enable actual empirical data to be gathered relating the actual size of a mold cavity to the resulting bullet size, and acquire the necessary instrumentation to perform the test. I realized that it would be necessary to be able to monitor and control temperatures accurately, so I built a dual PID temperature controller and posted this thread:

http://www.castboolits.gunloads.com/showthread.php?t=71208

I have made three 5-cavity molds, one each of 2024 aluminum, 7075 aluminum, and Dura-bar nodular iron. The cavity sizes are (roughly) 1/4”, 5/16”, 3/8”, 7/16”, and 1/2”. Each cavity was drilled 1/64” undersize and then reamed to nominal size. However, after examining the first mold, I was dissatisfied with the interior finish and so each cavity was bored out 0.005” to 0.020” oversize using a single point HSS tool. In order to be sure the mold and alloy are at the proper temperature, I put a band around each bullet with a little hook tool so that I can visually check the test slug for good fillout. See the pictures below for details.

The testing process will include three or four different alloys – almost pure lead (roof sheathing), straight WW, a Lyman #2 analog (9 lb WW +1 lb 50/50 solder), and possibly Linotype. These are the typical alloys available to the hobby caster and are materials I have at hand. I don't plan to buy pure materials from a vendor at this point, but I'm keeping that possibility open for later consideration. (Of course if a commercial vendor wanted to LOAN me some certified metals I would be glad to pay the postage both ways and return the extra materials at the conclusion of this test. And I would give credit in the report also.)

The test will be as follows:

1. Measure and record the diameter of each cavity in each mold at ambient temperature. I plan to measure the base band across the parting line with a small hole caliper micrometer.

2. Using a particular alloy, cast slugs at several different temperature ranges above the minimum needed for good fillout. I plan to preheat the mold first and then vary the casting furnace temperature to determine the minimum mold/alloy temperature for good fillout. I will record the furnace temperature, mold stabilization temperature and cycle time, based on how long it takes the sprue to freeze and not smear when cut. I do not plan to use any “assisted cooling” methods such as wet towels, etc. but I will have a fan blowing to provide some gentle air flow, mostly for fume control.

I plan to cast 25 or more slugs of each size at the various temperatures so I will have enough samples for a statistically valid test. Each slug will be measured at ambient temperature and the readings will be recorded and tabulated.

3. Do the math, write up the results, and publish in the public domain.

This is where I need a little help. One of the pieces of data I want to include is a BHN of the various materials. I do not have any hardness testing equipment. I would like to send three samples of each material to someone who can do a hardness test and who is willing to send me the results. I would like to know what machine you used and what the BHN number is for each sample. I can prepare the samples any way necessary and will pay the postage to get them to you. You can add them to your lead stock when you're done. It would be nice to have tests done on several different types of machines, to cover the range of equipment most used by hobby casters.

You will get full credit for your efforts in the report (by name, handle, or anonymously if you wish). I'll either post the report to Castboolits or put it on another site and post a link here. I plan to start the testing soon, but I might not finish it up (there will be a lot of work and time involved on my end) until the end of the year. I just want to line up some help early on.

Once I have this information available, I can move on the the next stage. The last real problem I can see is the need to improve my form cutters so I can make a tool of the exact profile necessary. I've been talking to a local shop and may have a line on a used Cincinnatti tool grinder. No big deal, I spent two years looking for a little shaper to cut vent lines in my molds and finally found one of those, and I can afford to be patient.

http://www.castboolits.gunloads.com/showthread.php?t=83273

Once get over the last hurdle, I should be able to reach my goal:

To make high quality multi-cavity bullet molds in a variety of materials that will drop a bullet of a specific size using a specific material when cast at a specific recommended temperature.

[.30/30 Guy]

I have a LBT hardness tester that is available. PM sent

[oldtoolsniper]

I am a retired Marine with lots of time on my hands, I use the commonly available Lee hardness tester mounted in a microscope and I would be more than willing to help you. I would do the test as described on the boolit cast in the directions provided with the kit from Lee.

[excess650]

I have a Cabinetree tester and can test your samples as well.

[MtGun44]

I have an LBT tester, mech eng degrees, willing to help but out of town on
business until mid Aug. If you can wait until then, very happy to assist this
EXCELLENT sounding project.

Regardless of the outcome of this particular post you deserve a hearty

"WELL DONE", sir for undertaking this project.


Thanks

Bill

[Catshooter]

Young man,

I have both an LBT and one of Buckshot's hardness testers. PM sent.


Cat

[Doughty]

perfessor,

I have a LBT tester. I'd be happy to help.

Richard

[theperfessor]

Thanks to all for the offers to help. Several people have even offered to loan me their equipment to use. I really appreciate the amount of trust this shows but I'm uncomfortable with the responsibility of using another persons tools so I will respectfully decline such offers. And I'd really like to have a rough idea of how close various hardness testers are when used by a number of different people who are testing the same alloy processed the same way (air cooled). I consider this a side benefit of this project.

I will bookmark this link and get back with you guys as the project gets a little further along.

Once again thanks.

[Calamity Jake]

I too have a Cabintree hardness tester that I calibrate with a certified pure lead sample.

PM me when your ready for testing.

[Catshooter]

No problem perfessor. I will be happy to test whatever you care to send me, if you care to.


Cat

[Casting Timmy]

I've often thought about machining of molds and think it's interesting in the differences between how bullet molds are made and commerical molds are made. I've seen 2 piece all the way up to a 5 piece molds machined as individual components and then assembled with perfect fits.

I wonder with the use of CNC machinery if anyone uses a smaller cherry with a circle interpelation on the program, but only on half of the mold instead of both halves at the same time. It would definitely help with chip removal while cutting and I've seen enough molds put together after machining I know mismatching the cavities to each other wouldn't be a problem.

Also just to help you save time if you decide to go into production. Have you thought about using a thread mill to cut the vent lines? I know there's a lot of different tool holders and inserts on thread mills. If you find one with the correct radius and spacing you could cut multiple vents lines at once.

Good work, it'll be interesting to hear your results.

[Bill*]

"And I'd really like to have a rough idea of how close various hardness testers are when used by a number of different people who are testing the same alloy processed the same way (air cooled). I consider this a side benefit of this project."

Hey perfessor; Somewhere on here is a thread ( from a few years ago ) involving 50 members ( I was one of them) using various brands of hardness testing equipment on identical samples. I'll try to find it for you.....stay tuned

http://castboolits.gunloads.com/showthread.php?t=27678&highlight=hardness+testing

BTW: count me in if needed

[44man]

Perfessor, You are about to enter the nut phase! :bigsmyl2:
First, those molds are beautiful and show super talent even though I think you should have made actual boolits! [smilie=s:
Now the nut part, I have made cherries a little oversize to allow for shrinkage and sizing and had the molds come out the exact size as the cherry and too large. So I cut another with the proper reduction only to have the boolits come out too small.
Even O-1 and A-2 cherries change things but it can happen with the same tool steel.
Each caliber seems to need a different allowance with diameter. Since I use the same lead, it can drive a guy nuts. I have also used the same scrap aircraft aluminum cut to all the same size blocks.
Since it takes me a day or more to make one cherry with a lot of hand work, because all I have is a Smithy, it gets frustrating. No matter how close I make the cherry to what I want, I never know what the boolit will drop at until I cast a few.
Now you are going to test mold material, all hardness and alloys AND different diameters along with temperatures.
I have a lot of dog hair so you can make a mullet to replace the hair loss and I am afraid you will resemble this guy--:veryconfu.
You should learn something having baseline cavities but when you start to figure what is needed for each different boolit you want to make will be the fun part.
I wish you luck and just maybe you can teach us non-machinest types something.

[44man]

One thing I really have trouble with is taking a hunk of band sawed scrap and turning it into a perfect rectangle with 90* sides, using the cheap Smithy mill-drill. How the heck do you hold a piece of aluminum to a mill table?
I have to use a vise.

[deltaenterprizes]

I've often thought about machining of molds and think it's interesting in the differences between how bullet molds are made and commerical molds are made. I've seen 2 piece all the way up to a 5 piece molds machined as individual components and then assembled with perfect fits.


The molds of which you speak cost at least $25,000 or more and are designed to produce hundred of thousands or millions of items.

Bullet molds are made for economy and are expendable items.

[BABore]

I wish you luck on your endevor as well. Your going to need it.

As 44Man mentioned, all things are not linear and many times come out not as you expect. Figuring the cavity size for different size cylinders is not to hard. When you add lube grooves of varying depths and complex band configurations, sometimes careful plans get thrown out the window. A cavity's diameter to length ratio will change the outcome. Long, skinny boolits will cast out tapered even though the cavity is perfectly cylindrical. The nose diameter will be close to cherry/cavity size and it will get progressively smaller as you get towards the base.

After you cut a 100 or so cherrys you will find that there are some base guidlines as far as how much bigger you have to go on diameter. During this time you will develope a gut feel for how a particular band/groove arrangement may mess with your normal outcome.

[cbrick]

And I'd really like to have a rough idea of how close various hardness testers are when used by a number of different people who are testing the same alloy processed the same way (air cooled). I consider this a side benefit of this project. Once again thanks.

perfessor,

Here is the info on BHN testers your looking for.

Cast Bullet BHN Tester Experiment (http://www.lasc.us/Shay-BHN-Tester-Experiment.htm)

Hope this helps, I use the LBT tester if you would like me to test some samples for you.

Rick

[cbrick]

Perfessor,

Did you get back to this thread, find the info you were looking for? Results? Outcome?

Curious minds want to know. :mrgreen:

Rick

[theperfessor]

Update

This project is still active but it's been on a temporary hold for several reasons. The primary reason is the heat. It's been 90* to over 100* in my shop for most of the day for the last few weeks. And the humidity has been at about the same level a lot of the time. I can work there in front of a fan for about 4-5 hours and then I'm wiped out. It ain't worth dying over.

I had designed several fixtures and tooling that would facilitate production and yield more accurate and consistent parts. Most of these could be made in one or two afternoons and could be started and stopped whenever I felt like it so that's what I've been working on while I wait for the heat to break. I posted one thread in Special Topics about an end squaring fixture and I've got a couple more I'll post there as soon as I get done processing the photos.

I've scrubbed the molds in dish soap and measured the cavities. I've got an Excel spreadsheet for all the relevant data that I will print out and fill out by hand and then transfer the data back in for analysis. My Lyman 20 pounder is full of junk alloy which I will use to break in the molds while I get a feel of some basic parameters such as temperature and sprue freeze time.

Cbrick - I appreciate the link to the hardness tests some of you guys participated in. I noticed that the testing was done on a single water quenched alloy. The information presented was very well documented and precise. As such it resulted in useful information and met the stated objectives. I have no criticism of this, it was very well done. But the test I hope to get help with will be done on air cooled alloys and should be less scheduling dependent. It will also test a range of hardness values. While this test is not the main purpose of the project I think it will also yield some useful information. I'd compare it to the difference between checking a micrometer on one set standard compared to checking it at several points throughout its range. Both types of tests have value.

I appreciate some of the advice and information that real mold makers, both hobbyist and commercial, have shared throughout this project. Nothing replaces real world experience and I respect those who have it and are willing to share it with others. I know that I still have a lot to learn, and that what I learn from this will still need to be augmented and modified by my own personal experiences. But it is just my nature to try and think things through as much as I can and to try to approach things in a rational and organized way. It's less work in the long run and shortens the learning curve a lot.

One other comment. In other threads several posters have shared links to references of different data tables on bullet shrinkage with different alloys. There is one on the lasc site for example. I also have several printed references of material property tables. In general they are in agreement. They tell you how much an object shrinks over some stated temperature range. But unless I've missed something (a real possibility and correct me please if I'm wrong) none of them equate mold cavity size versus final bullet size. Since the mold expands as it gets hot (and I did an actual test and posted a thread on that topic a while back) you also need to calculate the cavity expansion over the room-temperature to casting-temperature range. This is where I want baseline data with measured parameters. I want to deal with both problems - mold expansion and bullet shrinkage - in one step as this relates more closely to actual manufacturing practice.

[theperfessor]

Last week it was cool enough to break in my three test molds. My Lyman 20# BP pot was filled with some "junk" alloy so I used it. I set my PID at 375* for the hotplate to preheat the mold and 725* for the alloy temp in my casting furnace. The mold temperature was monitored with a screw-in thermocouple.

I had cleaned the molds by degreasing them with acetone followed by a good scrubbing in Palmolive dishwashing detergent. It only took three or four casts to get wrinkle free bullets, but I had to get the mold up to 425* to get square bases and perfect fillout of the bands.

I wanted to use this time not only to break in the molds but also as a way to practice casting and to determine if there were any problems with the overall setup. There were a couple of minor mechanical issues - one of the holes in one sprue plate had to be countersunk a little deeper, it was tearing a little, and all of the sprue plate screws had to be adjusted slightly for smooth operation - but other than that there were no problems.

I was pleased to note that the slugs fell out quite easily, so apparently I had the fixture centered properly on my lathe. One of the good points of lathe boring is the lack of burrs inside the cavities. Since the mold halves are clamped tightly together at all times there is no burring caused by tool breakout which can occur with the double-acting-vise and cherry method.

What was more difficult was to adjust my rhythm to deal with having to fill five cavities of different sizes and volumes. I'm not the most coordinated person in the world (an understatement!) so it took a little while to get used to but I eventually trained myself to deal with it.

At the conclusion of the break-in I drained the pot and shut everything down.

Yesterday was another nice day - 78* when I started in the morning. I cleaned the remaining residue from the pot and filled it with ingots of roof sheathing. It must have been close to pure lead as the pot temperature rose steadily to 623* - very close to the 621* melting point of pure lead - and then stayed there until the ingots melted. (It's the latent heat that occurs during the phase change from a solid to liquid.)

I had not changed the mold and pot temperatures on my PID from the break-in period but soon found out that these temperatures were to low for pure lead. I had to increase the pot temp to 775* and the mold temp to 475* before I got good slugs.

I used each mold in succession, casting until I got 35 to 40 good from each one. I tried to keep conditions as consistent as possible. It was no problem keeping the pot temp at 775* - the PID worked great, staying within +/- 3* throughout. I paid close attention to the mold temperature, filling the mold when it was within +/- 3* of my 475* set point temp.

It took about 15 to 20 seconds for each cycle. The temperature rise in the mold was about 8* to 20* and was very dependent on the amount of excess material poured on the sprue plate. The "average" temp rise was about 12* when I poured what I consider to be a normal puddle on the sprue plate. After cutting the sprue and dumping out the slugs I waited until the temp dropped before making the next pour.

I spent more than six hours to complete the whole process using all three molds.

Today I started the measurement process since my arms were too sore to do any more casting.

I spent most of the morning measuring the slugs from two of the three molds. I did a visual inspection and discarded any slugs that had any defects. Primarily these were slugs that had cold laps caused by splashing from adjacent cavities during the filling process. I don't consider this to be cherry picking or discarding of data that "doesn't fit" - it is exactly the same visual inspection most of us would use to cull bad bullets from good.

I measured 25 slugs of each size selected at random. Each slug was measured using an outside micrometer with a 0.0001" vernier scale. (I have now made more than 200 measurements and haven't even finished all the measurements needed for one alloy.) The data was recorded and will be entered into an Excel spreadsheet for later analysis.

If it stays cool this week I plan to fire up the casting pot and continue the test with some other alloys.

One observation - I was gratified but not surprised to note the dimensional consistency of the slugs. It reinforces my belief that temperature control is the key to getting consistent size bullets.

More to follow.

[Buckshot]

................Sounds like a lot of work there Perfesser! It should be interesting to see the result. I'd heard somewhere and don't know the validity of it that moulds made of aluminum (no alloy mentioned) should be cut to the desired boolit OD as the cavities expansion will give the desired boolit OD. Of course the higher the antimoney content the less boolit shrinkage you'll have so the statement might have said WW or something else and I'd just forgotten.

.................Buckshot