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Home-Shop Mould Making
by Tom Slater
What follows for this portion of the series is a discussion of the shop equipment I use and a list of materials for making your own moulds. Be aware that this article can get technical so please don't get discouraged, we were all new to this game at first. This information IS NOT required to enjoy this sport.

And PLEASE read the Disclaimer BEFORE you begin to undertake these instructions. Thank You.

What follows for this portion of the series is a discussion of the shop equipment I use and a list of materials for making your own mould.

Lathe - Almost any lathe commonly found in a home shop will do work to the accuracy we need for mould making, although some of the really big lathes (often purchased used) some of you may have can make the process a little clumsy....sort of like threading a needle with gloves on. At the other end of the size spectrum is the miniature lathe. Some of these are really tiny and could be considered jewelers lathes. These very small lathes can do work to an accuracy far greater than we require, but would have difficulty gripping the work in their miniature chucks. Eventually we will need to grip a cube shaped work-piece that is about 1 1/2" on any side. My lathe is an 8" X 48" and provides the ideal combination of size and accuracy for this work. Any lathe of 4" swing or thereabouts will do fine. A very important point on lathe bed (ways) wear must be made here. There are many WW2 era lathes in home shops now doing yeoman duty turning brake drums and making parts for old cars etc. It is common to find wear near the headstock on these lathes that render them unfit for precision mould making. The ways on these older lathes are occasionally worn to the point that the saddle is pointing "uphill" or "downhill" into the chuck when working near the headstock, or the saddle/ways contact area will permit a slight rocking horse motion. If you own one of these old workhorse lathes verify the positional accuracy of the saddle near the headstock....please! I used a terribly worn Logan lathe for my first trials at mould making and every hole bored with that lathe was pointing downhill into the headstock. This produced a hole at an angle to the work-piece, which of course produced a bullet with the heel at an angle to the centerline of the bullet. Accuracy was not quite as good as a shotgun pattern.

Milling machine - Any of you that have some experience with a lathe realize that it can be used for limited milling. If you have the fixturing for milling in the lathe some of the mill work can be done there, but the use of a milling machine will be hard to avoid. The important aspect of doing some of the work on the mill is that the "Z" axis can be "trammed" into perfect 90 deg orientation to the table. Many "bench top" mills cannot be trammed in because the head is fixed to the ram, but we can work around this limitation by shimming the work-piece into tram with the "Z" axis. Shimming the work-piece into tram is a slow process, but we aren't doing production work. My mill is a full sized vertical Bridgeport clone knee and column, and weighs around 2 tons. Fly-cutting the vent line is easiest and most accurate, using the knee motion for the Z axis movement, and is why I recommend using a mill for this work. The use of a drill press is not recommended as a substitute for milling machine work. Drilling and reaming for the mould alignment pins is one of those operations where a milling machine is almost a necessity, but I continue to learn, daily, that someone always has a viable alternative to the methods I propose. When any of you spot a weakness in what I do, or know of a better method; don't hesitate to speak up and suggest improvements.

Tools and tooling - I should have stated, at the outset, that the method I use to make moulds in the home shop is by boring in the lathe. (It would require a tool and cutter grinder to grind a cherry to cut the mould cavity). Tooling for the lathe will include a 4 jaw chuck to hold the work-piece accurately and tool holders for boring tools. (I am currently working on using a precision die grinder with various shaped cutters to cut mould cavities, but, for now, will direct my comments to cutting the cavity with single point boring tools). We will also need two dial indicators and mounting equipment for them. Why two dial indicators? Because we will be using two tool motions on the lathe and must control both of them with high accuracy. One of the motions is the "cross slide" which is used to control the diameter of the cavity by moving the tooling in and out in relation to the work-piece. The other motion will be the "compound", set in line with the axis of the lathe. The compound will be used to control the depth of the bullet cavity. Trying to use the dial skirt markings for accurate tool movement regulation is futile. There is too much backlash in dial movements and using the dial skirt marks would be frustrating. One dial indicator is set up to report tool motion by the cross slide, and the other dial indicator indicates motion of the compound. One comment is in order regarding quality of dial indicators available today...many dial indicators will gladly report a "rise" of less than .001" but fail when asked to show a "fall" in the opposite dial direction movement. Verify the truth of any dial indicator you may use. Buy high quality indicating and measuring tools....you will be rewarded with a lifetime of accuracy.

The use of single point tools implies a pedestal grinder and the ability to properly grind these tools. If you have miniature pre-ground boring bars, or small boring tools with insert tooling the grinder requirement is moot, but most home mechanics have a shop grinder for sharpening lawnmower blades etc. This grinder, when the wheels are properly dressed, will sharpen tool bits very well. If you are unfamiliar with grinding your own tools, check with a machine shop in your area. Small shops will grind the proper profile in tools for almost no charge, and are happy to encounter a serious home shop machinist that will admit to not knowing all there is to know about tool grinding. I picked up all sorts of odds and ends by visiting machine and asking for their help with something I did not understand.

For the milling machine a boring head or fly-cutting tool holders are required. These tools are used to cut the vent lines in one of the mould faces. Drills and reamers of the proper size for alignment pins are also required. One of the dial indicators will be used to report the rise of the knee for cutting vent lines. (The quill motion is not accurate enough for cutting these lines). While not necessary, if you know how to accurately tram the head of the mill, a milling cutter of ~1 1/4" is handy. If you can tram the head accurately the face milling cuts required can be made with smaller diameter milling cutters (1/2" maybe) by making multiple passes across the face of the work-piece. A small milling cutter (1/4" or 5/16") is used to make the cutouts in the side of the mould for the handles. An arbor to mate a drill chuck to the milling machine spindle is required. If this arbor is not available proper collets to hold all the drills, reamers and cutters will be necessary. A good milling machine vise and table clamps will also be used. A 90 deg countersink is used to cut the sprue hole, so start looking for one of these.

Taps and tap holders will also be required for production or our mould....there are a few threaded holes in every mould. An accurate 0" - 1" micrometer reading in ten thousandths is handy, but any good micrometer reading in thousandths will work.

Materials - I use 2024T351 aluminum for my moulds. I will be trying some brass in the near future, but aluminum is easy to work and, when only buying a foot or so, not too expensive. Blank moulds in iron (meehanite) are available from RCBS for a fee. This is the finest iron available for mould making, but is not cheap. I would recommend the beginner stay with aluminum or brass. The iron in RCBS moulds is soft and cuts like butter. Lyman moulds are very hard and difficult to cut. A small assortment of set screws in #8 and #6 size will be used, and proper drills and taps for these will be necessary. A 1/4" X 1/2" sprue plate hold down screw is used. Again, drills and taps are required for this size hardware. I use a short piece of 1/8" drill rod (RCBS style) to hold the mould halves to the handles, but there is nothing magical about this method. Any of the various styles of mould holding screws/pins for the handles will work just fine. I make my sprue plates from 1/4" stainless steel, but this is another area where individual preference comes into play. Any good grade of hard steel will work here....just don't use common hot rolled steel. It will dull in short order. Don't be daunted by the foregoing; common sense and resourcefulness will let some of the requirements outlined above be substituted by other methods. Beyond the machine tools most of what is required is available to most home mechanics. If you don't have the machine tools, ask around. I am amazed by the number of home shops that do have the machine tools required, and a request to use them, with proper cautions, is usually granted. I have several friends that use my tools often. If permission is granted to use someone else's tools a new milling cutter, a few drills or a reamer or two usually solicit a response that you are welcome anytime.

Home-Shop Mould Making; Pg. 2 of 4
Preparation of the two mould halves and milling machine; work on them follows.

The 2024T351 aluminum stock I use for mould making measures 1 1/2" X 1". The 1" dimension will be reduced to 3/4" in a little while, so if you can obtain the material in that thickness it would be more economical. I use that size stock for other work I do, so am only using what I have on hand.

I cut two pieces of the aluminum stock ~1 5/8" long, grip them in the four jaw chuck and face all ends. The o.a.l. of each piece must finish at 1.500" after facing. The finished ends of the work-pieces will be one of the surfaces gripped by the four jaw chuck while the bullet cavity is being bored.

The work-pieces from the above paragraph are now mounted, biggest side up, in the milling vise on the milling machine table. Make certain the milling machine spindle is at 90 deg to the table both front to rear and left to right. Locate the two work-pieces as far apart as practical in the milling vise jaws. This places equal load forces on the vise jaws and permits similar cuts to be made on both work-pieces, and one different cut to be made on one of the pieces. At this point I use an insert style face milling cutter to mill the 1" thickness of both mould halves to down to 3/4". This is the cut that is the same for both mould halves, and reduces the thickness of the mould halves to 3/4" mentioned earlier.

Both halves of the mould will remain in the milling vise for the next cut, but only one of the work-pieces will receive the cut. It is now that the vent lines will be cut. The description of cutting the vent lines is one of the most difficult to explain without illustration, but let's try. First, a brief explanation of mill motions is in order. There are three motions available on a milling machine. The table movement from left to right is the "X" motion. Table motion front to back is the "Y" motion, and the table motion up and down is "Z". The "Z" motion can be accomplished in two ways....1) with the quill, like a drill press and 2) by moving the "knee" to lift or lower the table. The most accurate control of the "Z" motion is by using the knee to change the elevation of the work-piece, and we will use the "knee" for the "Z" motion when cutting these vent lines. I have found that vent lines are only needed in one half of the mould when they are cut properly. With a fly-cutter, or boring bar mounted in a boring head crosswise, set the tooling to cut ~4" radius. Center one of the mould halves between you and the spindle so that the work-piece would travel, front to back, directly under the spindle if you cranked the handle that moved the "Y" motion. (As I said, this is very difficult to explain without illustration) We are going to make a cut that looks like a "smile" in one of the mould halves, and this is called a "record" cut because of the resemblance to the grooves in a phonograph record. Start with the work-piece between you and the spindle. Bring the work-piece under the spindle so that the first vent line will be cut about 1/16" down from the leading edge of the work-piece. Elevate the knee with the "Z" motion and cut the first vent line .005" to .006" deep with the tooling and note the dial skirt reading. Drop the knee and advance the work-piece under the spindle with the "Y" motion 1/16". Elevate the knee and cut another vent line to the same depth as the first. Drop the knee and advance the table into the spindle again etc, etc, etc. You will have to make about 22 to 25 vent line cuts on the 1 1/2" dimension of the work-piece.

It's a lot of cranking up and down, and in and out, but produces very accurate cuts. The bottom of the record cut, the "smile" should be closest to you, the operator, while making this cut. The lowest portion of this "smile" will be the bottom of the bullet cavity within the mould when the cavity is cut. If you have an LBT mould, take a look at it. It illustrates the cut I have just described. For over 20 years I have used the cut for venting my moulds, and I learned it from a machinist that cut vent lines in plates used for plastic injection molding. All the foregoing could be explained with one picture. The comment would be "Oh, I see!!!!!

The next operation is to drill holes for the alignment pins. I use 1/4" roll pins for alignment of the two block halves. Bring the two halves of the mould together, face to face, and clamp in the milling vise. I locate the two alignment holes in opposite corners of the mould, but can't say for certain that this is necessary. What is important is to be aware of the orientation of the "record" cut that was just completed. You must always be alert to locating the lowest portion of the "smile" to the bottom of the mould. Layout the hole location 3/8" from the edges at the corners and drill 1/4" holes for the alignment pins through one of the block halves and halfway through the mating half. (About 3/8" into the mating half). The 1/4" hole completely through one of the block halves is used "as is". The receiving hole for the alignment pin is reamed to .2525". Grind a gentle taper on one end of each of the 1/4" roll pins. This ground portion on the roll pin eases entry into the oversize (by .0025") mating hole in the other block half. The roll pins should be about 3/4" long. Drive the two roll pins into the block, with the hole clear through it, till they project about 3/16" toward the mating block. Please note that the alignment pins should be driven in from the "outside" of the block. The tapered end that was ground on one end of the roll pin should enter the hole first. This is so the taper you ground on the roll pin is available for entry into the mating hole on the other block half. With the mating hole for the roll pin reamed .0025" oversize there is usually very little "working" of the two mould halves to get the roll pins to enter their respective holes with ease.

The two mould halves are now vented and aligned, and are ready for boring in the lathe. Centering the two block halves in the lathe is a great mystery for most of us, but is really quite simple. That is what is coming up next....and boring the bullet cavity.

Home-Shop Mould Making Part 3 of 4
If you have come this far you know we have a mould with vent lines cut and alignment pins installed.

We are now ready to clamp the mould in the four jaw chuck in the lathe and center it for boring. If, during drilling/reaming for the alignment pins, the two block halves slipped slightly (and this is common) first grip the assembled mould in the four jaw and make a light cleanup facing cut on the ends of the mould so the ends are even. This should only require the removal of a few thousandths of material. Centering the mould for this facing cut is not critical....we just want the ends of the mould halves to be even with each other.

The next operation is gripping the mould for boring the cavity and centering the two halves of the mould on the lathe centerline. The problem becomes stopping the chuck jaws in the same place every time while shifting the work-piece for centering. If you have a lathe with exposed headstock gearing (common on older home shop lathes) the problem of stopping the chuck in the same location is simplified. Just locate a gear in the headstock with an even number of teeth and devise a way to index to opposite teeth at 180 deg spacing. Some Logan lathes even have 24 indexing holes drilled around the outside of one of the headstock gears....possibly other lathes do also. The first thing to do is to locate the mould in the four jaw with the parting line vertical and eyeball the center of the mould to approximately the centerline of the lathe with the jaws that touch the work-piece at the parting line. This would be the jaws on the top and bottom of the work-piece. Centering the work-piece in this orientation is not critical...it is done only to center the cavity cut in the direction of the parting line. Centering the cavity ACROSS the plane of the parting line takes a little more work. My lathe has totally enclosed gearing in the headstock in an oil bath. I had to devise a method to accurately locate/stop the chuck at the required 180 degree intervals. The method I use sounds a little bit "hoaky" but works with good accuracy. I simply use a "stop rod" from the lathe bed to the chuck jaw I wish to locate. This stop rod is machined to fit one of the inverted "V" ways of the lathe bed and has a "step" on the other end for positioning against the chuck jaw. Mount a dial indicator to the cross slide for centering a work-piece and orient the chuck with the "stop rod" so that a reading can be taken from the work-piece. Check the centering with the parting line still vertical, but this time the jaws closest and farthest from the operator are used to center the halves ACROSS the plane of the parting line. Crank the cross slide in and out to check centering as you index the chuck 180 degrees between dial indicator readings. Use the "stop rod" against the chuck jaw each time to stop the jaw in same location. Cutting the "stop rod" so that it contacts the chuck with the jaws close to horizontal helps a lot. You are moving the two halves toward or away from you with the parting line vertical. This is the important centering operation. If done properly the two mould halves will each have exactly 1/2 of the cavity and bullets from the mould will literally drop from the cavity. Take your time with this centering operation. Do not have any of the setscrews set tightly on the cross slide adjustment gibs....doing so causes some "jump" in the motion of the cross slide. If done carefully it is entirely possible to center the two mould halves with about .0002" difference, and this is lots closer than required. It just makes the bullets drop from the cavity like magic.

Now make a facing cut across the mould you have mounted in the chuck. Making this facing cut assures that the top of the mould will be square to the cavity you are about to cut. Here again only a few thousandths (maybe .020" to .030") should be required to clean up the mould halves. Before drilling a pilot hole and starting to cut the cavity, make a drawing of the cavity (bullet profile) you propose to cut. Put dimensions on the drawing. You will refer to this drawing throughout the cavity boring operation. I would recommend something simple for a first mould. Consider a wadcutter for a handgun. I floundered around for a long time trying to cut complex profile moulds till I decided to try something simple. Please don't try to run till you can walk reliably.

Now center drill and make a pilot hole between the two mould halves. I find 1/4" is a good pilot hole for 30 cal. 5/16" works for 38 cal. and 25/64" is about right for 44 cal. I don't recommend the beginner attempt anything smaller than 30 cal because of the small tooling required and the extremely light cuts this tooling demands. Use tools ground to a threading profile. This produces cuts without any right angles in the grooves and ridges within the cavity, and helps promote good bullet release from the mould. Ogive nose radiuses can be cut with form ground tools, but that is beyond the scope of this introduction. If you know how to grind tools that is great! Possibly you can bypass some of the elementary steps and bore more complex bullet shapes at the outset. I recommend the simplest bullet profiles for the beginner. Some of my earliest bullet moulds had a nose profile that was nothing but the tip of the pilot drill, and these worked surprisingly well. Probably a ballistic wasteland, but I was learning. Set the compound to align with the lathe axis. Mount two dial indicators....one to report the cross slide motion and the other to show the compound movement. Make the first cut into the pilot hole by advancing the compound rest. Carefully measure the diameter of the hole as you enlarge it. This hole will be a benchmark and the diameter is important. If, for some reason, you must change tools you can use the point at which the new tool touches this hole as a reference. It is common to break tools when boring, or it might be necessary to sharpen a tool at some point in the operation and being able to locate the tool at some starting point is essential. Take your time boring the bullet cavity. Don't work more than about an hour at a time. Make light cuts. Refer often to the drawing of the cavity you propose to produce. You will probably have 4 to 8 hours work in just boring the cavity on your first attempts, so don't get rushed. Make a note of the dial indicator readings on your drawing as you progress through boring the cavity. Don't become discouraged. I made about 10 or 12 moulds till I finally produced one that could be considered a success, but I didn't have anyone walking me through it. (I would hurry and make outrageous mistakes). Just take it slow and easy.

Next time we will discuss the finishing steps. . Making the sprue plate, cutting the slots for the handles, retaining screws for the handles etc. Fairly straightforward stuff. Not so much confusion and detailed descriptions.

Home-Shop Mould Making Pg.4 of 4
This will finish the series. All that remains to complete the mould are the details that follow.

If you are left handed this is an excellent opportunity to have a mould that works the way you do. The sprue plate can swing from either side of the mould.

I use stainless steel to make my sprue plates. I buy it in 1/4" X 2" strips about 3' long. The side that contacts the mould must be milled (or ground) perfectly flat. One edge of the sprue plate must be milled off leaving a "knock" ear on the end of the sprue plate. I use my mill to make these cuts. Working stainless steel can be a problem, but use tools that are very sharp and flood the work with cutting fluid. Lay out the hole locations for the sprue plate pivot screw and sprue cup on the sprue plate material. I use a 1/4" X 1/2" bolt for the pivot screw and drill a 1/4" hole through the sprue plate for this bolt. I make my sprue cup hole by starting with a 5/64" pilot hole through the sprue plate. This is followed by cutting the sprue cup with a 90 deg countersink, but a 100 deg or 110 deg countersink would work just fine. I use a 90 deg because that is what I had available years ago, and I still have the original tool. A greater included angle on the countersink would provide a larger sprue puddle for bigger bullets to draw upon during the "shrink" period that the sprue solidifies. Make certain that the stainless is "backed up" while making the holes for the hold down bolt and sprue opening. It requires a lot of down pressure to drill through stainless, and this pressure will raise all kinds of burrs on the other side of the plate. When I am finished making holes in the sprue plate I remove burrs on the mould side of the plate by rubbing the sprue plate on 320 grit emery paper placed on polished granite.

Mill 5/16" slots about 1/4" deep along each mould half for the casting handles. Drill and tap holes for the sprue plate hold down bolt, and a #6-32 retaining setscrew for that bolt. Holes for the bolts or pins that mount the mould to the handles must be drilled and tapped. I use 1/8" drill rod to mount the mould halves to the handles, and hold the drill rod in place with #8-32 setscrews which push the retaining pin into the hole and lock it there. Note that the setscrew for the mounting pins is not "crosswise", but pushes the retaining/mounting drill rod into the hole. It is "in line" with the mounting drill rod. Small numbered hardware could also be used to mount the mould halves to the handles, but it must be hardened or stainless because of the continual "bumping" encountered by these parts during casting.

Mount the sprue plate to the top of the mould with a "Belleville" or "wave" washer under the retaining bolt. This washer places the sprue plate under slight pressure all the time and allows for expansion during casting. You should be ready to try your new mould.

I'm certain that portions of what I have written leave a lot to be desired. Please email me with any questions you may have. I will try to better explain whatever might need improvement.

You can see that mould making is a whole LOT of little steps that are all related. If one of the steps is done "sloppily" it will throw the rest of the work off. If you try mould making just remember to take is slowly and think through each step. Write down what you have done and what remains. A checklist is one of the best tools to help reduce error. Don't work when tired, and don't work for extended periods. And expect to make mistakes.....but learn from them.
Good judgment comes from experience.....experience comes from bad judgment.


Tom Slater


Adamsville, Ohio USA

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