Lapping a Lee mold

[Wayne Smith]

In the quest for a mold large enough for my Steyr rifles (.334") I've come to the conclusion that I'll have to lap a mold. If I can get an oversized Karibiner mold (Thanks, Oldtimer) I'll likely have to lap it round. If not, I'll get a couple of the Lee .329" molds and try lapping them larger.

My question is simple, I've never worked much with Aluminum - If I mold a bullet of pure lead and roll it in grit, at what grit do I start? I have an assortment of ground carborandum and a steel plate designed for sharpening chisels and plane blades - that's a start. I can impregnate the bullet with the chosen grit on the plate. What is my best sequence of grits to use?

I also assume that the easiest way to find center of the bullet is to drill through the sprue with the plate in place, nichts var?

What else do I need to know before I do this?

[Tom Myers]

Wayne,

What has worked for me in the past is to wrap the bullet in 4-5 layers of electrical tape and lightly chuck the bullet in a drill press or hand drill and spin the bullet while holding the drill bit to the center of the base. The spinning bullet will guide the bit to the center and you can lightly press the bit in to start the hole.

The best vice that I have found to hold the bullet while drilling the hole is the mold itself. If the drill is not advanced too fast, the bullet can usually be drilled out by placing it in the mold with the parting line at right angles with the mold halves and then, while holding the mold handles tightly closed, advance the spinning drill slowly into the base of the bullet.

Be sure to use a drill that is sized so that the screw threads just get a purchase. Too small a hole and the screw expands the bullet. Too large and the screw threads will strip and not be able to spin the bullet.

Remove the head from a screw that has an unthreaded shank portion and then chuck the unthreaded portion into the drill and spin it to make sure that it is running true. If not, either straighten it or get another.

If possible, try to fasten the screw into a T-handle so that the bullet may be turned by hand instead of a power dirll. It seems that no matter how true the setup is, power turning will tend to make the cavity more out-of-round than hand turning will.

When placing the grit impregnated bullet in the mold, orient the parting line so that it matches the parting of the mold halves and lightly scrape the grit from the parting line on the bullet so that the closing mold halves do not scrape the grit from the bullet and deposit it between the faces of the mold.

There is probably more, but that is what comes off the top of my mind right now.

Hope this helps.

Tom Myers
Precision Ballistics and Records

[Maven]

Wayne, Take a look at this:

http://www.castpics.net/RandD/hone_mould/hone_mould.htm

[Ol'Scudder]

Here's a little gizmo sometimes called a "VIX-bit" i used to find indispensable when
installing things like cabinet door hinges - or other things where it was necessary to center the hole for the screw in a counter-sunk hole in a hinge.

http://www.leevalley.com/wood/page.a...40,53317,42265

I haven't tried this yet on a boolit mold, although i intend to, but it would add a lot to my peace of mind if i were drilling thru a sprue plate opening.

Have a good one, Stan

[Buckshot]

...............Problem with honing out a mould is that in the process you also blurr sharp details, and this begins immediately. Why not just get a 338 mould and size'em down to .344"? Lee makes one.

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

[dragonrider]

Ol"Scudder
excellet thought and I have a couple of those around. thanks.

[tom barthel]

I ordered bullets and lapping compound from Marshal Stanton with Beartooth Bullets. Don't know if he has the size you are looking for. Do a search for Beartooth Bullets and e-mail him. He is very good to work with.

[grumpy one]

It seems as if we have each developed our own process, and they vary a bit.

1. To drill the bullet you need some process that has a self-centering tendency. That is why chucking the bullet in a lathe works: the stationary drill tends to move toward the lowest sliding speed in the bullet, which is the center of the bullet. If you rotate the drill into a stationary bullet, you haven't much hope of a decent result.

2. Oldfeller's sticky gives most of the information you need for the actual lapping. If you treat it as gospel, and only get inventive in places where he hasn't told you what to do, it should work out well.

3. If you use a deck screw or self-tapping screw, grind off the point. If you don't, any resistance to rotation screws the screw in further and expands your lap. You just can't control the diameter that way. When you need a new lap, make one - don't try to expand the old one. It will only expand in a localized area if you force the screw in further, and you need uniform expansion.

4. Mount the screw in the drill press. Gently close the mould on the bullet - which is not a lap yet because you haven't put any abrasive on it at this stage. Start the drill and apply gentle pressure to the mould halves for 5 seconds. Stop the drill and inspect the bullet. What should have happened, is the bullet should have become round. It will have been a bit oval as-cast, and you want it round before you use it as a lap.

5. Choose your abrasive. I use the usual coarse grade of valve lapping compound if I need to increase the bullet diameter by .002" or more. After rolling the new lap, with fairly heavy pressure, between two flat steel surfaces with abrasive on one of them, and wiping off as much abrasive from the lap as you can with very gentle rubbing, you need to file down all the places where you don't want it to lap. As Buckshot said, if you don't take care, you'll end up with no crimping groove, hardly any grease groove, and an oversized gas check area. Just spin the coated lap in the bench drill and apply a coarse file and/or a hacksaw blade (good for grease and crimping grooves). You must know at this point whether you are going to lap the nose or not. If you don't know, don't lap it - you can come back to it later if necessary. To keep the nose from being lapped, just file down the nose of the lap.

5. As Oldfeller explains, you need a liquid to keep the whole thing from seizing up during lapping. He recommends liquid soap, which is what I use. My method is to put the soap into the mould cavity, close it very gently onto the lap, start the drill, and stop after about five seconds - because the mould will not have closed properly and you will therefore be lapping the cavity oval at this point. Clean the cavity, and especially, remove all the soapy abrasive that will have found its way into the gap between the halves of the mould and will be keeping it from closing fully. Repeat the process until the mould is closing completely, with no abrasive between the halves. This will have removed all the excess abrasive from the lap, and pressed the remainder pretty firmly in place. Clean the lap again.

6. Now you should be ready to start the serious part. Put fresh liquid soap in the mould cavity, close gently on the lap and start the drill spinning. If it is an aluminium mould, apply a moderate-tension spring clamp across the two mould halves to keep them together. If it is an iron or steel mould, use a C clamp for this. The pressure applied by this clamp controls whether you make the cavity more oval or less oval during the lapping process. If it's a Lee mould there's a good chance it will have started off bigger parallel to the parting line than perpendicular to the parting line - you'll know this from measuring bullet castings you've made before you started. If you want to increase the dimension perpendicular to the parting line more than you do parallel to the parting line, you'll want a spring clamp that is in the medium range - say about 15 pounds hand pressure - but you need to lap in small bites until you get a feel for this. Only lap for 15 seconds this first time.

7. Stop, clean the mould carefully, and look at it. It is very easy to see where you have been cutting and where you haven't. If it is a two cavity mould, compare the metal removal patterns in the two cavities. Then cast twenty or so bullets (after mould warm-up) in each cavity, making sure you have used the same alloy, temperature, and mould temperature you will use for full production. Drop the bullets from each cavity into separate water buckets or onto separate pads. Measure the bullets after they are completely cool. Check diameter both parallel to the parting line and across the parting line, and check each band separately. Compare the dimensions with the bullets cast before lapping. Figure out how fast it is cutting and where it is cutting. If you are removing metal from the right places, but not reducing the ovality, change the spring clamp pressure to suit.

8. The next run, you will not be in the dark because the lap has settled in and you know what it is doing. Most likely you will have removed well under .001". If you have, say, .002" to go, and you liked the way the ovality adjustment seemed to be going on the first run, let it go for 30 seconds next time. Then stop, clean, inspect, and cast another batch of samples.

9. By the time you have been through two or three iterations you should know what you are doing, and you may find that you still have some way to go on diameter but it is no longer removing much metal. If that happens, take one of your last batch of sample bullets and make it into a new lap, then go through the whole process again. Alternatively you may find you are getting close to the right diameter. That still calls for a new lap, but you apply fine lapping compound instead of coarse.

There isn't any rocket science in all this, but the first time you do it, especially with an aluminium mould, you need to go very carefully and you may overshoot and ruin the mould. Use the worst, single cavity mould you can find. I actually started off with a nice new double cavity 311291 but luck was with me, plus iron moulds are much easier to work with than aluminium ones, but I wouldn't recommend that approach - using a relatively cheap and nasty mould will make you learn faster, and you won't have as much to lose.

Geoff

[slughammer]

As Grumpy One just said, along with his thorough explanation, is to read the Lapping Sticky at the top of the page.

http://www.castboolits.gunloads.com/...ead.php?t=3172

I will say to pay special attention to the idea of embeding the grit, and then brushing off the excess with a tooth brush and dishwater. This serves to have grit only where you want to expand.

[swheeler]

Problem with honing out a mould is that in the process you also blurr sharp details, and this begins immediately. Why not just get a 338 mould and size'em down to .344"? Lee makes one.

.............Buckshot
.334

[Buckshot]

Problem with honing out a mould is that in the process you also blurr sharp details, and this begins immediately. Why not just get a 338 mould and size'em down to .344"? Lee makes one.

.............Buckshot
.334

...............Oops, thanks. .334"

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

[Wayne Smith]

Wow! Lot to digest in those posts. Lot more to it than I had imagined, too. Probably too much precision work for a psychologist - unless I'm willing to buy three or four for practice first! Probably not worth doing simply to avoid .338 gas checks!

Rick, let me do another chamber cast (different rifle that will get a scope) and get with you for a sizer.

[44man]

It is very hard to lap a mould and get anything round out of it. You will not get the blocks closed with a boolit and grit so the cutting will lead at the start of each parting line of the blocks.
I had some luck by cutting a pile of brass disks the exact size I wanted the drive bands to be. I made them the same heighth of each drive band, threaded the center and ran a screw up from the inside. I turned it counter clockwise to keep the screw tight and lapped each drive band by itself, changing the lap when worn. I turned it mostly by hand with a handle but slow speed on a variable drill would work. The mold came out rounder then any other way I have tried.
You could also stack the disks with spacers for the grease grooves so all drive bands could be lapped at the same time, but it takes time to set up.