What lapping compound to use?

[mtgrs737]

I have just recieved a new Lee 2 cavity mould in 6.5mm x 55mm Swedish from Midsouth and I am having trouble with boolits sticking in one side of the mould. I would like to lap the mould so that they release the boolit upon opening and a gentle handle hing tap. What lapping compound do you folks recomend? I assume that it will be a non-embeding compound that is very fine. I am getting .268" diameter boolits and wouldn't mind opening it up a half to one thousandth.

[Leftoverdj]

I bought a Clover kit 20-30 years ago with six cans of varying coarseness. For the job you describe, I'd reach for the 600 grit can. That'll remove burrs but a minimal amount of metal. 400 grit would also be suitable. Clover uses some oddball nominclature that I could not be bothered to learn so I marked the cans with grit equivalent as soon as I got them.

The carrier is petroleum based so you do have to degrease throughly when you are done, but that's the only drawback I have found.

[S.R.Custom]

Toothpaste. It's quite fine, but aggressive enough to put a polish on aluminum, and it's water based.

[Razor]

Go to the MOULDS forum and check out the sticke on 'LEE-MENTING' ...
It covers lapping a LEE mould...

PS.. Is that the 170gr 6.5x55 mould ??

Razor

[drinks]

Before you do any lapping, check very carefully for any tiny burrs or fins on the cavitys.
I drag the back of an Exacto knife over the edges just hard enough to burnish the edges then check by wiping the edges with a Q-tip and see if any fibers catch, if so touch up that spot again.

[mtgrs737]

Thanks guys! I love this forum! So many good people that have aready been down the road I'm on.


Razor, Yes it is 170gr. that I think Midsouth had Lee do a spl. run of fat boolits for the Swede. I learned about it on this forum and they had some in stock so I ordered up. I also have a six cavity group buy in the works but who knows when that will come in.

drinks, the boolits stick at the gas check area, the rest of the boolit will swing out of the mould and be held there by the base. I need to get my glasses to see well enough to determine what the cause is for sure. I do think I saw a burr across the top of the mould on one side when I first inspected them but I was in a hurry to cast some and didn't get the magnifiers out. I will check it out before the next session.

[Buckshot]

.............To polish and remove tiny pigs ear bits and just generally improve an already 'pretty good' mould, I'd ditto SuperMag's suggestion of toothpaste, or Pearldrops toothpaste. Both very mild but effective.

Heavier duty cleanup would then require a more agressive medium like Leftoverdj suggested. Although even for a pretty good mould the suggestion used lightly works good too, and would be the choice if you actually wanted to open it a bit (but be carefull).

Lots of times on a mould, regardless of how it's made you get these small remnants left. I don't know what aluminum alloy Lee uses, but it seems soft. Two things seem to afflict Lee moulds. One is metal smeared from one cavity surface across the parting line into the other half. The other is a raised burr on one or both sides of a lube groove or drive band feature. Both affect how a booit releases.

Sometimes you'd think a sofer metal would be easier to get a nice finish on, but it isn't always so. Looking at a much magnified cross section of a freshly turned surface and then of a stop action pic of the operation shows why. As the metal passes the cutting edge of the tool it is actually compressed slightly untii it fractures and parts. The parted off piece becoming the chip which is waste.

As the tool passes over the parting line, a tiny bit of metal is pushed across while still attached to the parent half and creates a tiny lip. Since they are sometimes so tiny, the act of opening the blocks pulls them loose and the cleaning process flushes them away. They may appear as miniscule sparkles to the eye. These too could be the tag ends of heavier metal pushed across. You can sometimes see it by holding the blocks at a sharp angle and looking across the face.

For the lube groove, drive band issue the tool has a tooth (positive surface) to cut a drive band, or a notch (negative surface) for the lube groove. Sometimes all features are combined into one tool. Since it's hard to grind in good relief on such tiny bits, this seems to be the most afflicted area. The notched tool for the lube groove for example has metal passing through it so it's cutting on 2 inside edges and the bottom. It's common to see a very tiny ridge on either corner of the lube groove inside the cavity. These will also cause the boolit to hang.

When everything is just right, like SPM (Surface Feet per Minute) tool sharpness and geometry, and cutting fluid you get a cavity like silver. Doesn't take much to makes things not just right though.

BTW, that 170gr 6.5 boolit Mid-South has was a group buy here 1st. :-)

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

[mtgrs737]

When it comes to machining aluminum I am sure that there is more to it than meets theye. I don't think that Lee spends a lot of time on each mould because if they did they wouldn't sell for the prices they do. The boolits look good when I can get them out of the mould without damage, I can't wait to give the sizing die you made me a try on them.

I have the mould inside the house and will get my BIG magnifier on it to see what the problem might be.

What overall length are you setting this boolit to? It is a long one!

I have this feeling that all the folks that got in on the 6.5mm x 55mm Lee Six cavity Group buy just might be hearing from Garandsrus the honcho real soon. But I could be wrong.