Aluminum for lead molds

Been doing a little research on making a few molds. When searching for best aluminum to use, I find quick the variety in recommendations. I know Tom has insight on casted aluminum, but which is best for running through cnc machine and longevity of mold? Not a lot of detail, but a few tight tolerances

Most cnc molds are made from aluminum bar stock. Do-It uses sand cast molds to cast their sinker and jig molds and that seems to be a really good way to get a quality product at a much cheaper cost than cnc molds.

For what its worth, my experience with cnc made jig molds has been far from positive. Lead quality is a huge concern when it comes to de-molding the cast heads as some alloys do not shrink and getting the castings to come loose is a challenge. Even molds treated with drop-out or any other graphite mold release agents doesn’t seem to help matters. Cnc molds have very exacting tolerances with ultra smooth mold cavity surfaces and the surface tension between the mold and the lead makes it all but impossible to get free releases. Sand cast mold cavities break up surface tension a great deal so castings as a rule will simply pop out when the sprue is tapped or lifted a hair. With reasonably hot lead and molds at a good casting temperature the sand cast molds’ castings are as smooth and shiny as the cnc castings.

Do-It’s sand cast molds have an expected life of abut 300,000 castings before the hinge pins might need replacing making the mold good for another 300,000 casting cycles. Hinges in cnc molds are not nearly as durable and when they get replaced and often not line up like the original hinge did creating flash on the castings.

Tom, no doubt do-it makes great molds. Problem for me it they don’t alter their existing molds for my specs.

I have access for running some small projects on a cnc machine, so for now that’s the way I need to go

Maybe the answer is to machine on a CNC, then send the blocks out for texturing?

http://www.stpaulengraving.com/custom-mold-texturing-services.html

HRG

I don’t know lead molds, but I do know plastic injection molds. I would think 6061 aluminum would work well. If you want it textured for easier release you could sand blast the jig head and runner and gate areas. If you sand blast I would recommend taping the parting line with masking tape and then cutting out around the cavities to the edges as sharp as possible.

Randy, 6061 machines nice as does 7075. 7075 is considered more of an aircraft grade aluminum so may be more expensive

And Arctic is correct in bead blasting will release better. You don’t need a fancy one either. For fishing equipment bead blast finish will be fine unless you’re looking for lens quality finishes

Randy,

Why don’t you just purchase a blank Do-It mold? Then you can machine whatever cavity you want.

Make sure that you can identify the grade before you actually machine the mold.6061-T651 would be good,also Mic6(tooling plate)if you have some.

Thanks got what I needed to know