Cutting lube/grease grooves in a bullet mold - how?

[H Wally]

Ok, so I understand that a convenional smooth conical bullet mold can be made by drilling strait into the mold with the reamer.

However, how do you cut a mold with grease grooves in it? Since two part mold blocks are milled clamped together I can't figure out how one would ream the grooves. I've looked on the net but everyone who discusses it clearly understands it, so don't bother explaining it.

 

[legi0n]

the cavities are first drilled in with a smaller drill bit and then milled with a "cherry"
I assume in the past when CNCs were not available the finishing happened on a lathe with a profiled tool.

 

[H Wally]

Unfortunately that still doesn't answer my question. It's the milling bit with the cherry that has me lost - however they do the milling obviously allows for cutting the grooves, but I can't figure out how.


I understand how molds were traditionally cut with a cherry made to the exact size of the bullet to be case and the two halves were slowly pressed onto the rotating cherry which would allow for grooves... but on a clamped block I'm lost.

However, looking at the build alongs it looks like the molds are cut while clamped - they're roughed out with a drill and then a D reamer or something similar is used to ream to the final profile. My problem with this is that since the mold has at least one constricted inner diameter that is the grease groove, the reamer cannot simply be fed into the mold because it would remove the material that would form the grooves in the bullet. Since the block remains clamped throughout the procedure there's no opportunity to press the two portions around the cherry.

Edit - partially answered my own question. Basically the answer is that I need a mill or a lathe in order to offset the reamer from the center axis of rotation.

[youtube]Q5BM6dNXFyY&feature=relmfu[/youtube]

 

[legi0n]

this might help you out: Making Multi-Cavity Bullet Molds

 

[legi0n]

this too: Cherries

 

[BCRider]

The boreing head is one way but he's running it for much too long between settings. Basically by the time the machine is up to speed the cut is done and you can switch it off again. Running it for as long as he does simply wears out the cutter edge and results in the blackness from burnishing the metals.

With a profile cutter in the lathe you can run out the cutter from center to a known distance to make the form in one cut.

All this works best if you're looking at the idea of a flat nose. Because with the single point cutting that's what you'll get when you extend the sides out for the grooves. If you want a round nose you'll need to run another round ended cutter down to complete the ogive section that is a separate cutter.

The cherry cutter link is nice if you have CNC. But the job was done in other ways for many decades before CNC. One option is a jig to close the sides accurately onto a turning cutter. Or to clamp the blocks parallel to each other with enough space to allow the cutter to lower between then and then move the table or cutter back and forth with precision to cut the two halves of the mold.

All in all it makes the cost of buying a mold at around $30 for a double seem pretty reasonable, doesn't it?

 

[ckid]

All of the bullet molds that I have made have been done on a lathe... Cherry cutting mold blocks is really not an option in my opinion for the home shop machinist... By doing the process on a lathe working with the mold blocks clamped together ensures a perfectly round bullet that is centred on the parting line... It is a fairly time consuming process that requires a multitude of hand ground internal boring cutters... I use a single flute hand made form tool to cut the nose portion, and a variety of internal turning and grooving tools, and profile cutters for the lube and crimp grooves...

The set up for a single cavity mold is a lot simpler than multi-cavity... To do multicavity molds efficiently one must make a dedicated fixture to fastens to the face plate that allows the mold blocks to be accurately indexed to each individual cavity quickly with repeatable accuracy... The reason for this is to be able to perform each individual cutting operation on each cavity before making a cutter change, this ensure repeatability to all cavities are uniform...

This should be a fairly obvious point but the larger the diameter the bullet the easier the process is to accomplish... So far I have only gone as low as .35 cal... .30 should be doable as well, but in my opinion going any smaller the tooling would become increasing fragile and could result in a lot of headaches... If you destroy a custom ground internal boring tool bit in the hole chances are that set of blocks is pooched and re-grinding a perfectly identical cutter would be very tough....

 

[trevj]

Best suggestion I can offer, is to draw out the cross section of the mold in larger scale, and get your head around how to move the tool without seeing it.

You have to get used to working blind.

Cheers
Trev

 

[ciphery]

Ok, so I understand that a convenional smooth conical bullet mold can be made by drilling strait into the mold with the reamer.

However, how do you cut a mold with grease grooves in it? Since two part mold blocks are milled clamped together I can't figure out how one would ream the grooves. I've looked on the net but everyone who discusses it clearly understands it, so don't bother explaining it.

First you need to understand that a mold is a NEGATIVE. So if you want grease grooves in your bullet, you need 'lands' in your mold. And thus your cherry (reamer) needs to have grooves in it as it is a POSATIVE.
1) Pilot hole is drilled under size of the bullets final Dia.
2) A cherry(reamer) is not inserted into the hole but rather it takes a sideways cut at one half of the mold, then the other.
3) The two halves of the mold are then clamped around the inserted finishing cherry and the mold is reamed in place.

 

[ciphery]

.....In your project could it be that the D reamer was inserted through the pilot hole into the CENTRE of the cavity, but the D reamer is less than the max finished diameter of the mold in cross section? Essentially the D reamer is working as an off set tool so it cuts a larger hole than its blade is wide because of the offset.
(The cutting edge is not concentric to the axis of rotation. Just like a boring bar or a fly cutter)