What machine to use if I have cherries?

[500bfrman]

I realize this is a stupid question but what do you use to cut molds with a cherry? Mill I'm guessing? thanks

[grumpy one]

The nature of the cherrying process requires that the double-acting vice be held stationary, so that it can be closed progressively as the cutting proceeds. The vice base is not moved relative to the axis of the rotating cherry. This can be done on a lathe if the vice is attached to the toolpost and the cherry is held in the chuck, but setting up the vertical position of the vice then requires shimming, which would be slow and laborious. It is therefore considerably easier to use a milling machine, since the table can be moved in at least X and Y directions, and usually Z as well, while the cherry can usually be moved in the Z direction. This makes setting up a straightforward operation using the X, Y and Z screws.

Use of a lathe for mould-making works best with NC boring techniques, or use of a form tool, with the mould blank held in the chuck, rather than with the cherrying system. In the hands of an expert a lathe can do many things including cherrying, but it may not be the easiest or quickest way to do jobs that are suited to milling.

[Bent Ramrod]

Henry Beverige wrote up a procedure by which he made bullet molds in one of the old Handloader magazines. He used a drill press to locate the minor diameter hole in the center of the blocks. He then put the blocks in a pair of mold handles which he had specially modified to allow the blocks to rock from side to side to a greater extent than they normally do. He then put guide pins through the alignment pin holes in both the blocks, chucked the cherry in the drill press, and, running slowly and cleaning chips and checking frequently, managed to get the cavity formed and centered. He would then remove the guide pins and drive alignment pins into one of the block halves to mate with the holes in the other one.

He offered molds for sale for specialty Sheutzen bullets around that time; I don't know if he made them all this way but it seemed to me that it would be a procedure that took a considerable amount of skill and even finesse.

[grumpy one]

It sounds to me as if there would be some witchcraft involved in keeping the blocks from jumping around as the cherry chattered during cutting, ending up with a thoroughly awful looking mould cavity. This might all be avoided if he had hit upon a cutting edge geometry, feed rate (rate of closing the vice) and spindle speed that just liked to cut smoothly, though. It would probably involve lots of small teeth on the cherry, which would make it a pain to resharpen.

To make the process reliable and versatile it is standard practice to try to make the machine and the work-piece mounting as rigid as possible. From your description he was trying to make it as unrigid as possible - instead of pushing the resonant frequency up above the working range, he was aiming to keep the cutting forces low and consistent so there was no tendency to chatter, and the mould blocks could writhe around to compensate for tool runout etc. It can work - I've even done it - but I don't know that it's repeatable.

Geoff

[Bent Ramrod]

Grumpy One,

He did make a cherry, in .32 caliber, if I recall correctly. Filed the reliefs, hardened it with a torch and oil and stoned it by hand. There were multiple grease grooves; I think he used a 0.10 inch parting tool to cut the grooves. As I remember his mold blocks were brass. But he did hold the blocks in the handles and gradually squeeze them around the cherry. Apparently, if done right, the resistance of both sides evens out, if the center hole has been located correctly. Certainly, a double-acting vise would remove much of the potential for spoiling the work from the operation.

[Buckshot]

..............I have the article, and after making the mould he cast up some boolits from it and shot them in a schuetzen rifle. Pretty nice group, too!

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

[jcadwell]

Why not cut each mold half one at a time. No weird vices, etc. Seems straightforward to indicate a block and cut into it... Does the cherry approach reduce chatter?

[beagle]

There's an article in a Fouling Shot about 6 moths ago about how to make a vice for this. Might be worth researching to see the solution.

Too complicated for my feeble mind but I expect a machinist would understand it./beagle

[44man]

My home made mould vise and some blocks.

[snowman]

44man,

Any chance of seeing some closeups on that vice?

[500bfrman]

There's an article in a Fouling Shot about 6 moths ago about how to make a vice for this. Might be worth researching to see the solution.

Too complicated for my feeble mind but I expect a machinist would understand it./beagle

Fouling Shot 181-9

[500bfrman]

My home made mould vise and some blocks.

Very Cool. Do you use a smithy to make your stuff 44man?

[44man]

Yes, a cheap Smithy! I will try and take better pictures to post.

[grumpy one]

Why not cut each mold half one at a time. No weird vices, etc. Seems straightforward to indicate a block and cut into it... Does the cherry approach reduce chatter?

There would be an advantage in cutting the mould halves one at a time: the swarf would not get between the mould halves and prevent them from closing fully on the cherry. The main problem would be rigidity, since the cherry would be pushed sideways by the cutting force against the block, and this would not be balanced by an equal and opposite force from cutting the other mould-half simultaneously. Since the cherry is cantilivered (i.e. only supported from one end) the deflection would be substantial, especially at the nose. Consequently you couldn't end up with a round mould cavity at the nose end - it would be oval. Even more importantly a one-sided load on a rather springy cherry would be very prone to causing chatter, as you suggested. Aside from that the only problem I see is alignment issues, getting the two mould halves to line up after they were cut separately. It could be done by closing the two halves accurately over a dummy cherry, then drilling the alignment pin holes through the closed mould.

All of the cherrying options look rather awkward to me compared with simply boring with an NC lathe, which I think is what Lee does. Of course being Lee, they do it with such an enormous axial feed rate that it ends up looking like a thread has been cut into the mould cavity - or they did on the only example I own anyway.


Geoff

[Buckshot]

.............I read something funny in an old Fouling shot once by a guy using an old lathe to bore mould blocks. He said that as the carriage approched closer to the headstock, wear on the way caused the boring tool to dip which bored the cavity slanted in the blocks.

Now wear close to the headstock is a fact of life, since that's where 95% of the carriage movement takes place, and that's where the swarf lands too. I don't know if he was telling a 'stretcher', had his measurements screwed up or just didn't know. However he had otherwise written a pretty good article. The fact of the matter is, is that if your boring tool drops down you will STILL produce a round hole EQUALLY large in both block halves. This is assuming the blocks are matched.

You will not bore a concentric hole off axis to the spindle's centerline. If your tool gradually drops, your nice hole begins to assume a widening cone shape as the carriage and everything hooked to it drops below the spindle's axis, as it advances. I think I caught the guy fibbing about what he'd actually done

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

[44man]

My blocks are pinned and milled before I cherry. They are locked solid in the vise and can't move. I open the jaws and de-burr without removing the blocks. I open and vacuum often and flush chips so none are between the blocks. I get my cavities as round as any mould I have ever bought.