Anybody try 3d milling a slug mold?

[Spike_9]

I have a 3 axis CNC mill in my shop and I have been thinking about slug designs that I could machine into molds for casting. My thoughts are to make the mold cavity slightly larger than the nominal diameter of the final size of the slug to allow for shrinkage and tolerances that will be addressed in resizing through a die. 

 

[Greg_E]

Accurate molds is all CNC, not sure if they are using a mill with and controlled boring head, or if he had them in a CNC lathe. The problem with how he does them is the minimum size for the boring bar, the flat me plate has a minimum size.



I think NOE may be CNC, but I think he uses traditional "cherries" to cut the cavities.



But I've wondered if you couldn't cut the halves separately with a small ball nose mill and just mate them up. With the accuracy of many CNC machines being 0.0005 or smaller, seems like the halves would just fit.



Now the art portion of this is know how much a certain alloy shrinks. I ordered an Accurate Molds for pure lead in 0.510 (+0.002 -0.000) and that damn thing dropped the first 40 pours right at 0.511. Every one was essentially the same size. The interior looks like it was polished, the rounds fell right out with zero issues. Just totally impressed.



Now all that said, if you could set up and create hollow points from regular molds at a cheaper price, you might also have a winner. I'd love to be able to alter the weight with various size hollow points on this same 0.510 rounds, plus maybe on some Lee molds.

 

[Spike_9]

Thank you for your insight!!

Those were my thoughts exactly, I would rough out the cavities with a 3d adaptive strategy and finish it will a small ball end mill for the two mold bodies in the same setup. This would be easier than making a d bit reamer with the profile of the slug as I don't have a cnc lathe...yet. Injection molds are made much the same way. 

That is an interesting idea. I am no stranger to lee molds and have a collection of them. I think they are a good starting point for hp modifications. Adjustability could be accomplished with a mandrel with a threaded shank to control both the depth of the hollow point and weight of the slug. 

 

[Greg_E]

The MP Molds type of hollow point is neat, but even the Lyman style gets work done. I have one Lyman single cavity hollow point, slow but gets stuff dropping in the tray.

 

[Spike_9]

Here is the experimental mold I am working on. I am starting with smaller projectiles first before working up to large bore. These if they work, they will be 15 grain 177 slugs with molds that will be cnc milled in the morning. 

 

[Outer_Rondacker]

I would save yourself a load of work and buy a blank Lee mold. Here is a link. Now you just have to poke a few holes. Just a suggestion. If you figure it out I would be interested in buying one. I think the simple bullet look will fly just fine. 



https://www.titanreloading.com/?s=blank+mold&post_type=product 

 

[thomasair]

If you have a CNC mill….then you also have a CNC lathe, of sorts. Long before I had both….I would clamp lathe tools in the mill vise and put the material in the spindle. It works well and would make short work of any lathe needs for objects whose material is within the size of your biggest collet on the mill spindle.

Mike

 

[Greg_E]

If you have a CNC mill….then you also have a CNC lathe, of sorts. Long before I had both….I would clamp lathe tools in the mill vise and put the material in the spindle. It works well and would make short work of any lathe needs for objects whose material is within the size of your biggest collet on the mill spindle.

Mike

I need to get some lathe tooling to do this, I think I need to make a PEEK poppet for one of my rifles. Partly to say I made it, partly to see if performance changes. Going to look into this over the weekend and get costs together. Though if I can get my "workshop" cleaned out and set up with a decent bench, I'm buying a lathe. Something big enough to stuff a barrel through the chuck so I can cut barrels out of blanks and fix crowns, etc. Need one that can do metric and imperial threads too.



My only concern with the above slug design is the very short amount of straight bullet. It seems like it would be very easy to get the above to go in crooked and therefor fly poorly. I may be wrong, but something to think about before you spend too many hours cutting it out.

 

[Spike_9]

I thought about that too. I could add drive bands to help with that if I run into alignment issues. I designed the mold to allow a 1/16 ball endmill to contour the mold (it's the smallest ball endmill on hand) I have the aluminum scrap to work with and the program wont take long to run. Less than 30 minutes with setup. If I need to modify the design, the CAD/CAM will automatically update the tool paths, reflecting the new changes. 

 

[Greg_E]

I want pictures of the process, very interesting to watch. Video would be cool and should be safe enough to post on Odysee not sure about YouTube anymore.

 

[Spike_9]

Here is the mold I machined today. These are dropping 1 grain under than projected. I am using 40:1 lead alloy. 3d milling worked out well machining out the cavities but trying to cast these little slugs are a pain to cast with out a spur plate. I am using a razor blade to trim off the excess. Now I just need a break in the weather to test them out before I move the project forward. 

 

[jking]

I'll give you an A+ for giving it a go. A sprue plate ought to be a piece of cake with the skills and equipment you have. What gun, barrel twist and speed are you going to try them in?

jking

 

[Greg_E]

You need the scratches in the mating surfaces to let air out, what's the smallest engraving tool you can buy or make?

Otherwise definitely a step in the right direction. Look for Bob's Boat tail drawings over on Gateway, he generally releases all of his designs for free and I think he has a couple that no one has cut molds to make. He might be very interested in seeing what some of these designs can do since you can cut one off.

 

[thomasair]

Good for you in making a plan and carrying it out. I wish you luck, and hope that you can , ultimately, get exactly what you are after.

As another encouragement….if you can make a casting mold….you can likely make a swage die, too.

Mike.

 

[Spike_9]

I'll give you an A+ for giving it a go. A sprue plate ought to be a piece of cake with the skills and equipment you have. What gun, barrel twist and speed are you going to try them in?

jking

Thanks. It's been a fun project while answering the curiosity on the methods of making custom projectiles without the need to make form tools and the hours spent doing it. 

I am going to test them in my P35 177 that has a CZ barrel. The twist IIRC is 16.7:1. 

 

[Spike_9]

You need the scratches in the mating surfaces to let air out, what's the smallest engraving tool you can buy or make?

Otherwise definitely a step in the right direction. Look for Bob's Boat tail drawings over on Gateway, he generally releases all of his designs for free and I think he has a couple that no one has cut molds to make. He might be very interested in seeing what some of these designs can do since you can cut one off.

Good call! I can do that with a fly cutter to form the cross hatch pattern. I will try some semi course emery cloth against a flat surface with the mold that is already made to give the surface some texture without removing much material. 

Bob Stern is a huge asset to the airgun community with the wealth of knowledge he has shared over the years. I enjoy his airgun guild forum. I will take a look at his designs.

 

[Spike_9]

Good for you in making a plan and carrying it out. I wish you luck, and hope that you can , ultimately, get exactly what you are after.

As another encouragement….if you can make a casting mold….you can likely make a swage die, too.

Mike.

Thanks Mike! I've never made swagging dies but that is likely the direction I will be headed after nearing the final slug design. 

 

[Spike_9]

Today's casting session for group testing later. 

 

[Spike_9]

I tested 10 of them over the chrony out of my modified P35 in 177. They were coming out of the muzzle at 850 PFS +/- 3 FPS. I then tested them at 15 yards using the Caldwell DeadShot FieldPod Max Shooting Rest and sitting down for stability. The first two shots landed where I was aiming on the right side target but the last couple key holed. The left side target had the same results. I was pleasantly surprised that a few of them did fly straight not knowing what to expect so the results are encouraging to continue onto improving the design so solve the issues I encountered. The first one being without a proper spur plate, I was using a razor blade against the top of the mold as a guide to trim off the overflow from the base of the slug. If the technique was off, it left excess, uneven material on the base (I haven't made one yet because I haven't settled on a mold body design). The other issue is the feeding the slugs from the magazine. They wanted to nose dive which caused a few feeding issues and likely the key holing we see. I simplified the slug design by removing the curved geometry near the base and flattening the bearing surface.

*The marked out red areas are the screw holes that held the target.

The positive outcome is that is answered my question about the ability to rapidly manufacture and test slugs without needing special form cutters which makes it cheaper and faster to experiment with different slug designs. A few of them did fly where intended which is encouraging. Lastly, once I find a combination that works, I will have the ability to make my own slugs cheaply without relying so heavily on supply chains in times of unavailability. If I can get them to group under an inch at 50 yards, I would call this project a success. 

 

[Greg_E]

Look on Gateway for Bob's latest design and scale it down to 177, that might fly more true and you certainly should be able to cut it with small ball nose mills. I think he posted 1.5x, 2x, and 2.5x length to diameter designs and may have even giving the numbers for 177 size.