Donation

All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

mold design questions....

(1/2) > >>

scion19801:
ok so.. I've tired to get someone to help me get a cutter for Bob's redesigned boat tail in the machining gate.
just talked to the guy who is going to deck my mold for me. I need to more specific info on how exactly to make the slug shaped cutter. my machinist has never done it, but is willing to cut me a mold if I can get a cutter made the price is going to drop significantly.
he also told me that he could make some so that I could offer them for sale to others.
the catch is if I can get the materials he needs to do the job. the less the price of a mold would be.

I know basically all one has to do is turn the bullet profile on a lathe. cut the bullet in half and grind some proper cutter angles and clearances to make the cutter. What are the proper angles and clearances to do this? does this differ for say brass or aluminum? does the cutter need to be heat treated?
Any and all pertaining info to get this done will help.

subscriber:
Dan,

If it was me, I would make the "cherry" bullet mold cutter from A2 air hardening steel.  It is easy to machine in the annealed state.  You harden it by heating bright red, and then air quenching.
 So, very little distortion compared to oil or water quenching tool steel:  https://www.mcmaster.com/a2-tool-steel/multipurpose-air-hardening-a2-tool-steel-rods-and-discs/

You would temper after hardening to a straw color; or about 400 degrees F.

Sure, you could use "drill rod" and oil quench after machining:  https://www.mcmaster.com/drill-rods/tight-tolerance-multipurpose-oil-hardening-o1-tool-steel-rods/

Tempering would be similar for D2 as for A2, although looking up the exact tempering temperature / hardness would be useful.

You can also buy high speed steel in the hardened state.  That would have to be ground, as it is too hard to turn.  https://www.mcmaster.com/high-speed-steel-rod/hardened-oversized-high-speed-m2-tool-steel-rods/

Making a cherry from soft steel and using it unhardened may be possible for one mold.  Or it might dull halfway through.  Certainly, you would not be able to make multiple molds without hardening the cherry to the high 50s on the Rockwell C scale (like a good knife). Over 60 Rc might be better, but is not essential. 

I would create a cherry with at least three flutes to help keep it stable.  Depending on the caliber, more flutes may be better.  Straight flutes are the simplest, but spiral flutes should cut smoother.  That said, I would read the links below about cherry making, before I start.  I am pretty sure they would include rake and relief angles. 

You are correct that the ideal tool angles for aluminum and brass are not the same.  Brass needs the "top" of the tool (if this were for a lathe) to be "flat", rather than steeply raked.  Else, the tool tends to draw itself in and cut too fast.  If the info at the links is confusing, I will find some pictures about tool angles to make this clearer - later.

Final sharpening would be done after heat treatment.  This could be as simple as honing the flat "tops" of the flutes with a hand stone. 

Your mold cherry needs to be larger than the finished bullet size you want.  Lead shrinks on cooling, and you want to leave a few thousands of an inch to size the slugs down after casting.  The cherry may also shrink or expand after heat treatment, depending on the steel.  You need to allow some material for sharpening.


https://castboolits.gunloads.com/showthread.php?29918-Making-moulds
https://castboolits.gunloads.com/showthread.php?7027-Designing-a-bullet-Making-a-cherry
https://castboolits.gunloads.com/showthread.php?345130-what-does-a-mold-cherry-look-like
https://castboolits.gunloads.com/showthread.php?137747-Teach-me-about-cherries-and-the-mold-making-process
https://castboolits.gunloads.com/showthread.php?357999-Who-machines-cherry-cutters-for-molds
https://castboolits.gunloads.com/showthread.php?4740-Grinding-my-own-cherry-cutter
https://castboolits.gunloads.com/showthread.php?126402-Mold-Cherry-Cutters
https://castboolits.gunloads.com/showthread.php?1446-I-m-making-a-new-475-cherry
https://castboolits.gunloads.com/showthread.php?10715-What-machine-to-use-if-I-have-cherries


If the above links don't answer your questions, I am sure there are tons more threads to be found the way I found them:  https://www.google.com/search?q=site%3Attps%3A%2F%2Fcastboolits.gunloads.com+cutting+a+cherry

subscriber:
Dan,

I think that making one's own molds would be an exciting project, hence my input, above.  That said, a shortcut to obtaining a working mold might be to order it from a mold making company.  This may be done by contacting Accurate Molds and NOE Bullet Molds.

If you follow the Accurate Molds links below, step by step, it will lead you through the process.  I believe you can order just one mold, if you like:

http://accuratemolds.com/submitNewDesign.php
http://accuratemolds.com/moldDesigns.php
http://accuratemolds.com/contact.php
http://accuratemolds.com/FAQ.php



NOE Bullet Molds has a good reputation for custom molds, although I believe they have a minimum number of molds (10?) that need to be ordered before they will tool up for it.  Contact them and ask:  https://noebulletmolds.com/site/about-us-2/contact-us/



Or, stick with your plan of making your molds from scratch, for maximum fun, learning and sense of achievement.

subscriber:
Bob has had lots of experience with custom mold design and procurement.  He should really be the one advising you:


--- Quote from: rsterne on August 29, 2018, 12:33:05 AM ---Do you mean several different cavities in one mould?.... The problem I can see with that is that these are all RG style moulds, and the cavities for the base pins are machined at the same time.... Each design uses a different RG pin, or if the same caliber at the very least a different length.... If you have never seen the way NOE makes its moulds (they have a video on their website) they make many all at the same time, with the CNC mill moving from one mould block to the next, doing the same operation over and over.... The cutters are an undersized "cherry" which is a custom made tool bit ground to the profile of the bullet, but small enough in OD to pass through the smallest bullet diameter.... That is why making small pellets is a challenge, to keep the tool from breaking.... Every bullet design starts with the production of a cherry unique to that design....

Accurate use a tiny boring bar which enters a predrilled hole in the mould block through the base, and then spirals out as it moves deeper into the hole to create the cavity.... This limits them to making .30 cal and up.... and also limits the smallest diameter to 0.060" smaller than the largest diameter.... However, it does allow them to mix cavities.... Each companies methods have strengths and weaknesses....

NOE has taken advantage of the ability to use different "RG" base pins to vary the weight and CG within each pellet design, at no additional cost.... In the first 2 moulds they produced, Al included a flat base pin to enable the caster to try a pellet with a flat base.... I don't know if that will be continued, as we never got any good feedback on the solid base pellets.... yet !!!

One little trick I used on the design of the .22 cal "Target" pellet.... It uses the same cherry as the .22 cal "Hunter", but is run into the mould block 0.2 calibers further, which shortens the pellet by 0.044", and provides a wadcutter nose.... Al will be able to make both moulds with a single set of tooling.... He was quite excited about that idea.... Hmmmmmmmmmm…. I wonder if I can convince him to make a 4 cavity mould with 2 Hunters and 2 Target cavities.... Might be possible?....

Bob

--- End quote ---

subscriber:
Dan, perhaps the first video is what you had in mind:  Making what amounts to a partial round form tool.  That is brilliant in its simplicity.  Perhaps not as rigid as a multi-flute "reamer" style cutter, but much easier in terms of managing the mold halves.

The first video below shows how cutting the cherry in half enables reaching inside the closed mold halves, inside a lathe.  Dispensing with the need to close the mold halves as the internal shape is cut:





The second and third video shows a "reamer" style cherry, with symmetrically closing mold halves:







Self centering vice to enable the above, available here:  https://www.grizzly.com/products/grizzly-precision-self-centering-vise/h7576



General mold and cherry images and links I found "along the way" to the above:

Mold making tutorial:  http://www.castpics.net/subsite2/HowTo/MakingBulletMolds.pdf




https://www.reloadingtool.com/bullet-lubricators


https://www.reloadingtool.com/l-n-walker-bullet-mold


https://civilwartalk.com/threads/civil-war-bullet-mold.141976/

Navigation

[0] Message Index

[#] Next page