GTA
All Springer/NP/PCP Air Gun Discussion General => Projectiles => Boolit and Pellet Casting => Topic started by: sb327 on April 27, 2021, 06:27:58 AM
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First, I am trying to learn how to do pics in post, I will have several posts so bear with me b4 commenting, thanks.
Most have an opinion how a proper mold needs to be made. I don't. I have a way that I do it that I have had the best success with over the years. I have tried several ways, this is just the one I prefer.
This way can be done exclusively on a lathe. I have a mini-lathe that I can set at, drink coffee, and relax. I also have a 12x60 Clausing. I used the mini for this project.
So here we go.
Here I am doing the initial turning of O-1 drill rod (air hardening rod works well too, its a preference thing here). I get to about .001" then use 220grit paper to get to final dimension. Also, since I am using a 3jaw chuck, I will not remove the cutter from the lathe until ALL operations are complete.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357800;image)
Here I am turning the nose with a ball turner. The ball turner is about the simplest you can make and works just fine. If you would like to have more detail on it, I can provide info on how I made mine.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357802;image)
And here is just an image showing how I measure distance for features. Just a simple, cheap digital unit from HF mounted to a piece of angle clamped to the ways.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357804;image)
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Here is the finished profile. Take a picture of the one you make, cuz it gets ugly after this point, lol!
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357812;image)
Here I am cutting the profile in half. Some say perfectly half way, some a thou over, and some a thou under. I go a thou under because this is not a 'D-reamer', it is simply a profile cutter. I purposefully used a dull endmill to raise a good burr to show up well in the picture. I kinda over did it, lol. In reality, you need to keep the burr created small, but the burr will come in useful later, during sharpening. This step can be done with a file in the lathe or vice, just keep things level nose to tail.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357814;image)
And here I show to leave a small portion of the cutting edge when relieving the back and bottom. How much the profile gets releived depends on the shape of bullet. Rule of thumb, smaller than the smallest bullet o.d. aft of the nose. It needs to fit in a hole that size without touching (until it gets to the nose portion inside mold). More detail on this later. (Notice the excessive burr left at the cutting edge) Be sure to leave the burr.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357816;image)
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At this point, I harden my bit. I start heating at the body (shank) of the tool until it is up to temp and then get the cutting end hot. If you are not familiar with reading various temps by available light vs. brightness of the red, just keep a magnet handy. When the steel becomes non-magnetic, it is time to quench. Now, if you read all of what is out there on how to harden and heat treat, you will likely never get to cut a mold. Because to do it 'by the book' requires a controlled furnace temp, controlled oil temp, controlled O2 environment and so on and so forth. I will say, 0-1 is very forgiving. My cutters and reamers have all performed well. I have cut MANY chamber reamers for various PB rifles/pistols and they cut steel just fine. Obviously, for a reamer, distortion is a concern. Chucking a reamer (fluted type) in a drill press and running it slow while heating and having your quench oil below to plunge while turning, has yielded excellent, no distortion results. A D-type is different and at bullet length, not a real concern about distortion.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357818;image)
Immediately quench. I use a light oil that is a mix of diesel and 30-wt. Room temp. This will be very smoky but I always heat/quench inside the shop for purpose of reading temps. Keep the bit in the oil, stirring it around, for a while. Oil cools the part way slower than water. When you are finished quenching, be careful not to drop, it can break easily. Check the back edge with a file to make sure you got a good quench. A file should just skate off it.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357820;image)
After hardening, it will be VERY brittle. I cook in a toaster oven for about an hour at 400-450. (mold cutters such as this 450, its more import that it not be brittle than it is to be hard)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357822;image)
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At this point, we need to do an initial honing of the top. Here I am using a medium stone but one of the small, fine grit diamond stone works too.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357824;image)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357826;image)
Then we need to start back relieving as before, only this time use a fine diamond file. We are starting at the bottom of bit (top in the picture) and working our way to the cutting edge. This does not need to be much relief at all. The important thing is to go slow and NEVER take off more at the cutting edge than needed. This is where the burr comes in handy. If you watch it carefully as you go, it will act as an indicator as to how close you are getting. We want to remove all evidence (a noticeable dark line just below the cutting edge) of the burr, but NO MORE. And it needs to be perfectly smooth here so you end up with a smooth bullet. THIS IS THE MOST CRITICAL PART OF THE PROCESS, because you do not have machine contols to go by.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357828;image)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357830;image)
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357832;image)
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I forgot to get a picture of relieving the nose. It needs a good cutting edge as well because it will be cutting in a plunge fashion for at least a portion of the mold.
I can't modify my first post now. I was gonna take out that first line.
I got the picture posting figured out and will take some more.
Go ahead with comments or questions whatever at this point, I'll add more as we go.
Dave
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Here is a sketch of what we are trying to accomplish in the relieving process. All the shaded area gets removed. We don’t want to relieve more than necessary though because the tool still needs strength.
Arrow points to cutting edge.
Dave
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nice little write up Dave. very helpful and much appreciated. so how are you mounting your blocks and getting things indicated? I'm thinking some sort of mill vice setup would be bestso the molds blocks could be moved around a bit to open the cavity to proper size. but had seen others mount their blocks to the faceplate and put the reamer in the tool post and go that way.
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In the lathe with a four jaw is how I originally started but now use a homemade face plate just for molds. Very simple to make. I’ll have it posted further in the write up here.
Dave
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Here is my faceplate I made. Just a 3/4” shaft welded to a 1/4” plate. I use a collet in my lathe. The 3/4” shaft is drilled/reamed to 1/4” and I have a 1/4” pointed shaft for setting up blocks perfectly centered. Then pointed shaft is removed and plate mounted in chuck.
I only clamp one mold half so the other gets clamped to it. This way I can cast a bullet, measure and return back to 0 in the lathe easily.
Dave
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Wow!! Quite a write up Dave; thank you! :D Will be PDF-ing this page once you've completed the series...
Jesse
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Very nice, Dave.
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nice face plate mounting setup. definitely helping me get things dialed in, in my mind. as i see more this looks like i could easily do my own 4 cavity mold. my jig setup would have to be a bit more elaborate to allow more room. i think my 10k south bend should be able to accomplish it with no issue.
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Very helpful article, I learned a LOT....
Bob
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I have a dumb question / suggestion: Would it be possible to turn a cherry perhaps .04" smaller in diameter than the largest diameter of the mold; then just mill that cherry down flat to its midline? Doing that would seem to incorporate all of the clearance grinding by virtue of the difference in radius. See image below.
Surely all you need to do is cut the profile at the cherry "equator" to incorporate the radial differentials and nose radius that you wanted in the full diameter cherry (because this is just a form tool). Then you zero off that one edge with the tool top face level. Then use it, just like a full diameter cherry that is clearance ground.
The only thing that you "loose" is seeing your full-size "bullet", before you deck the full diameter cherry, and cut all the relief into it. If you can stand to see and verify your smaller OD cherry in CAD, then you have just taken a shortcut with no downside I can see.
See attached image and tell me what you think.
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You certainly can. Diameters would be print minus .040” (or whatever). Your ball turner would still need to be set to print dimension.
You could also four flute instead of D, plunge it with a mill to depth into a mold set up on a rotary table. Then offset x or y and rotate table.
Lots of ways to skin a cat.
Dave
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wow, tons of good info coming from this. this one is going to deserve a "STICKY"
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This is not unlike a chamber reamer, except that you need the smaller diameter throughout in order to be able to plunge to depth when there are undercuts in the profile.... When making reamers, you don't cut away the diameter at all, but you cut the flat below the centerline to provide the relief angle.... The further below the centerline, the rougher and faster the cut.... Here is a drawing of a 3-flute reamer....
(https://hosting.photobucket.com/albums/oo221/rsterne/22 cal Disco Double/.highres/Reamer_zpsywtq5w0p.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/d8768b6a-4979-4d94-aef4-f723fe8fbdb2/p/41dc9d7e-b591-4166-a143-99b9fa90105b)
You can also make a single flute reamer by milling out a 90 degree segment as shown by the dotted line.... In either case, notice the flat that forms where the cutting edge intersects the OD is milled past the centerline by 5% of the diameter.... I have found that (5.7 deg.) provides a good balance between speed of cut and finish.... You can also cut the reamer straight across at that point, to form a "D"-drill, but that weakens it a lot....
I see no reason that you couldn't use something like this as a cherry, if there were no reductions in the diameter behind the nose.... ie a tangent ogive nose, followed by a straight midbody, like the way a swaged slug is shaped.... There is certainly no provision to clear chips, other than in the one main flute groove, whether that would cause a problem or not I don't know.... It doesn't when reaming chambers....
Note that the drawing is reversed (you are looking at it from the back/shank), as this reamer is intended to be installed in the tailstock, with the work rotating in the forward direction in a lathe....
Bob
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Thanks Bob.
Now for the block. Pretty simple really. I did say when I started this that all the operations could be done on the lathe. Well that groove down the side might be a little bit tricky on a lathe without a milling attachment. You can clamp to a qctp.
If using Lee handles, make the groove 3/16” x 1/4” deep. I just put my stock in the mill and do one groove before cutting into smaller blocks.
Next would be to face the two inside surfaces. Clamp together. Drill the pin holes through one block and partially through the second. Drill under 1/4” and ream to .249”. I use 1/4” drill rod just because it’s usually .250”. Round/polish one end of each. Chamfer ALL inside holes. We don’t want burrs or interference fit pushout interfering with our blocks mating. Press or drive pins to where they just start fitting snug. (If you go a little far and it seems too tight but you can still pull apart with your hands, don’t worry. Aluminum expands at a greater rate than steel and will loosen upon heating.)
(If your setup only allows drill/reaming one hole then unclamping to drill other, install one pin before reclamping and drilling second hole).
I didn’t get pics of drilling/reaming.
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Once the pins are installed, face off the top. This assures that both tops are perfectly flat. No pics of that either. If you want to face the ends/bottom, you can do that now as well. This gets us a blank body to work with.
I am going to highly stress making this little plate I use. It works fantastic compared to a four jaw. I do not have a way of ACCURATELY measuring the driving band (most critical dimension) inside that tiny hole, on a boattail especially. Therefore, I like to cast a bullet or two during the process just to see where I am in the process. Once I get a good reference, I stop just shy, cast another/measure, and make final cut. Each time I stop to cast, I do not have to re-zero with the little plate. I just unclamp one half from the half that is clamped to plate, then clamp it back. This can actually be done without removing from machine by using a 'funnel'.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357884;image)
Once the block is setup in the lathe, you can drill out as much material as your bullet design will allow. If it is going to be a hollow point, drill and ream pin hole all the way through. Here I show cutting to depth with a 1/8" endmill because this is a flatnose profile.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357886;image)
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Once you have removed some bulk material, it is time to setup your cutter in the toolpost. Clamp it good and get your height set (I set just a touch high so the cutter is not as likely to 'pull' into the work).
I set it by rotating the toolpost until I have two known points the correct distance from one another. You can also set it by indicating along the shank that is exposed in the toolpost. Your choice. I like knowing exactly where my cutting edge is. Tighten the toolpost down TIGHT.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357890;image)
Now we can plunge to depth. Set your carriage stop.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357896;image)
Then start cutting the profile. Keep track of your 'zero', I mark mine with a marker on the cross slide wheel. That way when clearing chips/backing out, I don't cut my groove ridges.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357894;image)
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Here I have taken the fixture off and poured a bullet. No sprue plate is ok. If you are doing this in a four jaw, make a little funnel. I use 1/2" thinwall brass tube. Cut part way down and spread it open to make a U shape. Put a cleaning patch on a bolt to make a snug fit and push it in to about a 1/2" from split open end. This keeps the lead from running down the wrong way. Put the 'funnel' end squarely up against the mold with the mold hole at the lower edge of funnel. Slide your tool up to hold it in place. Heat up the mold some so you get a decent pour and make your pour.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357899;image)
Now measure what size your bullet is. Remount block. Indicate back to zero if using four jaw. Continue making cut. Just remember, we only get to go bigger. Check again a few thou from finished size.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357901;image)
Here is what the cuttings will look like as you have full profile engagement. Basically dust. Depending on the length of bullet, it may take a while to cut .0005" (that is not a typo). Let it clean up. Engage another .0005" (or .001" for short bullets). Don't get in a hurry here. We have the PERFECT setup for chatter. You can play with your spindle speed some here. Just dont get too slow or crazy fast. Patience is key.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357903;image)
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Now if you are happy with the bullet its dropping, we can make a sprue plate. I put the pivot on the left (handle side to me). Put the block with the pins on the right. You can put the sprue stop on the left or furthest away, whatever suits you. I don't get too technical here, its just a sprue plate. I use whatever steel, this piece came off some kind of exercise equipment I think. Thickness needs to be about 3/16". Too thin, not much funnel. Too thick, funnel will be too wide at top or have a straight side that grabs sprues and doesn't let them fall away.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357905;image)
I use a 10-32 for the pivot and come in from the side with a 6-32 to lock it from turning. For the sprue stop, I use a 6-32. Sand the surface that touches the mold smooth. I don't bother getting the rest of paint off if using painted scrap, the lead doesn't seem to bother it.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357907;image)
Once your sprue plate is mounted, align the mold cavity with the spindle of your press/mill.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357909;image)
Close plate and spot drill
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357911;image)
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Remove the plate and make your funnel in it. Hole size....I like as small as I can get a quick fill from, meaning, small cavity like this one about .106". If it's a big 45, I'll go as big as the hole in my ladle. I try to get the funnel shape as close to bottom as possible without opening up the hole. This is done with a countersink. I have some piloted ones I use but I have used regular before. Less chatter with the piloted.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357913;image)
Now here is where you need to pay attention, as you get close to bottom with the countersink, the backside will start belling out. You need to keep this drawfiled flat with the surface, else it will scar the top of your mold. In this pic I drawfiled just enough to show how pronounced it can be.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357915;image)
In this one it is back flat.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357917;image)
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Handles. If you have a set, well you kinda know what to do now. I drill center of slot, center of mold, from the bottom and tap for 8-32. I drill across the slot into other side (top part of slot) about an 1/8"
Now if you don't have a set, well here is a solution. Find a cheap set of pliers that are not slip joint. Make a couple of ears.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357919;image)
Weld em on. It's best to have the ears mounted in the mold with the jaws of pliers opened a little bit when you tack weld the ears to the jaws. Make sure everything is aligned to have some slop/play in the movement of each mold half. All alignment should only come from the mold faces and pins.
(https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=186722.0;attach=357921;image)
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And then test it out. I prep my mold by cleaning the cavity with a q-tip soaked with starting fluid. Then I smoke it with a butane cigarette lighter.
I’m sure I’ve probably left a lot out, I’ll try to follow up on any questions there may be.
Dave
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One question for clarity; since I have never in my life held a bullet mold-so please don't laugh ;)-but the "ears" are a slightly loose fit in the slots; and on the pins, to allow floating for the mold's alignment pins to work-correct?
Jesse
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That is correct. The handles hold the halves in just enough alignment the pins will start in the holes. The mold halves kinda just rattle around when they are open.
Dave
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Thanks; for the answer to the question and for the thread. :D
Hoping to get the headstock for my lathe project in semi-finished running order before the end of the week... Lot's more to be done on it, but you can bet with the current pellet shortages the way they are what one of my priority projects will be...
Jesse
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That is a great way to recycle an old pair of pliers like that. I did something similar with a old screwdriver to make a very light weight lead hammer.
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Good luck getting it going Jesse.
I’ve been meaning to make one of those lead hammers.
I forgot to add how I do a hollow point pin.
Here is my .257 improved bbt. It shows how the pin is held tight against the bottom of mold and when the mold opens, swings out. The spring is a feeler gauge .012” (iirc). The handle pin holds the spring in place but allows some movement for pin to align.
Dave
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I like the pin setter, not so much flopping around like the NOE pins.
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You can also cut the reamer straight across at that point, to form a "D"-drill, but that weakens it a lot....
This comment is mostly for Dan, who has another thread running about cherry making:
I think the significance of not just the fragility, but the tendency to chatter of a half circle cherries cannot be overstated. Especially if anyone is thinking of making .22 or .17 caliber molds. For perhaps a .45 caliber mold, the reduction in stiffness in the cutter should not slow things down very much.
If one can make a D-shaped cutter that works and can be plunged into the cavity, then making it as a 3-flute should not be more difficult. Just more work.
Using a 3-flute cherry with undercuts and no centering vice is still easy, providing the cherry is run in a mill spindle, and the mold body is turned in a rotary table with its axis vertical. To produce a bullet with drive bands, the largest cherry diameter would have to be just smaller than the smallest bullet diameter. Then the X or Y-axis on the mill would be used to offset the cherry's axis of rotation relative to the mold cavity's axis of rotation by the difference between cherry radius and desired cavity radius (plus radial clearance when coaxial).
If you wanted to use a three-flute cheery in a lathe to create a bullet with drive bands (undercuts), then the cherry would have to be placed in the tool holder and fed in with the cross slide (like with a D-bit). The two extra flutes would be "spares" that act to stiffen the cherry, not involved in cutting. The design would have to be checked for interference, where the taller the drive bands, the greater the risk of interference. This implies that the max cutter OD is a little smaller than the bullet's smallest feature diameter. If boat tailed, that might be the minor diameter of the boat tail.
For a flat base bullet, the delta in radius between cutter and bullet could be as little as 0.008" for a .257 caliber, when starting coaxial. This assumes barrel land height of 0.003", with a 0.002" clearance between lands and the bullet shank between driving bands. Add the radial shrinkage expected for the bullet and the amount you expect to size it down, plus one thousands spare for general tolerance.
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I am awestruck, Dave
To see the way you solve tricky problems, using skill to implement a series of clever ideas was like enjoying a large New York strip steak with all the fat still attached. This, when throwing money at problems seems to be what those blessed with less skill and patience tend to do. And then, often their results are not as good as they were expecting.
The finish inside your mold cavity is perfect. I think the way you let your D-bit run until it stops cutting, after each tiny incremental feed, results in an almost burnished surface. Your set-up that enables opening the mold to check the as-cast size, then closing it to carry on cutting is brilliant!
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Thank you for the comments. You put it so eloquently. Round here we just say 'poor folks have poor ways', lol. Seriously though, thank you for picking up on the fact I do not concern myself too much with things that are not going to affect the finished product. Like a sprue plate. You can make one that fits perfect and functions perfect by just eyeballing the measurements.
A lot of the things I do comes from necessity or ignorance. When I started, I didn't have the internet to tell me I couldn't, so I had to learn on my own. Like heat treating tool steel. Look up (on the internet) how to heat treat 0-1 and you are going to find a myriad of answers. If you wait until you have all the equipment to do it 'right', you may never get to actually making a mold. When I started making cutters, all I had was 2 propane torches for heat treating. Took forever to get things up to quench temp. Then I tempered back using colors with one of the propane torches. Making knives taught me a great deal about steels and heat treating.
I had mentioned these can be made with just a lathe and then remembered the slot. I have included a pic of what a setup would look like to mill that slot in a lathe without a milling attachment. Just imagine the al stock in the chuck is an endmill.
I have also included a pic of various cutters I have made through the years. Several are pb chamber reamers with pilots. In case anyone wonders why mold cutters are referred to as 'cherries', I have also included one I made for a roundball mold for a black powder rifle.
And then one of the bottom of a hp to show how spring is mounted to the handle screw (stud in this case). It has a jam nut because the spring is not held tight at this point. It needs some float for alignment of pin while still mainting pressure pushing the pin 'up'.
Dave
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awesome info Dave.
so looking my new lathe over. it looks like I can easily mount a 4 cavity mold to my faceplate.
so once I get things installed it should be pretty easy to make an adjustable jig to to hold everything in position. looks like I need to get some round stock ordered, as I cant seem to find any locally.
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That looks like it will work fine!
I need to send you the cutter I made for this tutorial, I won’t need it again. I’ll see if I have some drill rod you can practice on.
Maybe a couple chunks aluminum as well.
Pm me your addy.
Have you read up on tool bit grinding? Insert tooling is fine but doesn’t leave as nice a finish on lighter cuts. The carbide likes a bit of pressure to work well.
Dave
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yeah I've been reading everything i can. i need to find info on tool type( carbide, hhs) for a particular type of stock being used.
I know hhs is good for brass and aluminum. I know there are different cut angles in the tool for different materials as well. drill rod may need carbide???? need to do some more researching.
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HSS is fine for drill rod. Until it gets hardened.
I use HSS for everything on my mini lathe and a lot on my big lathe. I do have some insert tools for the big lathe though.
Tool angles for steel work fine for aluminum. The big change is brass.
Dave
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About forgot, changing your motor to a pmdc from an old treadmill will keep you from needing to do belt changes. Some people like to keep things all original though. I put treadmill motors/controllers on everything. Even my swage press, lol.
Dave
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I think a tool made like this might work, and chatter less than a "D" shape, for the original system where the mould is rotating in the lathe chuck and the cherry is stationary in the tool holder....
(https://hosting.photobucket.com/images/oo221/rsterne/Cherry.jpg?width=1920&height=1080&fit=bounds) (https://app.photobucket.com/u/rsterne/a/8a1f0fa0-fce3-4227-8f61-b397601e0866/p/ee082099-5ca8-48bc-a0cd-8c9a8b58fbca)
You could turn to the finished profile (so you can measure it), which is the black line.... Then you mill a notch into it to create the cutting edge.... That notch has to be wide enough so that the cutting edge enters the hole for the HP pin.... If there is no HP, then mill it just past the centerline, removing just over 90 degrees of the cherry.... Then grind away the outer radius for about 3/4 of the circumference (blue line), so that the width is smaller than the minimum diameter of the mould cavity, including the tangent to the cutting edge.... You have to start your plunge over a bit, so that the cutting edge (and the backside of the tool) are within the smallest diameter of the finished cavity....
Just a thought....
Bob
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Dan,
HSS can be made to a sharper edge than tungsten carbide. The latter usually has less acute angles because it tends to chip if shocked.
Brass likes flat top rake angles, but not a dull edge. Cutting steel and aluminum required more rake angle regardless of tool material.
As long as the drill rod is annealed or at a temper no harder than around 40 Rockwell C, a properly sharpened and angled HHS cutter will do fine. Annealed drill rod (the way you buy it) cuts very nicely and is not appreciably harder than mild steel.
HSS tools will wear faster than "carbide", but they usually start sharper and produce a better finish. They are also very easy to resharpen.
The height of the cutting edge relative to the lathe center line is rather important, as it changes the effective angles of the tool - both cutting and clearance.
You will find typical tool profiles from many sources. Cross check them to see that they are in fact correct. Tool angles are more a matter of principle than absolute law. Here are a few sources I found in a fast search:
https://littlemachineshop.com/images/gallery/instructions/GrindingToolBits.pdf (https://littlemachineshop.com/images/gallery/instructions/GrindingToolBits.pdf)
http://www.steves-workshop.co.uk/tips/toolgrinding/toolgrinding.htm (http://www.steves-workshop.co.uk/tips/toolgrinding/toolgrinding.htm)
https://www.practicalmachinist.com/vb/general/first-attempt-grinding-cutter-259588/ (https://www.practicalmachinist.com/vb/general/first-attempt-grinding-cutter-259588/)
http://www.mini-lathe.com/Mini_lathe/Tool_grinding/tool_grinding.htm (http://www.mini-lathe.com/Mini_lathe/Tool_grinding/tool_grinding.htm)
https://www.youtube.com/watch?v=MgMpI7PZqHk (https://www.youtube.com/watch?v=MgMpI7PZqHk)
Chip breaker tool is for steel. Definitely not for brass:
https://www.youtube.com/watch?v=9oKLCFj9hMw (https://www.youtube.com/watch?v=9oKLCFj9hMw)
https://www.youtube.com/watch?v=brBiTaEo0a8 (https://www.youtube.com/watch?v=brBiTaEo0a8)
https://www.youtube.com/watch?v=9gW9H3lACx8 (https://www.youtube.com/watch?v=9gW9H3lACx8)
https://www.youtube.com/watch?v=_FNoi5hHRNA (https://www.youtube.com/watch?v=_FNoi5hHRNA)
"Carbide" tools contain cobalt as a binder. Breathing cobalt dust is very bad for your lungs. A little edge honing is OK, but grinding a form tool with lots of dust exposure is a bad idea. Some HSS may also contain significant cobalt.
Having air flow away from you is a good idea. As is wet grinding, or wearing a dust mask. No need to be paranoid, but I would hate for you to develop pneumonia because you were not aware of the risk and precautions:
https://nj.gov/health/eoh/rtkweb/documents/fs/1960.pdf (https://nj.gov/health/eoh/rtkweb/documents/fs/1960.pdf)
https://carbideprocessors.com/pages/technical-info/grinding-carbide-health-and-safety-risks.html (https://carbideprocessors.com/pages/technical-info/grinding-carbide-health-and-safety-risks.html)
http://www.mitsubishicarbide.com/application/files/2114/5214/0004/sds_hss_en-gl.pdf (http://www.mitsubishicarbide.com/application/files/2114/5214/0004/sds_hss_en-gl.pdf)
https://www.vodex.co.uk/blog/dangers-metal-dust-fumes/ (https://www.vodex.co.uk/blog/dangers-metal-dust-fumes/)
Rather than scare you, just be aware of anything that irritates your nose or lungs. The scare stuff is the tungsten carbide. I discovered that after grinding some form tools. Fortunately I set things up to spray the bulk of dust away from me and don't stand close breathing in the "cloud". Whatever exposure I had, had no effect on me.
Lathes are more likely to grab your sleeve and rip your hand or arm off. They seem docile, but I consider them more dangerous than a milling machine. The latter will just rip the flesh off a finger, rather than feed you into the machine. The larger the machine, the more it can hurt you...