D bits vs Fluted reamers for custom work

I'm working on making special bullet manufacturing dies (nothing hydraulic or automated or mass production) anyways with these die sets in the final die the overall shape of the bullet is made. Lots of pressure is used in forming the shape and so releasing the swaged projectile and backing it out of the die can be an issue. Now I've been making a few of these point form dies as they are known with D bits I make, The problem is I can't get as nice of a finish as I would like inside. and making a 2nd piece that is the exact same shape as the D bit for a lap would be very hard as this is all done on a manual lathe. Would it be prudent if I just learned how and started making my own fluted reamers? I'm thinking the finish would be mirror just about and keep me from having to fight with the ejection punch all the time.

A "D" Bit is also called a single lip cutter. The very good news about these tools, is they are a one flute reamer. Drill out the material with a drill and leave a little for the "D" Bit to ream. Obviously you won't be able to feed it as fast as a multi flute reamer, but they don't chatter and won't go oversize. (The half round drill) = "D" Bit. come with a sort of a triangular point. You can just grind it flat on the end with some bottom clearance and some relief on the, half of the point, which will be running backwards.

Regards,

Stan-

A d bit should leave a good finish, you don't say what material you're using them in, but bear in mind the finish on the tool will be replicated in the work

For a lap, why not cast some lead laps with a say a brass rod core -using of course the reamer, to make the mould.

From what I've heard/read, and from what a guy many years ago told me about making swaging dies, they are hand polished after reaming. No reamer alone is going to leave a good enough finish, and lapping will just leave polished grooves since the lap really can't be stroked.

I think the technique he used was a wood stick with diamond compound.

The dies are made out of unheat treated 0-1 the D bits are out of heat treated 0-1. I'm not sure how the finish on the took could be much better. Its heat treated and its sharp and there is a smooth taper on the bullet point of the tool so nothing abrupt or interrupted.

I'll give it a few more tries then I may plop down some cash for the 5C hex collet holders that will allow me to dable in the fluted reamer arena.

For me, a D-bit has always been a reamer for a size you don't own or can't get quick enough to satisfy the job. Its a shop-made tool which works reasonably well.

If you want lots of same-sized holes quickly then I'd invest in a spiral fluted reamer of the size intended.

Usual notes about the reamer not straightening the hole.

Besides the essential good finish you need the whole of the cutting edge to be evenly (very) sharp and operating at a constant cutting angle. Any variation is liable to tear the metal in narrow regions where the tool is fractionally blunter / operating at a more negative rake / otherwise less efficient between two real sharp areas. Think of it as the tiny not quite as sharp bit not cutting quite as well as the real sharp bits each side which lift the chip cleanly away bringing the less effectively cut potion with it leaving a torn mark rather a cleanly cut surface. Its all fairly subtle. Basically you get bitten where "usually good enough" drops into the "not quite region" for any of a number of reasons from material variation on. If you start polishing too early its awfully easy to end up with slight relative bluntness where you have taken out fine grinding marks.

Multi-flute cutters can, to a degree, average out at the best cutting portions spread over all the flutes.

Clive

Just a thought - IME, If a D bit is under .5 diameter it will not cut cleanly (or to size) ...... oh and when I say sharp I'm talking fine oilstone finish sharp.

matt_isserstedt said:

For me, a D-bit has always been a reamer for a size you don't own or can't get quick enough to satisfy the job. Its a shop-made tool which works reasonably well.

If you want lots of same-sized holes quickly then I'd invest in a spiral fluted reamer of the size intended.

Usual notes about the reamer not straightening the hole.

Click to expand...

Matt, what the OP really wants is a single lip cutter ground to a profile other than straight. Basically a bullet shaped cutter, since he's using it to cut cavities that make, well, bullets. So spiral fluted reamers aren't going to do him any good, and I doubt shop mde straight flute profile cutters are going to give any better finish than the single lip.

What is the problem... Chatter, or concentric lines in the profile?

Dennis

I'm getting concentric lines towards the top part of the D bit I guess the part that has to do the most cutting. Here is a layout of how I do it I first drill a hole all the way through the die for the ejection punch this also serves as a guide for the reamer later on then I use a larger drill to work my way up to the near final diameter I need. the picture shows a D bit for a .375 swage die. so I would take a 3/8 reamer and ream out the area that will be the bullet body and then use this D bit to form the ogive of the bullet, the D bit is doing a lot of work but its still as sharp as when I made it.

What are you lubing the d bit with? Looks like your getting a slight built up edge that then gouges the finish. Personally i would ruff them with the d bit, then give it a quick light final hone and the and only then fill cavity partially with the thickest best cutting oil you can get and take a final slow few thou of cut with a nice fine feed, you want to be damn near shaving the metal off.

Getting a clean finish on any steel part with any kinda form tool in my experience needs a damn near mirror smooth cutting edge, honed with the finest stone you can get so the hone marks go into the edge, not along. It needs oil constantly to stop it picking up - forming a BUE which would account for your score marks. Equally there are clear ring like marks showing on the end of your reamer.

Other thing is, even though by hand you can not make 2 perfectly identical reamers, you could make a ruffing one and a finishing one that only has to remove the last 10 thou or so tops!

adama said:

What are you lubing the d bit with? Looks like your getting a slight built up edge that then gouges the finish. Personally i would ruff them with the d bit, then give it a quick light final hone and the and only then fill cavity partially with the thickest best cutting oil you can get and take a final slow few thou of cut with a nice fine feed, you want to be damn near shaving the metal off.

Getting a clean finish on any steel part with any kinda form tool in my experience needs a damn near mirror smooth cutting edge, honed with the finest stone you can get so the hone marks go into the edge, not along. It needs oil constantly to stop it picking up - forming a BUE which would account for your score marks. Equally there are clear ring like marks showing on the end of your reamer.

Other thing is, even though by hand you can not make 2 perfectly identical reamers, you could make a ruffing one and a finishing one that only has to remove the last 10 thou or so tops!

Click to expand...

Not sure what the oil is I'm using its just general stuff we have laying around, probably motor oil at best. The chips I get are more large filings really not shavings if that helps really. I like the idea of making a 2nd rougher that I could do I'm sure I just learned D bits about 6 months ago when I started this project so I'm still learning them. The first one I made was just for a odd size reamed hole that needed to be precise but the hole was a pass through so that was easy and the finish was excellent. The relief on it may not have been enough and allowed oil to work its magic. I'll try grinding more away next time and allow more oil to flow, chip clearing and everything was frequent.

Re a hex collet block ... you really don't want the flutes evenly spaced. It will chatter like a mother. Machinery's Handbook has guidelines on staggering flutes on reamers.

Re D bits being only suitable for desperation dealing with an odd diameter ... a local screw machine shop used to use nothing but D reamers for precise bores. He bored a shallow pilot hole first. The D bit would give a straighter rounder hole than a multi flute reamer.

On a forming operation like this in steel, if its cutting right and to get a near mirror finish, the final chips should look a bit like wood planeings do. Just sort of a thin wafer like chip.

As to relief im a bit lost there? A d bit is simply ground to half the diameter that simple, anything else and i think you will find it wont work.

adama said:

On a forming operation like this in steel, if its cutting right and to get a near mirror finish, the final chips should look a bit like wood planeings do. Just sort of a thin wafer like chip.

As to relief im a bit lost there? A d bit is simply ground to half the diameter that simple, anything else and i think you will find it wont work.

Click to expand...

X2 ..... the man is right.

adama said:

As to relief I'm a bit lost there? A d bit is simply ground to half the diameter that simple, anything else and i think you will find it wont work.

Click to expand...

The OP is thinking of a single lip engraving cutter, which is ground with a relief:

Product Zoom

However, these are intended to cut laterally. The simple D bit only cuts with its tip as it advances straight down, so no need for relief. I'm not sure relief would help, and may only cause chatter. A D bit can't chatter because it has half it's circumferance supported by the work. Relief would just give it room to back away from the chip.

It would seem to me that the anular rings are caused by one of two things; chipping of the cutting edge, or metal sticking to the cutting edge, where this built up edge then rubs against the work and galls. In the first case separate rougher and finish cutters might help, with the finish cutter only needing to shave off a whisker of material. In the later case, better cutting lube than motor oil may be the answer. I think I'd try tapping fluid, heavy sulphered cutting oil, and finally Molly-D, in that order. Retracting the cutter and stoning the edge before taking a final light cut may help.

At last resort, make a wood plug and polish with Clover compound to remove the lines, then finish with diamond compound.

Dennis

Although a D bit for a parallel sided hole needs no relief on the sides of the tool, the same is not true for a form cutter, which is what the OP is making and using.
The curved portion requires relief, which should be terminated just past the intersection of the radius with the parallel sides so the form cutter can cut instead of rubbing.
The OP has another thing working against him; both the workpiece and the cutting tool are made of the same steel; the only difference being the hardness of the cutter compared to the workpiece.
This makes any entrapped chips more prone to gall on the sides of the bore, and it looks as though there has been some of that occurring.
It's visible on the body of the D bit up near the point.
Switching to something like A2 or HSS will likely help although it's going to be much more difficult to make the form cutter if HSS is chosen.
In any event, insufficient or no relief on the curved front of the tool is likely what's causing the bulk of his trouble.
That and his expectations of a mirror finish from a form tool in a steel like O-1 which tears quite easily in the annealed state especially when a wide chip is taken at low surface speed.

Another big help would be a pressure lubricant rig like the gunsmiths use when they chamber a barrel.
Flushing the chips out the back as they are generated is super helpful to get the best possible finish and the continuous flood lubricant keeps "built up edge" to a minimum.

Another worthwhile experiment would be to harden the workpiece and then draw it back to 32 RC or so, and see if that improves the finish.
Sometimes it can be a big help to get the steel just a bit harder than annealed; the chips come off better and the tearing goes away.

Last is a change in workpiece material is worth considering; I've had good success with 17-4 PH condition H900 in similar applications.
Stressproof or Leadloy or 303 stainless might also be worth experimenting with if their softness is not a problem for the application.
Cheers

Marcus
Implant Mechanix – Design & Innovation - home
Vancouver Wire EDM -- Wire EDM Machining

Marcus,

I agree with most of what you said, including relief on the round nose of the punch, IF he was trying to drive this cutter straight down into solid stock. However, he mentions an ejector punch, so I assume he's chasing the through hole for the punch with the cutter. I think the first step he should take is to try some cutting fluid other than motor oil; something with some extreme pressure additives to help keep the chip from welding onto the lip of the cutter.

Dennis