Custom D-Drill

Any tips for making my own custom D-Drill and getting dimensions right other than sneak up on it, test it, and try again?

I often drill hing pins on gravity casting molds with 3 operations. They are simple operations, but still three. If I'm doing a batch of identical molds its no big deal. I run the same tool on all the parts with a self centering vise and never turn off the spindle. Then I swap the tool and run them all again. While that is certainly faster than swapping tools three times for each hole its still slower than having a custom tool.

I'm not even sure a D-bit drill is the right tool, but I can probably make one out of the shank of an old broken carbide mill with my tool & cutter grinder. Yes I am aware that I can have tools custom made, but I'd like to make this one myself.

I also am considering starting with something like a 3/8 carbide screw machine drill and grinding that to a series of diameters ending in a chamfer. When I get a nice chamfer the depth is correct. When drilling with the quill, this would also save a moment of setup. Because the tolerance for depth is relatively loose I'd no longer need to even set a stop. When I get a chamfer its deep enough.

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You could experiment with a step drill to see how to deal with a tool that doesn't clear chips, lacks back clearance and may not be good at center cutting. I make my D bits from HSS drill rod because my tool grinding equipment is rather primitive:

The carbide screw machine drill idea sounds good, like a Bullet Point. Can you grind back relief on the chamfer cutting edge?

I've used taper point wood screw bits in aluminum, to drill an internally tapered air nozzle. They cut smoothly but quickly jam with chips.

I think I can bring to dimension by spinning the collet. Then angle back the head, and bring to dimensions just a little further up the tool cutting the final depth of cut and back relief at the same time on a drill by by setting the 180 degree stop and finishing one side and then the other. I think the best I'll get is "ruler" length dimension, but for this application it should be good enough. I think I'd get the back relief on the chamfer/step the same way on a twist drill or on a d-drill.

The more I think about it the more I think starting with a split point carbide drill is the way to go.

I know HSS and hardenable drill rod are the tool maker's tools of choice, but I just much prefer carbide for aluminum. I do have some W1 around somewhere in a tube as well, but I've got diamond wheels for my TC grinder. I'd be more inclined to use drill rod for something I need to turn on the lathe like a cherry for a bullet mold. The funny part is the only time I did anything like that was a cleanup reamer for a shotgun. I made it out of mild steel and case hardened it. I'm not proud of it, but it worked.

I know HSS and hardenable drill rod are the tool maker's tools of choice, but I just much prefer carbide for aluminum. I do have some W1 around somewhere in a tube as well, but I've got diamond wheels for my TC grinder. I'd be more inclined to use drill rod for something I need to turn on the lathe like a cherry for a bullet mold. The funny part is the only time I did anything like that was a cleanup reamer for a shotgun. I made it out of mild steel and case hardened it. I'm not proud of it, but it worked.

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My mention of HSS isn't a recommendation, it's an admission that I don't have machinery suited for carbide. My machine tools would have outfitted a nice model or inventor's shop back in the 60's, when they were new and unworn, but they were never intended for high volume production. The lever feed horizontal mill might date from the -18- 60's.

I'm stepping back and thinking maybe I can tr the idea with a screw machine length cobalt/hss split point first. Of course that means I have to take the diamond wheel off the TC grinder. I already have those drills in multiples anyway.

I'm stepping back and thinking maybe I can tr the idea with a screw machine length cobalt/hss split point first. Of course that means I have to take the diamond wheel off the TC grinder. I already have those drills in multiples anyway.

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Can you swap diamond wheels without dressing them? I haven't used mine because I don't have extra Sopko adapters for them.

I have a diamond nib mounted on the grinder for dressing non-diamond wheels. Usually only takes two light swings to get an even sizzle all the way across the wheel.

I still do not really know how to properly dress the diamond wheels. I use a full sweep method for finishing so it comes out uniform (or good enough) anyway. Some day I need to look into it more.