Trepanning D-2 disks

Man I stand in awe. I would have said no way can you trepan 1"+ deep in a hard material.

I would have used the mill. A CNC makes a job like this trivial. Maybe its time for you to learn, WAY easier than ladder logic. A rotary table is another approach. If you don't care if your knockout is a bit ruff, chain drill all the way around, then put in the same size endmill and milldrill between each hole. This goes way fast, drilling is the fastest way to remove material.

Karl

You should get higher surface speeds, but not necessarily higher feed rates. Yes, they're more likely to break, but there should be no difference with a continuous cut. They're more brittle but they're at least as strong.

You probably could get better performance with a stiffer toolholder.

It's interesting that you found 5% cobalt square bits (M35 or T4?). I was looking fo rthem for years, because I inherited some and they worked great in my South Bend. I no longer have the need so I quit looking. M42 was too brittle for interrupted cuts on my SB. They chipped. I was cutting grooves in splined shafts.

If you get really bored, have them blanked with wirecut EDM. You're looking at about 1/2 hour per cut. Is your time worth $30 per blank?

Plasma cut (CNC?) and then finish up? Plasma doesn't care about the hardness of the material, only the conductivity. Should take about 10 seconds per hole.

I surface-ground the worn lower surface of the compound on my 10L so I could tighten the gibs to cut tapers, and solved several other looseness problems as well. The toolpost slot area and the two "OIL" pads gave enough distributed support on the mag chuck.

jsw

I trepanned a bunch of 2 inch discs in 1 inch 6AL4V titanium plate to save time. To avoid tool breakage when breaking through I trepanned from both sides. The face of the tool was ground at an angle so that when the disc broke free there was still a web to support the disc in the hole. Eric

Oh boy, I SURE remember doing this job on the drill press! Then, on a very old lathe driven by leather belts, then drilling with up to 3" drills. I still have those big bits, thank God I haven't used them for many, many years. Thanks for the memories!

I would love a CNC mill, maybe someday...

I figure my time isn't worth anything, I only spend about an hour or so a day on it so far. I have the tool holder fit perfectly to a quick-change so it's as rigid as can be, I learned THAT lesson long ago. Rigidity is KING! We remachined and ground the cheapie quick-change post and tool holders and replaced the metric fasteners with SAE but it is clearly at the limits for that toolpost, It's not the biggest one

Would there be a heat-affected zone that would be hard? I still have to finish the bore with a boring bar and machine two slots for drive pins. The disks will be rotary knives for wire cutting.

Probably, but not likely that thick. Waterjet would probably do nicely without any heat, but it's certainly less DIY.

I did something like this only with cast iron rounds, the outer 1" had been chilled by the continuous casting process, so was a real bear with normal HSS bits. I got some Tantung-branded bits, no more problems. The higher percentage cobalt HSS bits will hold an edge longer and/or will run faster, but only if you get the right geometry, they get more brittle the higher percentage Co you go. You could see the transition between the inner grey iron and the chilled area, the swarf went from grey powder to small shiny white curls. With HSS, that was where the bits went dull after a couple of revs. I like Tantung stuff for large internal threading, it means I don't have to stop mid-job, sharpen the bit and pick up the thread again. Don't even know if it's available now, has a lot of now-expensive elements in it that used to be a whole lot cheaper. A non-steel tool material. Touch it up with a diamond hone after grinding and your cut surface will be almost polished.

Stan

I probably could tighten up my machine to that it would do better. But mine was never in commercial, military, or school service, so it's not worn. The frosting is still visible over the entire bed. It's been a lightly-used hobby machine since my uncle bought it as unused surplus, still in its navy Cosmoline in 1948.

Aha. Well, I'm sure you've figured out where any potential flexing may be in the toolholder, but a shop-made holder probably could be deeper and wider. And there's no reason to harden it; it wouldn't be any stiffer if you did. You could make it from 12L14 or 1018 and it would be as stiff as tool steel.

Good luck.

The piece of D2 he's dicking around trying to salvage is worth about = $15.00 each--apparently, his time isn't very valuable....

If (when) I break another bit I'll try the 5%. I did get one more done today in just over 45 minutes. (between disasters)

Nowadays, I do this sort of stuff with a CNC milling machine, milling out a helical spiral. I just give it a command and go away until it is finished, I do not care how long it takes.

Show off!