carbide tutorial please

A

alinwa

oft dis'd member
I've always heard of using carbide drill bits to drill out broken taps and such but I've never done it.

Today I snapped off the tip of an 1/8" centerdrill leaving it in the hole. I was able to flip the piece and drill back into it and proceed but I'd like to know HOW to drill one out for future.

-where do I buy 1/8"carbide bits and how do I use them?
-speed/feed? Do I want the carbide to try to "bite" like a HSS drill or just chip it's way along?
-What about heat? Do I crank the speed up like a Dremel tool or low and slow like HSS?
-How much down pressure?

I need real-world details. What works and what will just scrap my bit..... I've got no plan here.... no understanding of the characteristics of teeeny carbide spinners. Are they tough or brittle? Do they burn up? Shatter? How do they handle interrupted cuts like drilling a tap?

Anyone got the time to 'splain it to me? I've got some pieces coming up that I can't flip and drill back to.... I'll only get the one shot to start the little 1/8" centerdrill into a center-punched divot....... I expect to be doing some carbide drilling. :)


thanks


al
 
I think we'd all like to know. I don't think there is a 100% right answer. Sometimes it works, and sometimes it don't. A ridged fixture is a start and small bits are a bit@h in the equation. JMO--Mike Ezell
 
First, I hope you have a mill, otherwise your very likely going to have crunchy carbide to dig out of the hole as well.
As stated, your set up can not be rigid enough. Lock down your gibbs and ensure your part is held rigid

I personally shy away from the drills. I've have two methods for shanked taps.

1. 1/16th and larger carbide four flute center cutting endmills (depending on tap size) The spendy coated micrograin buggers seem to work best. Call any reputable tooling vendor and ask for a tech. That's the best advise.
1. Carbide dental burrs and a (eak) Dremel tool.

Spin with as much RPM as you can muster and use flood coolant/oil. Use the largest end mill that does not exceed the minor hole diameter.

I personally don't have much luck using the quill so I lock it down and run the knee up instead. Just easier to control. Your feed rate will be a snail's pace. Think Bruce Willis/Armageddon/asteroid.

Best of luck, these things are a real bugger sometimes.

Chad
 
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I Do Things............................................ .....

A little different than Chad. I use a carbide 4 flute ball endmill and slow RPM's to drill out broken taps. The endmill is just big enough to remove the web of the tap, the chips are a silver color as their blown out of the hole by air.
 
AJ300MAG said:
A little different than Chad. I use a carbide 4 flute ball endmill and slow RPM's to drill out broken taps. The endmill is just big enough to remove the web of the tap, the chips are a silver color as their blown out of the hole by air.
Click to expand...

OK,

We're talking about 1/8" stuff here..... still apply?

al
 
Al,

If the part you are drilling is not critical as far as heat treatment goes just hit it with a propane torch till the broken bit is red hot then let it cool...when it has cooled run a 1/8th slot drill into it and drill it out...always worked for me with broken taps that break off because of work harding the metal.

Steve
 
Al

I've always had more luck with the slower rpm's and air blowing the chips out like AJ said. I never tried a ball mill though. With a standard carbide mill, the corners seem to chip less with the slower rpm's. AND be very careful when you are about to break thru the bottom. That's where most of the tool breakage occurs, when everything becomes loose and binds and crunches.
 
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Al
Carbide cutters are not brittle, they are VERY brittle. Small diameter ones will snap in less than 1/2 a heartbeat if there is ANY side load - which is why you have to have your fixturing very rigid. Best way is probably EDM, and a "simple" "Tap Burner" set up can be home made using the carbon center of old alkaline batteries as the electrode - or even just a brass tube some smaller than the hole to be cleared. And this set up can even be used to clear broken carbide tooling from a hole.
 
alinwa said:
We're talking about 1/8" stuff here..... still apply?
Click to expand...

Use a 1/8 ball, check it often as you'll be able to dig the broken tip out with a dental pick before you reach bottom. I drill em out on a CNC mill, the "Z" feedrate can be set at .0001" per click on the control wheel. Generally I don't drill a small center drill to depth due to breakage. I'll us the next bigger sized center drill, only drill down .020" akin to a spot drill. The hole can be chamfered after drilling.
 
I really like sharp, quality, new centerdrills when drilling tool steel or high-carbon alloys. Dull centerdrills get the tips ground off and tossed into the "broken high speed" box. Slow them down, use good cutting oil and don't push them.
As AJ300MAG said, do not go deep with the centerdrill . I just use them to spot the hole on tool steel but do go deep on aluminum, sometimes.
I broke a lot of centerdrills when I was younger. Rarely break c'drills or taps, anymore.
A few years ago I was working with an engineer that insisted on D2 steel for a part and I had to tap 0-80 holes through about 7/16 of material. Sweated a lot on that one but didn't break any taps. Sadly, he didn't want to harden the D2 so it was not a good choice but it was his money so he got what he wanted.

Jay, Idaho
 
Rotsa ruck cutting a HSSCo tap with a carbide endmill. Buy a set of tap extractors for that kind of work (or a Elox EDM burner).
Example, the Travers #15 15PC TAP EXTRACTOR SET Product: 15-936-215 .

With Tool Steel taps, a carbide endmill might work but not HSSCo tap.
 
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A few years ago I was working with an engineer that insisted on D2 steel for a part and I had to tap 0-80 holes through about 7/16 of material. Sweated a lot on that one but didn't break any taps. Sadly, he didn't want to harden the D2 so it was not a good choice but it was his money so he got what he wanted.
Click to expand...

He must have attended the same college a few of the engineers I have the "privilege" to work with...:D
 
I think the picture I'm getting is clear........ RIGID setup on the mill, low pressure, slow feed and don't screw up! :)

Now the "EDM with a battery" thing....vibe, are you saying to grab the graphite/carbon center post from a 'C' cell battery, sharpen it up and hook it to an arc welder or what? How set the heat etc??? Like a TIG setup? I need particulars.....

re the "brass tube smaller than the hole"...... can't imagine this. Some sort of brass capillary tubing?

I like the propane torch idea. For what I'm doing ( steel stock for a rifle ) heating isn't critical. I tried this once using oxy/acet and found the heat to be too much, too abrupt.

good stuff so far, gonna' go search Elox EDM burner.......

al
 
re the "brass tube smaller than the hole"...... can't imagine this. Some sort of brass capillary tubing?
Click to expand...

The tap burners that I've ran use a piece of brass tube for the electrode. Coolant flows out the bottom of the tube to flush the burn akin to an EDM electrode.
 
AJ300MAG said:
The tap burners that I've ran use a piece of brass tube for the electrode. Coolant flows out the bottom of the tube to flush the burn akin to an EDM electrode.
Click to expand...

Thats the kind. The tube is usually a copper alloy and you set it up to where the tube size is a size where the tube cuts the web of the tap flutes. That way the tap center just falls out and then the tap teeth fall out.
 
I'm with Al

Lots of air!!! NO coolant. The use of coolant only dulls your carbide. Don't worry about heat. I learned all this from a old guy at Danti tool. He let me ruin several end mills first. Then he showed me the light. Mark

PS... it's not a perfect science. When you brake something it often comes with some price.
 
Mark.....

Then you get to learn terms like thermal shock and micro-fracturing...:D


Jerry, don't think I've ever seen one in "new" condition. Wish I had one at my current place of employment.
 
AJ300MAG said:
Then you get to learn terms like thermal shock and micro-fracturing...:D


Jerry, don't think I've ever seen one in "new" condition. Wish I had one at my current place of employment.
Click to expand...

The life of an Elox tap burner is about 40 years anyway. Even in a big shop, they are only operated less than an hour per week. If a shop has a process where they are breaking several taps a day they are screwed up to start with. Export the job to Communist China, they starve and beat anyone who would dare break a tap!!!
 
alinwa said:
Now the "EDM with a battery" thing....vibe, are you saying to grab the graphite/carbon center post from a 'C' cell battery, sharpen it up and hook it to an arc welder or what? How set the heat etc??? Like a TIG setup? I need particulars.....
Click to expand...
Yeah lots of "particulars" - too many to try and espress here. But a welder would have lots more amps available than it really requires. Not a lot of "heat" involved - you are not trying to melt the material out, closer to fast etching.

alinwa said:
re the "brass tube smaller than the hole"...... can't imagine this. Some sort of brass capillary tubing?
Click to expand...
We use a "dedicated" EDM drill at work for pilot holes to thread the wire EDM wire through. I know we use down to 0.015" OD hollow electrodes in that one , and up to 3/16" - but it is for small detailed work through up to 8" thick material

alinwa said:
gonna' go search Elox EDM burner.......

al
Click to expand...
Probably a good place to start. :D
 
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