Drilling

J

jw517

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Oct 5, 2007
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I am getting a carbide drill and I know this may be a old ? but how many RPM'S is too much? I think my press is 900 at the slowest. Should i try my cordless? I would hate to burn this bit in 5 sec.!!!
 
Generally carbide is run at higher speeds than HSS or cobalt. The danger is that carbide is more brittle, and you run the risk of breaking it if you snag the bit. However, carbide is designed to handle the higher heats generated by higher speeds/feeds. When drilling deeper holes/thicker materials with carbide, I like to use cutting oil or coolant.
 
I run a cheap Harbor Freight Drill press as slow as it will go.Useing solid carbide straight flute drills.I had problems at higher speeds.
 
See im opposite.on my cheaper drill presses i run the carbide at almost full speed with great success.when i slow it down they're almost gauranteed to chip or break.on the mill using a collet i can use any speed.
 
I don't have cool tool just oil. I take it not to press real hard on the stock. Called around EauClaire Wi. to machine shops and they told they can't drill a R-58!
 
Ask two machinists about using carbide bits and you will get three different answers.
Stacy

Nathan, what do you recommend?
 
900 will work just fine. Just do not use too much pressure. Take your time and use some kind of cooling on the bit. I know this was not much helped but with practice you will master the technique. :)
 
Depends on the size of the drill and the material it will be cutting. Use oil as coolants tend to fracture the edges (microfracture) under heat and sometimes create a catastrophic failure of the bit. I have used carbide endmills and drills to cut out broken taps at work and generally only use air to clear the chips, but I think the advantage is to use oil for lubricity.

Bill
 
bladsmth said:
Ask two machinists about using carbide bits and you will get three different answers.
Stacy

Nathan, what do you recommend?
Click to expand...


My multi personalities counts as three machinists, and my rambling answer counts as ten.

Carbide operates at higher surface feet per minute. Off the top my head, I'd guess 100 SFM in hard steel with uncoated carbide in an optimum setup. So obviously, the smaller the tool, this higher the RPM to reach those SFM.

There are three things that makes carbide special.

It is harder
It is stiffer
It tolerates more heat

The primary problem with carbide is it is fragile, meaning a blow that would simply dent steel will break carbide.

The reason I'm going into all this is because understanding these things will explain everything you see going from HSS tooling to carbide. Longer life and cuts harder stuff because it is hard, better finish and accuracy because it is stiff, higher RPM because it tolerates heat.

Now, that last one, higher RPM. This is great in industry because we kind of have to live with certain chip loads per tooth, so our productivity is directly related to SFM. If you can crank it up, you can crank the parts out. But, with your home shop tools, you don't have the stiffness and rigidity we have with our 10,000 pound machines. Your 200 pound machines flex during a cut, leading to chatter. HSS tolerates chatter, carbide doesn't. Chatter is a function of rigidity and SFM. If you have a flexy setup, you have to run it slow to avoid chatter, which will eat up carbide because it ain't very tough.

Running carbide slow causes another problem, which is chip welding. I know this is counter intuitive, but (generally) the faster you cut, the less welding you get. Welding causes a bad finish because gunk is making your cut, not your sharp polished cutting edge. And when it builds up big enough, it breaks off, often bringing a little piece of your cutter with it.

So, to sum up. Run carbide as fast as you can without chatter. If you're using it in an application where you are utilizing it's hardness, such as cutting hard steel, I don't think a specific RPM makes as much difference as feed per tooth and avoiding chatter. I have a hard time not over feeding at low RPM, so I bust up carbide at low RPM, as balibalistic said. And if I had a cheep Harbor Freight drill press with sloppy bearings like sharpeknives, I'd have problems at high speed due to chatter.

Industry dials in a specific SFM, and a specific chip load to drive their feed rate. Then they tinker with coolants etc and find their optimum setup, which are speeds and feeds that would reduce carbide to rubble on home shop equipment, so you have to figure out what works on your machine. They often shoot for a 15 minute cutter life too...
 
Would you also run a twist carbide drill at fast speed like the fluted drill???? I use a lot of #41 bit and I found out that I get more life out of the twist at slower speeds. I haven't found the #41 in a flutted bit. What is your though on this. Mike
 
Nathan, You need to save that explanation. It will be asked again and it is the best one I have heard yet.
 
Nathan that was alot of info.GOOD INFO. Thanks man.
By the way, I got a new drill press the old HF is on the chopping block.
 
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