Drill bit temperature?


I was drilling some 1/2" holes today in some 3/8" mild steel today (for the
base clamp of a drill press stand I am putting together), and was wondering
about drill bit temperatures.
I'm using "Rapid Tap" as a cutting fluid, and when it starts to smoke off, I
stop and put some more on. I am keeping my chips/spirals from getting to
the straw colored stage, and measuring the bit (HSS) temperature with a
non-contact thermometer tells me that my bit is at about 160F.
At what temperature should one limit a HSS drill bit to in order to prolong
the life of the bit? Does anyone have any numbers?
Thanks,
Jon
Reply to
Jon Danniken
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It depends on the grade of HSS. Good-quality drill bits, typically made of M2, can tolerate around 1000 deg. F without losing temper. But don't try it, because, especially with drill bits, the hottest part of the cutting edge typically is hundreds of degrees hotter than the bulk of the tip, and a non-contact thermometer isn't likely to catch it. If the extreme edge is just starting to turn blue, you've hit the limit, even though that's a few hundred degrees cooler, theoretically, than the steel can tolerate.
The trouble is that a lot of cheaper drill bits are made of M50 or something like that, and the Chinese "equivalent" can't take much heat at all. It typically contains no tungsten and it doesn't really precipitation-harden very much.
Any decent HSS can take turning straw color, or somewhat darker, with no problem. If it doesn't, it's junk steel.
Reply to
Ed Huntress
More than a little bit.
Reply to
Wild_Bill
So you thinking like 200F or 300F would be fine? Higher?
Just kind of making sure I don't bork my spendy bits.
Jon
Reply to
Jon Danniken
If these are decent bits, I wouldn't worry about the temperature at all when drilling the holes you are talking about. If you are drilling at 600 to 700 rpms or less, and if the bit is cutting (not just turning in the hole), you should be able to keep drilling until you get through the hole. The only thing that would make me stop drilling those holes would be if the shavings started to clog the bit and drag the drill motor down. But that's not likely in that size of hole. One shot of your oil or whatever should be enough.
Pete Stanaitis ---------------------
J>
Reply to
spaco
I was just making use of the word: bit.
Ed H has presented info regarding quality HSS steel. You won't rapidly wear out good quality drills when using a good cutting lubricant.
I'm more particular about a clean drilling area, than about drill cutting edge temperatures. Rust and dirt can can dull cutting edges. I think you're using new steel, so that shouldn't be much of a problem with this project. Beware of hard spots in cheap materials such as OBF old bed frame angle iron. Hard spots can occur in new stock, but they're fairly uncommon. Hard spots can quickly wipe out the cutting edges of a sharp drill.
It may be useful to use a cutting lubricant dispenser bottle, like a poly lab-type wash bottle. These bottles don't need to be tipped upside-down to dispense liquid, making them very easy to use for cutting lubricants because they don't distract the user from the operation of the machine. The spouts on the wash bottles easily direct the cutting lube to the actual cutting area.
With a handy dispenser, you can keep drilling instead of letting up on the feed pressure. A small amount of cutting edge rubbing can take place as a drill is allowed to retract from the cutting area during drilling.. this rubbing is more detrimental to the cutting edge than heat, IME.
Once good chip flow is achieved, I generally keep the drill cutting all the way thru.. while adding small amounts of cutting lube to the hole with the dispenser bottle in my other hand.
Eventually, the drills are going to need sharpened, so be on the lookout for the type of tools or equipment you'll want to use for sharpening.
There are a lot of good fixtures and sharpening machines available. Developing a reliable hand sharpening technique with a bench grinder is about the lowest cost method available.
Reply to
Wild_Bill
Thanks Bill. I was considering putting together what could be called a "pulsed mist" device, but I like your idea of a wash bottle better. Hopefully I can source one of those locally.
Aye, that is a skill I would like to learn. Don't think it will happen for this job, but if I end up buying another $30 bit I'll probably have a go at it.
Jon
Reply to
Jon Danniken
Ah, thanks Ed, I hadn't thought of the leading edge being hotter.
The bits I'm using are American, Chicago-Latrobe actually (my local supplier has them for a very good price). I'll go ahead and keep my eye on the chip color as my best indicator.
Jon
Reply to
Jon Danniken

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