A Question for the Machinists!
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Topic: A Question for the Machinists!
Posted By: EdK
Subject: A Question for the Machinists!
Date Posted: 10 Nov 2010 at 3:02pm
| When I fabricate anything for my tractors, since I do not weld, I need to make a lot of holes in metal so that they can be bolted together. My problem is that a large diameter, (3/16 to 5/8 inch), drill bit lasts for about 4 to 6 holes, then becomes extremely dull. I've tried buying the best, (highest priced), drills at Home Depot, Lowe's and Ace Hardware with no success. I've tried drilling with and without cutting oil. I've tried stepping the holes up in size in hopes of putting less stress on the bits. Nothing seems to help. Where do professional machinists purchase their drill bits? Do they have the same problems I have keeping drill bits sharp enough to drill metal? |
Replies:
Posted By: DonDittmar
Date Posted: 10 Nov 2010 at 3:06pm
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Professional Machinsts usually sharpen there own bits on a bench grinder. ------------- Experience is a fancy name for past mistakes. "Great moments are born from great opportunity" 1968 D15D,1962 D19D Also 1965 Cub Loboy and 1958 JD 720 Diesel Pony Start |
Posted By: split51
Date Posted: 10 Nov 2010 at 3:07pm
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I have had good luck with the cobalt bits from the Mac tool man but they are pricey. The good thing about the set is anything above 1/4" is lifetime warrantied. ------------- 1929 20-35 sn17662 B1 w/snow blade B10 w/sickle mower B110 w/mower deck B110 w/tiller B112 w/grader blade B210 w/plo |
Posted By: CTuckerNWIL
Date Posted: 10 Nov 2010 at 3:20pm
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Cobalt bits are good but not necessary for the run of the mill steel you would be working with. If you can't sharpen a drill bit, they might help for a time. The hardest thing on a drill is running too fast, followed by trying to force a dull bit into the work. A properly sharpened drill bit is a wonderful thing. Learn how to sharpen them and when to sharpen them and save yourself a lot of time. Pay for my plane ticket and I'll come and show you how to sharpen one. LOL
------------- http://www.ae-ta.com" rel="nofollow - http://www.ae-ta.com Lena 1935 WC12xxx, Willie 1951 CA6xx Dad bought new, 1954WD45 PS, 1960 D17 NF |
Posted By: TMiller/NC
Date Posted: 10 Nov 2010 at 3:33pm
| We had a "Drill Doctor" that would sharpen up through 3/4", either 118 or the 135 degree split point. Works really well if the directions are followed to the letter. |
Posted By: M Diesel
Date Posted: 10 Nov 2010 at 3:44pm
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Well, agreed about fast but the hardest thing is getting them too hot, and high speed zooms up the temperature. They need to be run slow, and be generous with the cooling oil. Second big problem is almost always the bit pressure is too light to cut well and the associated bit chatter knocks the edges right off. Should have at least chips or preferably a pair of curls if things are completely right. A lot of factory bits will only cut a single curl though. And they should cut 50 holes without much change when treated well. 4 to 6 just means bad practice is at hand, and that can be remedied. |
Posted By: Gary
Date Posted: 10 Nov 2010 at 3:47pm
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About a year ago I bought a 'Drill Doctor' drill bit sharpener when it was on sale for about $50. Model 350X . Does 3/32 up to 1/2"
It is about the best $50 I think I ever spent.
Over many years I had accumulated probably 100 'dull' drill bits.
Once I got the nack of using it, I sharpened every one to like new condition.
A 'must have' for anyone that is drilling steel.
I always use one of my 2 drill presses ( 1/2" and 3/4" ) whenever I can.
Having the correct drill speed (RPM ) and applying the correct steady pressure is important ( along with a SHARP drill bit )
Gary
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Posted By: jaybmiller
Date Posted: 10 Nov 2010 at 4:11pm
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When I read the original post I thought I'd written it !!! Glad I'm NOT the only guy with dull bits.The old Dormer brand bits lasted forever,sigh. Yes, oil helps a lot, and I have 2 coffee cans FULL of dull bits. Hopefully Santa will bring me a drill doctor.... ------------- 3 D-14s,A-C forklift, B-112 Kubota BX23S lil' TOOT( The Other Orange Tractor) Never burn your bridges, unless you can walk on water |
Posted By: Burgie
Date Posted: 10 Nov 2010 at 5:32pm
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Usually any drill bit that is anything can be sharpened to cut. Like what was said learn to sharpen the bits. I even have good luck with those China ones. Sharpening is the key. ------------- "Burgie" |
Posted By: Pa.Pete
Date Posted: 10 Nov 2010 at 5:35pm
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As stated before running to many RPM's is hard on them, pay attention to the chip it will tell everything, if you are running to fast they will be small and probally blue in color, you want a nice curl of both flutes, if you are only getting one chip it is only cutting on one side, make sure the cutting edges are the same length on both sides and that it is relieved (tapered down) from the cutting edge back. Also let off the pressure every few seconds to break the chip and you can't use too much cutting oil.
Hope this helps kind of hard to explain.
Pete
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Posted By: Bryan
Date Posted: 10 Nov 2010 at 6:07pm
| Ed, alot has to do with your drill speed. The bigger the hole the slower the drill speed. Some of the parts I machine at work, the holes are 6 mm and the spindle is running 9925 rpms. |
Posted By: BillinValpo
Date Posted: 10 Nov 2010 at 6:07pm
| Always remember speed kills with cutting tools. a constant force is needed and lots of oil. For the work you are doing a 135 degree split point works best. The drill doctor is a good machine. I have sold cutting tools for 30 years. |
Posted By: Gerald J.
Date Posted: 10 Nov 2010 at 6:56pm
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I've been buying 135 degree split point drills from McMaster -Carr. www.mcmaster.com A 21/32" drill did about 60 holes in 1/2 and 3/4 steel with cutting oil (I use pipe threading oil for steel, though Mistic Metal Mover has a great reputation and I now own some but I've not opened the container yet), and no pilot holes. Turning about 450 RPM. That's just a hair over 5/8". The drill has a 1/2" shank with flats. Gerald J. |
Posted By: TMiller/NC
Date Posted: 10 Nov 2010 at 7:18pm
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Formula for drill speed = 4 x cutting speed / diameter = RPM We used 80 fpm for cutting speed using high speed steel tools. For a 1/2" dia drill the formula would be............4 X 80 / 1/2= 320 / 1/2= 640 RPM. If I remember correctly from class 35 yrs ago. |
Posted By: Lonn
Date Posted: 10 Nov 2010 at 7:22pm
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Ex BIL worked at McNeilus and when drilling holes in the truck frames for cement trucks and garbage trucks they went as fast and as hard as they could. Their bits lasted. I don't know what brand they used but they used and abused the heck out of them. ------------- -- --- .... .- -- -- .- -.. / .-- .- ... / .- / -- ..- .-. -.. . .-. .. -. --. / -.-. .... .. .-.. -.. / .-. .- .--. .. ... - Wink I am a Russian Bot |
Posted By: Butch(OH)
Date Posted: 10 Nov 2010 at 9:06pm
| For those not inclined to get a calculator out to figure spindle RPMs a basic rule for any HSS cutting tool is to watch your chip color. Blue means tool is going bye bye in the next 5 seconds if you dont slow down. Gold means you have a couple more seconds to get it slowed down. Straw means your pushing your luck but you might get awat with it. No color is safe. With Colbalt your safe range goes into the straw color. Carbide is sparks, LOL. |
Posted By: Gatz in NE
Date Posted: 10 Nov 2010 at 10:22pm
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Not using the correct RPM is usually the reason for drills to dull; especially as quickly as you've described. You didnt say what kind of machine you were using, but whatever it is, it must have some method of varying the spindle RPM to match the diameter of the drill and the material (SFM)
Some other factors are; rigidity, coolant (cutting oil) and feed rate or downward pressure.
Read through this to get a better understanding of how the material, drill size and RPM are inter-related.
http://its.fvtc.edu/machshop1/drillpress/cutspeeds.htm - Machine Shop 1 Drilling Machines
Here's a site that you can practice by just entering some values to see how the related values change. You can get the SFM from the above site.
http://www.custompartnet.com/calculator/drilling-speed-and-feed - Drilling Speed and Feed Calculator
There are many other online sites for this topic...just type in
rpm calculator for drill
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Posted By: Dave A
Date Posted: 11 Nov 2010 at 6:38am
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speed kills cutting tools. also not all drill bits are a like. some have a 118 degree tip some are 135 and some 90. Try the 118 degree tip with not a lot of back rake (to much back rake will cause the bit to chip on steal) and use good cutting oil. When sharping the bit aline the grinding wheel with the flite and sharpen cutting edge to heal. The amount you take off the heal is called back rake the moke you take off the faster the bit cuts but it also weekens the cutting edge if too much is taken . on the bigger bit some guys will cut some of the back side of the cutting edge flite off to help chips remove with alot a heat ------------- Play the game for more than you can afford to lose... only then will you learn the game. Winston Churchill |
Posted By: DonDittmar
Date Posted: 11 Nov 2010 at 7:21am
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I guess I typed my reponse before fully understanding the question. Bought a set from Snap-on once, the only Snap-on tool I hated, they sucked. The best set I bought was from a flea market vendor at a tractor show, called Winters Drill Bit City. They cut good, been sharpened many times over in the drill doctor. I broke a few, but that was no fault to the bit, operator error. ------------- Experience is a fancy name for past mistakes. "Great moments are born from great opportunity" 1968 D15D,1962 D19D Also 1965 Cub Loboy and 1958 JD 720 Diesel Pony Start |
Posted By: steve(ill)
Date Posted: 11 Nov 2010 at 8:06am
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i have the drill press set about 400 RPM and nver change it. Been that way for 30 years. I have to get a small set up to 3/8 inch every 5-6 years due to breakage or kids using them.. My 1/2 inch to 1 inch drills have been there for 30 years. I sharpen each once or twice a year. You dont have to run fast to cut good. Cutting a little slow dont hurt. I seldom use oil unless the stuff is real hard. Pilot holes help when drilling 1-2 to 1 inch holes. ------------- Like them all, but love the "B"s. |
Posted By: Gerald J.
Date Posted: 11 Nov 2010 at 9:51am
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With the blunt center of the standard 118 degree grind, pilot holes are absolutely necessary. The split point 135 degree cuts to the center and doesn't benefit from a pilot hole. Turning small drills slowly is why you break them, from expecting them to remove metal with that very slow speed at the cutting edge. You put too much pressure on them and they take too deep a cut. Gerald J. |
Posted By: Dick L
Date Posted: 11 Nov 2010 at 10:39am
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Actually giving "proper" speed, "proper" down pressure are only guide lines. Along with had sharpening drill bits on a bench grinder, which I have been doing for over 50 years, is something you have to learn a feel for. I had to make a part out of pre hard steel yesterday that took three trips to the bench grinder with a high speed steel drill bit. I couldn't find a carbide in the correct size. You learn the amount of rake it takes for the different steels or you make extra trips to the bench grinder. I haven't seen a drill doctor that could figure the different rake for different drilling jobs.
I buy mostly high speed steel drill bits and work in mostly pre hard mold steel. I bought a few sets of cobalt in the past in both drill bits and mill cutters. I keep some carbide around but mostly in insert cutters.
 |
Posted By: CTuckerNWIL
Date Posted: 11 Nov 2010 at 10:52am
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I might add all drill doctors are not equal. Our purchasing agent where I used to work bought one from the Snap-On guy several years ago. It never worked on one bit. The relief would start going back up about half way back. Burnt heals was all I ever got out of it. For some reason our PA didn't want to mess with getting it replaced so it was back to the post grinder. ------------- http://www.ae-ta.com" rel="nofollow - http://www.ae-ta.com Lena 1935 WC12xxx, Willie 1951 CA6xx Dad bought new, 1954WD45 PS, 1960 D17 NF |
Posted By: Brian Jasper co. Ia
Date Posted: 11 Nov 2010 at 11:20am
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The best set of drills I've found for us ordinary non machinist guys are Rodman brand. They have some sort of really hard inserted tip in them. I've found that I can use them to dress an ordinary grinder wheel. It takes a diamond wheel to sharpen them. As soon as i saw the guy selling them poke holes in a file, I figured that was a bit that would hold it's edge. Nice thing about them is they are life time guaranteed. Break them, knock the tip off, they replace them free. I do remember the guy saying a drill doctor would work well on them if it had a diamond wheel in it. ------------- "Any man who thinks he can be happy and prosperous by letting the government take care of him better take a closer look at the American Indian." Henry Ford |
Posted By: firebrick43
Date Posted: 11 Nov 2010 at 11:34am
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Is you drill press in decent shape? Runout/spindle play is death to drill bits. Its amazing to double or even triple speeds and feeds with good ridged and powerful equipment with good coolant flow and get improved tool life to boot. If you are doing low run type stuff Enco is a decent place to buy consumables for a decent price. Not crap but not high quality either. For multiple holes in a production enviroment you need mist/flood cooling and carbide tooling. We have some drills in the 1" range at work made of solid carbide that cost 900 dollars a piece. The can drill twice as fast and last 8-10 times as long(unless they hit a sl*g pocket) so they are worth it. Boy is it spectacular when they do explode Some steels it imparitive to keep them cool so they don't harden, especially stainless. Cutting to slow/without coolant is death to bits in this type of metal. Cutting to slow with bits results in breakage. |
Posted By: BobHnwO
Date Posted: 11 Nov 2010 at 11:34am
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I use Mobil 1 for cutting oil,works great,bits stay sharp longer.
------------- Why do today what you can put off til tomorrow. |
Posted By: mlpankey
Date Posted: 11 Nov 2010 at 2:49pm
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i use plain water seams that i am more wastefull with it since it doesnt cost as much and the more i waste the cooler the bit stays. ------------- people if they don't already know it you can't tell them. quote yogi berra |
Posted By: GBACBFan
Date Posted: 11 Nov 2010 at 3:02pm
I've had really good luck with Oatey clear thread cutting oil. It's around 6 bucks a 16oz bottle at our local Menards, and is easy to apply at the point of the drill.
 ------------- "The trouble with quotes on the Internet is that you can never know if they are genuine." - Mark Twain |
Posted By: M Diesel
Date Posted: 11 Nov 2010 at 6:12pm
Having several blacksmiths in the family history, I like that. Just needs to be cool. "Cutting oil" kinda rankles my dad at times. Gotta say that water isn't all that friendly at times. I don't drill enough any more to worry about cost. For just some only kinda partly somewhat related info, the latest circuit board drills are now running over 400,000 rpm with 1,000,000 expected soon. Unbelievable feet per second past the spindle. Air cooled.
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mlpankey wrote:Posted By: ChuckLuedtkeSEWI
Date Posted: 11 Nov 2010 at 6:15pm
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Are you using a drill press? Drill bits in a drill press always seem to last longer for me then using them in a corded/cordless drill. Keeps the bit straight and true. On my D17, when I drilled out the rear hubs and put in wheel studs, I drilled by hand, and went through drill bits like crazy. Sharpened them alot, but alot broke as I was drilling by hand. I was almost tempted to take the time and take it all apart, drill in the drill press and then put back together. Would have taken some time, but would have saved it clamping and drilling properly in the drill press. I just drilled some 1/2" holes in 5/8" plate for some loader mounts and I did them in the drill press. 12 holes, did them in about 15 minutes. Started with an 1/8" then 1/4" then the 1/2". Same drill bit on all the holes. I keep my drill press on the slowest setting all the time as well. Just make sure you're material is clamped or secured properly. I have a finger that the tip was sliced off on my dad's drill press when I was about 12. Tough lesson to learn but I never forgot it. ------------- 1955 WD45 diesel 203322 was my dad's tractor, 1966 D15 23530, 1961 HD3 Crawler 1918, 1966 D17 IV 83495, 1937 WC 41255, 1962 D19 6221 |
Posted By: EdK
Date Posted: 11 Nov 2010 at 8:02pm
| I want to thank everyone who participated in my question. Today after sharpening an old 3/8 inch drill bit on a Drill Doctor I bought about 3 years ago and never really used, and cutting the drill speed on my bench drill press to it's lowest, (about 650 rpm), I was able to drill 24 holes in a 1/4 inch angle iron with no problem. And the drill bit still seems sharp. I'll have to dig out the rest of my old bits and sharpen them all. Again thanks to all for your advice. |
Posted By: DREAM
Date Posted: 11 Nov 2010 at 8:30pm
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I have used Champion bits in the past. Still have some of them. Very good bits if treated properly. I do mostly hand work, so breakage usually gets mine.
On anything over 3/8", I use the hole maker with annular cutters. This works really well for all of the structural work that I do. Use a Jancy Holemaker 2 magnetic base with cutters from 7/16" up to 1 1/4" on all structural steel in all positions. It's awesome to be able to stick that thing to the underside of a beam, strap the safety strap around, and poke a 7/8" hole through a 13/16" thick beam flange without breaking a sweat. Hardest part is getting it lined up and turning on the magnet. Chucked the coolant tank when I took it out of the case the first time. Use a spray bottle with Renocool in generous quantities. Just had to jump in here. I know this really doesn't pertain to the right way to use and maintain drill bits, but I have had to hand drill holes in beams for many years, and if anyone out there is still using a hand drill for structural work, one of those babies will change your life.LOL! The holemaker with mag base is so nice, I even use it with the chuck kit and standard HSS bits on the workbench for small fab jobs. Works as well as a drillpress. Very slow speed. ------------- I didn't do it! It was a short, fat, tall, skinny guy that looked like me! |
Posted By: DaveKamp
Date Posted: 11 Nov 2010 at 10:18pm
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Glad to hear that after sharpening, and slowing it down, that you're having better success. Guys have made notes here about speed, color, etc., and they're good rules-of-thumb to keep in mind. One thing that's frequently overlooked- there are many drill presses and hand drills out there. You noted that your slowest speed is 650rpm... your drill press obviously was intented for general-purpose drilling, mostly for smaller holes in materials like wood, plastics, and very soft metals. There IS a difference between machine made for general purpose, and those made for doing real metalwork. The Jancy mag-drill that Dream referred to, is specifically designed for drilling ferrous materials- not just because of the magnetic base (and he's right, they're awesome!), but also because of the INTENDED SPEED RANGE. Drilling holes falls into the exact same category of cutting as ANY OTHER type of cutting machinework... meaning... non-abrasive, and non-electrical machining. Metal cutting tools, regardless of wether they're a twist-drill, a file, a lathe toolbit, or a milling cutter, all cut using a very basic technique- sharp edge RIPPING AWAY metal in a methodical sweep. The earliest chapters of ANY machinist's textbook, involves using basic cutting tools, and the tool bit geometry- rake, relief, speed, and feedrate. You saw the reference to FPM... Feet Per Minute... Consider a bandsaw... an average metal-cutting bandsaw... one of mine is set up for 120fpm. That means a tooth crosses the workpiece at a speed of 120ft every minute... a 12' band blade makes 10 revolutions in one minute. Compare that to a woodcutting bandsaw... it's flyin' along at 1000+ feet per minute. This is because the material being cut (wood) is softer, and the blade teeth are much more coarse, than a metal-cutting bandsaw. On a lathe, an example: the workpiece turns while the bit takes a cut along the outside diameter. If the diameter of the workpiece is around 6", that means the circumference is a little over 18". To make 120fpm at the CUTTING SURFACE, the workpiece must spin at about 80rpm, in order to yield that 120fpm. If the diameter of the workpiece is only 1", that means the necessary RPM to make 120fpm, is around 460rpm. This is what they mean by 'surface feet per minute'. Now, consider that instead of swinging a 6" workpiece in a lathe, you're spinning a 6" DRILL BIT... yep, 80rpm. Recalculate for 1"... now you're at 460. Recalculate for a 1/4" drill bit... that's a circumference of 0.785"... which will have to turn a bit over 1800 rotations in one minute, to yield a 120fpm speed. Is it always the same case? No. Not all materials are the same. Softer workpiece materials will cut at different speeds than harder, and harder-surfaced bits can cut faster than softer-surface bits. Not all drill bit metalurgy and coatings are equal, and quite frankly, the imported twist drill bits you buy nowdays are made of some of the lousiest excuses for tool steel on the face of the earth. Some are so soft that they can be made incredibly sharp, but won't hold the edge if you put it in the front pocket of your Levi's. Likewise, I've had some that were lousy metal, but hardened to the point that a brand-new bit fell out of a box, landed just two feet lower on the bed of my radial drill, and shattered like it was a wine glass. As noted, the GEOMETRY of the drill bit... not just the point, but the rake and relief, determine how well a drill bit works in a given application. Finally, the drill bit may, or may not have an additional cutting surface. Most of my machine tools use high-speed-steel bits (HSS), but I also use carbide-tipped tools. Generally speaking, high speeds will result in the metal hardening itself to an unworkable state (when the base metal's metallurgy will allow). While it's a good general rule to go slow enough to avoid overheating, realize that carbide cutting tools MUST be run at higher speeds than HSS in order for the bit to 1) work properly and 2) last any length of time. When I run carbide in my lathes, I find that the proper feedrate is typically TWICE (if not more) than running high-speed steel cutters... and when I'm cutting some types of stainless, the waste isn't chips or strings, it's swarf... long, blue swarf, that for the first inch or so coming off the cutter, is red-hot... of course, I'm cutting lots of metal, moving fast, and getting mirror-finish cuts. This doesn't happen with HSS... and unfortunately, once you START a cut like that, slowing down can be a serious thing, because that red-hot metal will basically freeze and jamb the tool bit IN the workpiece. If you plan on doing lots of metal cutting, find any common machinist's textbook, and do some extended reading... it'll really help your understanding of the physics of cutting tools of ALL types. Finally... if you don't weld, take the time to learn to use a stick and MIG welder- neither har 'hard', but you'll never learn if you don't attack it. |
Posted By: Rawleigh
Date Posted: 12 Nov 2010 at 10:12am
| I buy drill bits from Travers tools online. They are a commercial supply company for machine shops and they have different grades of bits available. I love their 135 degree cobalt bits. They last much longer than any hardware store bits and usually are cost competitive. They can be resharpened and not loose their hardness, unlike TIN coated steel bits. |
Posted By: Dusty MI
Date Posted: 12 Nov 2010 at 11:37am
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I have a Drill Doctor that sharpens up to 1/2". I bought an additional chuck that will hold/sharpen to 3/4". It works well up to 23/32" but for some reason it doesn't do the 3/4" right. Dusty ------------- 917 H, '48 G, '65 D-10 series III "Allis Express" |
Posted By: Lonn
Date Posted: 12 Nov 2010 at 12:05pm
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My neighbor has a punch. For flat steel you can't beat a punch for speed. We made brackets to mount a 2250 CaseIH loader to the D19. 1/2" steel and it punch through like it was butter. BTW After using it on the D19 the loader is destined for the 190. Way better tractor for loader work. ------------- -- --- .... .- -- -- .- -.. / .-- .- ... / .- / -- ..- .-. -.. . .-. .. -. --. / -.-. .... .. .-.. -.. / .-. .- .--. .. ... - Wink I am a Russian Bot |
Posted By: Coke-in-MN
Date Posted: 12 Nov 2010 at 12:26pm
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Although most of the heat essential for efficient cutting exits with the chip, any increase in the temperature of the component will make accurate measuring difficult. Coolant can be used to reduce this effect. Coolant can be used to drive away any swarf which might interfere with the cutting edge, particularly in boring operations. Coolant can help reduce vibration, especially where rigidity is limited. Where interrupted cutting with CBN inserts occurs, coolant should not be used as this will thermally shock the CBN tool as it comes out of the cut, resulting in premature failure. Although interrupted cutting with coolant will never improve tool life, it is possible to use coolant http://carbideinserts.blogspot.com/2007/11/cbn-machining-applications-where-is-cbn.html - machining hardened stee http://carbideinserts.blogspot.com/2007/11/cbn-machining-applications-where-is-cbn.html - l with http://dreng.co.uk/dr50450.html - DR-450 CBN inserts and coolant can be used when http://www.pgstools.com/servlet/the-template/machiningcastiron/Page - machining cast iron with CBN , that is not hardened, under all conditions. http://carbideinserts.blogspot.com/2008/03/using-coolant-cbn-inserts-interrupted.html - http://carbideinserts.blogspot.com/2008/03/using-coolant-cbn-inserts-interrupted.html I was always told not to use coolants with carbide tools , this is something one might want to research more. ------------- Faith isn't a jump in the dark. It is a walk in the light. Faith is not guessing; it is knowing something. "Challenges are what make life interesting; overcoming them is what makes life meaningful." |
Posted By: mlpankey
Date Posted: 12 Nov 2010 at 1:20pm
------------- people if they don't already know it you can't tell them. quote yogi berra |
Posted By: murphy
Date Posted: 12 Nov 2010 at 8:03pm
| dont drill too big of a pilot hole! |
Posted By: DaveKamp
Date Posted: 13 Nov 2010 at 1:39am
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Yes, when all is 'RIGHT', the heat of the metal-ripping process is primarily absorbed into the waste, and carried away. Not only does this keep the workpiece from work-hardening amidst a cut (which really sucks, especially when you only have one chance to do it...), it also maintains the best dimensional stability... if the workpiece or bit get hot, that means the cut made will not give the same result of a hole cut when all was at ambient temp. Also- there IS such a thing as cutting too slow. As the ripping occurs, the waste 'curls' away from the cutting edge. The ripping action will naturally generate heat... if the chip hardens after passing the tool, it breaks off at fairly regular intervals and becomes waste in the pan. IF it hardens WHILE passing the tool, it becomes an irregular load on the machine, and will usually hog into the workpiece, oftentimes dislodge it from it's anchoring, and deflect or damage the cutting tool. Going too slow also allows the waste to transfer heat into the cutting tool edge. |