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Grind-It-Yourself Drill bits
Hi
I redid some bits, and they work very well. Did them with an angle grinder. Used a cutting disc so it could get into the flutes. Started by putting a much steeper cutting edge on the end, steeper in both directions, so the cut is more aggressive and the bit ends up more pointed. Then went inside the flutes to grind away some of the centre metal, so the central blunt section is smaller. Then went over the cutting edge within the flutes lightly, to sharpen them up nicely. Finally removed the bulk of the trailing material behind the cutting edges. Result is a bit that doesnt wander, cuts much faster with much less force, and works better on steel as well as on wood. Makes me wonder why they grind twist drills the way they normally do, cos these are far better. Only thing I havent done with them is use them on hard concrete or stone, and I wouldnt expect them to do so well with concrete. But, some day I'll find out. Anyone else have experience doing this? Regards, NT |
Grind-It-Yourself Drill bits
N. Thornton formulated on Tuesday :
Only thing I havent done with them is use them on hard concrete or stone, and I wouldnt expect them to do so well with concrete. But, some day I'll find out. Anyone else have experience doing this? If you meant drilling concrete or stone with an HSS bit, then not deliberatly ;-) If you mean sharpening them like that for use in steel, then yes. I have in circumstances where I have not been able to get enough purchase to get enough weight behind the drill, but sharpened like that the bits do not last very long. There will also be a greater tendancy to shatter as they break through. If you need to drill holes in heavy material, the way to do it is by drilling a small pilot hole first. The pilot drill will have a much smaller face in contact with the material and (if sharped correctly) cut faster than bits with unusual sharpening methods. -- -- Regards, Harry (M1BYT) (L) http://www.ukradioamateur.org |
Grind-It-Yourself Drill bits
"N. Thornton" wrote in message om... Hi I redid some bits, and they work very well. Did them with an angle grinder. Used a cutting disc so it could get into the flutes. How big are the drills, that you can get an angle grinder into the flutes? They must be huge to do that. Started by putting a much steeper cutting edge on the end, steeper in both directions, so the cut is more aggressive and the bit ends up more pointed. By making the cut 'more aggressive (the rake) you have weakened the area behind the cutting edge. This will result in it breaking or chipping more easily, as there is no metal backing up the cutting edge. Or It will corkscrew into the material you are drilling. This results in no true hole, but a slot that the drill as followed. By making the tip more pointed, you will have altered the chisel tip point and it will not cut as good as at the optimum angle. You may have had success so far by not drilling hard metals. Softer ones can be quite successfully drilled by altering the drill in the way you have done, but try drilling hard metals and you will end up with a totally blunt tip. If indeed you have anything of the tip left at all, after trying :-) Then went inside the flutes to grind away some of the centre metal, so the central blunt section is smaller. Then went over the cutting edge within the flutes lightly, to sharpen them up nicely. Here you are going into the realms of the specialist drills group and what you use this drill for will depend on how it performs. If drilling steel, mild or otherwise, then you risk losing the cutting tip edge, at least, even more if you are at least unlucky Finally removed the bulk of the trailing material behind the cutting edges. This is the same as making the cutting angle sharper as you have mentioned above. The metal that supports the cutting edge is not there and will result in the cutting edge detraining so much more quickly. The drill may perform better for a short while, but it will need sharpening a lot sooner than normal My experience and it is not inconsiderable, is that:- For a normal style twist drill to drill soft materials, go for the alterations that you suggest, but if you want to drill anything harder than wood or aluminium, stick to the drill makers recommendations on drill angles. Result is a bit that doesnt wander, A drill that does not wander is a sharp drill. cuts much faster with much less force, and works better on steel as well as on wood. A properly ground drill always outperforms a poorly ground one. If I could reliably grind a one millimetre drill and try to drill a one millimetre piece of wire, I should end up with nothing more that the swarf generated by this operation. Makes me wonder why they grind twist drills the way they normally do, cos these are far better. No they are not. Twist drills have far more history about how they work than you have. They have been around for many more years than both you and I have been. A sobering thought in life Only thing I havent done with them is use them on hard concrete or stone, and I wouldnt expect them to do so well with concrete. But, some day I'll find out. Don't even think about trying it. Anyone else have experience doing this? Lots :-) You wrote this back to front. That last question should have been your first. Regards Dave |
Grind-It-Yourself Drill bits
Harry Bloomfield wrote in message o.uk...
N. Thornton formulated on Tuesday : Only thing I havent done with them is use them on hard concrete or stone, and I wouldnt expect them to do so well with concrete. But, some day I'll find out. Anyone else have experience doing this? If you mean sharpening them like that for use in steel, then yes. I have in circumstances where I have not been able to get enough purchase to get enough weight behind the drill, but sharpened like that the bits do not last very long. There will also be a greater tendancy to shatter as they break through. I fully understand the idea that a steeper cutting pitch and thinner steel would lead to faster wear, but there is more to it. From using the traditional bits I know that they get very hot in use - very hot. So hot in fact that they can even be melted when drilling steel. The result is that one has to go slow to avoid blunting the thing while drilling just ONE hole. Yes I've done it. Even on wood I've had bits that have got smoking hot and lost their cutting ability. The thing with these sharper bits is they need far less pressure while drilling, and work well at the lowest speed on the drill. Much less force equals less chance of breaking on exit. Much less force plus much less speed equals far less heating, and heat is the prime enemy of steel drill bits, causing them to blunt very much quicker. So although the cutting edge is thinner, because of the heat factor I would expect them to still outlast traditional bits. I have yet to see, I've only been using them a few months, but so far they've performed very well. Last holes I drilled were in steel, and the bit behaved impressively, much better than I had expected. The progress was fast, even at minimum drill speed, break through was much smoother, the hole was left neat, and there was no sign of heating or loss of edge on the bit. So far so good... Regards, NT |
Grind-It-Yourself Drill bits
On Wed, 24 Mar 2004 22:31:36 +0000 (UTC), "davenpat"
wrote: Anyone else have experience doing this? Lots :-) You wrote this back to front. That last question should have been your first. OK how do you sharpen drill bits? cheers, Pete. |
Grind-It-Yourself Drill bits
Pete C wrote
"davenpat" wrote: Anyone else have experience doing this? Lots :-) You wrote this back to front. That last question should have been your first. OK how do you sharpen drill bits? Buy a job lot of secondhand ex-engineering works HSS bits from an autojumble. I haven't bought (or sharpened) a drill bit in ages. :) Cheapo bits (even those marked as HSS or 'Titanium coated' [hah]) just aren't worth the bother HTH Paul. |
Grind-It-Yourself Drill bits
"N. Thornton" wrote in message om... Harry Bloomfield wrote in message o.uk... I fully understand the idea that a steeper cutting pitch and thinner steel would lead to faster wear, but there is more to it. From using the traditional bits I know that they get very hot in use - very hot. Too fast rotation speed will do this, as will too light a feed rate. So hot in fact that they can even be melted when drilling steel. Then you are using twist drills that are not up to the job. The only drill I have ever seen that has burnt out, was one that drilled into a mains cable. What can happen with a quality drill, is that the tip changes colour and the cutting edge gets rounded. The result is a hot drill. The cause is too fast rotation or lack of push to keep the drill drilling. Or both. The result is that one has to go slow to avoid blunting the thing while drilling just ONE hole. Yes I've done it. Even on wood I've had bits that have got smoking hot and lost their cutting ability. Wrong drill angles, that's all that was wrong. Drill angle depends on the material to be drilled. Change the material and you change the drill angles to those that work best. The thing with these sharper bits is they need far less pressure while drilling, and work well at the lowest speed on the drill. Much less force equals less chance of breaking on exit. Much less force plus much less speed equals far less heating, and heat is the prime enemy of steel drill bits, causing them to blunt very much quicker. In my time in the engineering industry, I have had to drill some very, very hard steel. It has been my experience that if the twist drill is up to the hardness of the metal and has been correctly ground, with the correct angles for the metal it is asked to drill and the speed is kept down to prevent any heat generated, then you will produce a hole of the correct size and more importantly, the correct shape. Not all holes made by the way you describe are anywhere near round. So although the cutting edge is thinner, because of the heat factor I would expect them to still outlast traditional bits. I have yet to see, I've only been using them a few months, but so far they've performed very well. I look forward to your posts about 'How can I remove the cutting tip of a twist drill that broke on a job I was doing;. Last holes I drilled were in steel, and the bit behaved impressively, much better than I had expected. The progress was fast, even at minimum drill speed, break through was much smoother, the hole was left neat, and there was no sign of heating or loss of edge on the bit. So far so good... Must have been the softest of steels that you come across then. Dave |
Grind-It-Yourself Drill bits
"davenpat" wrote in message ...
"N. Thornton" wrote in message om... Harry Bloomfield wrote in message o.uk... What can happen with a quality drill, is that the tip changes colour and the cutting edge gets rounded. The result is a hot drill. The cause is too fast rotation or lack of push to keep the drill drilling. Or both. The result is that one has to go slow to avoid blunting the thing while drilling just ONE hole. Yes I've done it. Even on wood I've had bits that have got smoking hot and lost their cutting ability. Wrong drill angles, that's all that was wrong. Drill angle depends on the material to be drilled. Change the material and you change the drill angles to those that work best. I suspect thats the key to all this. Twist drills are generally multipurpose, which means their angles are wrong for almost everything. For wood theyre terrible. Along comes my a with a steeper angle, its better matched and sails through. But presumably it would not do well on harder materials like stone, concrete and iron. But for the things I use them for they do well. Regards, NT |
Grind-It-Yourself Drill bits
"N. Thornton" wrote:
Various contributors said: What can happen with a quality drill, is that the tip changes colour and the cutting edge gets rounded. The result is a hot drill. The cause is too fast rotation or lack of push to keep the drill drilling. Or both. It doesn't help when the bit is used on another job without being re-sharpened (and possibly re-hardened). Once it's got too hot it's useless without re-hardening/sharpening, both of which it is *possible* to do at home. The result is that one has to go slow to avoid blunting the thing while drilling just ONE hole. Yes I've done it. Even on wood I've had bits that have got smoking hot and lost their cutting ability. This *could* be due to the flutes becoming choked. If so, lifting the bit partly out of the hole will fix the problem. This also goes for drilling holes in masonry - keep pulling the bit back every so often to prevent dust causing the bit to bind in the hole (and possibly shear off there). Wrong drill angles, that's all that was wrong. Drill angle depends on the material to be drilled. Change the material and you change the drill angles to those that work best. I suspect thats the key to all this. Twist drills are generally multipurpose, which means their angles are wrong for almost everything. For wood theyre terrible. They're fine for drilling steel, timber, plastic - *if they're sharp*. It takes very little to blunt a drill, and then problems multiply fast. Along comes my a with a steeper angle, its better matched and sails through. But presumably it would not do well on harder materials like stone, concrete and iron. The problem with HSS and masonry is that the bit will blunt very quickly indeed if you touch (say) the bit on concrete, render, brick or whatever. Just one hole drilled with a HSS bit into masonry will shag it. It won't be just blunt, the flutes will wear too, and the whole thing tend towards a taper shape. That's why for TCT bits the diameter of the hole is distated by the TC piece brazed into the end of the drill. The flutes haven't got any guiding job to do, they just clear masonry fragments from the hole. N.B. you should still sharpen TCT bits every so often, it makes a great difference to speedy results. Do *NOT* quench hot TCT bits after grinding, let them cool naturally or even wrapped in cloth (N.B. rags!). J.B. |
Grind-It-Yourself Drill bits
Jerry Built ] wrote:
"N. Thornton" wrote: Various contributors said: What can happen with a quality drill, is that the tip changes colour and the cutting edge gets rounded. The result is a hot drill. The cause is too fast rotation or lack of push to keep the drill drilling. Or both. It doesn't help when the bit is used on another job without being re-sharpened (and possibly re-hardened). Once it's got too hot it's useless without re-hardening/sharpening, both of which it is *possible* to do at home. I'd disagree. For HSS bits, it's practically impossible for most people to do retempering at home. |
Grind-It-Yourself Drill bits
Ian Stirling wrote:
Jerry Built wrote: [ HSS drill bits ] Once it's got too hot it's useless without re-hardening/sharpening, both of which it is *possible* to do at home. I'd disagree. For HSS bits, it's practically impossible for most people to do retempering at home. Well, I said it was possible, not that most people can do it without some sort of guidance. Hardening is easy, then all you've got to do is warm up the shank slowly until the tip's right and quench. What's the difficulty? -- J.B. |
Grind-It-Yourself Drill bits
Ian Stirling wrote:
Jerry Built wrote: Once [the drill bit has ] got too hot it's useless without re-hardening/sharpening, both of which it is *possible* to do at home. I'd disagree. For HSS bits, it's practically impossible for most people to do retempering at home. I thought I'd replied, but it seems not, so here again: I said possible,not that most people can do it without knowing how. What's the difficulty with hardening, then warming the shank until the tip is right, and quenching? What's the difficulty, I'm puzzled (unless you're talking about small drills) ? -- J.B. |
Grind-It-Yourself Drill bits
|
Grind-It-Yourself Drill bits
Jerry Built ] wrote:
Ian Stirling wrote: Jerry Built wrote: Once [the drill bit has ] got too hot it's useless without re-hardening/sharpening, both of which it is *possible* to do at home. I'd disagree. For HSS bits, it's practically impossible for most people to do retempering at home. I thought I'd replied, but it seems not, so here again: I said possible,not that most people can do it without knowing how. What's the difficulty with hardening, then warming the shank until the tip is right, and quenching? That can be done with carbon steel, for HSS, you need to hit temperature limits to around 1% in a reducing atmosphere, at around 1100C. |
Grind-It-Yourself Drill bits
"davenpat" wrote in message ...
"N. Thornton" wrote in message om... I redid some bits, and they work very well. Did them with an angle grinder. Used a cutting disc so it could get into the flutes. How big are the drills, that you can get an angle grinder into the flutes? They must be huge to do that. The smallest one I managed to do that with is 3.5mm. Started by putting a much steeper cutting edge on the end, steeper in both directions, so the cut is more aggressive and the bit ends up more pointed. By making the cut 'more aggressive (the rake) you have weakened the area behind the cutting edge. This will result in it breaking or chipping more easily, as there is no metal backing up the cutting edge. That is true /only/ if it is subjected to the same amount of presure, drill time, and heat. Since it performs so much better, and the cutting angle is so much more aggressive, it is not subjected to anything like the same treatment as the bits out of the box. This seems to be a key point that keeps getting overlooked here. By making the tip more pointed, you will have altered the chisel tip point and it will not cut as good as at the optimum angle. It is now closer to the optimum angle for wood, and in fact cuts much better. Clearly multipurpose twist drills can not be ideally angled for wood, brick and concrete all at the same time. You may have had success so far by not drilling hard metals. Softer ones can be quite successfully drilled by altering the drill in the way you have done, but try drilling hard metals and you will end up with a totally blunt tip. If indeed you have anything of the tip left at all, after trying :-) Yes I quite agree. So far I've only tried drilling thick steel once, and it worked very well, much better than expected, to my surprise. Then went inside the flutes to grind away some of the centre metal, so the central blunt section is smaller. Then went over the cutting edge within the flutes lightly, to sharpen them up nicely. Here you are going into the realms of the specialist drills group and what you use this drill for will depend on how it performs. If drilling steel, mild or otherwise, then you risk losing the cutting tip edge, at least, even more if you are at least unlucky Indeed, not that that is any big deal. I ground them for wood, and they work very well in wood. They seem to work on steel too, though I didnt do them for that. Finally removed the bulk of the trailing material behind the cutting edges. This is the same as making the cutting angle sharper as you have mentioned above. not quite the same: I left some metal there but removed... let me sketch it: | | | | | | |___| | | | | | / |_/ OK, this is an ASCII restricted view of just one cutting edge. Originally the bits were all not far off flat, as above, though of course there was some angle to them. I steepened the cutting edge angle, and kept some trailing supporting metal but removed quite a bit as well. My initial thinking was now the down push on the bit is spread out over a smaller area, so much less force is needed, and much less heat generated. Practice reveals that indeed these bits work well when treated relatively gently. The metal that supports the cutting edge is not there and will result in the cutting edge detraining so much more quickly. In steel sure, but for wood I dont expect so. If the existing bits have enough metal to support their use in steel then less supporting metal is needed when drilling wood. The drill may perform better for a short while, but it will need sharpening a lot sooner than normal of course that is true of every sharpened edge: the sharper it is the sooner it needs resharpening. However thats not a good reason not to sharpen. These particular drills are elementary to resharpen after theyre ground. A quick touch with the grinder inside the flute will restore the sharp edge several times, then eventually regrinding the end would be needed again. My experience and it is not inconsiderable, I understand that, and you have contributed much knowledge on this. I just think you seem to be overlooking a few significant points. is that:- For a normal style twist drill to drill soft materials, go for the alterations that you suggest, but if you want to drill anything harder than wood or aluminium, stick to the drill makers recommendations on drill angles. we agree then Result is a bit that doesnt wander, A drill that does not wander is a sharp drill. All I can say is that was not my experience - with the boxed bits the angles were so far off ideal for wood, and the central unsharpenable area considerable. Consequently wander was a problem. Makes me wonder why they grind twist drills the way they normally do, cos these are far better. No they are not. Twist drills have far more history about how they work than you have. They have been around for many more years than both you and I have been. A sobering thought in life Yes thats obvious. It is equally obvious there are reasons for the angles commonly in use. I suggest they are so the bit will survive use in concrete, plus assorted abuse. My point is that these reground bits are much better suited to woodwork than the gen purp bits most of us crawl along with. Only thing I havent done with them is use them on hard concrete or stone, and I wouldnt expect them to do so well with concrete. But, some day I'll find out. Don't even think about trying it. Might be vaguely interesting to see what happens... I really doubt they'd survive though. I assume they'd just chip off. Anyone else have experience doing this? Lots :-) You wrote this back to front. That last question should have been your first. I took it as obvious that the whole engineering world had a lot more experience. That does not however mean that one can not up one's work rate by using sharper angled drills than the usual twist bits. These bits are performing much better, as long as you accept the limitation that they are for wood and not to be used in concrete etc. If one has 2 or more sets of bits and wishes to work faster and more accurately, these bits make good sense. So far they have turned wood drilling into a more precise, faster, much easier, and more reliable process. Regards, NT |
Grind-It-Yourself Drill bits
N. Thornton wrote: My point is that these reground bits are much better suited to woodwork than the gen purp bits most of us crawl along with. I took it as obvious that the whole engineering world had a lot more experience. That does not however mean that one can not up one's work rate by using sharper angled drills than the usual twist bits. These bits are performing much better, as long as you accept the limitation that they are for wood and not to be used in concrete etc. Hollow grinding and "spear-point" grinding are used where the material being drilled requires, brass requires a very shallow grind (the exact opposite). I've hand sharpened upto 2 inch twist drills, and hollow grinding to reduce the web on larger drills is quite the norm, in smaller sizes less so, either way grind them to suit the job, not to some idealised average and you'll always get a better result. Some rolled twist drills with slow twist will never drill true and round even if/when they are straight, but then they are for fast production use to do a job and get binned when they blunt, higher quality drills are worth re-grinding, the average monkey cannot re-grind a drill these days, so often all you find is cheap, crap, drill bits upto 13mm, if you find good ones I'd get several sets and keep one for steel, and another for wood, ground to your own spec. I still use a slip stone to fine tune drills and other tools, but then I'm rather old school and passe these days! Niel. |
Grind-It-Yourself Drill bits
Pete C wrote
(Zymurgy) wrote: Pete C wrote "davenpat" wrote: You wrote this back to front. That last question should have been your first. OK how do you sharpen drill bits? Buy a job lot of secondhand ex-engineering works HSS bits from an autojumble. I haven't bought (or sharpened) a drill bit in ages. :) I was just wondering why Dave hasn't offered any hints on how to sharpen them. Mmm, I generally use a carborundum stone, as i'm usually only freshening the edge anyway. However, since I got a selection it's not been necessary. Quality bits keep their edge, and using them in a drill press prolongues the life. Cheers, Paul. |
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