Twist Drill Geometry TIPS #465 LISLE grinder tubalcain

how would he once again this is tubal-cain your youtube shop teacher welcome back to the shop and in a recent videos you saw me rebuild as lyall drill grinder and in upcoming video I intend to show how to use it and that'll probably be a several part video before I get into that I think it is totally necessary to spend some time talking about the geometry of drill bits and the tip of a drill bit which is where the action is and if you do not understand the geometry of a drill bit and all of the angles it'll be very troubling for you to attempt to sharpen drill bits so this video will be devoted to drill bit geometry first let me talk about some of the resources that are available that might help you understand geometry of a drill bit and that you can study now it was very difficult when I was teaching to hold the drill bit up in front of a class of 24 kids and talk about it and have them be able to see the tip matter of fact it was impossible so I had developed at that time when I had my small business called Petersen products a drill bit teaching aid and that's about the size of a two pound hill Hills brothers coffee can and I used though I sold many of those when I had my business long and defunct now that is me with my face covered to protect the innocence standing before a class showing how to use it and you can see that was large enough that it would be pretty useful if I had one right now but as far as I know none of these exist years ago all the major companies and in this case it's Cleveland twister all I had free giveaways and here's the Cleveland trademark trademark this is a 50 page pamphlet on drill bits how to sharpen them how to use them and just a great deal of information I had to buy this off of ebay I think it was $5 as a pretty good condition is probably from 1959 so something like that it's just great in addition here's one put out by the Morse twist drill company the practical machinist guide and it has about four or five pages also on twist drill terms and the grinding of bits and also picture showing the tips of the drill bit this is one of my favorites also put out by Cleveland and has printed on heavy stock with a spiral binding so it opens and stays open and there's a lot of information about drilling speeds and near the end here there's a nice section also on drill bit geometry first aid for drill bits how to repair them precondition them and also on the back pictures of the tips I love this engineers black book recently given to me by a Bruce with them and there's also a nice section in this book on drill bit grinding and it included which I have out on my optical comparator this nice metal gauge here for sharpening you'll see that later on but it was tucked here in this little pouch in the back so this is a great book get yourself one of these the instruction sheet that came with a Lyle grinder model 91,000 has about six pages on how to use the grinder we'll talk about that in the next chapter but on the back of it here also is the fundamentals of drill sharpening there were scores of machine shop books this one is the old a shop Theory Henry Ford but and I'm showing yes yeah I think it's out of print and maybe the copyright to you is no longer in effect but there and I will be using this here in a few minutes again but there are several pages here also on drills and drill minding this is a particularly nice book I think there's a lot of these probably available on the internet so there's about six pages on drill bits [Music] in addition you will be needing a drill grinding gauge so get yourself either a starett like this and this is adjustable up and down on the rule this is actually an attachment for one of the six-inch rules here's another brand but similarly made and these are 59 degrees but you can also find probably I don't know if they give these away anymore but here's again a Cleveland advertising gauge it could be put in your pocket so for the tips and the main angle there's one by Butterfield that is a double ender so try to find one of those you probably can get one at the hardware store or even make your own or make it outta cardboard and a SIL would be accurate enough for the general purposes first let's talk about the parts and the terminology used with drill bits all drill bits have a point which is the very end here where the cutting takes place the body and a shank they may have tapered shanks or they may have straight shanks and there are even other shanks available years ago they used a square shank on the end of the taper there is a Tang that is what does the driving on larger bits but most likely here we're gonna be dealing with just taper bits taper shank bits and straight shank whether they're step-down like this sometimes called silver and Deming or the regular smaller bits that you're going to use in the shop all drill bits have what we call flutes and that's the spiral grooves right here and most commonly is the two flute which is really what we're concerned with today but they also make a three flute and a for fluid those are generally called core drills they are used to enlarge holes that have been either pre drilled or precast the purpose of the fluids is to help form the geometry here of the tip as well as to allow coolant and oil to get down to the tip where the cutting is taking place and to allow the chips to escape and spiral up and out of the hole so that's the purpose of the flue looking at the side now the area here between this point and this point is called the land this is the margin only the margin is touching the side of the hole this is body clearance if the entire side here the entire land touched the side of the hole there'd be a lot of friction so this reduces friction and heat by having the body clearance the margin here is not a cutting edge it is on a reamer or this area is the cutting edge on a reamer but it does not cut it only supports the drill in the hole the main support of a drill bit is called the web it's like the spine of the drill bit it gives it strength it is thicker near the bottom than it is near the top but of course you certainly can't tell that by just looking at a drill bit but I'm gonna show you proof of that right now looking at the end on any drill bit this is called the web right here now I took the liberty of taking a 1/2 inch drill bit and cutting it in half to prove the point or make a point here and it looked like that originally but looking at it right here you can see that the web is approximately 2 millimeters and then on the lower part that I cut off and then Irish arpund it the web is three and a half millimeters therefore it's really too thick right here to do when you're drilling unless you thin that web or pre-drill the hole with a pilot that is at least the diameter of the thickness of the web I thought you'd find that interesting probably 90% of all the drill bits you come in contact will be ground at 59 degrees or total included angle of 118 degrees certainly there are many other drill angles that can be used but for the purposes of our talk here it'll be confined to the 59 degree and that's what you're going to find at all the box stores and they're called jobbers bits that are just the traditional length with the traditional point of 59 degrees included angle and again that's where you need your drill gauge to check that angle this is the lip of the drill bit now that's the actual cutting edge and there are two of those on a two flute drill bit and we have to have a relief or a clearance here of all 12 degrees approximately and that's going to vary with the diameter of the drill larger drills need possibly less than the twelve degrees and smaller drills will need 12 maybe even up to 15 degrees so that only the cutting edge is touching the work this is relief back here now if you have too much you're going to end up with probably chipping here of the cutting lip and a short life too little and you're going to have rubbing and you don't want this to touch this is called the heel back here so this is the lip this is the heel and here's a good picture out of the Ford book showing the 12 degree clearance as I told you your lip relief your clearance is going to vary depending on the diameter of the drill bit and this chart according to Cleveland is approximately what you should use for your lip relief and you know we're not going to be concerned with those small drill bits because I'm just going to tell you throwaway dull bits that are under eighth inch don't even consider them but in the quarter inch range they're calling for 16 degrees what seems a little excessive to me 11 for the 1/2 and then we get it into bigger bits like one inch and two inch there are eight degrees and seven degrees and then even only six degrees for the three inch before we go any further I'd like to point out that drill bit points are sharpened at many different angles and different clearances depending on the materials to be drilled it might be plastic or titanium or just about anything you could think of in that for efficiency in industry these points might be ground to whatever you see here or whatever specified we do not typically do that in the home shop we're sticking with what I told you 118 degrees these pictures from the Lyle instructions notice that they're talking here about lip clearance again incorrect correct and incorrect here we actually have negative clearance that's correct and this is excessive note also in the above picture here this is the top view of the drill bits that when you get this angle in the wrong amount it's going to change the angle of the chisel point and you will not get the hundred and thirty five or anywhere near it unless you have the correct lip relief of usually eight ten twelve degrees here's an example of a drill bit with too much clearance and you can see that the cutting lip broke off now let me show you one with two little here's an example of a poorly ground from the factory drill bit it's an import can you see that there's virtually no clearance or maybe even negative clearance right here now I'll set it up with the height gauge to show you that but this drill bit would not cut it would rub from this view using a height gauge you can see that pretty much this is the exact same height right at the clip that's the cut and the heel so that it needs to be reground and that's the same way on the other side very unfortunate that something would be shipped out from a factory in that condition this is called the chisel point the chisel point on a drill actually does not do any cutting it displaces the metal so if the chisel point there at the web it's too thick like that you're gonna have trouble drilling unless you have a pilot hole and there is to be an angle there that is the angle between the lip pier and the web or the chisel point should be around 135 degrees but that certainly can vary you can check it with a protractor right there and you can see it's not quite 135 but yet it's okay doesn't have to be exactly 135 but it needs to be in that ballpark all right let's review those three angles that are most critical now first of all the angle of the point should be 59 degrees check that with a gauge this is a brand-new bit again it can vary just a little bit as long as both lips are the same and then looking at it from this direction we want approximately a 12 degree relief here between the lip and the heel that also can vary just a little bit and finally we're looking here at the chisel point and it ought to be about a hundred and thirty-five degrees you're going to see that that varies greatly even on commercially ground drill bits but it's approximately a hundred and thirty-five it's not even right on here but there I'm using a Lufkin protractor set at 135 next let me say that the chisel point needs to be in the very center of the drill bit that is this slip must be the same length as this slip in other words right here this lip needs to be the same as as this lip and if it is the chisel point will be in the center now if it isn't in the center your drill bit is going to drill oversize in fact some old-timers would grind it with uneven lips so that the hole would drill over size for whatever purpose they had I don't know why they just didn't use another drill bit but that's what I've been told anyway so be very careful of that as you sharpen your drill bits if the drill bit is sharp and both lips are browned equally you should get two chips coming out of the hole and the chip should be of equal size and thickness how do you know when a drill bit needs to be sharpened sometimes it will be obvious that is the bit just will not drill or it will smoke or I'll heat up or something like that you know that you need to sharpen it but you can also and you really should examine a a bit each time you use it and see if the point is suitable to use or do you need to touch it up and you know this can be done by hand but in the next video I'm going to show you how to do it with the Lyle drill grinder in one of my older videos I do show how to do it by hand I'll give you the link or the name of that video now here is a drill bit that has way too much lip clearance and should be reground that will dull rapidly because the the edge the lip is too delicate I buy a lot of used drill bits at garage sales and auctions and often they've been ground by people that don't know what they're doing but here's one that you can see that has absolutely no relief or even possibly a little negative relief so that bit needs to be sharpened before use here's a bit that's been sharpened by somebody that didn't know what they're doing and you can see it's chipped already there but notice that it's not ground smoothly it has different facets on it so every time it was put back on the grinding wheel this would have been done freehand it was grown at a slightly different angle so this this is just terrible a drill bit has wear on it every time it's used now in the home shop you're not going to see that kind of wear but certainly in industry they wear drill bits out and it'll typically be near the end near the point and the margin will literally wear down to where it is it has gone and it's just flush all the way across here and if that is the case really a portion of the drill has to be removed so that you have a good land so you might have to remove a half inch or even an inch and then you probably will have to thin the web again I'm not going to talk about thinning webs but as the web gets thicker and thicker so examine the the land to see if there is damage to it or where again I do not have an example to show you but if a drill bit has been overheated you're going to see that it's blue it's very dull and often again the margin just burnt off you will have to remove a portion of it or in the smaller drill bit sizes I just recommend throw it away discard it because the drill bits aren't that expensive but in the larger sizes you may have to salvage it and amputate a portion of it but if you do that be very careful you don't overheat it and take the temper out and ruin it in your attempt to recondition it I guess my point is that sometimes drill bits wear out rather than just dull and Cleveland in the booklet here has attempted to show you that I'm not sure how well it shows up here but they're talking about how the land wears and that's what I just showed you and that it's necessary to remove the worn section as mentioned earlier as a drill bit gets shorter and ground down the web gets thicker and has to be thinned so here is an example of a couple that have been thinned and I will not cover that even in the following video because that's almost the subject in itself that you can see how that's been ground probably freehand but there is machinery that will do it to reduce the thickness of the web on the chisel point in summary now I've shown you the different angles that we need to be familiar with before we start grinding drill bits and some of the defects that you're going to see in use drill bits and how to identify dull drill bits and that concludes this video so be sure and watch the follow-up videos where I show you how to use the Lyle 91,000 grinder and that will probably also be two parts as I show you how to set up the machine and then how to grind your drill bits and renew their tips so hope you enjoyed the video you might have to watch it more than once thank you for watching this is a tubal-cain saying so long for now you

Channel: mrpete222

Views: 54,878

Rating: 4.944417 out of 5

Keywords: lisle, lathe, milling machine, mrpete222, lyle peterson, atlas lathe, powercraft lathe

Id: EtnNN5pEjaU

Length: 21min 38sec (1298 seconds)

Published: Sun Jun 10 2018