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Motorsport Fabrication Fundamentals: Sharpening Drill Bits

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Sharpening Drill Bits


00:00 - As we've already seen, drilling holes is a fundamental part of almost any motorsport fabrication job but our ability to drill accurate and consistent holes does rely on using a sharp, straight drill bit.
00:12 These drill bits are a consumable and they can be bent or become worn as we use them.
00:16 Fortunately though, we can also resharpen a dull or blunt drill bit with relative ease, returning it to its former glory and saving ourselves a bunch of money compared to simply throwing it in the bin and reaching for a new one.
00:28 We can perform two simple checks before we start drilling our holes to make sure that our drill bits aren't bent.
00:35 The first is to roll the drill along a flat steel bench top to make sure that it rolls smoothly.
00:41 If it does, chances are the drill is fine for use.
00:44 The second method is to rotate the drill bit in the cordless drill chuck and look for any visible signs of off centre rotation of the tip.
00:52 A bent drill will visibly wobble which is very obvious to the eye.
00:56 As drills are made out of very high carbon steel, it's incredibly difficult to straighten a drill without snapping it, so unfortunately a bent drill isn't recoverable.
01:05 A blunt, damaged or incorrectly sharpened drill bit on the other hand is relatively easy to correct by resharpening.
01:12 The tools we use to sharpen a drill bit are a bench grinder and a drill bit angle gauge or protractor.
01:18 There are a number of drill sharpening machines or attachments on the market but once you've mastered the technique, it's possible to get great results by hand on a bench grinder.
01:27 To correctly sharpen the drill bit, first we need to understand a few of its dimensions.
01:32 The point angle of a drill bit measures 118°, this means each side of the drill bit needs to be an equal length and an angle of 59° to achieve the overall 118°.
01:45 While this angle of 118° is a general drill bit angle that suits mild steel, aluminium and cast iron, tougher steels and deeper holes may require or benefit from a larger angle of 130 to 140°.
02:00 Before turning on our bench grinder to start our sharpening process, we need to inspect the wheel and make sure that it's in sound condition.
02:07 The grinding wheel must be square and clean with no grooves in the stone in order to allow our drill bit to remain square as we sharpen it.
02:15 You can use any bench grinder of any size but make sure you're using a medium or fine grit stone to get a nice sharp edge on your drill bit.
02:24 And make sure you have a small tub of water on hand to cool the drill bit as you go through the sharpening process as it begins to get warm.
02:31 If the wheel is loaded up with materials or has grooves worn into it, its ability to cut properly will be significantly reduced.
02:40 A wheel like this will need to be dressed with the dressing tool which removes a layer of the bonded grit off the wheel, exposing a clean and straight cutting surface.
02:49 Once dressed, the wheel will be slightly smaller in diameter than before and this may require the tool rest to be readjusted to be within 2 mm of the wheel surface.
02:58 We can then use our protractor to mark a line on the tool rest to indicate the 59° of angle that we need in order to give us the overall 118° point angle of our drill bit.
03:11 The first step is to rest the drill bit on the tool rest and ensure that we have our drill bit correctly lined up to our reference mark.
03:18 Lightly touch each cutting face on the wheel to begin the sharpening process and refresh the face of the drill.
03:25 If your drill has any chips or damage then you're going to need to grind the drill bit back to expose an undamaged area.
03:32 With our cutting face angle set, we can now slightly tilt the drill and rotate clockwise at the same time.
03:39 This motion wil relieve the cutting edge and restore the lip clearance angle.
03:42 The reason we relieve the cutting face by rotating the drill up and out of the wheel is to give the cutting face the first point of contact.
03:50 Too much relief will expose the cutting face and make it wear faster while not enough will affect the speed in which the drill will be able to cut.
03:59 We can now repeat this process for the other cutting face of our drill bit.
04:03 During this process, the drill will naturally get hot so it's a good idea to periodically dip it in some water at regular intervals to prevent overheating.
04:11 If you have overheated the drill bit, this will be obvious from discolouration near the tip.
04:15 A straw colour indicates the tip is getting hot while blue colours indicate severe overheating.
04:21 Using a drill angle gauge or protractor, we can double check that both our drill point angle and our cutting lip lengths are equal.
04:29 It's worth noting that small drill bits such as 3 mm and below are extremely difficult to sharpen.
04:35 The tiny cutting surfaces make them almost impossible to see and sharpen accurately, therefore it's hard to confirm you have the angles and lengths right.
04:44 For this reason, these drill bits are usually best replaced when they become worn.
04:48 Larger drills take longer to sharpen but offer a much wider cutting face to measure.
04:53 While the technique of sharpening drill bits will take some practice to master, it's an essential skill that will save you time and money while insuring the accuracy of your holes.

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