Confirmation for reasons to scribe internal corners on skirting

Discussion in 'Carpenters' Talk' started by ShabbaPlanks, Nov 7, 2006.

  1. chippie244

    chippie244 Super Member

    It's a long time since I was taught the names the names but I do sharpen my drill bits, chisels, planes and knives but here goes.
    1, looking from the top down is the angle between the cutting edge, looking from the front is the bevel and from the side the downwards angle.
    2 Forgotten
    3 Forgotten
    4 Flute
    5 Rake is the front angle, clearance is the side angle on #1
    6 Where the saw blade doesn't point into the material, often for cutting ali.
    7 Countersink is a small depression to take a screw head, counterbore is a deeper hole
    8 Tool steel is harder than high carbon steel
    9 Tungsten carbide tooling
    10 clearance is wider than the screw and is in the bit your fixing, pilot is smaller than the screw and is in the bit your fixing too.
    11 bevel is full depth, chamfer is like an arris
    12 Because you pull it over the wood?

    KEVIN NAIRN Member

    Yes, what you've all been waiting for, the quiz answers!
    1) The 2 cutting edges on a twist drill are called the "lips" so when sharpening you look for: Equal lip length; Equal lip angles; equal lip clearance (the slope away from the lip).
    2) The inclusive angle on twist drills used to be 118 deg but now a lot of them are 135 deg, don't know why. The old trick was to Araldite 2 big hexagon nuts together, to use as a gauge as they make an angle of 120 deg, so only 2 deg out. You sharpen the drill until it fits between the nuts.
    3) The helical groove in a twist drill is called a flute. Note I said helical and not spiral.
    4) The raised part of a drill next to the flute is called the Land. It stops the whole circumference of the drill rubbing in the hole, so reduces friction and wear. When measuring a drill with digital callipers, measure the non flute part, or you'll get a false reading (as long as it's not too badly worn).
    5) Clearance is the part of a cutting tool, that's ground away to stop it rubbing on the material being cut. The rake angle is the part of a cutting tool ground away to allow waste material to be carried away to prevent it choking the cutting area.
    6) There are 3 types of rake angles a) Positive rake where a sawblade tooth faces forward. b) Zero rake where the tooth is in line with the centre of the blade (if you extended the rake angle it would go through the centre of the blade). c) Negative rake is where the rake angle on the tooth slopes backwards. The teeth on negative rake don't cut, they "bash" the wood off, a bit like a masonry drill has negative rake to "grind" the masonry.
    7) A countersink (CSK) is a 90 deg V shaped hole to allow the head of a csk headed wood screw or machine screw (or rivet) to be let into the surface of the material so it finishes slightly below the surface. A counterbore is a flat bottomed hole. (countersink come from sinking screws into countertops).
    8) High Carbon steel (HCS) is iron + 1.4% carbon, tool steel is HCS + other alloys such as vanadium and tungsten. HCS is harder but rusts more easily, Clifton planes use HCS cutters.
    9) TCT stands for Tungsten Carbide Tipped, a very hard but brittle metal. "Tips" of tungsten carbide are brazed to the plate of sawblades or masonry drills.
    10) A clearance hole is slightly bigger than the screw, a pilot hole is slightly smaller than the screw and about the diameter of the screw minus the 2 threads either side. 5mm screw: clearance 5.5-6mm, pilot 2.5-3mm. Pilot means "guide".
    11) A bevel is a slope from one face to the edge, a chamfer is a slope - usually 45 deg on the sharp edge called the arris. You can use a block plane to chamfer the edge to stop splintering. In the trade this is known as "killing the edge".
    12) When sliding mitre saws first came out, they were called "pullover saws" as you had to pull the saw over the work, drop it down and cut from back to front. If you tried pulling the saw towards you, it would "race" across the wood and mash it up, and maybe cut your hand. This was because the tooth shape was wrong. The tooth shape was changed to negative rake to stop the "racing" and now it's a slightly positive rake.

    These are some of the questions I was asked when I went for a job at Wormwood Scrubs prison as a carpenter. There was also a "Trade Test" for reserved occupation tradesmen during the 2nd world war. You had to know your stuff.

    Some of you guys gave great answers.

    New quiz coming soon.

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