Whatever. I'm not getting into a discussion with you. If you know anything about the micromechanisms of chip formation you'll know that it is all about the geometry of the cutting edge and nothing to do with the material that the drill bit is made of.
what's wrong with consulting drill charts. They state cutting speeds for different types of drills and for different materials (ft/min) and extrapolate that out into drill sizes and drill speeds in rpm The charts are available in many places, internet, engineering books, vendors who sell drill bits, machine shops, your wife's brother's best mate etc. I don't know why there's an argument
First of all you get an understanding of how fast the drill bit should be turning by consulting the charts You can find your max hand held drill speed by looking at the label on the handle failing that, check with the manufacturer and add it to the handle now you can get the speed in the ball park by running the drill at full, 3/4, 1/2 or 1/4 speed on a variable speed drill A fixed speed hand drill is only really designed for a narrow range of drill bits. Large hand held fixed speed drills may have a 2 speed gear box for larger drill bits So as an example if you have a 15mm drill bit, the ideal speed for mild steel is 500 to 600 rpm. For aluminium its 1200 to 1800 rpm. In a variable speed hand held drill that has a max speed of 2500 rpm you would use around 1/4 speed in mild steel, in aluminium 1/2 to 3/4 speed If you had a fixed speed drill at 2500rpm you should not attempt to drill a 15mm hole into mild steel as this will damage the bit (breakages, burnt tips and locking up in the hole), in aluminium you may get away with it. I know that ignorance is bliss for some and you're not one of them @davidoft, can you agree that knowing what speed a drill bit is designed for into what material goes a long way in determining how to operate the hand drill that's driving it Drill charts will also have feed rates and this is useful for determining how much force should be applied Rick
Yes but when you have a box of consistently blunt different type drills as opposed to a fully equipped modern workshop, where do you start? I promise to find such a chart though and I thank you for that. That and some of the recommendations for good drills and what not to get are really what I was originally asking about. I've also ordered a new fine grindstone for my bench grinder (the current one has a big groove in it), so I can try sharpening some of my existing drills - not much to lose there.
Or a new box of drills for Christmas to include a Christmas tree cutter ( or should i say step drill)
We do suffer from most of the largest DIY chains selling low quality drill bits at "competitive" prices .. you pay as little for 10 bits in a box as two decent 4mm drill bits. And Bosch e.g. dont help their brand image by playing along with the race to the bottom. Strangely, the "Middle of Lidl" is either really quite good or cheese metal. But you can tell by the price. Close to £20 - good. Close to £10 - avoid.
