On 08/12/12 07:32, Cliff Coggin wrote:
I've never actually had to pay for them, but a quick google showed up that price range. Ebay list them at around 1 ukp each in quantity, but no idea what the quality is like. At least for the < 2mm sized hss drills, half of them are not properly sharpened if you buy from the cheapest sources. RS take the biscuit for carbide though: 23.89 ukp each at 1 off. Don't know how they have the nerve to do it, but someone must be paying it.
My experience of carbide drills is for pcb work and the sharp end won't take any lateral force at all. I won't say the ends fall off just by looking at them, but it seems that way sometimes :-).
Just so you don't think i'm being completely unsympathetic, Gareth, a few notes on tempering, which I wrote yesterday evening:
The tempering is probably the most difficult part if you haven't done it before. If you have a whole tape rule or other material to play with, you can try several sections until you get it right. Polish until shiny with fine sandpaper or emery after hardening, then warm up evenly using the blowlamp until you see the right colour, then quench fast. A more accurate and even method, is to use and electric cooker hotplate. Starting from cold or low temperature, switch on the hotplate at low heat and watch the colours change as the hotplate and section warm up together, then quench in a cup of water. The purists would say use oil for the quenching, but for material as thin as that, water will do fine. None of this is overly critical, in that the aim is only to remove enough of the hardness so that the material is no longer brittle, while at the same time still heving enough hardness to act as a spring.
The nice thing about doing this is that you can get exactly the spring characteristics you need, by experimenting with different tempering colours and besides, it's fun doing the work anyway :-)...
Regards,
Chris
I've never actually had to pay for them, but a quick google showed up that price range. Ebay list them at around 1 ukp each in quantity, but no idea what the quality is like. At least for the < 2mm sized hss drills, half of them are not properly sharpened if you buy from the cheapest sources. RS take the biscuit for carbide though: 23.89 ukp each at 1 off. Don't know how they have the nerve to do it, but someone must be paying it.
My experience of carbide drills is for pcb work and the sharp end won't take any lateral force at all. I won't say the ends fall off just by looking at them, but it seems that way sometimes :-).
Just so you don't think i'm being completely unsympathetic, Gareth, a few notes on tempering, which I wrote yesterday evening:
The tempering is probably the most difficult part if you haven't done it before. If you have a whole tape rule or other material to play with, you can try several sections until you get it right. Polish until shiny with fine sandpaper or emery after hardening, then warm up evenly using the blowlamp until you see the right colour, then quench fast. A more accurate and even method, is to use and electric cooker hotplate. Starting from cold or low temperature, switch on the hotplate at low heat and watch the colours change as the hotplate and section warm up together, then quench in a cup of water. The purists would say use oil for the quenching, but for material as thin as that, water will do fine. None of this is overly critical, in that the aim is only to remove enough of the hardness so that the material is no longer brittle, while at the same time still heving enough hardness to act as a spring.
The nice thing about doing this is that you can get exactly the spring characteristics you need, by experimenting with different tempering colours and besides, it's fun doing the work anyway :-)...
Regards,
Chris