Well if you are that cack handed, then you shouldn't have started :-).
All kinds of stuff can get in the way of getting a job done if you are really determined, but it's not as though you need a first class machine shop to do a job like that. Even if you haven't done such a job before, you will learn and know how next time :-). Sorry, but it's school metalwork class level.
Have you checked the price of small dia carbide drills recently ?. 1.5mm tungsten carbide drill, between 5.00 and 30.00 ukp each, though ebay will be much cheaper. Not the sort of job you could do with a black and decker hand drill either...
If you are paying those sort of prices Chris, it is no wonder you prefer an alternative method of making the hole. I buy carbide drills 50 at a time for less than a pound each in the expectation of breaking at least one on every job. The saving of my time makes them well worthwhile.
Thanks for all the contributions, especially the sympathetic trials and tribulations from Peter, but a "coward's way out" has now presented itself, and it is this, at the risk of SWMBO instituting divorce proceedings, to find the largest dressmaking needle or darning needle in her sewing box, which comes closest to the desired hole size (test hole drilled in a bit of scrap ally) and, being hardened steel of the right size, bang it through.
If you are going to pierce the steel with what sounds essentially like a nail, then it is likely to split, or at best leave a ragged hole that will need to be fettled. You really need to cut the hole with either a drill or a punch.
Why is everyone getting so exited about this job? Spring temper is in the early 40's HRC. Just drill the darn thing with any drill that's not made out of butter!
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 :-)...
For strip perhaps. For a 4" dia BB, whoch *HAS* to remain circular less so. The carbide drills are indeed fragile, however so are HSS in tiny sizes.
Interestingly after Id made the prototype and the ops manager had to sub it out (I did it as a freebie, only took about 30 mins) 2 engineering firms declined to quote, and the third charged =A3150 for 2 drills!
Without actually intending to so do, this is what I ended up with, except that the punching block was the pendulum end itself, insofar as it already had the slit,and the 8BA holes (Took the coward's way out and used the less-likely-to-snap smaller tap)
I punched through with the scribing tool (which bent the tool slightly :-( ) leaving a ragged hole, but then ran the 8BA tap through it again, and all was sweetness and light.
(Not so much precision engineering, more a case of bodging a prototype! :-) )
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