10BA clearance holes

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
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On 11/08/12 19:00, ChrisQ wrote:

Or a carbide drill....
But buy at least two, if you buy one it will most likely break. If you buy 2 or 3 then either all or none of them will break. Buy 4 and no matter how cackhanded or unlucky you are you should be able to drill one hole.
Of course circumstances (see my last post) may conspire to increase the hole requirement - so buy 10. You will get at least six holes from ten drills. Hopefully that will be enough.
Note, if you buy 2 or 3 then there is no correlation between whether they all break and whether, if you had only bought a single one, that one would break.
-- Peter Fairbrother
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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 150 for 2 drills!
Dave
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wrote:

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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On 08/18/12 09:43, gareth wrote:

Engineering is about getting the job done, even when you don't have all the "right" tools. Present imperfect.
You can always straighten out the scriber later :-)...
Regards,
Chris
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On 03/08/2012 20:15, gareth wrote:

The way I do it is to fold a piece of brass, make, the required size of hole, in the brass Then make punch out of silver steel, harden and temper. It is then easy to put the spring steel between the folded brass and punch the required hole without the need to annealing the spring
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I have heard of a technique; -never used it personally;- "Put a piece of steel rod with a square end and of just over clearance size in the drill chuck; bring it into contact with the spring where you want to drill the hole and run the drill at high speed with a fair amount of pressure. The friction will heat up the spring at that spot and anneal it. Then drill with a normal high speed drill."
--
Chris Holford

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On Friday, August 3, 2012 8:15:42 PM UTC+1, gareth wrote:

If the material is thin as in a steel tape you could easily make up a simple punch and die set using silver steel and harden it. you could then punch the holes easily, have a look at making pendulum clock suspension springs. Peter
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Thank-you Peter. based upon previous contributions that is indeed the way that I have chosen to go.
Now, being of a nervous disposition, I'll need to use a slitting saw to make the slot to take the flat metal spring, both for the die and also for the Meccano***** rod that will form the pendulum.
Are there any dos and don'ts for this exercise, because with what will essentially be an electric saw running with no guard, it could well be a s*itting saw for me?
*****Meccano still in occasional use here. One "boiler" is used as a soldering iron guard.
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