# broken drill bits on spring steel



## ship (Apr 1, 2008)

So I was up way late last night in making some spring clip attachments of top hats to Mac 250 fixtures. Must have broken about upwards of twenty drill bits, this following three or four center punches in just making the initial holes. Fairly easy to bend and cut a Menards type sliding door screen spring clip to that which I needed and they were already black in color. 

Sure just punch the initial hole with the center punch, pound it flat, pound another hole with pointed punch from the other side, pound flat again and pound again hard in now opening up a hole. Than drill away once the hole is there. Step up the drill bits 1/64" at a time until at #30 size for a rivet. 

Sounds simple enough, weaken the metal, punch a small hole for setting it up and drill away.

Didn’t work so hot on these couldn’t be more than 1/32" thick spring clips I was attempting to rivet to the top hat flange. The normal 82 degree tip angle black oxide coated drill bits cut great for the first hole, than not so well on the second or not much more if at all and much less for following holes in stepping up my drilling. TICN coated etc. bits didn’t work so well either. Cutting oil was even less effective yet.

Only at the point when breaking drill bits that suddenly punched thru the material did I note something. A broken drill bit still in the chuck almost no matter what type in not mattering as long as if had a flute left seemed to drill thru the spring steel better and easier than a slightly dull bit.

Why is that that a broken drill bit would cut thru spring steel better than a pointed drill bit? Other more optimum ways to open up a rivet hole in the spring steel? Drill speed? I was at about 1,750 RPM on fresh cordless batteries and more likely normally about 1,200 RPM.


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## soundman (Apr 2, 2008)

Going out on a limb but was it because spring steel has a high yield point if the bit wasn't sharp as a tack it would just push and bend the steel until it broke through. Like trying to punch through a trash bag. Where as a broken bit would kind of cut a circleish hole it the spring steel producing a hole quicker - scribing like a glass cutter. How did the holes look once they were punched through, nice and flat or was there a lip/hat? 

Also wouldn't all that hammer work harden then steel a bit. 

Was a cordless drill the best option, I don't know the size of the work piece but could a drill press be a better option. 

I am all for step drilling but your step size seems a bit small for such a thin piece, did you try jumping to a 1/1th6 then an 1/8th the #30 to finish?


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## ship (Apr 8, 2008)

proper drilling speed would be a good thing no doubt, and I was surprised that our metals shop was able to hole saw cut 4.1/8" holes in some stainless steel kitchen type mixing bowls without completely trashing the bit. I was thinking plazma cutter.

So following the backstage handbook guidelines, it would seem I was way too fast in drilling speed. For a 1/16" bit given the Stainless Steel type which is similar perhaps most closely it should have been about 900 RPM or 450 RPM for the 1/8" or #30 size. Perhaps a bit or a lot slower still given the material is not the same and harder yet to drill. Really hard to drill spring steel and in the past I have tried lower gears in going both slow and fast. Neither works in drilling it. I still note that coated and special expensive drill bits last a bit longer (experience with all forms of drill speed in drilling it), but don't really help efficiently.

Still curious about the broken bit drilling concept, as above or sort of a grinder in doing so, it was very efficient.

Still curious about just plain drilling say a 1/32" thick piece of spring steel, how to effectively. Perhaps slow the speed down to like 180 RPM and use cutting oil? Just never had success with it. Can bend it, can cut it, just can't drill it.


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