Countersink for cast iron

[Oscar43634]

I have a cast iron table for my disc sander who's holes are not countersunk.
Can anyone recommend a good countersink bit that can handle this?
I have a pillar drill but not done much metal drilling so any tips much appreciated.

 

[eribaMotters]

You need a High Speed Steel bit with as many flutes or cutting edges as possible. Typically they are usually about 5 flute. I did initially think of the bits with a hole across there conical end, but I doubt this would do the job as too much resistance on the one cutting edge as opposed to the five. They were originally designed for metal, but to be used on thin sheet material.

Colin

 

[clogs]

u may be lucky with some cast iron........BUT it's full of impurities......
this needs carbide to do the job properly.....
whats to loose but a few quid with HSS......worth a try.....
in all my time with cast iron n HSS, spent more time sharpening.....
I now only use carbide......perhaps if it's just those holes and HSS won't crack it take to an engineers at lunch time.......

 

[TheTiddles]

Cast iron is soft, any countersink should do it, I’ve used cheap snail-shell ones to do similar with no problems. It self-lubricates too so for your application I wouldn’t even bother with oil

 

[Phil Pascoe]

You could do it with a cheap conical grindstone.

 

[Oscar43634]

Thanks for advice guys, I noticed wealden tools had some not too pricey hss countersinks may give one of those a try.