You could splash out on a rotabroach. Depends if you have to do many in the future.

Best regards,

Steve.

Just a thought, how about drilling the pilot size right through with a known good drill bit, then the pilot drill has nothing to do except guide, and doesn't take up any of the available 'push' or torque. As you drill this advance pilot hole you may be able to sense whether the C.I. is harder at some levels than others.

Another thought; if the pilot drill has blunted, and so slowed progress, then perhaps the resultant light or non-existent loading on the hole saw teeth has caused them to become blunt in turn.

Thought number three (crikey, that 's a record for one day) if all else fails, use the saw groove already produced as a guide, and drill through with the largest drill it will accommodate, at close centres all round the groove, then knock out the centre from the other side. On reflection, that's not the best thought of the three, but just a few small through holes would break up the cut and let some swarf grains escape.

Hello Lee,

If you drill right through at the pilot drill size, then turning the sheet over and cutting again from the back will get you another step further. It also allows all the current swarf to fall out and give another bite of the cherry from the first side.. You may still have to change the hole saw if it has gone blunt.

You might have hit a hard spot too but at 1/4 penetration it sounds a little unlikely

Regards

Brian

As stated earlier also…..

I would try drilling a series of smaller holes crossing the path of the hole saw cut but not more.
This may allow the chips to clear more easily, it also should help the saw teeth to bite more easily.

For a lubricant maybe plain water? Oil only clogs and it will help the saw slip. You will still need to clear the chips often.

Regards
John

Cast Iron is not always cut dry Particularly drilling and tapping.

I think trepanning with a hole saw as Lee Hawkins is doing it in this case may benefit from cutting fluid also. It is always worth trying a different method if the current one is not working.

Good discussion here
**LINK**

Regards
John

…I wondered that Michael — I rather liked the old one.

Lubricant for cast iron – though we usually work it dry, the recommendation in the lid of the box of my BA taps and dies is to use soluble oil and water, and I think that is worth a try with a hole saw, if only to flush out all the dust.   I have used it when (Myford users look away) cutting a hole in a cast iron lathe bed with a hole saw, and it didn't do any harm.  Still took a while though.

Edited By Robbo on 05/04/2014 23:10:07