Cutting a hole in Cast Iron

Hello

Anyone have any ideas of cutting a 65mm diameter hole in 1 inch thick cast iron sheet, the iron sheet is from about 1940 period, at the moment I am using a 65mm starett hole saw, but it has cut about 1/4 way through and now seems to of stalled, it is so so slow going , the saw don't seem to be biting in to the metal, not sure if it has work hardened, thats if this can happen with cast iron, I have never known it to, I have always found cast iron to be softer than mild steel when drilling.

really getting to me this one, I dont have a lathe now, so boring it is out the question

Any advice would be most appreciated

lee

In my experience of drilling holes in thick metal the big problem is clearance of the swarf. This will be worse in cast iron because the swarf will be a fine powder that will tend to stay in the groove. If it is at all possible I would suggest you drill some holes through the slab, say 6 mm diameter, that break into the cut.. This provide somewhere for the swarf to escape. Remove the holesaw from the cut frequently to allow the swarf to clear. This problem also occurs when drilling wood with a hole saw.

If the drilling has become slow it maybe that the holesaw is now blunted and needs sharpening.

Hope this helps

Mike

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.

I have tried nearly all thats been mentioned so far apart, apart from the rotabroach

I have also did the stitching hole method in the past on a number of occasion, very messy approach, also very hard to get a accurate hole in the end, so much tidying up the edges, thanks for the ideas though

Wish I had one of those Cole Drills, they seem to chew through anything

thanks

lee

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

what is your drilling speed?

The cast Iron sheet came from a lathe counter shaft Base Built during the war time mid 1940s, I am beginning to think it is junk iron, could be all sorts of stuff in the mix, and I have hit something really Hard,

I am thinking of going to local machine shop I have used before, I get on alright with the owner, maybe see if he could bore it out for me, trouble is though he so laid back he takes along time to do things

lee

I feel your pain, Iv'e drilled countless 1-1/4" holes in cast iron fall pipes using a hole saw in a cordless drill, never a problem, two minute job, then a couple of weeks ago I encountered one made from cast kryptonite .......hard does not even come close, took an hour with a corded drill and killed two starret cutters......funny stuff cast iron!

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 best cut dry, no lubricant

Brian

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

... So who changed the nice poetic title of this thread ???

...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

Hi Lee,
A carbide grit hole saw might work.

Les.