Boring Cast Iron

[ROBERT BLACKSHAWParticipant @robertblackshaw40066]

[ROBERT BLACKSHAWParticipant @robertblackshaw40066]

I've looked for any postings on this on a search but no results. I am to bore out a 18mm hole in cast iron, am I doing this correctly. Drill out several holes to within 1mm of 18mm, then using a boring bar,which is an index tool,and leave the top flat. Bore out .1mm or .2mm on dia till .1mm under size, I have a 18mm reamer is this best to use or carry on with the boring tool to size. I intend to lap the hole after to get a reflective finish, then make the piston to fit. The hole is 50mm long, my min speed on the machine is 100 rpm and I don't intend to use any lubricant.

Thanks for any replies for this basic question

[Clive HartlandParticipant @clivehartland94829]

Sounds good apart from the reamer, if you are lapping there is no point in reaming. You will get black dust everywhere so lay a cloth on the lathe/machine bed to save a lot of cleaning up.

Clive

[JasonBModerator @jasonb]

Check that your indexable tool is meant to have the top flat, many slope down towards the corner doing the cutting whick helps stop the side of the tip rubbing.

I'd probably take a bit more off on the first couple of passes and then reduce the amount and finally run the tool through at the same setting as I got close to finish size so any spring can work its way out. I would bot bother with the reamer myself

I also tend to prefer to do the last 1mm or so with a HSS cutter as I find they deflect less than the tipped tools so you hopefully get a more parallel bore

[Neil WyattModerator @neilwyatt]

+1 for finishing with a razor sharp but round-nosed HSS tool.

Boring is superior to reaming if done well.

Neil

[ROBERT BLACKSHAWParticipant @robertblackshaw40066]

I have to make two of these cylinders, I over sized the first so the reamer was not used, I used a HSS tool with a sharp round nose as suggested for a 18.1mm but getting a reflective finish I'm finding hard to achieve either in the hole using the boring tool and out side using a lathe tool with slight round cutting edge, is this normal when working with cast iron.

[JasonBModerator @jasonb]

You are unlikely to get a reflective finish from a lathe tool on CI and not much point as the lapping process will leave a matt surface,

I actually prefer anangular corner to the tool as I find it less likely to get pushed away but I do have a low clearance angle.

[MWParticipant @mw27036]

It used to be common practice to run the tool up and down a boring to "take the spring out of it".

Michael W

[Nigel McBurney 1Participant @nigelmcburney1]

Running the tool a number of times to take out the "spring " seems to be a model practice ,not used in full size practise, looking at the photo I would reduce the length of bar protruding from the tool post so that the tool only just can protrude from the back end of the bore,to make the tool more rigid. The only real advantage of reaming is it should provide a parallel bore which could be necessary if the lathe is worn and turns taper. Keep the rad on the tool tip to a minimum ,just enough to give the required finish ,too big a rad can induce chatter.As for speed I would use between 100 and 200 rpm,depends on how well its balanced,go too fast and the tool will wear,go too slow and no harm will be done and the tool edge lasts a long time.Honing will produce a nice bore,use lubricant 50/50 light oil and white spirit,works well on the hot air engines I have made.

[MWParticipant @mw27036]

Posted by Nigel McBurney 1 on 17/09/2016 19:58:32:

Honing will produce a nice bore,use lubricant 50/50 light oil and white spirit,works well on the hot air engines I have made.

I'm only interested as to what advantage this has say, over 3 in 1 or wd40? I'm only asking because i've heard it said before, yet not really explained, white spirit is a rather nuisance chemical to use considering it's harmful. Can you elaborate on what this combination provides than another lubricant wouldn't?

Michael W

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