A puzzle and small disaster

Just musing .... did you deliberately turn the mandrel with a slight taper or did it come about accidentally due to a small machine alignment inaccuracy? If the latter, is it possible the flywheel bore ended up with the same (slight) taper?

Assembling two matched tiny tapers like that could easily cause hard jamming (ask my wife about her stainless-steel mixing bowls).

Peter Greene: Thanks for you response. I see your point, but the flywheel was reamed, so presumably a parallel bore.
This was actually my second mandrel, the first had a slight taper - the wrong way round - so I adjusted accordingly and turned the second pretty much dead-on parallel. The slight taper was imparted with fine emery and much checking with a mic. (about .-0.005 in 50mm).

Howard Lewis: Thanks for your response. The flywheel had actually been sitting on the bench while I was turning the mandrel - so if either component was warm from machining it would have been the mandrel and as time passed the fit should have been looser. I did actually try the judicious application of heat to the flywheel hoping that expansion would loosen it - but no such luck.
I successfully machined the replacement much as you suggest.

Hi James, if that happened to me, I would would have drill the mandrel out as big as I thought I could without drilling into the flywheel and then see if the wheel would come off and maybe bored the last bit out until the last bit of the mandrel collapsed. You said that it twisted and and then locked up, which suggests that it either had a small piece of swarf trapped and picked up or it galled up and is probably what made it break when trying to drift it out.

Regards Nick.

Ah yes, I see where you said it was reamed before.
My apologies.

Nicholas Farr: Yes, I should have tried drilling it out but impatience got the better of me, I'm afraid.

I'd wondered about a piece of trapped swarf, but 'galled up' is a new one on me - could you educate me here please.

You could have drilled the mandrel until only a thin wall remained, then tapped it out. f the bore got damaged you could have made an oversize crankshaft.

Neil

Galling James is when two pieces of similar metal rub against each other as in fitting together. It can happen when you least expect it and is rapid occurance and virtually immoveable. Aluminium is probably the worst, followed by mild steel and then brass - though I have only worked with stainless on rare occasion I believe it too is also likely to gall.

It is very unlikely that steel would gall on cast, nor cast on cast but if you do manage to get the parts apart there will be a distinct witness of where the galling occurred.

When I built the Atomatic engine the aluminium cylinder head galled on the crankcase - despite gingerly trying the thread on I felt it 'go' and no amount of trying would reverse it. The case was held in the lathe and could not be moved so the head had to be machined off and remade, the galling just one small spot in the thread which had to be re-cut.

Hope that explains it for you

Tug

Edited By Ramon Wilson on 07/02/2022 18:06:07

Hi, galling doesn't always happen between cast iron and steel but it can and does at times, it only needs one tiny hard bit in one or the other and it will normally gouge the cast iron, normally happens during twisting one on the other but I have seen it when pressing steel shafts out of cast iron pulleys that are held in place with a gib head key, but these may have twisted a few thou during their use.

Regards Nick.

Hi Ramon, the A2 and A4 stainless steel nuts and bolts are some of the worst things I've found to gall and it can happen before you even get the nut nipping, always best to use a lubricant with these, doesn't often happen with an A2 nut on an A4 bolt though but you don't see those two used together normally.

Regards Nick.

Hi Nicholas - I've never been aware of cast galling on steel but of course if there are hard spots or inclusions I could see that may occur. For the most part for instance En1a steel in cast is a fine bearing combination or indeed ideal piston and liner combination in IC engines.

I had to go out earlier tonight but was trying to find these few pictures beforehand.

These show the pick up that occurred on the Atomatic build

The initial screwcutting.

Trying the previously screw cut head to check the thread - this galled without warning. Just about to machine it off

Final break through

The galled spot - small but compacted this resisted all attempts to unscrew the head

After re cutting the thread. There were a lot of screw thread fits on this particular IC engine so a lot of nervous moments when trying fits and the use of plenty of anti galling grease from this point on!

Hope this helps you James to visualise what galling means.

Regards - Tug

Ramon Wilson, Nicholas Farr: Thanks for the info. on galling. I found this too, which is informative - https://en.wikipedia.org/wiki/Galling.

Galling tends to occur when two metals of the same composition are run against each other, with minimal or no lubrication, .such a shaft /bearing configuration, or as shown a like and like register with relative movement.

There is localised welding and relative motion only makes matters worse!

Whether it is caused by molecular attraction is not certain, but adequate prior lubrication is a good preventative measure.

Howard

Howard Lewis: Thanks - I'm beginning to see that my automatic reaction of giving the flywheel a twist when it became reticent to come off the mandrel was probably the last thing that I should have done. I will bear this very much in mind in future along with the need for lubrication.