Turning a finned aluminium cylinder barrel for a motorcycle

[Brian OldfordParticipant @brianoldford70365]

Posted by duncan webster on 04/04/2017 12:38:37:

If you go down the parting tool route, Tubal Cain recommended that you incorporate a leg going straight down from the business end resting on the cross slide. Makes the whole set up a lot stiffer

On a par with a rear tool-post.

[John FlackParticipant @johnflack59079]

I think that the advice given to Andrew is mistaken. If upon viewing the cylinder casting the problem would be more obvious. There is also a risk that I am wrong.

The cylinder shapes I have seen show in non technical terms show a squashed circular shape with the bore offset to one side, thus one side has very little finning and the opposite side a lot of finning. The deeper side has U shaped cut outs presumably for push rod tubes.if you turn on C/L of bore you can only achieve the depth of fin for the short fin side. If you move to a false centre you leave both sides short of the depth of finning

I would assume that there is a "cooling" requirement to leave sufficient "meat" around the cylinder both for strength and cooling. The "Side on" shape of the also a factor as it requires the taper on the fins to adjusted to each fin

I think that is Andrews problem to which he seeks help

[JasonBModerator @jasonb]

John, can you put up a link to where teh photos can be seen

[John FlackParticipant @johnflack59079]

Jason…… Sorry no I lack the ability to do . As I mentioned earlier I sought info from AMOC, the owners club, their engine spares list has an image which I assumed was similar to Andrews. It's very small but when seen machining from solid is beyond my conception .

John

[John Stevenson 1Participant @johnstevenson1]

Jason, this is the photo in question.

Because the fins are tapered and the cylinder is offset from the main shape, it would be very hard to turn the profile of the fins and keep the taper equal.

This is why I suggested a build up either for a pattern or as a finished barrel with separate fins.

[JasonBModerator @jasonb]

Js I thought this was the type being talked about which has the "U shaped" cutouts in which case it may be possible to turn the grooves assuming there is an equal wall thickness left around the cyliner bore and follow up by shaping the fins and doing the cutouts. Still nasty deep cuts and the broken cut would make it even nastier

CNC "discs" routed from MDF would be easy to add taper too and glue into a stack with spacers if you went the pattern route

Edited By JasonB on 05/04/2017 20:53:53

[Brian OldfordParticipant @brianoldford70365]

Posted by JasonB on 05/04/2017 20:52:52:

. . . . . . . . .CNC "discs" routed from MDF would be easy to add taper too and glue into a stack with spacers if you went the pattern route

Edited By JasonB on 05/04/2017 20:53:53

Although mechanically well suited to the job's needs I would strongly advise against the idea of using MDF. Machining MDF produces large quantities of dust which, without very good extraction, is a very real health hazard. Even with that problem aside machined MDF has, what is best described as, a furry surface which requires no insignificant amount of sealing and flatting back. In a pm to Andrew I have suggested and offered some Sikablock which is a "professional" pattern making material ideally suited to the job in hand. . . . . . . .Cue a google search for "Sikablock".

 

Edited By Brian Oldford on 06/04/2017 08:33:42

[John FlackParticipant @johnflack59079]

Jason….my memory suggests thats the 1947 type

More fins than Helsinki!!!!!!!!

[Ian S CParticipant @iansc]

Jason, to turn fins on that cylinder it might be best to turn the fins first, then machine the U shaped cut outs. That would save the interrupted cuts.

Ian S C

[JasonBModerator @jasonb]

Ian, I was thinking more about the fact the main bore is off ctr to the round billet, would imaginge all profiling of fins and the cut outs would be done after the fins were cut, at least that is how I tend to do it on the aero engines.

[Ian S CParticipant @iansc]

The eccentric cutting shouldn't be too much of a problem, although it's probably bigger than anything I would like to attempt on my lathe, I think I would go and see one of my friends with his big DS&G. The only thing is that with that plan shape of the fins, machining it won't give the fins the correct taper that cast fins would have, I don't know if parallel slots would look quite right.

Ian S C

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