OLIVER TIGER MK III - 5cc ENGINE BUILD
Part 4  by Ramon Wilson
Part four - by Ramon Wilson

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Still a lot of work to do to finish this but the shape is there.

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Ready for the final op to define that venturi section. Each op is done on each case (three being built) rather than repeating a series of ops, that way tabs can be kept on each step.

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Next was to set the venturi true to the spindle. I turned a threaded insert to fit then held it in a threaded bush and centre drilled it after cutting the slot. This was set tight in each case in turn and centred using a ground point (discarded cutter ground to 60 degrees).

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The milling was done using the same 1/8 ball nose slot drill in a combination of plunge and rotary motion. The depth was judged purely by eye as small rotary movements were made on the last cut.

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This was about the maximum removed - far better to leave a bit more on for filing etc than to overdo it.

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Here's the result after about an hours fettling on each case - mainly done with the rotary burrs and then finished off with rifflers. Though the basic shape is now there they are still not 'finished' - still a few minor machining ops to do on the lugs and the webs before the final surface finish is tackled. The one in the background has just been machined.

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Final stages. First was to mill the four transfer passages using a cutter made previously for another engine.

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The ends of the lugs were milled at a 10 degree angle and then then the R/T swung at 5 degrees to to mill the webs to profile.

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With all ops completed it was just a matter of a final fettle on any high spots and then giving the whole thing a going over with a grinding point to accentuate the texture. As referred to previously - if the point is regularly dipped in paraffin this prevents the point loading up. It's run at low speed and allowed to 'judder' over the surface as opposed to removing any material. It perhaps looks far worse than it appears - it's hard to feel the surface distress by finger pressure.

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And finally, after a good bead blast, the effect I was hoping for.  The front housing has had a skim to clean up but will be reduced to final diameter when the housing itself is bored.



Part one here. Part two. Part three. Part four. Part five. Part six. Part seven

Part eight Part nine Part ten

 
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