Scribing an exhaust collector ring

[johnd]

Hello all...

I've got a number of Airfix kits with cowlings that lack detail (Blenheim, Stirling etc) and I'd like to add some. I can scribe straight lines easily enough but I'm not sure how to go about the exhaust collector ring, i.e. the concentric circle near the front. In an ideal world I'd stick it in a lathe and touch the edge of a scalpel on it, but I haven't got a lathe. Any tips would be appreciated.

Thanks,

John.

[JosephLalor]

The only suggestion I can come up with, and I've never tried it myself, is to position a length of Dymo tape round the cowling and use the edge as a guide for scribing.

Joseph

[CliffB]

Hi John

I think that your other suggestion of masking could be a good way to go. Paint the cowling colour(s) first, then use a thin strip (say 1mm), of good quality masking tape to define the rear edge of the collector ring. Then apply additional masking behind the thin strip it to cover the rest of the cowling as necessary. If you have any 3D details on the cowling behind the collector ring (which may be difficult to put masking tape over), try using masking fluid flooded in behind your initial 1mm strip of tape. Finish off by painting the collector ring.

In 1/72 I'm sure you won't notice the lack of a scribed line, as long as the paint demarcation is crisp.

Good luck!

Cliff

[johnd]

Thanks for the replies.

I tried the Dymo tape but it doesn't have the adhesion or the flexibility to provide a good guide so I'll try the masking and see how I get on.

Another thought I had was to make a template with a hole the same diameter as the collector ring rear, place the cowling through it and try to scribe round that. I have a feeling that it would be tricky to line it up properly though.

John.

Edited July 10, 2011 by johnd

[Bertie McBoatface]

Thanks for the replies.

I tried the Dymo tape but it doesn't have the adhesion or the flexibility to provide a good guide so I'll try the masking and see how I get on.

Another thought I had was to make a template with a hole the same diameter as the collector ring rear, place the cowling through it and try to scribe round that. I have a feeling that it would be tricky to line it up properly though.

John.

You could use a standard circle drawing template available from stationery stores and level it up by proping the template up on tinlets or something and then offering up the cowling on sheets of say, post it notes.

[Giorgio N]

Best solution I've found to scribe on a round surface like a radial engine cowling: take your cowling and lay this on your workbench with the aperture up or down (more on this later). Then take your scriber, lay it horizontal with something of the right thickness under it so that the scriber hits the cowling at the right height. If the height is not right, use something else under it (plasticard, books, magazines...whatever you find!), what's important is that the scriber is horizontal. Then keep the scriber firmly in place and rotate the cowling so that the scriber will scribe a perfectly round line at the exact distance from the cowling opening. It's like havinga lathe, your cowling is the rotating part and the scriber the fixed tool. Now if the cowling has parallel top and bottom, you can keep either side on the bench, if not just keep the front aperture side on the bench.

If you need masking to paint on the same cowling, I use electric insulation tape for this, cut in thin stripes. This can be stretched to follow the curvature of the part and is much better than anything else for parts with sharp tapers.

Edited July 15, 2011 by Giorgio N