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Cutting curves in plastic

3442 Views 16 Replies 13 Participants Last post by  Pete Thornton
I'm about to have to fit a sand dome on a new boiler, and to cut down the smokebox saddle on my new project loco. Both the dome and the saddle have to fit a curved surface about 1+" radius, (2.375" diameter actually. It's a ten-wheeler conversion, so the dome is moulded in to the top of the old boiler.)

I can think of a few ways of doing this, but I'm wondering if you clever guys know any other way besdies the following:

- using a coping saw (hand version of a band saw,) carefully cut to approx the right diameter and then file or sand smooth,

- using a large curved file, just file away until it fits,

- buy a grinding bit for my drill and grind the plastic away.

How would you make a sand dome fit a new boiler?
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Posted By Robert on 12/18/2008 12:04 PM
Steve the link was very helpful, but how was the original "wavey line" created

The original template for the Steam/Sand dome base was part of the drawings provided by David Fletcher for the MasterClass 2002 Building a Mason Bogie.

However, you should be able to create one for any specific need.

Draw an end elevation of the boiler & dome base as depicted in the diagram on the left. Draw a quarter-circle of the diameter of the dome (bottom of diagram on left), cut the arc into three equal parts, extend vertical lines parallel to the vertical centerline of the end elevation so that they extend from the baseline thru where the two segment lines cut the quarter-circle until they intersect the boiler arc.

Mark out a line equal to the circumference of the dome base (right diagram) cut it into twelve segments equal to the cord of quarter-circle segments, the height of each line is equal to the respective numbered line extending from the baseline to the boiler in the left diagram.

If I've got it wrong somewhere along the line I'm sure that Rick Marty can straighten me out.
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