Rounding misaligned resin parts

[DeltaVee]

Afraid I know the answer to this question, but I'll ask: If you have a cylindrical resin part like the typical Star Trek warp nacelle, and the mold halves were ever so slightly misaligned, what's the best way to fix that when building?

You can putty the low side and/or sand the high side, but it will never be right, I'm guessing. And I guess it only looks worse if you draw or scribe on panel lines?

I've spent most of the past year getting seriously into resin kits. I've had fun. Recently decided to dip into my stash of Starcraft kits and am finding the above-mentioned issue.

[Johnnycrash]

You can putty the low side and/or sand the high side, but it will never be right, I'm guessing. .

Yeah, it will never be "right". But, if you do a little of booth, you can make it look pretty. A little putty, and a little sanding, splitting the difference.

[Romulan Spy]

It might be worth investing in a Flex-Frame. Basically a small aluminum frame that holds a narrow ribbon of sanding film. Using a plain flat file or sanding stick usually results in grinding a flat surface, something you want to avoid with those nacelles. The Flex-Frame follows the curvature of the piece.

[ajmadison]

Frankly, you don't even need a Flex-frame, albeit the idea is the same. The one thing you want to avoid is applying a flat sanding block against your seam. Long before Flex-frame existed, I was talking long strips of wet-dry sand paper and running them back and forth at a right angle to the seam, letting the paper wrap around the sides of the cylinder. You sort of need a third hand. Clamp the part in some sort of vice and use both hands for the paper. For example, take a dish cloth, wrap it around the end of the kit part/s and gently tighten a wood working clamp around the cloth, just enough to hold the model part/s. If the cylinder is hollow, clamp a section of evergreen or plastruct tubing, and stick, your part over the tube. Or, if the interior of the cylinder is exposed, but covered by an end cap, drill a hole into it, and drive a screw into the kit part/s.

I've done this with tank model barrels and have gotten a very credible looking gun barrel despite it being split down the middle.

You didn't describe the exact sub-assembly. Sometimes I just replace the cylinder, with a section of rod, tubing, or pipe, but then again I scratch build, so it doesn't require extensive rebuilding, I'll saw off the details and glue them to the replacement cylinder.

[DeltaVee]

Thanks. Thought I had a flexiframe but didn't find it. I may go the second route with the clamp and sandpaper. The trouble spots are domes, tapered cylinders, and leading edges, and I'm no machinist. I'll work with sandpaper, hit it with some primer so I can see better, and go from there.

[Kylwell]

http://www.flex-i-file.com/flex-i-file.php

One of the handiest things ever.

As to DeltaVee's question, short of chucking the object into a lathe there's no easy way to re-profile the mis-aligned part and even with a lathe you'd lose detail. I generally build up the low end and carefully sand it down.

[DeltaVee]

Mr. Moderator,
What is your technique with a flexifile? Do you hold the part in one hand and draw the file across the part like a bow across a violin?

[Kylwell]

Yes. You can flex the frame for more or less curvature as needed and angle it to get more pressure on an edge.

[Romulan Spy]

The ribbons are available in every grit from coarse to ultra-fine, and can be used wet or dry, very important for working resin.

[Mark Yungblut]

I aslo suggest you make a contour template for the piece. Tatke a piece of styrene and cut a hole and finish a hole with the inner diameter of your whole matching the exact diameter of the piece. Cut this in half and run it over the piece. Firt it will show you jus how far off it is and second you can use it to see if you have used enough putty to get close to the righ shape. Then as you sand stop periotically and run the gage down the length. Thsi will show you where to sand mor or less to get to the finished shape.

Hope this helps.

Mark