Scales question: inner edge

[2bit_collie]

Attached is a photo of my latest scales

still a work in progress, I need to round over the edges, but the outline is basically done and I’ve sanded out the bandsaw marks from the faces.

my issue is pretty clearly visible. My only power sanding tools are a hand sander (intended for flat surfaces) and a Dremel. The hand sander works great for establishing a nice arc on the convex edge, but it doesn’t excel on the concave edge. It’s too flat. And the Dremel is too small in diameter. So the concave edge tends to look like several straight lines connected by shallow corners.

when cutting from a big sheet of material, eg acrylic,I can usually cut a nice arc with the scroll blade in my jigsaw. But I have to cut in sections when cutting the scale from a 1”x6” blank.
Any suggestions on how to refine the concave curve?

 

[Darth Scandalous]

I've used 80 grit by hand with mixed results. I cut the scales with a coping saw, with one edge clamped to the edge of the bench, and just loose enough that I can rotate the piece as I cut it. I let the spine of the saw ride against the side of the bench to keep it plumb and stable. Getting a good shape cut first helps obviously.

I've also tried using a small, sharp round file to refine the curve. I think carefully blending out the straight lines with 80 grit has worked the best. But none of them have been perfect.

 

[LJS]

Doing by hand is the safest. First, spending time to make a nice clean cut to start saves lots of time. But you have plenty of options. Rasps, files, or/and coarse sand paper to start and shape. Don’t waste you time with anything too fine. The more grits you use in a progression the less work you will have to do, less time spent, and nicer end result. Good luck

 

[H Brad Boonshaft]

Yes, you never cut to your finish line. Cut to a rough demotions, rough line.

When cutting with a hand coping or jewelers saw turn the blade. Make a bird’s mouth table that clamps to a table or work bench for unlimited rotation and flexibility. Small table with V notch.

Then glue them together with Scotch double stick tape and with paper template glued to outside, sand or scrape to final shape together. You should have glued them together before you drilled your holes to ensure they will line up. Once glued they stay together until finished. There is also less risk of breakage as they are twice as thick.

Plastic files and scrapes well, scrape with a cabinet scraper, sharp knife or make a scraper from a putty knife, file the edge sharp. Bring to finish size with sandpaper glued to sticks. Finish with sandpaper wrapped around a wine cork sanding to 1k.

 

[Gamma]

Generally, I cut the basic shape 'out side the lines' with a dremel using either a cut off disc and/or a sanding drum. Then usually shape the 'top' curve with a file, cut the basic exterior 'bevel' with a sanding drum, and then finish by hand.

 

[alpster]

If you have a drill press, use a cheap large diameter sanding drum. Works a charm.

 

[H Brad Boonshaft]

You can buy an inexpensive 1X30 belt sander,(under $50), The same sander is sold under a number of brands. There are tons of quality belts available for this sander.

You can sand and shape a pair of scales in minutes with one of these sanders. There are also a bunch of videos on “tuning” these sanders to make them run smoother with just a bit of hacking.