Template sanding bumps

[bradleyheathhays]

I'm brand new to making templates and I'm finding out making a good one is not as simple as it looks. Luckily I've got the Ridgid oscillating edge belt/spindle sander to make it easier for me. My problem is making smooth inside arcs. After about an hour of practice my outside arcs or curves are nice and smooth, but my inside curves feel lumpy when you run your finger down the edge.

What I figured out that got my outside curves smooth out was that almost all sanding passes must be made as long as possible. I zeroed in on flattening down the proud parts by doing long passes and keeping a steady speed, but then doing a gradual application of pressure at those sections. I applied this technique to my inside curves but because I have to work on the curved part of the sanding belt I'm not able to get the same effect. I'm sure it's because the flat part of the sander is more forgiving than the curved part which has a much smaller sanding 'foot,' or contact patch I'll say. I've tried to lessen this effect by keeping my approach angle as shallow as possible but this still isn't producing the smooth edge I'm after.

So what am I missing? Do I just need to keep refining my sanding technique to be even lighter and sneak up on the template edge even slower doing more long and shallow passes? Or is there some kind of technique out there I haven't run up on yet?

I'm using 3/4 melamine for making this piece. Paper template is on the bottom side for the pic.

 

[Ron Swanson Jr.]

You may want to try a spokeshave or an oscillating spindle sander for that inside curved profile. 

[Mark J]

Try switching the Rigid to spindle mode.  Try filing with a half round file.

[pkinneb]

 I would use a long board in my case a 1/8" piece of hard board 3" x 20" with self adhesive sandpaper on the back and a handle on one end, for this looks like a shorter one would work, it really helps to even things out. Let me know if you want to see a pic and I can post one later. Now I use my Shaper Origin so not really a problem but the long board was a lot cheaper solution.

[wtnhighlander]

What @pkinneb said. Get close with the sander, but switch to a flexible sanding strip to get the fairest curve. Follows the general curve, removing the high spots, much like a jointer plane follows the general "flatness" of a board and removes high spots.

[Chestnut]

What Pkinneb and Wtnhighlander said above. Video for reference and ideas.

https://thewoodwhisperer.com/videos/flexible-sanding-strip/

[Ronn W]

I use a spindle sander for both inside and outside curves (don't have a belt sander) and I can get really close to smooth but a flexible sanding board that can bridge across the low spots is necessary for final smoothness.

[gee-dub]

On that nice, open curve I would spoke shave if your template is MDF, file otherwise.  Once close, a flexible sanding block can help you fair the curve . . .