Tip: Edge distance around a rivet

[slngsht]

There are several places in the build, where there is a doubler with a rivet at the end, and plans call for the doubler to be trimmed to a quarter inch around the last rivet.

I used to cut the taper, then mark the curve around the last rivet, rough cut, then get at it with the sander to get the finished product.

While it worked ok, I never got a perfect curve.

Tonight I had a little time on my hand, and played around with this setup - worked perfectly out of the box.

DISCLAIMER: I have not looked to see if others do something similar - so if this is a d'oh post, sorry...

so, step 1, take a flat bar, drill a hole near the edge (maybe one for -3, and one for -4 rivets), then clamp it to the sander table. Distance from center of hole to sanding disk should match your intended radius.

https://scontent-iad3-1.xx.fbcdn.net...4f&oe=596EC72B

Put your piece in, insert a rivet, fire up the sander, and around you go. All you have to do is kinda rough cut to minimize sanding, and your starting point needs to be at the right distance.

https://scontent-iad3-1.xx.fbcdn.net...1e&oe=5938D1B9

Did a scrap piece to test it out.
https://scontent-iad3-1.xx.fbcdn.net...31&oe=593EF198

[tgmillso]

Whilst I appreciate your dedication to precision, and admire the ingenuity, I have an alternate solution for those seeking a slightly faster result (in the days of instant gratification). Not that I am one to talk, given that I have some stratospheric precision OCD problems myself, however on this one, I found that I don't even put the item on the sanding table most of the time, as I discovered (especially with an alclad part) that just the smallest piece of debris on your table will cause you to scratch the part. Thus what I do is reach for my tool draw and find a socket of the radius I want, use this as a guide to draw a line around the corner of the part, then hold the item free-hand as horizontally as possible and work the corner on the downward going side of the disc sander until you match your desired profile. Before you know it, you'll become so good at it you won't even need to get the sockets out to mark a line, plus you'll have no scratches on the bottom of your part. That said, if it was make-or-break precision I was looking for, I'd go with slngsht's solution.
Tom.

[rzbill]

That's a handy tool.

In my experience with toolmakers in the molding industry, there is a variation in skill level between those that can hand form a radius well and those not so well.

Here is a technique that might help those that want to do it by hand without a fixture.

Starting with a rectangular corner, decide what radius you want to impose and then grind off the corner until the flat you create is just shy of the desired radius. Finish with a couple of quick sweeps to nip of the small amount of material left near the tangent points.

The angle in the image shown below is 45 degrees but the actual flat length is practically insensitive to the fabricator being off a bit (like +/- 15 degrees which is a LOT).

I find doing it this way produces a much more uniform radius than one would get by "sweeping" from the beginning of the fabrication.

A bit of practice and this becomes quite easy in my experience.