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How do I make a corner radius on a NON-90-DEGREE corner???

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Forum topic by RGKeen posted 01-31-2018 05:17 PM 4165 views 0 times favorited 24 replies Add to Favorites Watch
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RGKeen

3 posts in 24 days


01-31-2018 05:17 PM

Long time lurker. I’m by no means as good as most of the folks here, so I use this as a “textbook” for building skills. I can usually figure out some way to do things with my rudimentary skills and marginal equipment, but this one has me stumped.

I ran into the need to make a radiused edge on a transportable wood cabinet that is not a 90-degree corner. I only need to do a few of these, so it’s not something that I can afford to go buy equipment to make, and my local commercial cabinet makers don’t want to bother doing it for me for less than the gross national product of a modest sized country.

The cabinet is trapezoidal. It’s ~26” at the widest extent on the bottom, but only ~23” wide at the top. The sides slant in by 11.75 degrees, and need to have a 0.75” radius on the four corners. I got the non-square fingerjointing to make the case figured out, but I’m stumped about how to make decent looking radiused corners.

Here’s what I’ve thought of first:
- do it all by hand by rasp and sandpaper; OK for starters, but no two radiuses will be the same, and it will be visible.
- use a belt sander and sheer artistry and finesse to make the radiuses by hand; same issues as above, but now power equipment lets me ruin wood faster.
- use the inside of a 1-1/2” PVC pipe as a round-template, gluing in sandpaper; the inside of schedule 80 PCB in 1-1/2” is 1.5” diameter, 0.75” radius, and I can split this on the table saw to a sub-90-degree section to act as a concave holder for sand paper to get consistency on the corners, if a lot of work
- Split an iron pipe length and grind the end to a sharp edge to cut the radii; My table saw has problems with doing this.
- make up some kind of jig I can temporarily attach to the cabinet that guides a sanding block along the length of the corner, and allows me to rotate it to sand the radius

I get to there and I’m stumped by the difficulties with all of these. I have this feeling that there is an “Oh YEAH!! That’s how you do it!” that I’m just missing here, so I appeal to the wood-gods. Any other clever suggestions?


24 replies so far

View Loren's profile

Loren

9981 posts in 3557 days


#1 posted 01-31-2018 05:24 PM

You want to put a round over on the case
corners, correct?

I would probably use a bearing guided
round over bit in a router to remove most
of the waste and complete it by hand. Coarse
cloth sanding belt glued to a length of flat
material makes a decent “sanding plane”.

Perhaps there’s something I don’t comprehend
about the effect you’re after though.

View bondogaposis's profile

bondogaposis

4611 posts in 2260 days


#2 posted 01-31-2018 05:37 PM

Rasp and sandpaper is the way I would go. You’d be surprised how good you could make them look if you take some care in doing it.

-- Bondo Gaposis

View jbay's profile

jbay

2006 posts in 808 days


#3 posted 01-31-2018 05:53 PM

Clamp a board to the face to use as a fence, and then use the router.

Let the base of the router ride the fence. Experiment! Take off a little at a time until you get the radius you like,
then you will have to finish a little by hand to make the radius flow.

-- If anyone would like to see my Portfolio, PM me and I would be glad to send you the link.

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a1Jim

116913 posts in 3486 days


#4 posted 01-31-2018 05:54 PM

Like Bondo said rasp and sanding or just sanding depending on what kind of sanders you have, your wise to stay away from a belt sander if you don’t have much experience with them. If you only have a belt sander you could make a jig to use it as an edge sander.
As far as making them the same radius it’s one of those things if it looks alike it is alike.

https://www.youtube.com/watch?v=zHmM5gRq0lI

-- http://artisticwoodstudio.com Custom furniture

View EarlS's profile

EarlS

751 posts in 2257 days


#5 posted 01-31-2018 06:01 PM

Part of becoming a better woodworker is learning skills like how to make a roundover on odd edges.

For 1/8” or smaller round overs, I just put some 180 grit psa sandpaper across my fingers and sand along the edge. The pressure pushes the paper into my fingers creating a nice rounded profile.

For larger round overs (1/4”) I typically use my random orbit sander with some worn out 220 grit paper. Start on one face and roll the sander over the edge until it is sanding on the perpendicular pace. Be careful to keep the ROS even along the edge or you will get an uneven round over. Hit it with some 180 sandpaper like I mentioned above to even things out.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

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a1Jim

116913 posts in 3486 days


#6 posted 01-31-2018 06:09 PM

Earl makes a good point about developing skills and gaining confidence in your skills, also the point he makes about how big a radius makes a big difference what approach you take to round over, small radiuses I just use a random orbital sander.If in doubt make the same kind of corners out of scape and practice rounding them first.

BTW Welcome to Ljs

-- http://artisticwoodstudio.com Custom furniture

View William Shelley's profile

William Shelley

538 posts in 1378 days


#7 posted 01-31-2018 06:11 PM

I wonder if this actually exists… I’m thinking the solution here would be to have a handplane that is profiled to do slightly over half of the roundover, like 48 degrees, and register against the workpiece. You’d run it one way to cut half the roundover and then the opposite direction registered against the other face to cut the other half of the roundover.

Not sure if that makes sense. Might be easy to make with a junk chisel and a grinder though.

-- Woodworking from an engineer's perspective

View dhazelton's profile

dhazelton

2689 posts in 2206 days


#8 posted 01-31-2018 06:13 PM

If the top and legs are not yet attached you can use a round over radius hand plane.

View Tim's profile

Tim

3734 posts in 1870 days


#9 posted 01-31-2018 06:23 PM

I’d use a hand plane, but wouldn’t recommend that if you didn’t already have one ready to do. Getting a round over close to round is easy if you keep the ratio at 5 passes at 45 degrees then 1 pass each at 22.5 and 67.5. Ok it’s easier just to think of taking off the corner at 5 passes and those two new corners 1 pass each. You’d be surprised how good that looks already, then a little sanding or scraping would finish it nicely.

Making a 1/4” radius scraper would also help even out the roundover made from sanding or a rasp. If you have a scraper or piece of an old saw, layout and file a 1/4” radius into one corner and use that to scrape the roundover. You may need to ease the edges of the corners to keep them from digging in.

View sras's profile

sras

4749 posts in 3038 days


#10 posted 01-31-2018 06:24 PM

One of the tricks when hand working a radius is to mark a line on each side that you can rasp/file a 45 degree chamfer. Then mark guide lines to file the ridges down. At this point you have 3 filed surfaces – hand work by eye/feel into a radius.

For a 3/4 inch radius on a 90 deg corner, the first pair of lines would be 0.44 inches from the corner.

After filing the chamfer, then mark a set of lines 0.16 inches from each side of the new corner.

Your numbers would be a little smaller since you are dealing with less than 90 degrees. But then you don’t need to be exactly at 3/4 inch radius.

-- Steve - Impatience is Expensive

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sras

4749 posts in 3038 days


#11 posted 01-31-2018 06:26 PM

Looks like Tim & I were typing at the same time! A plane is a better option than a rasp/file.

-- Steve - Impatience is Expensive

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summerfi

3821 posts in 1596 days


#12 posted 01-31-2018 06:44 PM

Agree with using a plane, but it must be sharp for end/cross grain work. A good sharp spokeshave would do the job as well. Follow up with coarse sandpaper on a wood block, then finer paper for finishing. The marking of lines to ensure consistent removal of material is also wise.

-- Bob, Missoula, MT -- Rocky Mountain Saw Works http://www.rmsaws.com/p/about-us.html

View dhazelton's profile

dhazelton

2689 posts in 2206 days


#13 posted 01-31-2018 07:06 PM

After re-reading how you made the carcass are you sure you can do a 3/4 inch radius WITHOUT exposing part of the finger joint? I’d do a practice piece first.

View MrRon's profile

MrRon

4638 posts in 3152 days


#14 posted 01-31-2018 07:50 PM

If I understand correctly, the box joints are on the 4 vertical corners and those are what you want to radius. Using a plane, you would be planing cross grain on the box joints. It would seem the joint fingers would get tear out from planing. I would just sand the corners to the radius and use a template to check the radius as you go. If you have a belt sander, that is what I would use. There really isn’t that much material to remove.

View jerkylips's profile

jerkylips

362 posts in 2479 days


#15 posted 01-31-2018 08:47 PM


You want to put a round over on the case
corners, correct?

I would probably use a bearing guided
round over bit in a router to remove most
of the waste and complete it by hand. Coarse
cloth sanding belt glued to a length of flat
material makes a decent “sanding plane”.

Perhaps there s something I don t comprehend
about the effect you re after though.

- Loren

I believe what he’s saying with the “sides slant at 11 degrees” part is that the vertical portion is not perpendicular to the top – so I don’t think a router is going to work.
(like this)

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