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View Full Version : Help on best way to do a quarter radius joint



kyle85
6th May 2014, 07:24 PM
Hi guys, I have taken on a challenge as i am still a newbie with wood lathes. a friend has asked me to make a cabinet for him but with round corners. I found a pic and i have a pretty god idea how i will have to go about this but any advise would be greatfull. Here is a pic of something similar to what i will be making.

malb
6th May 2014, 07:41 PM
Any ideas on overall cabinet size (overall W, D, H) and radius (internal/external) for the corners, shelf thickness etc? These would help ensure that suggestions made were appropriate to your circumstances. Maybe a bit of info about tools and machinery available for the task would help as well.

IanW
6th May 2014, 07:55 PM
The only way I can see a lathe being part of the act would be to turn a cylinder for the 4 corners. Now this will be a bit tricky, especially for a newbie. The simplest way is to glue up four square bits of wood, with paper in-between the joints to allow easy separation of the four pieces after you have turned your cylinder. Hollowing out a large cylinder is not child's play, and will need a sturdy chuck & some heavy-duty tools. You will also end up with the grain running along the quarter-circles, which will mean it is probably running the wrong way for the sides (assuming they are regular boards. To get around this, you really need to make up your 4 pieces with the grain running cross-wise. This is not technically a problem, but you will probably have to glue up several blocks to get the width.

Good luck,

Hermit
6th May 2014, 10:03 PM
Interesting, and not as easy as it first looks. It's not really a job for the lathe, I reckon. Always stand correcting, though.

Those dimensions would help, but I'd be looking at maybe a segmented glue-up, then rounding the inner and outer radii to a compass-marked line with a bandsaw then a large disc sander and large drum or spindle sander. To get the depth, you might possibly need to do each corner in two thinner pieces then glue it up, finishing with hand sanding to blend them.
The outer radius sanding could be done on a large disc on the lathe with paper glued to it. An impromptu 'table' on the lathe bed would keep things square.

Just tossing around ideas. There's probably an easier/better way.

Just looking at the original again, it's very thick. Possibly it's hollow, assembled from thin pieces at the front and back sandwiching blocks for the curves, then sanded as above.

chuck1
7th May 2014, 06:42 AM
I have seen a technique where you bandsaw wedges out so it will bend and once the radius is achieved it then needs to be glued and clamped. It would involve full scale drawings and a really straight cutting bandsaw.

IanW
7th May 2014, 08:47 AM
.....Just looking at the original again, it's very thick. Possibly it's hollow, assembled from thin pieces at the front and back sandwiching blocks for the curves, then sanded as above...

Steve, I noted the apparent thickness, too, & thought it could be built as a frame over which thin bending ply or layers of veneer have been glued. If done carefully & all joins neat & tight, the paintwork would hide it all. If I were making it, & depending on the actual dimensions, I think that's the way I'd go about it, rather than turning the corners & using solid-wood joinery. Requires less gear, & the end result would be a bit more portable. There are obviously several ways it could be done, though....

Cheers,

Hermit
7th May 2014, 09:08 AM
Steve, I noted the apparent thickness, too, & thought it could be built as a frame over which thin bending ply or layers of veneer have been glued. If done carefully & all joins neat & tight, the paintwork would hide it all. If I were making it, & depending on the actual dimensions, I think that's the way I'd go about it, rather than turning the corners & using solid-wood joinery. Requires less gear, & the end result would be a bit more portable. There are obviously several ways it could be done, though....

Cheers,

Of course! I got it half right, (and half wrong) - was thinking of ply for the front & back, but didn't consider bent ply for the curves.

Full marks, Ian, I'd lay odds that's how the original was made. All said and done, it looks way too thick to be solid.

Charlie was pretty close, too, with his idea. A miniature version of that method, (saw cuts then bending), is used inside acoustic guitar bodies, where the top and bottom meet the front and back, to strengthen the joints.

Simplicity
7th May 2014, 11:28 AM
I would use the kerfing method
Google pics will help there
One large board with the kerfs at the corners
Then a lipping put over the top and routed off later to the kerf line
Sorry I'm at work
Can explain more later if needed