Build Dilemma

[rpd]

Plywood is also full of abrasive glue.

True, but very little wood would be being removed, and hand plane blades are not that hard to resharpen.

[reible]

Just for fun and because I can....

Here are a few graphical images show just one joint and the errors caused by being off by the indicated amount.

44_5.jpg (12.48 KiB) Viewed 4602 times

44.jpg (13.65 KiB) Viewed 4602 times

43_5.jpg (14.04 KiB) Viewed 4602 times

43.jpg (12.93 KiB) Viewed 4602 times

As you can see a minor error shows up pretty fast. You can then add things like the width of the board and if you are at a true right angle for the cut, the different lengths of each piece when more then one joint is being made. Things like how flat the wood is, a slight warp or twist and things change very fast. Layout and measurements have to be right on to come close to perfect.

So now I have to get on to some real work, watching TV.

Ed

[JPG]

1/16 over 3/4 is approximately a 4.8 degree angle.

Contributed from 8 sources = 0.6 degree each.

True enough. But the face width of the bevel is 0.75 * SQRT(2), which is 1.06", giving a 3.4 degree total angle.

With all four corners clamped, I was assuming that the carcase was squared up, and each joint had that 1/16" gap. Thus only the two bevels local to a given joint would contribute to its gap.

Yep overlooked that 'detail'. 0.4 degree each.

[Ed in Tampa]

Hi Dennis,

Actually this was a second attempt. The first was way off and I recut all the bevels after recalibrating my 45 degree stops.

For the shorter pieces which are 17 long by 14 wide, I just guided the short edges on the rip fence set on an floating table which was fairly close to the main table.

For the long pieces which are 48 x 14, I did notice the flex issue which was worse with all the weight supported on the rip fence which was almost to the floor on my first attempt. You are right that there's no good way to support this. I tried the adjustable legs that come with the 520, but they didn't really make a difference because I couldn't get them close enough to the low end to do much good. Ultimately, when I recut the bevels on the longer pieces, I switched to my Incra Miter 5000 sled (thanks again, Jack Wilson) and extended the fence and stop to support the bottom corner and clamped the piece firmly in place in two places along the long edge.

I like your tip on cutting slightly over acute. Maybe next time. Or a Festool.

" Or a Festool".
Now you are talking!
But before you jump go to Eurekazone.com and check out what they offer.
http://www.eurekazone.com/category_s/2054.htm

[algale]

I took the case apart to add a divider, which sits in a dado. When I put it back together for another dry fit with pipe clamps, I got all four corners to fit beautifully!

Then came the glue up. Total disaster (I'll post photos when I'm done).

How would you clamp such long miters? My method simply did not produce acceptable results.

[dusty]

Hi Dennis,

Actually this was a second attempt. The first was way off and I recut all the bevels after recalibrating my 45 degree stops.

For the shorter pieces which are 17 long by 14 wide, I just guided the short edges on the rip fence set on an floating table which was fairly close to the main table.

For the long pieces which are 48 x 14, I did notice the flex issue which was worse with all the weight supported on the rip fence which was almost to the floor on my first attempt. You are right that there's no good way to support this. I tried the adjustable legs that come with the 520, but they didn't really make a difference because I couldn't get them close enough to the low end to do much good. Ultimately, when I recut the bevels on the longer pieces, I switched to my Incra Miter 5000 sled (thanks again, Jack Wilson) and extended the fence and stop to support the bottom corner and clamped the piece firmly in place in two places along the long edge.

I like your tip on cutting slightly over acute. Maybe next time. Or a Festool.

" Or a Festool".
Now you are talking!
But before you jump go to Eurekazone.com and check out what they offer.
http://www.eurekazone.com/category_s/2054.htm

For Ed in Tampa (who seems to be hung up on Festool). http://www.festoolproducts.com/?gclid=C ... aQodW20NWA

[masonsailor2]

I agree with Ed. Facing the plywood edge will add strength to the joint and look nice. You could make the edge banding out of a contrasting wood which would add a nice touch. It sounds like you are set on a 45 degree miter but another option is to add a square piece in the corner and lamello the plywood to it. Again you can use contrasting wood for effect
Paul

[rpd]

Frank Howarth just posted this video.
Check out starting at 9:45, clamping a miter joint on long stock
[youtube]https://www.youtube.com/watch?v=B5uGpevRR_A[/youtube]

[algale]

Frank Howarth just posted this video.
Check out starting at 9:45, clamping a miter joint on long stock
[youtube]https://www.youtube.com/watch?v=B5uGpevRR_A[/youtube]

Thanks for posting this! Exactly what I was looking for!