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How do I cut this joint with a compound angle?

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Forum topic by SimonSKL posted 01-12-2011 10:03 PM 5304 views 0 times favorited 17 replies Add to Favorites Watch
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SimonSKL

185 posts in 2699 days


01-12-2011 10:03 PM

Topic tags/keywords: compound angle tenon joint joining

I am planning to build a church pulpit with a design like this but I am foreseeing some difficulty in cutting the tenon joint at the top of the two supporting legs. The two legs are turned 15 degree from the vertical axis and the top is angled up (15 degree) from back to front as well as from sides to the top (~4 degree).

I don’t know how to calculate the compound angles but if my Sketchup drawing is accurate, the tenon joint looks like this: 14.5 degree from back to front and 4 degree from side toward the middle. My question is how can I cut this joint accurately using any of my power tools (table saw, band saw, or compound saw)? Any help would be appreciated.

-- Simon, Danville, IL


17 replies so far

View richgreer's profile

richgreer

4541 posts in 2534 days


#1 posted 01-12-2011 10:27 PM

This is very much like the challenge you face when making a box with splayed sides. However, this is more difficult because you want to make a tenon and not just have a clean end cut.

Once you get the math figured out you will want to make a cut on your table saw with the blade tilted a little and the miter gauge at the right angle. b.t.w. there are tables of numbers to help with the math.

Personally, I would get a clean end cut and then set up my router (perhaps with a jig I would rig up) to cut a mortise that is perpendicular to the end surface. Then I would glue in a loose tenon.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

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PurpLev

8523 posts in 3108 days


#2 posted 01-12-2011 10:32 PM

+1 for loose tenon using the material from the same board – will reduce the complexity of this joint by a significant amount, the only thing it’ll leave you with is cutting 1 compound angle using the TS by tilting the blade, and setting the miter gauge to a set angle.

would be interested to see how it worked out.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

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Loren

8294 posts in 3107 days


#3 posted 01-12-2011 11:13 PM

I wouldn’t recommend cutting such a joint with machines unless
you have a multi-router or similar machine. The tricky part is the
tenon shoulders. For just a one-off piece, I’d cut the joints by
hand personally. It’s not really that hard.

A loose tenon would be plenty strong two, as suggested, but
making the hole at 4 degrees is a complication as well without
a multi-router type jig, Leigh FMT type jig slot mortiser with a
tilting table.

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SimonSKL

185 posts in 2699 days


#4 posted 01-13-2011 12:27 AM

Thank you all for your input and suggestion. I agree a loose tenon is probably easier if I can figure out a jig to make a 4 degrees mortise at the end of a 1.5” thick board. Any suggestion on how to make such a jig?

I also need to think of a way to hide the microphone wire. At this time I am think cutting a channel at the back of one of the legs and then cover it with a strip of wood. But the strip has to be removable in case the wire needs to be replaced. Any suggestion on making the strip removable?

-- Simon, Danville, IL

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richgreer

4541 posts in 2534 days


#5 posted 01-13-2011 01:48 AM

This may be hard to describe in words but I will try.

For the jig I would make a 6/4 slab of lumber that is at least 2 inches wider than the table leg. I would make a cut at the 4° angle about 6” from one end. I would find some way (there are several) to place one piece on each side of the leg and clamp them in place such that the 2 pieces of the board and the end of the leg are all flush.

I would then put a strip of wood on the board you created parallel to the end of the leg and at the right distance from the leg that I could run the edge of the router against.

If you felt it necessary, you could put in a stop and start piece of wood also.

Go slow and take a small bite with each pass until you are deep enough.

Does this make sense?

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

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SimonSKL

185 posts in 2699 days


#6 posted 01-13-2011 02:38 AM

bentlyj, thanks for the picture. It makes it a lot easier to see how it can be done.

-- Simon, Danville, IL

View BertFlores58's profile

BertFlores58

1684 posts in 2382 days


#7 posted 01-13-2011 05:54 AM

This is a good challenge for making compound angles. I have experience in cutting a rhumboid out of square rods. I cut first the vertical axis without worrying with the horizontal. However I have to offset the cut already by lifting the board (by using wedges on the other end raising to correct angle. ) After cutting, take out the wedge then lay the board flat…. adjust the horizontal angle now by following the contour on the one you cut. I used Sliding compound miter saw. You can try cutting this rhomboid 60 deg.. but when it is laid flat from a square rod then you end up a set up of 45 degrees horizontal (y axis) and 35 degrees vertical (x axis) Hard to explain…

Once you find the exach angle of the cut then it is easier to cut the tenon… Make a complimentary plate inclined on the desired angle for the router base to run. This way you can cut the tenon.

I will experiment on this on the weekend if time warrants.

-- Bert

View bigike's profile

bigike

4048 posts in 2748 days


#8 posted 01-13-2011 05:58 AM

you should be able to cut something like that on the table saw, by moving the miter gauge and tilting the blade a few degrees

-- Ike, Big Daddies Woodshop, http://www.icombadaniels@yahoo.com

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SimonSKL

185 posts in 2699 days


#9 posted 01-13-2011 04:22 PM

Ike, what you described is true for cutting the compound angles at the end of the leg. What is difficult is cutting the shoulders of the tenon or in the case of a loose tenon, the mortise at the end of the leg.

-- Simon, Danville, IL

View TopamaxSurvivor's profile

TopamaxSurvivor

17654 posts in 3135 days


#10 posted 01-14-2011 10:44 AM

Edit: forget that. I mistook where the 4 degree angle is. Back tothe drawing board ;-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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TopamaxSurvivor

17654 posts in 3135 days


#11 posted 01-14-2011 10:54 AM

Looks to me like bentlyj has the solution.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View canadianchips's profile

canadianchips

2343 posts in 2457 days


#12 posted 01-14-2011 02:30 PM

These might help show how to on a table saw. My saw is a left tilt blade, the sketches are exagerated to try to help explain. You might want to attach a guide to your fence to help hold the legs at 90 degrees on the first cuts.
I am not sure what you have for a table saw.
Personally I would use dowel pins for this project. Much simpler & quite strong.

-- "My mission in life - make everyone smile !"

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SimonSKL

185 posts in 2699 days


#13 posted 01-14-2011 04:50 PM

Canadianchip, Thanks for the diagrams. Should I cut the 15% first on the table saw with my miter gauge before the first cut in your diagram? From your diagrams it seems once I set the 4 degree tilt angle of my saw blade, I can keep that same angle and cut the rest of the shoulders, correct? I will try to do some test cuts with scraps.

-- Simon, Danville, IL

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SimonSKL

185 posts in 2699 days


#14 posted 01-14-2011 07:51 PM

I did a little bit of virtual cutting on Sketchup. It seems for the third cut I will have to cut on the right side of the fence. I think the trick now is the height of the blade as well as the fence position in each cut to get shoulders on the same plane. I think this is quite doable for me. Thank you Canadianchip for the cutting tip!

After I cut the 15 degree, here is the first cut

Second cut

Third cut

Final cut

-- Simon, Danville, IL

View canadianchips's profile

canadianchips

2343 posts in 2457 days


#15 posted 01-14-2011 10:22 PM

Yes ,you want to cut the 15 degree at the top of each leg first.
One of the 4 degree cuts needs to be deeper than the other.
Sorry I ddin’t get back to you sooner, I am babysitting, WE needed NAP time here.

-- "My mission in life - make everyone smile !"

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