How to make this angled sliding DT joint?
#21
(01-22-2017, 09:59 PM)atgcpaul Wrote: Yes, a horizontal router table seems like the way to go for the male DT.  When I'm cutting the DT shoulder on the "inside" face, won't the piece be trapped between the bit and table?  Maybe if I cut most of that away first on the table saw, it won't be as much of an issue?


Yes, but it does not present a real problem.  The work piece is securely held to the X-Table, which has enough mass to prevent the bit from wanting to climb cut.  I offer these as proof:  

[Image: A0kG5k0gBXIlLHF6sEOLTwwZPmwieF15qC3Pr_LV...38-h628-no]

[Image: cSqaAdfyO73_j3O19HUSvkFduE0ySFo2I22c8j2D...38-h628-no]

Note that on one side you actually are climb cutting to make the stopped cut, yet it was safe to do. 

John
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#22
You might be able to have flat top rip blades ground to, say, 5° and 10° or whatever angles you require. I think you could cut both parts quite accurately with the proper jig set up.

I use a blade ground to 7° for mass producing dovetails. I like it much better then a router plus I can set the location wherever I want. Then I cut the pins by hand.
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#23
First thought that comes to mind is that you could end up with problems with short-grain if you don't shallow out the angles more.  And depending on the angle the cross-pieces are to intersect, you may need two different angles for the dovetail to minimize short-grain.

Looking at the picture of the table you linked, is there room instead to use a mechanical fastener which could be accessed from the underside?  A miniature version of a handrail bolt perhaps?  Use a dowel to align and prevent twist at the top and a miniature handrail bolt at the bottom.  Or if you still wanted a little bit of visual interested at the top, just an angled housing joint to align and prevent twist with the bolt providing the compression to keep it all together.
Don't sweat the petty things and don't pet the sweaty things. -- G. Carlin
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#24
(01-23-2017, 10:49 AM)Rob Young Wrote: First thought that comes to mind is that you could end up with problems with short-grain if you don't shallow out the angles more.  And depending on the angle the cross-pieces are to intersect, you may need two different angles for the dovetail to minimize short-grain.

Looking at the picture of the table you linked, is there room instead to use a mechanical fastener which could be accessed from the underside?  A miniature version of a handrail bolt perhaps?  Use a dowel to align and prevent twist at the top and a miniature handrail bolt at the bottom.  Or if you still wanted a little bit of visual interested at the top, just an angled housing joint to align and prevent twist with the bolt providing the compression to keep it all together.

Rob, yes, I have some of the same concerns regarding the short grain.

I didn't mind the challenge of figuring out these angled DTs, but I think the solution you describe will accomplish what I want and not bother me too much that I chickened out.  At least I can get it done sooner.  I will make several angled mortises using the Domino and the tenons should prevent twist.  I'll find a cam fastener to keep them together.
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#25
Here is a sketch of the jig I tried to describe.  It's pretty simple to make and will easily and safely cut the dovetails on the end of your parts. 

[Image: n8XKHwSdEVZ60541NCe4TCfxo5JU7NgSAvw3Edkn...06-h455-no]


[Image: l42TkeLrLLj1aIUe_RKdOK2dYV7WcE_vKVvRiLUi...06-h455-no]


Mount the angled fence at the angle you need.  Cut off the end of your workpiece to the angle you need and slide it up against the bottom of the top piece and clamp it.  The slot in the top is sized for an appropriate sized guide bushing.  You'd have to bore an access hole at one end of the slot to insert the bit down through the top.  I was too lazy to draw that.  You would cut one side, then insert a spacers between the workpiece and angled fence, clamp it, and then cut the other side.  With just a little bit of trigonometry you can calculate how wide that spacer needs to be to fit the female dovetail in the mating part.  Fine tuning can be done with paper shims.  

John
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#26
(01-23-2017, 12:50 PM)jteneyck Wrote: Here is a sketch of the jig I tried to describe.  It's pretty simple to make and will easily and safely cut the dovetails on the end of your parts. 

[Image: n8XKHwSdEVZ60541NCe4TCfxo5JU7NgSAvw3Edkn...06-h455-no]


[Image: l42TkeLrLLj1aIUe_RKdOK2dYV7WcE_vKVvRiLUi...06-h455-no]


John

John, a picture really is worth a 1000 words!  I think you could have typed out a 1000 words and I'd still be scratching my head.  Reading comprehension was never my thing.  Thank you for taking the time to post those other pics and sketching this out.

Now you've got me thinking that this sliding DT thing is still doable.  At least I've got options.

Thank you everyone,
Paul
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#27
(01-23-2017, 10:15 AM)atgcpaul Wrote: Ha Ha!  Understatement of the year!





I want to make this coffee table (You've got to scroll about half way down the page).  http://www.archiexpo.com/prod/bark/produ...02726.html

I have a rectangular piece of glass so that's why the cross pieces won't meet at a 90deg angle.  I want to be able to pack it flat for storage and transport so that's why I don't want to assemble it as half laps.  The idea is to glue one whole loop together and that would have the female DT slots.  The other loop would actually be in two pieces and have the male DTs.  Come assembly time, the two halves would slip upwards into the slots.  From above it would look like a half lap joint.  From below I'd route a recess to receive a metal plate to prevent them from sliding out.

One alternate idea I have is to join them with half laps, but leave the bottom stretcher of one loop unglued.  I plan on joining the loops with Dominoes.  The bottom stretcher could be screwed to its uprights from underneath.  The only reason why I don't want to do this is for the "feel".  I know if I were to see this in a showroom, the first thing I'd do is go check out the half lap joint.  Then I'd run my hands across the joints where the stretchers meet the uprights.  Personally, I would not want to feel any bump or divot in the transition.  If I leave the stretcher "loose", I think over time I would feel it.

Yes, I have a little OCD.

Paul

Ok that gives a reason for why, but I still like the more than one way to skin that cat school of thought. I've actually seen a table much like this with a wooden top that was meant for breakdown, and used hinges close to the finished woods color to collapse the legs, and in that case it was also hinged to the top so the legs folded down onto the top. With glass that last part will be difficult. But if you had a horizontal mortising platform you could have a lot of fun.
Big Grin

I still don't get any $$$ for saying this, but John's is a very nice platform, and as you can already see the Customer Service, and Tech desk are as good as it gets
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Worst thing they can do is cook ya and eat ya

GW
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#28
I finally went and looked at the table you want to build.  I would not use sliding dovetails to join where they meet in the middle; they won't provide the stiffness needed.  I would use half lap joints as others have suggested.  Of course to do that and still be able to brake it down flat for storage, you can't glue up one of the frames.  So, I would make the joints as half laps and join them with screws from underneath.  One frame can be glued up completely.  With the other only the top cross bar and two side legs would be glued up.  The bottom cross bar would be joined by a dry fit Domino or other loose tenon with a very snug fit and a screw from the bottom.  Alternatively, you could install a threaded insert in the legs and use a bolt instead of a screw. 


John
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#29
Quick update on my progress.  All the joinery is done and I'm at the finishing stage.  I've got some sap wood I want to color match but everything else is cake at this point.

One half of the base is secured with bolts and threaded inserts.  The dominoes keep everything nicely aligned.

If your kids ever ask you why they need to learn trig (or at least need to know how to Google search a refresher on it), tell them it's for cutting angle half laps.


   


The base is upside down.

   


Paul
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#30
Looks like a great job from here.
"I tried being reasonable..........I didn't like it." Clint Eastwood
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