Sliding DT's...tapered? not tapered?

[Scott W]

I am making a tv shelf this weekend and want to use my new (to me) DT plane. I was watching/reading and it seems some do and some don't taper them. Is ease of assembly the on reason?

Thoughts?

[Steve N]

Maybe I'm not understanding what you mean by "tapered"



The good news is, because of how they work, they can be entirely functional, and you only need to taper one half, and they will still operate the same.




Otherwise you just have a dado.

[Martin S.]

I don't think that's what he meant.

Some folks taper sliding dovetails along the length of the joint.

Some don't.

I think the taper is to help the joint slide together.

I think Chris Becksvoort just puts glue on the last couple of inches of the joint on each end. I am not sure if he tapers or not.

I have never made this joint, so I am interested as well.

[YSU65]

I did tapered sliding dovetails for an assembly table. I saw this used for a rough assembly table in Lake Placid. This was not 'Fine Woodworking.' I just wanted to do them. The top was done with two identical halves. I cut the dovetail and slot to be tight. I then tapered the dovetail to be tight at the back with a hand plane, looser at the front. I drove in the DT's into one side then the other. Tight in center, loose at edges to allow for expansion. I tapered the dovetail, not the slot as is normally done. This not not something you could do if you want to drive in from the back. The table is 'rustic' but is very strong.

[Derek Cohen]

That's not a sliding dovetail.

A sliding dovetail tapers along the length of BOTH socket and dovetail. It only require a small amount of taper, perhaps 1/8" over 24". Sliding in the dovetail, it will be loose until the very end of its length, when the two sides come together. Then it tightens up.

My preference is to use tapered sliding dovetails for anything over 4". On my Lingerie Chest, all the case joints are sliding dovetails. However, these were under 4" (and some were gang cut), which resulted in parallel sliding dovetails. They slide together more easily if you use hide glue.

Regards from Perth

Derek

[Anji12305]

Frank Strazza has a nice video of making these by hand.

They're not difficult, they're fiddly.
I've made four this way, and they work as designed.

The neat part about this joint is that it is mechanically strong; you might not even need glue (although I dab a little in the narrowest confine of the groove to be cut).

I like to leave the tailed section a little 'proud' to get the faces flush
with a plane after assembly.

The video linked is long, but there are no jump cuts or hidden steps.

Around 13:00 the critical transfer marking steps are shown.
(That's where I make my mistakes, EVERY time.)

https://youtu.be/8g0QA2Nwkc0

[ac445ab]

Anji12305 said:

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Frank Strazza has a nice video of making these by hand.


https://youtu.be/8g0QA2Nwkc0

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Thanks for this, a very well done video.
With longer sections my be could be easier cutting dovetails by a dedicate plane rather than a saw. Also I think a plane is easy to use for adjusting the male for the final assembling of the joint.

[Derek Cohen]

I have made a few dovetail planes, as has Giuliano. My latest is a modification of a Stanley #79. and the easiest of all to use. Plus it does both male- and female sides.





More details here: http://www.inthewoodshop.com/Furniture/S...ls-LC.html

Regards from Perth

Derek

[wmickley]

Generally hand made sliding dovetails are tapered and machine made sliding dovetails are not tapered. I think tapering might be a little more awkward by machine. A tapered dovetail can be a made little tighter because you don't have to slide it all the way in while it is as tight as it is going to get.

Short joints of this type, like on the ends of rails between drawers, are usually called dovetail housings and are not tapered. And sometimes we make a shelf where there is a short dovetail housing at the front of the joint and a shallow dado the rest of the way back.

[Doug_H]

Scott,

Looks like you have received plenty of good advice.

FWIW I use a router to cut the "pin" board (the dado) and a plane to cut the tail board (shelf). Yes, I know this is hand tool forum. I hog out the neck diameter in the pin board with a straight bit before cutting the dado to relieve the pressure on the router bit (DT bits are surprisingly thin at the neck, as you can observe.) That makes a non-tapered dado, so I taper the DT itself slightly. Tapering the dado with a router is do-able but not worth the fuss in my opinion.

My real reason for adding my two cents is this: these joints are fiddly, as an earlier post said. They are very prone to jam before they close all the way. In my experience a "perfectly" fit joint will jam after the glue is applied, if for no other reason that the friction will make the glue grab. Then, after a few moments, if the joint is not together, the glue swells the wood and the big rubber mallet has to come out. (Am I disclosing too much here??) That's the deciding factor in whether you should taper them. A mostly dry joint with a bit of glue at the end that goes in last is definitely a good idea.

Happy dovetailing

Doug