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Dado vs sliding dovetail

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Forum topic by MarkCh posted 09-27-2020 11:08 PM 425 views 0 times favorited 17 replies Add to Favorites Watch
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MarkCh

20 posts in 113 days


09-27-2020 11:08 PM

Topic tags/keywords: sliding dovetail dado

I’m building a nightstand that will have a bottom panel for a bookshelf. Currently I’m planning on attaching it using a sliding dovetail because (1) I want to play with a new whiteside bit, (2) I want to gain practice in this for an eventual trestle table. (3) is much lower: add some stability over a dado.

Question is, is there a reason /not/ to do this? Particularly since the force will be downward on what will be thinner material relative to sliding into a dado (originally 5/4 oak stair treads that are being repurposed).

Any rule of thumb for depth/width of a sliding dovetail? Also, the bit is a 1/2” shank whiteside dovetail bit. Any suggestions on how to push this into oak?


17 replies so far

View Aj2's profile

Aj2

3422 posts in 2684 days


#1 posted 09-27-2020 11:20 PM

Sure why not sounds like fun to me. Ive done a few shelves with sliding dts. I put the dt on the end grain not the long grain side. The way you have your board sitting expansion will be left to right. If you use the end grain it will be front to back.
They are fun to make but beware they can be fussy either way you choose:)

Good Luck

-- Aj

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MarkCh

20 posts in 113 days


#2 posted 09-27-2020 11:21 PM

Ah, yeah, I had the board turned relative to reality—will be end grain dt

View Loren's profile

Loren

10720 posts in 4534 days


#3 posted 09-27-2020 11:39 PM

sliding dovetails are tricky to get right and if they’re too tight because you’re hurrying the wood can split or worse. Tracking down the high spots can be tricky and glue may be less satisfying at filling the gaps than you’d hope.

Consider the half sliding dovetail where one side can be fitted with a hand plane. You can scoop out the middle a bit so it’s tight at the ends if they show but has enough play in the middle getting the pieces together are easier. It’s like twice as easy as sliding dovetails, which are not easy imo. I’m a guy who goes for dowels though, having largely got over the appeal of fancier joinery.

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Robert

4058 posts in 2367 days


#4 posted 09-28-2020 12:03 AM

Do a tapered DT or you’re in for quite an ordeal.

-- Everything is a prototype thats why its one of a kind!!

View Rich's profile

Rich

6000 posts in 1475 days


#5 posted 09-28-2020 12:45 AM

I don’t get part 3. How is it lower?

Sliding dovetails for shelves offer the benefit of helping to lock the joint together. Other than that, a dado will do just fine in your situation.

Also, the dado doesn’t have to be more than 1/8” deep. Woodworkers often assume it should be half the thickness of the side panel, but that’s just a waste of material. In the case of a board with dadoes on each side, it also is impossible to do since you’re going to cut all the way through the board.

Joints like that are in shear stress. A 1/8” dado provides all of the support you need for that, regardless of the load on the shelf.

If you do decide on a sliding dovetail, work slowly and do test fits as you go. The wood will only split if you do something stupid like taking a hammer to it. There will also be no high and low spots if you cut it right.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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MarkCh

20 posts in 113 days


#6 posted 09-28-2020 01:20 AM

#3 is lower in priority than 1 & 2—both are probably strong enough to hold a book – that is in my hands while I’m standing on it.

I don’t intend on closing up the back, so I’m hoping the sliding dovetail can help with racking. The top is mitered dovetail and is decently strong.

View Rich's profile

Rich

6000 posts in 1475 days


#7 posted 09-28-2020 01:45 AM


I don’t intend on closing up the back, so I’m hoping the sliding dovetail can help with racking. The top is mitered dovetail and is decently strong.

- MarkCh

It really won’t help with racking any more than a dado would. It’s main function is to tie the two sides together. To prevent racking consider attaching a stretcher across the back, just under the top. It won’t show substantially, and will definitely inhibit racking.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View Loren's profile

Loren

10720 posts in 4534 days


#8 posted 09-28-2020 01:50 AM

I was thinking in a box form that small racking wouldn’t be a big issue. But I suppose I was thinking you would hang it on the wall to hold books or some other low intensity usage. It depends how you want to use it.

View SMP's profile

SMP

2678 posts in 791 days


#9 posted 09-28-2020 02:07 AM

I’ve always wanted to experiment with the sliding DTs but always been scared. I’ve made plenty of shelving units and other cabinets with shelves and have done dados with glue and brads and have never had any come apart. But i’ll usually add a stretcher as mentioned or something else that will prevent racking depending on what will be seen etc, could even be corner blocks. If/when I decide to try sliding DTs it will be on pine, cheaper mistakes and more forgiving.

View Rich's profile

Rich

6000 posts in 1475 days


#10 posted 09-28-2020 02:28 AM

I initially missed the grain orientation between the shelf and box side. Aj2 didn’t. He pointed it out in post #1.

If you choose to build it that way (you shouldn’t) then you really have no choice but to do a sliding dovetail. If you glue that shelf edge into the side along its full length—whether it’s sliding dovetail or a dado—it will fail due to the direction of the wood movement.

The reason you want to do the sliding dovetail is that you should only apply glue to about an inch or two of the joint, so the board can move by sliding in the dovetail. When you build something that way, you want to apply the glue to the front inch or two of the joint. That way when the wood moves it will do it towards the back where it won’t show. If you were to glue the back of the joint, then when the board moves, it will protrude and recede from the front and it will show.

If you try that with a dado it will be weak, since nothing about that joint ties the two together.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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MarkCh

20 posts in 113 days


#11 posted 09-28-2020 02:35 AM

Yeah, I took the picture in a hurry and neglected to hold the panel in the right orientation—it’ll be end-grain.

View Rich's profile

Rich

6000 posts in 1475 days


#12 posted 09-28-2020 02:41 AM


Yeah, I took the picture in a hurry and neglected to hold the panel in the right orientation—it ll be end-grain.

- MarkCh

You’re all set then. However, it is sometimes part of the design that requires that very cross-grain joint. You’d never orient the grain for a shelf from front to back because it would be weak. However, you will see some pieces like sideboards with the side grain running horizontally, and when you attach a shelf to it with grain running sideways, you will need to use the sliding dovetail and spot gluing I discussed above.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View Robert's profile

Robert

4058 posts in 2367 days


#13 posted 09-28-2020 02:29 PM

Don’t you’ll never going to get it tight enough to prevent racking unless you do a tapered DT.

Even with that, its asking too much. I would install a coupel reils top and bottom.

I sure hope you take the advice on tapered.

-- Everything is a prototype thats why its one of a kind!!

View JackDuren's profile

JackDuren

1344 posts in 1845 days


#14 posted 09-28-2020 02:49 PM

If you want to try dovetails and want the challenge then go for it. I did, went well and moved on to the things…

View MarkCh's profile

MarkCh

20 posts in 113 days


#15 posted 09-28-2020 03:47 PM

Very clean! I think my take home message from this discussion, and any real discussion that starts with an advice question, is to go buy some 5/4 scrap pieces and do a bunch of tests.

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