[OP]
Contributor
I’m planning a walnut credenza build with the side/top joint being a half blind dovetail so the top is face grain all the way across. Is it a bad idea to do 1:6 half blind dovetails to make the carcass? The current plan is to leave about 1/4” lip which would make the dovetails only 1/2” deep on the side.
Should I change up my plan and buy some 5/4 or 6/4 stock for the top? Aesthetically as well as structurally.
Moderator
Please clarify...are you using the dovetails to build the carcass and then putting the credenza top on that or is the credenza top part of the carcase and will be flush with the sides? I think you mean the latter. Also, and I could be mixing this up, but I thing 1:6 is for softwoods and 1:8 is for hardwoods typically. To your other question, a thicker top could make the joinery easier, but it has to work with the proportions/aesthetics you want to achieve with the piece.
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The most expensive tool is the one you buy "cheaply" and often...
[OP]
Contributor
Hopefully this picture helps as this is roughly what I’m going for. I’m going with 1:6 for the steeper angle since the dovetails will only be 1/2” long. 1:6 will work fine for hardwoods.
IMG_9009.jpg
Moderator
Makes sense. The top thickness decision remains one of proportion and design. You can make it work either way. Don't think that you need to do small, closely spaced dovetails like in that photo, however. For carcases, it's not uncommon to use wider dovetails...again, it's about visual design since it will be strong once glued either way.
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The most expensive tool is the one you buy "cheaply" and often...
[OP]
Contributor
Thanks for the feedback. Aesthetically I’d like to keep everything made out of 4/4 stock. I just wanted a gut check that shallow dovetails wouldn’t be a problem from a strength standpoint. I’m likely going to do some variable spacing on the dovetails since they’ll be so visible.
Moderator
There are structural reason why dovetail angles for softwood and hardwood vary, but it's not an unbreakable rule. Since you're doing these by machine, you're limited to the angles of the tooling available to you. You actually could effectively use the steeper angle more easily if you made the dovetails wider like I mentioned. If you were doing through dovetails, which was/is a very common way to do carcass construction, it's not atypical to have very wide tails and very narrow pins. (hopefully, I didn't reverse the names since I don't do a lot of dovetail work) That's super easy to do hand-cutting, of course. Now if you're going to use a fixture to cut your half-blinds and it's not a Leigh D4 or similar, evenly spaced is most likely going to be the easiest to do.
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The most expensive tool is the one you buy "cheaply" and often...
[OP]
Contributor
I’ll be hand cutting these. It wasn’t specifically related to the tools themselves, so I posted this in general woodworking over the Neanderthal forum.
Contributor
3/4" is plenty as far as the dovetails are concerned. Aesthetically I think 1/4" is too much of a lip - I'd do more like 1/8" or 3/16". And I would use the 1:6 angle, keep the pins narrow, and make the tails wider (fewer pins). If you are going to hand cut them, might as well make them look hand cut instead of machine made.
If you are hand cutting them, I'd go with a 1:7 or 1:8 ratio so that they are more distinguishable as hand cut. I'd also suggest a ⅛" lip.
Mike
Contributor
+1 but I might go with a 3/16 lip.Originally Posted by Mike King
Mike
Go into the world and do well. But more importantly, go into the world and do good.
[OP]
Contributor
Thanks again for the input. I think the thinner lip is a good idea. I’m putting together a 3D model and a 3/16” lip does look better. I’ll model a few different options on dovetail layout and 1:6/1:8 ratios and get some more feedback.
Contributor
i am mostly in agreement with both Mike’s that posted, except I might push the lip to 1/4”, as I was taught the 1/3 - 2/3 ratio for half blind dovetails.
Contributor
My input if we are taking about the lip being the thickness of the wood at the end of the tails. I find it looks best if it’s slightly wider then the thinnest part of the pins. Never thinner.
I think the strength of walnut is going to be fine for 3/4 but the joint should very well made.
Half blind on wide cases is quite the accomplishment everything from squaring up the large panels accurate sawing then getting it all glued up square.
I been making drawers the past 2 weeks with Alder and poplar. White pine bottoms and drawer slips. I really enjoy dovetailing because I use set of saw and chisels dedicated fine joinery.
I lay out everything 8 degrees and use my chisels for pin width. I’m not sure if it’s 1:8 but it looks nice.
Good Luck on your build
Aj
Contributor
Better yet make samples in scrap!
Contributor
Hi Will
He strength from a dovetail joint lies with the mechanical construction rather than the glue area. Ideally, the strength would be increased by including more dovetails rather than fewer. Having said this, at the level you are working, it should be fine no matter what you do.
The construction really is more about the aesthetic than pure strength. I think both can be achieved with a couple of modifications to your layout - these are my personal preferences, and if you choose to do something different, it will not matter in the end.
Firstly, make the web as thin as you dare - this pushes the half-blinds closer into through dovetail territory, increasing the glue area. I also prefer thin webs. How thin? 2-3mm
Secondly, I like 1:7 for drawers and through dovetails, but as one goes smaller, the angles need to be enhanced, otherwise you end up with something looking like a inter joint. 1:8 would be the worst choice. 1:6 is your best ratio.
Thirdly, the tip of the tail looks better to my eye when it is narrow. On drawers I tend to make it close to zero. On cases I like 1/8”- 5/16”, depending on the thickness of the boards. For 3/4” I would probably go with 1/8” (3mm).
Fourthly, find a dovetail spread/number that looks better to you. More is stronger, but you probably have a strong enough construction to focus on the aesthetic. Do what pleases your eye.
Lastly, as an alternative in case ultimate strength is important. In which case, you need through dovetails as these maximise glue area. For cases, what gives this design a big tick over half-blinds is that you can mitre the ends. Mitres also offer an advantage at the rear for rebates (to hide the case back). Here are three such examples …
Regards from Perth
Derek
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