Dovetail issue.

[Ollie78]

Hi

I have a couple of small dovetailing issues.
I am making a toolbox using 20mm thick hard maple, 2 boards glued together to get the required width, having cut all the pieces to size I have hand cut the dovetails.
The first question is how tight should the joints be ? currently I can tap them together about half way in with a bit of force, they begin to squeak and bind up at this point, of course I know that really they should only go together once for a good joint.

Should I make them looser so they slide together or trust that when I clamp them up they will go in ? I am a bit worried that I could end up stuck at three quarters in and can`t move them in or out...

The other thing is that since I cut the panels and joints some of the boards have developed a slight cup. Only very small but it is causing a problem lining up the joints . Is there any tricks to getting the joints in? I am hoping that when I assemble the case the joints will `pull` the slight cup out. Is the slight cupping causing the tightness issue ?

Any advice appreciated, I don`t want to cock it up as the wood is not cheap and I have already invested a lot of time in cutting the joints.


Ollie

 

[Teckel]

First of all your dovetails should be a nice snug fit from start to finish. If it was me I'd loosen them up, if you don't you will most likely end up breaking or chipping your tails.
If the boards are not cupped that much I wouldn't worry about it. Once you put some glue on that joint.....I'm telling you lad it ain't going anywhere. Just tidy up the bit of cupping when glue has set.

 

[Jacob]

Yes cupped boards will probably pull in. You could ease your joints where they bind perhaps. Look closely for the shiny patches.
But I'm afraid you might have to waste a bit of wood before you get your technique it right, everybody else does believe me! Or put up with you first DT job looking like "his first DT job". A lot of my things look like that. :roll:

 

[wcndave]

Remember that white glue is water based and will make the wood swell slightly, so better a tiny bit loose than hammering it in. Otherwise by the time you've spread the glue on all pieces and ready to go you might need severe force.

 

[thick_mike]

I had a similar problem with one of my first projects in reclaimed sapele. I ended up forcing the joint together and splitting the wood in half due to mis-alignment of the pins and tails! I had to disassemble the joint, glue along the split and then ease the pins. These Internet gurus make it look easy! After I'd watched ten or twenty of the speed dovetail videos, I thought, "how hard can this be?"! It really is worthwhile practising on some scrap wood and making sure the wood is a consistent thickness and square all round before you start. The gurus seem to gloss over the preparation part, but it's the most important bit if you ask me, it's really hard to make a good dovetail joint with wood that's varying thickness and not square at the ends (I can show you plenty of examples of how it goes wrong!!).

 

[Ollie78]

Thanks guys.

Excellent advice I will ease them up a bit at a time. I think it might be because the few dovetails I did for practice were on much thinner stock (10mm ish ) so went together easier.

I will post pictures when I finish it ( if its not too embarrassing !! )

Thanks again

Ollie

 

[AndyT]

A sensible question not often raised. At school, we only learned to make joints on cheap pine. When I first cut dovetails in harder wood (mahogany, ash) it was a revelation - it was much easier to get an accurate cut in the right place, but if I didn't the joint would not work - the soft pine was so much more forgiving / crushable!

One old book I read described a 'technique' of cutting the pins a bit skinny and a bit long and then hammering on the ends to spread the fibres - it called it 'bishoping' the dovetails. Not a high-class technique, I think.

 

[Jacob]

...
One old book I read described a 'technique' of cutting the pins a bit skinny and a bit long and then hammering on the ends to spread the fibres - it called it 'bishoping' the dovetails. Not a high-class technique, I think.

Sounds good to me. If it looks high class it is high class IMHO.

 

[monkeybiter]

Wouldn't it work loose after a relatively short period of time?

 

[katellwood]

Its obvious you are talking about dovetails for a wide area, e.g. for a chest or similar.

In my experience when dovetails are tight when you put them together there is often a tendency for the fibres/grain to roll up here

and make the ends of the tails unsightly

If circumstances allow I always make the pins 3mm longer than the tail board then put a small chamfer on this 3mm which guides the tails into the sockets and alliviates the roll up e.g.

you just clean off this 3mm when the box is glued up

heres a couple of pics where I have used this technique on a previous project

 

[Ollie78]

Hi guys

Well , I managed to get all the joints to slide nicely together with hardly any pressure. I dry assembled the box, made sure it sat square and nice. Great, I thought. I will now glue and clamp it together.

When I came to assemble it with the glue on I could not get the pins to seat correctly so now I have crappy joints. I thought about taking it apart again but the glue has started to dry.

Any idea as to why this has happened ? It will still function but it will never be `good`, yet it was quite good when dry assembled.

This is very annoying...


Ollie

 

[Jacob]

I guess that they have expanded with the glue, faster than you've been able to get it together.
Now is the time to carefully cut off the corners (over a TS?) and try again for a smaller box!
Not being sarcastic - bin there dunnit. Learning curve.
Photos?

 

[Benchwayze]

Ollie,

If your tails are okay, just cut off the pins and start afresh from there and accept a shorter carcass.

If it's too late for that, start from fresh, re-cut the four joints and accept a smaller carcass all-round, as already advised.

No need to waste the timber.
HTH

 

[monkeybiter]

Have you made pencil marks [or similar] so you can't mix up your sides/ends; it's easy to fettle the joints and dry fit, then when the glue's applied you reassemble the opposite way round and it no longer fits properly.

 

[AndyT]

Ollie

What glue did you use? A lot of PVA is aimed at builders and boasts of only needing 10 minutes to set. That is not long enough to work around a box, especially if it's your first time - it's possible that by the time you got the clamps on, the glue was already getting stiff, and would not allow your joints to pull up tight. I've taken to using Titebond Liquid Hide Glue because it has a much longer open time.

 

[Mr T]

Hi

It is important to ensure that the bottom corners of the pins and tails are nice and clean, it is surprising how a little nib in the corner can prevent the piece seating properly.

Now I might be accused of heresy here, but I usually put my dovetails fully together just once before gluing up, just to check for this problem. Hope I won't get banned from the forum!

Chris

 

[Jacob]

Hi

It is important to ensure that the bottom corners of the pins and tails are nice and clean, it is surprising how a little nib in the corner can prevent the piece seating properly.

That's why traditionally the pin holes are always over-cut, so nothing can remain in the corner

Now I might be accused of heresy here, but I usually put my dovetails fully together just once before gluing up, just to check for this problem. Hope I won't get banned from the forum!

Chris

That's absolutely appalling! :roll: Ban ban!

 

[woodbloke]

Now I might be accused of heresy here, but I usually put my dovetails fully together just once before gluing up, just to check for this problem. Hope I won't get banned from the forum!

Chris

Now that really is a banning offence! You should be ashamed of yourself Mr T, not that I'd ever do anything like that...sometimes :-"

On a serious note though, I usually pull them up around half way and make a mark with a pencil of any that are really squeaky and where the wood is shiny when it comes apart...the pins ONLY can then be pared a smidge until you have a firm fit. It's also relatively easy to see at this point if all the cuts are parallel on the pins and again, easy to adjust at this point. As for glue, most PVA's have an open time of anything from 10 to 20 minutes, which isn't really long enough for a complicated glue-up, 'specially in hot weather. I've re-tried Cascamite recently which has an open time of around 45-60minsish and is much better, giving you more time to get things together

Edit - excellent piece in the latest edition of F&C about correcting d/t issues - Rob