Bookcase: rescuing a disaster

[Andy Kev.]

I've recently completed a bookcase. The problems I had with it stem from the fact that the shelves are attached to the sides via wedged through tenons. The real root of the problem was that the wood is pine and I find it so difficult to work with. In this case the mortices looked more like exit wounds than carefully crafted bits of joinery. So I put the bookcase on the back burner while thinking about how to rescue the matter.

Eventually I thought I might be able to make a virtue of a vice. I marked shapes around the mortices and then used a router plane to get them to about 3 mm deep. I then glued pieces of aspen into the resulting shallow holes. The problem was that the pine had played up again and in places the junction of aspen and pine was a mess. So I got some 5 mm wide strips of mahogany (from an old boat building model kit), marked them across the joins, routed again and superglued them in. The results are just about acceptable:

And here it is "in use":

I don't quite know what the lessons are to be drawn from this (apart from the fact that pine is clearly the poor man's Wood From Hell and should be avoided) but there is a bit of decorative potential in the repair work.

 

[MikeG.]

Wedged through tenons in 20-ish mm thickness? It'd be nice to see some close-up photos.

 

[AndyT]

Thanks for posting this - it's nice to read about a project which didn't go quite as expected - I'm sure we've all had them.
In retrospect, do you think a simple housing would have worked better?

And btw, I prefer the contents of the bottom shelf to the others - no surprise there!

 

[Andy Kev.]

MikeG: Yep, 20 mm. I got the idea (which I modified quite a bit) from a plan in Woodwork, the complete step-by-step manual published by DK (3rd book in from the right on the bottom shelf) and their plan calls for 20 mm oak.

Do you think that is too thick for such a joint?

AndyT: I wondered if a sliding dovetail might be a better solution but having no experience of that joint, I wonder if it would be strong enough to take a shelf full of books. The contents of the bottom shelf needed a proper home and it was them that led me to want to build the case. I reckon that it's a matter of honour to build something to house the Hayward books because they are so good!

 

[Orraloon]

Quite a good rescue. In fact being able to cover up a stuffup is an essential woodworking skill.
Regards
John

 

[Just4Fun]

the mortices looked more like exit wounds than carefully crafted bits of joinery

Thanks for that. It made me laugh.

I don't quite know what the lessons are to be drawn from this (apart from the fact that pine is clearly the poor man's Wood From Hell and should be avoided)

I have a love-hate relationship with pine. I use it a lot because I have a limited choice of what I can get locally but it does require care (and sharp tools).
As for other possible lessons it could be worth considering why your mortices looked like exit wounds. How did you cut them? Did you cut through from the inside of the board to the outside, or cut in from both sides of the board?

 

[Andy Kev.]

Just4Fun: I cut the mortices from both sides using chisels which were freshly and carefully sharpened (a lesson learned from previous working of pine). Of the total of 16 joints, about 5 were acceptable i.e. they would have served a decorative purpose. I think the problem starts with the initial marking with an (also freshly sharpened) marking knife.

Whether you mark with or across the grain, with pine there is the potential for it to be iffy either because of the well known tendency of hard bits of wood to deflect the blade when marking along the grain or the tendency for it to be deflected upwards in a series of hops when marking across the grain. It was well dried and therefore particularly hard. I did of course start with light knife strokes, gradually pressing more and getting deeper. I deliberately used more marking strokes than I would on e.g. American Poplar which requires far fewer but no matter what, when it came to chiselling, the wood insisted on producing small fractures.

I suspect the answer is to have the patience of Job and mark up to about 2 mm deep and then emphasise it with a chisel all before cutting starts. The alternative would be to use power tools but going down that road would would mean a lot less pleasure and indeed a sense of a sort of failure (at least for me).

I've been umming and ahhing about trying to build the case again but in mahogany - the local timber yard having a nice supply of dry stuff - and I imagine that it would be a lot easier. Maybe even cherry would be a good alternative.

 

[Just4Fun]

It sounds like you were particularly careful. Your conclusion that the issue originated with the initial marking out is a useful lesson in itself. Especially because at the marking-out stage it may not be too late to correct/avoid the problem. That is something we should all bear in mind.

 

[AndyT]

I think anyone would struggle to get a set of through tenons to look good in softwood. I've still not got round to trying, but I remember the first time I cut dovetails in hardwood - mahogany -what a difference! It was so refreshing that the cuts were so much cleaner. Much less of a problem of dubbing over the edges. No need to allow for the wood to be compressed, the edges just stayed where they should.
I think if you were to try again in mahogany or cherry you'd be very pleasantly surprised.

If I was making that design in softwood I would use plain housing joints. If there was any risk of it splaying out or racking, I would put a few small nails in under the shelf ends, angled through into the vertical sides. They disappear quite easily.

You may not need them if the back is reinforcing everything.

You could also screw battens under the ends of the bottom, fixed up to the bottom and sideways into the ends, hidden by the toeboard.

Then again, sliding dovetails aren't as hard as they sound and the tapered sort are easier than the straight.

 

[Andy Kev.]

Andy, now that you say that, maybe alarm bells should have rung as the plan in the book called for oak. In other words they may not have specified a softwood for the reasons you point out. I just thought it would look good in pine.

I decided it would have a back on it after reading in The Anarchist's Design Book that it adds a lot of rigidity to the case. I grooved the underside of the top curved piece and a piece under the back of the bottom shelf. They were 3/4" pieces so there was 1/4" glued under/over respectively, 1/4" groove and 1/4" untouched. Rebates on the tops and bottoms of the back pieces fitted into the grooves. The back pieces were nailed to the backs of the shelves as per the idea in the ADB.

So it is structurally very robust and in any event I don't like bookcases without backs.

Maybe another go in hardwood is something for after Christmas.

One technical question though: if one were to use straightforward housing joints and if the sides were 3/4" or 7/8" thick, how deep should the housings be to afford the necessary structural strength?

 

[AndyT]

One technical question though: if one were to use straightforward housing joints and if the sides were 3/4" or 7/8" thick, how deep should the housings be to afford the necessary structural strength?

I'd say about 3/16" to 1/4" deep. You don't want to weaken the side by removing a lot of wood and the shear strength of the ends of the shelves is independent of the depth . The downside of keeping the housings shallow is that you won't have a lot of glue area if you are expecting glue to hold the shelves into the sides to stop them splaying - hence my suggestion of nailing, which is also handy if you don't have any big clamps.

 

[Cheshirechappie]

The term 'pine' can cover several species - don't know whether that's true in Germany, but it certainly is in the UK - and some of them work better than others. 'Whitewood' (spruce, I think) is pretty awful, and a real pain to do anything neatly with.

Another factor is that pine (as in bog-standard builder's merchant's Redwood) seems to have changed with time. The stuff currently available seems faster-grown, and thus has wider growth rings, than older stuff. I recently recycled an old bench I made about 30 years ago from nothing special, and was surprised at how close the growth rings were. It worked much more cleanly than currently available redwood.

Consequently, I wouldn't be too quick to beat yourself up about struggling to work pine cleanly. I think it's OK for interior and exterior joinery work with butt joints, mitres and copings, but even the most experienced cabinetmakers would find it a challenging furniture wood, these days.

 

[MikeG.]

One technical question though: if one were to use straightforward housing joints and if the sides were 3/4" or 7/8" thick, how deep should the housings be to afford the necessary structural strength?

I'd say about 3/16" to 1/4" deep........

Yep. I generally go for about one third depth.......so 20mm board would be housed out to roughly 6 or 7mm. I've often nailed and filled shelves made like this ("dovetail" your nails). If it's to be painted, screw and fill.

-

If you used wedged through tenons, surely alignment isn't absolutely critical anyway? I mean, you splay out the mortice somewhat such that the wedged part of the tenon expands into it when the wedge is knocked home, don't you? That's what I do, anyway. So if your marking out wasn't perfect, and you were just marking out the same size rectangle on both faces, then no matter, because the outside face rectangle needs to be bigger (in the up-down direction).

The other way to approach this is to drill the biggest hole you can through from one side to the other, and offset your markings from that.

 

[thetyreman]

where are the tenons? can't see any from the pics, or am I missing something?...

 

[Andy Kev.]

You are missing something, I'm afraid (see my first post). What you can see is the cover up job to hide the extremely messy through tenons.

 

[woodywoodwood]

In my day job there is very little room for any error as MFC is very unforgiving (read naff). Its a shame because I have found that overcoming obstacles has been a large, and consistent part of my woodworking. I think there will always be some problems with my handcut dovetails, for instance, but I am able to make good on the job, so to speak.
Im going to doff my hat to you - I think they look good.