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Finger jointing a laminated panel

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Forum topic by leftcoaster posted 04-21-2018 05:40 PM 405 views 0 times favorited 20 replies Add to Favorites Watch
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leftcoaster

224 posts in 961 days


04-21-2018 05:40 PM

If I make a bench with laminated, squared 8/4 and used varied lengths to form finger joints, am I going to run into expansion problems?

I will be joining the two sides to the top in this way, such that the tops of the sides are jointed into the ends of the top.


20 replies so far

View darthford's profile

darthford

611 posts in 2009 days


#1 posted 04-21-2018 06:15 PM

Stop, first what is your desired end use for your bench? Does it need to be dead flat for layout and glue up of projects or is it just a work holding bench? Begin with the end in mind.

Wood is an imperfect material for a work bench. Its likely to expand, shrink, cup, or bow. Its not the year 1880 there are modern alternatives. BuildPro makes steel work benches that are 5/8 inch thick steel, precision CNC drilled with a gigantic assortment of work holding and layout accessories. The tops are accurate to .002 over 12 inches and will remain flat and true throughout the seasons. The nitride coated tops are impervious to glue, epoxy, or any other goop, scrape the drips off with a chisel and its good as new.

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Loren

10477 posts in 3733 days


#2 posted 04-21-2018 06:40 PM

Solid wood always moves in width. This can
be ignored in little boxes up to perhaps 8”
wide but beyond that if you don’t plan for
the movement there will be a risk.

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leftcoaster

224 posts in 961 days


#3 posted 04-21-2018 06:54 PM

Furniture bench for sitting, not a work bench

If the boards are laminated, width to width and finger jointed, they will move together right?

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Loren

10477 posts in 3733 days


#4 posted 04-21-2018 07:04 PM

If it’s glued up in any way it will all move together
in width. If you want to be fussy about it you
could mill all the parts to perhaps 2” square and
then join them in such a way that the grain
orientation from the tree comes closest to matching
on all the parts. Quarter sawn grain occurs on
the edge of flatsawn boards for example. That’s
why you’ll see ray flecks on the edge of a flatsawn
maple board. The quartersawn moves less in width
so if you wanted to minimize movement you could
try to use the most close to quartersawn faces
for the show face of your glue-up.

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leftcoaster

224 posts in 961 days


#5 posted 04-21-2018 07:40 PM

As an alternative – suppose I make a conventional mortise and tenon table structure. How can I join a panel on the sides ? I need it closed and my spouse asked me not to use plywood.

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Loren

10477 posts in 3733 days


#6 posted 04-21-2018 08:01 PM

It sounds to me like you’re wanting to make
something like this .

Is that correct or do you have something else
in mind?

I’m not sure what you mean when you say “sides”.
Are you trying to make a closed box out of solid
wood?

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leftcoaster

224 posts in 961 days


#7 posted 04-22-2018 12:07 PM

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bondogaposis

4898 posts in 2436 days


#8 posted 04-22-2018 02:56 PM

I guess I am not seeing where the finger joints come in.

-- Bondo Gaposis

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leftcoaster

224 posts in 961 days


#9 posted 04-22-2018 03:02 PM

That was just an idea. How would you build this without using plywood?

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ArtMann

1009 posts in 901 days


#10 posted 04-22-2018 03:06 PM

I don’t think the original poster is using the term “finger joints” in the way that most of us understand. I don’t see any finger joints in the picture and I don’t see any need for any. Based on what I understand to be the idea, my opinion is that there will be no problem with expansion/contraction. I think Loren is answering a more complex question than the person is asking but I am not sure.

View Aj2's profile

Aj2

1585 posts in 1883 days


#11 posted 04-22-2018 03:15 PM

My guess is your thinking of a joint like this lefty coaster.

Since you mention using wood of various lengths.
A very difficult joint to get right for a hobby shop

-- Aj

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ArtMann

1009 posts in 901 days


#12 posted 04-22-2018 04:30 PM

If the (real) finger joints in the picture above is what the OP is talking about then Aj2 is absolutely right. That is a difficult and unnecessary joint to use. There are tens of thousands of maple bench tops that are made by putting square butt ends against each other and putting solid pieces on either side. There isn’t any problem with those. The finger joint is a solution without a problem in this particular situation, in my opinion.

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leftcoaster

224 posts in 961 days


#13 posted 04-22-2018 04:43 PM

Finger jointing is one approach to joining the sides to the top – basically 2/3 of a box on its side. I am open to other approaches that address the expansion problem.

View Loren's profile

Loren

10477 posts in 3733 days


#14 posted 04-22-2018 04:43 PM

Without plywood at the very least you can do
the ends with case miters like in the bench I
showed above, or use a butt joint of some
kind. I like dowels on a budget for this sort
of thing because with jigs like the Jessem jig
or Dowelmax jig you can get the parts drilled
so those corners go together very close to
perfectly flush. Biscuits are more forgiving
but may not turn out quite as flush, and pocket
screws are difficult to install without the screws
pulling the corners out of alignment a little.

The grain direction on the side panels is not going
to match the grain on either the top or the sides.
You can’t have it both ways. You can make the
glue up wide with short pieces or narrow with
long pieces. In either case you must plan for
movement in the width of the side panels, so
I must be done with a frame and panel or with
an expansion gap, as shown in the picture of the
cat hideout. A frame and panel is a hassle to
make if you haven’t done it before, so if the
expansion gap is acceptable, I’d attach the
panel using metal corner brackets with elongated
holes to allow the screws to slide as the wood
expands and contracts. Corner blocks with
elongated holes can be made of wood too. If
suitable steel ones can’t be found I think the
quickest way to do it is with lengths of aluminum
angle stock. The metal is soft and elongated
holes can be made easily by chain drilling and
a little filing or with a router jig and a small bit.

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Aj2

1585 posts in 1883 days


#15 posted 04-22-2018 05:48 PM

There is no expansion problem if the grain is running in the same direction. One board horizontal that you sit on the other board on the side vertical. It’s ok use any method to attach.
When your crossing the grain then it gets interesting.
I’m trying to understand maybe I’m off point here. But hay I’m probably 1000 miles away flying blind here.:)

-- Aj

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