Benchtop Laminating Tolerances
- This topic has 19 replies, 10 voices, and was last updated 9 years, 2 months ago by
.
-
Posts
-
I am planing some HEM-FIR 2x4s (the crummy, knotty, rounded corner ones from HD) for a Paul Sellers style benchtop and I have a couple of questions.
1) How straight and flat do the board faces (the sides that will be glued together) need to be in order to be clamped together tightly enough to form a solid benchtop? I’ve noticed that most of my boards are cupped and bowed across their width before and after planing. I started checking the board with a straight edge across the width at several points down the length and trying to plane flat enough so that I can’t see light between the board and the straight edge. It seems like this will lead to a flat board, but it might be overkill and, in the process I have created some cupping along the length.
2) How rough do the board faces need to be in order for the glue to penetrate and bond to them together? Perhaps related to my potential over-planing a lot of the board faces are very smooth and shiny. Will that cause problems with the adhesion?
Just as a side note, I’ve been spending between 30 and 45 minutes per face, is that about right?
I don’t have a Sellers-style bench yet, but I did laminate my top the way he shows. It was also my first time using a hand plane. The only part I regret was actually trying to plane them straight and square 🙂 That process, coupled with my inexperienced, actually created problems. The bottom line is that in the end, you’re gonna have to square up the glued up slab, so trying to square up each board before gluing is a lot of effort not well spent (IMO).
I think the most important thing is to remove a consistent amount down the board, and to remove as little as possible. My biggest mistake was to allow the boards to vary too much in thickness from end to end. If you do that you’ll end up with a slab that’s way out of square. Bowing–sch’mowing, I say let the clamps take care of that 🙂
I seem to recall reading that wood glue bonds are a cellular process, and not strictly an interface-type joint like CA or something like that? In other words, I don’t think you need to scuff up wood surfaces for PVA. But don’t quote me! 0_0
I haven’t actually tried this myself yet, I am still fighting with some large old jarrah beams in my spare time, to try to get the wood to laminate the top. From what I understand though, if you put your boards together as if you were to glue them, but so that the joint is a horizontal surface, they shouldn’t be able to spin. Having a small gap in the middle is ok, but convexity is bad. Basically, just test the fit and hit the high spots, then cross your fingers. I guess it depends on the sizes of wood you’re working with too.
And in my experience, PVA will soak in between the fibres of the wood and set like nobody’s business, so I wouldn’t worry too much about that. Smoother is probably better actually.
@danw I’m a noob myself, planning to build my own bench. If you watch Paul’s videos – which I have done several times now – you’ll notice his boards were machined square and have at least one surface free of knots. I think his message to beginners is: get these as well.
Don’t forget that all you’re supposed to be doing when you plane each part prior to laminating them is to remove all the milling marks. You should have the plane set to a reasonably light cut if you re-watch Paul’s videos pay as much attention to the sound of the plane as to what you can see.
Once I’d planed a pair of boards, I copied Paul’s ‘press the part together by hand’ test. If that worked I then went ahead with the next pair until I’d finished the lot. I then glued up (after a clamp up rehearsal). If you get the parts properly aligned and clamped, you should then find that there’s not too much work needed to square/flatten the tops. Mine came out in wind so I had the underside flattened in about 20 minutes.
When you’re doing the hand pressure test a slight gap in the middle of the joint is OK – as long as you can clamp it out. You’ve made a spring joint and that’s a method of board glue-up that’s been around for ages. If there’s any gaps at the ends though, you’ll have to work on the timber a bit more.
It can be pretty soul destroying if you get into a circular plane/test/plane/test routine where you don’t seem to be going anywhere and your precious timber is ending up on the floor as shavings so just take it one joint at a time and take a break if your start feeling any pressure or frustrations – remember; this is the recreation of your choice so it’s supposed to be fun.
Once you have a joint that’s good – mark it up so you don’t plane it again by mistake (don’t ask me how I know about this 😉 )
Once the boards are planed smooth, they are ready for glue-up. I certainly didn’t rough mine by sanding afterwards. Each face took me about 10 minutes (although some were quicker than others) but that was me, at that time, on a nice day, with the radio on, in no particular hurry. If it takes you longer then it might be you have higher standards than me rather than I’m quicker than you so don’t measure your work by the clock.
Above all, have fun – I promise you that the sense of achievement you’ll get when you unclamp (declamp?) that big slab of timber will be worth all the time you invest in it.
Keep Calm and have a Cup of Tea
If you can remove any gap between two boards by hand pressure that’s good.
When laminating the top use cawls on the ends to keep the laminated boards level. Lay some wax paper between the cawls and top to prevent gluing them together.
-Canada
I know this isn’t your question, but it will make a lot of difference when you’re going to plane the top. It’s obvious, but I didn’t think about it till later 🙂
You want to make sure you do that the GRAIN of the side of the board that is going to be the top of the bench is going in the SAME direction for each board before you glue up.
If the grain isn’t going in the same direction it makes for a tough time plaining the top flat.
Thanks everyone for your suggestions! I especially like the idea of planing them in matching pairs. I’m going to go match them up and do it that way.
You want to make sure you do that the GRAIN of the side of the board that is going to be the top of the bench is going in the SAME direction for each board before you glue up.
I agree with this, and suggest you write a slash mark ( / or \ ) on the face of each board to indicate if the grain slopes to the right or left. This will help you later on during sorting and glue up so you do not have to re-check the boards.
-Scott Los Angeles
I have the bench top laminated and am working on flattening the bottom now. One thing I notice is that the bottom, while it is getting flatter, is way out of square with the sides (see attached pictures). It seems like having the sides out of square with the bottom could cause a huge problem in getting the apron housing dado to mate with the legs.
I think that I might have messed up the glue-up, with the boards being clamped together with a slant. Can anyone give some advice on how to get the bottom straight across the length and width and also square to the edges?
It seems like I keep creating small areas that are flat, but then find that that area is not in a hollow, or out of square. I’m a little frustrated that I can’t seem to get everything right at the same time.
Dan I would concentrate on the bottom surface at this point. Try going diagonally in one direction across the bottom then alternate and go diagonally the other way. Once you get continuouse shavings diagonally star going with the grain. The bottom does not need to be pretty, just flat. After the bottom is flat, square the long edges to the bottom. That should make the assembly of the bench square. Once the assembly is done you can then flatten the top.
You are doing just fine. We have all been there. Don’t panic, just take one step at a time. Concentrate on a square assembly. Once you have that you can easily dress the top.
Keep us posted.
http://hillbillydaiku.com
Dan, make yourself some winding sticks, these will help you determine where you need to remove material. The boards staircased during glue up and created the twist.
The easiest way to plane the high spots is diagonally.
-Canada
[…] After the bottom is flat, square the long edges to the bottom. […]
Greg, wouldn’t the long edges already be square the faces, to the bottom, since the studs are pre-dimensioned lumber?
New Jersey, U.S.A.
@handworkenthusiast the individual boards may have been square to begin with but we are now talking about the lamination. The boards shifted slightly during glue up. It looks like the clamp pressure may have been stronger on one face than the other as well. Now Dan is squaring up the entire lamination. Once he flattens the bottom face more than likely the edges will be close to square again. So it will take very little effort to ensure that the 3 sides are square each other.
Never trust that dimensioned lumber is square. Especially in a lamination such as the bench top. One board out of square can cause the entire assembly to be out.
http://hillbillydaiku.com
Dan, I really feel your pain: you’ve spent money on the timber, worked through to this point and now it seems that every time you apply the plane to the timber something’s going against you. When this happened to me, all I could think of was the amount of timber I was wasting as my 1″ tabletop became a 7/8″ tabletop. Planeing something like this for the first time is hard enough when the glue-up works flawlessly but when you’ve introduced a twist it seems an impossible task. You are actually closer to success than you think though: ignoring the squareness for a moment, the actual bottom seems reasonably close and shouldn’t take too long to sort out. Once you’ve flattened the bottom of the lamination, I think you may be pleasantly surprised at how straightforward the rest of the planeing goes.
Make yourself some winding sticks and then follow Greg’s advice. Before you know it, you’ll have a lovely flat square lamination.
Keep Calm and have a Cup of Tea
- You must be logged in to reply to this topic.