0

I'm trying to edge joint boards without a jointer or a table saw....

I have a small router table with an 18" fence (Only 9" outfeed fence) which I tried to use with some jointing shims. I ran two boards through and the resulting edge was fairly flat but if I hold them up to a light I can see some gaps.

How flat is flat enough to edge join boards?

I assume that it might be a slightly different answer for each of the following.

  1. Plain Butt
  2. Tongue and Groove
  3. Doweled
  4. Spline

Are there any numerical/measurement based specifications?

TheDude
  • 3
  • 1
  • Hi, welcome to Woodworking. It's not clear how much, if any, troubleshooting you've done to try to rectify the problem here and there happens to be this highly related previous Q What are some techniques for jointing boards using a router table? from just a few days ago. "Are there any numerical/measurement based specifications?" There are, but you can ignore them for anything but a plain butt joint. – Graphus Feb 14 '22 at 19:05
  • 1
    Two important clarifying questions. Do you have any hand planes you could use to tweak the edges you already have? And what width is the keyboard tray you're working on, i.e. what length are your boards? – Graphus Feb 14 '22 at 19:12
  • Tray dimensions are 40" x 25". I have a small lie block plane, but I don't think I could flatten the edge by hand with it. – TheDude Feb 14 '22 at 22:28
  • "I have a small lie block plane, but I don't think I could flatten the edge by hand with it." I got beaten to the punchline by @VolframK but you don't have to do the whole edge, you only need to improve what you have. Planing off high spots is pretty easy once you know where they are, takes only a little practice to get good at it (and you can do well first time). Plus, learning to do this now will pay dividends any time in the future you get a similar result. But as the above Answer and the link in it show, there are methods which can ensure perfectly jointed edges sans both TS and jointer. – Graphus Feb 15 '22 at 13:45
  • They used to do it so that the ends of the boards fit a little more snugly than the centers so that the added pressure at the ends makes the joints just a little bit tighter at the edges. – gnicko Feb 17 '22 at 00:19

2 Answers2

2

You don't say how big gaps are but if they are small edges are already very close to straight so it is easy to improve them by planing.

  • Hold 2 boards together edge to edge to find high areas, mark them with pencil. Or chalk flat surface and rub board edges on it, chalk will mark high areas for you.

  • Plane off pencil or chalk.

  • Have plane adjusted for fine cut and check progress often, maybe after every shaving. 3 shavings too much!

Jointing by hand is easier with larger planes because of effect of long sole bridging gaps, but you can do it with your block plane. Work carefully to plane only marked areas.

How flat is flat enough to edge join boards?

No visible gap is usual.

With plain glued joint small gap in center only is acceptable, sometimes used deliberately. Uneven gaps and gap at ends of boards never acceptable.

2, 3, and 4 always made straight.

Are there any numerical/measurement based specifications?

|Some say yes, some say no. There is not a single number, it must be small enough that it can be closed by hand.

  • on short boards it must be very small.
  • Can be bigger on long boards, maximum approx 1/32" (0,8mm). This is total gap, so curvature on each edge 1/64" (0,4mm) or less.
  • Gap must be smaller on thicker boards because wood is stronger.
Volfram K
  • 2,119
  • 1
  • 5
  • 20
1

"It depends"

the point of a good glue joint, is a good surface area that can be bonded together. The more surface area the stronger the glue joint. Where you can see light that is a weak spot that won't be bonding.

Is it good enough? What materials are you joining AND what kind of finish are you going for? Those 'gaps' can be obvious on a finely finished table top, but maybe less on other works.

I like to get my joins with a clean line across the whole joint. while this isn't needed for a good glue up job, having gaps that let light through I think is a too much.

So if you are doing a straight butt joint you might want to try harder to get a tight fit, you might be able to glue some sand paper down to a flat surface and run the boards like a plane over it, I assume a keyboard tray isn't going to be 3 or 4 feet long. So short enough for this to easily work. I am assuming that you are fairly close so a few passes on a 80-100 grit should flatten it up enough and then a few more with 150 and you should be good to go.

bowlturner
  • 15,982
  • 6
  • 42
  • 92
  • I'm building a keyboard tray for my wife out of figured maple with a figured walnut boarder. Ideally I would like a no-gap edge, but I haven't figured out how to do this with my equipment.... Perhaps I can lengthen the fence to extend beyond the table to pick up some extra precision.

    I'm thinking I'll need to use either a tongue and groove or a spline joint since there will be weight/pressure on the boards.

     – TheDude Feb 14 '22 at 18:33
  • @TheDude well if they are pretty close, you might be able to glue some sand paper down to a flat surface and run the boards like a plane over it, I assume a keyboard tray isn't going to be 3 or 4 feet long. So short enough for this to work. – bowlturner Feb 14 '22 at 18:40
  • 1
    @bowlturner, as covered many times previously, biscuits, dowels and splines actually aren't reinforcements; as strange as it sounds they (and Dominos!) can actually weaken an edge joint like this! They end up acting purely as alignment aids during assembly. This alone is a good enough reason to use them in some circumstances, but thinking they add strength isn't right. – Graphus Feb 14 '22 at 19:16
  • @Graphus If it was anyone but you I'd doubt it. But since it is you, I'm trying to accept it, (biscuits make sense and I don't know why I added them) but if you have an article or something I can read up on splines I would really appreciate it, I'd like to understand the physics behind it. – bowlturner Feb 15 '22 at 02:16
  • Biscuits, dowels and Dominos (or shop-made floating tenons) interrupt the glue line and provide sites from which cracks can propagate. The joints are (can be) still very strong, and likely strong enough for service, but there is a chance they've actually weakened that specific edge joint. We are assuming they are done well naturally, and this is very relevant because they can easily be done poorly (the usual sloppy fit of biscuits in their slots is always a concern in this regard) which of course exacerbates the problem. – Graphus Feb 15 '22 at 13:23
  • Splines are a trickier thing to argue against because more glue surface area. But we know long-grain butt joints are stronger than the wood itself, right? So we start from that knowledge. In any accident severe enough to split a panel a butt joint is already stronger than the wood. Theoretically long-grain splines should be stronger than a plain butt joint, although testing sometimes shows they aren't (because of numerous variables). But let's just accept they are just for the sake of argument aand punchline: the wood is going to break either way. So even if stronger, it doesn't matter. – Graphus Feb 15 '22 at 13:39
  • @Graphus OK that all does make sense. However, it is based on a good butt joint with good jointing. Doesn't it make sense a good spline would strengthen a poorly joined butt joint, by adding that extra surface area where the butt isn't touching? Not trying to be an asshere but do want to understand. – bowlturner Feb 15 '22 at 13:50
  • But what if the fit of the spline isn't super tight? You only need a slightly gappy fit of the spline in either or both slots for the spline to basically be a liability (strength-wise, it'll still work well for alignment) unless you're not using PVA, which of course most are. And isn't cutting the spline and the slots two much trickier milling operations to get just so compared to just getting 90°, or complementary angle, edges in the first place? – Graphus Feb 15 '22 at 14:28
  • Plus how many even realise how vital it is for splines to be that tight, given how common it is for woodworkers (both amateur and pro) these days to be happy with slip-fit tenons? [They shouldn't be, this is too loose for strength with the most popular glues used, including all common PVAs and original Gorilla glue.] – Graphus Feb 15 '22 at 14:30
  • 1
    @Graphus Thanks for taking the time to help me understand. I'll update this answer soon to reflect this. – bowlturner Feb 15 '22 at 15:12
  • @Graphus "Slip-fit"...as in easily slips together? – gnicko Feb 16 '22 at 02:49
  • 2
    @gnicko, yes, somewhere in that ballpark. It's becoming more and more common for woodworking instructors (on YT especially but in the magazines also) to advise that M&Ts shouldn't be a tight fit, sometimes going out of their way to specifically state that they shouldn't need to be knocked together with a mallet. This is directly counter to old-school advice. And what's more the very same woodworking gurus telling learners this have no problem demonstrating dovetails that need to be tapped together o_O – Graphus Feb 16 '22 at 14:47
  • 1
    Thanks for that last one @Graphus. I always thought M&T joints needed to be snug and was confused by all the more recent advice that they not be. – FreeMan Feb 16 '22 at 17:31
  • @FreeMan, very welcome. I suspect it's partly to make M&Ts less intimidating for the learner, and it's not like they aren't challenging (regardless if done by hand or by machine). But setting people up for joints that will fail earlier/more easily just to make the subject more digestible is no way to teach. I hate to say this but it may also be due to fundamental misunderstandings, so many people (including most of the Big Names in online instruction) still don't understand PVA properly — the "don't overtighten your clamps" brigade. This is literally impossible in most home shops! [contd] – Graphus Feb 17 '22 at 04:37
  • Either way thankfully this is one thing that can be easily remedied, by not using the commonest glues (glue with epoxy instead) and/or by pegging or drawboring. Oh wait, drawboring is challenging for the beginner, can't recommend that ^_^ – Graphus Feb 17 '22 at 04:39