07 August 2011

Micro Joinery

I started off yesterday by lamenting my lack of woodworking knowledge. This is no joke. I have done just enough woodworking to realize how little I know, and how difficult it will be to accumulate the kind of experience that 'real' woodworkers have.

For instance, in building my first few blocks (including more than a few that ended up on the scrap pile), I discovered how difficult it is to keep a flat surface flat while sanding or planing it. No matter how careful I was, I invariably ended up with a rounded surface (high in the middle with low spots on the edges) or a slanting surface (higher on one end than the other), or some even more complexly distorted surface. Anything but flat!

This makes it all but impossible to make good glue joints, which demand two flat surfaces, face to face. 

I had been using thickened epoxy to fill the rolling gaps between the spacers and cheeks, but that kind of slap-dash approach didn't seem right to me this time... Surely it wasn't impossible to get two small bits of wood to match up perfectly. I was determined to discover this woodworking secret.

However, the first challenge was to extract two rough cheeks, and two rough spacers -- with the right grain dictions -- from the slab of white oak on my work bench. This wasn't too difficult. The slab was 10/8" thick, so I thought I could cut three 3/8" thick cheeks from one piece, allowing some loss from sawing. 

I didn't take photos of this process, but here is the result: a roughly-square block, after the one 3/8" slice has been already been take off on the bandsaw. It only remains to re-saw this into two pieces that will become the cheeks.

A roughly square block
Even my less-than-professional quality bandsaw (that's putting a kind spin on it) is more than capable of doing the job quickly and neatly.

Re-sawn into two cheeks
I also cut out two spacers of the right size and grain orientation. Because I'd made my previous blocks from finished boards, the grain in the spacers always had to be up and down. This created an end-grain glue joint, which as even I know, is almost the worst kind of glue joint (the worst being end-grain to end-grain.)

From the photo below, it looks like these roughly cut pieces are already flat. They are in fact close, but being freshly sawn, they need to be sanded smooth before assembly. This is where my previous efforts had turned nearly-flat bits of wood into smoothly-humped bits of wood. Very frustrating.

Spacer cut for a long-grain to long-grain glue joint
To solve this problem, I build a kind of sanding platform out of a piece of marine plywood and a strip of oak. I varnished it to make it easy to stick tape to (and because I think varnishing is fun.)

My flat-sanding jig
My basic idea was to tape sandpaper to the platform, using double-sided scotch tape, and just rub the piece on the flat sand paper. The theory was it would be impossible to round off the edges using this simple technique, and in fact, it worked perfectly!

The key to flat sanding: move piece, not sand paper!
The purpose of the oak strip was to make it easy to sand small pieces, like the spacers, while keeping the faces 90 degrees to each other. This was another problem I'd had... when sanding with a sanding block, it is all to easy to end up with slanting faces. 

By holding the piece against the rail and rubbing the piece up and down the rail, I was able to sand the piece while keeping the edges square to each other. 

Keeping small pieces square
Finally, it's important that the two spacers be the same height, for obvious reasons. I'd already ruined several spacers by sanding a bit off this one, then a bit off the other, trying to make them the same size, but ending up with two toothpicks.

By holding the two spacers pressed together, it was easy to sand them both at the same time, thus guaranteeing two spacers of the same height.

Two spacers exactly the same size! Wow!
I'm sure real woodworkers have a more efficient way of doing this, but this approach didn't require the purchase of any new equipment (I'm determined to make these blocks for as nearly free as possible) or sophisticated techniques.  With some double-sided tape and various grades of big-box sand paper, I ended up with smooth, square, and flat cheeks and spacers.


Here's how the bits look when laid together for fit. I discovered I could actually make the block a bit smaller than I had planned, so the cheeks are a little long.

I cut the recess in the bottom spacer and the rope-groove in the top spacer using my micro-plane rasps, as shown in a previous blog post.

How the pieces fit together
By this time, I had a lot of work invested in those small pieces, so I was strangely reluctant to glue them together, less I make some fatal mistake. But after much dithering, I gathered my courage and took the final step.

The moment of truth...
And here is the assembly, glued up. It's really difficult to put clamps on such a small assembly without moving something out of line, so rather than use clamps, I just put a 5 lb. pig of lead on top of the whole thing (with saran wrap in-between). This gives moderate clamping pressure, without the risk of ruining the assembly at the last moment.

At least, that was the theory. Only time would tell. But as I was gazing admiringly at this tiny bit of woodwork, I realized I'd made one potentially serious mistake...

>>> Next Episode: Tail Block Takes Shape


  1. John,
    I like the sanding jig.
    In his DVD on building a sawhorse Chris Schwarz has to find a way for inexperienced woodworkers to flatten tenons for the legs. This bears comparison with what you're trying to achieve.
    He starts with a wooden carpenters clamp and planes one face so that the two jaws are flat - fairly straightforward.
    Then he places his tenon between them so that the lower edge is level with one of the jaws. By planing across the jaws he flattens the tenon and squares is up with it's sides.
    Then he takes it out of the clamp and puts the other, unlevelled tenons alongside and planes them all together so that the higher ones are brought down to the level of the lowest that he just levelled.
    This gives him a longer surface to plane - less chance of rounding it all over because the plane has more to register against.
    The pieces he's planing are a bit smaller than the cheeks of your blocks but not by much. It could be worth investigating - it's harder to explain than to do!

  2. They say that beginner sand too much, and I'm definitely guilty of that. I'm reading some books on basic joinery, hoping to figure out how 'real' woodworkers would do this work. What you are describing sounds real good. Thanks!

  3. John, You might consider using Titebond III. It is just as waterproof as epoxy , has great gap filling properties, water clean-up and costs less. We use it quite a bit in our boat shop. Epoxy is great stuff and we have mechanical pump for those occasions. Also try wood screw clamps. getting them parallel will stop the "sliding around" small pieces do. You can slowly increase the pressure. Of course, if using epoxy, you will want to go easy on the pressure.

  4. Hi John,
    Glad to see you back posting. I like the sanding jig, my only addition would be to put a strip on the bottom front of the jig and turn it into more of a bench hook. This way, you may not need to use the clamps. I don't clamp down shooting board, since your essentially pushing in only one direction, and any bench hook type items that may move around, I usually just lean against it, or clamp it into the front vise. Enjoying the blog... Thanks!

  5. Jim: thanks for the tip on Titebond. I'll take a look at it.

    Also on the wood screw clamps. I've never used them, but now that you point them out, I can see how they might work better than C clamps for this sort of work. The rotating motion of the C clamp end certainly doesn't help keep things in place. I'll have to find a small pair and give them a try.

    Thanks for the tip.

  6. Steve: Interesting idea! Maybe I'll make another one with a cleat on the bottom to use as you suggest. Thanks for the tip!

  7. Hi John,
    I know this is an old post - but is there any chance you can resurrect the photos that go with it?

    1. Ah... didn't even realize this photos were broken. Give me a day or two and I'll restore them. Thanks for letting me know.


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