A Question On My Alignment System

Question:

Paul,

I don’t understand what the alignment pieces did. Their tenons are smaller than the mortises, so they don’t register the two sides vertically relative to each other. The two sides are rigidly clamped when we put in the alignment pieces, so it doesn’t seem they can move anything into position. Would you please give some examples of problems they would catch and what you would see?

Ed

Answer:

It’s a good question. Clamping up a table frame with two mortises to each leg is a simple enough task. You can glue the whole of eight mortise and tenons all at once pretty well. More complex frames with the added raised panels within the frame can be difficult. It’s more critical when the tenons fit without air between the walls of the mortise because of things like glue freeze, air pockets at the bottom of the mortises and then additional alignment issues that come as a result of clamping pressures.

It’s not uncommon to glue up subassemblies as opposites—two end frames or a front and a back. Set them aside to dry and then do the counterparts later. Simple! Well, not necessarily. In the case of this chest it was especially difficult because the clamps are not square on to flat faces as say with a normal table or chest. The angled presentation means they are clamped on rounded corners. This in tun means that the pressure can cant the leg under the clamping pressures, causing the adjacent mortises to misalign along the long axis of the chest. Using my method means the the insides of the mortise holes enable me to use the parallel walls of the mortise hole to perfectly orient the legs and thereby the mortises so that when the subassemblies as frames dry they are ready to receive the adjacent rails and panels. The stubby temporary rails keep everything perfectly parallel because the stops in these temporary rails prevent anything but exactness.

Basically what we have achieved is a risk free gluing up system for what could otherwise be a very difficult glue up. That said, I would do this with non complex glue ups too.

10 comments on “A Question On My Alignment System

  1. Thank you! It makes perfect sense now. Would it be foolish to use the actual rails for alignment rather than the short alignment rails? It would be one less thing to fabricate. Ah, wait….is that why the stubby alignment rail tenons aren’t full width? It lets you whack them free if some glue creeps in, but with the full tenons on the actual rails, you’d really be stuck? You’d have no wiggle room at all. So, it’s actually quite important to keep the tenons on the alignment rail the proper thickness, so they meet the mortise walls and give good alignment, but definitely *not* the full width?

  2. So in the last picture, looking at the rails from the bottom view, the short alignment pieces stop the rails from rotating clockwise or counter-clockwise.

    • That’s right. You see, clamps are a brilliant invention but they often cause problems for a wide range of reasons. In this case that can, even with well fitting tenons, cause a twist within the jointed areas. The alignment pieces work in tandem with the tenoned rail tenons to keep dead on alignment.

  3. I absolutely love this type of critical thinking to solve problems! Woodworking using almost all hand tool methods has engaged all of my senses. This has allowed me to solve some pretty difficult issues in my day job. I only wish more people would understand the benefit of crafting or gardening to learn how to think for themselves; become a more complete person. Thank you Paul!

  4. I really liked that latest episode! Thank you for NOT showing a trouble-free gluing of your work, but in stead a situation where you run into little problems here and there. For us who didn’t live a long life with professional woodworking it’s always exciting to try new techniques and to see how well (or if) we succeed. But of course we get into trouble from time to time.

    So it was just fantastic to see how you didn’t panic but instead took your time to analyze the problem and showed us how to get along and end up with a perfect result. I will do my very best to keep as calm as you did, when I find myself in similar trouble. And I’m sure I will…

  5. re clamping: I’ve found that “Spanish windlasses” or ratchet straps can help with clamping against irregular surfaces. do you ever use them? obviously, you have to check for squareness and even pressure on all corners… your thoughts?

  6. I did wonder, but now the explanation makes it very clear. O to get beautiful wood like this in Australia without taking out a Bank loan

  7. Paul,
    I see clamp right pads on your “budget clamps” with the blue clamp faces. Where were those adpapted from?

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