Marking mortices (Part I)

[Derek Cohen]

Whenever I see photos of someone checking a stretcher for square, it looks like this ...


http://i13.photobucket.com/albums/a262/Derek50/Marking%20mortices/4_zps5fcf47be.jpg


It looks square, even when you hold it up to the light ...


http://i13.photobucket.com/albums/a262/Derek50/Marking%20mortices/5_zps0ed2c2f8.jpg


However, if you reverse the square and measure across the wide side, any error present is magnified and is easier to see ...


http://i13.photobucket.com/albums/a262/Derek50/Marking%20mortices/6_zps5fa14473.jpg


http://i13.photobucket.com/albums/a262/Derek50/Marking%20mortices/7_zps0974e6dd.jpg


Is this degree of accuracy necessary? Well, errors can be additive, and door/panel frames need all the help to end up flat. Anyway, it is better practice to measure for square across the wide side than across the narrow end.


Regards from Perth


Derek

[Jessica Pierce-LaRose]

I've taken to "feeling" for square - sliding the square onto the corner, you can feel/hear the square tick onto the surface. You should feel one solid tick as it seats into place; the blade contacts the entire surface at once. If it's out of square, you can feel two ticks and the square rock as you press it down. Takes a half second to do with the square in both orientations, and you don't need to bend down to sight. I've no idea if it's as accurate as properly sighting when you need super accuracy, but it's works great when planing stock on the bench. I think I first learned about this from an article about Bridge City Tools - something on the PW blog. I do a poor job describing it in words.

[Mike Holbrook]

Yea Derek! I am looking forward to more parts. I am in the process of practicing mortises and tenons and dovetail/finger joints. I am also trying to figure out what measuring/marking tools to use to mark for these joints.

[Derek Cohen]

Hi Mike

I have written a few articles on mortice-and-tenon joints. Here is one from 4 years ago ..

http://www.inthewoodshop.com/Furniture/AHandcutMorticeandTenonPrimer-BlindMortice.html

And the most recent is here ..

http://www.inthewoodshop.com/Furniture/MorticingByChisel.html

Regards from Perth

Derek

[Ben J Lowery]

I do exactly the same thing when jointing edges for a panel glue up. One other nice bit is that if the panel face does not have to be perfectly flat, it can have a bit of cup. If you use the "normal" method, your edge will end up being square to the cup at the edge of the board, whereas if you use this method, you can still end up square to the overall face.

[Sean Hughto]

No doubt a valid and useful tip. But I think it prompts a broader question of what level of perfection is necessary in various circumstances, and how much time should be devoted to perfecting stock on the front side versus accounting for tiny variations in the fitting and clean-up on the backside. There is also the problem of physical limits on how much stock is available to remove without ruining the stick for use because it is no longer the right dimension or uniform in dimension to its mates. In short, sometimes I think it is better to hand fit your joints and plan to plane at the end to yield a flat square door, for example, than to spend a lot of time four squaring stock that often will change again overnight. Experience tells us what is close enough and allows us to determine what imperfections and in what circumstances warrant attention.

[Daniel Rode]

...I think it prompts a broader question of what level of perfection is necessary in various circumstances, and how much time should be devoted to perfecting stock on the front side versus accounting for tiny variations in the fitting and clean-up on the backside...

This is a great point, Sean. For me, I want to be able to measure, mark and alter the stock with as much accuracy as possible. However, I've come to learn that I don't need to employ the same level of accuracy everywhere. The reference face, for example, is just that. It needs to be as perfect as possible but it's companion on the other side might not be parallel or flat in any direction and have no bearing on the build or the final product. Another example might be a table top. It needs to feel and look smooth and flat and even but it's actual flatness is unimportant.

Regardless, I want to know the state of the stock with accuracy and them make a decision about how to proceed.

[Mike Henderson]

If you have a square edge to one side of a board and not to the other, either your square is out of square, the sides of the board are not parallel to each other, or you have cupping of the board. If I found the problem Derek demonstrates in the opening post, I'd want to find out what the cause was.

Assuming you can't find anything wrong, I'd choose a reference side to work from and proceed from there.

Mike

[Derek Cohen]

Hi Sean and Dan

I fear that both of you have assumed that the wide side needs tuning if the face edge (with the mortice) is out of square. However the wide side is the reference side, and reversing the square does not alter the focus on the face edge (this technique simply enables one to magnify any error in square). If any adjustment is needed, it will only be to the face edge.

Regards from Perth

Derek

[Sean Hughto]

I understood, my point is still: how perfect is enough in given circumstances where more tuning will follow in the many subsequent steps? If holding a true square to the reference side and seeing no light on the face edge, I think I'm unlikely to have a warped door because of a .001 degree error. A cocked mortise or tenon is much more likely to be the issue in my experience. Mind you I'm not against perfect squares or advocating ignoring the issue, just thinking out loud about what I've expereinced at the bench.

By the way, which do you choose as your reference here? I'd choose the back of the door? What is your preference?

[David Weaver]

As a matter of practice, I have only ever gone to this extent when making the infill for a plane (referencing off of the edge to check the face instead of the converse). I have, as Sean says, had a lot more trouble with cocked mortises than with lack of squareness of face to edge. The first method of measuring the edge is generally plenty accurate, and I'd consider correcting it so that the second picture is perfect as something I wish I hadn't done or learned of if I felt the need to check as shown in picture #2 even when picture #1 looked good.

[Jim Foster]

The accumulation or error can add up quickly. Each degree off square adds .017 per inch error. Accumulating several errors of this nature over a 24" stretcher could be noticeable. Thanks for the suggestion Derek.

[Jim Matthews]

I've taken to "housing" the shoulder with a small cut out at the shoulder joint.

It gives me a little wiggle room, and hides many sins during glue up.
The "pocket" can't be much more than a 64th of an inch deep.

I make it with a knife line and router plane.

I'm not consistent enough with this joint to fit this cleanly every time.

[Mike Holbrook]

Derek,

Thanks for those links, I did go and review your methods and the tools you use again. Great illustrations and they make more sense now that I am attempting to make more of those joints.