Skip to content

correcting an out-of-square mortise

Welcome! Forums General Woodworking Discussions Woodworking Methods and Techniques correcting an out-of-square mortise

Viewing 11 posts - 1 through 11 (of 11 total)
  • Author
    Posts
  • #133562
    hoddy2000
    Participant

    I just finished two bed end frames. They are oak and the cross rails are two-inch deep 5/8 wide tenons into 3 in wide square posts. On my first one I had the end of my chisel sharpened a little out of square which caused my mortise hole angles to go out of square. Because I turned the post end for end when I did the second mortise I have one cross rail out a few degrees one way and the other out a few degrees the other way. It wouldn’t be so bad if they were both out the same way! But now I have a crooked end frame. What can I do? Do I need to redo the post? It’s laminated from 3 1″ boards. But is there anyway to modify the mortise and then drawbore instead of gluing? Or modify the tenon and compensate with a little wooden insert during glue up? Any help would be appreciated. You can see in the pic it’s out by about 1/2 -3/4 in.
    Bill

    Attachments:
    #133568

    What kind of glue did you use? If you used hide glue it would be easy to pull the joints apart after soaking them with warm water. But if you used regular wood glue like Titebond 1, 2, 3, and try to “fix” the joint you will probably destroy it.

    The first thing i would try is to torque the assembly in the opposite direction of the out of squareness. See if you can stress it back into alignment. Don’t over do it. You do not want to split any of the wood.

    If that does not help, can it be pulled square when you attach the other parts of the bed to it? Can you pre-assemble to see how it looks?

    If you can get back close, you may decide to let it be. If you are a stickler, re do it.

    Located in Honeoye Falls NY USA. The Finger Lakes region of Western NY.

    "If you give me 6 hours to fell a tree, I will take the first 4 to sharpen my axe" Abe Lincoln

    #133570
    chemical_cake
    Participant

    You can true up the mortise and then glue a little shim to one cheek of the tenon and re-fit. Should be fine if you pay particular attention to how this might move each rail, i.e. any offset from the original position of tenon/mortise must be duplicated at the other end of each rail to avoid developing a new type of crooked.

    Mortises that size I think I would tend towards boring out the waste first, something to consider next time if you found the chopping a bit laborious.

    It might also be helpful to put some practice into chopping mortises to develop your feel for what is perpendicular, a square chisel edge should be aimed at but shouldn’t be relied upon to guide a mortise.

    Matt

    Southampton, UK

    #133571
    Scott Chensoda
    Participant

    I would not try to force the unit square as it will not warn you that it’s about to pop, it will just suddenly split. Is it worth taking that chance?

    Personally, I would go with Matt’s idea but take it a stage or two further. If you true up the tenon as Matt suggested you are going to end up with the mortise a couple of mill longer at each end yes? Why not go another 2 or 3mm longer each end but just on the face of the mortise and chamfer the mortise edges downward so they recieve a couple of fine wedges. By the time they are glued, planed and scraped nobody will ever notice and only you will know.

    I must confess though I still fail to understand how using an off square chisel can form a trapezoidal mortise. Working to knife walls would prevent it as long as they were set out square.

    Not to worry Bill, adapt and overcome as they say. Treat it as your first challenge of 2016. I’m sure there are a few more waiting down the line. Whatever you do, don’t spill your beer.

    #133573
    hoddy2000
    Participant

    Ok thanks for the thoughts gents. The good news is I haven’t glued up yet, so I will true up the mortise holes and glue a shim to the tenon and see how that goes. This’ll be a first. I include my journal entry on this matter to see if you agree with my analysis. I hope you can read it. Happy New Year.

    Attachments:
    #133576
    Scott Chensoda
    Participant

    Hellfire Bill!! Moments?….Force?…. Next you’ll be trying to calculate how many Newtons you need to deliver to the chisel head to make the edge penetrate 1mm into the wood!

    I wouldn’t waste time and energy on analysing such a basic thing. Instead of your physics sketches etc, it all boils down to a very basic equation.
    An un-square edged and/or blunt chisel = Codge up (or words to that effect)

    Now sup up and start afresh in the morning.

    #133580
    Derek Long
    Participant

    You can help prevent this with a mortising guide (just a square block of wood will do) to keep your chisel perpendicular to the face, and make sure you stay in control of the chisel and don’t let it twist, which is another problem altogether.

    Joiners in centuries past didn’t worry about engineering-tolerance-square chisels. They made furniture just fine. Don’t sweat it.

    Derek Long
    Denver, Colorado

    #133588
    hoddy2000
    Participant

    I didn’t have much time today gents – too much parenting, but I got the worst mortise squared up by the removal of about 1/8 in. I planed up a thin shim and have glued it to one side of the tenon, taking the tenon on that side just about back to the original thickness. Tomorrow I’ll fit this tenon and post a pic of what I hope to be a straight rail coming out of the post.

    Brimstone! Scott if I’d known you liked engineering as much I’d have thrown in a few equations.

    Attachments:
    #133595
    Scott Chensoda
    Participant

    I appreciate the parenting thing Bill, I’ve had 45 years of it and not much sign of any let up yet.

    Forget the equations but you can work out how much force I need to apply to the outside circumference of this pint glass to stop it from slipping out of my fingers if you like.

    I’m sure your shims will work out just fine even though you might have to pare the leading edges a tad to ease fitment. Be nice to see it all assembled and square. Wish you well.

    #133621
    hoddy2000
    Participant

    I redid the two worst joints and they squared up really nicely. I dry assembled after doing just one, but it was still too wonky. After the second joint there is only about a 1/4 in. out of square across the frame and I can deal with that. Thanks for the tips and encouragement. Onward and upward! Thanks for the tips and encouragement.

    Attachments:
    #133646
    Matt McGrane
    Participant

    That’s great, @hoddy2000 . Figuring out solutions to these problems is a big part of woodworking and craft work. We wish it wasn’t such a big part sometimes, but …

    Good luck on the rest of the project.

    Matt, Northern California - Started a blog in 2016: http://tinyshopww.blogspot.com/

Viewing 11 posts - 1 through 11 (of 11 total)
  • You must be logged in to reply to this topic.