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  1. #1
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    Default Improving mortise chopping efficiency

    My arms are hanging limply against my sides, and lifting up my fingers to type this post is an undertaking in itself. Simply put, I am shattered from chopping large mortises this afternoon, and I have another bunch to do tomorrow.

    I have a little mortising experience, but nothing on this scale. I was chopping 25 mm mortises through 90 mm Tasmanian Oak legs.

    I found that when making my digging cuts (bevel facing the direction of travel), each successive ďstepĒ was only a mm or so lower than the previous one. Iím sure with previous projects each step was greater.

    I tried taking a larger bite, then smaller but it made no perceivable difference. Is it simply a factor of the 25 mm edge wonít penetrate as far as a 6 or 12 mm chisel?

    Would proper mortising chisels work better (I could probably hit them harder than my bevel edge chisels).

    As it was, I would chop the length of the mortise (90 mm), and then turn around. By the time I got back to the start, having travelled 180 mm, I was at half depth (45 mm) or at least close to it, so had to turn around again to get the rest of the mortise to that depth. Then flip the leg over and start again from the other side.

    Tomorrowís mortises will be 180 mm long, so may do 12 or 16 mm mortises for those ones.

    On the bright side, I was not at all cold in the shed today from the exertion, and the results did look pretty good.

    And thoughts would be appreciated.

    Lance

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  3. #2
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    Without knowing how you are fully doing your mortise, I always think of it as waste removal. I would think what is the quickest and easiest way to remove the bulk of the waste before picking up a chisel.
    Drills and routers are my preferred method.
    Recently I needed to fit a mortise lock in a solid core door. I was filled with dread. I did not want to spend hours trying to drill square and then clean up with my mottle collection of half sharp chisels. I lashed out on a lock mortise jig and started a thread asking for advice and tips on how to use. Unfortunately the thread disappeared in an upgrade so my first use of it (and only use) was a learning curve. It assisted greatly, not perfect but probably saved me a lot of time and angst. Still needed to clean up the mortise and make it square.

    If the mortise has a width of 25mm, then a 25mm chisel that is sharp can become your best friend.

    Good luck with your mortises.

  4. #3
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    Chopping 25mm mortises with just a chisel? Even if you could actually find a 1" mortise chisel (they do exist but are exceedingly rare) it is still going to be hard work. The one time I did mortises on this scale I bored out the majority of the waste with a brace and bit first.

  5. #4
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    As Mark and others say, remove the bulk of the mortise by drilling it out, preferably using a drill press. After marking the position of the mortise using a marking gauge and marking knife, drill holes along the centre line of the mortise, close together but not overlapping. If possible, the holes should be within about 1mm of the sides and ends of the mortise.
    After the holes are drilled, use a chisel to make cuts parallel to the ends of the mortise, level with the edges of the holes. These are to prevent splinters breaking out past the ends of the mortise.
    Then, chop out the wood between the holes, until the sides are straight and vertical. If it is a stopped mortise, use a mortising chisel to flatten the bottom. If it is a through mortise, work from both edges towards the middle.
    When the mortise sides are straight and deep enough, pare them out to their final positions, setting the chisel in the marking gauge marks to cut the final width. Square the mortise to the marks you previously cut. Finally, with a sharp mortising chisel, pare back to the ends of the mortise.
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  6. #5
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    Default Improving mortise chopping efficiency

    Thanks HandyJack and Mark,

    Now I feel like an idiot. Iíve been doing a bunch of reading and it appears that youíre both correct, nobody chops 25 mm mortises with just a chisel like Iíve been doing, and as Mark suggested, you canít even buy morticing chisels that large!

    Iíve got one more that has to match the others, so must be 25 mm. Iíll try removing some waste with the drill first... if I can lift my arms tomorrow.

    Thanks again
    Lance

  7. #6
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    Thanks for the detailed explanation Alex. Iíll read it again in the morning before attempting it.

    Kind regards,
    Lance

  8. #7
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    Another thing to add to Alex's instructions... If you can clamp a small square block to the top face of the piece, level with the edge of the mortise, you'll have a guide to work from to keep your chisel nice and square to the face.

  9. #8
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    Lance, there are occasions when a 25mm wide mortice is used (such as a bench), however the rule with something this wide is to do a double 6mm mortice/tenon joint.




    Regards from Perth

    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

  10. #9
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    A mortise chisel would improve your efficiency, but you probably won't find a 1" width. I can't say I've even seen one.

    Derek's suggestion is good, but if you don't want to do that for aesthetic reasons, or just because it wouldn't be consistent with what you've already done, then ultimately boring out the bulk of the waste is the best answer aside from "Use a hollow chisel mortiser". After you've bored out what you can, your bench chisel will be far better suited for the task at hand. The fact that your mortises are through mortises makes this all the more appropriate. Personally, I would use a drill press so as to keep your holes nice and straight.

    Also, I'm not sure what your comfort level is with sharpening, but you need to be damn sharp for this, so that may be something to consider.

    Hope that helps,
    Luke

  11. #10
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    Most of the time I use a router to mortice. This is the jig I built ...









    Holding the stretcher ready for morticing ....







    Regards from Perth

    Derek
    Visit www.inthewoodshop.com for tutorials on constructing handtools, handtool reviews, and my trials and tribulations with furniture builds.

  12. #11
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    Thank you Elan, Luke and Derek.

    Elan, yes lying in bed last night I was tossing up what to do, and had considered a block of some sort as a vertical aid. It is good to have it confirmed.

    Luke, my sharpening is pretty good. Good enough that after a lot of hand tool work my wife and kids tease me, telling me I look like Iím wearing a bear suit, as my arm hair abruptly stops at my left wrist! I need to find a more socially conforming manner of testing sharpness. So in short, I have no concerns with the chisel being sharp enough to do paring cuts across the edges after a rough out.

    I remembered last night that years ago I made a post and rail fence and used the router to make the mortices.

    Derek, I was lying in bed last night contemplating m&t joints in thick members when I had an aha moment regarding double mortises.

    Am I correct in my assumption that with stretchers there is little requirement for sheer strength at the joint, so a thick tenon as I have done is really not necessary? I.e. in my case Iím joining a 45x90 rail into a 90x90 leg. The rail may may serve as the base of a shelf at some point. Is a double 6 mm still adequate (aesthetics aside)?

    Also your clamp jig looks good.

    Iím now off to the shed (brrrr). I do have a drill press and router, so will contemplate my way forward.

    Thank-you all for your advice.

    Lance

    P.S. I must apologise for spelling mortice incorrectly. Despite having my spell checker set to AU, it still keeps changing it to ďmortiseĒ. I can only hope the Queen isnít reading this thread, I feel sure she would be disappointed.

  13. #12
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    I reckon in the size you're looking at, there'll be more than adequate shear strength for most things, and in fact, the double mortise will be stronger under tension (i.e. pulling the joint apart) than a single, because of the extra area of the glued faces.
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  14. #13
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    Quote Originally Posted by LanceC View Post
    it appears that you’re both correct, nobody chops 25 mm mortises with just a chisel like I’ve been doing,
    I can't offer any better advice than that posted above but I can confirm that you're not the only one. When I made my bench 3 years ago my through mortices were shorter than yours but were 31mm wide in jarrah and well aged kapur. I reckon I did more than half of them with chisel only before giving in and drilling out the waste so I can sympathise with the sore arms/hands.
    Cheers, Bob the labrat

    Measure once and.... the phone rings!

  15. #14
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    Quote Originally Posted by labr@ View Post
    I can't offer any better advice than that posted above but I can confirm that you're not the only one. When I made my bench 3 years ago my through mortices were shorter than yours but were 31mm wide in jarrah and well aged kapur. I reckon I did more than half of them with chisel only before giving in and drilling out the waste so I can sympathise with the sore arms/hands.
    Thanks for commiserating with me. I guess these are the lessons you learn as you go.

    Kind regards,
    Lance

  16. #15
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    You could always buy a mortiser to improve your efficiency
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