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Thread: Mortising machine - clean mortises?

  1. #1
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    Mortising machine - clean mortises?

    I have a project in mind that will require 1/4" through mortises. A lot of them. I pretty much stink at making mortises by hand. In your experience, does a mortising machine make clean through mortises? Do you have to turn the piece over and finish the mortise from the other side to get clean through mortises? I want a little group wisdom and experience before I purchase a tool.

    Also, your thoughts on what is a decent mortising machine are welcome. Money IS an object (and probably always will be in our household).

  2. #2
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    I have done through mortises on mine. The problem is the auger wobbles slightly and leaves a slightly round vertical line and it plows out slightly more wood than the side of the chisel. I took my modeling file and worked the sides to even things up and then cut the tenon to fit. It came out very well. I read once about someone using a file to change the diameter of the auger to alleviate this issue, but have not tried this.

  3. #3
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    If I want to have a clean, magazine-photo looking mortise, I have to follow my Delta mortiser with a router to clean it up. And it often isn't a perfectly vertical cut. Probably my technique and setup, but still not as easy as it looks on video. Lots of care needed in the clamping and un-clamping, and setting the chisel up to be parallel to the fence. Still better than doing by hand.

  4. #4
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    Like a lot of our "serious hobbyist" level machines, small mortisers work OK, floor standing beasts work better. One's success varies with the method they have mastered . . . OK, mastered is too strong a word but you get my drift ;-)

    For a through mortise I like a router if I can do the whole thickness (not flip things over). Clamp the material firmly to a spoil board to assure a clean exit. If the material is thick I will drill the bulk of the spoil out and chisel it from both sides. Lots of tips and videos, the blue tape trick and a block to guide you true can be found on Fine Woodworking. Tom McLauglin does a lot of through mortise work, Mike Pekovich does as well.

    https://www.finewoodworking.com/2020...pping-mortises

    https://www.finewoodworking.com/2013...rough-mortises

    https://www.finewoodworking.com/2014...rough-mortises
    Last edited by glenn bradley; 12-03-2020 at 10:06 AM.
    "A hen is only an egg's way of making another egg".


    – Samuel Butler

  5. #5
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    Perhaps I'm looking at this wrong. When you make a through mortise with a mortising machine, are your mortises clean on one side? I can cut from the outside and any chip out, etc. will be hidden by the other piece on the inside.

    By the way, I'm not tied to a particular wood species for this. Might be anything from oak to pine. If that makes a difference . . .

  6. #6
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    Not the fastest method--but one of the cleanest-- is a router with an edge guide followed up by a chisel. It also happens to be one of the least expensive, because i assume you own a router with an edge guide. A good quality bit with a mediocre router should give you great results.

  7. #7
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    There have been more than one recent threads on mortising machines that you may want to read through to get opinions.

    If you do go the hollow chisel route, it's imperative that the machine be setup properly including appropriate sharpening of the chisels and insuring that the drill bit is set so it does the work and the square chisel just cleans up after it. The heavier the machine, the likelihood of better quality results with less manual cleanup.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  8. #8
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    I’ve used an inexpensive Delta mortising machine for this. But hone the chisels before doing so. Even new chisels need some work.
    Regards,

    Tom

  9. #9
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    Thanks, all. A router will not do (at least won't give me square edges).

  10. #10
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    I have the benchtop Delta mortiser. I haven't done a ton of through mortises with it, but in my experience you can't count on a clean exit every time, especially when doing splintery woods. A finely honed chisel helps, as does a perfectly clean and smooth backer board beneath the workpiece. But even then it will sometimes tear out some on exit. Going halfway from each side is the most reliable way to get clean holes on both sides, but requires care (and stop blocks) to maintain alignment. Squareness of the bit to the fence is crucial as well.
    --I had my patience tested. I'm negative--

  11. #11
    sharp chisels is the important thing. have an 1,800 lb machine and chisels have to be sharp or it doesnt work well. Out of the box ones in the past didnt work well. Either flip and cut other side or id think pushed down hard with a bottom board might give you clean enough on the exit side. T hen it becomes will the chisel be long enough,. British wadkin chisels came in two lengths. I dont get too hung up on how clean they are inside, accurate is what matters. Same as a tennon, you can cut one on dadoe blades and it looks like a beaver chewed it but if its accurate its no big deal and likely glue better than one that looks like a Mercedes.

  12. #12
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    A full through mortise will depend upon the thickness of the work piece and the width of the mortise you intend to make..

    With a mortise machine and a sacrificial piece, under your work piece, I don't see why you wouldn't get a clean mortise edge on both sides.

    This might help you decide.



    Here's the link if you can't see the video
    https://www.youtube.com/watch?v=jIJWNBAUtyk

  13. #13
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    ChrisA, thanks for the tip on putting material under to prevent blowout as you go through the piece being through-mortised. I hadn't thought of that.

    Like all machines, proper setup with a hollow chisel mortiser is imperative to get proper results. The chisel must be aligned parallel with the material. The chisel must be sharp, sharp, sharp. I use both a handle sharpener when I deem it necessary and use a conical diamond hone before and during each mortising job as necessary with my General International benchtop mounted on it's own stand. I like to sharpen the bit and hone the chisel before I start each mortising job. I also flatten the outer edges of the hollow chisel in the honing process. I always sharpen, set up the machine and then run a test piece to insure the side of the chisel is parallel to the fence so my mortise is parallel to the material's edge against the fence. I don't use my GI hollow mortiser often but do enjoy it. One project I built, a porch swing, had IIRC 82 mortises and my hollow chisel made in reasonably enjoyable.
    Ken

    So much to learn, so little time.....

  14. #14
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    Quote Originally Posted by Dan Gill View Post
    I have a project in mind that will require 1/4" through mortises. A lot of them. I pretty much stink at making mortises by hand. In your experience, does a mortising machine make clean through mortises? Do you have to turn the piece over and finish the mortise from the other side to get clean through mortises? I want a little group wisdom and experience before I purchase a tool.

    Also, your thoughts on what is a decent mortising machine are welcome. Money IS an object (and probably always will be in our household).
    The Delta bench top mortiser is pretty good at 1/4" mortises, with some help.

    1/4" mortise chisels push the limits of the technology. The 5/16" chisels work better, there is better chip clearing. However, I do make a lot of 1/4" mortises. Some jobs will require thousands.

    The chisel mist be very sharp, and never burn. The auger needs a sharp edge, too. If your chisel is burning, stop and change whatever is making it burn, re-sharpen, and continue.

    I pre-drill 1/4" mortises with a 3/16" dill on a drill press. All it takes is a few holes, and there is better chip clearance and cooling. Pre-drilled mortises go so much faster and better that the time spent pre-drilling is worth it.

    Through mortises are best made from two sides. If your wood is flat, square, and cut off square, transferring lines within tolerance will go fine.

  15. #15
    You are more likely to get a clean cut on both sides if you enter from both sides. If you do mortise all the way from one side, start on the show side, or use a fresh sacrificial piece on the exit cut every time.

    Squaring up the corners of a routed mortise by hand is a bit tedious but no worse than dealing with the almost inevitable slight circular scallops caused by an auger bit overcutting its hollow chisel outline- as said, a quality bit carefully tuned and set up is key to clean results.

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