Mortising jig
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- This topic has 14 replies, 6 voices, and was last updated 6 years, 3 months ago by Spencer Gaskins.
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9 January 2018 at 7:17 pm #431759
Technical question: When determining the depth of the router to mark the mortise and the tenons, how does one determine the depth quickly.
For example, I want my tenon to be a half inch. Easy enough, as I am going to be using a half inch chisel. And my board which will have the mortise is 1 inch thick. So, that means that I will have a (slightly less than… approx. 1/32nd) 1/4 inch depth on the router. The formula would be 1 inch thick minus 1/2 inch mortise divided by 2… and then reduce by 1/32. So, the depth of the router would be 7/32nds deep.
This is all well and good and easy math. However, Paul Sellers doesn’t mention this in the video on the mortising jig, and seems to me that he is doing this by some other innate method very quickly to get a centered mortise. Does anyone know if he is using some other method?
Also, the jig does work very well for off-centered mortises… but, you would need to use two routers and math.
For the life of me it appears that Paul Sellers is using some other magic to derive… is there some other method when using the mortising jig?
9 January 2018 at 9:32 pm #431828when you use the morticing gauge you, set its fence distance so both points hit at the same spot when registered from either face..
9 January 2018 at 11:11 pm #431886Hi Ron,
Thanks for the reply.
However, I am not asking about the use of a mortising gauge, but specifically about the Paul Sellers mortising method/jig which specifically calls for (and is relatively dependent upon) the use of a hand router (or two, or three :))
Hi Spencer,
Hope all is well with you.
I’ve not tried this technique, but I’m going to go out on a limb and say that it’s probably eyeballed or eyeballed with a rule. In your example with a 1/2″ thick tenon and 1″ thick stock you are going to need to set the router at less than 1/4″ deep by some small arbitrary amount. How small an amount will dictate how much paring of the mortice sides is needed to match the thickness of the tenon. If it’s less than 1/4″ you should always get a good fit and it will always be centered on the piece.
What I think will be important is accuracy in the thickness of the 2 pieces you are joining. If you are out you will end up with either a lose or tight joint.
It could be you are seeing a problem that I’m missing though, in which case I look forward to hearing back from you π
All my best,
Paul@ARCTAIN , it’s an interesting and perceptive question. I think there are good reasons for the traditional methods that are lost with the router. This practice is taking the corners off of the blade, which of course you can sharpen back. The first time you slip with the router and get yourself, it’s not going to be pretty. The mortise gauge seems faster to me and is how he taught us in class. You put the chisel between the points, eyeball center, press to get two dots, flip to the other face, and then adjust until you get the same from both sides. What’s critical to understand at this point, especially if you milled the wood by hand, is that you then lock things down and make all your marks on all equivalent pieces from the reference face and don’t ever check again from the non-reference face. If you use a method that works relative to more than one face and more than one edge, then that method is assuming perfectly milled lumber. I suspect, with no authority, that is a total waste of time unless you are milling with machines.
10 January 2018 at 3:10 am #431989I think Paul is almost certainly setting the depth of the router by trial and error. Making small marks from either side of the work, then checking with his chisel to see if itβs close. Aim for a dimension a hair wider than your chisel. The extra can be pared off after chopping the mortise.
I did something similar but used a mortise gauge set a little wider than my mortising chisel and I ran the gauge from one reference surface only. I used trial and error to get the gauge lines very close to perfectly centered on the work. I laid out my chisel guide block with the same gauge setting.
Whatever the final router depth I used in making the guide block, I kept that depth setting and used it for the final trimming of the tenon cheeks. As Paul does, I still had to make use of two router planes; one set for the final cut and the other to get close.
Hope this helps!
- This reply was modified 6 years, 3 months ago by Harvey Kimsey.
10 January 2018 at 7:49 am #432075Thanks for the replies.
@ed – I really wanted to come to class last year, and had an opportunity for a 9 day class as someone dropped out last minute. I attempted to juggle my schedule and had it all worked out except for one thing I could not move. And wo, I missed out as I was planning on class this year, when it was announced that there would be no classes in 2018. Here’s hoping for 2019! Funny you should mention the mortise gauge as the method taught in class as Mr. Sellers mentioned in the mortising jig video that the reason he came up with this mortise jig method is because so many students were having trouble with mortises in class, and it bothered him. So, he expanded on his, already proven, method of creating a mortise jig – and one that specifically relies on the boards being perfectly milled and the hand router.I am currently using a mortise gauge, but want to switch over to the mortise jig much like I have with the dovetail jig (huge time-saver there…). While my mortises aren’t ragged, and my tenons fit well, expanding the toolset is always on my mind.
He might be eyeballing it – and that’s fine. He might be doing the math quickly in his head, and that’s great! With a mortise gauge, I know exactly where to cut the mortise because I have, as you all have said, found the center with trial and error. I am hoping for something besides trial and error with the jig – be it math, or some other magic π
Thanks for your responses – I very much appreciate them.
10 January 2018 at 5:57 pm #432580Hkimsey – thanks.
The technique you describe is almost exactly what I am doing now. I use the mortise gauge to layout, and then cut and pare with the chisel, and then clean up and fit with the hand router.
I just would li,e to know if it is by math or by eye that Mr Sellers is doing this π
@ARCTAIN , we cut the mortises for the lid & bottom of the tool chest, the mortises for the coffee table, and the mortises for the rocking chair using just the mortise gauge and the chisel mortising guide. Actually, there were a few mortises on the chair (rear post) for which the guide block could not be used. Everyone completed the projects. I don’t recall any problems, really.
One can easily buy or make several gauges, set them, and leave them for the duration of portions of the project. You cannot buy that many router planes. Also, the route blade cuts on the wrong side of the line, while you could tune the pins on a mortise gauge to bruise just the waste.
I should look at the video again, but I just don’t see the big advantage vs. using a mortise gauge or marking gauge and I do see disadvantages.
10 January 2018 at 11:08 pm #432920Ed,et al – yes, take a look at the video…in tools and techniques under masterclass videos from Aug 2017. New and improved…
Thanks, maybe you can see abit more clearly there…
Spencer
I know i’m laboring this, but…
For me it’s all in the statement at around 2:34 where (I paraphrase) he says that he’s marked 1 mm wider than the width of the chisel, but it could be up to 3mm. To me that means marking 1/8″ (3.175mm) over size would probably be just fine. Taking that further and being intentionally flippant, you could chose your imperial chisel to match your marking π
Centering is never going to be an issue since he references from the opposing faces on both the mortice and the tenon.
It certainly isn’t going to work for morticing different thickness of stock together.
I have previously used the router as a marking gauge and I agree with @ed that if you slip it really does have the potential to ruin your day.
Cheers,
Paul11 January 2018 at 3:04 am #433106Hi Paul,
No – you aren’t belabouring the point π I feel I am not making myself clear – which is probably true π
I agree that he says that – which is why I made the tenon 1/32nd inch over-sized (1mm). The question I have – and perhaps it’s just me – but HOW does he determine the depth in the first place from where to remove that 1 mm (up to 3 mm) ???
Maths, I assume –
Start with a 12 mm chisel. Know the thickness of the rail – remove the 12 mm from the thickness and divide the remainder by 2 – and then remove 1 mm and set the router to that depth.
It works – and is enough to get me moving – this isn’t keeping me from working π
But, since Paul doesn’t mention it, and he does it with the depth of the router already set, I am just wondering if he did the arithmetic off camera, or if he has a shortcut π
Thanks for taking a look at the video – I really appreciate it… perhaps I am getting hung up on nothing since I have a ready-made answer π
Good to hear from you – hope things are well, Paul, and that you are working wood! π
Spencer
Hi Spencer,
I assume off the camera math too, and exactly as you describe, and then an arbitrary setting on the router along those lines. Agreed, I would be useful to have an absolute answer and there’s only one person that can provide that. As you point out the video doesn’t. Perhaps Paul S will chime in?
As to my activities, I’ve spent the last several months experimenting with creating composite greenland kayak paddles (Carbon/Glass fiber and epoxy, plugs, molds and a very steep learning curve), so not too much on the woodworking side, but it’s become way too cold to do that in my workspace and the interest in wood always seems to win out anyway. Hence, back here and back to some fun woodworking projects.
kind regards,
Paul- This reply was modified 6 years, 3 months ago by prbayliss.
- This reply was modified 6 years, 3 months ago by prbayliss.
11 January 2018 at 5:45 pm #433614I just watched the bridal joint video and paul describes the process very well there with known width, known chisel and known offset for the tenon you mark both and they come out equal the extra he talks of, i think ,is just safe cutting distance to leave something to pare back to the line with the router plane
12 January 2018 at 5:45 am #434103Thank you @deanbecker!
That’s exactly what I was looking for – math is how he does it.
Thanks!
Spencer
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