Making Repetitive Mortises


Leaseman

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As I continue to practice making mortise and tenons I'm finding the biggest problem I'm having is making mortises that are identical. We have ways of cutting boards to identical lengths using stop blocks. We rip stock to identical widths using a rip fence, dowels joints are easy. Just use the same drill bit every time. But when making mortises we have to eyeball our measurements and cuts resulting in some variance albeit small. And when making loose tenons as I like to do this causes a problem because you are left with some tenons being a little to loose and some being too tight requiring me to make adjustments on the individual tenons. It would be cool to make a bunch of tenons all the same size and they all fit perfectly in the all the mortises. Are there methods I don't know about to make identical mortises? I use a jig that holds the router to the side of the board just fine but it's the cutting of the mortises to exacting dimensions repetitively that I find the struggle.

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Well for 1 the length of the mortise doesn't matter much unless you go too far and the shoulder doesn't cover it up or you don't go far enough and the tenon doesn't fit. having a gap on the end grain portion of the mortise is not concerning at all. In fact little to no strength is generated from the rounded portions of the mortise because it's an end grain glue joint. We all should know how weak end grain glue joints are. If your loose tenons are falling out your tenon material is probably a hair to thin and should be thicker to achieve a friction fit.

This pictures illustrates my point. I cut the mortise with a wiggling drill thingy (the domino) but the method you use doesn't matter. This is why there hasn't been much R&D put into the situation your talking about.

2451041977275992443.thumb.jpg.4e9553ef42cb5bcc194541dc9bedc183.jpg

There are methods with guide bushings and templates to make exact mortises that have stops. Marc's Morris chair build is phenomenal in explaining multiple ways to do M&T. Check my build journal i cover a few of them.

Ok that's a lie festool made the domino but so many people think it's too expensive so ....

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So is that to say that its common in woodworking to not have tight ends as you illustrate? In other words woodworkers don't worry about the length just as long as the sides are tight?  I'm trying to follow proper protocol as best as I can and want to cut has few corners as I can when learning new techniques (no pun intended!)

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Chestnuts pic is an extreme example but he is right.  I usually do the mortises with an router and rather than squaring of the ends of the hole with a chisel I round over the ends of the tenons.  A little gap beween the tenon and the end of the mortise is fine,  I an most concerned about the width having a nice fit.  There are times that you want a more exact fit like for through tenons, etc but those are less common and you will know it when you see it.

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28 minutes ago, Leaseman said:

So is that to say that its common in woodworking to not have tight ends as you illustrate? In other words woodworkers don't worry about the length just as long as the sides are tight?  I'm trying to follow proper protocol as best as I can and want to cut has few corners as I can when learning new techniques (no pun intended!)

So i guess this gets complicated because I'm struggling for how to explain this. In the image I provided above i can get some slight left movement. A common practice is to create the tenon to just fit the mortise so that movement is limited or non existent. This helps during glue ups but can also create issues. In floating tenon operations where not everything is perfectly oriented having an over long mortise will allow some fudging 1 way or another with out sacrificing strength.

My example is extreme as @Ronn W points out but it's a non structural part so I'm not concerned about maximum glue surface it was just a very convenient picture. The main reason people round things out and make as big of tenons as possible is to maximize glue area to make the strongest joint possible. Most times it's over kill though. I can only think of a few pieces of furniture where that amount of ultimate strength is necessary #1 being chairs. #2 anything that gets moved frequently like a coffee table or ottoman.

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Leaseman, 

It sounds like you're dealing with a few different issues. To make matters easier, let's get the terminology in sync.

1. Below is a drawing of the parts and their corresponding names. In short, The length is the measurement from the shoulder to the tip along the grain. The width is the measurement across the gain from edge to edge. The thickness is the measurement from face to face.

1632983057_ScreenShot2018-09-11at3_49_44PM.jpg.9ce68ccd50e75bdaada646990d975f74.jpg

2. There are multiple methods of cutting mortise and tenons. You're cutting them with a router. Lot's of factors can come into play to cause slop or looseness in a mortise - bit runout, improper or inconsistent feed direction relative to your edge guide, dull tooling, taking too much in one pass, etc. I would also recommend watching Marc's videos and spending some time looking through the journals on this site. Also, I'd recommend looking into Philip Morley's blog or youtube channel. His mortising fixture is easy to make and works great. https://philipmorleyfurniture.com/video/

3. As I said above, there are multiple ways to make a mortise and tenon joint. For the big majority of my work, I use loose, or floating tenons. That is, you cut mortises in both pieces and glue in a tenon section milled to fit precisely. They much easier and I'd argue, in most cases stronger than integral tenons because because they're easier to make precisely, so they fit and hold better.

There's certainly nothing wrong with learning to make traditional mortise & tenon joints, but I'd recommend reading, watching and experimenting with a variety of methods and techniques to find one that works best for you.

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I don't make mortises the same way you do- I use a router table or a hollow chisel mortiser- but, in general, I am always looking for a way to use some sort of a stop block- so that I can measure everything beforehand, and then I don't have to "freehand" start/stop points. I imagine there's probably a way to set up some sort of a stop block even if you're doing a hand-held router with an edge guide, no? Clamp something to the beginning and end of where you want the base plate of the router to be? If you have a stop block on both sides, you can make some sort of "spacer" and use it to set start/stop blocks for each mortise, that way you're ensuring that each one you cut is going to be almost exactly the same, probably to within a few thousandths.

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If your making them on the router table clamp a stop block to your fence and all you need is to have a start mark. If your router table fence is long enough you could do the same for the start. The problem is reference face and the stop block  needing to be swapped sides frequently. With the HCM i believe some of the floor standing models have start and stops. I might be wrong. After i saw how expensive an HCM was i determined the Domino was the better tool for MY shop.

I've done router table and i don't like it. I prefer doing it with an edge guide and a plunge base. I typically mark the center point for the start and center point for the end plunge the start and stop and then clear the waste in between. Doing this i made all the mortises for 2 morris chairs in about 45 min that were dead accurate. Again i don't think stops have hit development because it's difficult and the demand isn't really there.

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If I'm making multiple mortises in this more traditional style, I prefer to use a router with dual edge guides and stop blocks so that I can easily repeat the process on each part.  Another easy way to do it is to create a template with center lines and clamp it to the work piece.  From there, just a router bit and bushing to follow the template.

Both create repeatable results and get used often in my shop!

Of course the modern method is the Domino but, that certainly comes with a price!

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4 hours ago, ..Kev said:

If I'm making multiple mortises in this more traditional style, I prefer to use a router with dual edge guides and stop blocks so that I can easily repeat the process on each part.  Another easy way to do it is to create a template with center lines and clamp it to the work piece.  From there, just a router bit and bushing to follow the template.

Both create repeatable results and get used often in my shop!

Of course the modern method is the Domino but, that certainly comes with a price!

I like using my router with the dual edge guides myself but how do you incorporate stop blocks in this set up? This would be even more challenging when making the mortises at the end of a board. How would you employ stop blocks in this scenario?

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5 hours ago, Leaseman said:

I like using my router with the dual edge guides myself but how do you incorporate stop blocks in this set up? This would be even more challenging when making the mortises at the end of a board. How would you employ stop blocks in this scenario?

You can place anything off the end of a board to create that stop.  In fact, it's probably easier this way as you have something clamped to the bench that becomes a almost a jig as you set the next part in place.

2 hours ago, Wood Basher said:

Can I ask why? I understand why if you are using a domino but if you are not using a domino what advantage do loose tenons give?

Sometimes you simply want a larger floating M&T than the domino (either) will provide.

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6 hours ago, Leaseman said:

I like using my router with the dual edge guides myself but how do you incorporate stop blocks in this set up? This would be even more challenging when making the mortises at the end of a board. How would you employ stop blocks in this scenario? 

You can also take a look at building a router jig similar to one Michael Fourtune designed. Allows clamping and start and stop blocks for your mortises.

***I forgot that you can not post PDF's here so i hacked it up into 2 jpgs....I'm to lazy to try to combine it to one...sorry***

Mortising Jig-1.jpg

Mortising Jig-2.jpg

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4 hours ago, Wood Basher said:

Can I ask why? I understand why if you are using a domino but if you are not using a domino what advantage do loose tenons give?

Loose M&T gives some advantages when weird angles are in play or even curves. I disagree with kev though if i want a wider M&T the Domino is still a great tool plunge a few times side by side and make some tenon stock and it's no different than any other method.

I still struggle to understand why this matters. It seems like a lot of work to just cover it up to never be seen again. In 50 years when someone is hauling all my junk to the landfill no one is going to comment on how all the mortises are identical.

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I am also in the camp that uses floating tenons or traditional tenons as works best for the situation.  I sometimes square the mortise, I sometimes round the edges of the tenon.  Certainly a mortise done with a router and jig allows great accuracy and repeatability.  I think your lack of repeatability comes from stops lacking in your setup.  If you jig mounts securely your width is controlled.  all we have to do is find a reliable start and stop position.

I would build one of the many shop made jigs you can find in the magazines or on the internet, Michael Fortune's version looks fine.  Just be sure the version you choose allows for a reliable start/stop block or template bushing control.  You could also put a "Want To Buy" add around for a Mortise Pal (no longer made). 

MP-Stop.jpg.f93d77cda4840a31f19d8b1b1edb258b.jpg

It comes with a variety of templates and you can easily add more of your own.

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Although I have a Domino, it is not an end-all / be-all mortiser.  It is a very useful tool but, only one blade in my Swiss army knife of tools and methods.

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