# Jig for accurately spacing mortises for slats



## botanist (Sep 17, 2008)

I'm planning to build a new bed for my wife and I that involves slats fit into mortises on the head board and footboard. I was planning on using a forstner bit in my drill press to rough out the mortises and I wanted to build a jig to streamline the process and less prone for error. I don't trust my accuracy to do this free hand

The jig would have to be able to support a long piece (over 60" as we have a queen-sized mattress) and I need the jig to do two things: accurately space adjacent mortises, and create mortises of the same size. I can then use a kerfmaker to create the tenons on the slats. My inspiration is the spacing guide on the Festool domino (which if I could afford one would make the process even easier). Anyone have any ideas?


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## LeeBarker (Aug 6, 2010)

You've got a simple math problem here. You'll spend as much time building a device to space your mortises as you will laying them out.

If you know the span, and the width of the slats, you're just about there.

Add up the slats, subtract that from the span, and divide that answer by the number of slats plus one and you have the gap.

If you can, clamp the top and bottom pieces together for the layout process.

Check your work carefully.

Build a carriage to hold the material vertical on the DP table; you'll need outboard support of course.

Commence to bore! Since you'll be cleaning out the mortises anyway, (I presume) you will be able to true up the ends where round meets square.

Ring my chime if this isn't clear, botanist. I'd like to see this be a delightful part of the project for you.

Kindly,

Lee


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## botanist (Sep 17, 2008)

The other option I was thinking of (and it sounds easier because I can do it on my bench) was to use a router jig. I would screw the router to a base with a couple of pins (one to help determine the correct spacing between slats, the other to determine the correct width of the mortise). I just have trouble visualizing what it would look like. Or I would just need one pin. The spacing between the pin and the bit would represent the spacing between slats and the pin would slip inside a preexisting mortise and that would limit the travel of the bit to the width of the mortise.


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## CharlieM1958 (Nov 7, 2006)

Here is one way to lay out the slats evenly. Now let me quickly add that I've never done this…. it just popped into my head as a result of your question. So maybe someone will jump in and say why it's a bad idea, but…

Lay out the two end slats where you want them to be, then use your measuring tape to find dead center between the two end slats, and lay out a slat there. Now just keep repeating that center-finding process between the previously-laid-out slats until you have as many slats as you want.


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## botanist (Sep 17, 2008)

I'm not too concerned about the layout or spacing of the slats-that part's easy. I'm concerned about creating a jig I can use to make sure that my spacing and mortise width are consistent when I'm cutting them.


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## Loren (May 30, 2008)

Do you have a plunge router?

It is simple to make a jig that you run a template
guide in and plunge your mortises to the same
size.

Assuming you start at one end and work towards
the other, the problem with using an indexing pin to space
mortises is compounding errors. I do not recommend
it. Your rails will not come out with the same
spacing of the mortises… not dead-on. You could
start from the center slat, but then you have to
do more setups of the jig to cut the mortises
referencing from different faces of the work 
being mortised.

Indexing pins work with dowels because 
the variation in hole size and centering from
hole to hole will tend to be small enough to
be insignificant.

You want your slats lined up evenly, right?

My advice is to use the plunge router, mark 
the mortise locations out by hand and get
the result you want the first time.

Further, if you put shoulders on your tenons
instead of using "slats" variations in the mortises
won't be visible.

You can go ahead and make a jig with a pin to
space router mortises, but you'll spend a lot of
time clamping, moving and unclamping it. 
The work will go quicker if you mark the joints
and cut them with a minimal router jig like a hardboard
template or a router fence i


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## CharlieM1958 (Nov 7, 2006)

It seems to me that once you have the mortises laid out and pencil marked, your only problem is supporting the work piece properly. A simple fence clamped to the table would ensure the cuts were properly centered front-to-back, and roller stands or some sort of purpose-built sawhorses on either side would support the ends. If you are 1/32" off in eyeballing bringing your bit into your pencil markings, it will never be visible to the naked eye. If you really want to be anal about it (  ) you can make a pencil mark exactly 1/2 the distance of the bit's diameter from the edge of the mortise layout mark, knowing this is where your bit point must make first contact.


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## botanist (Sep 17, 2008)

Loren, my idea was to lay out everything together (top and bottom) to make sure I've got the spacing right and then use the jig for cutting the mortises (keeping in mind that there will be some error involved and correcting for it). If I can make small corrections for each mortise maybe I can reduce the error. I was planning on putting shoulders on the tenon to hide any variations in the mortises.

Charlie, I'm pretty picky about stuff like that, so that's probably something I would do.


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## runswithscissors (Nov 8, 2012)

I agree you should have shoulders on your tenons. If not, the slats would have to be a perfect fit, or gaps would show. One suggestion: However you make your mortises (aside from a tenoning machine, which makes a square hole), there's no need to square the ends. Round off the tenons instead. Another time when I suggested this, one response was that rounded tenons wouldn't be as strong. But if this were so, it would mean the Domino tenons must not be as strong, and I've never seen anyone suggest that. It is a lot easier to round the edges of the tenon than to square the ends of the mortise. They don't have to be perfect.

By making the faces of the tenons a little narrower than the mortises, you gain some flexibility in correcting any spacing errors.


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## a1Jim (Aug 9, 2008)

It's simple you are the jig lay it out and go for it,this is how we get better at each woodworking technique. I know when you haven't done a certain operation many times before it's a little scary but once you have done it next time you will feel more confident. You can lay it out double check the measurements and the do you drilling and chiseling,if you have sharp chisels you will have it done in no time. If your concerned with your tenon fitting your morticies do a couple practice pieces on some scrap.


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## pintodeluxe (Sep 12, 2010)

I would recommend a benchtop hollow chisel mortiser. They are more affordable now than ever. 
The problem I have with hand chopped mortises is the workpiece will be full of dents on the back side. 
Using a drill press and chisels is a time honored way to do this, however it's not something you will do again after you get a mortiser. 
Layout becomes much easier once you are using a square bit to cut a square mortise.


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## oldnovice (Mar 7, 2009)

Here is a totally off the wall idea!

Make a jig as shown below:










Locate the center mortise position and by using the cross hairs on the back side of the template (barely visible in the image), cut the center mortise location using a router and a guide bushing (the first mortise has been highlighted in gray).
The template has a "dummy" slat that fits into the previous opening and locates the next mortise.
Fit the "dummy" into the opening, using the dowel to maintain lateral alignment, and cut the next mortise.
Move along the rail until the last mortise is cut.

Flip the jig 180° and repeat the mortises down the other side of the rail.
Then do the next rail in a same manner!

The jig consist of:

3/16" Plexiglas with the "dummy" slat and the router opening at the desired spacing. If the spacing is off it will be consistent.
Two dowels to keep the jig square to the rail. *It is important that these are properly located so when the jig is rotated that the lateral alignment is maintained!*

By changing the bushing to a larger size another mortise can be cut inside of the previous one or a dowel can be located by using the hole in the Plexiglass and the "dummy" slat.

I used this method to create opening for false tenons as shown below.


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## botanist (Sep 17, 2008)

Oldnovice, I like the idea of using plexiglass but I'm concerned about it's tendency to crack. How would I cut the hole for the mortise in the plexiglass? Can I use a router bit?


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## oldnovice (Mar 7, 2009)

Yes you can cut Plexiglass with a router but it works better cutting a slow speed. If you are concerned about cracking you can always step up to 1/4" thick or more. I used 1/8" and raised the template so my bushings would work. If a crack starts, use some Plexiglass cement to glue it back together … that's what I did.

Remember the template will give you the exact cut out so make it as precise as possible … trial and error is the best as it took me three attempts to bet mine "perfect". Make it smaller and then you can always enlarge it. I cut mine with a combination of router and files to get it the size I wanted.

The dowels must be precisely located if you are going to flip the jig.

Lastly, make the template large enough to support you router base and *clamp* the template *securely* for the cuts. There is nothing more unnerving as to have the template move during a cut.


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## joeyinsouthaustin (Sep 22, 2012)

*+ 10 on laying it out by hand*. My experience in spacing jigs for projects like this is that it doesn't take much to get off. 1/64' will quickly build up to 1/2" You will need to be able to micro adjust the jig to 1ooo/th of an inch. Combine the two methods. Build one jig to get consistent mortises, Your main goal, then reference that jig off of center lines. Use the negative space layout* Lee Barker* clearly gives (op +1) This way you just center the mortise jig on the layout you did. It will go muuuuch faster than trying to fine tune a spacing jig.

If you are not concerned with the spacing on the far left and right side, use the peg style jig that* old novice*, and *loren describe* I would add one thing to that jig. Mount the post in a channel with a compression fit from the top, so that it can be adjusted left and right, both for micro adjusting, and to make it more useful. Then cut everything long and trim the left and right equally to get to final size.

My ten cents


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## botanist (Sep 17, 2008)

joeyinsouthaustin-I like the idea of putting the post in a channel to make it more adjustable. I don't want to just make a spacing jig and then hope that it gives the correct spacing the entire length of the piece. I was hoping to do the layout on the top and bottom pieces together and then do the cutting with the jig, adjusting it to cut exactly where I laid out the mortises. Or I could skip the pin altogether and just have a hole for the mortises that I need, that way I'm not compounding my errors or making things too complicated.


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## joeyinsouthaustin (Sep 22, 2012)

Adjustable peg is a plus, but if you want all the negative space to be equal, I would lay out by hand and reference to a center line on the mortise jig, I still maintain that in my experience using a spacing jig in situations where the all the negative space must be exact and confined to a set dimension is not very effective. It only takes sixteen spaces for a 1/64" error to add up to 1/4". If I were doing it, I would honestly do what *a1jim* suggests. I routinely lay out by hand and just take it over to my box mortising station and put the chisel on the mark using just my eyes. However lately I have been also using a TREND jig, used for mortising deep mortise locks, and a plunge router. But primarily because it adjust faster, has clear center lines and….not to get the ocd forum going again, it has better dust collection :0


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## botanist (Sep 17, 2008)

A big problem I have is money. Getting the lumber for this project is going to be tough enough, let alone buying something like a TREND jig or hollow chisel mortiser (both of which would be great tools to own). I'm more likely to buy a new drill press before I purchase any one of those. I'm also pretty constrained by time (the perils of traveling for my job when it's warm enough to be in the garage and having a 15-month old daughter). I like the idea of a router template because it could save some time (in theory)


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## joeyinsouthaustin (Sep 22, 2012)

Here is an example of a cheap to build jig. Imagine a wider table at the top, for more stable work, with the dimensions for your mortise. For mortising with a plunge router, you will want to set it up to work with a collar. Note the center lines for quick alignment. Note this can also be made with one leg, for easy clamping to work piece, and shimming to adjust centering. (the jig pictured is once again for mortising doors)


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## oldnovice (Mar 7, 2009)

Here is an alternative that doesn't use the "dummy slat".










The two dowel are used to make a self centering jig. The two dowels reference both sides of the material and therefore locate the center.

The router opening must be located properly between the dowels and the vertical hairlines are used to line up to the layout lines on the work material.

*The router opening is located 1/2 way between the horizontal and vertical location of the dowels.*
If you work material is uniform in thickness or even slightly off, this jig will locate the mortise in the center!

If you want more details on locating the router opening PM me and I will send you a PDF print.


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## oldnovice (Mar 7, 2009)

*Correction on the post above!*

If the thickness of the material varies the router mortise opening will still be centered *but not parallel to the edges*!


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## RogerInColorado (Jan 18, 2013)

Have you considered simply cutting grooves in the top and bottom rails and filling the spaces between the slats with a "filler strip". I've seen that done, and if you don't know what to look for you will never see it after the finish is applied. I is much less stressful than worrying about tolerance stack-ups and the router slipping.


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## RogerInColorado (Jan 18, 2013)

Further to my post 3 days ago, The Woodsmith Shop TV show covers this exact technique in the "Morris Chair" episode of season 6 (current season). If you get it on PBS, make sure to watch for it. You can buy all 13 episodes for about $30.


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## woodman88 (Feb 24, 2011)

There is a plan on PLANS NOW for a classic cherry bed that uses 1/2 thick slats mortiise into 1 1/2 thick stock 
I have built 3 of these works great. There is a plan for the jig also using a router


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## BigMig (Mar 31, 2011)

perhaps others covered this already, but I'd "gang" your mating parts together to ensure that the holes align exactly. So the jig might contain two holes for the plunging router .


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