Slot Mortiser - handheld & cordless using the Makita trim router

In this video I'm going to make a handheld cordless slot morticing machine using a Makita trim router and some scraps of wood and metal from my workshop.

I'm sure we'd all love a Festool Domino machine for cutting mortises, but not all of us can afford one or justify the high cost.

This build is highly inspired by Neil at Pask Makes' video where he made one quite recently, I'll put a link to that video in the description box below, and this isn't a new idea, Stumpy Nubs channel made it's own version of one of these machines, and prior to that apparently a Russian woodworker came up with the idea. But for me the Pask Makes version was the one that really clicked with me and made me want to make one.  I haven't bought his plans though as I wanted the challenge of designing and making one for myself.  But I do regret that decision!  And I'll talk some more about that at the end of the video.  I did lots of drawings in sketchup and made multiple prototypes before making the one featured in this video to get it as good as I could get it.  

So the router I'm going to be using is the Makita DRT50 in the UK, XTR01 in the US, and I bought mine from the US so that's the one I have here but I believe they're both exactly the same.  There's also a corded version of this router available which is the RT0700, and there's even a clone of the tool by a company called Katsu which is actually quite a well regarded tool especially considering the low price - this can be had for about a quarter of the price of the Makita. 

And I won't be needing the router base for this project.

And there were a couple of bits I needed to buy to make this project - first I needed to replace the original collet that comes with the router with this new 8mm one, this was only a few pounts on Amazon and I'll link to it in the description box.  As you can see it just pushes in place and is retained by the bolt.  And the scond thing I bought was this 35mm long 8mm wide spiral upcut bit which will do the cutting of the slot mortices.  This bit was from Amazon too and the price was around £23 - link in the description box for that too.

The first job was to make the main case of the machiine so here I'm making the rip cuts at the tablesaw here based on the dimensions from my drawing, and I'm using some offcuts of 12mm hardwood plywood that I had spare.   And I made the cross cuts at the mitre saw.

So here are what will be the front panel, the base panel, and two side panels.

First I worked on shaping side panels based on the dimensions from the drawing again, I used a speedsquare and an oil can to mark up the curves.

I made the cuts at the bandsaw

And then I could glue and nail the side panels to the base panel. I make sure that the front edges are perfectly flush and then add glue and add the front panel.  Once everything was held in place with brad nails I added some clamps to get nice tight glue joints.

To make the sliding mechanism for the mortiser I needed some metal rods and you can buy metal rod in whatever size you want which would be ideal for this but as usual I like to use stuff I already have laying around and I had this router guide fence from an old router that broke years ago.  I just unscrewed them and then measured them with my calipers and they were 8mm in diameter.

I cut them to length with my angle grinder.

And they were a little rusty and messy so I cleaned it up with some sanding to make sure they were smooth.

Next I went looking for some hardwood that I could use to mount the rods to, and I pulled out some offcuts of oak

Using the tablesaw and mitresaw I cut 4 equal sized pieces based on the dimensions from my drawing

And then I marked up where I'd need to drill holes for the rods and I used my combination square to keep all of the marks consistent.

The marks I'm making here are offset slightly from the centre and I will explain the reason for that shortly.

I used an awl to mark a hole at the centre of each cross.

And then over at the drill press using an 8mm drill bit I drilled out both the holes in two of the pieces of oak. I'm using a brad point drill bit to make sure I'm centred to the holes I made with the awl before drilling.

Then I changed my drill bit to a 9mm brad point bit for both holes in the other two pieces.

So now I have two pieces with 9mm holes which will be for the mobile carriage on the rails which slide easily as you can see.  And two with 8mm holes which are nice and tight and these will be the end stops.

I marked them up so I wouldn't get the pieces confused.

I also marked up the top of each piece with an X, and this is why I slightly offset the holes from the centre earlier - herre you can see that by orienting the two end stop pieces in the opposite way to the two carriage pieces gave me a couple of mm clearance so that the carriage pieces can move backwards and forwards on the rails while the end stops are lower down and will be later secured to the base of the mortiser.

Next I cut two more pieces of 12mm plywood.

The first will be a platform for the carriage and it's just a simple rectangle but it'd need a hole at one end right in the centre, so I used my combination square to make a mark from both sides to find the centre of it, and then I drilled a hole which will later accommodate a bolt.  I was having some camera issues here so apologies for the flashing.

The second piece of ply will be used to make a pivoting platform that sits on top of the carriage and will hold the router.  I marked up the shape I wanted the piece to be.  This would have a hole in the centre too.  And it was shaped a bit like a pear.  Then I marked up for some housing joints which will later be used to attach the router and for that I'll be using some of these large hose clamps.

I chose these because a) they'll hold the router nice and secure to the pivoting platform b) because they're thin they won't not take up much space which allowed me to make the mortiser slightly smaller and more compact in size and c) they would allow me to maximise the pivoting motion to give a wider mortise cut if I ever need it.

I set up my cross cut sled at the tablesaw.  I raised the blade to cut about a quarter of the way through the 12mm thickness of the board, and then made a series of cuts to remove the material to form the grooves. I deliberately cut the slots while the board was still square, and then I could cut out the shape at the bandsaw.

Both the carriage platform and the pivoting platform would need to be nice and smooth and hardwearing to prevent wear, so I applied a coat of spray varnish, after waiting for that to try, I sanded it smooth with some 400 grit, and then added another coat of varnish. 

Next I cold glue and nail the carriage platform to the carriage mounts.  I left an overhang at the front as you can see.  And I found that those 9mm holes had given me just the right amount of movement needed without any play, but I knew that if I did have some side to side play here that I could always glue on some wood to the carriage mounts to remove the play, but I didn't have to - it worked great.

I used some super glue to stick some washers to the bottom of the pivoting platform.

And using some 240 grit paper I wet sanded the face of the washers to make sure they were flush and nice and smooth.

And it looked a bit like a face at this point 

Then I added a bolt through the pivoting platform, through a washer and then through the carriage base

And that got secured with a nut from the underside and I tightened the bolt to remove any play but still keep a nice pivoting motion and then added a second nut to lock everything in place.

The idea of using the washers was mainly to get a nice smooth motion and minimal friction when pivoting.  I'm not totally sure that this will work better in the long run than just wood rubbing on wood, but in my head it made sense to try it.

Next I marked up another piece of 12mm ply which would be used to elevate the router and keep it sitting level on the platform.  After cutting it to shape I glued it to the platform with some super glue.

In order to get the carriage to push all the way forward, I'd need to remove some material from the front end stop piece to make way for the bolt.  I used a forstner bit and chisels to do that.

And here you can see that the carriage will now be able to slide all the way forward.

I could then add the sliding mechanism to the shell, and I decided to secure this just with screws and no glue so that I can remove it later if I need to make any adjustments to it.  I drilled pilot holes from underneath using a countersink bit, and added some screws.

I also drilled some pilot holes through the metal rods and added a couple of nails just to make sure they couldn't slide out of the end blocks.  

Next using a piece of 25mm aluminium angle I cut a piece to length that I could use to keep the pivoting platform from tilting forward.  I marked up for some holes which I then drilled with a countersink bit and then I could drill some pilot holes to the carriage platform to secure it in place.

It took a bit of sanding to the pivoting platform to get this working nice and smoothly but eventually the router moved forwards and backwards, and left and right, but it couldn't tilt up or down - perfect!

I turned the router on and made some plunge cuts through the front panel to create a slot.

And I checked to see if the slot was at 90 degrees to the panel and it looked perfect.

Then I pivoted the router to square up the bit to the front panel and made reference marks either side of the bit, and from there I could find the centre point, and I marked up 10mm intervals.  This allowed me to pivot the router lining up the bit with those marks, and then mark up lines on to the carriage platform to correspond to cutting a 40mm wide slot, a 60mm slot or an 80mm slot.

Next I wanted to make some pivot stops, so I first cut a piece of aluminium angle and then totally forgot how hot metal gets when you cut it.

So I gave it a cold bath

I drilled a hole in it with a countersink bit and then I could offer it up and screw it in place.  I did the same for each of the three size settings - the 40, the 60 and the 80 and I did the same on the other side of the pivot platform too.

I started making the fence for the mortiser, so I cut all the pieces at the tablesaw and cut some 45 degree brackets at the mitre saw.

The bottom of the fence would need to have a vision panel in it so that I'd later be able to see the reference lines for centering the mortiser to the workpiece, so I marked that up, and used a 10mm drill bit to create a clearance hole for the jigsaw blade so that I could cut out the shape.

I assembled the fence with glue and brad nails.

And then I checked for square and it looked bang on.

Then I wanted to cut two slots for the fence to be adjustable, I marked up some holes with an awl, drilled them out, marked up the slots and then used the multi tool to cut them out,  It always amazes me how accurately you can cut with one of these when you want to.

And here's yet another face.

I had to do a bit of filing of the slots so that I could fit a piece of threaded rod in.  I wanted them to be a snug fit, not too tight not too loose.

And I'd already cut the heads off some bolts to give me the threaded rods.  And both ends of both rods got a washer and a wing nut so that I could easily hand tighten the fence to the front panel without using any tools.

I then clamped on the fence to the front panel so that I could drill through the slots and through the fence to give me holes in the right place. I added the wing nuts and surprise surprise, another face.

Here's how the fence adjusts. And I can use my small square to make sure it's straight. But I also decided to add some markings to the front panel so that I could easily set it to cut at 10mm intervals.  Once those bolts were tightened by hand it's really rigid so that worked nicely

I'd also need to make the fence non-slip, otherwise the force from pivoting the router bit left and right in the wood would cause the mortiser to slip - and that was a problem I had on a previous prototype. So on this one, I used some rubber from an old bicycle innertube.  

I scuffed up the bottom of the fence with some sandpaper to help get a better gluing surface and then added some super glue. Then I added the rubber stretching it out as tight as possible and clamping a scrap piece of plywood on top 

After the glue had set I could trim the excess rubber.  And this rubber was really grippy and it worked out well.

I decided to add a spring to the bars - this is another thing Neil from Pask Makes did on his version and I wasn't sure if I'd do it but then I found a spring from an old desk lamp in one of my drawers so I thought I'd give that a try and I think a little spring back is a good thing.

The case got my makers mark.

Next I starteed working on making a handle.  I glued a couple of pieces of 12mm ply together.

And using a hand plane I rounded over the front edge.

I marked up a place for my hand to go, found the nearest forstner bit to that size that I could and drilled a couple of holes and finished off the cuts with my multitool.

Then I marked up some roundovers and cut those at the bandsaw.

I could then glue and clamp the handle to the top of the front panel and you can see here there's a slight overlap where the handle meets the back of the front panel to get a bit of extra gluing surface for maximum strength.

I cut another piece of aluminium angle to use as a maximum depth stop.  This is pretty primitive, mainly because I expect most of the slots I'll want to cut will be full depth, so I don't expect to change the position of these regularly, but if I do need to I can just screw them in further back. 

At this point I decided to cut my first slot.

And that went reasonably well. And the slot looked really nice and clean.

But in order to make the mortiser more useable I'd need a centre point on the fence.  So I first used a square to set the bit as straight as I could, and then I could mark up the centre of the bit on to the fence.  So then I could mark a line on a test workpiece, line up the fence with that line, and cut a 40mm slot.  And to check if the centre line on my fence was accurate I offered up my tape and I could see that it was way off - the slot was about 21mm wide on the right hand side of the centre line and 17mm on the left hand side, so I needed to adjust the line on my fence by 2mm. And after that I took another test cut and it was nicely centred.

I just want to spend a bit of time talking about the good, the bad and the ugly about this project in case you're thinking of making something similar, because you might be thinking at this point that this looks like it's a pretty successful project but I want to confess a few things - so first the stuff that doesn't work well, and there are three things:

Firstly, I wanted the router to be easily removeable so I could use it as a trim router and then put it back in and use it as a mortiser again.  But the problem is that when I put the mortiser back in, I've found that the centre of the bit isn't always centred to the centre line on the fence.  I had assumed that using the hose clamps would make it self-centering, but that is not the case.  So I think that the plywood router mount that Neil at Pask Makes used on his is a better design than mine.  

Secondly, I was quite happy for my mortiser not to have dust collection, as it's only an occasional tool I could just use it wearing a respirator and sweep up the mess, or as it was cordless I could use it outside.  But what I hadn't anticipated was the amount of chips that would end up getting down in to the sliding mechaniser, so after cutting each slot I kind of need to blow the chips away which I can see getting a bit annoying.  On a previous prototype I had added a dust collection inlet, but that just wasn't really effective enough at collecting dust, so on the final version I decided not to bother with it.  Again, Neil at Pask Makes mortiser design appears to deal with dust really effectively, but as I didn't have the right components to add that to mine and also mine was designed to be used without dust collection I'm not sure I could add it to mine.

And thirdly, it's not the most comfortable thing to use, I found that if I held the router when pivoting it, my finger would bash in to the pivot stops, so I ended up holding it by the battery instead which works ok but I'm not convinced it's the best solution.  I did think about making the pivoting platform longer with a handle on the end so I could hold that rather than the router itself, but to be honest I'm now totally burned out with this project and I just don't have the motivation to experiment anymore with it. 

To be honest I completely underestimated how difficult a project this would be, anything with moving parts is always going to be a challenge, but it just became a burden to me to spend any more time on the project, especially at a time when I have quite a lot of paid work that I was committed to doing, and other project ideas of my own that I was more excited by than this.

It's not the mortiser takes a long time to build, you could easily build one in a day, it's the design part that's the real challenge and I think the version I ended up with was the fourth version I made, so that's probably 4 days I've got invested in it and I still don't have a tool that works as well as I'd hoped.  I do have a new found appreciation for tool designers, I had no idea how much work goes in to making a tool ergonomic to use and perform well.  And I already had a huge level of appreciation for Neil at Pask Makes, but now that level of appreciation is even higher!!

It's not all bad though, and there were a few things that worked really well and I'll talk about those things too: 

Using 12mm instead of 18mm plywood was a really good idea, I used 18mm on a previous prototype but because the makita cordless router is pretty heavy, mostly due to the extra weight of the battery which is obviously right at the back and made it quite cumbersome to hold by the front handle, but using 12mm plywood and also making the fence have more surface area made the newer version a huge improvement.

The fence adjustment works really well, I like that a lot. 

The rubber I added to the fence to make it non-slip works really well, on one of my previous prototypes I didn't add anything to the under side of the fence as I didn't think it was needed, I figured I could just hold it down firmly, and boy was I wrong.

The sliding mechanism worked well, although most of that was borrowed from Neil at Pask Makes again, but I think my version was possibly a bit simpler and easier to replicate.

And I love that it's cordless too, although that's not something that I can take credit for, that's down to Makita!

So in summary, does it work, yes, is it perfect, no, will I be using it in future projects, maybe, will I re-visit it some day, possibly when I'm less busy, would I recommend building one like this, probably not, would I recommend building one like Neil's version - yes, if you want one then you should watch his video and buy his plans, would I recommend designing one for youself - if you want a challenge then yes why not, but if you're anything like me, if I could have my time back, I would have just bought Neil's plans and built that.  And by the way I am going to buy his plans anyway just as a token of my appreciation for the idea. 

I'm sorry that it's not as good and as complete a project as I had hoped it would be but I hope that it was useful to you in some way, or at the very least I hope it was entertaining.