Adventures with Kumiko - Introduction

[pulleyt]

I came across the world of Kumiko December 2019 and set off on a journey of discovery from that point on. I posted photos of the various projects I’ve completed if you want to see the kind projects I undertook.

As there seems to be some interest, I thought I’d document the sources of inspiration and explain how I go about making Kumiko panels.

In my mind, there are four distinct processes involved in the creation of Kumiko panels and I have made jigs to aid each of the processes.

1. Cutting Kumiko Strips
2. Final thicknessing of Kumiko strips
3. Cutting grid work joints
4. Shaping the infill pieces

I have tried several ways to complete the work so I’ll submit a separate post for each of the four processes and detail the various methods I tried and my preferences going forward.

 

[pulleyt]

Adventures with Kumiko - Cutting Kumiko strips

I have tried three different methods to cut the thin strips needed for Kumiko work. I have settled on a width of 12mm for all strips. The final thickness of the strips to make up the gridwork is determined by the method of cutting the joints in the gridwork which I’ll cover in the next post.

The starting point for each method is to dimension boards to a thickness of 12mm with both edges squared using my planer/thicknesser.

The first method I used the band saw and the P/T. I started by ripping a strip of both edges of each board at around 1mm over size of the desired finished thickness. Then I took the board back to P/T to square both the edges again before ripping two more strips on the bandsaw, repeating as many times as possible before the boards became too narrow to handle safely on the P/T. This was a tedious process and produced strips that needed considerable work to reduce to the finished width.

I wasn’t happy with most of the table saw methods I’d seen on YouTube where the strips were cut with the saw blade the thickness of the strip from the fence i.e.

.

I hadn’t had much joy with a thin-rip jig either because of the nature of the fence on my table saw. So I decided to make a jig to use with my track saw which I detailed in a previous post (Thin Rip Jig for the Track Saw). The idea came from a video demonstrating some guides made to fix to a track (no longer available to buy, but beyond my budget in any case –



The track saw left a good enough finish on the faces of the strips and was a more efficient method of production. With this method I can carry on cutting strips from the board to within the final 10mm of each board. This has been how I have cut most of the strips I’ve used so far.

While the second method worked well, I wanted to find a workable thin-rip jig to use on my table saw. Most of the jigs I’d found made use of an adjustable point of contact to determine thickness of the ‘waste’ side of the cut when the stock is presented to the blade as in this example:

.

The main problem I find with this approach is that the fence on my table saw uses a single cam locking mechanism which is rock solid when fully tightened but when loosened to move it the fence is no longer reliably parallel to the mitre guide until finally tightened. Therefore, I need to set the point of contact of the thin rip jig as close as possible to the rip fence rail where the cam clamp operates to minimise any deviation as the fence lock is tightened. This moves the point of contact quite a way before the blade so, without support near the blade, the accuracy of the thickness at the point of the cut is compromised.

My solution was to make a combined thin rip jig and feather board to ensure constant lateral pressure against the fence all the way to just before the stock meets the blade so that I only need to concern myself with push stick to feed the stock forward and past the blade.

I have been pleased with this jig although it does mean I don’t use the final 20mm of each board to avoid cutting too close to the fence. And this is probably the method I’ll continue to use as it is the quickest and produces good results.

Adrian Preda has a video showing how he cuts the strips by hand. I’ve not been tempted to try this method but it may suit others

 

[pulleyt]

Adventures with Kumiko - Final thicknessing

The strips for the gridwork need to be finished to the thickness of the half-lap joints used to complete the grid. I have a 4mm FTG blade, and the more standard 2.2mm general purpose blade. When I’m cutting the joints on the table saw I need to get the thickness to fit the saw kerf and I have a block with a kerf cut in it to test the strips. Any strips that are too loose in the kerf are set aside for infill pieces that don’t use any joints.

If I am cutting the joints by hand then I cut the joint to the thickness of the strip and I have settled on a thickness of 3mm for these strips.

Again, I’ve tried three ways to finalise the thickness.

The first method which I used on the strips cut on the band saw, was to attach the planed surface of each strip to a sled using double sided tape and send the sled through the thicknesser e.g.



This was pretty successful, but some of the more splintery woods that I tried were prone to shattering. I don’t recommend this method.

The second method is to use a thicknessing jig for use with a hand plane, an idea I got from the Adrian Preda video:



My version of the jig has adjustable runners for the low angle jack plane that I use instead of using packers to change the thickness achieved.

The construction of this jig is as follows:

I started by gluing together two 18mm MRMDF boards with a width of approx. 110mm. The top board was about 60mm shorter in length to allow for a stop block. I then ripped two strips at a width 25mm that would be used as the side runners. Finally I ripped the remainder to width x (where x = the width of the plane blade + 2mm).

On the Main Bed I drilled 3 holes in both sides of the upper board to accept M6 screw inserts. On the Side Runners I drilled and cut out slots corresponding to the screw inserts.

I glued and pinned a couple of 6mm MRMDF strips on top of Side Runners leaving a distance of y from the inner edge (where y = (the width of the plane body + 1mm – x) / 2)

Finally, I reduced a piece of 18mm MRMDF to 17.5mm to make a stop block that would sit below the plane blade and screwed it to the side runners.

This jig offers variable thickness options (and tapered thicknessing which might come in handy for other projects). To set the thickness, I clamp the Main Bed to a flat bench and set the Side Runners on top of material of the desired thickness and clamp the Side Runners to the Main Bed with M6 bolts.

This jig was successful but slow going. It is well suited to short strips but full length thin strips did occasionally buckle against the Stop Block when planning harder woods.

In the end, I used the excuse to buy a drum sander and I’m very pleased I did. To speed things up I use a sled to send multiple strips through at a time. As long as the initial cut is close to the finished thickness then this is a very time efficient method and will be the main way I proceed.

 

[pulleyt]

Adventures with Kumiko - Cutting grid work joints

For the smaller, square grid panels I have cut the joints by hand following the advice of Des King. His videos are very detailed and were great in giving me the confidence to attempt these by hand. (I have also bought the first three of his books which go into great detail of the basics and many of the different patterns and which I really do recommend).

A good introductory project is a Kumiko Coaster as demonstrated in Des King’s video,

.

The thickness of the strips can be to your choice but I first worked with 3mm x 12mm kumiko strips. I made my version of the Kumiko cutting jig out of 18mm and 6mm MRMDF ( I have a lot of offcuts from various projects).

The jig comprises five components. The Main Bed is a length of 19mm MRMDF with two dog holes to anchor it on my MFT workbench. This is very convenient as you need to flip the jig around quite regularly in use and it is much easier to relocate over a couple of bench dogs that release and reclamp, but clamping would work as well.

To the Main Bed I screwed a strip of 18mm MRMDF ripped to a width of 24mm to act as the Back Stop. Once screwed flush with the bottom face of the Main Bed the Back Stop would be at 6mm higher than the top face of the Main Bed. This is only screwed so that I can replace it when it is excessively marred by the saw marks.

In addition there are two Side Stops screwed onto the Main Bed that are at 90⁰ to the Back Stop. I also cut a small relief rabbet on the bottom inside edge to avoid the build up of sawdust against the stops.

The final component is the Clamping Strip made from 6mm MRMDF which is screwed to the Main Bed to hold the Kumiko strips against the Back Stop. The 6mm Clamping Strip and the 6mm projection of the Back Stop serve as depth indicators when cutting the half lap joints to a tad over 6mm (thus my choice of a 12mm thickness for the Kuniko strips).

Recently, I was lucky enough to buy a second Japanese cross-cut Gyokucho dozuki saw from a forum member and I have attached a depth stop using double sided carpet tape so I’m not as reliant on the visual depth guide of the jig.

I also use a David Barron 90⁰ Guide (David Barron 90° Guide) to keep my saw cuts vertical – you probably won’t find this necessary.

To ‘pop out’ the waste from the joints I ground an old screw driver to a width of just under 3mm and put a chisel edge on it. This is why I choose a thickness of 3mm when cutting the joints by hand. Popping the waste is possibly the most satisfying part of the entire process

Before removing the Kumiko strips from the Cutting Jig, I like to check the fit. If I’ve messed up and the half lap cuts are two narrow I use a narrow sanding block to ease the fit. If the joint is too big, I start again and set the bad strips aside for use as infill pieces.

Where the gridwork was either larger or to be used for the diamond shaped gridwork I created a cross cut sled to work with the 4mm FTG blade on the table saw based on a video from Johnny Tromboukis



My version is for use with my 4mm FTG blade and looks like this but the construction and operation are mostly as described in Johnny’s video above.

Once I have set the pitch of the grid i.e. the distance between the half laps, the Auxiliary 60⁰ fence is lined up with the main fixed 60⁰ fence to provide support for the Kumiko strip at the point where I set the half lap over the key. When I push the sled through the blade I hold the Kumiko strip tight against the fixed fence with the Clamping Block and I support the strip against the Auxiliary fence with the rubber end of a pencil. I am comfortable that my digits are far enough away from the blade.

 

[pulleyt]

Adventures with Kumiko - Shaping the infill pieces

The grids hold themselves together by virtue of the half lap joints. The infill pieces are held in place by friction. This does require some precise cutting of both length and angled ends of the infill pieces. (While this is true, I also glue everything in place with small dabs of white glue for permanence once I’m happy with the dry fit).

The common angles needed to shape the ends of the infill pieces are 45⁰, 67.5⁰ and 22.5⁰ for the square grid work. The common angles for diamond gridwork are 30 and 60.

Hand cutting these angles is shown in Des King’s video suitable for a taster project.



I used another Johnny Tromboukis video as a guide to making my Kumiko jigs



I went all-in and made double ended jigs covering each of the angles mentioned above making sure I paired a ‘square’ angle with a ‘diamond’ angle

My preference is to use a chisel to trim the infill pieces but you may prefer to use a block plane

When I was trimming some ‘accent’ hard woods I found the jigs and chisel more difficult to achieve a clean cut. So I came up with an alternative method using my disc sander. I have the Jet combination Disc/Belt sander and the table for the disc sander has two slots perpendicular to each other. I made an auxiliary table to sit in these slots for a secure and easy set up when using the auxiliary table.

There is a fence made from 6mmMRMDF on the table that is parallel to the face of the sanding disc. I have jigs that will slide up to this fence.

Again I went all in and created a jig for all angles

With these jigs I hold the kumiko piece against the fence and up to the stop and then advance the jig towards the disc until the jig rides against the fence on the auxiliary table.

This auxiliary table has other uses including the variable jig to add a chamfer the ends of the square stock I used to make frames for the Kumiko panels

I’ve still a lot to learn but I do find making Kumiko panels very calming and extremely rewarding.