Using Kumiko Jigs

Thanks to everyone who has purchased kumiko jigs since I listed them for sale a couple weeks ago.  I wasn’t sure what kind of interest there would be, and was surprised when orders started coming in.

With that in mind I thought I would share how I use the jigs for cutting kumiko pattern pieces, and also point out a few issues that can come up when using them.

The first step in making any pattern is usually to cut the jigumi or grid work, whether it is square, diamond, or hexagonal shaped.  Regardless of the kind and quality of jig you use, if your jigumi isn’t accurately made, fitting the pattern pieces will be more time consuming and require more fine tuning.  When making the jigumi it’s important to mark and cut the half-lap joints so that each space is as close to identical as possible.  If you have an even spacing, then once you determine the length of your pattern pieces, you should be able to mass produce them and then assemble the pattern piece by piece.  But, if your jigumi has an uneven spacing, then each pattern piece will need to be trimmed to fit individually, which is much more time consuming.

So to illustrate the basics of using kumiko jigs, here I’ve cut a square jigumi grid for an asa-no-ha pattern.

The next step is to roughly mark and cut a test piece for the diagonal pattern pieces.

You can then set the test piece in the kumiko jig and set the stop so that the end of the piece just hangs out enough to be cleanly trimmed.

When trimming kumiko with a chisel you can cut faster and take off more material than when using a plane, but I’ve found that it’s still important to take light passes, otherwise the chisel can have a tendency to dive into the kumiko piece, or the cutting jig…. especially if the chisel is a bit dull.

After trimming one side flush to the jig flip it and cut the other side

Once both ends are trimmed you can see how it fits the jigumi.  I clearly have a lot more to go here.

At this point it’s simply a matter of shifting the stop over a little bit in the kumiko jig and trimming the test piece again until it fits the jigumi.

At this point I will take that test piece and see how it fits in the other sections of the jigumi.  If your marking and cutting was accurate it should fit pretty much the same everywhere.  But if not, then it’s helpful to go through and locate all the spots that the piece does fit, and cut and trim pattern pieces for those locations, before readjusting the kumiko jig to cut any larger or smaller pieces.

Now that you know the final length of your pattern piece you can go ahead and cut the remaining pieces to rough length.  For that job I like to use a makeshift miter box setup, with an adjustable stop.

Using the pattern piece you just fit, you can set the stop to cut the remaining pieces.

I usually gang pieces together to speed up the process….

The remaining pattern pieces are cut in a similar manner using the kumiko jigs, and hopefully the general process is clear.  The finished pattern should look like this.

Now to cover a few problems that can arise when using kumiko jigs.

These problems are pretty obvious, but nonetheless they pop up, especially when you are cutting a lot of pieces.

One of the most common problems I’ve had is not getting a square cut on the end that has been trimmed, and usually this is due to me not keeping the piece tight to the back edge of the groove, and tight to the end stop.  This happens most often when the pieces are really small and hard to hold, and when your chisel starts getting dull.  If you use a dull chisel you naturally have more resistance in cutting, which can cause the pattern piece to pull away from the back edge when cutting.

Here’s an example of a piece cut when it wasn’t held flush to the back edge.  It’s a really subtle thing, but if you hold that piece up to a square you will see the problem.

Another issue pops up when you cut a piece that doesn’t have a square cut on the end.  You can see in the picture a slight tapering gap between the end of the kumiko piece and the stop.

If you proceed to cut that piece one end will be trimmed nicely ….

But when you flip it and trim the other end that is out of square, all looks good at first…..

But if you look closely, you’ll see that the pattern piece is still not square and is not fully trimmed.  If you put pieces like that in your kumiko pattern you’ll end up with little gaps that do not want to disappear.

Hopefully this is helpful to some of you who are getting started in kumiko work.  The problems and steps may seem somewhat obvious, but when you are doing something as repetitive as kumiko work it seems like it’s the little things that are easiest to overlook that come back to bite you in the ass.