Screen Play (16)

Well, the jig is up. I’m done for! What I mean is, it was time to build a jig to assist with the accurate processing of the kōshi (grillbars). Whenever making a number of parts with identical cuts, the way to go is to jig it up. Japanese traditional shōji makers employ jigs in the processes of hand sawing and processing the lap joints in kumiko assemblies. I’m following the same strategy, however instead of using purpose-built hand tools, like depth-stop fences clamped to sawblades and special trenching chisels, I am jigging up to use a router to process these cuts. It’s the most accurate way I know how to do it.

I now introduce a few of the cast members in ‘dis here thingamajig. I have processed a couple of trenches across a piece of MDF and made up a pair of keying pieces out of some scrap Bloodwood:

With some slight tuning of the material with my shoulder plane, the keying pieces fit like so:

The purpose of the pieces is to align one part of the jig, the top, which guides the cutter, with another part of the jig, the base piece, which holds the sticks of wood in position:

Those Bloodwood pieces are a real plus, ha!

Since the days are gone, apparently, where one could rely upon factory-cut MDF to be square at the corners, I set one of the fences on the lower section using a try square along with a 24″ long Mitsutoyo combo square blade:

Now I know that the brand name on the tool says ‘Mitutoyo’, but take it from me, this is a peculiarity that comes from an antiquated method of Romanizing Japanese, where the sound ‘tsu’, written ‘つ’, once got written as ‘tu’. Most English speakers would agree, I’m sure, that ‘tsu’ and ‘tu’ have different pronunciations. So, ‘Mitutoyo’ should be pronounced Mitsutoyo. They are unlikely to revise the company name written on their tools of course, because it is a brand and image continuity is important, and it sure would be expensive to change it now!

So, where was I? Once I had the jig parts sorted out, it was time to fasten it together and take a test cut or three to calibrate the jig. Here it is, totally cramping my style:

That attempt at humor was for the British readers out there.

Peekaboo!: in the window there’s a section of scrap grill bar stock which will have a trench cut across it:

Cue router (set up with a PC template guide on an acrylic sub-base):

I must say that Festool totally sucks when it comes to the cheesy system they have for templet guides. Any Festool guide that you click into their base will move around slightly, thus spoiling accuracy. Having long ago learned my lesson in this regard, I therefore fit a Pat Warner sub-base using his special centering tool (and not Festool’s goofy centering tool either!).

The carnage:

Target dimension for the lap width is 0.3750″:

It was absolutely devastating to miss the mark like that, but I guess I can find a way to live with a 0.001″ discrepancy. Hopefully I will be able to carry on, I don’t know.

I am kidding – the result was a pleasant surprise! That part of the jig was right on the money.

Next step in calibration was the spacing between the laps – in the following photo you can see I’ve placed a pair of black gauge blocks into one of those grooves, so as to serve as a 0.375″ detent, and the grill bar has been placed atop:

I then reassembled the jig and routed a lap in the next section of the bar. Then I took it apart, and checked the spacing on the laps – the target dimension here is 7.125″:

I was very surprised at the close accuracy I achieved here, given that the jig is MDF and such a minor difference as 0.001″ from target is usually only going to happen with aluminum jig parts. In fact, the 0.001″ difference is entirely due, I suspect, to the width of the lap being 0.3760″ instead of 0.3750″.

Cool- calibration is over with no adjustments needed at all from the initial set up. If the result had not been so favorable, I would have made adjustments and further test cuts until the desired result was achieved.

It was time for a cup of tea. Earl Gray is my poison, with one lump of sugar and a dollop of Vanilla soymilk. It’s a tough concoction to choke down, but I’ve been training since childhood.

Next task was to skim the kōshi stock with my plane. I set up a couple of sawhorses outside and laid a piece of quarter-sawn Swiss Pearwood on it’s edge to serve as a planing beam:

And we’re off to the races:

Since most of the laps in this assemblage are mitered and housed, the exact dimensions on the bars are not super critical. I did measure from time to time to see where I was at, but the main goal was to clean the faces up and keep things square.

Here’s my tidy little pile of bars after the planing was over:

A couple of the bars are not perfectly straight, but I’m out of material and they should be okay once the laps have been cut. Maybe I’m kidding myself and should get a bit more material?

Well, we all know that Jack Nicholson and Morgan Freeman had their, uh, kick at the can – now it’s my turn and here’s my ‘bucket list’:

Where’s yours?

Thanks for dropping in and tuning in today my friends. Comments always welcome.

Looking for more punishment? Okay! – on to post 17

6 thoughts on “Screen Play (16)

  1. Dale,

    that sawhorse is barely holding together, but I think it's serve out until the end of this project at least :^)

    One day I'll make something out of that plank of Pearwood – I have two planks actually – the planing beam is but a temporary use.


  2. Chris

    Earl Grey with soymilk is a most comforting drink.

    Its just great to be able to follow your progress with the tsuitate. I'm sure the koshi will be wonderful, but what have you envisioned for the panel? Something very light? Enquiring minds want to know.


  3. Tom,

    the panel, ah yes…the panel. It's been a bit of a toss up between American Black Cherry and Bubinga. Both materials I have on hand right now. The cherry is curly and will lighten over time, and the Bubinga is quite interestingly figured and seems quite color stable in my experience. As of today, I am leaning towards using the bubinga.


    I bought the Swiss Pearwood as a wide, waney-edged 8/4 plank a few years back from World Timber Corporation in North Carolina. At the moment they are only listing 4/4 Pearwood but you might want to call them to see if they have any fresh material coming in. The stuff wasn't cheap – I paid around $19 a board foot back then.

    My plank came from the center of a 20″ thick trunk. I'm not a fan of slab construction, so I had no intention of using the material as it came to me. I ripped the waney edges off and sliced the piece into three, discarding a narrow 1″ wide section with the pith in it. Of the two pieces, each with perfect vertical grain, one has slightly twisted since then, so I imagine when it comes time to use the stuff, that one piece will be yielding 6/4 at best. I also have plans to use it for a cabinet at some point!


  4. Addenda:

    it seems I may have been claiming in error that American Black Cherry gets lighter with time – I've been assured by a reader that Black Cherry darkens with time and sun exposure.

    My previous experience with using Black Cherry on the West Coast was that it lightened with time in the sun. Perhaps this was a different variety of Cherry or perhaps I'm simply confused (?) I'll go with the latter for now!

    Oh well- if the Cherry indeed does darken over time, then it is off my list for use as panels in this frame.


Anything to add?