Wednesday, May 5, 2010

Screen Play (12)

Twelfth post in the series describing the construction of a Japanese free-standing screen, or tsuitate. Previous installments can be found archived at the right of the page.

It was now time to process the joinery cuts for the cross-wise feet. That meant an opportunity to try out the new Mulitco mortiser to see what was what. Without the mortiser, it would have been a matter of drilling out and then chiseling. With the mortiser, it is a matter of drilling out and some chisel paring afterwards.

The first thing I discovered was that the bit which came with the machine, along with both collets supplied, were differently sized at the shank than my Japanese Star-M mortising bits. Since the General International tilt head mortiser I used to own did fit my Japanese hollow chisels, I conclude that there is yet some other standard, perhaps a British standard of chisel sizes. It's a little aggravating to have the various size standards in these chisels, for no good reason I can think of, but whatever. It reminds me of bicycle parts in the 1980's where there were all these various size standards in play.

So, I'll need to get another collet machined up for the Multico to accept my Star-M's, which is about the simplest job to give a machine shop, so it should be cheap enough.

The one bit which did come with my machine, an English Clico bit happened to be just the right size at 3/8" for my purposes, though hardly what one might call sharp. Having driven half an hour to get to the location I am storing my mortiser, I was loathe to return home just to get sharpening materials, so I elected to give it a try and see how it worked. I reasoned that if it chewed the hole up a little I could always use a chisel to pare it out clean afterward and make the pegs sized to fit that.

Here I am set up to go:


The clamping assembly, or 'cramping' as the Brit's would probably say, doesn't push the piece quite parallel to the table, so I am keeping things where they need to be with a Bessey clamp as back-up. I should be able to fine tune that clamp assembly later on, possibly with some shims or re-machining if need be (possible aggro sledgehammering - just kidding!).

The moment of truth arrives:


Well, despite the bit's dullness, the result was fine:


Next I needed to process the cut for the main mortise, which is 1.25" wide. I didn't have a chisel that large, however a 30 mm bit (= 1.181") does come with my other mortising machine, a Makita beam mortiser, so I gave that a go:


Unfortunately, Mahogany is just a bit too hard for such a large mortising bit to work well, and after about 10mm of depth was attained, I bailed on the 30mm bit and put in a 15mm instead:


Of course, plunging four holes instead of one to complete the mortise added a little time, but so what?:


The completed mortise is now roughed out:


Next I used my router to dimension the mortise to the desired number:


Then a little chisel work to pare the end grain walls and corners:


Here's the cleaned-out and dimensionally-accurate mortise:


Here's a slightly different view:


Next is the cogged lap joint atop the crosspiece - I began by kerfing the first chunk of wood to be removed in the cut-out, using my circular saw:


Jumping ahead a little now (where was my camera?), here is the completed cogged lap:


I'm leaving the rounded portions in the lower corners for the time being, as the frame cross-tie will be chamfered and I need to cut the corners of the piece above to suit those chamfers. The router bit I was using was a little dull, hence the burn marks in the corners despite taking light passes - time for a new bit. Pattern bits, if resharpened, lose their dimensional relationship to the bearing, and I use spiral carbide bits for regular cutting, so it is not worth it to me to pay to have the bit re-sharpened. Router tooling is essentially disposable, and with careful (not full-time) use, I got about 2 years out of that particular bit, which was decent ROI.

Another view:


And one last picture for good measure, showing the two cross-wise feet now complete though the joinery stage:


Next step with these feet (excuse the pun!) will be to cut them into their final shape, which will be a template routing and spoke-shaving fun-fest.

Thanks for coming by today. Next: post 13

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