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How to make an Arts and Crafts style lamp shade #4: Rabbet for the mica

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Blog entry by splintergroup posted 12-04-2018 08:01 PM 821 reads 0 times favorited 3 comments Add to Favorites Watch
« Part 3: Assemble the Frame Part 4 of How to make an Arts and Crafts style lamp shade series Part 5: Completing the Assembly »

Cut the Rabbets

The next step in my method is to rabbet for the mica panel. This is optional and I admit it takes the bulk of the time, but in my opinion it produces the cleanest results.

Some instructions have the mica panels cut to the full width dimensions of the shade frame. The corners are secured where they butt together with silicone and/or tacks/screws into the shades corner spokes. While this will work, in my opinion it detracts from the look of the shade.

With rabbets to hold the individual mica panels, they can be installed with a smaller reveal towards the shades outside and also can be better secured to the shade frame for a gapless fit.

The rabbet I create is 1/2” deep (provides a 1/8” reveal on the top and bottom rails) and 1/4” wide.
I generally hate cleaning up routed recess corners to get rid of the radius and make them square. With these shades I left the corners rounded, but they are deep enough that one will never notice from the outside.

To get this rabbet, I used a Rockler 1/2” bottom bearing hinge mortice bit and a template on my router table.

Since the bit trims flush with the bearing, I made the template 1/4” oversized from two layers of 1/4” plywood strips double sided taped together with overlapping corner joints. The template is 1/2” thick so the router bit bearing has a place to ride when taking the first small cut.

The template is double sided taped (of course 8^) to the shade frame with the alignment done by eye with scribe lines 1/4” inboard. This is all done before cutting the frame side angles since afterwards there will be very little stile surface left for tape to stick to.

A good modification to this process would be to make the template larger so that alignment blocks could be placed to hold the frame in position on three sides. Maybe only two pieces of tape are then needed to keep the two together.

The reason I mentioned this takes the most time is you cannot cut the rabbet in one pass (at least I can’t with this bit). My approach for the 1/2” deep cut is to take 3/16” deep cuts for each pass. I run the frame to take a very shallow cut to establish a relief and prevent any tear out from trashing the edge. A few more passes with deeper cuts gets me to the point the router bearing contacts the template. I then raise the bit another 3/16” and repeat. The final passes are done with the bit cutting to 1/2” leaving a clean rabbet with rounded corners.

The mica panels are trimmed to size/shape by tracing a line with the router template. I recommend using a fine tipped marker so the lines are visible.

The mica sheets seem to all be standard sizes and eight panels (two shades) can be easily extracted from each sheet. This sheet is 0.030” thick and is called “light amber”. It produces a nice glow. I have used “dark amber” and it produced minimal glow. Sheets are available eBay and elsewhere.

I cut the mica on my bandsaw with my installed resaw blade (4 TPI). No need to use a finer toothed blade in my opinion. The big thing to worry about is flaking and blowing out on the backside of the cut. To prevent this I cut part way through a scrap of thin plywood or masonite and double side tape this to the saw table (instant zero-clearance insert)

Remember to cut on or slightly inside the line you drew with the template. You don’t want the parts to need further trimming since taking off small strips from the mica risks delimitation.

As an alternative to a bandsaw, I have tried using a utility knife and straight edge. It takes multiple passes for each cut but it does work (and is a lot of work!). Some places recommend sandwiching the mica between two boards to prevent flaking. That would work great, but I had no issues with the bandsaw and ZCI.

The sheets should drop right into the frames (I used scissors to hand trim the round corners).

All mica panels are ready!

My main concern with any project that has a part that can be broken/damaged (like the glass in a picture frame), is to leave in the ability to replace that part. For these frames I may have gone a bit overboard (you’ll see what I did later 8^)

With the rabbets and mica cut, options for holding them in place become easier. A bead of silicone certainly will work well and can look acceptable if carefully applied, but I consider that cheating 8^).
I thought I had a perfectly simple method using “glazier points” which are basically small flat retainers that are pushed into the frame.

Unfortunately my walnut was too hard and they kept bending.
Another thing to consider is the mica is installed after the shade is fully assembled which limits easy ways to get leverage with pliers, etc. to force these points into the stiles.

Anyway, I’ll show my solution next time as I detail the cutting of the stile bevels to complete the shade structure.



3 comments so far

View rustynails's profile

rustynails

802 posts in 2732 days


#1 posted 12-05-2018 12:12 AM

Great work so far and on the blog.

View stefang's profile

stefang

16144 posts in 3537 days


#2 posted 12-05-2018 01:21 PM

Effective and well thought out process.

-- Mike, an American living in Norway.

View EarlS's profile

EarlS

1939 posts in 2551 days


#3 posted 12-05-2018 07:34 PM

Your explanation is much better than the drawings and “how-to” booklet from Schlabaugh and Sons.

-- Earl "I'm a pessamist - generally that increases the chance that things will turn out better than expected"

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