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Greene & Greene Gamble House Side Chair #14: Back Leg Mortises and Back Seat Rail

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Blog entry by TungOil posted 12-23-2017 02:59 AM 2092 reads 0 times favorited 10 comments Add to Favorites Watch
« Part 13: CNC Templates and Begin Back Leg Fabrication Part 14 of Greene & Greene Gamble House Side Chair series Part 15: Crest Rails »

Now that the back legs are routed to shape, I move on to cutting the mortises. I start with the back seat rail mortises. The back seat rail sits flush with the inside of the back leg, so it makes sense to cut both mortises using the same setup to assure the parts fit perfectly flush.

I first lay out the mortise on the end of the back seat rail setup piece, which is made from poplar. The Leigh FMT jig only requires that the center of the mortise be marked with cross hairs, but as a double check I layout the full mortise to verify size and location along with the mortises for the back slats and the final profile of the rail.

Next I lay out the matching mortise on the leg and verify that everything is aligned correctly.

The Leigh FMT jig is equipped with toggle clamps and a stop that, once setup, allow multiple parts to be made very quickly with perfect repeatability.

The cross hairs that mark the center of the mortise are used in conjunction with the ‘targeting sight’ on the FMT to very accurately locate the center of the mortise.

First, I cut all of the mortises on the ends of the back seat rails. All mortising is done before I bandsaw the back scalloped profile to provide large flat clamping surfaces.

Next, I route the matching mortises in the back legs utilizing the same setup in the FMT, assuring a perfectly flush fit. Since the mortises are near the center of the back leg, I must use the extension feature of the FMT to create a stop with a scrap block of wood and a clamp.

The legs are mortised in mirror image pairs, so two setups are required on the FMT to make sets of left and right legs.

With the back seat rail mortises complete, I move on to creating the mortises for the crest rails. These mortises are cut at an angle into a curved section of the leg, so the FMT jig will not work easily for these mortises.

To solve this problem, I use a jig made from two CNC machined templates. Together they form a jig for routing the mortise. One template has an oversize slot that matches a router bushing. The other template has a leg shaped opening that positions the leg to properly mortise. This image shows the bottom of the jig with a leg fit in place, ready to be flipped over to route the mortise.

The template is designed to be used for both the left and right hand legs by simply switching the locating template to the other side. After a little fine tuning of the opening in the template to allow my router bushing to clear smoothly, I cut all of the mortises.

The remaining mortises on the back legs for the side seat rails and lower stretchers are parallel to the front face. These will be cut later.

Next I build a mortising jig to cut the four mortises on the top of the back seat rail that will be used for the back seat slats. Since two of these mortises are angled, the FMT would be difficult to use. I build the jig from a CNC cut template that locates all four mortises.

The finished mortises are quick to cut using the jig.

With all of the mortises cut in the back seat rail, I bandsaw the scalloped outer profile.

To prepare for pattern sanding the profile, I assemble another jig using a toggle clamp and CNC cut template. The template mounts to the bottom of the jig and is 1/4” undersize to account for the pattern follower mounted on the spindle sander.

The pattern sanding technique does a nice job cleaning up the bandsaw marks and developing the final shape on the rails. Due to the height of the part, the top 1/8” of the seat rail does not get sanded. It is easily cleaned up using a spiral pattern bit in the router table after the sanding is completed.

The back seat rails are now ready for final sanding.

I do a quick test fit to verify everything looks correct.

So far so good!

Next step: fabricate the crest rails.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"



10 comments so far

View pottz's profile

pottz

2434 posts in 858 days


#1 posted 12-23-2017 03:21 AM

damn tung you make feel lazy buddy-lol.im lovin the journey,lets go for a ride!

-- sawdust the bigger the pile the bigger my smile-larry,so cal.

View EarlS's profile

EarlS

685 posts in 2222 days


#2 posted 12-23-2017 05:15 AM

I’m worn out just reading all of the work you’ve accomplished. That is a lot of work that you’ve completed. Sounds like things are going smoothly as well.

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

View stefang's profile

stefang

15713 posts in 3208 days


#3 posted 12-23-2017 10:11 AM

I can already see that your meticulous efforts are going to result in some really fine chairs. I love the G&G style. Looking forward to seeing them finished.

-- Mike, an American living in Norway.

View CaptainSkully's profile

CaptainSkully

1538 posts in 3432 days


#4 posted 12-23-2017 04:47 PM

Yeah! This is better than Saturday morning cartoons!

-- You can't control the wind, but you can trim your sails

View sras's profile

sras

4691 posts in 3003 days


#5 posted 12-23-2017 05:13 PM

So much fun to follow along on this!

-- Steve - Impatience is Expensive

View TungOil's profile

TungOil

806 posts in 369 days


#6 posted 12-23-2017 07:46 PM

Having a few days off work certainly helped with my progress.

The hardest parts are coming up next. The crest rails will be quite a bit of work, since they are curved and profiled. The back slats are going to be very challenging as well since they are also curved on all four sides and the ends have a compound miter cut and need to fit exactly.

After those parts are finished, the rest of the construction is actually pretty straightforward.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

View Mean_Dean's profile

Mean_Dean

5827 posts in 3021 days


#7 posted 12-27-2017 10:40 PM

Looks like you’re making some amazing progress!

So, how do you like routing your mortises, as opposed to using a dedicated mortising machine?

I have a mortising machine, but it tends to leave the mortises a little rough, which then need to be cleaned up. I like the idea of using a router, as it gives nice, clean mortises—but then you need to make all sorts of routing jigs. So you’re sort of damned if you do, damned if you don’t. Anyway, just curious what you think.

-- Dean -- "Don't give up the ship -- fight her 'till she sinks!" Capt James Lawrence USN

View pintodeluxe's profile

pintodeluxe

5544 posts in 2687 days


#8 posted 12-27-2017 10:52 PM

I love watching chair builds. Yours is right up there with the best I’ve seen.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View TungOil's profile

TungOil

806 posts in 369 days


#9 posted 12-28-2017 02:24 AM



So, how do you like routing your mortises, as opposed to using a dedicated mortising machine?

I have a mortising machine, but it tends to leave the mortises a little rough, which then need to be cleaned up. I like the idea of using a router, as it gives nice, clean mortises—but then you need to make all sorts of routing jigs. So you re sort of damned if you do, damned if you don t. Anyway, just curious what you think.

- Mean_Dean

I’ve preferred routing mortises for a long time. I have a home made mortising block (the Jeff Miller design that was published in Fine Woodworking years back) that I have used for many years. I use it to cut the mortises then cut the tenons on the TS or use floating tenons. Works great for straight mortises, but kind of a pain for angled work. The Leigh FMT is certainly a more refined and flexible jig for mortising and it produces a very nice joint, especially on the angled work.

I’ve used hollow chisel mortisers in the past with similar results to what you describe. A bit of a choppy looking mortise. They can be finicky to set up in my experience, but would certainly work for these chairs with the right jigs.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

View splintergroup's profile

splintergroup

1819 posts in 1096 days


#10 posted 12-28-2017 03:22 PM

I’m envious of your methodical and detailed approach to all this 8^)

It must be some mental gymnastics to get the part setup, cut, and profiled, then realize you have “x” more to do (where “x” is a large number 8^)

Your investment in the templates really proves their value, truly some quality craftsmanship.

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