LumberJocks

Building the Stone and Wood Bridge Bench

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Blog entry by BenhamDesign posted 12-20-2018 07:49 PM 708 reads 0 times favorited 4 comments Add to Favorites Watch

My latest design/build, a bench with a mahogany top fitted around a stone leg. The supporting arch is one piece that passes through hand cut angled mortises in the cross braces. The arch and cross braces are walnut, and the leg is mahogany wedged in place using a through tenon and walnut wedges. I hollowed out the stone with an angle grinder to make the weight more manageable.
“If you want to check out how I built it
:https://youtu.be/5hF5l6Q_o-w

Recap of the build video

For today’s Project I’m going to build a bench. It has a carved opening for it to fit around the top of the stone leg, and some hand cut through mortise the arch support passes through.
To get this project started, I’m going to get the most physically demanding part of the build out of the way, and that’s dealing with the stone leg.
The granite boulder was more than I could lift by myself so I used an engine puller to get it out of the back of my truck.
Once out of my truck I rolled it around to the back of the shop and used an angle grinder to score around the bottom so I could cut it to size.
I cut as deep as the grinding disc would allow and then used a coal chisels to break the bottom off.
I wanted to make it light enough so a client could pick it up and move it by themselves. So I started grinding out the inside of the rock with a 4” angle grinder. This was quite the workout and took a full a day to completely grind out the inside of that rock, my arms grew three sizes that day.
As I was positing picture on Instagram of my progress, I got a friendly ribbing from the usual suspects, on what possessed me to come up with such a crazy design.
The jumping off point for this design came from an Architect friend of mine Eric Reinhold from 30 by 40 design. He designed a house where they took a granite boulder from the site and craned it through the roof of the house and turned it into fireplace in the living room.
There were a lot of challenges in fitting such an organic piece in a contemporary setting, so this got me thinking how I could incorporate stone in my work.
The idea bounced around in my head for quite a while trying to figure out what the piece should look like.
Then on a trip back to Oregon and a short hike through the cascades, it all came together. Bridging the gap between refined joinery and organic shapes.
Now that I ground out enough of the rock so the weight was manageable, and started milling the lumber for the top of the bench.
After the glue dried I started carving out for the rock to pass through the top. To get started I drilled some holes through the top, and started chopping out the opening with a chisel.
To figure out how much wood I needed to remove, I set the board in place and traced the shape out on the underside.
Now for those that were yelling at your screen that I was going to ruin the angle grinder on the stone, you would be correct.
With a power carving disc installed on the grinder I started reliving the material leading up to the line I had traced earlier.
I test fitted as I went using a mallet to tap on the top so the stone would dent the wood leave a mark showing where to grind. As I got closer to the stone fitting I switched to some smaller burs, and just kept repeating the process, until I got really close to a nice fit. This took most of the afternoon to do.
Once I was down to the final fitting I switched to hand rasps and files, slowly removing material until I was happy with the fit. The final step was to use some sandpaper to round over any sharp edges and create a little space between the rock and wood. This will allow for some wood movement in seasonal changes.
Now that the carving is taken care of I moved onto gluing up the leg.
Once the glue was dry I set up a stacked dado head in the table saw to cut the tenon.
The tenon is going to be wedged in place so I used my shop made jig to safely cut 2 slots in the tenon to accept the wedges.
To add some visual interest to the leg, I used the band saw to cut a few tapers on the leg, and cleaned up the saw marks on the jointer.
Then I milled some walnut for the wedges. To create the wedge shape on such a thin strip. I cut a notch in some scrap wood to help hold the piece as I used a hand plane to plane a taper on one end. Just enough to it would slide into the slot on the tenon and tighten up.
I made a jig that fit around the tenon and use it to route out a mortise in the top of the bench.
I squared it up with a chisel and did a quick test fit.
To add some additional stability to the bench I made a custom bracket to bolt the wood and stone together. This required me to drill a few holes where the wood and stone met. I used at Glass drill bit cooled with water to drill out the holes.
Of course with the shape of the rock all over the place it was hard to get a reference to what would be level to the bench top, so the steel rod was pointing down. To solve that, I cut a notch with an angle grinder, bent the steel, did a little test fit and filled the void with a fat weld.
I cut a piece of flat bar to weld to the rods stuck in the stone, drilled some holes for the bolts, and welded it in place.

I transferred the bolt hole locations to the bench top, and drilled and taped the holes for some bolts
Now moving onto the arch,
I made a quick bending form out of plywood, and covered it with packing tape so the glue wouldn’t stick to it.
I cut some strips from walnut to bend around the form to create the arch, and glued them up. When I glued them together I made sure I kept them in the same order as I cut them so the grain would blend together hiding the cut line.
After the glue set up overnight, I cleaned up the squeeze out at the jointer, and cut it to length with a Japanese pull saw.
I scribed the angle of the leg onto the arch and cut the bulk of the material off at the band saw. Then using a hand plane and multiple test fits I refined the angle until it fit snugly at the top and bottom.
Once I was happy with the fit I rounded over ends at the disc sander.
I did a little layout for the placement of the crosspieces, and transferred the angle from the arch to my cross support pieces.
I finished laying the through mortises and hogged out the bulk of the material at the drill press.
Then I started chiseling towards my layout lines. As I chiseled closer to the line I paid attention to the angle I was holding the chisel and match it to the angle of the arch.
Working from both sides and a few test fits I snuck up on the fit little by little, refining as I went until I had a nice tight fitting mortise all the way around.
I cut it to length and I repeated the process for the rest of the cross braces.
It’s easier to sand everything, before assembly so I wrapped the leg in tape so I wouldn’t get any glue on my freshly sanded surface.
Once I got the leg glued up and in place I drove the walnut wedges in to secure everything.
After the glue dried I flush trimmed them with a pull saw and cleaned it up with a block plain.
When freshly milled, mahogany has kind of an ugly pink hue to it. To get it back to that rich look we are all use to seeing I used some water based die to darken it up and pop the grain.
And before assembling the arch I prefinished all the parts.
The final step before assembly I decided to fill the void I carved in the rock with spray foam. The rock hand a natural crack in it and after removing the bulk of the structure I wanted to make sure in didn’t come apart. The spray foam filled all the nooks and crannies and is extremely sticky so once dry the shell of the rock should always stay suck in place to the foam.
I filled it up little by little so it wouldn’t over expand breaking the rock apart. Once dry, I flush trimmed it off with an old saw. I covered the bottom with felt to protect the floor, and trimmed it to the shape of the stone base.
It was finally time to assemble all the pieces. I used a slow set epoxy so I would have plenty of time to fiddle with the fit of the arch and to be sure everything was tight and aligned perfectly.
Since the arch was a hard shape to clamp I used screws to hold it in place while the glue dried, I then came back with some dowels to plug the holes and add a little decorative feature.
Of course down to the last detail as I drilled out the hole a piece splintered off. No big deal. I used some CA glue to glue it back in place, flushed it up with a chisel, drove home the dowel, sanded and touched up the finish.
The last thing to do was to bolt it to the rock. It is really easy to over tighten and strip out wood threads, so I generally only tighten it until the washer stops moving. This will ensure I don’t strip the threads and that there is enough give that the wood can move without splitting the top.
Thank you for making it to the end of the project. If you would like to see what my upcoming projects are, and new designs I am working on please join me over on patreon.
Also if you are interested in Architecture check out my friends channel 30×40 designs he has some great stuff going on over there, and gave me the initial idea for this build.
And as always, if you haven’t already, click the subscribe button and hit that bell to be notified when my next video will be out.

Thanks
Brian Benham

-- What I do in and out of the shop at http://www.BriansBenham.com



4 comments so far

View pottz's profile (online now)

pottz

3846 posts in 1225 days


#1 posted 12-20-2018 07:58 PM

brian you never fail to impress me with your design and craftsmanship,your work is always top notch.i was wondering what this bench weighed then i read you had hollowed out the stone.dont have time to watch the vid right now but i will later,your video’s are also top notch.once again i cant say enough buddy.

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

View BenhamDesign's profile

BenhamDesign

174 posts in 1661 days


#2 posted 12-20-2018 09:23 PM



brian you never fail to impress me with your design and craftsmanship,your work is always top notch.i was wondering what this bench weighed then i read you had hollowed out the stone.dont have time to watch the vid right now but i will later,your video s are also top notch.once again i cant say enough buddy.

- pottz


Thanks man

-- What I do in and out of the shop at http://www.BriansBenham.com

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BB1

1254 posts in 1088 days


#3 posted 12-20-2018 11:45 PM

Wow agsin…thanks so much for providing this text version of your journey with the project. Very inspiring to read. Smiled when you mentioned your Oregon hike as contributing to the design.

View metolius's profile

metolius

76 posts in 971 days


#4 posted 12-21-2018 12:30 AM

Very creative work !
The video of your process was well done and enjoyed.

Great bench ! Where is it going to live ?

Nice bridgetown shirt.

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