A Japanese Bunmawashi (Beam Compass)

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Project by Lemongrasspicker posted 06-01-2017 01:37 PM 2676 views 7 times favorited 4 comments Add to Favorites Watch

If you prefer not to read, the build video is here

View on YouTube

I first heard of this tool from the Toshio Odate book on Japanese tools. I thought it was pretty fascinating and I tucked it away in the back of my mind as a “do it someday” project.

Well the excuse to build came when one of the youtubers I follow made an announcement about a tool build off/giveaway that he is holding this year. I thought this was a prime opportunity to make a special one that hopefully someone can get some use out of.

I have no clue as to what the average size of one of these would’ve been back in the day. But looking at modern compasses they come in all shapes and sizes for various tasks. The only other one of these I had ever seen made was by our own Mafe-san here on the site.

The small one in the photos is the one I made for myself to use on projects our of some scrap red oak. The beam on it is about 10”/254mm or so.

The beam on this one however is 25”/635mm! You could easily scribe out a fairly large table top with this one tool.

I had gotten ahold of some tremendously old and aged cherry that I thought would work really well for this build. Cherry is just gorgeous in my opinion and I really enjoy working with it.

One thing I learned with this build is a method to get some decently accurate rip cuts with a saw. Previously I had just freehanded cuts and used lines and knife walls. For this I wanted to be absolutely certain that I made the rips as accurate as I possibly could since I don’t have access to an electric saw. I simply took a piece of scrap and made one edge flat and square. Then I marked the cut line on my stock and clamped the scrap to the piece. Leaving a bit of the scrap piece on the over hang allowed me to keep my ryoba saw fairly straight and square to the stock when cutting.

One the rip cuts were done it was time to square and plane them down. I really love using wood bodied planes, the sheen that you get on the wood is just awesome!

Putting the parts put together in a test fit before the final shaping To shape the conical portion I used my big ship builders gouge to hog off big pieces. Saved alot of time.

Making the pins was fairly straight forward, looking back I could’ve just clamped my drill in the vise and run my file over the stock and rounded it just as easily instead of moving the drill over the file. Either way, they got made.

And after final shaping and finishing. For the finish I just used natural danish oil. I’m becoming more of a fan of this stuff the more I use it.

Compared to my daily use bunmawashi (little guy made of red oak). This guy is so big that I couldn’t scribe out a circle using the entirety of the beam. It would’ve been wider than my back porch. I didn’t even have a piece of timber big enough to handle it!

Anyways this was a really fun project and I really had alot of fun making it, Thanks for reading/watching!


4 comments so far

View WayneC's profile


14359 posts in 4952 days

#1 posted 06-01-2017 02:18 PM

Absolutely lovely work.

-- We must guard our enthusiasm as we would our life - James Krenov

View JADobson's profile


1449 posts in 2966 days

#2 posted 06-01-2017 03:36 PM

Very cool.

-- No craft is very far from the line beyond which is magic. -- Lord Dunsany — Instagram @grailwoodworks

View mafe's profile


12609 posts in 3944 days

#3 posted 06-01-2017 07:41 PM

Lovely beam compasses, fine work.
Not only are they a joy for the user, but also for the eye.
I love them my self, made my first some years back and just made a x-tra large for a friend who is an artist and she love it.
Best thoughts,

-- MAD F, the fanatical rhykenologist and vintage architect. Democraticwoodworking.

View woodcox's profile


2386 posts in 2866 days

#4 posted 06-02-2017 05:40 AM

Nice set of tools you have made there. I will have to try your ryoba rip guide solution, it looks like a simple way to keep it on track. Thank you for sharing that one.

-- "My god has more wood than your god" ... G. Carlin.

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