Making a Spar Plane Inexpensively

James Krenov shows a simple way to make custom wood planes in his book, “The Fine Art of Cabinetmaking”. The only problem for a boatbuilder, who might need a half dozen spar planes of different sizes, is the price of high-quality, aftermarket irons of sufficient thickness for a wood-bodied plane.

There is a less expensive way to a high-quality end, and that is converting old flea-market woodies. Auburn, Ohio Tool, Fulton, and dozens of other 19th-Century manufacturers competed hard with each other in quality and value. These planes are generally beech with thick, tempered cast-steel irons…some of them laminated like today’s Japanese blades…and mild steel cap irons. The ones the collectors don’t want are worn, scruffy and cracked with the logos stamped into the wood illegible…. you see them at swap meets and on Ebay for as little as 5 dollars each. We’ll use the same modern-glue rationale to make permanent repairs as Krenov used in making split-bodied planes. Make sure the one you buy has the original thick iron with some length left in it and not too much pitting on the back side near the edge.



Here’s an old, worn-out Ohio Tool coffin smoother above I’ll remake into a spar plane. I’ve jointed the cracked sole flat, and will laminate a thick, squared-up piece of beech to it. How thick? Thicker than the plane and cap iron assembly will penetrate the jointed sole of the body….plus a little more for good measure. Also note the rapid technique for marking center lines in the photo.



I laminate using boatbuilder’s epoxy…a coat of unthickened on each faying surface followed by a thickened coat…I worked the unthickened coat into the cracks in the sole using gentle heat for penetration…and used a lead-weighted mallet as a “clamp”. Epoxy doesn’t like a lot of clamping pressure.



I use the same heat technique to repair the many cracks in the plane’s top side…cleaning those cracks with a thin solvent, first like acetone or trichloroethylene to remove any oil. I dye the epoxy to match the wood, merely for cosmetics.



Old woodies like these generally wear much more at the toe than heel, which changes the iron’s angle of attack, so I rip the sole parallel on the table saw.



Now I chop out a new throat from the throat side of the plane. The rear of the throat is a 45-degree angle and the front bevel of the throat needed to clear shavings is about 20 degrees in the opposite direction. I merely index the chisels against the plane body and tap and pare.



I continue to remove wedge-shaped waste until the back of the throat and the front of the throat meet…



…in a nice, clean “V” about halfway to the bottom of my over-thick sole stock. The cleaner and more accurately-indexed your new throat, the cleaner the resulting mouth will be…. which I’ll cut shortly on the table saw.



To lay out the eventual depth of cut of the cove I am about to mill, I measure the depth to the bottom of the “V” and transfer that measurement to the plane body.

Continued…

 

There are two basic ways to lay out a cove cut on the table saw…either by the depth of the cove or the width of the cove, and I’ll show both methods. The resulting radius will always be a segment of a circle and is variable in size from the radius of the table saw blade downward. To lay out the cove by depth, set the saw blade to the desired depth and adjust the parallel ruler until both legs touch the blade. To lay out the cove by width, set the width of the legs first using a rule, and adjust the parallel ruler on the saw table and the height of the blade until the legs touch. The results will be the angle required for the temporary fence, and the depth of the cut.

Also note also the inked tick mark on the red blade insert….that marks the exact center of the arbor and is used to fine tune the fence, centering the cut by insuring the center line of the plane body passes over the center of the saw blade teeth at the arbor.

Shown is the layout of a rather wide-radius cove I’ll use on this plane…



…for a narrower-radius cove for a small spar, the fence must be positioned at a more acute angle to the saw blade.

How do I get the exact radius and depth required for a specific spar size? Trial and error cutting scrap and testing against an existing spar of the size I desire, that’s how. I’m sure there are more sophisticated ways to lay them out…but it’d probably make my head hurt puzzling them out.



As the cove radius for this plane is wider than the plane body, I cyano on some temporary outriggers to make the cut. A freshly-jointed temporary fence is securely clamped to the saw table at the angle indicated by the parallel ruler. The cuts are made in 1/16th” vertical increments until the desired depth is reached using multiple passes by raising the blade with each succeeding pass.

Beginning at a shallow 1/16th, it is a simple matter to check that the cut is centered and to test the radius against the spar you are trying to duplicate…and adjusting the temporary fence as needed.



Once satisfied with my fence settings, I continue making passes until I reach the desired depth…. the desired depth in this case being a perfectly formed mouth in the sole as shown below.

Now…if you’ve been getting away with bad table saw habits all this time, doing your first cove cut may bring them to light with great surprise and violence:

Insure the saw blade is sharp and true…the more teeth the cleaner the cut…insure your temporary fence is dead straight and the edge square to the table…insure you use a push stick that applies pressure to the toe as well as the heel of the piece….with added pressure in direction of the fence…and under no circumstances pull the work piece backwards into the saw blade, which will promptly throw it through the wall and perhaps drag your fingers into the blade as it takes off. Remember that the machine can’t hear you cry.

A vertical temporary fence and featherboards can also be rigged (and are a good idea) when coving long stock…but wouldn’t be effective coving a short plane.



Now that I have a mouth, I clean up the applied sole and and scribe the plane iron for grinding.



I rough grind to the scribe line before attempting to regrind the bevel…



…then I reinsert the iron and scribe the bevel from the opposite side. A similar plane blade serves as a model for how I will transition the corners of the bevel.



Then I rough grind the bevel to my marks.

I could have used the grinding wheel, or dressed a grinding wheel to the radius desired….but I prefer 26-grit heavy abrasive disks mounted to an old wheel with contact cement. A 9” disk mounted to an 8” wheel provides a flexible, forgiving grinding edge, and the coarse disks grind significantly cooler than carborundum wheels. I can do the most of the entire grind without cooling the iron in water.

Continued…

 

I finish the rough grind on the bevel using the Dremel with chainsaw grinding stones…



…and do the cap iron using the same techniques.

I like to buff and phosphate blue the steel before final honing…the blue acts as an indicator fluid and the phosphate followed by oil protects from rust.



Final honing of the irons is done with oil stones and round slip stones…but can be done using any sharpening system and abrasive paper wrapped around dowels. A goodly bit of time was spent getting the iron’s back dead flat with coarse and fine stones before honing the bevel with the slip stone.



The cap iron was bent and honed for a tight fit to the flattened back of the plane iron….I strop the edges on the buffing wheel so I can see them better…and you can see on the left that both it and the plane iron radius need one more slight adjustment, which can be done by hand with the stones.



When I’m satisfied with the iron assembly, I double check it by mounting and setting for a fine cut…then give the plane a test run:



The wide shavings and quality of the resulting surface are the real test.