an ecomonical scarfing jig

[jan nicolaisen]

Hi,

Being a mere amateur, I'm on shaky ground teaching anybody about boatbuilding. Nevertheless, here's something I picked up some years in the past, relating to a subject frequently discussed on various boatbuilding fora:

Scarfs are superior to butt-joints, right? For me it's more work, but the results are mostly fair, smooth and invisible on painted surfaces. Doing them with a block plane is the time tested, fool proof method. It is almost like woodworking, too, except off course the medium is not wood. So, to me the charm wears off quick.

A while ago I built a river dory to the design of Tracy O'Brien. Not my type of boat, but a friend wanted me to do it for him. The good thing about that project was the scarfing jig concept that O'Brien included with the plans: Simple, inexpensive, effective. Home made in less than 30 min. Fits any circular saw. Does up to 9mm ply. So perfect for our boats.

I've used the old Version 1.0 for almost a decade now, and it works really well. With a steady hand there's no clean up needed, and the leading edge of the scarf is feathered to nothing.

Unfortunately I don't have the original building instructions any more, so these pictures and a short description is all I can offer. Proceed with caution!

Go ahead and remove the blade guard completely from your saw. Actually make sure it is unplugged first, then the guard business. Get a carbide tipped 8" blade from the hardware store to replace the standard 7 1/4" blade, or else the jig won't do 9mm ply. Most saws have room for this conversion.

Now make the screwed together fence shown in the pics. The angle in relation to the blade is 6 degrees. Rip a 32" long scrap of 'two by fir' on the tablesaw with the blade set at 6 degrees. Cut the piece in half and assemble it like shown with a row of screws, neatly predrilled and countersunk. You now have a 16" long fence, with a tall bevel on the front face. Clamp it to the baseplate of the saw, with the outside corner of the fence just shy of the blade where it meets the baseplate, and bore a couple of holes for #10 machine screws to hold it in place. Done.

Use as shown. Go slow and steady with firm downward pressure on the fence. Do only one layer of plywood at a time. Towards the end of the cut with less fence on the plywood there is a chance of skewing the jig, so be even steadier here.

Remember that the guard has been removed when handling the saw.

Good luck!

Jan

[Frank Hagan]

Wow! What a great jig ... I love these things, especially when they are quick and simple like this one.

[Charlie Jones]

Kewl- exact same principal as the Gougeon's Scarffer attachment, but shop made. I already have the extra saw too

If you were really worried about that blade, I suppose you COULD screw another block to the OTHER side, leaving room for the ply between. Then the blade would be hidden from the sides.

[jan nicolaisen]

yep, great idea about the housed blade, charlie. might make the next OSHA

inspection less stressful?

jan

[Charlie Jones]

LOL- since my three employees are me, myself and I, we get to tell OSHA to buzz off;)....

But anytime you can make something safer, it's not bad to do so.

I used to communicate with Tracy, some years ago. Lordy- almost 20 years ago now.!!! We discussed some mods to a 24 footer he had designed, but nothing came of it. Also engine choices on his Kayleigh- he is a fan of British Seagulls, I am not

Nice guy and somewhere in the files I have a set of plans for a Meghan. May still built it one day.

[Peter HK]

G'day

Here is a photo of the west scarffer which I bought 4 boats ago and has done a great job (about $50). It does have a shield but I don't usually fit it. I've seen and made jigs to fit a router but they don't seem to work as well. Stepped scarfs, where a ridge is left for positioning, are significantly weaker when I have tested them. The ridge left on thicker ply is rapidly removed with a belt sander.

Peter HK

[Hirilonde]

No scarfs for the Minipaw I start today, but going to make that jig to prep for my Spindrift 9N later this winter. Thanks for the info Jan, very clever jig.

What ratio (length of scarf/1" of material) are most of you using? For box masts on Concordias we have been using 12:1. Which for 1/4" ply is 3 " long. Jan's instructions show 6 degrees, but anything that shallow I would think can lead to slight variations when used and need a little doctoring up by hand.

[jan nicolaisen]

Dave,

I'm glad you might find this useful.

The six degrees should yield the 8:1 scarf that seems to be what most experts in the field recommends for plywood. I have used down to 6:1 with no apparent problems...

You're right though, with such a shallow angle it just takes a slight error in setting up the tablesaw for the bevel cut, for example, to change things. This would mean that different versions of the jig may not come out at precisely 8:1. On the other hand it has shown consistency in replicating whatever scarf size it makes over and over, with minimal clean-up.

Don't you all love talking boats and boatbuilding? I will have to pry myself away from the screen soon, and actually head out in the shop on this gray sunday morning.

Later, Jan

[Charlie Jones]

I've found that 8 - 1 on ply and 10 - 1 on solid is a good workable ratio. 12 - 1 would be good, but that can take a LOT of shop space cutting solid lumber. I have a table saw jig that I use for stringers, etc and I can cut good solid 10 - 1 scarfs in seconds using that.

Perhaps Graham will see this ( or Tom Lathrop) and chime in with their thoughts on the matter.

[jan nicolaisen]

Charlie,

Tracy's excellent plans and instruction sheets taught me how to do stitch and glue. The boat came out well too, mostly thanks to Tracy and a good portion of luck from my side.

How long have you been tinkering with boats? Seems like it must have been a long time.

Off go to 'work' now...

Jan

[Charlie Jones]

lol- not so long really. Or so it seems.

I first climbed into a sailboat in 1957. Started messing around rebuilding, repairing, etc in about 1965. REALLY got innto it about 1969 and started my first large one, a Cross 35 ketch rigged trimaran in 1976.

Counted up the other day and the Core Sound 20 underway in the shop now is the 10th boat I've built since 2000, mostly for customers. A MiniPaw dinghy and two Birders were for us. This CS willl be the 6th B and B boat I've done- so far

In total I think (If I haven't missed any) I've built 15 boats, and done complete, gut out to the hull, rebuilds/restorations on 4. Those since 96. This doesn't count rebuilds, repairs, etc on various small boats like Sunfish, Dolphin Srs, Hobies, Prindles and boats of that nature- just the bigger ones.

And a few (very few) power boats

I think that's about it

[Tom Lathrop]

Charlie,

About 19 years ago, Graham gave a talk to our local sailing club about a racing tri they were building for the World 1000 race alongshore from Ft Lauderdale to Virginia Beach. I was recently retired and building our house but thought boatbuilding would be more interesting. The beginning of a long and fruitful association.

The first job Graham gave me was to scarf 40' of 3mm plywood for a wing mast. After that initiation, no plywood scarfing job since has presented me with as much problems as dealing with that floppy noodle of wood. Because of limited space it was necessary to roll the completed sections when doing the next joints. I do think the Gougeon jig and the John Henry jig make some sense although I have never used either and doubt they would be suitable for 3mm ply.

I use a combination of power plane, belt sander and hand plane to make scarfs. I stack at least 4 sheets and do them together in one go. Other jigs that I have seen or heard about seem to be making a fundamentally simple job more involved than it needs to be.

[Hirilonde]

Thanks for the comments on ratios all. I just have to finish this Mini and I can try my hand at ply scarfing.

12 - 1 would be good, but that can take a LOT of shop space cutting solid lumber.

We use a router jig that fits onto the end of the board. It is made out of polycarbonate and consists of a beveled slide that accepts a piece that holds the router. Makes short work of it but only works well for the ends of boards. It can also work for scarfing in repairs for damaged sections of box masts. Our boat sheds are up to 100' long, so space isn't the issue. Our workshop is a shoe box :cry:

[Greg Luckett]

I've found that 8 - 1 on ply and 10 - 1 on solid is a good workable ratio. 12 - 1 would be good' date=' but that can take a LOT of shop space cutting solid lumber. I have a table saw jig that I use for stringers, etc and I can cut good solid 10 - 1 scarfs in seconds using that.

Perhaps Graham will see this ( or Tom Lathrop) and chime in with their thoughts on the matter.[/quote']

How about sharing a pic of that table saw jig, Charlie?

We used a 10:1 scarf ratio on the 12mm Merianti ply used to plank the lobster boat. All those scarfs were done with a power hand planer and finished with a belt sander. There were a few mistakes at first but after that we all were able to do scarfing fast and accurate. A jig would take away some worry of wasting materials.

Thanks

[Charlie Jones]

I can do that Greg- I'll have to set it up tomorrow and shoot some pics

[Joe Nelson CS#35]

My two cents...I just had my first experience with scarfing. It is a lot more intimidating than it really is. I stacked up $500 worth of plywood, spaced it at the proper distance for 8:1 ( 4" for half and 2" for quarter). Went at it with my power planer and finished with a good sharp hand plane. Came out great! The biggest problem with scarfing is that you loose plywood. Butt joints dont loose any plywood. If you are covering the plywood with glass, you can get by with 7:1. That saves a bit of ply. Use some 1/8" milled fiberglass fibers in your glue mixture to improve strength...just a pinch until it looks like snot...then thicken with silica and woodflour mix. Epoxy glue is brittle. The milled glass helps to bridge the glue and make it stronger. I would use it anywhere you are making a structural fillet and dont plan to cover it with tape. Or makes a super strong fillet if covered with glass tape or biaxial tape. Would be good for making motor mounts etc..

[PAR]

With epoxy you don't need a real nice scarf fit. I've used a big angle grinder, literally hacking away enough wood, on a taper to fit another in place on top of it. Butter with thickened epoxy and call it done. I've repaired many a plank this way, on the boat, scabbing in an upside down pyramid sort of repair into the ground back repair area. With some cloth and filler you can also do the same thing with more strength.

On varnish jobs, I've found jigs are handy if you have a bunch to do, but a power plane, belt sander and dressing up with a hand plane the fastest if you only need one or two that day.

I have a beveled edge to a table that can handle a full sheet. Each table side has a different angle, which the saw runs in, but these aren't the best scarfs made. Blade flex can be troublesome. I also have two tapered ramp and a router jigs, which I use for machine like precision scarfs. The ramps are adjustable, so different thicknesses are covered. This is slower then my hack it or hand plane method, but they are very precise.

On masts I like a 12:1 scarf and 8:1 is the minimum scarf I'll do.

[Peter HK]

Joe said

Use some 1/8" milled fiberglass fibers in your glue mixture to improve strength...just a pinch until it looks like snot...then thicken with silica and woodflour mix. Epoxy glue is brittle. The milled glass helps to bridge the glue and make it stronger.

I think you can overkill the problem. I've made a large number of scarfs, 8 to 1, with standard epoxy and filler (not lightweight sanding filler), using the west scarffer. I've always tested the offcuts and did so a couple of days ago, one more time. When the scarf is subjected to maximum stress, the ply just next to it fails. I've never found it to be different.

It only has to be a strong as the ply 8)

Peter HK

[Garry]

I can feel the woodworkers cringe. I scarfed the plywood for my Spindrift 11N without a jig or a plane! I marked the plywood on both sides with the appropriate slope dimension (~3"?). I stacked the plywood in steps based on the marks. I marked the heel of each scarf with a black marker so I could tell when I got near them. Then started grinding away with a belt sander and 36 grit belt. I made a lot of sawdust but it didn't take long to get the bulk of material gone. The stacked slope got me started at the right angle. Then I simply watched the glue-lines and black marker lines and took away more material where needed until the lines were all fairly even.

To assemble, I used the lines as a guide to get the right spacing. Thickened epoxy did the trick and they came out great.