A different 8 siding (spar) gauge

[Jon Etheredge]

Bob has posted a great article on using an 8-siding gauge or spar gauge as I call them. A few months ago, there was a short piece in WoodenBoat about an articulated spar gauge that is owned by Mystic Seaport. I have always used the quick-and-dirty gauges like Bob is showing but I was intrigued by the one in WoodenBoat. So I designed my own version of an articulated spar gauge. Here is a photo:

<CENTER>

</CENTER>

This particular gauge is made of some Cuban Mahogany scrap that I had stashed away. The wear plates, pivots, and fastenings are made of brass. The scribers are drill rod (carbon steel).

The gauge does seem to work a bit better than the more traditional type. No pencil points to break for one thing. And the offset pivots mean that it always marks perfectly even when there is lots of taper in the spar. It's also better looking than the tradtional ones [img]smile.gif[/img]

[Bob Smalser]

"Right Click....Save As...."

....for sometime next winter.

Niiice work, Jon.

[Ian McColgin]

Very nice. I've also seen the one at Mystic.

Pete Culler's type, which I use, has round posts with bushings as rollers for the side guides. I like this because no error is induced as you get a smaller and smaller spar compared to that for which the guide was designed. But the error is small and the ease of operation may be a good trade off. And, like the way boat builders knock off planes for particular projects so by the time they are a master, the plane kit as a couple dozen, so with eightsiding guides.

Truth is, half the time I don't have the thing with me when I want it. A bit of stock, a couple of 10d nails and a couple of sharp brads end up doing the duty.

[almeyer]

Jon, is that intended as a tool? Looks too pretty to use....needs a few scratches, dings, and glue blobs on it. Nice work.

[Ian McColgin]

Bob's companion post shows a nicely made version of what I knock out. You want the guage to be only a little slack at the spar's thickest point.

I do not divide the spaces into three equal sides, but rather use the shipwright's traditional 5 - 7 - 5 ratio.

Say the stock is 8" thick at it's thickest. Four halves are only 16 units and we need some multiple of 17 units, but we also need a bit of slack. So a tool with 8-1/2" (17/2") between the inside edges of the posts would be good. Then arrange the scribes such that the points are just 2-1/2" (5/2") from each inside edged of the posts, leaving 10/2" between them. The ratio will remain fine even with a bit of taper.

If you draw the top of a square and divide the top by the 5 - 7 - 5 and also mark 5 units on the upper part of the two uprights and draw in the hypotenuses that show the faces left after planing you'll see the ration. Five squared plus five squared is near enough to 7 squared for this job.

G'luck

[Bob Smalser]

Originally posted by Ian McColgin:

I do not divide the spaces into three equal sides, but rather use the shipwright's traditional 5 - 7 - 5 ratio.

G'luck

Keep on the outside rdge of your pencil lines when drawing the tangent, again when transferring to the block to be drilled, and when planing and you have pretty close to that without the math.

I usually take a shaving off of the "clean" surface anyway to remove the pencil lines.

[Ian McColgin]

Dave Fleming, help me out here.

I think it depends on how large a scale one's working in, how accuratly you need to land at a predetermined cross section, how much wood you want to lop off and how hard you want to work.

Dividing the square faces evenly by three and planing to those marks produces the four new sides about 41% (root 2) larger than what's left of the four original faces. This may well be acceptable especially in small jobs of more or less arbitrary size. Also, many experienced folk manage to do it just fine purely by eye or eye slightly correcting the scribed mark.

Just that for me that it's as easy to make a guide that's 5-7-5 as to make one that's accuratly 1-1-1.

Different boats, different long splices.

[Jon Etheredge]

Yeah, I lay out the correct spacing when I make a spar gauge instead of 3 equal divisions. Rather than doing the math though, I just do a geometric layout with a compass and a combination square to lay down 45 degree tangents to the circle. For me, this is quicker and less prone to error from faulty cipherin' [img]smile.gif[/img]

[Bob Smalser]

Laying out a large spar is a different critter than oar making, where like in all woodworking, I like to coach "eye and feel"...you can see a 32nd...but you can feel a 64th.

Making a 2" loom, how you treat your pencil lines based on what pleases your eye accounts for most of your accuracy.



The left hand oar is post-draw knife...the right hand oar is post-planing. Working to the outside of the lines with both tools, followed by taking a fine shaving off the face to remove the pencil lines and any dents from the shaving horse...

...produces bevels that are closer to 5-7-5 than they are to 1-1-1...

...merely because it looked good as I first did it that way longer ago than I care to admit.

[ 06-17-2004, 02:47 PM: Message edited by: Bob Smalser ]

[Ian McColgin]

Very nice oars. Pleasing tapers and all. I'll bet they have a nice little spring, a bit of life, as you apply some norweegan steam.

[Bob Smalser]

Thanks, Ian...I think they'll do.

[L.W. Baxter]

Bob, those look fantastic.

I've got an observation about the orientation of laminations. I hope you don't mind me posting a pic of some oars I made a few months back for illustrative purposes:



Obviously, I laminated flat to the face of the oar blade, whereas you've laminated with with glue lines perpendicular to the blade face.

My observation is, the way you've done it makes a neater transition from shaft to blade.

And I imagine that the orientation of the laminations would have some effect on oar strength or flexibility? Or even the durability of the blade itself?

My guess would be, flat laminations like mine would result in a springier, but ultimately weaker oar.

I eight-sided and tapered my oars by eye, by the way. They're far from perfectly smooth and fair... but they seem to work. The next pair will be better, I hope.

--Lee

[Mike Field]

Originally posted by Ian McColgin:
Dividing the square faces evenly by three and planing to those marks produces the four new sides about 41% (root 2) larger than what's left of the four original faces. This may well be acceptable especially in small jobs of more or less arbitrary size. Also, many experienced folk manage to do it just fine purely by eye or eye slightly correcting the scribed mark.

I use a gauge similar to the one in Bob's thread, but with wooden dowels for the outside posts and with Jon's metal scribers rather than pencils (the pencil points always seemed to break when I didn't want them to.)

If the gauge is a good fit for the spar at its widest point, and the distance between the posts is divided in the ratio 0.3, 0.4, 0.3, with the scribing points located accordingly, then the gauge gives true proportions at that point on the spar. (There's a drawing here.)

As long as the posts are not too thick and the spar's taper too excessive, lines drawn on the balk remain essentially the same ratio apart (with minor discrepancies creeping in at the ends, which I usually correct by eye.)

Bob's narrower posts seem a better idea though to reduce the tapering discrepancies further, and Ian's bushes on the posts would certainly help make the gauge move more smoothly. But I especially like Jon's Mystic pattern -- that's definitely a "Right Click....Save As...."
.

[Bill Perkins]

Very nice Jon . I wondered if anyone else here had been impressed with the Mystic gage.