Cutting Gains - How to Do It?

Discussion in 'Wooden Boat Building and Restoration' started by adt2, Apr 14, 2012.

  1. adt2
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    adt2 Senior Member

    Well, I thought I was being really clever last weekend. I jury-rigged a fancy router jig to cut the 1-3/8" x 30" long gains on my lapstrake build. Worked like a charm for the garboard planks - which had a straight edge to work from.

    Moving on the next pair of planks, my system worked okay for the gains at the aft ends of the plank, which had a fairly straight edge to work from. But the forward ends are another matter entirely. The curve at the forward ends of the planks prevents my fancy jig from working.

    What I did was to clamp the plank upright, on edge. Then I clamped a straight piece of 2x material to the plank, flush with the top edge of the plank, just to give me a wider base to work from. Next, I clamped a piece of 1/4" cold-rolled steel to the (now 2-1/4" wide) top surface. I aligned the edge of the steel with the start (flush with the outside face of the plank) and end (flush with the inside edge of the plank) marks and clamped it into place.

    Next it was a relatively simple process of running a bearing-guided straight bit along the edge of the steel to cut the sloping rabbets. As I said, this setup worked fine as long as the plank edge was straight (or nearly so).

    All of this was necessary because I do not have a rabbet plane. Which brings me to the actual point of this rambling post: How do you people cut gains? Has anyone built the "gain-o-matic" jig and could share some photos? I think since it works by routing from the face of the plank, the curved edge wouldn't be a problem, but I can't find any decent photos of the thing and I don't have a copy of the book.

    Any other clever ideas would be welcomed. I tried using a regular plane, but I'm going to tear up the plank, the plane, or something else out of sheer frustration if I continue down that road.
     
  2. ancient kayaker
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    ancient kayaker aka Terry Haines

    Haven't done it but I read that the usual practice without using a rabbet plane is to cut a slot with a back saw and remove the material with a chisel. not very ingenious but it would work. I'm interested in the topic because I have a lapstrake planned for a future build.

    Can you post a pic of your router jig?
     
  3. jehardiman
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    jehardiman Senior Member

    Yep, rabbet plane is better and faster. FWIW, unless you are doing hundreds and need < 1 mm percision, hand tools will be faster than building and fiddling with a jig. Try it, you'll like it. A stanley rabbet plane is ~$70.00, if it took you more than two hours to build a jig, you are way behind in cost. And it's good for cabnet work jointing also.
     
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  4. adt2
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    adt2 Senior Member

    Found the answer. Way faster than hand tools, way quicker than 2 hours, and way cheaper than $70.

    Find a board thick enough that when turned on edge (i.e. the 1-1/2" dimension of a 2x4) it's wide enough to support your router base. If you're using a trim router, a 2x4 (or two 1x boards nailed together) is plenty. Lay the board on its side and lay out your gain. Mine are 30" long and being cut into 3/4"-thick planks. So, I measured 30" down one edge of the 2x4, measured up 3/4", and made a mark. Now draw a diagonal line from the corner of the board (representing 0,0) and the mark you just made (30, 3/4 in my case). Be sure to extend the line well beyond the mark you made.

    Use whatever your preferred method is to cut along this line. Mine is a Festool plunge cut saw riding on guide rails. Make the ramp a good deal longer than the finished gain will be (maybe 1/3 to 1/2-again as long). Now, set the ramp on your stock, with the gain-length mark (30" in my case) on the inboard end of your gain. Set your router on the ramp and adjust the bit so it just kisses the plank face at the inboard end of the gain. If you find, like I did, that the router bit is too short or too tall, slide the ramp one way or the other until you find the right height (i.e. hold the router with the bit fixed at the inboard end of the gain, then slide the ramp underneath it until the router sits firmly on the ramp and the end of the bit just touches the plank).

    Clamp the ramp some distance from the edge of the plank (I used about 1/8" per pass, your mileage may vary), put the router on the ramp beyond the end of the gain (so the tip of the bit is off the plank), and slowly guide the router down the ramp. (It should be obvious that we are using a bearing-guided bit here, with the bearing above the cutter.)

    Unclamp the ramp, move it over 1/8" or so, re-clamp, rout, lather, rinse, repeat. Voila. Gains are cut. I touched mine up just a hair (like, one pass) with a block plane after routing.

    Now, if I had more than four of these left to do (which, thankfully, I do not), I would fashion a better jig. Probably something along the lines of the gain-o-matic out of the Glued Lapstrake book. Next time I'll know better, I guess.
     
  5. gonzo
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    gonzo Senior Member

    A rabbet plane is the right tool for the job. It takes less time to mark the edge with a back saw and plane it than to rig all that complicated jig and planer thing. Gains change bevel depending on the location, so you would have to build a jig to accommodate the changes. Also, there are two styles of gains. The first has a sharp shoulder and is like a ramp. The other is triangular in shape and is cut on both planks. They both work well.
     
  6. BATAAN
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    BATAAN Senior Member

    Gains

    Here's some 'gain' info and discussion.
    http://www.boatbanter.com/archive/index.php/t-5771.html
    I was shown the ins and outs of rapid clinker planking by a blindingly-fast master who was trained in UK and have used the method in boats to 32 feet.
    Gains are started with a saw against a guide stick, then cut with a 1" razor-sharp paring chisel, then finished with a small rabbet plane, or not... if you do a good job with the chisel.
    This paring tool I'm talking about is very long, about 18", and easily controlled and pushed with two hands.
    A short chisel won't work well here as it's too hard to 'steer'.
    The router is a cabinet maker's tool, and rarely saves time or effort on a boat, except in rounding over edges to make them look machined instead of crafted, and in some mortising jobs, rare on a boat hull but common in interior joinery.
    I may be a luddite, but being a shipwright since the early 70s, I still don't own one and am considered a very fast worker....
    The upper edge of the attached plank on the boat has its gain cut with this paring chisel, with a twist to it, not straight and parallel, usually about 20 plank thicknesses in length (1/2" plank gets a 10" or so of gain).
    In other words, the plane surface being cut on the lower plank is parallel to plank face at after end where it starts, then becomes angled into the stem where it meets that member.
    This reduces the amount of wood removed from the rabbeted gain.
    The lower, inner edge of next plank being hung has a matching twist planed to the gain area, but no actual rabbet cut.
    This twist gives more meat in the gained joint by reducing the rabbeted part, important in conventional (non-plywood) riveted lapstrake boatbuilding, that does not use glue.
    Done right, the lapped seam tapers nicely to flush out the planking at the stem and remains perfectly tight for many years.
    It also is very quick to fit, once you get a little practice, and much much faster than setting up a router and jig.
    Machines have replaced skill it seems, and our wooden boats have become poorer as a result, since we 'can't' build them without power now.
    In the 1840s, Lachlan McKay's yard was producing four ships per year out of Oak and Yellow Pine, all over 500 tons, all built with hand tools, with a work force of about 60.
    Try that with a router.
     
  7. BATAAN
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    BATAAN Senior Member

    And it usually takes about 20 minutes to fit.
     
  8. ancient kayaker
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    ancient kayaker aka Terry Haines

    If you make the gains with a rolling bevel cut on both mating sides, a low angle block plane is probably the best tool to use for the second plank edge, especially for small boats with thin planking; maybe more commonly found in the average amateur builders tool kit than a rabbet plane. I don't see any reason why it couldn't be done for the first plank too while it's on the bench; the lap bevel can then be blended in.
     
  9. BATAAN
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    BATAAN Senior Member

    Yes, LE block plane is quite common in most wood worker's tool boxes and a very appropriate tool for the job on light ply plank IF using rolling bevels, which I don't like for the reasons below.
    Watching a real pro, use a very long and slender paring chisel only, cut and finish a perfect, twisting, curved, rabbeted gain in less than 5 minutes is a revelation though, and I have seen it many times in one particular shop, usually while the practitioner was chatting about world affairs, smoking a cigarette and drinking a cup of coffee at the same time, but can't do it that fast myself.
    Gain usually incorporates a rabbet in the upper edge of plank fastened to boat and bevel only on the plank being applied over it, leaving the under plank thinner than the over plank at the stem.
    The reason for this is it leaves more thickness in the outer of the two lapped planks at the stem, providing more beef to fasten and not split.
    If you use a rolling bevel, half the stock removal is from the upper plank and half the lower, giving a thinner upper exposed plank at the stem which is harder to fasten down and more easily split or crushed in installation or use, thus the reason for a rabbeted gain on the upper outside edge of the existing plank, since it is trapped under the new plank going on, and does not require the extra wood since what it there is sandwiched between the stem and next plank going on, which is quite a bit thicker at that point, for the above reasons.
    All this long winded-ness just says it's usually best to cut a proper rabbeted gain, and not a rolling bevel for a properly engineered and workmanlike job, unless plank is very thin and plywood, which is usual these days.
    -
    The example I gave in my earlier post was/is common professional practice as done in Whitby UK to build 36' heavy, beach-launched motor fishing cobles with near-1" lapped and riveted larch plank nailed to sawn oak frames, which are fitted and installed after the planking defines the shape.
    These are built without plans or molds of any kind, not even a half-midsection 'shadow mold' to keep track, just the shape of the boat, and the planks, firmly in the builder's mind.
    They have a very effective and clever tunnel stern with heavy beaching/prop flow control skegs and a "net clearing port' in the center line 'ram' plank made of bronze at the apex of the prop tunnel and very near the waterline, that unscrews and is just the proper size to get a sweater-clad arm jammed in as a plug and hack at a jammed net with a knife. Notice very nicely faired-in and fastened gains at stem and no gains at transom, but joggled there to keep full strength and thickness for fastenings.
    They are a marvel of evolved effective industrial-use (not toy...) lapstrake build out of non-exotic woods without glue or modern sealants. Keel and all crooked grown frames on boat described to me by one of its 3 builders were local English Oak and plank was larch, bedding was red lead, plank rivet fastenings copper, frame nails and keel bolts galvanized steel.
    In this 1970s build story my lapstrake teacher passed on to me, the time required from felling the oak tree to cut out the keel with skilsaw and axe, to the customer going out to sea and setting his new gear from his brand-new boat and starting to make money instead of spend it, was 90 days.
    -
    Delicate ply planking on a recreational boat is something quite different and low angle block plane (very very very sharp at all times of course) with a light touch is all that you need if 1/4" or under and you are not going to cut rabbeted gains but prefer rolling bevels.
    Doing both on bench is problematic and usual practice is to use a guide stick and ribband to bevel and 'gain' the lower plank's upper edge to the point that little or no bevel is done to the next plank's lower, inner edge, and its 'gains' are slight rolling bevels in the last few inches of lap at stem and transom, fasten it off, now its upper (on finished boat) edge gets the bevel/gain treatment.
    Some commercial, high-volume, lap-ply builders cut a half rabbet (three times wide as deep) on the upper plank, no bevel on the under plank, use the shoulder of the rabbet to key the plank into place with no nonsense, and fill the resultant gaping outside fit with glue and filler or some use various rubber products like polyurethanes or polysulphides. This gives a thick glue line, appropriate to these products. It also enables the builder to manufacture a quantity of shaped planks in advance and get the same shape boat every time.
     

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  10. PAR
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    PAR Yacht Designer/Builder

    This assumes a half lapped gain, which is traditional, but not always the case. The first Lyman I rebuilt showed me a different method, which I've used ever since; the rolling bevel dory lap. As the name suggests it's just a tapered lap, but uses a rolling bevel so the lap disappears, just like typically seen in traditional lapped dory builds. If you are building a glued lap project, then a belt sander is all you need. If a traditional or bright finish is required, then some hand plane work after roughing in with a power plane or belt sander will do. I can do a well fitted gain on a plank end, in the time it takes most to setup a jig of some sort.
     
  11. BATAAN
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    BATAAN Senior Member

    Yes, rolling bevel dory lap works well enough and is very easy to fit like you said with a belt sander, but for a fastened and not-glued plank, I believe the approach that leaves the most meat in the outer plank gives a stronger fastening base than the dory bevel does.
    The dory bevel is a manufacturer's short cut to save time, which it certainly achieves, but gives a lap at the stem which is not as robust in the long run, since the lower exposed outer edge is now thinner.
    With glued plank, little of this matters, and it's an arcane and obsolete technique applied to nailed/screwed plank, and the difference between old hand work, and sped-up, good enough for the job, commercial builders' developments from that.
     
  12. PAR
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    PAR Yacht Designer/Builder

    Typical dory laps are 2:1, but the gains are often 3:1, which provides enough meat I think, particularly considering the stem or transom is right there to help support the weakest end of the joint. Having rebuilt a number of Lymans over the years, I've never noticed an issue with this lap over the more conventional half lap gain. In fact I've repeatedly seen Lyman building methods exceed other manufacture's techniques. Lyman was one of the last to use sealants between the laps, which they started to do in the mid 60's, while others such as Chris Craft had begun in the 50's, yet their craftsmanship and technique was good enough to hold this "new development" off at least a decade.

    In short a 3:1 rolling bevel, starting say 12" away from a major structural element (stem or transom) isn't much to ask. Personally, I like slightly longer gains, but it's purely an visual consideration. In most boats, you'll have a few frames to land on too, in the length of the gain to stem or transom, further supporting the lap edges.
     
  13. BATAAN
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    BATAAN Senior Member

    I certainly agree as to the general fit and quality of Lymans, so whatever worked well for them works, period.
    If it gives a smooth surface at the stem, stays tight and looks right, it's right.
     
  14. PAR
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    PAR Yacht Designer/Builder

    I have to admit to blatant theft and stealing of ideas, techniques and processes I've found that worked well over the years.
     

  15. BATAAN
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    BATAAN Senior Member

    Don't we all? Few things we've invented ourselves, when it comes to wooden boats, which seem to go back more than 50,000 years.
     
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