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Thread: Nice rowboat, nothing fancy.
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5th October 2013, 10:41 AM #31Senior Member
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So I got a bit impatient and pulled the laminated frames out of the forms. They've had over 40 hours clamped up and curing conditions have been good.
Springback was negligible (about 1mm or 1/16" each side at the sheer). However, there are slight signs of compression failure at the tightest part of the bend. You can see this if you look carefully. It shows as intermittent shallow creases across the grain.
This wont be a problem with the laminated construction, but in terms of laminate thickness and bend radius I wouldn't try to push the bending further than this. Surian is the same species as Ausssie cedar, and is a fairly good bending timber. Radius/thickness for this bend is 43:1. My 2c is that 50:1 is pretty safe for just about anything if steamed first (I've done oregon to that yonks ago). Steamed frames in older boats often went down to 20:1 or even less, but then as we all know steamed frames in older boats often crack after time.
So, if anyone wants to try this sort of thing, I'd suggest sticking with strips about 1/50 of the bend radius. My 2c.
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5th October 2013, 10:51 AM #32
Well done. Good result for being adventurous enough to exceed 5-6mm on such a tight radius.
Craig
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5th October 2013, 11:03 AM #33Senior Member
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Rough rule of thumb I worked out years ago was that 100:1 for dry bends and 50:1 for steamed is pretty safe with just about any straight-grained timber.
No responsibility taken if that breaks for you, as I didn't test it exhaustively with every species on the planet. It seemed to work for oregon (Douglas fir) though, which is not known as being good for bending.
ETA: Also, I was bending around spaced blocks. If bending around a continuous fair form, things would probably be less prone to failure. I doubt that most amateur builders will be doing that though.
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5th October 2013, 11:39 AM #34
Have to say I agree with your ratios, but would treat that as the limits personally only for aesthetic laminating. I take the path of working well inside the limits for items I deem structural...the more lams, the more glue, the more grain variation & reduced amount of stress in the final piece.
With such minimal initial springback you'll be fine I'm sure, but I reckon you just snuck in (evident by the small amount of compression failure). Once again, good work.
Craig
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5th October 2013, 12:02 PM #35Senior Member
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Well TBH, I just hate the "more lams, more glue" scenario and prefer to keep that to a reasonable minimum. In purely structural terms I agree with what you're saying, but this is supposed to be fun. As long as it works and looks pretty good, I'm happy.
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5th October 2013, 12:20 PM #36
Fair enough.
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5th October 2013, 06:28 PM #37Senior Member
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Cleaned up all the frozen snot, dressed for thickness, and got 'em sanded. Starting to look sorta boaty, but I think a few bits are still missing. Better check the plans again.
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7th October 2013, 06:07 PM #38Senior Member
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Got a bit more done.
The latest is I took the sheets of 3mm MDF that I'd used for the backing for the bending/laminating forms, and cut them up into patterns. This means I can lay the patterns on top on the frames/stem/transom blanks and trace around them. After that it's cutting frames, etc to shape and bevelling them, which is where the fun bit really starts. I'm looking forward to hewing out the stem. It's always enjoyable watching the curves and rolling bevel on a stem come together.
I'll keep the patterns in case I want to build a copy of this boat at some stage (or someone else local wants to). They can still be used for bending more frames just by screwing blocks to them again.
(I really should copy them over to some polyester drafting film, but can't be bothered at the moment).
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8th October 2013, 10:46 AM #39Senior Member
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Cut the stem profile. I just freehand routed both profile edges with a large straight cut bit, then flipped it and finished it them off with a flush trim bit. Would have done it in one go, but didn't have enough depth of cut on the straight bit. Marking out and bevelling next.
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16th October 2013, 05:57 PM #40Senior Member
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Ripped and dressed the stock for chine logs, stringers, sheer clamps and gunwales*. Progress of a sort. Still need to scarf the the bits for length, and they'll get a small radius (around 3mm) on exposed edges.
Stringers will also be rebated to hide the edges of the planks. Yes, I know it's a bit fiddly, but I don't like looking at plywood edges. Cutting the rebates with a basic router jig isn't hard. It'll look nicer when it's all together.
*Gatecrashed the local Men's Shed, crossed their palms with silver, and availed myself of a table saw and thicknesser. Yee_ha.
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21st October 2013, 01:32 PM #41Senior Member
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So, since the next bit is to rebate and bullnose all the long and skinny bitz, I decided I want a router table. No point buying one when I can make something simple and satisfactory myself. I checked out some of the local metalworking places and managed to score an offcut of 3mm aluminium sheet. I told the bloke I needed something around a foot square. He handed me a 1200x400 sheet and said I could have it for nothing. I didn't argue.
So, now to make a router table...................
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21st October 2013, 07:38 PM #42Senior Member
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And here it is. Still needs a bit of finishing off (some sort of fence, a few fastenings, etc) but the basics are there. I'll add the finishing touches in the next day or so.
For the timber base, I just used the same base I'd made for my impromptu router-powered "thicknesser", with a couple of extra bits of framing added. Since I have access to a real thicknesser now I wont be needing the Flintstone model.
The lift-out plate has two holes: one for working with small bits and another for working with larger bits. The spare one makes a good finger hole for lifting the plate out.
I'm not going to put it on legs for now. My current plan is just to sit it about halfway along the strongback for this particular bit of work. This will enable me to use the rest of the strongback to support the long and floppy bits, which is handy, and the height is convenient to work with. I can always put it on legs later if I feel like it.
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22nd October 2013, 07:32 PM #43Senior Member
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This is basically finished. The two spare mounting holes for the router take the clamping thingy, to hold the lift-out plate firmly in place. This just swaps to whichever holes aren't being used, depending on which end the router is set up.
The fence is just going to be clamped in place for now. No matter how I do it, it'd have to have some sort of clamping arrangement, so might as well use clamps. They work.
I'll be using it with a finger board to hold the stock against the fence. Will also be using a push stick, of course.
Probably wont bother with anything fancy in the way of guards. A suitable bit of wood clamped in the right place will do. It's not required to be idiot-proof. If any idiot wants to duplicate it and take their idiot fingers off, that's their problem. I've managed to keep mine for over half a century by using my brain. Seems to work.
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23rd October 2013, 03:27 PM #44Senior Member
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Router table works a treat. Stringers are rebated.
For this job I had to raise the fence off the table slightly, to get the crud to clear from the bit. If the fence was on the table it all clogged up pretty quickly. Still wasn't perfect even with a 6mm gap under the fence.
I had to raise the piece I was working on off the table at times and hit it with the leaf blower to clear things out. Using the leaf blower meant cedar dust all over the place, which would be a bummer if I didn't like cedar. I may be sneezing a bit, but I smell fantastic.
Also had to go over some sections twice after they started rising up on crud, but no big deal. I had one of the fence spacers on the outfeed side set out from the fence by 14mm. Since the MDF scraps I was using for spacers are the same thickness as the planking I'll be using, this worked well to support the stringers past the router bit. This, in turn, meant that re-running some sections to clean them up was easy and accurate.
Fingers are all present and accounted for (subject to change without notice).
Currently having a late lunch, then will rebate the sheer clamps.
After that, beer.
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26th October 2013, 07:30 PM #45Senior Member
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Got the frames and transom rough cut. This was just getting rid of most of the waste, cutting about 1mm outside the finished line. They'll get finished to the exact line tomorrow. I'll do this by tacking the patterns back onto the frames, and running a flush trim router bit around them. This is the easiest way to get the control face. After that it'll be notching for the stringers, and bevelling the edges.
The three reddish frames are the laminated cedar ones which will stay in the finished boat. These have had a 3mm round over run around their inner edges. The other two whitish frames are just temporary ones to hold the shape during building.
The stringers have had the same 3mm round over treatment on both exposed (inner) edges. Sheer clamps and chine logs have been given an 8mm radius on one edge, which suits them better. The sheer clamps are rebated like the stringers, to hide the edge grain of the plywood planking.
PS: This router table is worth its weight in gold. Should have made one ages ago.
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