View Full Version : Ash for tiller side...
12-07-2003, 05:48 PM
'nother stupid question. I'd like to fabricate the sides of my tiller (are these called cheeks?) from ash. The current design calls for large 1/2" thick pieces and the port and starboard pieces will each be cut from a piece that will be about 18" tall and a bit over 14" wide. Obviously, this is too wide for a single piece so of Ash so I'm assuming that the piece will need to be joined from smaller boards (can you detect my woodworking ignorance coming out here). If this was a piece of furnature, I'm assuming I'd just square up three 5" wide pieces on a joiner and butt-glue them together. This part, however will resisting the side load on the rudder. If I epoxy a three 5" wide pieces together will it be strong enough at the joint? Should I consider a different style of joint?
Thanks in advance...
12-07-2003, 05:51 PM
Yup, as far as I know, them things are cheeks! ;)
Asking from ignorance, I wonder if some biscuits in the joints wouldn't help?
12-07-2003, 06:07 PM
I'd join the pieces with 3/16" splines (thin strips of wood set into grooves in the edges to be joined), either coming to the end-grain edges or stopping them about 3/4" from the ends. The splines should be just a smidgen narrower than the total depth of the slot they go in, to allow space for the adhesive. How will these cheeks be fastened to the rudder? Glue, epoxy, screws?
Maybe a machine screw near the slot for the tiller.
12-07-2003, 06:15 PM
Aren't a spline and a biscuit effectively the same thing?
12-07-2003, 06:50 PM
If the pieces are properly jointed all you need to do is butt them and glue them.
Buscuits, because they are made of randomly oriented strand, do serve as somewhat a tenon making it possible to assemble face frames for cabinets for example without mortise and tenon, but provide minimal strength, virtually none in panel glue ups. They are also useful for alignment, as when you are attaching a long piece of edge trim to a piece of sheet goods or solid stock.
I think either are a waste of time in this application re increased strength. The glued up piece will be as strong as a solid piece, if done properly. If you are concerned about torsional strength put some drifts in.
Oh, and if you are gluing with epoxy, DON'T OVERCLAMP. The number one cause of failure in an epoxied joint such as this is a glue-starvation. Too much clamping pressure, and all the glue gets squeezed out.
Biscuits are generally compressed beech, which, in the presence of water, or water based adhesive, swell to fill the gap, providing a stronger joint. Holzbt told me that. I've never used one.
12-07-2003, 07:34 PM
Biscuits are generally compressed beech, which, in the presence of water, or water based adhesive True enough, which make them easier to assemble than dowels or splines. They are essentially chips of beech that are compressed and cut into those little football shapes.
Don't get me wrong, in some applications they're great. They still don't have the strength of a mortise and tenon in frame construction, and I don't see any advantage in this application.
P.S. And a little reading has brought me more up to date on buscuits in frame construction. They've come a long way since I last used them. While still not up to the inherent strength of a mortise and tenon, they aren't too shabby anymore, but I still don't think they will buy you anything in the situation under discussion.
[ 12-07-2003, 08:16 PM: Message edited by: Jack Heinlen ]
12-07-2003, 09:36 PM
Drifts in 1/2" thick material? Otherwise, what Jack said. Biskets are handy for alining the panels until the glue dries or if you are the phoney Norm, for selling more power tools.
If I visualize the cheeks we are talking about here they will sandwich the rudder which will extend on down into the water. There will also be a piece between the cheeks above the tiller slot. If that is correct then the rudder and top piece will reinforce the cheeks adequately.
..or if you are the phoney Norm, for selling more power tools. Sheesh! I there anything in life that isn't a conspiracy with evil intent? Norm's probably more liberal than you are, considering his homeland. :rolleyes:
12-08-2003, 09:16 AM
Why not just scarf the joints. I would stay away from biscuits in boats.
12-08-2003, 09:30 AM
Snile, Donn. Don't smarl.
12-08-2003, 09:39 AM
I overlooked the thickness. Norm is correct, it's too thin for drifts.
I think just following the plans with glued up stock is the ticket. If it will give you some added peace of mind, and doesn't throw anything else out of whack, increase the thickness to 5/8.
12-08-2003, 09:42 AM
Hmmm...1/2" thick, 14" x 18" -- are you sure the design doesn't call for plywood? Cheeks take a lot of stress and I would be very concerned about them splitting, but it all depends on exactly how everything fits together. If the design calls for solid wood then you should be fine, if the design calls for plywood then I would use plywood.
If you do end up using solid wood I would just joint the pieces and glue them together. A half-way decently made glue joint of this type is as strong as the wood itself. Even if splines or biscuits did reinforce the joint, what would you gain by making the joint stronger than the surrounding wood? And, I'm fairly certain that Fine Woodworking did an analysis of just this situation a few years ago and concluded that in this sort of joint biscuits and splines, if anything, weakened the joint. This would be especially true with a hard wood like ash, because whatever you make the spline or biscuits of is unlikely to be much stronger than ash. Splines also have the disadvantage that they show on the edge.
Of course, for joints where you have end grain coming against side grain then biscuits add greatly to the strength, and for situations where holding parts in alignment would be difficult biscuits can be just the thing.
12-08-2003, 10:35 AM
I think your terms are mixed up. You intended to say rudder, not tiller. That changes everything... Don't know if you ended up with one of Arch's designs or not but my rudder is made from 1/2" ply and yes, they are called cheeks.
Hope this clears things up. This forum is a terrific resource. Saved my butt many a time last winter. Use it, the guys enjoy assisting in any way they can.
12-08-2003, 10:44 AM
As this progresses, it sure sounds more like a rudder than a tiller...I'd use marine plywood laid up with epoxy and covered with fabric and more epoxy before painting.
12-08-2003, 10:44 AM
Maybe too much. We don't need accurate descriptions of the situation nor to know what we are talking about thus two negatives make a positive. Cheeky cusses, we.
12-08-2003, 11:29 AM
Use 'feathers' or some call them splines made from the same as stock you're using for the cheeks. I'd make the feathers 3/16"X by about 1". Biscuits are oblong little do-dads that require a 'biscuit'cutter. Feathers are long strips of wood that are married into the edges of planks or whatever then glued (not to much pressure) and clamped up with pipe clamps to make wide stock to work from. In my opinion there's no place for biscuits on a boat except in tins. Use a marine glue like UF109.
Make sure the ash boards are edge grain. Glue
and thru bolt the cheeks to the rudder using bronze or stainless ready rod, about 1/2".
12-08-2003, 03:20 PM
Is this a kick up rudder? If so, I'd never make the cheeks out of soid wood if plywood were available. These parts take stress in all directions and ply is much better at that than a single layer of lumber.
If it's a fixed rudder then butt joined lumber to make up the cheeks with the grain off angled to the grain in the rudder stock which will take care of splitting problems. An angle of 20 degrees is adequate to prevent splits and not so much as to create delamination problems due to differential shrinkage in such a wide piece.
12-08-2003, 03:28 PM
Sorry for the ambiguity. I guess I don't know where the tiller ends and the rudder begins. The pieces in question are the green ones in the following image. It's my own design so it's hard to fathom the designer's intent! I guess I was leaning towards Ash over plywood for aesthetics but based on the forum's comments, perhaps plywood is a better choice. It certainly solves the size problems.
12-08-2003, 03:46 PM
Originally posted by Jack Heinlen:
</font><blockquote>quote:</font><hr /> Biscuits are generally compressed beech, which, in the presence of water, or water based adhesive True enough, which make them easier to assemble than dowels or splines. They are essentially chips of beech that are compressed and cut into those little football shapes.
Don't get me wrong, in some applications they're great. They still don't have the strength of a mortise and tenon in frame construction, and I don't see any advantage in this application.</font>[/QUOTE]Actually a single-biscuited joint, because the joint is virtually all shoulder, is about equivablent in strength as a proper mortice-and-tenon in the same piece. And if double-biscuited, the joint can actually be stronger than a mortice and tenon.
FWW (#148, Mar/Apr 2001) ran a piece a couple years back by a testing engineer who tested different joints to failure entitled "Testing Joints to the Breaking Point", by Bruce Gray ("Surprising results surface in an analysis of commonly used furniture joints").
On paper, biscuits should be weaker than a mortice-and-tenon becaus the tenon is much stronger in shear, but in actual practice, the load is almost always racking—it's virtually never a true shear load. In that situation, the enormous shoulder area of the biscuit joint in relationship to the biscuit size provides a lot of compressive strength.
All than being said, biscuits would be a lousy choice for marine construction, as beech is neither stable nor durable.
Beech's very instability is in fact why biscuits are made from it: the compressed beech expands—a lot—when it comes in contact with moisture in the glue.
12-08-2003, 03:57 PM
A quick question on your illustration, before getting into things deeper.
I was thinking that the tiller was supposed to fit down between the green pieces and rest on the pink piece. However, the tiller seems to be much thicker than the pink piece and the rudder. So, how does the tiller fit together with the other pieces? This is one place where there will be a lot of stress.
If the tiller does fit down between the cheeks and if it is supposed to be allowed to rotate up then I think you have an issue beyond plywood vs. solid wood. If the tiller is lifted up so that most of it is above the cheeks I think you will have a blow-out at the pivot point not matter what you use for the side cheeks.
[ 12-08-2003, 04:12 PM: Message edited by: Bruce Hooke ]
12-08-2003, 04:03 PM
Nicholas -- the piece run by Fine Woodworking was, if I remember correctly, about two pieces of wood coming together at right angles (as in the "frame" part of a frame and panel), which would be a typical location for a mortise and tenon joint. That is a butt joint with end grain coming against face grain, and it would obviously be very weak without either a mortise and tenon, biscuits, or something similar.
In the case of these rudder cheeks, however, we are talking about edge joining two pieces. For edge joining I really don't think biscuits do anything other than help with alignment during the glue-up. Even if they do add strength all you've done is make the joint stronger than the surroundind wood, which doesn't achieve much of anything.
Note: After writing the above I re-read what you were responding to and I see that you were responding to the general question of mortise and tenon vs. biscuits. In that general case I would not dispute what you said. However, I will leave what I wrote because I think it's important to make the point (even thought I think you are aware of this point) that the relative strength of biscuits vs. mortise and tenon joints really does not apply directly to the situation at hand.
[ 12-08-2003, 04:07 PM: Message edited by: Bruce Hooke ]
12-09-2003, 12:17 AM
Save yer money, lad. Biscut-slot-makers, pocket-screw-drillers, dowel-jigs--all substitutes for taking a little relaxing time to develop skill.
I'd consider splining if I thought some mechanical assistance was necessary in edge-joining two sticks. HOWEVER. If you want the spline to do any real good (other than indexing the two boards, the grain of the spline should be cross-grain, that is: run athwartships of the grain of the sticks what gots the slots. This pretty much limits the spline stock to the width of whatever board you're cutting it out of. But who sez the spline has to be one continuous piece?
I spline with a table saw. Cuts the slot, makes the spline. Done this way I've put splines in pretty thin stuff. Make the spline of the same species. And don't cut the slot through the ends of the stock--stop the cuts short and taper the ends of your splines if you think they should run to near the ends of the boards you're gluing up, and Bob's yer uncle.
12-09-2003, 02:49 AM
Save yer money, lad. Biscut-slot-makers, pocket-screw-drillers, dowel-jigs--all substitutes for taking a little relaxing time to develop skill. Ditto...encourage beginners to learn to cut joints.
Typical forumite on the woodworking forums is a beginning 30-year-old with a new family and the nesting instinct many of us once felt...
...and usually with no money to waste.
I'm a fan of these production techniques for commercial cabinet production...making a living at craft has never been easy...don't ask me how many jobs I netted $.50/hr on. And if that kitchen cabinet is gonna be torn out in 30 years, it doesn't much matter if it's ****eboard pinned together with cheap drywall screws and T-Nuts.
But to watch the consumerist bombardment of these beginners trying to create heirlooms by "gurus" trying to sell gizmos, books, videos, 200-dollar block planes, 100-dollar trysquares and other unneeded stuff makes me want to scream sometimes...especially when they are promoting lesser-quality construction.
Sorry for the rant:
When I occasionally need splines in edgejoining, I prefer 1/4" hardwood plywood scraps as splines and a router and slotting cutter for the groove. The router follows irregular boards nicely and if you flip the board and also have a go from the other side, you are guaranteed a perfectly-centered groove.
[ 12-09-2003, 02:59 AM: Message edited by: Bob Smalser ]
12-09-2003, 12:39 PM
I'd use plywood and laminate ash veneer to it,for looks.I have some that I'd give you.
About the spline/biscuit/tenon thing,they only strengthen the joint,not the adjacent area.That's why drifts would work better,they cross all of those weak grain lines,EXCEPT that drifts,dowels and long tenons don't allow for shrinkage and could CAUSE the thing to crack,though it wouldn't fall apart.
12-09-2003, 02:46 PM
Another key question is what is the proposed material for the center (pink) piece and how will this piece be attached to the cheeks? How close, and critical, is the fit between the pink piece and the rudder? If this fit needs to be very close then you may need to use plywood for everything (except the tiller) just for the stability.
12-09-2003, 03:46 PM
Those cheeks really want to be plywood, as does the center spacer. Rudder blade would be happy to be edge- epoxy- glued stock. As drawn , tiller could be one piece ash.
12-09-2003, 07:54 PM
Wow... great advice. Plywood for the cheeks it is then. And I'll stick to Ash for the tiller.
Thanks for pointing out what I fear was an embarassing design flaw. I'm going to redesign it to sandwich the tiller inbetween the cheeks instead of lapping on the outside. I should be able to rework the tiller pivot so that the tiller remains firmly between the cheeks even when lifted. This this will address your concerns?
12-09-2003, 10:20 PM
Yeah, now you're talkin'. Now that I remember the boat, and see the drawing, plywood for the cheeks. And I think I want to see at least 5/8 in there, maybe 3/4. It isn't unusual to see an aluminum or stainless fabrication in this application. Some of the forces on a rudder in this type of boat can be tremendous at times. Look at some similar boats before you finallize your plans.
Just remember, if it fails you can always build another.
P.S. Ya know someone who might be worth a holler is Warren, um Wild Wassa. He doesn't post here much anymore, Aussie, chased off by the politics, but he's into racing smaller dinghy. Write him and explain your dilemma. A nice chap, I'm sure he would help if he can.
I'm leaning toward having a stainless weldment made, just an intuition, seat of the pants, but the forces on that rudder are going to be signifigant.
[ 12-10-2003, 12:53 AM: Message edited by: Jack Heinlen ]
12-11-2003, 12:02 AM
Yes, that sounds like it should do the trick. I would try to keep the pivot point for the tiller back near the aft edge of the assembly because it will be stronger that way. Actually you could put the pivot near the front edge but extend the tiller aft of the pivot and let the back end drop down when the tiller is lifted and achieve the same end. The idea is to give the tiller as much surface as possible to bear on inside the cheeks.
As to materials, I am not convinced that solid ash would not work for the cheeks & pink piece. The tiller would span the week grain direction and effectively reinforce it. However, the design (as it presently stands) does feel like it's more oriented towards plywood -- especially given the hole in the middle of the cheeks. Is that a hand-hold?
You could probably reduce the width of the green pieces and the diameter of the circular section at the top of the rudder. I'm not sure what you gain by making those pieces as wide as they are -- but there may be some part of the geometery of how they move that I am overlooking.
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