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Discussion Starter · #1 ·
I've envisioned something that might turn out to be over my head, but I'm hoping with a little thought and help, it wont turn out to be too bad.

If this were in days of yore, I'd be talking to a cooper, but I don't know any.

Ok, so what I'm trying to do is make a wooden tub.

I want to make it from, lets say, 100 2 inch slats, plus tongue and groove width.

I'm open to the specific shape of the tone and grooves. I've envisioned anything from a blunt wedge like this,

------\ \ -----------------
-------\ \
---A---| | B
-------/ /
------/ /----------------

to something like the thomas the train wooden railway tongue and grooves. I can't draw that in ascii, the but the main point is that I want some kind of joint that improves total surface area of the slat joint, so that water expansion will cause it to seal up tight.

The main thing I'm looking for is a shape that is either easy to get get right, or small error tolerant, or both.

It would be NICE for the joint to be more like the thomas rail joint, or like a very loose dovetail etc, as it holding itself in place while I set it all up and install the metal band around the outside would be helpful, but that is not required. Being error tolerant and pitchable (is that a word?) is the big deal.

Once I have that shape, I'll be figuring out how to create a 2 degree offset on each of the slats so that the total angle for both sides is 4 degrees.

So, the shape of the tongue also needs to lend itself to being slightly offset without requiring a CNC to get it right.

I suspect that no matter how careful I am, the final 1-2 pieces will be a bit custom to close the circle.

I wanted to also angle the slats so that the top was 2 inches +t&g and the bottom was 1.5 inches +t&g, but that just seemed like asking for trouble.

At the end, I'll route a dado into the end of each slat, which will be used to fit onto the bit circular floor of the tub. Which will be constructed in the same way. So I'll be putting slats into the slots on the slats.

Open to opinions as to why this is a terrible idea, or how to do it better, or best of all, how to accomplish my goal.

That goal in summary:
develop either a jig, or a procedure, that allows me to make 100 2 degree angled tongues of some kind, and 100 2 degree angled grooves that match the tongue, (with one groove and one tongue on each piece). A single bit or bitset that can do this would be amazing, but I suspect I'll be left with using some other kind of bit and some creative cutting.
 

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The technique is beyond me, if we have 100 slats, 1.5" wide at the bottom and 2" wide at the top, if my math is right the diameter is about 42" at the base and 63" at the top? Pretty big tub, filling it with anything much heavier than styrofoam peanuts will most likely require some sort of outer band.

Both sides of the slats angled at 1.8 degrees should give you a circular shape--that's about as far as i can go with it!!

Good luck.

earl
 

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Here you go - MLCS' write up says for canoes, hot tubs, etc. so it sounds as if it's just what you're looking for. MLCS Flute and Bead and Tambour Door Router Bits I don't understand the 2° offset, the design of the joint is going to allow you to "curve" the assembly as you put it together - 60 +/- hot tub? As far as the taper, the slat is going to register on your fence so would cut the profile on a tapered width part with no problem.

Are you planning to assemble and clamp the parts so that you can cut the rabbet at the end of the slats to fit in the groove in the floor?
 

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Discussion Starter · #4 ·
The technique is beyond me, if we have 100 slats, 1.5" wide at the bottom and 2" wide at the top, if my math is right the diameter is about 42" at the base and 63" at the top? Pretty big tub, filling it with anything much heavier than styrofoam peanuts will most likely require some sort of outer band.
...
Good luck.

earl
Thanks, I am sure I will need some luck, but wanted to make sure I asked the experts before moving on to the "just try it!" stage.

regarding the band:

It would be NICE for the joint to be more like the thomas rail joint, or like a very loose dovetail etc, as it holding itself in place while I set it all up and install the metal band around the outside would be helpful, but that is not required. Being error tolerant and pitchable (is that a word?) is the big deal.

I plan to use 3 bands of 14g stainless. My plan is to get 14g sheet cut to 4 inch wide strips that will by 4"X 10' (or 22' if I'm lucky and they have some full length stock in)

Since I probably wont be that lucky, I'll just cut each strap to half its needed length, get 12 rectangular column blocks of billet stainless, drill and tap each one with open or threaded holes (3 of each), then use 3 bolts each and probably 2 external nuts after bolt exits the threaded block. Tig weld the blocks to the strap, test fit and all that. With any luck, that should insure that while the wood might fail, the top, middle and bottom straps will not.
 

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Discussion Starter · #5 ·
Here you go - MLCS' write up says for canoes, hot tubs, etc. so it sounds as if it's just what you're looking for.
(I cant post urls)

I don't understand the 2° offset, the design of the joint is going to allow you to "curve" the assembly as you put it together - 60 +/- hot tub? As far as the taper, the slat is going to register on your fence so would cut the profile on a tapered width part with no problem.

Are you planning to assemble and clamp the parts so that you can cut the rabbet at the end of the slats to fit in the groove in the floor?

Thank you!, that product sounds perfect for what I'm talking about. Especially the error tolerant part.

I was thinking I would handle it a couple of ways if needed.

Start by making each slat about 12 inches over length. In case I need to try more than once.

Cut the dados for the floor after routing the edges at a 12.5 degree (if the trig I just learned is correct), and it should sit in flush and tight.

If that doesnt work, then yes, but I am hoping math triumphs and it only takes one try.


The 2 degrees was a sloppy way to reach the full circle,
100 sided polygon
total interior angles is x-2(180) (then you divide by side count, and thats degrees, divide that in half (and get 1.8) and thats how much each cut needs to allow in angle.
 

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One thing you didn't mention is the end use and whether it will have to hold water. Traditional coopering was all done by hand and eye and the finished product became watertight when the steel bands wouldn't allow it to spread out when the wood began absorbing fluid and swelled up. The canoe joint would work under those circumstances but I'm not sure what would happen with a T & G joint or a spline joint which is what I would recommend for a tub that will stay dry.
 

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Ok, so what I'm trying to do is make a wooden tub.
I know this isn't what you asked, but I have a little experience to offer. I've built a few buckets and planters. Unless you are determined to do it without glue, why not just cut your staves on the tablesaw at an angle? Glue it with polyurethane glue and the bands and fit are not quite so important. I have one bucket in daily use that will hold water for weeks. I developed a spreadsheet a few years ago that calculates the taper angles and blade angles for the staves if you don't want the sides to be vertical. See the attachment.
 

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One thing I forgot to mention is the difficulty of assembling all of those (almost) vertical pieces into a bucket or tub. I know that's one reason you'd like to have a joint that captures one piece in relation to its neighbors. I tried building assembly jigs without much success, even for 16 sided buckets. The one thing I found that worked for me is to lay a couple of strips of painter's tape sticky side up on the workbench. For larger pieces you'd probably need duct tape. Then, lay your bucket strips out horizontally so the tape will be on the outside of the bucket. If the bucket is tapered, you'll have to use several shorter, overlapping strips to keep it on track. Then you can start at one end and lift and roll the pieces into position. Once you have the staves in sort of the right position, wrap the entire thing in bungee cords or such so you have the flexibility to work the bucket bottom into position. Take one stave out at a time and apply glue, then re-insert. I'd really suggest you start with a smaller bucket without so many pieces to start. Maybe a scaled model of the real thing.
 
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If anyone wants to see how they were originally made then go to Youtube and search for Guinness Brewery Cooperage. It's a very interesting clip.
 

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Discussion Starter · #13 ·
I just wanted to say thanks to everyone that gave me some great info, along with some great ideas and alternates to consider. I'll be taking a few videos and pics of the project while I do it, so however it ends up, I'll post how it went here.
 

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DonkeyHody's approach definitely works. To that I would add cutting sheets of stiff cardboard to match the diameter of the circle and rolling the staves around it as Andy described. Once the glue has set simply cut the cardboard out with a knife. If your concerned about glue sticking to the cardboard wrap painters tape or plastic wrap around the outside edge of the cardboard.
 
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