Hot Tub Help

[blair]

On holiday in Sweden I saw traditional wooden hot tubs heated by submersible wood fired stoves. These tubs are available in the UK but cost around £2000.

The problem with diy construction is that it requires precise cooperage skills to ensure watertightness. I've experimented with scaffolding board and an old pond liner and have made an oblong tub that is watertight. I plan to have a tub liner made to measure (about £200) and install a woodfired heater (about £400). The thing is I would much preffer a circular tub. The way I think that a circular tub could be made would be using three foot high sections of saffold board (I've got dozens of these boards). I'm planning to create a D shaped groove along the length of one side of these boards and plane the opposite side into a shallow C shape. The boards will fit together with the C side of one board fitting into the D side of its partner. I'm thinking that this will obviate the need for precise joint measurements. The base will be a circle of marine ply. Waterproofing will be provided by a vinyl liner.

My problem is that I have very basic carpentry skills. Would it be easy to make a curved edge on one side of an inch and a half board and a C shaped groove on the other using a router? I've never used a router. Any advice would be appreciated.

Cheers!

 

[Steve Maskery]

Hi Blair, and welcome to the forum.

What's the proposed diameter of your hot tub? The C?D technique you describe is viable, I think, but you also need to consider how you are going to prevent them all falling away from each other, leaving party goers less submerged than you intended and not knowing what to reach for first.

Routing the C/D joint will require specialist router cutters and they in turn will probably specify router table use only. and you'll need a substantial table to take a 3ft scaffolding board. I think a better way, for a one-off job at least, would be to get hold of an old-fashioned pair of round & hollow planes. It'll be a bit of a workout for you, but straighforward.

That's how I would cut such a joint, anyway.

How are the Scandinavian ones made?

Cheers
Steve

 

[Newbie_Neil]

Hi Blair

Welcome to UKW.

Cheers
Neil

 

[Anonymous]

You must enter a message when posting

 

[blair]

Steve, thanks for the welcome. I've seen some tubs that are assembled with the "ball and socket" method I've described. This is only viable with tubs that do not taper and have a consistent circumference from top to bottom (fine by me), other tubs taper in at the bottom and seem to be made by planing a slight angle along each side of every board. I think that they use computer measuring to do this though.

I plan to cut a half inch horizontal groove two inches from bottom of every plank which should create one contiuous groove into which the plywood disc base will slot. This should provide some outward directed stability which I intend to counter balance with nylon tension bands (in lieu of the traditional steel hoops). Water preasure should take care of any inclination to collapse inwards (I hope!). This should ensure no naked spillage incidents. What do you think?

Shaped hand planes sound right up my street. Have you ide where I might obtain them Steve?

Thank you very much for your advice and thanks to both you and Neil for the welcome.

Cheers!
Blair

 

[blair]

Jacob, thanks for your input.

I'm not confident that my creation would be waterproof, so I intend to buy a made to measure vinyl hot tub liner. These liner are designed to cure leakage problems in old wooden hot tubs.

The prototype I was mucking about with was an oblong scaffold board box lined with an old pond liner. This was an ugly method of waterproofing but the scaffolding "tub" was not unnatractive and did, in fact, look much like a Japanese offuro (Sp?). It would be easy enough to get a vinyl liner for this and rig it up to a wood burning Chofu or Scuba stove. If you just want the experience of hot soak in the open air I'd say that this is a very managable project. I'm still wedded to the circular tub project myself. I'll let you know how it goes.

Cheers!

Blair

 

[blair]

Guys, sorry for my multiple postings. I forgot to ask what a "spindle moulder" is?

 

[Newbie_Neil]

Hi Blair

A spindle moulder is the next step up from a router mounted in a table.

Cheers
Neil

 

[Scrit]

Hi Blair, welcome to the forum

......other tubs taper in at the bottom and seem to be made by planing a slight angle along each side of every board. I think that they use computer measuring to do this though.

I'm sure any cooper would be thrilled to be called a computer measurer 8) - or then again maybe not! What you are actually doing is making a large coopered 'wet' bucket or vat. Your bottom groove is actually called a croze groove in 'cooper speak' and is put in after the bucket has been assembled and hooped using a special tool called a croze before the bottom in knocked in. To help get the bottom in the insides of the staves is tapered (and called a chime) like this:

The job could as easily be done with a router mounted on a board with a slotting bit.

If you are going to mill the staves I reckon that Jacob's suggestion of using a spindle with a tapered jig and a planer block would be good, but personally I'd think in terms of getting a vari-angle cutterblock in a spindle and with a ring fence. That way once an accurate template had been made the task of cutting the pieces would just be a template/repetition job. Personally I'm not so sure that a router would be up to the job and it would be more likely to suffer from lumps and bumps in the edges. Whichever way you go the key is going to be in working out the angles and making an accurate taper jig. Using tapers and hoops with some natural spring will result in a tub which will not collapse in on itself and there will be no need to worry about this.

I think you'll possibly have problems if you use nylon hoops - nylon will tend to slide on the timber (it's used to make bearings after all) and I suspect that to get a similar tensile strength to steel that it's going to need to be pretty chunky. It can also be a pain to cut (I machine it from time to time) and get a good surface finish on - any band will need to be cut as a semi-circle to accommodate the spring in the (tapered) sides whereas steel can be cold-formed to the required semi-circular shape. It's also going to cost a lot more than steel (£3,000/tonne against £400/tonne.....).

I think that you might benefit from taking a trip to one of the breweries or distilleries which still has a cooperage, or by going to see a demonstration of cooperage at somewhere like the Weald and Downland Museum. There's a goodish page on cooperage at the Craft Owl site which has a Real Player video of coopering - only I can't get it to play

A very basic description of coopering can also be found here

Hope I've not put you off too much.

Scrit

 

[jasonB]

I would be tempted not to use a box welded liner but go for a free standing circular tank. The 86" would be a cosy size for half a dozen people :lol:

You will then not have to worry about the timber work being structural, you could just chamfer the edges with a circular saw and clean up with a hand plane. The ends of the boards will be covered by the top lip and you could even add a layer of polystyrene between the tank & boards for insulation

I assume you mean nylon straps as in the ratchet strap type of webbing, this could work or you can buy brass banding in rolls which could be fixed witha few brass roundheads.

Jason

 

[Marky]

welcome blair...

All the other questions seem to be covered.

I see you like the idea of a wood fired heater, But lets say you have 600 gallons of hot water, how are you going to stop that getting dirty.

I know you will probably use chlorine / bromine etc, but you will have to do a lot of water changes without filters.

Just interested as I did my own tub last year... Not timber but having seen this thread, I may change to one of these myself.

I fitted my own heater, pump, blower and filtration myself with good results.

Marky

 

[Anonymous]

You must enter a message when posting

 

[Marky]

so when you change the water.... do you use a hose pipe.

Or better still use the water that leaks from the thames water main..

Although, I would say that even with washing you would have to change the water a lot as even when you think your clean, you still give off oils etc... These make the water cloudy really quickly.

Add to that the ability of hot stagnant water in our climate to breed little friends and you could get quite ill...

Wood fired heaters would take at least 24hrs to get the water hot, so you would have to plan in advance...

Marky

 

[Scott]

Blair, yer a brave man pal! A hot tub in Scotland!!! The thought of getting my kit off to get in it would put me off! I love the place dearly but I baled out to warmer climes!

The rain would keep it topped up though!

Best o luck! :wink:

 

[jasonB]

Blair, yer a brave man pal! A hot tub in Scotland!!! The thought of getting my kit off to get in it would put me off! I love the place dearly but I baled out to warmer climes!

Was that a typo Scott, did you mean to say Getting my kit off or getting my KILT off

Jason

 

[engineer one]

surely a useful way to deal with leakage, is to design the
sides like those on a boat??

and then fix caulking between each plank, might well make the
edge finishing easier too, plus give you two ways of keeping the
water in.

maybe look at the Wooden Boat(murrican) web site to get some ideas.

paul :wink:

 

[Steve Maskery]

Blair,
I don't know where you would get hollows and rounds thee days, you could try asking on the Hand Tools board. Time was when every woodshop had an entire set. My dad had a set and we let them go. I regret that now, but they do take p a lot of room when you have a few dozen.

Sorry I can't be more helpful.

Cheers
Steve

 

[Scott]

Blair, yer a brave man pal! A hot tub in Scotland!!! The thought of getting my kit off to get in it would put me off! I love the place dearly but I baled out to warmer climes!

Was that a typo Scott, did you mean to say Getting my kit off or getting my KILT off

Ha! Whatever! Kit or Kilt I'd imagine! A kilt is actually very warm, 'specially a military weight one. Only if you keep it on though!

 

[George_N]

Blair,
I don't know where you would get hollows and rounds thee days,
Steve

Try here. Likely to go pretty cheaply too as there has been no interest so far (I have no connection with the seller, just browsing and I remembered the hollow and round planes being mentioned). Not sure I'd know how to sharpen them though.

cheers

George

 

[Scrit]

You'll probably find it more difficult to plane a mating hollow and round than to plane two flats at a slight angle, especially if you don't know how to set the planes up. H&Rs don't have fences so you need to set up some way to get them to plane true, and even thenthe edges are going to have to be slightly chamfered (and tapered if you are not having a vertical side tub) before you start. Seems like the wrong tool for the job if you ask me.

Scrit