Tripp Trapp

[dedee]

Has anyone made a chair along similar design principles to the Tripp Trapp

We have been given one for one of our daughters to aid her muscular development and posture and now of course the other 2 want one each as well. They are such a good idea, growing with the child and very comfortable even for an adult I thought they should not be too difficult to make. Retail is about £100.

I was thinking of using 1 inch faced ply for the side frames and 1/2 ply for the seat/footrest and back support.
The metal bars (which tension the chair together and prevent the seat and foot rest from moving) may need to be studding with an outer shell of tubing.
I'm not sure if I can make the curved back rest but I think if they were made straight it would not be uncomfortable.

Andy

 

[Shultzy]

Why not make it in solid beech, you won't have to worry about lippings. To make the curved back make a former out of MDF and use 1/8" ply cut into strips. The grain needs to be across the strip to allow it to bend more easily. Glue the strips, put in former, cramp up and then cut to size.

 

[dedee]

Shultzy,
I thought by using a quality faced birch ply I could cut the side frames from one piece and therefore not have to worry about the joint between the upright and the "feet". On the original the seat, foot rest and back, are all made from faced ply without lipping and the effect is quite pleasing (to my eye).
My dining room furniture is oak so if I make a success of the 1st one (prototype :wink: ) the second (and probably 3rd) may well be in oak.

I have done cold forming as you suggest with some walnut handles, without a bandsaw I am not sure I can cut wide enough strips for the back rest - I'll give it some more thought.

Andy

 

[SketchUp Guru]

We have one of those Stokke chairs. It's pretty cool. I've thought about makking one, too but the back rest parts are slowing me down. I suppose you could laminate and vacuum bag those once you got a shape for the mold. I have thought about a modification using some wide nylon webbing straps for the back rest. It would require a modification to the frame--maybe a length of dowel or rod between the side frames.

The plywood they use is the equivalent of Baltic Birch. This is very nice because there are no voids. I like the look of the plies being visible. I'm building some toy boxes for my son from BB plywood. Nice to work with.

 

[Shultzy]

dedee - I take your point about the ply, I just don't like the ply edges to be visible. I think its a throw back from my childhood, dad always made things from plywood and never covered the edges. As for the strips for the back, you can get these cut at B&Q etc. or use a CS and guide strip.

 

[Scrit]

Andy

I'd suggest using Finnish birch plywood - Baltic in the UK generally means Latvian or even Russian, both of which are of lower quality and tend to have more obvious repairs and more voids than the Finnish - and look for a B/B (or B/BB) grade if you can get it. The Finnish stuff can generally be had in 5ft square (150mm square) sizes which is very useful for furniture work. There should be no need to edge the material at all so long as you bullnose the edges with a cutter like these from Wealden then sand off and seal. From experience I'd recommend the T2525-1/2 used with an 18mm guide bush, although I'd suggest caution using this combination as the cutter is quite large (I've used this cutter to make children's furniture on both CNC and overhead pin router). BTW 18mm will be strong enough for your needs, 1in/25mm is possibly overkill and will result in a much heavier piece.

Personally, I'd avoid using rodding because it is a potential catch area. Instead I'd go for something like mild steel or silver steel rod cut to length and then threaded. Most engineer's merchants should be able to supply you with rod, nuts and washers and a cheap die holder and die will only cost you a few pounds. I'd also get hold of domed nuts for use on the ends rather than leaving any exposed threads, etc. If you wanted to avoid steel stretchers and instead use wooden ones another approach might be to use Scan bolts, such as these sold by Woodfit which are used in conjunction with a cross dowel. They are similar to the fastenings used on the Swedish Balans chairs

The curved back elements might be most quickly made using something like two layers of 9mm bendy MDF formed around a band-sawn or jig-sawn forme and glued together. Bendy ply is another approach, or even layers of 4mm MDF could be bent and glue-laminated to form the stretchers. I'd keep to using a curved back stretcher if at all possible as it considerably improves the comfort and useability of the piece

Main thing in terms of accuracy, though, is to make a template before you start and to clamp both sides together and gang drill them on a drill press if at all possible. For strength with plywood I'd also make the V-shaped sides as a single piece

Good luck with your project

Scrit

 

[dedee]

Scrit, thanks for the head up on the 5ft square panels. I'll have a hunt around locally. I've only every bought 8x4 sheets before from Alsfords, not sure if Finnish but I've yet to find a void. A 5ft square panel, if economical would ceratinly be easier to handle.

I've been thinking along similar lines for the rods. The length of these rods is critical as they tie the whole piece together so I'm not sure if the doomed nuts will be suitable - trial and error I guess. On the original the rods are threaded on the inside with a bolt passed though the frame .

The template/plan will be taken from the original.

Andy

 

[Scrit]

Andy

If nothing else Silvermann's should be able to supply you with Finnish birch plywood in the South East.

I've been thinking along similar lines for the rods. The length of these rods is critical as they tie the whole piece together so I'm not sure if the doomed nuts will be suitable - trial and error I guess. On the original the rods are threaded on the inside with a bolt passed though the frame.

I had some second thoughts about fastenings and revised my original post to include a reference to the Scan fasteners used in stuff like the Balans chairs. That way the ties could be made from timber and any metalworking avoided

Scrit

 

[dedee]

Scrit, brilliant - now why didn't I not think of that.

Andy

 

[Anonymous]

Hi Andy,
My little lad has that exact same stokke chair, its solid as a rock he's had it about 4 years now. Strong enough for me to plant my backside in :lol:

Anyway, looking at the 2 curved back's, they seem identical. I expect they make a sheet to that profile in thier factory then cut strips off (like slicing bread). If you use the baltic/birch ply couldnt you make the back's from lanimated birch veneer so it would match the rest of the construction? You'd only need a simple forme made of scrap ply or mdf, make it 100 mm wide then rip it into 2x50 mm strips?? You could wrap the laminates with stretched inner tubing if you havent clamps or Daves air bag thing. Its not a tight radius so shouldnt be hard to do?

Are the ties in Scrits post like the ones you get in knockout IKEA furniture with like a set bolt and a threaded barrel? I agree that wood cross ties would look better.
Cheers Jonathan

PS it sounds like I'm sudgesting you rip the forme in 2, but what I really meant is to make the forme and the laminates 100mm+, let the laminate cure, THEN rip into 2 50 mm piece's :lol:

 

[Scrit]

Are the ties in Scrits post like the ones you get in knockout IKEA furniture with like a set bolt and a threaded barrel? I agree that wood cross ties would look better.

Yes. That's why I used the generic name of "Scan fasteners" (at least I think it's generic). There's a far wider range of fittings than Woodfit stock, it's just that they're the only stockists local (-ish) to me who carry them. And they do retail mail-order as well - but no affiliation on my part I'd hasten to add.

Scrit

 

[promhandicam]

Hi Dedee.

With the special seating that I designed and made, I used 18mm ply and didn't bother with any horizontal bracing in the form of rods as the back rest is fixed and so is the base. On the prototype larger chair - which took some inspiration from a chair similar to the TrippTrapp, the angle of the chair could also be adjusted which for some children is important in helping to overcome poor head / neck control. This is a link to the original post which has a photo of the chair in question) With regards to shaping the back, the physio that I worked with prefered to use triangular section foam which was covered in faux cuir, (imitation leather - not sure what the name of it would be in the UK) These were attached with velcro strips to allow easy adjustment and enable them to be removed for washing. Don't know if this is of any use - let me know if you need any more info on special seating.

Steve

 

[engineer one]

i wonder whether any of you have considered the other way of providing the horizontal supports.

cut a tube which is the width of the chair. next find some nuts which fit inside the tube, so i suggest a one inch/25mm tube in something like 531 or whatever the present equivalent of reynolds tube is . then find some nuts which go inside the tube, i would guess 12.5/14mm dia nuts would fit.
using a vice crush the nuts into the tube. do it with bolts inside so as not to crush the thread. drill the side pieces and thread through the tubes.
next use BIG washers, and a shortish bolt and screw into the nuts. until it pinches up.

now that's an idea which goes back to about the ark, or at least world war one.

youcould probably use any old mild steel actually as the tube, talk to
your local steel providor. cut the tube on the inside of the overall width to allow it to pinch up properly

paul :wink:

 

[David C]

I built one of those for my son who is now 24. It is a great design.

Used sycamore, with birch ply for the seat/footrest.

The whole thing was mortice and tennoned, and did not have the through rods, it is still perfectly intact today and was often sat on by adults.
The rods and or fixings will make for a much easier job as the tennons on the ends of the curved elements were not so easy. The two main cross rails were through tennoned and wedged.

The picture does not show the Bow shaped bendy rail which acted as a seat belt for very small/young children. This was one of the more difficult bits. 3 layers of solid laminated in my case. This rail was sprung into place when used.

The curved backs could be cut from solid, laminated in 3 or 4 mm solid, or perhaps many layers of birch skin ply (Silvermans) which is 1.5 mm thick, makes a very smart, strong job. 1/8" would also work.

Nicely sanded birch ply edges are very satisfactory, two small radius roundovers would be less intimidating to cut than full bullnose.

My experience is that at about four yr. old a child will no longer sit in what is seen as a baby apparatus!

Happy new year,
David

 

[dedee]

Steve,
Thanks for reminding me about your post, excellent chairs. The horizontal braces in the trip trapp enable the seat and and foot rest to be easily moved as the child grows. They just slide in and out when the horizontal braces are slackened off.

Paul,
a typical engineering solution, I like that idea a lot.

David C
a typical woodworkers solution (through tenoned and wedged). I do not have the bendy seat belt for the existing chair. We are using an ordinary booster seat web strapping and I think in a few months that will not be required for twin 2. Twin 1 does not need restraining already.

One of the reasons I think these chairs are so comfortable (even for 5 & 6 year olds IME) is that they can rest their feet while siting. Try sitting with your legs dangling it soon becomes uncomfortable.

Many thanks for all the input.

Will try to get Silvermans to sell be a single sheet of ply later without paying through the nose to have it delivered. Either that or I'll need to collect and cut in quarters to get in the car.

Andy