Kid Learning/ helping tower design questions

[sebr023]

Hi guys!

Don’t know if I post in the right place.

But I’m planning on building a helping/learning tower for my kid.

I will be laser cutting 1/4in Baltic birch plywood and laminating it to make a 1/2in. Having the outer plywood bigger by 2mm to be able to flush trim it. Also using 3/4-1” dowel to align both, and using it as a “design” element.

Almost all the design I see out there and the design I use to draw mine, seems to have adjustable heights.

My first question is:
If having adjustable height would make the structure weaker? Should I put more bracing?
Would having my kid standing on the “shelf” make the 1/2in plywood bend/flex in the middle?

Second question:
If having adjustable height is still a good idea.
I was thinking of having some ways to secure the step and the shelf in place.
I was thinking about 1/4 dowel, screws, or having them protrude on each side and it a wedge to lock them in place.

Aesthetic is important.
If using screws I would probably paint them the same colour as the outermost plywood layer for making them disappear.  If going with screws, I’d use flathead hex 10-24 and insert hen in plywood? But seems a bit thin for 1/4 inch plywood. So maybe button head hex screws.

I don’t know how I would make dowel “easily removable” for when you want to adjust height. And having them aesthetically pleasing.

So yeah, I’d like to have your input on this simple design.

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[luvmytoolz]

I can't comment on the adjustability aspect, but I would consider 1/2" ply to be too thin for safety?

Wouldn't take much for a rowdy young one to snap the shelf or seat.

 

[tsmi243]

If you don't mind the hardware showing, a cross dowel would work really well for holding the steps in the dados.

 

[sebr023]

If you don't mind the hardware showing, a cross dowel would work really well for holding the steps in the dados.

Mmm.
Id rather not?! But that’s the only option I’m seeing other than gluing, but I would loose adjustability.

I like your idea. Didn’t know the name of this type of hardwire.

How the hole for the screws is made in the steps? Like the one length wise?!

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[sebr023]

I can't comment on the adjustability aspect, but I would consider 1/2" ply to be too thin for safety?

Wouldn't take much for a rowdy young one to snap the shelf or seat.

Even if Baltic birch plywood?! Forgot to mention it in the first post.

My kid is 25 pound. Doesn’t seem too heavy in my Mind for this. But that’s why I’m asking you guys!

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[Crazyraceguy]

If you are making the vertical members from a glue-up of 2 layers of 1/4" BB ply, it creates two issues that I see.
First, the grooves are only 1/4" deep. That's not horrible or a deal breaker, but at least a concern.

Second, and more importantly, the outer skin is also only 1/4" thick.
Most wooden-step ladders have a metal rod below them, for safety. It keeps the tread trapped in the dado and would support a person, of the wooden tread actually broke.

I realize that you are talking about a small/light child, and this is not very high either, but the thinness of the material has me concerned. There just isn't enough material there to hold the sides to the steps and stretchers and still maintain a "no hardware" appearance.

If you could bump this up to 3/4" thick, options open up.  At that point, I would probably ditch the dados, hold things in place with a combination of Dominos and Domino connectors. The connector screw holes could be under the steps and be unseen, keeping the adjustability. All the time being aware that the child is going to outgrow it by weight fairly soon.
At least one metal rod going from side to side is still preferable, but it's up to you and what you are comfortable with.

 

[luvmytoolz]

I can't comment on the adjustability aspect, but I would consider 1/2" ply to be too thin for safety?

Wouldn't take much for a rowdy young one to snap the shelf or seat.

Even if Baltic birch plywood?! Forgot to mention it in the first post.

My kid is 25 pound. Doesn’t seem too heavy in my Mind for this. But that’s why I’m asking you guys!

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Having had 4 kids, we discovered they found ways to break things and injure themselves in ways we would never have dreamed of. You would have to assume at some point the child will take a flying leap onto (or off) the step, would it support the impact/force?

Keep in mind also the racking forces when it's used.

 

[sebr023]

If you are making the vertical members from a glue-up of 2 layers of 1/4" BB ply, it creates two issues that I see.
First, the grooves are only 1/4" deep. That's not horrible or a deal breaker, but at least a concern.

Second, and more importantly, the outer skin is also only 1/4" thick.
Most wooden-step ladders have a metal rod below them, for safety. It keeps the tread trapped in the dado and would support a person, of the wooden tread actually broke.

I realize that you are talking about a small/light child, and this is not very high either, but the thinness of the material has me concerned. There just isn't enough material there to hold the sides to the steps and stretchers and still maintain a "no hardware" appearance.

If you could bump this up to 3/4" thick, options open up.  At that point, I would probably ditch the dados, hold things in place with a combination of Dominos and Domino connectors. The connector screw holes could be under the steps and be unseen, keeping the adjustability. All the time being aware that the child is going to outgrow it by weight fairly soon.
At least one metal rod going from side to side is still preferable, but it's up to you and what you are comfortable with.

I don’t have a domino, and don’t know what a domino connectors are.

I could go to 3/4, there’s room left on my 4x8 sheet and that only would be add another 1/4 layering. But even if I go with 3/4, the outmost (green) layer would still be only 1/4?! Or the dado would be 1/4 deep. Kinda have the same problem as your mentioning in your comment.

Just wanted to make things a bit more clear:

All the cross member (represented in blue) would be glued. The whole thing is 40cm wide. So not even 16in. And it’s 35in high, so like 90cm (counter top height) the dado will have like 1mm of play in order to be able to slide the stair/step in and out. So not much room for it to flex and bend and get out of the dado.

And from previous comment, I was planning to  use cross dowel and screw to old the step, the shelf and the legs together.

But if going 3/4 is a general consensus, that’s what I would do.

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[luvmytoolz]

40cm is awfully wide for a young child, and would make breaking things much easier being that wide. I definitely wouldn't go anything less than 3/4" thick for all materials myself.

 

[Packard]

Your design closely follows the concept of the Montessori learning tower, which has been around for many years. 

This ad includes enough dimensions to replicate the original.  Since the original has been tested for many years and proven stable and safe, I would probably try to copy that proven design as closely as possible.

You will note that the assembly is by Confirmat screws.  Confirmat screws require a special stepped drill.  There are various sizes, but 5mm and 7mm are the more common ones. 

Confirmat screws have two significant advantages.

1.  They are designed to screw into the ends of sheets of plywood, MDF, particle board, etc. 

2.  They can be installed and removed multiple times without losing any holding power.  So the adjustability will remain.

3.  They have vastly more racking strength (side to side wobble strength) than almost any other mechanical fastener.  An important consideration for this tower.

The RTA manufacturers association (ready to assemble—think “IKEA”) contracted a testing firm to test a variety of fastenters/joinery systems.

It was intersecting to note that dadoes add almost zero strength to the racking.  The dadoes in this illustration apparently are for location purposes only.  The Confirmats are supplying almost all the joint strength. 

You could choose to use dowels or dominoes for location purposes along with the Confirmats.

I get mine from AH Turf—but you need to assemble a significant order to have that make sense.  Amazon sells smaller quantities at a higher cost.  The step drill has to match the size of the confirmats.

Do not try to convince yourself that construction screws or drywall screws are “just as good”.  They are not.

I agree with other who mentioned that 1/2” thick seems too thin.  Mostly it will be too thin for any worthwhile fastener.  So stick with 3/4”.

I have seen ads for Montessori Towers made from solid wood and others from “highly compressed pine products” (probably particle board or MDF).

Lowes sells glued up 3/4” thick pine in wide planks, if you want to go solid wood.

I would probably go with plywood.  I would round over the edges and fill them with wood filler or grain filler for a smooth appearance. 
https://busywisy.com/products/kids-step-stool

Note: I could not find any ads for the original Montessori towers.  I had seen them when I went with a friend to the Montessori school for her daughter many years ago.

There is a “genuine” Montessori School learning tower.  I don’t know how to find that information.  The example I linked seems similar to what I saw all those years ago.  If you can find an original example to copy from, that would be excellent.  It is a classic.

 

[squall_line]

The model I'm building is all out of 1-by dimensional lumber; I did not look for plywood versions myself (mostly because my brother had already built 4 or 5 of them, and he sent me the link to get the plans).
http://www.ana-white.com/woodworking-projects/littlest-helper-tower

The link that [member=74278]Packard[/member] shared shows a model that, while plywood-looking in nature, is actually made from edge-glued panels of solid wood, adding strength that you wouldn't get from plywood, especially on the step.

 

[tsmi243]

Personally, I think 1/2" would be ideal.  Both for looks, and weight.  3/4 seems like overkill.

Dados- If you go with the cross dowels, I'd make the dados REAL shallow.  Like 1/8".  Combine that with a 1.5" cleat under the treads, and you'll have a hard time breaking anything. 

If you don't want fasteners, then yeah make the dados deeper.  And do 3/4" ply too, I guess.

When I say "cleat", there's probably a more correct word for it-  something like this, 3rd one down

 

[Packard]

And your next project should be a replica of the Stokke Tripp Trapp chair (it would be mine, but I have no little kids beckoning).
https://www.stokke.com/USA/en-us/high-chairs/tripp-trapp/TT02.html?dwvar_TT02_color=535&cgid=

 

[Michael Kellough]

Another option to adding cleats to stiffen the horizontal parts is to add hardwood half round dowel.
3/4’ thick by 1-1/2” wide oak would add a lot of stiffness and the contrasting form (compared to all the extremely flat parts) could be a nice design element.

Adding the same molding tangent to the front of the sides would provide a better grip for ascending and answer crazy’s concern that the dados weaken the sides too much.

It wouldn’t hurt structurally and would maintain symmetry to do the same to the far side.

 

[Crazyraceguy]

I think that somewhere along the line, some people are missing the concept that this is a laser-cut project. The increments of 1/4" are part of the design.
With that in mind, and now knowing that parts of this will be permanently fastened/glued, I would modify my thoughts.
Add a third layer
Deepen the dados with that layer.
Add another layer onto the steps, but make it shorter, so that you don't have to increase the width of the dados. That layer would just be for stiffness, and an additional shoulder to help with racking.
I would still like to see a metal rod across it somewhere, probably the platform itself, but the confirmat screws may be enough.

 

[tsmi243]

I think that somewhere along the line, some people are missing the concept that this is a laser-cut project. The increments of 1/4" are part of the design.

Whoops  [big grin]

 

[Packard]

I did miss that.  If I was laser cutting, I would use 3/4” Baltic birch and instead of full-length dadoes, I would cut through slots that are stopped at both ends. 

The “tongue” of the shelves would fit into the slots. 

Alternatively, there could be two shorter slots and matching “tongues” to fit into both. 

I would use large diameter wood rods (about 1-1/2” diameter) with threaded inserts at both ends.  These would be used to tie the sides together.

This is similar to what I had in mind, though I don’t think I would make the slots that wide.  It would appear to compromise the panel strength too much.  Two smaller tabs or one where the tab is not quite so wide.

 

[luvmytoolz]

The important thing to note with the pic above, is the wide base to help stop it toppling over. Designing it so it as topple proof as possible is absolutely crucial in my book. Kids do fall and bounce quite well generally, but a kid falling in one of those could really do serious damage.

 

[4nthony]

How the hole for the screws is made in the steps? Like the one length wise?!

Both Woodpeckers and Rockler make a Cross Dowel Jig for this type of joinery.

 

[sebr023]

Your design closely follows the concept of the Montessori learning tower, which has been around for many years. 

This ad includes enough dimensions to replicate the original.  Since the original has been tested for many years and proven stable and safe, I would probably try to copy that proven design as closely as possible.

You will note that the assembly is by Confirmat screws.  Confirmat screws require a special stepped drill.  There are various sizes, but 5mm and 7mm are the more common ones. 

Confirmat screws have two significant advantages.

1.  They are designed to screw into the ends of sheets of plywood, MDF, particle board, etc. 

2.  They can be installed and removed multiple times without losing any holding power.  So the adjustability will remain.

3.  They have vastly more racking strength (side to side wobble strength) than almost any other mechanical fastener.  An important consideration for this tower.

The RTA manufacturers association (ready to assemble—think “IKEA”) contracted a testing firm to test a variety of fastenters/joinery systems.

It was intersecting to note that dadoes add almost zero strength to the racking.  The dadoes in this illustration apparently are for location purposes only.  The Confirmats are supplying almost all the joint strength. 

You could choose to use dowels or dominoes for location purposes along with the Confirmats.

I get mine from AH Turf—but you need to assemble a significant order to have that make sense.  Amazon sells smaller quantities at a higher cost.  The step drill has to match the size of the confirmats.

Do not try to convince yourself that construction screws or drywall screws are “just as good”.  They are not.

I agree with other who mentioned that 1/2” thick seems too thin.  Mostly it will be too thin for any worthwhile fastener.  So stick with 3/4”.

I have seen ads for Montessori Towers made from solid wood and others from “highly compressed pine products” (probably particle board or MDF).

Lowes sells glued up 3/4” thick pine in wide planks, if you want to go solid wood.

I would probably go with plywood.  I would round over the edges and fill them with wood filler or grain filler for a smooth appearance. 
https://busywisy.com/products/kids-step-stool

Note: I could not find any ads for the original Montessori towers.  I had seen them when I went with a friend to the Montessori school for her daughter many years ago.

There is a “genuine” Montessori School learning tower.  I don’t know how to find that information.  The example I linked seems similar to what I saw all those years ago.  If you can find an original example to copy from, that would be excellent.  It is a classic.

I based my design on this one: aka, I redraw it without any other I formation than height width and depth.
https://cocovillage.com/en-ca/collections/learning-towers/products/natural-wood-learning-tower

They don’t mention how thick is their product

Confirmat screws really screams IKEA imo. But I get what you’re saying.

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