Thread: Helix table help needed

If some one is available to help you with a CAD drawing that would help.
It's 50 years since i last drew an accurate helix!! I think I can still do it
but not 100% certain.

Damn!! now you have piqued my interest in having a go!!!

Thanks artme, I am glad there is someone else out there that can't resist a challenge.
Any sensible person would have told their daughter that a box or round column would look better.
My daughters know that i don't like furniture repairs, using pine or chipboard or doing multiple copies of the same thing. This daughter has responded by giving me challenging projects and her list of projects is growing. I need to complete a few soon or she might start asking me to make things out of pallets as a punishment.

I am sure I have used a math formula once upon a time but it hasn't risen from the depths of my muddle brain yet.

Google might know?

Originally Posted by artme

If some one is available to help you with a CAD drawing that would help.
It's 50 years since i last drew an accurate helix!! I think I can still do it
but not 100% certain.

Damn!! now you have piqued my interest in having a go!!!

Here is one technique to quickly draw a helix using SketchUp.
How to Quickly Make a Helix - YouTube


Scally, Do you intend to laminate the helix from solid timber? In your photo it appears that it may have been built as a box section. (ie hollow) There might be weight issues and possibly strength issues involved.

Personally, I have difficulty in thinking in strait lines, let alone 3-dimensional curves. Too hard for me, but I am intrigued as to how you will identify and solve the issues.

If you are not familiar with SketchUp (its a free download) or similar CAD software then its well worth learning. I did so a couple of years ago and then designed some draw units for my shed (drawing and construction practice) and then drew and completely rebuilt our kitchen. As I drew the detail into the kitchen I discovered many conceptual errors which were corrected at the drawing rather than the construction stage. So much quicker and more flexible than hand drawing that one takes fewer compromises.

If I cannot draw it, then I cannot build it. Elegant simplicity is the ideal!



Fair Winds

Graeme

Looks like it may be a bit of a challenge.


If you decide to give it a go, a WIP would be very intersting indeed. I'm sure many would agree.


Steven.

Graeme, I had a look at that link!. Bloody confusing to say the least!!

Think I could do a quicker job the old way on a drawing sheet using a pair of compasses,
a pencil, a straight edge and a french curve!!

Just had a quick squiz at some other You Tube stuphph and the number of people who think
a helix is a spiral or a spiral is a helix is amazing.

The issue of strength is of some concern with that helical set up but careful laminating
should negate any problems.

Originally Posted by artme

Graeme, I had a look at that link!. Bloody confusing to say the least!!

Think I could do a quicker job the old way on a drawing sheet using a pair of compasses,
a pencil, a straight edge and a french curve!!

Just had a quick squiz at some other You Tube stuphph and the number of people who think
a helix is a spiral or a spiral is a helix is amazing.

The issue of strength is of some concern with that helical set up but careful laminating
should negate any problems.

No way, Artme. If you have a basic understanding of Sketchup it is a two minute job.

Far quicker, more accurate and more flexible than hand drawing. I like traditional methods, but I will move into the twentieth century occasionally.

There is a little more than "careful laminating" required to get the helix strong enough. It also reads appropriate rigidity - remember, a coil spring is a helix.

Not sure why you would wish to start a debate on the alleged differences between spirals and helice - the maths is, at best, undecided. Perhaps you could start by explaining, in simple terms, the difference between a conical helix and a conical spiral.




Fair Winds

Graeme

What a challenge!!

I think the original table in the picture was made by a guy with a computer , who drew it, and had the form made on a cnc which he used to vacuum press his veneers to.

With problems like this , I don't know , I only draw with pencil and paper, I can see where a plan view from the top down and the bottom up would be needed to get the diameters of the circles and the starting and ending points of the twists.

To solve the problem the old way, I think you need to look at it like a paper lantern Maker , or a Christmas decoration maker . Or work it out like a sheet metal worker in paper or cardboard to scale , stick it together , sticky tape or glue and then stretch it apart to get the twists.
Fiddle with that till it looks right then figure out how to do it life size in Masonite for the twists and chipboard circles and stretch that, and take that shape as being the upper polishes surfaces.

The thing you need is a form to press the lamination's to.

some possibilities

Then make a mold of one of the twists, just the supposed top polished side, in plaster possibly, put down a thin layer of plastic, then build it up in layers till it's strong enough to take off and can be released , then strengthened and used to press lamination's down on to .

I did see a guy Vacuum press veneers on to a form for a big spiral stair case stringer, which was similar but larger than what you want. Its on a DVD I have some where on vacuum pressing .

Or take accurate measurements off the model to shape a form from built up cheap wood. Hmmm a cad drawing will give you all those measurements wont they ?


Did you ask you Daughter what the people selling these charge for them ? even made OS it's got to be pricey .

Rob

Rob, it is a great challenge for you. I have no doubt that you will do a good job. I am watching this one.

A few other things .
It's a very nice looking table as well, a stunner.
I think that spiral goes more than 180 degrees , more like 270 from what I can see, and its diameter is larger at the top than the bottom.
laminated up with veneers , cut and machined to 2.5 to 3mm each, all laid in the same direction and pressed with a two pack glue.
Then fitted nicely to the top and bottom circles . It would be a very strong table.

Rob

Hi Scally, what an interesting challenge!
Here are my preliminary thoughts on the problem: The inside and outside of the helix are strips of the same width that ascend from the horizontal at different constant angles. To calculate the angles, use the formula angle = tan^-1(rise per coil x 2 x pi x radius).
Cut strips over length and laminate them around cylindrical forms so that they stay at the desired radii, and then cut the tops and bottoms of each to the correct angle and height.
Next, fix the inside and outside helixes in the correct positions relative to each other. Probably the easiest way to do this is to cut trapezium shapes (but with curved sides) to fit between them at the top and bottom, and tack them in place with hot-melt glue. You will need to calculate the size of these. This assumes that the inside-to outside line is a radius, but if you want to get fancy, you could offset them.
You now have the correct shape, albeit very weak. If you want it to support anything, you need to turn it into a torsion box. Cut a number of plywood rectangular webs that will fit between the two inside and outside. I'm thinking that they should be perpendicular to the edges of the strips for maximum strength (and ease of assembly), but haven't done a structural analysis to confirm this. Or you could take the civil engineers' approach and use two or three times as many as you think you'll need.:roll eyes: Glue these in place.
The shape is now stronger, but you'll now need to laminate the top and bottom of the helix. As this will be made from a number of small sections, and you don't want the joins in each veneer at the same place, you should probably do just one veneer at a time. The first ones should be glued to the top and bottom of the webs, as well as the inside and outside of the helix.

As I say, these are my first thoughts, and are completely theoretical. The main issues I can see are getting the inside and outside to stay in place relative to each other when you're first gluing up, and consequently getting the top and bottom horizontal. (I haven't given any thought to the transition from helix to donut, but i think it's probably not to difficult.) If you have any questions, feel free to PM me, as I find this an interesting challenge and I'm sure there are things that won't stand up to scrutiny.

Thanks guys. You are amazing.

There is still a way to go before it makes sense to me.

The Helix table was advertised by an Australian company:

Helix Dining Table | THE DESIGN ESTABLISHMENT.
I saw one advertised at $6000. That should justify the work involved!!

Each spiral does appear to go through 270 degrees, or thereabouts.
I have used Sketchup several times over the years but run out of enough dedication to master it. I end up scribbling on paper and doing mock-ups.
I searched for help and selected the attached because they seemed to make some sense to me.
I found it interesting that if you cut a helix from top to bottom, you end up with a straight line diagonally from one corner to the other.
This might be the way to create the model for a form.

If I do as AlexS suggests and form an Inner and Outer helix, I could build it up with multiple thin strips. It would be a lot of thin strips and a lot of clamps.
A hollow construction covered with an attractive veneer seemed the obvious approach but I am worried that it wouldn't be strong enough.

Still a fair bit of thinking to do.

Originally Posted by GraemeCook

Not sure why you would wish to start a debate on the alleged differences between spirals and helice - the maths is, at best, undecided. Perhaps you could start by explaining, in simple terms, the difference between a conical helix and a conical spiral.

Fair Winds

Graeme

Just one of those "things" Graeme. I learnt, as a kid that a spiral was a flat, ie. two dimensional, shape and
tha helix was three dimensional, as in a spring or a screw thread.

I guess pig headedness and old learnings have a lot to answer for.

Apart from that I seem to have a penchant for red herrings.

Cheers, artme.

I reckon the idea of making a cardboard maquette first is good.
In the bottom of your last picture, the twisted veneer starts out horizontal. Try replacing those blocks with ones with straight sides, then start and finish the veneer attached to the vertical sides of the blocks, i.e., no twist in it. Then do a similar thing with a veneer or cardboard attached to the inside of the blocks. By playing around with this, you will get an idea of the relationship between the inner and outer walls of the helix.

To help visualise the helix, think of it like a helical staircase, like this.
Helical staircase.jpg
As far as strength goes, you could make it quite strong by making it as a torsion box as I said. Perhaps the webs inside the helix could be thought of like the treads and risers of a staircase, attached to the sides, top and bottom of the helix box.

How about starting with an annular disc of thin, flexible, ply with a radial slit and pulling it up so it forms a helix naturally. The cardboard mockup is hard to see, but think stretching a spring, or better putting a key into a keyring:

helix1.JPGhelix2.JPGphoto.JPG

Each disc gives you half the height.

Afterthought: A simple jig would hold the discs in place while you laminate, no need for a full form or difficult calculations - let nature do the work.