FRUNI / Free Range Univeristy..this is an inspiring idea with great beneficial consequences for students & those lecturers who are brave enough to post their lectures for the world to see.
I’m really inspired by this simple concept. It really encapsulates what el-learning could be like on a nationwide scale. It opens up the debate and points to why “open education resources” are a good thing.
It’s often the case in the metal workshop that the laws of physics are challenged in order to pursue a design aesthetic. Luckily, with some knowledge of physics and a little common sense we can employ these laws and prevent a lot of wasted time and effort.
In the case below, a square section tubular steel construction is required to support the weight of a person. It’s quite clear that if a person stands on the extended tube (fig.a) the rest of the frame will tip up (fig.b)
We will need to support the tube under her weight to prevent this from happening (fig.c below)
I know what you’re thinking; that the frame could still tip up from the back and she could fall forwards. Yes; do you see how our basic understanding of the laws of physics, are deeply routed within us?
So we have now arrived at fig.d a design a long way from the original, but one that will prevent the frame from tipping and be able to support the load.
However, this is not acceptable from the designer’s perspective and only fig.a will do.
We will need to prevent the frame from tipping and this can be done in a couple of obvious ways; by either counterbalancing the frame (fig.e) or bolting the frame to the floor (fig.f) this being the most acceptable from the designers point of view and leads us to our next problem:
What is the maximum distance the unsupported steel tube can extend from the rest of the frame before it will bend under the weight of the person standing on it?
And I suppose now we come to the essence of the document, as this simple question is not easy to answer and one that requires a much greater appreciation of the laws of physics and a determination in employing them to our advantage. Luckily the internet is a rich source of information and in particular http://www.physicsforums.com who’s members BTown and xxChrisxx did the hard work in providing me with the information necessary to answer the question.
First we must understand turning forces as it is clear that this is what we are referring to. The extended tube (acting as a lever) can no longer turn the frame and tip it up as it is bolted to the floor. However, when the woman stands on the tube the force to turn the frame is still there.
This turning force is called a ‘moment’ and is measured in Newtons per metre squared or Nm2. ‘Moments’ are calculated by multiplying the length of the lever (here the extended tube) by the amount or force applied to it (represented by the weight of the woman). However, weight is not the same as force. Weight is static, it has magnitude (measured in Kilograms) but it is going nowhere, whereas force (measured in newtons) has both magnitude and direction.
Fortunately, Isaac Newton can help us here: he states that 1kg falling to Earth has a force of 9.81N
Because the woman is raised up, she has a downwards force acting on the tube. Lets say she weighs 70kg (the average weight of a person) she has a force of 70 X 9.81 = 686.7N
If she stands ½ a meter away from the fixed point she exerts 0.5 x 686.7 = 343.35N/m2 of turning force
This helps us find the moment of turning force along any given point on the extended tube she stands on, but it doesn’t help us find out if this moment of turning force exceeds that of which the tube is capable of withstanding. For this we require some information about the properties of the material
There is no need to calculate this, it should be provided as a specification by the supplier of the material.
The yield strength was found here: http://www.roymech.co.uk/Useful_Tables/Matter/Strength_st.htm
The value depends on the quality of the material. In this instance the value of the yield strength was rated at 280Mpa (mega pascals) that of a construction quality steel.
Second Moment of Inertia
Also known as the second moment area, the area moment of inertia, moment of inertia of plane area, or second area moment, is a property of a cross section that can be used to predict the resistance of beams to bending and deflection, around an axis that lies in the cross-sectional plane.
There’s no need to calculate this either as once again it should be provided as a specification by the supplier of the material (see below).
Electro Resistance Welded (ERW) Square Hollow Section Table of Dimension and Properties
Area of Section
Second Moment of Area
mm x mm
The table above (an excerpt of http://www.roymech.co.uk/Useful_Tables/Sections/SHS_hf.html) refers to the steel tube that will be used in the final construction. The properties will change if using Rolled Hollow Section (RHS) even though the dimensions might stay the same, so it’s important to make sure you have the correct table of data.
There are 3 columns that are of interest to us:
Column 1 the size of the tube
Column 2 The thickness of the tube wall (T)
Column 3 Second Moment of Area
You can see in bold the row which we will be referring too as we will be using 25mm x 25mm with a 2mm wall thickness.
We also need to know the distance from the centre of the tube (x-x) to the outside edge in this case 12.5mm (fig.g) below.
The next step is to refer to the following equation and do some math. However, this is where my knowledge falters and I would really appreciate some input from someone who knows more about this subject than I do.
In the equation below * has been used as a multiplication symbol rather than x so as not to confuse it with x which is the unknown value we are trying to find.
Yield strength of steel = (moment of turning force)*(half the material thickness ÷ second moment of inertia)
We don’t know the amount (or ‘moment’) of turning force required to meet that of the yield strength of the steel as this is what we are trying to find out. But we do know that it is Force multiplied by an unknown distance. So we keep these two things apart in the equation as shown below in (696.7N/m2 * x)
Yield strength of this steel = 280Mpa
Force = 686.7N/m2
Distance = x (This is what we are trying to find out)
Half the material thickness =12.5mm
Second moment of inertia =1.56cm4
So the equation reads: 280Mpa = (686.7N/m2 *x)(12.5mm÷1.56cm4)
In the equation above you will notice (12.5mm ÷ 1.56cm4) we cant divide millimetres by centimetres so we will have to convert 1.56cm4 to mm which is 156000mm
280Mpa = (686.7N/m2 *x)(12.5mm÷156000)
280*15600 = 12.5*686.7*x
3244800 ÷ (12.5*686.7) = x
3244800 ÷ 8583.75 = x
378.01 = x
Or x (the yield point at which the metal will bend and not recover) = 378.01mm
As you can see, I’ve done the math without really explaing what has happened. This is because I do not know and am merely repeating what was explained to me on the physics forum by xxChrisxx and BTown. If anyone wishes to elaborate please feel free.
Below are details of how we made ball and socket joints for stop-motion armatures in the theatre metal workshop.
Although we have access to a milling machine, lathe and other specialist equipment I was keen to develop a manufacturing process that was transferable; using equipment that students would be able to access easily outside of the college. To that end, our ball and socket joints were manufactured almost entirely on a pillar drill with some simple extra tooling and the addition of hand tools.
The first thing to do is to establish the dimensions of the joints you wish to make. In this tutorial we are dealing with two joint plates made from 9mm x 20mm x 3.5mm steel with a stainless steel ball 6mm in diameter which can be used for armatures up to 350mm.
I should have really used a better quality steel for the joint plates than the commercial quality I used (a free cutting EN1A would have been nice) however, it doesn’t make any difference to the process.
Buy a length of 20mm x 3 or 3.5mm steel and chop it off to width. Above you can see how I fitted a bolt to the ‘stop’ on our bandsaw. This enabled us to saw each one acuratley to width. Other than the pillar drill, the bandsaw was the only other machine tool used.
You can of course use a hacksaw, but you need to cut each one accurately. The whole process will be undermined at this stage if you cut wonky, uneven, inaccurate joint plates.
For large armatures of around 300mm+ avoid using brass or aluminium for the joint plates, as the thread cannot withstand the force exerted on it when it’s tightenied up and can sheer clean away. This is my fear with the cheap steel I used, but so far it hasn’t happened.
Drilling the holes in the joint plates for the steel balls
To begin with I drilled 3mm holes right through each plate and then opened them out with a countersink drill. However, the double handling of each piece was time consuming so I used a 3mm ‘centre drill’ instead. See below
Centre drills are normally used to start holes off in the lathe where the standard ‘twist drill’ may wander if not pre-drilled. Here we use them as a drill and countersink combined. They are available from: Axminster tools and RS online components to name a few. I would buy High Speed Steel (HSS) rather than the cheaper Carbon Steel tools.
In the picture above, you can see how I have customised a standard drill vice in order to make it more accurate. A small step was machined into the top of the vice jaws so that I could sit each joint plate on it, thus avoiding having to use packing to raise the joint plate up. If you can’t machine a step like this, cut some 3mm plate and solder it to the front of the vice jaws with some lead solder, or drill tap and countersink it.
To the left and right of the rear vice jaw I drilled and tapped a 5mm threaded hole. On the right I screwed a static block of steel to act as a stop. On the left I did the same but drilled the stop block to take a small round rod that can be adjusted.
This way I can slide the joint plate from left to right and have each one drilled identically along the same centre line. It sounds a little pedantic, but I did try other methods which were unreliable. Either the plates never matched up when the balls were inserted causing the joint to rock around rather than fit snugly, or if they did match, the plates opposed each other at odd angles.
Drilling the thread and clearance holes
First mark one end of every joint plate with permanent market pen.
Adjust the drill so that you are drilling in the middle of each joint plate (centrally between the two holes previously drilled).
Make sure the same end of each joint plate locates against the stop (either the end marked with marker pen or the end NOT marked with marker pen.
Now with the start drill, drill a small ‘D’ dent into the surface of all of the joint plates. This will locate the thin twist drill which will be used later. Remeber to locate the same end against the stop everytime.
When drilled with the centre drill, divide you batch of joint plates in half.
Now drill half of them with a 2mm drill making sure that each one has the same end as before located against the stop.
Now drill the other half of the batch with a 3mm drill.
Tapping the 2mm hole with a 3mm tap
This is pretty straight forward, put the 3mm tap in the wrench and tap the 2mm hole. Obviously you can’t tap the 3mm hole with the 3mm tap as it falls straight through.
File the ends of each joint plate down
To ensure that there is plenty of movement around the ball joint, you will need to file down the ends of each joint plate. If you run the safe edge of the file against the vice jaw you should be able to keep the filing nice and straight.
As you can see, these were filed down before the centres were drilled, however it made it difficult to gauge where the middle was so I adjusted the order in which to do things.
The Cap screw
The 3mm cap screws were from RS online components. There are plenty of suppliers for these. I buy ones longer than necessary and cut them down, as there is little difference in price and it’s simple to do. Once again, buy good quality screws ‘unbako’ being the most expensive.
That’s it for the joint plates. unless you want to round them off with a file as I did here.
Sourcing the stainless steel balls
The stainless steel balls are avaiable from ebay at an what I think is an incredibly expensibe price. I sourced mine from a company called Spheric Trafalgar. The A302/304 grade stainless steel has proved itself fairly easy to machine. Follow this link if you intend to buy them: http://www.ballbiz.com/prod-ss-aisi302.html
The easiest way of drilling the ball is on the lathe. However as I have said, I wanted to develop a more achievable process outside of the college. This was done by mounting a self centering 3 jaw lathe chuck under the pillar drill. Cheap self centering chucks are being imported from China and fairly accurate. I got mine from a company called Chronos.
The chuck comes ‘un-mounted’ which means if you want to use it under the pillar drill you will have to make up a base plate to mount it on. I made mine from a piece of steel we had lying around. You might need to improvise with a couple of pieces of angle iron, or maybe a base plate from another machine.
Once you’ve found some material for the base plate, the chuck can be fitted with 3 cap screws as shown above.
Centre the ball under the drill press and pre drill with a centre drill.
Next; Change the drill, without moving the centred ball, and drill out the ball with a 3mm twist drill. We drilled ours clear through rather than stopping ‘blind’. This was the students choice.
Using silver solder to attach the ball to the steel rod.
File a little flat on the end of the steel rod. This will provide a little gap for the Silver Solder to flow into. If you are soldering into a blind hole, it also enables expanding air to escape.
Now follow the instructions for silver soldering and solder the ball to the rod. You can read how to silver solder by follwing this link.
The aims are of the OER (Open Education Resource) projects are:
CREATE dynamic teaching material that communicates the excellence of UAL
COLLABORATE with other UAL colleges and develop tools and policy to support these activities
SHARE these learning resources in a free and open manner using Creative Commons Licenses
PROMOTE the work of staff and students internally and with the world, and highlight the good practice in our learning and teaching culture
Using the above ideas, create an artwork that communicates these concepts. From a video, work of art, poster, performance or a garment – choose any medium that can best define these UAL values.
We advise the use of CC,NC,BY, license IMPORTANT please make sure you include the #ALTO-COMP tag in all your posts, only posts with he #ALTO-COMP will be judged
For more information on getting started and help links visit
Deadline for hand in will be Friday 11th November 2011
Prize will be judged by Donald Smith, Curator of Chelsea Space and Chelsea Future Space (TBC), Kay Barron Fashion features editor GRAZIA magazine, Michael Czerwinski from The Design Museum.
Winners will be announced on 23rd November 2011 at Camberwell Space.
Terms and Conditions:
Competition is open to all students across University of the Arts London, individuals and groups may enter
All submissions will be licenced under a Creative Commons share alike licence and can be used in the future to promote ALTO
You are required to document your creative process online athttp://process.arts.ac.uk/ – Login to process.arts using your UAL user name and password, create a personal profile, click on the create content tab, start uploading content showing your progress, we advise the use of CC,NC,BY, license IMPORTANT please make sure you include the #ALTO-COMP tag in all your posts, only posts with he #ALTO-COMP will be judged, for more information on getting started and help links visit – http://process.arts.ac.uk/content/alto-competition
Three prizes, of £1000 each, will be given to the named applicants
Featured post from process.arts.ac.uk – this is a video of me dancing to an Nigerian praise song I chose this particular song because I wanted to show how I give praise to God through dance. I also made my own dress that I would be dancing in for the show I didn’t want to get African fabric and make the dress from this because it wouldn’t be my own work. I made this dress out of satin fabric and sewed on colourful beads, buttons, roses and bows to create a pattern effect I also made various shapes and patterns out of lino so that I could print on the dress. I didn’t use block printing ink because you cannot get a range of colours to use so I decided to use acrylics instead because I mixed the different colours together to create a random colour. During my performance things may go wrong but its ok because that’s part of the process. Bits of the dance are improvised and the rest is a set dance. I am also going to wear African fabric on my head to create a head tie, as I wanted to still bring in the fabric in to my performance.
Log in to http://process.arts.ac.uk/ using your UAL user name and password and upload examples of your own studio arts practice - process.arts is an open resource, sharing and exploring process in arts practice through the day to day practice of staff and students at UAL.