Saturday, 30 July 2011

A round tuit

I'm not quite sure if the round tuit is a piece of equipment or some kind of storage container but I've heard that lots of projects will be finished once the engineer gets a round tuit.

Wednesday, 27 July 2011

Nuts and Bolts

One of the things I use quite a lot of in the workshop is bolts so I thought it would be worth researching a little.

Machine Screws vs Bolts

Thinking back to my time in the Dowty Aerospace apprentice workshop I do remember a debate about Machine Screws vs Bolts. The tutor there had a quite simple definition. If the item was put into a hole then it was a machine screw, if it required a nut then it was a bolt. I think this is a good definition but raises the interesting issue that a particular item could be both a bolt and a machine screw dependant on how you planned to use it.

Looking around the web the there still seem to be some slightly conflicting opinions, unfortunately none of them cite their sources so as someone commented on Wikipedia we can't really call them a definative reference.

Garrett D Euler - Bolt vs Screw
EHow - What is a machine screw
Hobbit House Glossary - bolts vs screws

*** Matt from Bolt Depot has provided an official reference from the USA ***

"The department of homeland security actually makes the call because it effects import duties."

see:

Distinguishing Bolts from Screws
and
Fasteners of Heading 7318

Their definitions are very similar to my old tutors.

Bolt and screw heads

Something that is clearly defined is the range of different head styles you can have on a bolt or screw. These are chosen for many reasons, often there is a functional reason such as the need to have head flush with the surface, spreading the load or ensuring that the correct torque is applied.

Bolt heads from Bolt Depot

In my workshop the head is often chosen for cosmetic reasons. For workshop tools, I'm a particular fan of the socket cap head partly because of it's appearance but also because it does not have jagged edges to catch my knuckles on. Older workshop equipment often has thin square headed bolts which are not so common now.

RDG Tools

You may also find yourself making a nut and bolt if the size, shape or material is unusual.

If you thought counter sunk screws were only to hide the heads then think again, in the countersinking handbook, Laroux Gillespie describes pages of reasons why you might want a countersink head on your fastener, from reducing stress points on the edge of holes to improving assembly and accuracy of tapping. He also looks at how shallower angled countersinks are suitable for use with sheet metal such as aeroplane wings.



As well as selecting the head style you can also choose the type of drive e.g. a straight slot or cross head for use with a screwdriver or a hexagonal hole for use with a allen key. There are also specialist drive types such as security and torx. You might want to standardise on drive in your workshop or projects or use a particular type to be historically accurate for a model. Access should also be considered as the bolt might be resessed down in a counter bore.

Bolt strength

The strength of your fasteners in model engineering is often not an issue as the loads are significantly smaller than in full scale engineering. In many cases it's the material that will define the strength. For example brass and stainless steel are less strong than carbon steel. Bolts with higher than standard strength are marked with lines or numbers which indicate their material and grade. Other factors to consider if strength is an issue are the diameter of the bolt, the length of the thread engaged with the nut/hole and the relationship between the hole and the edge of the material.

Ref: Strength of Threaded Fasteners
Bolt Grade Chart

Nuts

There is an even larger variety of nuts available, here's a selection. I've come across most of these in my time repairing bikes and disassembling various items.

Nuts from Bolt Depot

One type missing from this list is the T-Nut which is slotted into a mill or drill table to secure your work piece.

My intial attempt at making a t-nut

Althought I'd seen most of the above examples I was still surprised when I saw them all together. The variety and choice of bolts can be quite overwelming but there is plenty of advise available from nut and bolt suppliers so you can select the right one.

Many thanks to Bolt Depot for kindly allowing me to reproduce the images from their Fastener Type Chart

Wednesday, 20 July 2011

Welding and machining

Buildup welding is quite common on repairs to large axles and shafts as the cost of replacing the entire part is expensive. The idea is that extra material is welded onto the shaft, often by spray welding and then it's machined to the new size.

I decided to use this technique on a small project for a friend. He wanted a tool to fit the tails for some new valves on domestic radiators. You can see the tails being fitted here using a large radiator allen key.



His problem is that there's not enough space next to the radiator to get an allen key in place. We discussed the options and came up with a small gadget where one end could be slipped into a socket set and the other into the radiator tail.

Build up Welding

I took some hex bar of the required diameter and then built up weld around the middle of it. The welded part was then machined in the lathe producing the results above. Obviously if you had a mill and dividing head you could do this the other way around and machine the hex flats onto a larger bar but I have to work with the tools available.

Since completing this I spotted the following "drain plug keys" in Glickman's hardware store. These are actually for use on car and bike oil drains but you can see how they are quite similar to the design I came up with.

Monday, 18 July 2011

Maker interview - Mini Space invaders

Victor Coleiro from Melbourne Australia has made some interesting projects which he's shared on Youtube and Flickr.

Workshopshed: Victor, thank you for agreeing to be interviewed, how about we start with where you make your projects?

Victor Coleiro: I make all my projects at my home, actually in the living room to my wife's dismay.



Workshopshed: What kind of tools do you use?

For the 1/12 scale model house I mainly used a balsa wood cutting kit including a miniature mitre saw and balsa cutting knifes. About $800 of balsa wood went into the house and it took about a 1 1/2 years working on it on and off.

For the micro arcade machine the main tools used were: Fine tooth saw, JIgsaw, Cordless drill, Soldering Iron, Hot glue gun and Mini screw driver set.



Workshopshed: Where do you get your parts from for the arcade machines?

Victor Coleiro:Most of the parts I use are sourced of ebay, local electronics shops and online electronic shops.  Hardware tools and materials are mainly sourced from a large Hardware Warehouse chain in Australia called Bunnings; kind of like a Costco but with just Hardware, tools, materials etc.

Workshopshed: In particular where did you get the tiny coin slot for the Galaga?

Victor Coleiro: The coin slot on the Galaga machine is actually part of the plug and play game system that I butchered to make the Bartop arcade machine.  Its a Jakks Pacman plug and play tv game system.  I'm actually trying to model a coin door now to use for a micro cab using micro tactile switches.  Also planning to include an illuminated marquee on a micro cab.



Workshopshed: Do you have a background in model making?

Victor Coleiro: I dont have any model making background. I only started making models really when I built the scale model house which I did to refresh what I had learnt after doing a House Wood framing course; which I did with a mind to using the skills for renovating my home.



Workshopshed: Do you have a background in electronics?

Victor Coleiro: I don't have a background in electronics, although I did do an electronics class back in high school and have until recently been working as an IT Manager.

In regards to the arcade machine , I guess it was a bit of nostalgia, as I had grown up playing video games in the arcades after school almost everyday up until about the age of 14. Back then I was very into video games and even managed to win the Australian Colecovision video game championship when I was 14 which was televised, but thats a story in itself. Anyway, basically I decided to make Bartop arcade machines initially having been inspired by a few works I had seen on Youtube. I have made 3 of these, 2 Galaga machines and a Space Invaders.

Workshopshed: What's next?

Victor Coleiro: Either a Micro Racing arcade machine like a Outrun or Daytona with working steering wheel etc or another micro cab using a Caanoo and running mame, maybe a combo of both.



You can see the Galaga machine build photos and the micro space invaders build photos on Victor's flickr page

All images are copyright Victor Coleiro

Friday, 15 July 2011

Metal solids of constant width

I've mentioned before when I was looking at measuring tools, John Bryant and Chris Sangwin and the book "how round is your circle". One of the interesting items from the book was a selection of metal objects that had constant width but were not spherical. You can see some of these on the front of the book.



Hendrik Ball of Grand Illusions has manufactured some of these mathematical curiosities and has also written a short article on solids of constant width.

Solids of Constant Width from www.grand-illusions.com

Grand Illusions is also a great place to find other scientific "magic materials" such as nitinol memory wire, Thermochromic liquid crystals, optical gadgets and levitating magnets.

Tuesday, 12 July 2011

Three Phase RCDs

My previous post raised some questions on how does a three phase RCD work. If you've a three phase load then you can't just use three single phase RCD's attached to each of the phases. You'll need a specialist 3 Phase RCD such as this one from HSS.


Basically it works in the same way as a single phase one in that it's looking for a mismatch in current in and current out. It uses a "Core balance Current transformer" to sense this mismatch.

Wednesday, 6 July 2011

Plug into Safety

During National Shed Week, the Electrical Safety Council is reminding people of the electrical safety issues in their sheds with their Plug into Safety campaign.



"Of the top five ‘shed hazards’ identified below, three relate to electrical safety:

storing mains-powered tools uncovered - 32%;
not checking leads or plugs for damage - 28%;
using mains-powered tools without Residual Current Device (RCD) protection - 26%;
storing unsecured tins of chemicals such as weed, pest killer or paint - 38% and
leaving the sharp edges of garden tools uncovered - 58%"


I'm normally pretty good at checking my cables and using the RCD but I must confess to being guilty to leaving the tools uncovered.

Thanks to Plug into Safety's prompt I've done some more research into RCDs.

From: IET Wiring Matters Summer 2005

Characteristics of RCDs

RCDs are defined by a series of electrical characteristics, three main characteristics are:

1. The rating of the device in amperes, I.
2. The rated residual operating current of the protective device in amperes, IΔn.
3. Whether the device operates instantaneously or incorporates an intentional time delay to permit discrimination. Such devices are called ‘S’ or Selective.

The first issue I looked at is if you've got an RCD in your consumer unit then do you also need one in your shed or plug socket?

I got the answer to this from the IET Autumn 2005 wiring matters. For outside equipment you want to have a RCD that protects the person (rather than just the equipment) this means that it must NOT be selective and that it MUST be rated for residual operating current not exceeding 30mA.

Plugin type RCD from B&A

The second issue is if you have a consumer unit in your shed/garage then how do you stop faults there tripping the household one too?

This is where that "selective" rating comes in. "Discrimination" is when you have one or more RCDs in series and the one nearest the user would trip first, the one in the consumer unit would protect from faults occurring between the house and shed. So you won't need to walk back to the house to reset a second circuit breaker.

My next question I asked to lots of people, the Electrical Safety Council answered it for me. Several people on various forums commented that their welders tripped their circuits.

Do Arc Welders always trip an RCD?

"The majority of arc welders in terms of design should not trip an RCD under normal operating conditions, particularly the type with a 13-amp plug. They do, however, use high starting currents, which means that circuit breakers can trip out - not RCDs. Most circuit breakers or RCBOs (which is a combination of both a circuit breaker and an RCD) typically installed in homes are not designed for high starting currents, and these may trip out with an arc welder. If in doubt, contact the manufacturer."



For a similar reason it's always a good idea to unwind and extension cables you before use. If you know that your equipment (welders, lathes, milling machines etc) has a high surge current requirement then let your electrician know and they can select the right type of MCB for your consumer unit.

Another issue with engineering equipment is that it can sometimes have three phase motors so I checked another issue with the Electrical Safety Council.

RCDs can't be used with three phase equipment.

"This is a myth; they can. There is no difference between single-phase and three-phase equipment in terms of RCD protection. Three-phase is not very common in households."

Many thanks to the Electrical Safety Council for taking time to answer my questions and for raising the awareness of shed safety issues.

Why not try the Electrical Safety Council "Shed week" personality test.

See also:
Workshop Electrics
No Volt Release Switch
The RCD explained
Types of RCD

Tuesday, 5 July 2011

Latest from The Salvager

This month sees the introduction of a new magazine.

July 2011 Salvager

"Salvager" is by Rico Daniels from "The Salvager" and "Le Salvager" fame. In this first edition he tells a little about his history, about salvaging, Life in France including the problems of stripy potato beetles, Bulldog Bash and a showcase of salvage projects. Also a small feature on the markets of London.

The magazine also challenges any salvage enthusiasts to get in contact to take on other teams in the aim to make and sell items made from scrap.

Salvager Challenge

Monday, 4 July 2011

Things seen on holiday

Whilst I was on vacation I saw this rather unusual sundial. I did not count the dials but apparently there are a total of 51 of them.



I also saw this metal gate with a very distinctive design.



More info on the lecturn sundial

Winner of the shed of the year

It's good to see that this year's shed of the year winner is a workshop/studio. Jon Earl's shed is an old First World War billet hut that's been turned into a venue for recording acoustic music so he's named it "Songs from the Shed"

Songs from the Shed - Jon Earl records Pokey La Farge

Over 1000 songs have been recorded by bands from all over the globe in songs from the shed and there's a waiting list for people wanting to participate.

"Sometimes it’s not the quality of the building itself but what you do with it that makes a National Shed of the Year winner" says Uncle Wilco from readersheds. The prize this year was £1000 and shedload of product from the Sponsors Cuprinol.

Workshop Practice Series