Wednesday, 12 January 2011

Up and Running

So now I had my lathe all ready to run. I had installed a 240 volt 16A mains supply into my workshop, fed from the main consumer unit in my house to a standard IP44 CEE 16A blue socket. This was needed as the M250 manual quoted a maximum start up current of 15A. The standard UK ring main is only rated for 13A.

I removed the control panel from the lathe and gave it a quick dose of looking at. Whilst somewhat untidy, it was nevertheless safe. I made a mental note to rewire the panel; it would be fine for an initial test though. I connected a length of blue 2.5mm square "arctic" flex to the appropriate point and terminated this with a blue plug. This flex is designed for outdoor use and can carry 25A maximum. I replaced the panel and plugged in. Here you can see the panel as found with my addition of the arctic flex.

Sharped eyed readers will notice a component missing. When I plugged in the lathe, the lamp worked and the coolant pump motor ran, but the main motor did not. I checked to make sure that all of the interlock microswitches were in the correct state. Still nothing. Now, despite the main and coolant motors being 240 volts, the microswitches and control relays are all 110 volts. This is common industrial practice. Microswitches are not double insulated and as there is more chance of the operator coming into contact with them they are fed from a 110 volt supply. This has its centre tapping earthed to the machine frame. That way the maximum voltage the operator will see, between the frame and a conductor, is 55 volts.

I discovered that this 110 volt supply was absent. I suspected the supply transformer and sure enough its primary turned out to be open circuit. Hence the gap above - I took the photo after removing the offending item. Here is the original transformer.

And another view.

As can be seen, Harrison had every eventuality covered, despite this machine being a 240 volt variant. They clearly just used one transformer type throughout. The primary has tappings for 380 and 440 volts, voltages normally found in ship systems. I knew that Harrison supplied to HM Forces, and later discovered the M250 was common on Royal Navy vessels. The 12 volt secondary was unused.

I now had to find a replacement transformer of the same rating and form factor. Obviously a direct equivalent wasn't a problem; I didn't need all the tappings for the different mains inputs, nor did I need a 12 volt secondary. The trusty manual showed the original transformer was 50VA rating and manufactured by Romarsh. Enquiries quickly revealed that this was an obsolete product. I suppose if I had wanted to be a purist I could have had one made, but I just wanted to get the machine working.

I found an off the shelf 240 - 110 control transformer manufactured by a great little company called Douglas Electronic Industries LTD, in Lincolnshire. You can find them here:-

 The part number was GST50 240/110. The secondary was centre tapped and the dimensions fit the bill. I called them and they told me to send them a cheque and the transformer would be in the post that day. Perfect! 

If you are reading this and you have a 3 phase machine, do not despair. A 415 - 110 volt transformer is also available. The secondary wiring would be as described above, with the primary connected across two of the phases.

I  cleaned and rewired the panel using new equipment cable and fitted the new transformer. Here you can see the finished article.

Note the earthed secondary centre tap. The newly spruced up panel was refitted and a successful test of all the machines functions ensued. It was a great moment.

Tuesday, 11 January 2011

How (not) to Build a Workshop

In 2006 I fulfilled an ambition I'd held since I was twelve..I became the proud owner of a lathe. Now I could progress my rocket project. Or so I thought. The lathe I had bought was a fairly inexpensive Chinese import. It was of a type that boasted a mill/drill head incorporated into the headstock.

 You get what you pay for, and I soon realised the machines' shortcomings. I decided it was a better option to buy a second hand, high quality British lathe than to spend more on modifications to make my Chinese lathe into the machine I needed it to be. 

My requirements for a lathe were:-

Geared headstock
Screwcutting gearbox
Power crossfeed
Coolant system
Camlock chuck mount
Quick change toolpost
Single phase motor

I spent a good deal of time deliberating before I made a purchase. My initial port of call was the Myford range. Reckoned by many to be the ultimate amateurs lathe. I found it to be somewhat over priced for what is essentially an outmoded design.

I decided to go for a Harrison M250. The Harrison company has a pedigree going back to the halcyon days of the Industrial Revolution. It is situated in Heckmondwike, West Yorkshire. The county of my birth and the cradle of British Engineering. So called model engineering lathes often sacrifice some functionality in return for compactness and affordability. Whereas the M250 is a scaled down industrial quality machine, designed for small one off production work. It has many constructional features more usually associated with precision toolroom machines. They were in full production throughout the 1980s and 1990s and were much favoured by schools and colleges. There was also a factory single phase version. You can read more about the machine here:-

I found a genuine factory single phase M250 on a secondhand machine dealers site, here in the UK. My new (to me) machine arrived wrapped in polythene and bolted to a pallet. I had to chop out sections of the pallet with a circular saw, to make room for my engine crane. Once this was in I lifted the lathe off its' pallet and fitted the base with resilient, adjustable machine mounts.

 Once on terra firma I inspected the machine thoroughly. As I'd expected from the photos I had seen prior to purchase, it was in superb condition, basically just needing a good clean. I set to this and also changed the headstock, screwcutting and saddle gearbox oils. The well illustrated manual was excellent, giving recommended lubricants and equivalents. I also fitted a new 50 volt 60 watt bulb to the machine lamp. I got it here:- 

Inspection of the headstock gearbox revealed very little wear. The machine seemed hardly to have been used. This was also borne out by the condition of the paint on the pedestal; generally the coolant (especially the soluble variety) tends to lift the paint. The finish was more or less intact. I ran through the manual and adjusted the motor mounts and all the gibs in the ways. I decided not to use soluble coolant - it starts to smell and I have always questioned the wisdom of allowing a water based fluid to sit on precision steel surfaces. It causes corrosion, no matter what the manufacturers may say. I used Castrol Ilocut 486. Shining like a new pin and adjusted to perfection the machine was now ready to be tested.

While all this was going on, I had also invested in a mill/drill and a metal cutting bandsaw. The mill/drill and the saw were both of Far Eastern origin. In contrast to the purchase of my first lathe, I had been able to visit the dealer and inspect the machines thoroughly. I'm pleased to report that they were both well built, sturdy and workmanlike bits of kit. They have given me excellent service so far.

I now had the makings of a decent machining capability. Next I'll relate what happened when I switched the new lathe on for the first time.

Monday, 10 January 2011


Several years ago (more than I care to remember) I was studying at a fairly well known Aerospace Engineering educational establishment in Central England. Residing within the hallowed walls of this temple of technology was a reference collection widely regarded as the best Aeronautical Library outside of Cranfield University. 

Being a typical anoraky engineer I spent a lot of my free time in the library, either reading, trying to sober up (nice and quiet..plenty of booths to hide in..) or a combination of both. Here then was I introduced to GP Suttons' seminal text, "Rocket Propulsion Elements". I was also able to peruse a large number of fascinating reports on rocket engineering research and development. These were from the Royal Aeronautical Establishment (RAE) and elsewhere, going back to the late 1940s.

I was instantly hooked and started working through some of the design calculations detailed in Suttons' book. The results of these investigations, coupled with the practical and theoretical information in the RAE reports and my own engineering and materials experience, led me to conclude that the construction of a small Liquid Fuelled Rocket Engine would be perfectly feasible. In addition, the diversity of the design problems to be solved and the spread of constructional techniques to be employed would make it a highly absorbing and challenging project.

This idea remained on the back burner until mid 2006. By this time I had entered a different phase of my engineering career that had given me greater spare income and more free time. With the advent of the internet I had begun to research on my old idea and had discovered the NASA Technical Reports Server, not to mention Leroy Kryzyckis' "How to Design, Build and Test Small Liquid-Fuel Rocket Engines". This latter text had the much the same effect on me as the early RAE reports; it convinced me that building  a rocket engine was "do-able". So I bought a lathe and made a start.


Welcome to the British Reaction Research blog. The purpose of these postings is to document the progress of my attempt to design and build a Liquid Fuelled Rocket Engine.

Here you will find information on my research, design and constructional activities towards this end. I am starting this blog rather late, as I am something like eighteen months into what I would regard as the intensive period of my R & D and constructional effort. So you will see that the first few posts will not be what might be described as contemporaneous; rather they will be an attempt to bring the reader up to speed with activities thus far.

A lot of people ask me why I would go to the trouble of spending large amounts of my free time (not to mention significant quantities of my residual income) designing and building a rocket engine. I hope to use these spare scribblings to try to explore this question and explain my motivation to research, calculate, design and construct.

I read somewhere once that building a small Liquid Fuelled Rocket Engine is perhaps the ultimate home engineering project. I wouldn't like to be drawn on that one. What I will say is that it encompasses a reasonable degree of skill and dexterity in machining, welding, fitting and problem solving. That is without going into the developmental work I have done in the field of electronics and microcontrollers, for data acquisition and control. Hence I'm hoping there'll be information on these topics that will prove useful to the amateur engineering community at large, not just those engaged in rocketry.

My next few posts will explore the history of my mad obsession and how I came to have so much machine shop and welding equipment in my garage that I struggle to get my bike in there, let alone a car.