Archive for August, 2011

Links and Videos

Friday, August 26th, 2011

This is for all the people who want to know what Stotfold Engineering are getting up to and have an interest in what we do. We have created new videos to keep you up to date in the development of our company. You can now follow us on Twitter, join us on Facebook and watch us on youtube. If u like the blogs then u will LOVE the videos. We thank you for supporting us though www.stotfoldengineers.co.uk and hope you enjoy our other pages too.

YOUTUBE VIDEO LINKS

http://www.youtube.com/watch?v=FL2KZWQWwyE

http://www.youtube.com/watch?v=OUcPOWRVfOc

http://www.youtube.com/watch?v=zqE4JPwP15Y

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FOUR START THREAD CUTTING – for vintage car steering rack

Wednesday, August 24th, 2011

1. Close up of the thread as it is prepared for a final cut.

I am not going to go into to much detail regarding cutting threads on a lathe because its boring and i want to keep you, the reader interested in this short article about cutting or generating a four start thread on my Dean, Smith and Grace (D.S.G) lathe.

2. Screw cutting on the D.S.G. - you can see the female part of the thread held in the three jaws chuck & the cutting tool held in the turret slide.

The D.S.G. as it known, In its day it was the Rolls Royce or Brough Superior of lathes and I am proud to own one. They are awesome in the coarse pitches they can achieve.

The pitch of a thread is measured from the peak or apex of one thread to the next thread apex. If we look at a multitude of these peaks or apexes in a line on a shaft of metal we will see a a thread or screw.

The D.S.G. lathe at my works can easily cut a thread or screw or spiral grove on a round piece of metal bar, by turning the chuck, the chuck is the part of the machine that holds or grips the metal and turns it in a rotary fashion.  

3. The completed steering rack assembled.

The slide is the part that holds the cross slide that holds the turret slide that holds the cutting tool that is going to cut the thread or screw.

There is a lot of calculations in making the slide do what you want it to do because the slide is operated by what are known as back gears. 

4. The new steering rack conponents shown next to the old worn ones.

By arranging these back gears we can select what coarseness of the thread we require in relation to the rotation of the chuck. Rather than opting for calculations and maths on this particular job, i save the time by using trial and error until i get the coarseness of the thread that i require.

the thread or screw on the shaft in this case had to match a thread or screw that had to be made inside a bored out piece of bronze tube. The bronze tube, which would become the nut after screw cutting would be made after cutting the screw on the shaft. These two parts would match each other as the pitch set on the lathe would stay the same.

The pitch reqired for both parts were, as i was working from worn out original pattern parts, and had to replicate them, was about a movement of 4inches on the side to one turn of the chuck.

Out of interest, the coarsest pitch i have attained on the D.S.G is one turn of the chuck that will give 32inches of movement on the slide, this is coarse enough for refling gun barrels. to cut multiple coarse threads we need to set the cross slide dial to zero, “Remember that the cross slide holds the turret slide that holds the cutting tool” to set the zerowe need to get the chuck rotating and put the machine in gear so that the slide starts moving, as the cutting tool starts to pass over the metal we can stop the machine but leave it in gear and adjust the tool so it just touches the surface of the part that has stopped rotating. Once this is done we can set the dial to zero.

when the zero is set i turn the machine back on and put it in reverse and then put it back into forward drive with .020 inches onto the zero dial to take the first cut on the first thread of the four start thread.

once this thread is cut at ful depth we now look at the turret slide dial which had also been set at zero but not mentioned previously. the turned slide dial has to be turned to a given amount and then the whole operation starts again until the second thread is finished. Repeat for third and fourth thread until the four start screw is finished. all that is needed now is to run a file along the shaft edges of the screw cut until completely free of burrs.

The bronze nut is made in the same fashion but with a different tool that will cut threads internally.

A difficult  worm or thread that i have made was a six start thread for a laboratory.

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SWORD HANDLE

Wednesday, August 24th, 2011

Restoring museum artifacts come with an array of difficuties. Ancient clay pots can be pieced together using  glues that leave no visible sign of repair. Pieces of pot can be replicated and used to fill in the missing parts of the damaged pot, so matching any patterning. Carpets and tapestries can be restored using replicated piles, yarns and threads. Furnature can have its inlay’s, marketry and parketry restored, or replicated from looking at the reminants of what still exists.

Here at Stotfold Engineering we replicate metal artifacts more than we restore them. Most metal artifacts we get are in such a poor decayed condition that it is not possible to restore them. Some have decayed so badly they have become unrecognisable and we then have to start guessing at what it may have looked like, for example what is it’s original size, what sort of engraving and etching it may have had. We then have to research the object, looking at archives from museums who may have a similar item from the same period.

If the artifact is for example part of a full set of armourand all the related garb but a spear head is missing, we have to look at what shape it maybe in relation to what we have got to compliment it. when i say compilment, the part that we are making generally from scratch has to match exactly, etchings and all to what we have in hand even if it means wearing or rubbing out details. For instance we had to make a hand held shield for the Victoria and Albert museum. We started off with a dimension of the diameter of the shield that would have been used in the period. looking at the period pieces we found it was dished with a 15mm flat area around the edge of the rim. The rim was then rolled over a 2mm wire thus leaving a nice round safe edge. The steel sheet that i was working from was 2mm thick.

Hand beating commenced and 14 hours later we ended up with a hand shield that had to be descaled using the aqua blasting method. It then had to be covered in bee’s wax and hand etched to produce the figure of medusa using nitric acid to do the etching of the steel the job in the picture you see are parts of a sword handle .

These parts were cost effectively done on a manual lathe from very rough sketching. The parts were finished off and carefully profiled using hand held cutting tools in the lathe. The finishing tools are simular to wood turning tools.

The original way of making these parts would have been by hours of beating lumps of metal to attian the shapes you see. These parts now have to go thorugh the unnatural aging process to compliment the rest opf the sword.

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STAINLESS STEEL PETROL TANKS

Wednesday, August 24th, 2011

 

We regular have enquiries from people asking if we can make stainless steel  petrol tanks for their vintage and veteran cars or bikes. Our reply is “of course we can, as long as you supply have a pattern or drawing”.

Manufacturing custom stainless steel products has been at the forefront of Stotfold Engineering’s product turnover. We have been manufacturing stainless steel fabrications, fittings and tanks for food preparation companies for over 40 years of trading, so stainless steel fabrication is not a problem for us.

Stainless Steel Petrol Tanks

Stainless steel petrol tanks have the benefit of not rusting, cracking or having to be cleaned or lined due to internal rusting. A lot of vintage and veteran car and bike fuel tanks were folded and soldered along the seams, together with most of the fittings, such as flanges. After many years of service these soldered joints are liable to leak. Years of servicing, undoing and tightening tight nuts, bolts and fittings placed strain on the soldered joints causing cracks and therefore leaks. Over time these cracks would be patched up with solder, but would evenually give up the ghost and then they would find there way to us for replication in stainless. We have a passion for stainless steel work and welding it. When we receive an order to build a stainless steel fuel tank we will measure it up and take drawings before dismantaling it. It has to be dismantled as to ascertain where any internal fittings are fitted and to discover where the baffle plates lie.

Baffle plates are commonly used in car fuel tanks, these are used to stop fuel from slopping around and to strengthen the overall outer structure they even play an important roll in noise control, i.e. if you had a tank with no baffles and it was only part filled with fuel, the petrol would rush to one side of the tank if you put you brakes on or accelerated. stainless steel petrol tanks have many benefits over their counterparts as they do not corrode, they are more rigid and the weld joints are a lot more resilient and they are resistant to the affects of all fuels. Most costomers perfer originality, particualy if the fuel tank is exposed as on many veteran cars. This is no problem to us as we can fit all of the original brass fittings onto the new stainless steel petrol tanks. The stainless tanks can be painted with no special preperation and they will last you a life time with no servicing.

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STAINLESS STEEL FABRICATIONS

Wednesday, August 24th, 2011

1. Despenser made for food preparation industry.

2. Air filter cover and part of a hydrogen fuel cell.

3. Small turned parts in stainless

4. Stainless silencer and part of a thermal lance.

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Custom Motorcycles

Wednesday, August 24th, 2011

1. Colin's midly customised Honda 750

Motorcycles through the ages have metamorphosized to produce what we have today. But sometimes this is not the principle of what the buyer wants, but it is close, hence people find Stotfold Engineering is the place to find that enhancement or modification to there custom bike to bring it up to there own specifications.

A customer, such as Johno, approached us with a host of modifications on his already factory customised Yamaha V4 bike. The order or schedule was to fit a tool and satnav box in stainless 316 steel. This task was a very testing one as the box had a limited space to fit into and it had to be as large as possible so as to contain as much electrical and tooling aids as could be contained. The first thing was to ascertain what side profile would fit within the given space, i.e. if you looked at the side profile of the bike and looked at the gap where the box could be fitted. ‘What is the maximum size?’ The simplest plan is to make a cardboard profile and put a lot of thought into it, if you were to present me with a cardboard model you would have done 50% of the work, as all I would have to do is to replicate it in whatever material you wanted. Some custom parts are difficult to make models of, in this case it has to be made in the workshop out of metal tack welded together and holes drilled, tweaked and fitted to see if everything is in the right place. This process then forms the solid model that I would work from to produce the finished article.

Petrol tank customising is a tricky process as it is not a job that can be modelled in 3D. This type of work can only be marked out on the surface of the tank using tape or marker pen lines. Generally, customising tanks involves cutting apertures to take instruments such as speedometers (digital or mechanical) and things like scollops for clearance for Carburettor Bellmouths or velocity stacks.

There are instances when customising something cannot be modelled or marked out with any sort of precision, such as brake calliper mounts. The way I deal with a project like this is to take a plate of aluminium thicker than I need and roughly cut the profile but drill or tap the mounting holes precisely in there right positions. When this is done I mount the plate into its position and measure any offsets that are needed to bring the calliper into its right position in relation to the brake disc. The offsets are machined on the lean side so as not to throw any dimensions out leaving you having to use spacers or shims for alignments. We can always machine a few thou off to make everything look perfect. Remember that metal can’t be put back on to a machined surface without the completed job looking like it has been modified or adjusted with washers to take up inaccurate machining.

A customer approached us with a set of Webbs forks, he wanted us to use the existing design but using only billet machined parts to give a really modern twist on an old fashioned design. Of course with a job like this, models and marking out are not needed as we have the forks as our model.

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Ducati Performance Tuning

Wednesday, August 24th, 2011

Performance tuning a Ducati Mach 1

 The first thing to do is lighten everything throughout the engine, but not compromise on the strength and reliability of the working parts. The project was carried out by me to contest a Ducati Mach 1 in a two stroke class racing against Yamaha TDIC’s and Suzuki T20’s, and to attempt to beat some of the modern single cylinders in the National single cylinder championships. The only way to contest an old Ducati is to make it rev like it’s never revved before i.e. 13,500 RPM.

To make the machine competitive in all of the classic lightweight classes is to shorten the stroke by 4mm. I shortened mine by the same and used the 350cc barrel and piston which brings the overall cc to 236.

The standard Conrod was used as the steel ones are stronger and more reliable. The valves were enlarged considerably but the standard valve seats were retained but re-cut to suit the new valves; the valves were also machined to give good gas flow. To make the valves snap open and closed quick enough, stronger hair springs were fitted. The wire gauge of the springs is 156 thou thick. These were operated by red and white cam. If one uses too light a spring one would experience valve bounce.

The compression ratio measured with a burette was 14.5 to 1. Although I could measure 21 to 1 without a head gasket but this would compromise reliability and I would have to cheat using octane booster and any over revving would be detrimental to performance and reliability. The valve to piston clearance was measured as 050 thou using Plastigauge. I failed to mention the 350cc piston was highly modified by welding and re-cutting the valve seat pockets. The piston had to be modified due to lack of compression and the crown shape was wrong.

What I wanted the piston to do was to squish as much fuel without detonation but to burn everything down to the top compression ring. This is important as a lot of fuel sits just above the top compression ring being un-burnt and passing out through the exhaust port. Detonation is in many tuners minds, a bad thing to happen in an engine but this is not so as long as it is controlled. Head profile and piston crown clearances sort this problem out.

To attain top revs it is paramount to lighten all rotational weight. The thing to do is remove the Magdyno from the end of the crank and make an outrigger bearing in the primary chain case to support the crank, saving it from whipping at high revs. The next step is to look at lightening the gearbox; this is easy as all of the gears are thicker and heavier than they need to be. All of the gearbox gears can be lightened in two ways, drilling and machining on a lathe the skin hardness can be broken using a correctly sharpened masonry drill once through the surface hardness of a gear, the inner metal is like butter.

After weighing the gear train and subtracting what you have machined and drilled out you should have saved about 1.5 pounds in weight. Another critical part of the fuel burning process is the exhaust system design. The ideal length through calculations is about 9 1/2 foot for the header pipe and the silencer on the end amounts to approximately 13 foot long.

Having access to a Dynonometer to test the machine on, I found I could use the standard header pipe and develop a silencer to come within length and decibel tolerances to give maximum performance. A machine goes no where without correct carburation thus the standard Ducati carb could not live up to the demands of the drastically modified engine. Something more suitable was an Amal concentric as this carb has more scope for fine tuning and ease of obtaining accessories and upgrades. After all of the modifications it is a good idea to set the carb on the rich side so as to control detonation.

The ignition system is controlled using Rita ignition and a dyna coil with twin plug leads. The reason for the twin lead is that I have fitted a 10mm spark plug near the top bevel thus producing a twin plug head. Another important point to take into consideration is to modify the inlet tract so as to make it as straight as possible, you will find that when this is done that there will be a break out in the cylinder head. All you have to do is either weld the hole up or use Devcon aluminium filler, after filling, blend the inlet tract in. another important job is the front brake, I employed a Suzuki GT380 disc and callipers to produce a unit that I could use for very late breaking into corners.

A fairing was fitted to save about 2 horse power of wind drag and a low seat with minimal padding was used so as I could paddle start the bike. I have not gone into too much depth regarding all of the tuning modifications as I don’t want to bore you, the reader. But if you have any questions I will be happy to divulge the finer points.

The Ducati, when finished, should start with ease after a couple of paddles, you don’t have to stand by the side of your machine and bump start it. Prior to a serious race you will have to heat the engine oil up in a saucepan over a gas burner and pour it into the engine. The bike will also need a new plug fitted after it has been heated over the burner. The engine has now been primed ready for the start line without having to warm it up.

As with all Ducati’s, road holding is steady with warnings from the frame when it is being pushed too hard. In classic racing I use Dunlop KR 124 tyres and in modern racing I use Dunlop KR108 cut slicks. Both tyres work admirably in wet weather but the KR108’s have the edge due to there softer compound. All in all, the Ducati ultra, ultra short stroke is still a championship winner!

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Types of Air Rifles

Monday, August 22nd, 2011

Basic servicing

After purchasing or inheriting an air arm the first thing to do is to oil it. WD40 is ideal as it can be sprayed onto surfaces and mechanisms, left to soak and wiped away. WD40 doesn’t seem to attract dust onto mechanisms and is good for washing away dust residues that contain abrasive particles. Oiling should be carried out on regular intervals and become a habitual practice on spring or compressed air arms. Don’t spray anything down the barrel as what you are shooting is essentially lead. Lead used to be employed in fuel as an anti knock agent in car engines, it also acts as an anti seize and anti friction agent. The lead pellets lubricate the barrel. To test your sights aim at a target and fire one shot make sure you are relaxed. Realign your sights to suit the single shot you have taken. Take another shot in the same relayed position, if you are not within 12mm or ½ inch of your first shot, you are not relaxed and are trying to hard to hit the point. Do not try too hard, just relax and let your air gun do the work and you should be within the 1/2inch target. This is imperative as when you are out on the field and taking a shot you don’t want your game to be foul shot or maimed and suffer a difficult surmise.

When Should Your Air Gun be Serviced?

Spring operated air guns should be serviced every 3 years if you are pigeon shooting as standard springs lose there tension. On your first service ask for an “ox” spring to be fitted, these springs keep the air rifle within the legal maximum foot poundage and will not leave loads maim pigeons hopping around our town centres. Ox springs when fitted will keep up pigeon killing performance for 5 years if you’re a weekend shooter. Compressed air guns should be serviced every 5 years as the seals that are fitted are made of rubber and will perish and crack after being subjected to constant refills of compressed air. Stotfold engineering have developed their own seals that last for 10 years and are self lubricating, hence allowing you to have consistent power shooting over a much longer period cutting out service charges.

 Advanced servicing by a specialist

Advanced servicing or restoration is called for when the air rifle is not operating in the way you are accustomed to i.e. the trigger has become sluggish and heavy, the barrel has 1 or more shots jammed into it, The under or side lever does not locate and lock into position and the gun gives a very poor power shot. Hand pumped compressed air guns sometime lose pressure over several hours or overnight, this is caused by a leaking one way filler valve and it will need special attention.

 

Why Own an Air Rifle?

 Many people purchase air guns or pistols for general plinking and target shooting. If a farmer were to buy one he would have the added bonus of pest control i.e. rats and mice. I, for instance, love pigeon breast meat and this is what I mainly shoot for my meals and it saves a small fortune every year on my meat bill through the times of rising prices.

What Air Arm Should You Buy?

Depending on what you want to shoot will dictate what type of air rifle that should be used. Serious competition marksmen would generally use compressed air filled from a divers bottle, they will be very light in construction and will employ materials such as titanium and composites like carbon fibre and will have a price tag that reflects its high state of build. If you require one for serious hunting of rabbits and pigeons choose whatever you like the feel of, not what it looks like, as you will have it in your hands for quite long periods. Avoid guns that have plastic triggers and scope mountings as they never stand the test of time and can let you down in the field. I advocate a rifle above the mid range price, about £500 up to whatever you can afford above this. Cheap rifles never have the quality materials needed for good solid construction or long use so avoid them for hunting. For hunting purposes choose a bottle filled air rifle as you do not want to be scaring pigeons away by breaking the barrel on a spring loaded gun. Bottle filled rifles also don’t have any twangy recoil noise. Break barrel air rifles will give thousands of shots. But when hunting we will never bring back thousands of pigeons or rabbits. Compressed air guns will give you about 40-50 maximum power shots and this is more than you will need. When shooting at your prey you will need to get head shots for a good clean kill so your target will be quite small and will require a scope, as with air guns of quality you will require a scope of quality build but it does not need to be powerful anything up from 4×32 will be suitable.

The Calibre Required

177 is the calibre to use contaray to what most magazines and websites say, the reason being is I have shot at a pigeon’s neck and the 22 has glanced off the feathers. I have tested several types of 22 and 177 pellets of varying head shapes on dead pigeons and found that even a 22 sometimes glanced off of the head and very rarely pierced the body feathers. 177 caliber dome head pellets were defiantly the best for head shots. A 177 calibre flies faster at about a muzzle velocity of 800 feet per second whereas the 22 only travels at 600 feet per second because a 22 is a heavier pellet.

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