Hi
Well heres the text.
Dear Sir,
As every model engineer knows its often necessary to cut off a lump of metal, steel or brass etc, to a size that will fit in one of the machines. To me a hobby is something you do for pleasure, coming home after a hard day at work and standing at the bench vice hack sawing through inch thick steel bars is not a pleasure. One option is to take the bar to work and let Ben, the lad, cut it for me but this isnt always convenient, (and makes Ben curse a lot) because I usually need the bit at night or the weekend. What I needed was to keep Ben under the bench and bring him out when needed or get a machine to do it for me. Of course there are metal cutting saws on the market and much as I would love to pick up one of the many mail order catalogues and order one of everything a shortage in the cash department prevents this. So it was that I put my mind to solving the problem of how to make one. Most metalworkers Im sure have made there own tools of some sort, jigs and clamps etc. but this project would make the leap from making a hand tool to making a power tool. I quickly discounted the idea of a band saw, it would be far to complicated, and so decided that a powered hack saw was the answer. Over the next few weeks many scribblings and jottings started to clutter the bench but I still had the problem of what to power it with. The answer came to me one day at work; Im in the motor trade, while working on a car. The wipers were gracefully sweeping to and fro when it hit me. As I watched the movement everything seemed to fall into place. 12 volt. Why not. Much safer than playing about with mains powered motors and anyway many cordless power tools nowadays run on low voltage. Now Im not suggesting you should rush out and grab hold of the wipers on the old Mondeo but take it from me they are quite powerful. The motors work on a worm and gear arrangement and are very reliable, we very rarely have to fit new ones, and if you think about it they are capable of running for long periods of time. They very conveniently rotate at about the right speed, (Imagine cutting a piece of metal by hand while keeping in time with the wipers on your car) come fitted with a crank and have all the necessary links and bits and pieces etc that you will need. As I mentioned earlier Im in the motor trade so quickly had the parts stripped out of cars that were being scrapped. The photos show the complete mechanism from a 1993 Ford Escort and a Vauxhall Astra of about the same vintage, (this is how the mechanism comes out of the car, as a complete unit) also shown is the crank from a Rover 214. You will notice that although there are differences they all work on pretty much the same principle. I chose to use the one from the Ford Escort purely because it has the greater crank sweep of the three at 106mm which will give a saw stroke of the same amount compared to the Vauxhall at 78mm and the Rover at 80mm, although it wouldnt be to difficult to extend the crank by cutting in half and welding/riveting/ bolting a longer piece in. I havent investigated other makes and models of car wiper motors in depth but apart from the crank sweep as mentioned before they are all pretty much the same. The Escort and Astra units are fairly easy to remove, all done from under the bonnet. Other makes and models can be more difficult. If you dont know of anybody scrapping a car where you can get the bits for free and have to go to a car breakers you shouldnt have to pay much more than a tenner. One other thing, get the plug by chopping 6-8 inches or so off the end of the wiring loom, its not absolutely necessary but will make the wiring up easier and neater. Back home in the workshop a couple of quick experiments on power supplies was carried out. It will of course run off a car battery, it will also run quite happily off a 6-amp battery charger or a transformer. Having satisfied myself that the motor would power the saw it was time to empty out the boxes full of bits that will come in handy one day. At this point I think I ought to emphasise that although I wanted a power saw this project was purely experimental so I make no excuses for mixing imperial and metric and using whatever came to hand. As far as possible I will give measurements in mm. Hindsight being a wonderful thing, if I was making it again I would do things differently, but on the basis if it works leave it alone I probably wont. Wherever I can I will throw in suggestions of alternative methods or ideas and afterthoughts. I suggest therefore that you take a good look at the finished tool and use the measurements and drawings as a guide and adapt them accordingly. Its highly unlikely that there are two of us with the same box full of bits and pieces. As I have already said this was an experimental piece so engineering excellence it isnt but that said care was taken to keep things as square as possible where it mattered. Although I have used the lathe and milling machine on some parts this is not necessary and the whole thing could be made with basic tools, a pillar drill being advantageous. So let us begin. The idea I came up with is to have a saw frame slide to and fro on an arm that is pivoted at one end. The arm pivots up to take differing thicknesses of work and keeps pressure on the work via its own weight. The motor mounts directly on to the arm and drives the saw via one link thus doing away with the need for any complicated mechanisms. (Keeping things as simple as possible is always the best policy when carrying out experimental work I have always found.) A piece of steel channel will form the base onto which will be bolted a vertical post to mount the swinging arm to. A simple vice will be needed to hold the work. On the electrical side I will need an on\off switch and a switch that will cut the power as the saw reaches the end of the cut. With a few rough sketches and measurements I set about making it. Much of the flat steel and the box section steel I bought from B & Q. They have a good selection of brass, steel and alloy in a variety of flat, angle, round, square, tube and box sections. I started with the saw frame. This I decided should have a 140mm depth of cut so as to be able to accommodate larger tube sections as well as smaller solid parts. The frame is designed to take 10 inch blades purely because I had 20 or so in stock. Although not as common as the 12 inch blade they are still available. The saw has a stroke of 106mm and therefore will not use the entire blade anyway. It will of course keep the finished machine 2 inches shorter and the shorter frame will be more rigid. I can see no major problems with using 12 inch blades just remember to make the frame and the swinging arm 2 inches longer. I started with the saw frame. Cut a piece of 35mm x 20mm x 1.5mm oblong steel box section to 305mm in length and 4 pieces of 30mm x 4mm flat steel to 180mm in length. Clamp the flat steels together in pairs. Drill a 5mm hole through each pair to take the spacer and countersink the holes then cut\file\mill the 4mm slots that take the blade mounting blocks. One arm from the wiper mechanism must be removed. File or grind off the part of the wiper spindle that has been riveted over and lever off the arm. A square hole must now be cut in the side of the oblong steel section just big enough for the arm to slip in. (The position of this hole must be worked out. The type of motor used, crank sweep, the length of the connecting rod etc. will all have an effect on its position). Clamp the arm in place and drill 2 x 2mm holes through the box section and arm. Remove the arm and drill the 2 holes out to 5mm and tap 6mm. Drill out the two holes in the box section to 6mm. Make up two spacers to 20mm, (the same width as the oblong box section) I made mine on the lathe from 12mm hex steel bar, drilled and tapped 5mm that will take a 5mm x 12mm countersunk machine screw from each side. You could use a piece of tube as a spacer with a nut and bolt right through. Fit the spacers to the flat steels and then clamp to the oblong box section with mole grips and check with a square. To speed the job up a little I took the frame to work and welded the parts together. If possible do the same as welding makes a good solid frame. (Speak nicely to the guy at your local car welders)Alternatively use bolts\screws\rivets to fix the frame together. Using triangular plates at the corners will considerably strengthen the joint. Cut two 30mm lengths of the oblong box section to form the lower guides. Slide the frame onto a length of the box section; (that will become the swinging arm) slip the two short guides of box section into the frame and push them up to the top trapping the swinging arm in place. Secure the two guides with mole grips or clamps and check that the frame slides freely along the arm with the minimal amount of free play, adjust as necessary. Drill eight 1\8 inch holes through the sides of the frame and secure the short pieces in place with 1\8 pop rivets. Cut two blocks of steel 35mm x 20mm x 12mm to make the blade mountings. Cut out or mill off one corner. On one piece drill and tap 4mm for the blade mounting screw and drill through 4mm to take a 32mm length of 4mm rod. Very lightly peen the rod in its centre and press into the block so that it is central. On the other block drill and tap the same for mounting of the blade. Next drill 5mm to a depth of 10mm and tap 6mm to take the adjusting stud. Screw in a 25mm long bolt then drill through to take the 4mm bar, this will go through adjusting stud and hold it securely in place, lightly peen the rod and press through. Note that the 4mm rod is in a different position on each blade mounting block. Cut the head off the bolt, clean up the thread and fit a large washer and wing nut. When the blocks are fitted in their respective slots in the frame they are held rigidly and will not allow the blade to twist. The swinging arm is a 545mm length of the oblong box section. Drill through one end to take a 24mm length of 12mm tube with a 10mm bore. I brazed the tube in place but soft solder would do just as well. Cut a 120mm length of 14mm x 5mm steel and a 70mm length of 14mm x 5mm steel. These two pieces will make up the bracket for attaching the spring counter balance. Clamp the shorter piece to one end of the longer piece and drill through the two pieces with a 2mm drill at 50mm centres. Clamp the long piece to the bottom of the swinging arm and drill through with the 2mm drill. Drill out the holes in the long piece and the swinging arm to 6mm and drill the out the holes in the short piece to 5mm and tap 6mm. Drill a 4 mm hole in the other end of the long piece to which the spring will be attached. With the short piece pushed inside the swinging arm the long piece can now be bolted on from the outside with two 15mm long 6mm bolts. The motor mounts onto the swinging arm via a 3.2mm thick 130mm x 80mm steel plate. Cut an 80mm length of 25mm x 6mm steel and clamp to the bottom of the motor mounting plate. Drill two 2mm holes at 40mm centres through both pieces. Clamp the motor mounting plate to the swinging arm and drill through the two 2mm holes. The motor mounting plate and the swinging arm can now be drilled out to 6mm. Countersink the motor mounting plate. Drill out the piece of 80mm x 25mm steel to 5mm and tap out to 6mm. A 25mm hole must be made in the plate for the motor spindle to go through by drilling and filing. Three further holes must be drilled for the motor mountings. (The position of these to be taken from the motor you are using). By slipping the drilled and tapped plate inside the swinging arm the motor mounting plate can be fitted with two 6mm countersunk machine screws. Its a bit fiddly lining up the holes but once bolted up its nice and solid. Thats about it for the frame and swinging arm but its worth having a test run now to check that all runs sweetly. Fit the motor to its mounting plate. Clamp the swinging arm in a vice and slip on the saw frame using a little light oil (3 in 1). Press on the connecting rod. Connect the motor earth lead to the 12 volt power supply earth and touch the other wire onto the positive power supply. Its fairly safe doing this as we are only playing with 12 volts but be aware that it can kick out a decent spark. If alls well then the frame should move back and forth with no strain. I have to admit its very satisfying to see it move for the first time. If alls well then we can move onto making the base. The base is a piece of channel 45mm high x 95mm wide x 3.3mm thick x 525mm long. It already contained a few holes but these have no effect at all. The swinging arm of the saw is mounted on a vertical post bolted to the side of the channel. The post is made out of a piece of 185mm x 50mm x 8mm steel. Drill two 2mm holes at one end and clamp the post to the channel, use a square to make sure the post is true and vertical. Drill through the two holes with a 2mm drill then open out the holes in the post and the channel to 8mm. Cut a piece of 30mm x 4mm steel to 120mm in length and drill two 8 mm holes in one end to match the holes in the post. Drill a 4mm hole in the other end.
...... Yes Please Rich ........... btw, what do you use as the 12 volt power plant 
