See fig. 4.4 for an illustration on how to make the blades.

Preferably, the blades should be made from 1.25 mm mild steel. If this is not available, 1.00 mm will also do but then the maximum allowable head will be slightly lower, see par. 4.1.

Since the blades will be soldered with brass later on, all paint or zinc (if it was galvanised) or `roller skin' (the black layer that is present on new, warm-rolled steel) should be removed. Once the blades are cut and bent to shape, it is much more work to clean them, so better do it on the piece of steel sheet the blades will be cut from later. Use a steel scraper and coarse sand paper for the last finish. Sometimes `blank' steel sheet is sold, with a smooth silvery color. In that case there is no roller skin. Real roller skin is almost black with a slight blueish hue.

Eventually, the blades are bent from rectangular pieces of 61 x 19.0 mm. The corners should be straight since that makes it easier to make a straight runner later on. The blades can be cut in several ways:

• With a steel plate cutter, a scissor-like tool with one blade fixed to a bench and another one operated by a long handle.
• With a hacksaw (when measuring out, don't forget the 1 mm wide cut from the hacksaw itself).
• With a cold chisel.
• If there is a well-equiped metal workshop around, it might be possible to buy accurately cut pieces of 61.0 x 19.0 mm with neat edges and straight corners.

It is important that all pieces have the same size and shape as this makes it easier to built them into a straight runner later on. Also the edges should be smooth since irregularities could act as the start of a crack later on. Therefor cut slightly bigger pieces of say 61.5 x 19.5 mm and file them to shape. About 15 can be clamped carefully aligned in the vice and filed in one go. When using a cold chisel to cut the pieces, the initial sizes should be even a bit bigger, say 62 x 20 mm. The runner needs 27 blades, but better make some more so that a few off-types can be discarded.

Fig. 4.4: Making the blades.

Fig. 4.5: Bending blades with a makeshift press.

For bending them, you need a piece of shaft with a diameter of 28.2 mm (28.0 to 28.5 mm will do) and slightly longer than the blades themselves, say 6580 mm. In a steel workshop, such a rod can be made easily on a lathe. Then one only has to file a flat side on it so that it holds better in the vice.

If you have to make one yourself, get a piece of 30 mm shaft or a long 30 mm diameter bolt to start with. File 2 flat sides on it until the thickness between the sides is just 28.2 mm. Then start rounding off one of the curved ends until there is a smooth curve with a constant radius from one end to the other.

Put the rod and a blade together in the vice (see fig. 4.4). To prevent that the blade will bend in a screw-like shape, make sure that the rod is well-aligned with the blade. Then slowly hammer the blade around the rod. Turn the blade upside down to hammer the other end into shape. It will look as if you can't get the blades into shape because they will always bend back a little. This is no problem since the radius of the rod was made slightly smaller than the desired radius of the blades to compensate for this effect. If you would hammer too long on the edges, the blades won't be straight lengthwise anymore.

The side disks are very important parts. If they are built correctly and accurately, it is relatively easy to build a strong and straight runner that will work efficiently. Likewise, if the shape of the side disks is lousy, it will be much more difficult to build a proper runner.

The procedure described in detail below is meant for producing a few side disks by cutting them by hand. To cut the strongly curved slots for the blades, it makes use of jigsaw sawblades (the ones designed for use in a jigsaw machine) that are fixed in a homemade sawframe. Advantages are that little preparation work is needed and one can see what one is doing, making it possible to cut them reasonably accurately right from the start.

For making side disks in series, cutting by hand would take too long and it becomes economic to cut them using a jigsaw machine, see box 4.9.

The side disk drawn in fig. 4.6 shows the size and placing of blades. The firefly runner deviates from crossflow design theory, see box 4.7.

Fig. 4.6: Making side disks.

The side disk is drawn on scale 1 : 1 and indeed, it is quite small. This leads to two problems:

1. To make a proper side disk, one has to work very accurately. A vital step in this is to copy the design onto the material from which the side disk is being cut.
2. The radius of curvature of the slots for the blades is very small, too small to be cut with normal jigsaw sawblades for metal (see the cross section of an original sawblade in the lower drawings in fig. 4.7) or with any other commonly available kind of sawblade for metal.

Answering the first problem comes down to not trying to measure out all dimensions oneself, but merely copying it from paper onto steel.

• Make a copy of the side disk drawing of fig. 4.6. If the copying machine is very old or seems unreliable, check whether the dimensions are copied correctly: The outer diameter should be 75 mm both in vertical and horizontal direction. If it differs say 0.5 mm, this is still not a problem as long as the horizontal and vertical measurement are nearly equal.
• Cut out the drawing and glue it onto the material. The easiest way is by using double-sided Scotch tape but many other types of tape or glue should do. Don't use glue on water basis since it might make the paper expand temporarily.
• Mark all relevant points with a center punch through the paper into the steel. Those points are the center of the disk and all centers of curvature for the slots. Check whether all center points are at the right position, especially the one marking the center of the disk itself, then remove the paper.
• Mark all circles using compasses or a modified vernier calliper (see box 4.8). These circles are:
  • The outer radius of the disk: 37.5 mm
  • The radius at which the slots end: 22.5 mm (or 22 mm if blades are rounded at the inside, see box 4.3)
  • The radius of the large central hole if it will be the free side disk (see fig. 4.6): 10.0 mm.
  • The radius of the small hole if it will be the alternator side disk: 3.0 mm. It seems superfluous because this hole can be drilled using the center point as a start. But because it is important that this hole is well centered, it is nice to have a mark once drilling has started and the center point has gone.
  • The inward edge of all slots: 14.2 mm.
  • The outward edge of all slots: 15.6 mm. This again might seem superfluous but it comes in handy when the sawblade cuts into the slot: At times the outward edge is better visible while further on, the inward edge is easier to see.

To answer the second problem: Jigsaw sawblades have to be grinded off until they can make such sharp curves. The easiest way is by grinding off at the rear end only, see fig. 4.7, and this is the best way if one wants to use sawblades in a saw frame. It could best be done using a bench grinder. Standard sawblades for metal could be used, but they have a rather short usefull length of only 50 mm. It is worthwhile to look for extra long sawblades that are more efficient for sawing by hand.

Without special measures, such a grinded off sawblade can not be used in a jigsaw machine anymore because the rear end doesn't touch the support wheel any more. In a jigsaw machine with an orbital mechanism (meaning that the sawblade is pushed a bit forwards on the upward stroke), the vertical, up and down-going shaft might have so much play that the sawblade is still supported by the support wheel. But then there is still another problem: The rear end of the sawblade must have the right, slightly conical shape, which is difficult to achieve once one has been grinding off material at that end. So if one would like to use a jigsaw machine, it is better to modify sawblades according to fig. 4.10. See also box 4.9.

The shape of the sawframe itself is not so important, as long as it holds the sawblade well, see fig. 4.7. When using extra long sawblades, of course the sawframe should be adapted to this.

Fig. 4.7: Using modified jigsaw sawblades for cutting slots in side disks.

Addition to internet version: Hacksaw sawblades can be used also.

In charger building workshops in the Philippines, people used hacksaw sawblades of which about half of the height of the blade was grinded away and probably even more at the side where it touches the outer edge of the slot. With such sawblades fitted in a normal hacksaw, they could cut the slots quite fast. However, the side disks I have seen, had slots with radiuses quite a bit larger than the design value of 14.2 mm and consequently, blades will be less strong. Also the width at the teeth is only 1.0 mm instead of 1.4 mm for jigsaw sawblades. One could try to widen the slot by cutting away material from one of the sides, but this means extra work and a less smooth result. Normally, only 1.0 mm thick blades will fit in (instead of 1.25 mm) and this makes the blades even weaker. If you are interested, see the picture "Joel Cubit cutting a side disk" in:
http://www.microhydropower.net/mhp_group/portegijs/firefly_exp/ANEX_s.html

Some practical advice on cutting slots with a makeshift sawframe:

• Buy extra sawblades, to allow for blades breaking and to be able to get a new one once it gets blunt. Count on using one sawblade for each side disk that is cut and keeping 1 or two spares.
• After grinding off a sawblade, try it out on a piece of scrap metal of 3 mm thick to see whether it can cut such sharp bends.
• Scrape off all paint, roller skin, zinc before starting to cut. They should be clean before soldering and once they are cut, it is more work.
• Make sure to start cutting the slot in the right direction. If one would `cut a corner' in the beginnen, one can cut a more or less straight slot at the beginning, but then has to cut an even sharper bend later on and this is very difficult.
• With a drop of oil on the sawblade, cutting goes easier.
• The sawblades tend to get stuck because of the `waves' of the wave-set teeth. Probably cutting would be easier with a heavier sawframe, with the extra mass helping to push it through the points where it gets stuck. To achieve this, the handles of the sawframe could be replaced by lengths of 30 or 35 mm diameter shaft.
• Work at ease. When rushing things, quite likely the slots will end up a lot less accurate. Anyway, cutting 27 slots is quite a tiring job. With a sharp sawblade, cutting one slot should take no more than 2 or 3 minutes, even when working at ease.
• Fix the side disk properly in a vice or by using clamps.
• Sawblades might break, so wear safety glasses!.

Then the 6 mm hole in the center of the alternator side disk can be drilled in (try to get it as well-centered as possible). The 20 mm hole in het free side disk can be made by drilling first with the largest drill bit available and then filing out the rest (mark the 20 mm diameter circle before drilling away the centre point that represents its centre). Or it can be made by drilling a line of small holes along the edge, cutting out the center bit and then filing it to shape.

Box 4.8: Modifying a vernier calliper for marking circles on steel. The points at the jaws for `inside' measurements of a vernier calliper can be used already as compasses for steel: Have one jaw in a center point and scratch with the other over the material. The material of a proper vernier calliper is hard enough to scratch into steel without wearing out too fast. Problem is that one doesn't know exactly what radius the circle will get since the first jaw doesn't align well with the center point. To solve this, the vernier calliper can be modified a little: Adjust the calliper to 1.0 mm exactly and fix it well. Now the `inside' jaws largely overlap but the points themselves are 1.0 mm apart. Grind off the overlapping inside jaws until together they form one point shaped more or less like the point of a center punch (say: with 90° top angle). Now the vernier calliper can be used as compasses and the radius can be set using its scale. The one thing one has to remember, and is likely to forget, is that one should add 1.0 mm to the desired radius because, when adjusted to 1 mm, the points overlap again and the radius is 0. Because of its scale, such a modified vernier calliper is easier to use and more accurate than real compasses for steel. However, the points of its inside jaws are modified and therefor `inside' measurements of objects with only a small rim, will be more difficult. Fig. 4.8: A modified vernier calliper for marking circles on steel.

Box 4.9: Making side disks in series. For making series of side disks, a sturdy jigsaw machine can be used with an especially made foot plate that works as a circle guide. The pin of the circle guide falls into the holes of a mould that is clamped onto the side disk to be cut. To make it possible to cut at some speed without overheating sawblades, the sawblade should be cooled using drilling fluid. Therefor a container with drilling fluid is needed, with a support for the side disk being cut in the middle. With every stroke, the sawblade dips into the drilling fluid and is cooled in that way, see fig. 4.9. Advantages of this method are that up to 2 side disks per hour can be made, once everything works well. Accuracy of the side disks can be very good and if there are errors, quite likely all slots have the same error. Disadvantages are the investment costs of the jigsaw machine, it will take days of work before the first side disk can be cut, probably the first ones aren't that good and it takes quite some metal working skills to get everything to work properly. For use in a jigsaw machine, it is better to modify the sawblade according to fig. 4.10. To make that the support wheel will function well, the rear end of the sawblade should as much as possible keep its proper shape. So only at the outward, rear corner a bit is grinded off on a bench grinder. Take care with grinding off the inward side because the teeth themselves should not be touched. This can best be done with a small angle grinder. Clamp the sawblade horizontally in a vice, with a piece of steel sheet between its teeth and the very hard jaws of the vice. Fasten the vice only lightly because otherwise the teeth will break. This piece of steel sticks out above the sawblade and because the grinder disk has a rounded edge, it won't reach the teeth themselves easily. In Holland, special narrow sawblades with 3 mm pitch are available and it is better to start with these rather than the standard metal sawblades with 1.2 mm pitch. Because they are less wide, these blades can make sharper bends from themselves and only a little has to be grinded off at the inward side to make them suitable for cutting slots. The 3 mm pitch makes them more suitable for cutting through thick steel. There is another way to get large numbers of very accurately made side disks: Having them made by a specialised workshop that has laser cutter equipment. Such equipment will only be available in western countries or the largest industrial centers of the third world. With this method, having the side disk shape programmed into the machine is costly, but once everything is set up, prices could be quite low. Fig. 4.9: A jigsaw machine adapted for cutting side disks in series.   Fig. 4.10:A modified jigsaw sawblade for use with a jigsaw machine.

When a good jigsaw machine is available anyway, it would be tempting to use that instead of cutting by hand, but without investing in making the foot plate with circle guide etc. described in box: Making side disks in series. I think this is not recommendable because:

• Then sawblades have to be modified in a more complicated way, see above.
• Three mm steel is about the maximum a jigsaw machine can handle. Quite some force is needed to push the machine ahead. Problems could rise with respect to the jigsaw machine vibrating too much, sawblades breaking and sawblades becoming blunt prematurely due to overheating. At least a jigsaw machine with speed control is needed and one should use it at the lowest practicable speed (watch out for overheating the machine) and keep the sawblade oiled.

The blades can be soldered in the side disks with brass, a yellow colored alloy of copper and zinc. Often this is called `soldering with bronze', but in fact bronze is colored more brownish (bronze) and is an alloy of copper with tin. Apart from brass, there are several alloys of silver, with their proper flux, that can be used for soldering. Probably they are even stronger and easier to use, but more expensive than brass.

Quite likely, workshop people will suggest to use acethylene welding (so: Heating until the steel itself melts and using iron wire to add extra material) because it is cheaper. This is not recommendable: It would result in a much weaker runner because it is impossible to make the weld as smooth at the inside as can be done with brass. Also the runner would become distorted because of heat stresses.

For soldering with brass, an acethylene set is needed. It consists of two steel bottles (with acethylene and oxigen respectively), pressure reducers, hoses and the torch itself. Acethylene sets are mostly used for cutting steel but with a different torch, it can also be used for acethylene welding of thin steel or, in this case: Hard soldering. Acethylene equipment is quite expensive but essential for car and truck repair workshops and many types of metal working workshops. If the owners of such workshops are reluctant to cooperate, try a technical school. Of course also the brass rods themselves are needed, and a `flux' powder called `Borax' or `Boracit'.

It requires experience for working properly with acethylene equipment, not only for adjusting and operating the torch and the soldering itself, but also for the safety aspects. So for good reasons, workshop people probably won't allow you to do the soldering yourself. But insist that you are present during the soldering and make sure that the soldering is done according to the guidelines set out below.

The strength of the runner depends largely on the quality of soldering, see box 4.10. Of course the skills of the one doing the job are important, but things are a lot easier if the material is clean and if there is soldering flux everywhere where the brass should come to make a proper joint. Using brass rods with a core of flux is not enough: Once the joint is fully covered with brass from above, no more flux can flow down to clean the area where it matters most. Therefor:

• Before assembling the runner, make a stiff mash of flux powder and water and rub some into the slots of the side disks.
• Once the runner is assembled, put it in a container, make a more liquid mash and add as much that the lower side disk is submerged a few mm. Before turning it around to have the other one submerged as well, shake off the excess flux (a droplet of flux mash flowing down a blade could be followed by a droplet of brass during soldering, which is very hard to file away and would partially block the water flow later on). Then the runner can be dried.

This should make sure that there is ample flux everywhere. This flux powder melts when everything is heated up and then acts as a cleaning agent. It makes the brass creep into the smallest crevices and form a smooth, rounded weld at the inside of the runner where the blades stick out of the side disk.

Impurities like metal oxides will dissolve in the melted flux but when there is too much impurities around, it might not be able to deal with it all. The least that will happen is that the flux will become black instead of transparent, making it impossible to see the brass underneath it. That is why the roller skin has to be scraped off from the material for both the blades and the the side disk, even though the real joint will be in the slots and there is no need to cover the surfaces of the side disks with brass.

Before soldering, the runner must be assembled. Take the direction of rotation of the alternator into account, check this with fig. 4.6.

Usually either the blades are bent a bit irregular or the slots turn out to be slightly off-shape and this makes that the blades will fit quite tighly into their slots. They have to be hammered inwards from the outside towards the center of the runner. Use a light hammer and hold the runner in your hand while hammering. If blades fit too tightly and the lips between slots become bent while hammering in blades, try to bend the blades to shape better.

Once all blades are hammered in, it is difficult to change its form. So first fit a few blades at 3 places around the side disk and check whether the distance between the side disks is correct: 55 mm. Check at several points around the circumference. Hammering the side disks towards one another is easy, but watch out that the lips between slots for blades are not bent. If the side disks have to be pulled apart, stick a rod through the hole in the free side disk and with that, hammer the alternator side disk outwards. Also have a first check on whether the runner is straight, see below.

When all blades are fitted, first check whether no blades stick out through the side disks. If blades are too long or too short, have them well aligned at the alternator side disk. This surface should be flat since this is where the runner will be clamped against the rim of the pulley. Also forces are greatest at the alternator side disk, so if a blade is too short, it is better to have the free side disk being weakened by a blade that is a little sunken in.

Then check carefully whether the runner is straight: Hold a carpenters square against the alternator side disk (the one with the 6 mm hole in the center) and see whether the blades are well aligned with it. Check at least 4 point around the circumference.

Now the runner might look crooked even though it is as well aligned as possible if:

• Not all slots are cut until exactly the same depth (this determines the inner radius of the blades).
• Some blades are slightly wedge-shaped.

If this might be the case, check a few blades at each point and use the average. Or compare the circumferences of both side disks rather than the blades. Of course then the outer radius of both side disks should have been cut properly to give reliable results.

To correct the alignment if a deviation was found, hold the runner in your hand and hammer at the end of the side disk that is sticking out. Normally, blades will stick out a little radially so it will be a blade that has to absorb the blow. It doesn't matter if the blade is deformed a little since this part will be filed away later.

If the blades fit so tight that the runner can't be hammered to shape in this way, try fixing the alternator side disk on a flat, heavy piece of steel in the way it will be fixed later to the alternator shaft (so with an M6 bolt and the 20 mm washer). Then use a rod to hammer against the inside of the 20 mm hole in the free side disk rather than hammering against the outer edge.

There is an easier way to get the runner well-aligned: Fit it on the alternator shaft and check whether it wobbles. But then first the alternator shaft should be made fit for this (see par. 4.4) and somehow it seems more logic to build the runner first. If you want to use this method:

• Fix the M6 bolt only very loosely, as without the blades being soldered, the alternator side disk will bend easily.
• Clamp the alternator onto a table and hold a carpenters square upright from the table to see whether parts are well-centered.
• First get the alternator side disk well-centered, see with aligning the runner in par. 4.4.
• Now hold the square against the free side disk and get it well-centered using light hammering. Heavy blows could damage the alternator bearings and most likely are not necessary anyway.

Don't be satisfied too soon in getting the runner well-aligned. If it is not, then later a lot has to be filed off from the blades at the end that is sticking out and those blades will become significantly weaker.

During soldering, 2 side disks and 27 blades have to remain in the right position with respect to one another. Usually the blades fit quite tightly in the slots but to be sure, better put a few windings about 1 mm iron wire around it. If still a blade is a bit loose, make a mark with the center punch on the side disk close to its slot. Then at that spot, the slot will become narrower and the blade will stick well. Take care that the runner will not become deformed again so pack it properly when transporting it and when it is dropped accidentally, check the alignment again.

Then about the soldering itself. Below, it is written as if you will do the soldering yourself while in fact probably someone of a workshop will do it. At least make all preparations you can and try to explain how you would like to see it done.

• Before soldering, submerge both side disks in a quite liquid mash of flux as described above. Still it might make sense to use brass rods with a core of flux, or to add flux by dipping the hot rod into a container of flux.
• To melt brass, the temperature should be well into red-hot. I could see things better using the strong type of sunglasses that are used in mountaineering.
• Like with welding, the flame produces light by itself. But it has a reddish hue and I produced much better solderings if there was ample ambient light (full sunlight or strong lamps).
• To reduce heat losses, make a double-walled container of 1 liter tins, with at the bottom a small tin cut off at such a height that the side disk to be soldered just sticks out a little, see fig. 4.11. The double wall can be made by cutting out both top and bottom of a tin and then bending it until it fits in another tin of the same size. Without such an isolation, one needs a larger flame, will consume more acethylene and making good solderings is more difficult because the risc of overheating is much bigger. The double-walled container will especially reduce heat losses from the blades. This is important since the blades will tend to stay relatively cool since they have a small surface area that can be heated (the area that sticks through the side disk) and a large area that radiates away heat.
• Because of the isolation, the flame doesn't need to be that large. Try the smallest torch head from the set (no. 0, with a hole of ca. 0.8 mm diameter) first and adjust the flame so low that it is just able to heat up the material so much that the brass will melt. In this way, chances of overheating the brass (see below) are low, one can work at ease and the use of acethylene gas is minimal.
• Find a sheltered, quiet place to work. Put the container at a stand at a convenient height and in such a way that one can walk around it while soldering (otherwise one has to turn the hot container for soldering from the other end).
• For having all blades soldered well, at least 15 g of brass is needed for the two sides of one runner and more if slots ended up wider than 1.4 mm or if 1 mm blades were used. Normally quite a bit extra is needed because the brass will not be divided evenly over all welds and some will remain at the top surface of the side disk, so plan on using 20 - 25 g per runner. Weigh or calculate how much brass is in one brass rod (density of brass: 8.5 g/cm3) and plan how much of a rod you want to consume for soldering one side disk.
• Have pliers and a piece of iron wire with a hook ready to lift the runner out of the container and turn it over.
• Solder the free side disk first. This gives you an opportunity to practice before soldering the alternator side disk, which is more important from a strength point of view. If you feel unsure, practice on pieces of scrap metal first, having the same kind of joint to make (a thin blade sticking through a slot in a thick piece of steel) and using the container.
• Adjust the acethylene/oxigen ratio of the flame until the blueish cone that comes when there is an oversupply of acethylene, has just disappeared. Check whether the flame is formed regular and pointed. If not, clean out the hole in the torch with the special `torch drills' that go with it. - The flame should be adjusted so large that reasonably fast soldering is possible while the risc of overheating material is minimal. I had it so large that when soldering the edge of the first blade (see `go 1' below), it took about 5 seconds before the material was heated up enough (with subsequent blades, it will take less because they are pre-heated by the far end of the flame). When letting the brass sink into the joints, the flame was just large enough to keep the brass melted for the whole length of the weld.
• During soldering, use the white-hot cone of the flame to heat up the material. For applying a droplet of brass, also bring the end of the brass rod into this hot cone. - A warning against overheating: The white-hot cone of the flame is hot enough to melt steel and once it happens, it is impossible to get it back into shape. A more important effect is that overheating will make the zinc evaporate from the melted brass, so that only red copper will remain and this is much weaker than brass. There is only a small margin between heating up the material enough to make brass melt and heating it up too much to make the zinc evaporate. Only when the runner has cooled down and has been cleaned, you will find out whether it has been too hot. So:
  • With ample ambient light, it is easier to see what is going on.
  • Keep the flame constantly moving, even if you want to heat up a small area. Generally for soldering, the flame should never rest on one place.

Fig. 4.11: Soldering a runner.

Then on the actual soldering itself. First one could heat up the whole of the side disk for say 15 seconds, moving the flame around from above in large circles. I got the best results by working in 4 goes:

1. First make small joints at the outer circumference. Direct the flame almost horizontally from the outside towards the side disk and blade. In this way, one can heat up both the side disk and the blade and apply a droplet of brass once they are hot enough. Actually, there are 3 parts to heat up: the blade and the parts of the side disk at both ends of it (so there are 2 joints to make between these parts). These 3 parts will conduct away heat differently. So take care to direct the flame in such a way that they heat up evenly. I kept the flame more or less in line with the outer end of the blade (so: Not towards the centre of the runner, but at an angle). In this way, the next blade is already pre-heated by the far end of the flame and one can work faster. Once there are 2 small joints there, this will conduct heat from the side disk (that is heated up easily by the flame) to the blade (that will tend to remain too cool).
2. Then direct the flame from above to the side disk and apply brass to the length of the weld. Do not bother whether the brass sinks into the weld properly, but try to apply the right amount of brass (see above) and to apply it as regularly as possible.
3. Now heat up all welds until the brass sinks into the joints properly. Apply some more brass when it looks like there is only a very thin layer left on top. Move the flame in circles over the weld you are working on, while directing it already towards the next blade.
4. With the flame directed horizontally towards the edge, check the welds at the outer edges of the blades again (this is the critical point with regards to strength!!). Apply extra brass when necessary. Ideally, at the bottom end of the side disk, there should be a smooth, rounded weld between blades and side disk, with a radius of say 0.5 to 1 mm. Mind that you can file away excess brass there later, but can not add it.

When satisfied, turn it around and solder the other side disk.

When soldering is finished, take it out of the container and let it cool down for a few minutes. Never pour water on very hot objects as it might affect the quality of the steel. Only once it has cooled down to less than say 200 °C, you might let it cool down faster by pouring water over it.

to index page

next