The Mold
The alternator requires two rotors to be built. The first step is to build a wooden mold. Each rotor will be made from 12″ diameter steel disks each with 12 magnets on it. Once we’ve built the rotors we’ll cast polyester resin around them to keep the magnets in place and prevent corrosion. In order to make a neat casting we need to build a mold out of plywood. Like many other things in these plans, there are alternative ways of doing things. Here we’ll detail exactly what we’ve done. Some of the pictures show two molds in use, but you only need one. See the picture above for dimensions of all the parts
Materials list
– 3/4″ thick plywood, 2 squares 14″ x 14″ – 1/2″ thick plywood disk, 6.5″ diameter – 1/4″ plywood, 1 disk 2.75″ diameter – about 20 1″ long wood screws
 The mold is 14″ square. The hole in the center is 12.5″ in diameter and 3/4″ deep. In the center is an island 2.75″ diameter and 1/4″ thick. The lid is the scrap which we cut from the center of the mold (a 12.5″ diameter disk). The center of every part has a 1/4″ hole drilled through the center that we use to align everything during assembly. All the disks are easy to cut out with a bandsaw, or a jig saw. With some patience a coping saw would do fine as well. All the disks and the inside of the top that we cut out should be sanded smooth, and preferably slightly tapered so that the top of hte hole is slightly larger diameter than the bottom. Once all the parts are cut out, screw the 3 square pieces together so that the one with the 12.5″ diameter hole is on top. The screw the small 2.75″ dia disk down in the center – using the 1/4″ drill bit as a pin to center it perfectly. Caulk all the seams inside the mold so that resin can’t run into cracks. This, the sanded surfaces, and the tapered hole in the mold will make the molded pieces easy to remove.
The magnet template
The next tool you need to make is a template for placing the magnets. The one pictured was made at a local machine shop with a CNC water jet cutter out of 1/8″ thick aluminum and the cost was quite reasonable (about $25 USD). But you can just as well build it from thin plywood or plastic. It’s a 12″ diameter disk, with 4 1/2″ holes on a 4″ diameter (just like our magnet rotors) and 12 equally spaced cutouts the size of our magnets (1″ x 2″ x 1/2″ in this case). We do sell CAD-cut aluminum templates that are perfectly aligned for this — check our online store.
Building the magnet rotors
Materials
– 12″ diameter mild steel disk, 1/4″ thick, qty 2 – 1″ x 2″ x 1/2″ N35 grade NdFeB magnets, qty 24 – cyanocrylate glue with accelerator – fiberglass cloth or mat, 2 square feet – 1/2 gallon polyester resin
Start with two steel disks, 12″ diameter. Each disk should have 4 1/2″ holes on a 4″ diameter circle(a touch larger to provide some clearance is nice) and a 2.75″ hole in the center. You can build a rotating table and do a pretty neat job cutting these out with an oxy-acetaline cutting torch, but we usually have ours cut out by a fabrication shop. A CNC laser cutter, plasma cutter, or water jet cutter will do a very nice job. If you have it done, you might have them cut all the holes for you – it saves a lot of time and assures that things are accurate. Otherwise, if you decide to machine your own rotors, the first step is to cut a 2.75″ hole in the center of both rotors. Use a high quality bi-metal hole saw and a drill press for this. The drill press needs to be run very slowly and you need to use lots of oil. Easiest is to clamp both rotors together and cut both at the same time. Save the scraps from the center, we can use one of those later. Next, keeping both disks clamped together, drill out the 4 .5″ diameter holes equally spaced around a 4″ diameter circle. The easiest way to do this is to put the wheel hub on the rotors and clamp it there, and drill right through the holes on the wheel hub. This saves a lot of layout and assures accuracy. One of the disks needs 4 more holes 7/16″ dia (also spaced around the same 4″ diameter and located between the .5″ diameter holes we just finished) which we’ll tap 1/2″ – 13 for jacking screws to aid in the assembly/disassembly of the alternator. Again – we usually have this done at a fabrication shop – when they cutout the disks for us it’s easy for them to use the same CNC machine to make all the holes.
 Pictured above we’re tapping the 4 smaller holes 1/2″ – 13. It’s important to use lots of oil (or tapping fluid) when running the tap in. Try to keep the tap as straight as possible. Once it starts to cut threads, turn it just till things start getting tight, then back up a bit and ‘break the chip’. Continue this untill the tap goes all the way in and spins freely. Never force the tap in if things get too tight – always back it up, break the chip and then go foward again.
 Use a countersink to chamfer the edges of the 1/2″ diameter holes. This makes things assemble more easily and helps protect the threads on the studs that hold the alternator together. Once this is done, all the ‘metal work’ is finished for our rotors. Both rotors are oily (finger prints and oil from drilling and tapping) so we need to clean the carefully with some kind of solvent. We usually use laquer thinner. After that – try to keep grease off them, handle them with clean hands. You’re about to start putting magnets on them, so this is a good time to clean the work area. Metal chips from the drill press and grinder should be cleaned up, or you should move the work to a new cleaner environment.
 The steel disks don’t always come out perfectly flat. I expect some sheets of steel get bent in handling by forklifts and such and when the disks get cutout sometimes we find them slightly warped. Check for this with a straight edge. Flatening them can be done but it’s tricky. We usually locate the dimension in which it’s warped and we put our magnets on the most convex surface. (the surface facing up towards the straight edge in the picture is the surface we’d put the magnets on)
Put the magnet template down on one of the steel disks and line the holes up.
Place the other steel disk down on top of that, with the holes line up and pin the sandwich together with two 1/2″ drill bits (or wooden dowels or bolts or whatever).
Looking from the side you can see the ‘gaps’ in the template where the magnets will fit. Pick one gap and use a permanant marker to mark both sides of the gap. This is where we’ll place the first magnet on each disk.
(drilling into the top magnet rotor)
(drilling into the bottom magnet rotor)
Use a small drill bit (3/16″ is a nice size) and drill a divit (a dent – not a hole, don’t drill through) into both disks between the marks we made. These will be on the outsides of the magnet rotors and will serve as ‘indexing marks’ so that when we assemble the machine we’ll know how to line up the two rotors. Alignment of the rotors is critical in the operation of this alternator, they must always go together the same way with alternating magnetic poles facing one another. Once we’ve done all this we can take the top rotor back off the stack and put it aside in a safe place (away from the bottom rotor because were about to play with magnets).
 For this alternator we require qty 24 Grade 35 NdFeB magnets 1″ x 2″ x 1/2″ thick. These are available from many vendors, they usually come either epoxy coated or Nickel plated, either way is fine. These are very powerful magnets and need to be treated with extreme focus and caution! Two coming together on your finger could hurt very badly and leave blisters easily. Once we assemble these on the rotors we have some very powerful/dangerous magnetic assemblies. Two finished magnet rotors coming together on your fingers could easily break them! Build one magnet rotor at a time. When it’s finished- put it in a safe place. When building these be sure that all ferrous (anything containing iron which includes steel tools, wrenches, knives scissors etc) are away from the work area. Only handle one magnet at a time and always grip them firmly. If a magent flys onto a piece of steel or into another magnet at high velocity, it may break and send shards flying! Handle one at a time, handle them with a firm grip. Store them in a safe place away from kids and folks who don’t realize what they might be getting into. Keep them away from electronics/video tapes and other forms of magnetic storage medium. These magnets are perfectly safe when handled properly, but most folks are not familiar with the dangers and there can be surprises.
 The magnets are so strong they can be tricky to seperate off the stack. The best way is to place the stack on a wooden workbench and hold the stack firmly. Then grasp one magnet firmly with the other hand and slide it off. (you’ll not be able to just pull them apart, you have to ‘shear’ them apart)
Now we can place the first magnet on the bottom magnet rotor. The template is pinned to it and made of wood or Aluminum so it won’t move. But the magnet is strongly attracted to the steel disk so we need to hold that down with one hand. While firmly gripping the magnet in the other hand, bring it towards the edge of the rotor and ‘slide’ it into the slot. (don’t just try to put it down on – it will pull out of your hand and hit the rotor hard – possibly breaking the magnet!)
 The magnets need to be spaced around the disk with alternating poles facing up. All magnets have two poles, a North and a South. Opposite poles (North and South) attract one another, like poles repel. It doesn’t matter how we put the first magnet down so long as things alternate from there. The safe way to place the rest of the magnets is as follows: Hold the magnet rotor down firmly to the work bench with one hand which should be placed over the magnet that’s next to the one you’re about to place. Then, holding the next magnet firmly, bring it over your hand which is holding down the rotor. If the bottom of the magnet in your hand is repelling the one on the rotor, then slide it into the slot carefully in it’s current position. (Because we know that if the bottom of the one in your hand is repelling the top of the one on the rotor then we have like poles facing each other, so the one in your hand has the opposite pole facing up as the one on the magnet rotor)
 Once all the magnets are placed on the first rotor you can remove the pins and pry the template off. Do this carefully so the magnets don’t slide around.
Run a bead of thin viscosity cyanocrylate glue (Super Glue) down both sides of each magnet. Large bottles (2oz usually) are available at most hobby stores. It’s also handy to have ‘accelerator’ which will force the glue to harden immediately. The accelerator usually comes in a small spray bottle. We don’t rely on this glue to hold the magnets down forever, it’s a temporary means to keep things in place till we finish the casting. If cyanocrylate glue is not available then other glues should also work fine. Epoxy would probably be fine it just takes longer to dry.
I expect you could skip this part all together, but I believe it offers some insurance that our magnets will never fly out. Also – if the resin cracks this will keep things together for us. Take a roll of fiberglass drywall tape (this stuff is sticky on one side) and cut the roll with a razor knife so that you can peel off a strip of the tape about 1/2″ wide.
Wrap the tape around the magnets several times. Be sure that none of the tape sticks up above the top of the magnets.
Now that the first magnet rotor is finished, drive a nail somewhere in a wall in a high/safe place and hang it there. It’s a somewhat dangerous thing and should be kept in a safe place.
Now to begin the second magnet rotor. Put the template on it so that the 4 holes line up and one of the slots lines up with the marks we made earlier. This assures us that the magnets we place will be facing each other when the rotors are assembled. The top of the first magnet on this rotor must be the opposite pole as the top of the first magnet we placed on the first rotor. In other words, the two surfaces facing one another must attract one another. Once you get the first magnet down, follow the same proceedure as you did with the first magnet rotor.
Check your work!
You can easily double check your work now. Find a small magnet and hold it in your hand (dont turn it over – hold it in the same position always for the testing). Each magnet rotor has one magnet (the 1st one we placed) between the marks we made. The test magnet should attract this magnet on one magnet rotor, and repel it on the other. Then we can go around each magnet rotor and the test magnet should attract one magnet, repel the next one, attract the next one etc. If you made a mistake, you need to knock loose the offending magnets, put the template back on and get them right. Once all the magnets are placed and the tape is wrapped around them it’s a good idea to clean the magnets and the rotors one more time with laquer thinner to make sure there’s no grease. This will help the resin stick to the magnets.
Cut out two rings from fiberglass mat, or fabric. They should be 12″ in diameter, with a 6.5″ diameter hole in the center.
Grease the mold everywhere (Except on the bottom – that’s not necessary). A good mold release is car wax, or Johnsons wood wax. We’ve also used shortening from the kitchen and axel grease (axel grease is kind of gross and messy but it works). Grease it really well especially the first time you use the mold. The first coat tends to soak into the wood but after several applications it gets better. The point here is to make the mold greasy so the resin won’t stick to it. Once all the parts are greased well then run a bead of caulk around the outside of the 12.5″ hole in the mold. Also run a thin bead around the outside of the 1/2″ thick 6.5″ diameter disk. If it’s not still there, stick the 1/4″ drill bit in the center hole, we’ll need this for alignment.
Drop one of the magnet rotors into the mold carefully. It fit nicely on the smaller 2.75″ disk in the center of the mold so that the magnet rotor is a good fit and about pefectly centered.
Put the 6.5″ diameter disk down. The drill bit will serve to center it on the disk. The side that we’ve run caulk around should face down and we need to press it down onto the magnet rotor. The caulk will assure that no resin can run under it.
We use polyester resin to cast the rotors. We get this stuff from almost any autoparts store. It’s best to buy it by the gallon (it takes about exactly one gallon to build this whole machine). It comes with hardener in small plastic tubes.
It’s nasty stuff. It smells bad, the fumes are toxic. Best to work outside or in a very well ventelated area. Use safety glasses (the hardener is especially dangerous if you get it in your eyes), rubber gloves, and a respirator.
 It takes almost exactly 1 quart of resin to make 1 magnet rotor. (maybe a touch less) Usually a gallon of the resin comes with two tubes of hardener, each containing .77oz (22ml). When casting this stuff the resin tends to warm up and get hard much faster than it would in normal applications – especially if its warm outside and if the resin is warm to start with. We usually use about half the hardener that the instructions call for. This lets it harden more slowly – I believe it helps it to be stronger, shrink less and make things less likely to crack. There have been times when we’ve used half the tube for 1 quart (what the instructions call for) on warm days and the resin has become hard in 15 min or less! (it was hard before we could even pour it!) If it goes off too fast, there is also the risk of it catching fire. So be careful…
If you like, there are powders available to color the resin, or you can just use a little bit of acrylic enamel to give the resin a color. If you use enamel, I would use about 1 part paint to 50 parts resin.
Pour resin into the mold and over the tops of all the magnets. The mold needs to be level and it should be completely filled with resin.
Place the fiberglass ring over the top and work it in with a stick so it becomes saturated with resin. Work the air bubbles out as best you can.
Pour a bit more resin over the top and work that in. At this point it doesnt hurt to beat on the mold or vibrate it (with a vibrating sander or something) to work air bubbles out. Air bubbles won’t really hurt it, but they don’t look nice. We always get a few.
The lid also has a 1/4″ hole in the center. Place it down over the drill bit and on top of the magnet rotor. You can clamp it down with magnets, or bits of steel (wrenches etc..) because they’ll all stick to the magnets. C clamps are fine too but more work than necessary. Keep an eye on the resin that spills out of the mold. When it starts setting up clean the outside of the mold. Don’t take the lid off though untill you feel the resin is good and hard. In practice, depending on the tempurature and the amount of hardener we used I find this takes anywhere from 1/2 hour (which is scary fast – I expect cracks and shrinkage when it goes that fast) to 24 hours. It seems the slower the better with regard to shrinkage and cracking.
 Once the resin is completely setup we can remove the lid from the mold. Usually (if we made the mold well and greased it well) the rotor will just fall out of the mold when we turn it over. If it doesn’t, tap it on the back with a hammer and it should. Sometimes things get tricky and we have to pry it out, or even take the mold apart but this shouldn’t happen if we did everything correctly. The wooden disk on the inside of the rotor should knock out easily with a hammer through the hole on the back side of the magnet rotor. The edges of the rotor will be rough. We can cut the excess resin off with side cutters – or remove it with a sander. A belt sander works real well, but be sure to wear a dust mask. Clean up all the burrs so that nothing sticks up beyond the surface of the magnets.
 There we have a finished magnet rotor! Once one is finished – then repeat the process with the second one in the same mold. We actually use two molds (molds are easy to make) so that we can get all this done in one shot but if you’re not in a rush one at a time works fine.
 It’s only for cosmetic reasons and not important at all… but if you have a lathe available that’s large enough it’s fun to clean up all the edges that way. If you do, be careful and remember how feircely these rotors are attracted to steel. When cleaning up edges or deburring on the lathe, *DO NOT* use a steel file. Use sandpaper. A small flat sanding block is a handy tool on the lathe. A file, or any other steel tools that are not ‘part’ of the lathe should be kept away because of the magnets. I’ve seen magnets yank steel tools out of peoples hands on the lathe, it can be very dangerous. Again, this step is not needed – one does not require a lathe to build this wind turbine, it just makes things look nice. to return to the front page of this project.
5. ALTERNATOR ASSEMBLY
This page details how we assemble our alternator from all the finished parts. At this point we’ve completed all the metal work and it’s been painted. The magnet rotors and the stator are finished, and we’re finally assembling the machine.
Pictured above are the finished magnet rotors. They are identical, except that the front rotor (closest on the left in the picture) has 8 holes, 4 for the studs, and 4 for jacking screws which will allow us to lower it safely and raise it back off the alternator if necessary. Each rotor also has a small mark (a divet made with a drill bit) so that we can align the two rotors properly.
Here is the main chassis for the machine all painted and ready for assembly. It’s handy to have a stand so we can turn it around/position it for easy assembly.
Pictured above is the wheel hub, bearings, washer and nut. Not pictured is the cotter pin. Typically when we order the hub, we get the bearings. The washer, nut, and cotter pin comes with the spindle. The hub is Dexter part number 81- 9A, and the spindle is designed for this hub, but they are always sold seperately. Most trailer parts supply houses can provide this. I like the Dexter hub because it seems to be the most common one available, and it comes machined on both sides. Many hubs are machined only on one side which makes assembly more difficult. If a different sort of hub is used, I expect that the lengths of our allthread studs would change, and you may find the need to use extra shims to set the airgap between the magnet rotors properly. With this hub, things are very easy.
When delivered, the hub has 4 studs pressed into it (this is to accept the lug nuts that hold a trailer rim on). We need to knock those out with a hammer. It goes quite easily.
Pictured above is all the hardware required to assemble the machine except for the bolts/nuts that hold the tail on. I prefer to use all stainless hardware so that it can never rust, but this is optional except for the hardware that is near the edge of the magnet rotors that holds the stator. We will be relying on nuts and lock washers to act as ‘spacers’ between the magnet rotors, so it is important that we use fairly high grade hardware and make certain that all the nuts/washers that are used between the magnet rotors are the same height. I find that with cheap hardware this is not always the case, with stainless hardware it usually is. Here is a list of hardware:
- 1/2 – 13 nuts, qty 25
- 1/2 – 13 acorn nuts, qty 7 (we could use normal nuts instead – acorn nuts just look neat)
- 1/2 – 13 allthread 6.625″ long, qty 4
- 1/2 – 13 allthread 4″ long, qty 3
- 1/2″ lock washers, qty 18
- 1/2″ washer, qty 6 (I use the smaller AN style and they must be stainless. If we need to shim the airgap wider, we may require more than 6 of these)
These are the steel hubs we ‘sandwich’ the blade betwen. They are 6″ diameter with 4 holes on 4″ diameter to fit our Dexter hub. The one with the hole (2.75″) goes behind the blade, the other one goes in front of the blade. I show these now because they (one of them) come in handy when assembling our alternator. Otherwise we’ll not use them till we install the blades.
Before we assemble the alternator it’s important that the magnet rotors be clean. Often times while building these we find that bits of metal/grindings get stuck to the magnets. They lay pretty flat on there, but when we assemble the alternator (put the two magnet rotors on facing each other) all the chips will stand up and rub on the stator. We need to clean it now. A good way to remove metal chips from the magnet rotors is with duct tape.
The first step is to take the 4 pieces of allthread which are 6.625″ long and put one nut on. We screw the nut down on one end so that there is 7/8″ of allthread behind it.
Then we put the long end of the allthread through the backside of the wheel hub. Put on a lock washer, and another nut and finger tighten the allthread to the hub (no need to get things tight here – just finger tight is what we want). Do this with all 4 studs, and then run a nut onto the front of each stud so that about 1/4″ of allthread is protruding. So, if we look at one stud here starting at the front (left to right in the picture) here is whats important: 1/4″ of allthread, 1 nut, more allthread, a nut, a lock washer, the wheel hub, a nut, and then 7/8″ allthread.
We take the back magnet rotor (the one with only 4 holes) and turn it so that the magnets face down on the bench. (be sure the bench is clean from metal bits)
Take the back of the hub and put it into the hole in the magnet rotor, such that the ends of the studs (the ends that are 7/8″ long) are poking into the 4 holes. We do this to align things before we tighten anything.
Then we use one of the steel blade hubs (the ones above that are painted black) and place it over the studs on the top and it should come to rest on the 4 nuts that we put up there. (thats why we put those nuts there with 1/4″ of allthread sticking out). If we don’t have these blade hubs, we could use the front magnet rotor, I would do it with the magnets facing up so that we can tighten things without worrying about magnets grabbing our wrenches. If we do it this way with something to align our studs both at the top, and the bottom – we are fairly assured that the studs are well aligned and everything will fit together nicely.
Now we can tighten the nuts on both sides of the wheel hub. We should get them very tight, and the goal is to move only the top nut (the one with the lock washer under it) and not the bottom one, so that we are sure to have 7/8″ of allthread behind the back nut.
Then we can remove the hub from the top and the 4 nuts that held it there. We also remove the hub from the magnet rotor. Turn the hub upside down (so the back is facing up and we have 7/8″ of allthread sticking up). If the studs were cut accurately and the nuts positioned properly, the hub should sit pretty flat on the ends of the studs as pictured.
Carefully lower the back magnet rotor down onto the hub so that the studs go through the holes. The magnets should be facing down. Remember the hub is steel and the magnets will attract it strongly. If you bring it down right on center its fine, but if things are off center the rotor will grab the hub. Sometimes it’s handy to have someone holding the hub down and helping to keep things positioned.
On the back side of the magnet rotor each stud gets 1 lock washer and 1 nut. We can tighten these a bit with a wrech now, but it’s easier to really tighten these ones after the alternator is together.
Now we can grease our bearings. Press lots of grease into both bearings, work the rollers around for a while and be sure the bearing is well greased.
The front and back bearings are identical for this wheel hub. Put one of the bearings on the wheel spindle and push it back all the way. It’s probably a good time to mention… usually when you order a hub, it comes with a seal. We do not use the seal in a wind turbine, it creates too much friction and prevents easy startup. I believe if we grease the bearing well then they should be fine for quite a long time.
Carefully pick up the hub/back magnet rotor by the studs and place it onto the spindle, up against the back bearing.
Then insert the front bearing. Usually at this time I press a little more grease into the front of the bearing… can’t hurt.
The place the washer in front of the bearing.
Then tighten the nut over the bearing. Get the nut reasonably tight, and then back it off so that you can insert the cotter pin. Once the cotter pin is in, I usually back the nut off as much as the cotter pin will permit. We don’t want the nut tight, there should actually be a touch of play. You can feel how when the nut is tight, if you turn the hub it has a good bit more drag than when it’s just slightly loose. If the nut is too tight, the machine will not startup easily and the bearing will die young. There needs to be a touch of play here. This is a good time to spin the hub and see that the magnet rotor runs reasonably true. Rotors cut from 1/4″ steel are rarely perfectly flat, so we expect a bit of wobble and it won’t hurt anything, but the less the better. If there’s something seriosly wrong, now would be the time to catch it.
 Next we’ll mount the stator to the machine. Take the 3 pieces of allthread 4″ long and screw an acorn nut down all the way on one end. Then put one of the stainless washers on.
Insert them through the 3 1/2″ holes in the stator. On the back side of the stator we want another stainless washer, a lock washer, and another nut. We can finger tighen these – but we don’t want them real tight yet. Then run 1 more nut down about 1″.
Then put the assembly onto the wind turbine, the 3 studs should fit through the 3 holes in the stator bracket. We can adjust the back nut (the one against the stator bracket) with our fingers and set an approximate airgap (say 1/8″) between the stator and the magnet rotor now.
Now is the time to tighten the nuts on the stator. We should get these reasonably tight, but not so tight that we crack the resin. We won’t touch these again – any further adjustments should be made at the stator bracket, not the stator.
On the studs where they come out through the back of the stator bracket, we put a lock washer, and a nut. Now, using two wrenches we can set the clearance between the stator and the back magnet rotor. About 3/32″ is nice.
We also need to check and make sure that the stator is well centered around the wheel hub, we don’t want it rubbing here. If it’s not well centered – but our holes were drilled correctly in the stator then it’s usually because either nuts are not tight yet, or perhaps the stator bracket is warped. If need be we could bend the stator brackets a bit. If it’s not centered well it should be simple to find the problem and adjust for it somehow – but it’s very important that the stator have good clearance here.
 Pictured above are 4 Jacking screws (these were not shown or listed earliier with the hardware – these are tools, not part of the wind turbine). I like to cut them about 10″ long, they are made from 1/2″ -13 allthread. One end we double nut (jam two nuts together tightly) and the other end needs to have a slight chamfer ground on it. (this keeps them from getting ‘mushroomed out’ when they rub against the wheel hub) After we grind the end, we usually need to clean up the threads with a file. Test them by running a nut up on the end which was ground.
 Run the jacking screws into the front rotor so that about 3″ sticks out on the magnet side. Its nice to keep them very even (all of them poking out the same amount) or else things will bind up. Sometimes it’s a good idea to run a tap into the threads for the jacking screws before we do this – if the paint makes them hard to turn, clean the threads with a tap. A bit of oil on the screws doesn’t hurt either. It’s nice when these turn easily by hand.
Take note of the divet – it’s our alignment mark. I usually turn the back magnet rotor so that the alignment mark is poiting straight up (noon) and we’ll put the front magnet rotor on the same way – so that it’s alignment mark is also in the noon position.
Carefully pickup the front magnet rotor by the jacking screws (do not get your figers near the magnets – jacking screws make a nice safe handle) and place it over the studs sticking out of the alternator. Push it onto the alternator and you’ll feel the magnets ‘grab’ each other. It should pull down so the 4 jacking screws come to rest on the hub.
Then use a wrench and a bit of patience to lower the front rotor down. Keep the 4 jacking screws even. Usually it works best if we go around giving each jacking screw about 1 turn, and we go around the circle till the front rotor comes to rest on the 4 nuts which hold the studs to the wheel hub. This Dexter hub, and this arrangement of nuts/washers as spacers makes for about a perfect airgap if your stator is 1/2″ thick. If the stator is thicker than 1/2″, you may need to remove the front rotor and put washers behind it as shims. In most cases thats not necessary.
 At this point our alternator is assembled. The clearance between the rotors and the stator should be around 3/32″, 1/16″ is probably acceptable in some places but any less and I’d shim things out. One both rotors are on, we can fine tune the position of the stator using the nuts on both sides of the stator bracket. At this point we can test the alternator. One easy test is to short each phase. When any single phase is shorted it should become stiff – but kind of lumpy to turn (it will cog). When all 3 phases are shorted together it should become very stiff, yet very smooth to turn. If we have a tachometer we can also test it with regard to volts/rpm. If we run the output through a rectifier and measure DC voltage, we should be hitting ‘average’ battery voltage at around 140 rpm.
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