it was square

[hamitduk]

Well it was square, and now it is round, not the first step. I have completed the 3d Cad drawing and have started the machining on the plates. Looking forward to the spin testing in a day or two. This is getting more fun, it keeps me off the streets!

Hami

Hami

[SparWeb]

Nice work!

So by now you must know which takes longer: 5 hours slowly cutting that plate with a bandsaw at about 1 foot per minute, or 5 hours cranking the plate round and round plunging the cutter 10 thou per trip!  :-P

[hamitduk]

Yup, sure do, need to buy plasma cutter. It was this or my Dremel and the dremel was a chargeable so I used the mill. My next project after this is a CNC table with a replaceable mill/plasma cutter head.

Hami

[richhagen]

plasma cutter, yup, its fast, but I'm not good enough with it to cut a perfectly neat edged circle.  Last two small circles I cut required much more time turning them past my grinder than cutting them.  That looks slow and hard, but at least you have nice neat edges.  Rich

[hamitduk]

Naw, just make it rough round with the Plasma cutter and then turn it.

Hami

[paulb662000]

Try a google search for "plasma circle cutter" there were a number of links that have options that should be fairly easy to fabricate.

Paul

[hamitduk]

And now it round and ready to be turned!

[Ungrounded Lightning Rod]

Looks like good work.

= = = =

One thing I have wondered about:  Why not leave the edges of the disk rough and out-of-round if you don't have the tooling to conveniently and quickly make it round?

Balance isn't an issue: You'll need to static-balance the whole assembly anyhow once the blades are attached.  The rotors are very close together so dynamic imbalance from a small (or even large) error in the alternator disk edges should be tiny - especially compared to even a slight fore-aft offset of a blade tip or a blade's density.

Most of the field in the rotor disks goes essentially directly between adjacent magnets so edge wiggles won't foul the genny.  And the size of the rotor's edge is small enough that it won't be a big deal for wind resistance.

So it seems to me that, while a nice round edge makes things clean and pretty, the operation of the mill would be just fine with the disks having rough, or even polygonal, edges.  Just grind 'em smooth enough that they don't tear up things (like your hands) that come in contact with them during assembly or by mischance during operation.

[hamitduk]

It is not a issue of flux, it is aerodynamics and balance, any force that is consumed can't be used to create power. So if there is any drag or power used by rotation that is a wattage lost. One watt an hour, 24 hours a day, over a year its it's 8.6k. A 400 watt ginny thats 21.5 hours of fly time. Is it worth it?

If the flux went directly between adjacent magnet you would not need a steel backing plate?

I have a background in Auto racing and marine construction, I will not have a problem making my blades true. Maybe I just real anal from my history, but I have won more than I have lost. We will see if this works.

But you do have the equipment to make it round a simple grinder, the rotors just by there name rotates, mount them spin them with the grinder. There now round, you don't need a lathe to turn something.

Hami

[bj]

  Nice Hami--I will be following the same path.  Same backgrounds, I

expect

  bj

[Ungrounded Lightning Rod]

If the flux went directly between adjacent magnet you would not need a steel backing plate?

The flux comes out the back of the magnets and goes from one to another through the steel backing plate.  But it mostly goes between adjacent magnets and primarily through the part of the backing plate between them.  It spreads out some.  But out near the edge of the disk it isn't strong enough that much would try to hop through the air and reduce your strength.  Similarly in toward the middle.  The flux return path is mainly along the donut of the backing plate that is under the magnets.

I'm all for cleaning up and truing the disk.  Especially if you have the equipment and experience to do it easily, quickly, and well.  Then you know what you have and there are no surprises.

I was just wondering "aloud" whether those of use who DON'T have a lathe and years of shop experience might be able to make do by hacksawing a polygon, cutting a hand-guided bandsaw/sabersaw-accuracy disk, or making some other approximation to a true and smooth disk without incurring significant performance penalties.  (IMHO it should work quite well.)

[hamitduk]

We do with what we have, and share with those that don't.

Hami