Magnet leveling

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Thorlick
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Magnet leveling

Post by Thorlick » Fri Apr 03, 2020 3:52 pm

I determined that my original cast aluminum magnet spools were damaged by my last effort at leveling (that means I was over zealous with my hammer after the last engine rebuild). I am now setting up my magnets on my flywheel and am trying an alternate method.

I do not have a KW magnet setting tool. Erik kindly offered the loan of his tool. That would require about a 60 mile round trip and a second trip to return it. I am going to revert to my original method with a new twist.

I installed all new spools and screws. Next I measure the height of the keepers and enter them on a state of the art spread sheet.

Measuring magnet height with micrometer
Measuring magnet height with micrometer
High tech spread sheet
High tech spread sheet
What I do after listing the magnet heights is to determine the limits of variance in height I find acceptable. Having polled a few knowledgeable T mechanics I chose 0.010”. That translates to +/-.005”.

So after checking the spread sheet I identified the target height at .005” below the tallest magnet. The first step is to add shims to all magnets which fall more than .010” less than the highest one.

I obtained some fine imported Bavarian shim stock measuring .004”-.005”. Using a notebook hole punch and a larger gasket punch shims were produced.

I had planned on sanding down some of the higher magnet’s spools but that might leave the ends out of parallel. It soon became apparent that the required precision could be obtained with one to two shims.

Fine Bavarian shim stock and shims
Fine Bavarian shim stock and shims
Shim being inserted
Shim being inserted


The result was arrived at by repeating this process adding and removing shims and re-measuring about three times before planned accuracy was obtained.

Spool with shim in place
Spool with shim in place


The next step will be to verify the job by putting the flywheel back onto the crankshaft and turning it to measure each magnet against the same field coil pad using brass feeler gauges.

This method is easy and non-invasive, no magnets or spools were harmed in the performance of this task!

TH




Terry Horlick, Penn Valley, (Northern) CA
1927 Mountain Patrol Vehicle from the Los Angeles City Fire Department (L.A.F.D.)
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Chris Barker
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Re: Magnet leveling

Post by Chris Barker » Fri Apr 03, 2020 5:14 pm

Do you have a spare starter ring gear?

I found that if you lay this on top of the magnet plates you can check that the ring gear is parallel to the flywheel face with a vernier depth gauge and you can identify the high and low spots very easily.

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Re: Magnet leveling

Post by KWTownsend » Fri Apr 03, 2020 5:27 pm

Nice work Terry

: ^ )


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Re: Magnet leveling

Post by J1MGOLDEN » Fri Apr 03, 2020 5:42 pm

I went through that problem a few years ago.

I measured the height of all the new spools and thought I could just assemble the magnets, as they were all the same.

That did not work so goo!

The magnets were a complete original set with all the same markings and were randomly .018 difference in thickness.

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Re: Magnet leveling

Post by Steve Jelf » Sat Apr 04, 2020 12:06 am

The first time I read or heard of lowering the high magnets by whacking them down with a hammer I hated the idea. I still do. I make my shims out of brass stock I picked up at some auction. I get all the keepers within two or three thou. Within the prescribed range of .025" to .040" I figure .002" or .003" is no big deal.

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Re: Magnet leveling

Post by Allan » Sat Apr 04, 2020 1:45 am

I went through a similar process on my last two rebuilds. In a chance purchase of some other toolmakers stuff, I found a pair of steel blocks with multiple machined holes with their sizes stamped next to them. In another drawer were numerous hardened steel slugs, which were a precise fit for the various holes except for one missing one. Using brass shimstock, sandwiched between the plates, the slug is driven through to make a neat punched hole, first for the screw and then a larger one to complete the washer. I got lazy in the end and cut the sides out to make C shaped shims which could be slid in place without withdrawing the screw each time.

Because he could, I had my godson put the flywheel on their surfacing grinder, and he took the last .002" variation out once I had finished. It sure made setting the gap to the coilplate much easier.

Allan from down under.

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Re: Magnet leveling

Post by Thorlick » Sat Apr 04, 2020 11:42 am

Allan, very clever solution. Probably way past the precision needed for a T Model!

Terry
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Re: Magnet leveling

Post by TeveS-Nor Cal » Sat Apr 04, 2020 12:16 pm

Great "fix"!

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Re: Magnet leveling

Post by Thorlick » Thu Apr 16, 2020 11:31 am

It is now about 2 weeks past when I started this magnet job. I have discovered that my method of setting the magnets works but that the limits I chose to stick to based on suggestions caused great grief to me. A really good mechanic suggested that .010" on the magnets is about the limit. I translated that to +/- .005", that is what I used measuring off the back of the flywheel. Next setting the magneto in one crankshaft position allowed that error to be duplicated, spin the crankshaft and you double the error (now .020"). I installed the engine and without the fourth main in that was bad enough to get a magnet plate ticking against the field coil casting when hand cranked.

Next I pulled it all down and re-visited the magnet heights. I chose to do this by identifying the highest magnets with feelers between magnet and field coil. I removed shims if the magnet had them and if less than a shim was needed (beer can aluminum is .004"-.005" ... no I didn't consume the beverage) I had dressed the spool on a bastard file until I got to the target spool size.

The next thing I did was to reset the magneto to the more level magnets. I used the method mentioned in the current Vintage Ford. This works really well. You remove magneto shims and mount the mag with the bolts loose... at least .050" loose. Then you bolt the flywheel on (I have marked my crankshaft flange and flywheel so I always mate the the same holes). By pushing the magneto ring up against the magnets you can use a feeler gauge to measure the gap at each of the four mounting points. To be clear you are measuring the space between the mounting surface on the block and the back side of the magneto ring. You decide on the gap you want to end up with and subtract that from your measurement to get the shim size needed there. This sounds hard but it is way easier and more accurate than the trial and error (lots of error!) method I used before.

Another thing I discovered is that common mag gap setting I have gotten from mechanics and from reading the literature available is .025" so you won't end up crashing magnets against magneto. This allows for flexing of the crankshaft (yikes!!!) due to gravity fourth main tolerance, and any off center of driven plate shaft when running in horizontal position. All this comes down to trying to get the truest running flywheel for the strongest mag, not hitting and not flexing the crankshaft. I discovered that Ford specified the necessary gap in the shop manual as 1/32". That is .03125" which is .00625 more than what is now recommended! So not only have I been compounding my errors I was choosing to set the magnets closer than Ford recommended.

So now after assembling and disassembling, installing and pulling the engine several times I have arrived at an acceptable result. I hope to be driving it this evening.

The whole procedure was needed as last time (6 months ago) I got to a .001" magnet setting goal by whacking magnets and ruing the spools. Now by carefully setting up the magnets with a micrometer, shims and filing spools, the job can be done fairly easily.

My take away is use the KW magnet setting tool). If you don't have the tool then you can set the magnets by micrometer but you must hold to a maximum tolerance of +/-.0025" on magnet heights. Remember you have error on magnet height which doubles whilst setting the mag which will have some error when mag is shimmed to the block. If you feel +/- .010" is close enough for magnet to mag gap tolerance (on a .03125" gap) you are not going to get there by allowing +-.010" on the magnets. That would use up all of your wiggle room on your first step.

I am preparing to do the engine on my 1912 Omnibus. I will shoot for +/-.0005" on it's magnets. My method can get you there without too much effort once the procedure is learned.

TH


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Re: Magnet leveling

Post by Dan McEachern » Thu Apr 16, 2020 2:36 pm

Terry's posting highlights the importance of getting the magnet clamp heights all the same. IF you have the ability or access, another method that takes this to the next level is to roughly set the height, then chuck the entire flywheel in a lathe, indicate the rim of the flywheel and face off the magnet clamps. Then I also face the crank mounting flange surface of the flywheel, removing only a few thousandths. This 2nd step keeps the magnet clamp surface dead true to the crank flange, eliminating any source of runout.


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Re: Magnet leveling

Post by Allan » Thu Apr 16, 2020 8:35 pm

Dan, not being able to swing an assembled flywheel in my lathe led me to have the magnet clamps trued up by mounting the flywheel in the machine shop grinder set up for this purpose. The grinding process seems so much more gentle than the interrupted cuts made on a lathe. We proceeded gently, finally stopping just as the last of the keepers was kissed by the wheel. A side benefit of grinding is there is less cleaning up to do when the grinding is finished.

Allan from down under.


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Re: Magnet leveling

Post by Dan McEachern » Fri Apr 17, 2020 12:02 pm

Most automotive machine shops have flywheel grinders that would make short work of kissing the top of the magnet clamps but they would not be able to grind the mounting flange because they can't get down into the 4" dia counterbore. The interrupted cut in the lathe is never a problem because the cut is very light and we use a sharp tool with a diamond lapped point and small nose radius to keep the cutting forces to a minimum. An air blast during this makes short work of the tiny chips- must better in fact than trying to clean things up after.


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Re: Magnet leveling

Post by J and M Machine » Fri Apr 17, 2020 12:41 pm

You guys are going about leveling the hard way. As Dan McEachern says and it's the way we do it quick and easy.
Any local machine shop can resurface the magnets as we have .
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Re: Magnet leveling

Post by Steve Jelf » Fri Apr 17, 2020 12:44 pm

The official magneto gap is .025" to .040". That's a range of .015". Does a variation of .002" or .003" within that range really have any appreciable effect on magneto output?
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Re: Magnet leveling

Post by Thorlick » Fri Apr 17, 2020 5:56 pm

<<<The official magneto gap is .025" to .040". That's a range of .015". Does a variation of .002" or .003" within that range really have any appreciable effect on magneto output?

Steve, it is possible for some folks to misunderstand your post. You are referring to two different measurements. Gap between magnets and field coil and the totally different magnet height variation.

The allowable gap (.025"-.040" is a range of .005" ) can be expressed as .0325" +/- .0075.

So allowing the magnets to vary .003" means your gap must be held to .037"-.024" to remain in specs. The variation on magneto output varies with the square of the gap so no, a .003" change is negligable . Since the target gap is .030" the variance of .003" in magnet height is 10% of the gap. The square of 10% (.1 X .1 = .01) is 1%. If one magnet was moved .003" it's effect would be on 1/16 of the output since there are 16 magnets. So the output would decrease 1/16% which is 0.0625% truly negligable.

What my original post was concerned with is being able to assemble the flywheel with normal hand tools and not end up with a magnet striking the field coil or going out of specification. Leveling the magnet keepers with a surface grinder or on a lathe is absolutely the fastest and most accurate method. One could just about bolt anything up with no measuring and have a superlative result by grinding or turning. Of course the surface grinder or lathe is not a hand tool and not in every shop. You would also be well advised to dynamically balance the flywheel after surface grinding, and to remove all grinding particles from the magnets afterwards... I'm not sure how to do that (pressure washing?). Not everyone wants to add a shop charge on to the magnet setting procedure.

IMHO, TH
Terry Horlick, Penn Valley, (Northern) CA
1927 Mountain Patrol Vehicle from the Los Angeles City Fire Department (L.A.F.D.)
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Thorlick
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Re: Magnet leveling

Post by Thorlick » Fri Apr 17, 2020 6:20 pm

A quick question for the folks who surface grind their flywheel assembly. Back in the 1970's whilst I was awaiting the results of my dental board exams I worked in a machine shop which was surface grinding parts. The parts were held down with a magnetic chuck and ground under water coolant spray. Do your shops clamp the flywheels down or use a magnetic chuck?

The point of this question is I wonder if a magnetic chuck will affect the flywheel magnet's magnetism. I don't know if a magnet chuck works on DC or AC. I could see a chuck decreasing the magnet charge. It probably wouldn't be an issue on my flywheels as I always recharge the whole unit (I zapp it with my 50VDC 250 A arc welder).

TH
Terry Horlick, Penn Valley, (Northern) CA
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Re: Magnet leveling

Post by Dan McEachern » Fri Apr 17, 2020 7:30 pm

Most flywheel grinding machines do not have magnetic chucks- they use a center bolt and a centering cone to hold the flywheel to the grinder table. Just pointing out that a commonly available service of automotive machines shops is flywheel resurfacing, where as most automotive machines shops probably don't have a lathe large enough to chuck up a flywheel, and if they do, it probably means pulling the gap piece out of a smaller machine, which is a PITA= $$$.

Electromagnetic chucks use DC power. Running AC thru a chuck makes it into a demagnetizer.

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Re: Magnet leveling

Post by Thorlick » Sat Apr 18, 2020 12:13 am

Dan, you just hit the reason I wanted to know about AC on the chuck. I wondered if someone was using a demagnetizer to hold a flywheel down.

TH
Terry Horlick, Penn Valley, (Northern) CA
1927 Mountain Patrol Vehicle from the Los Angeles City Fire Department (L.A.F.D.)
1912 Omnibus project

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