Weston Bye Magnetic Gear Clock

[kvom]

After a weekend away from the shop, I made a few parts sufficient to mount the rotor shaft securely. Then attached the coils and pole pieces to the frame.  At this point, I should be able to hook up the circuit board and power supply, and see if the rotor will turn over.  It should turn at 1 RPM, as it drives the second hand directly.



I ordered the N52 magnets for the damper circuit today on eBay, so they should be here by the weekend.  I'm still working on the best way to machine the damper disk, which is 3.9" diameter but onlyt 1/16" thick.

I also decided to try to (try to) make the large magnet wheel from clear acrylic, and the chapter frame from acrylic as well.  I ordered a couple of 12x12x1/8 sheet from McMaster this morning.

[kvom]

This morning I made the damper disk for the second time.  My first try was from 1/8" brass that I tried to mill flat to 1/16", but the result was uneven and had a twist.  This version is made from 3/32" aluminum, thicker than in the plans but should be workable.  Disk diameter is 3.9".



In operation the steel fork at the bottom contains 2 neodymium magnets on either side of the disk.  When the rotor turns along with the disk, the magnets generate eddy currents that act as a brake to keep the rotor from overshooting.  I'm waiting for the magnets to show up in the mail, and the damper will be easy to test.  Presently when I spin the rotor it will keep going for several minutes; with the damper in operation it should slow much more quickly.

[kvom]

I received the neodymium magnets in the mail this morning, and inserted one into the eddy current bracket.  Even without the second one the braking is quite pronounced.  If I give the rotor a good spin it stops within a single revolution.  I'll need to insert the second when the rotor shaft is disassembled; it might not even be needed.

[kvom]

Today I took the frame/rotor and PCB to my friend's place, where he soldered push-on terminators to the coil leads and right-angle pins to the PCB.  Then when he tested the recommended JameCo wall-wart, which supposedly output 12V, we found it was giving 18V.  So then it was off to Radio-Shack to get another type.  Back after lunch, we measured 13.5V output, so he soldered on the terminators and hooked everything to the PCB.  With the power attached, we got no movement on the rotor.

He used a logic probe on some of the board leads to determine that its output seemed correct, each firing every three seconds.  After a nit of head scratching, we tested the magnetism on the pole pieces and got very weak force.  It turned out I'd used some drill rod for the coils that is only weakly magnetic.

Went home, found some steel rod that attracted the damper magnets strongly, cut to length, and replaced them in the coils.  After hooking it all up and plugging in the power, I got motion of the rotor.  Unfortunately that motion is jerky and mainly in the wrong direction,  So more fettling is needed.  I suspect that the separation between the rotor lugs and the poles is too large, and I'll need to remake the pole pieces. 

Here's a shot of the board and its connectors.

[kvom]

Here's wheel A made from 1/8" cast acrylic sheet, using almost identical machining.  None of the operations resulted in any chipping of the edges.  I used a 1/4" HSS O-flute mill, a type of cutter recommended to me on another site.  This tool has a single cutting edge and a very wide and long flute.  The 3 inner pockets were machined with this bit.  The outer rim I cut with a 2-flute carbide EM.  This left a sharper burr, but being plastic is not a real issue.  The inner pockets were chamfered, and this too worked well.

The photo shows the brass and plastic versions.



I now feel confident about making the large 7" diameter wheel from acrylic, as well as the chapter ring.

[Heffalump]

Fantastic work kvom. I'm really enjoying watching this.

[kvom]

Machined the large wheel using a piece of aluminum as the fixture plate.  For support I used a set of 12" vise jaws I got from Monster Jaws, in which I milled steps.



Then made the magnet pockets in brass strips that form the rim.  I had to make these in 3 separate pieces in order to fit 4" wide brass sheet.  The flat head 2-56 socket screws are stainless and thus non-magnetic.  Since the wheel is now effectively 1/4" thick I made the brass hub thicker by 1/8".



Then some test fits.  I discovered that I'd messed up the small wheel that is connected to the large wheel's shaft by countersinking the wrong side, and also not milling a relief groove to clear the bearing.  So that wheel will need to be remade.  I also did remake the bearing carrier as I noticed it was drilled off-center.

The shaft lengths seem to be critical in getting the wheels to be close but not touching.  The two intermediate shafts are easy to adjust, but the shafts that go through the bearing carriers are harder.  I won't really know until I get everything  assembled.

[kvom]

Remade wheel H, this time correctly plus the end of the shaft that attaches to it.  I'll wait to make the head of the shaft that clamps the large wheel when I have all the pieces assembled and can check clearance.

Then I mounted a scrap piece of 4x4" acrylic sheet and tested out engraving the numbers that will go on the chapter ring.  Used a 1/16" V-tip engraving bit I bought years ago but haven't ever used.  Looks as if a .005" depth gives the look I want.  It was hard to get a photo, but found this old wood background:



The acrylic bows when clamped in the vise, so I'll need to bolt down the big sheet on the fixture plate and try to it as level as possible to get even line widths.  I might even reset the stock height for each number.

The font is French MT.

[kvom]

Started the day trying to drill the mounting holes in the acylic sheet, but I've found that with the 12" aluminum jaws the vise interferes with the mill column on both the bridgeport and the CNC mill in order to get the full 11" Y travel needed to mill the chapter ring.  After some cogitation I think I have a plan that will work.  If it does I'll post the setup later.

Went back to the rotor test; enlarged the holes for mounting the electromagnets and moved the pole pieces closer to the rotor teeth.  Finally I'm able to get the rotor to turn, although it's motion is jerky.  Here's the test run:

<a href="https://www.youtube.com/watch?v=mf7RgXRrV60" target="_blank">http://www.youtube.com/watch?v=mf7RgXRrV60</a>

The rotor wobbles on its axis so I need to investigate and see if getting a flatter rotation will make it smoother.

[kvom]

Since I found that mounting the 12x12" sheet for the chapter ring wouldn't work with the vise, I took a different tack.

When I bought the CNC mill in 2009, I got it with the tall column, thinking this would allow me to machine much taller pieces if the need arose.  However, I failed to take into account that the Z travel is the same with either column, and as a result I could not reach the top of the vise jaws with tools even with the spindle all the way down.  My solution for the past 4+ years has been to mount vises on a 6" tall cast iron tilt table.  I was able to use the school's large surface grinder to grind the top of the tilt table, and it's been a quite good solution.

Now, with the vise removed, the top of the tilt table is still too low to machine flat stock fastened to its surface.  My new solution for this was to take 4 steel blocks, all approximately 2" cubes, and use the surface grinder to make 2 sides of each flat and square to the other.  By grinding all 4 blocks at the same time, all ended with the same height, to less than .001".  Then placing these on the mill table and under the tilt table, the mill's spindle nose is less than 2" above the tilt table surface.  This will be close enough to mill the chapter ring.  I'll need to hold the engraving tool in a drill chuck as it's too short to reach still.

Here's a pic of the tilt table and steel cubes on the mill table.  The tilt table surface is flat to within 5 tenths across the X direction, but the back surface is lower by 10 thousands compared to the front.  Not normally a big problem in normal milling, but I'll need to shim the acrylic sheet for the engraving.

[sshire]

Looking like you're
 closing in on it.

Dave (dreeves) had his running all weekend at Cabin Fever. Kept perfect time. Didn't miss a beat.

[kvom]

I got the fixture plate and acrylic sheet mounted to the table, so started the machining on the chapter ring.  Doing the numbers first while the sheet is relatively flat, I measured the height at each position using a DI compared with the surface at 0,0,0.  I wanted to ensure that the linewidths engraved were the same everywhere, and since the surface height varied by .01", I decided to use a separate machine OP for each variation in height.  Basically, programmed a tool change for each different height, moved the spindle over the next number to be engraved, and set the tool height using a gauge block.

All was going well until, with 4 positions to go on the seconds dial, the drill chuck holding the engraving bit decided to open, flinging the bit across the table and snapping its point.  Luckily no damage to the plastic sheet resulted.  So I ordered a carbide 60-degree chamfer bit from McMaster, which will be long enough to hold in a collet, and which will allow me to finish the last engraving.  In the meantime did the two center cutouts and shut the mill down with the spindle at the 0,0 position, so it will be ready when the new bit comes in.

[kvom]

While waiting for UPS to deliver my chamfer bit and let me finish the chapter ring, I decided to do a trial assembly of the parts I've completed.  The photo shows everything but one of the intermediate shafts with two wheels.



Found some things to fix,  mainly to remake the center shaft, where the rear part is about 1/8" too long.  The front intermediate wheel also rubs the center portion, so it's diamter can be a couple of thou smaller.  Also need to move the big wheel forward a bit and finish its shaft.

I'm debating whether to try to polish all the brass wheels before I glue the small magnets in their pockets.  In any case, leaving on a 2-week trip on Saturday, so that won't happen before then in any case.

[Kim]

That's looking pretty serious!  It's fun to see it come together, isn't it!
Kim

[kvom]

After 10 days away, including a visit to NAMES, time to get back to the clock.  Put it all together for a fit check and discovered two tight spots with clearance issues. 

The front 6 magnet wheel is very tight to the rotor, so dd a bit of filing.



And the front 24-magnet wheel is close to the collar of the center shaft.  Took .04 off the collar to clear.



Then took it all apart for some finishing.  I used a buffing wheel on wheel A to get an idea of how the brass would look polished, but I didn't care for the result.  The brass stock has marks from the rolling mill that would be too hard to polish out, and besides most brass clock movements are not polished.  So I just used some 600-grit paper on the 5 larger wheels to get a matte finish.

Then used some Casswell Perma-Blue to color the steel parts - rotor, damper frame, and the poles.



In most light they look grey rather than blue, but the coloring should prevent rust.

Finally, glued in half the magnets.  All the alternating holes with the same polarity.  The other holes will have the opposite polarity.  That's the job for the next day, followed by reassembly to see if the damn thing will work.



Here's a pic of the chapter ring I finished before leaving on my trip.



As an aside, here's an interesting version I saw at NAMES.  All made from Corian:



Seems any rigid, non-magnetic, machinable material could be used.