Retlas "Manchester" Dynamo

[Chipmaster]

The pattern Lucas C40 armature shafts are 15mm diameter and far too short for this dynamo.

IMG_2161 (2) by Andy, on Flickr

So 3/4" diameter precision ground mild steel bar was bored out to fit over the 15mm shafts .

IMG_2168 (2) by Andy, on Flickr

The results of boring out of the 3/4" bar were surprising, far better than expected, the fit is so good that the air trapped inside acts like a spring, but its not tight. Perhaps I'll have to file a small flat on the shafts otherwise most of the Loctite 638 will be blown out when I push the shafts home.

I hope to use the 3/4" shafts as the are, just shortened a bit.

IMG_2173 (2) by Andy, on Flickr

Andy

[Admiral_dk]

Perhaps I'll have to file a small flat on the shafts otherwise most of the Loctite 638 will be blown out when I push the shafts home.

Thinking out loud - how about drilling a very small hole in from the side or the other end to let the air out and keep the perfect alignment ...?

[Chipmaster]

Yes Per that's probably the best solution. I cleaned the parts with acetone in case there was an oil film but still had the same result, reckon my Colchester Chipmaster lathe surpassed itself on this occasion.

This afternoon I machined the two bronze bushes that fit in the bearing pedestals. They're 1" od 3/4" id and 2.1/2" long.

IMG_2206 by Andy, on Flickr

IMG_2208 (2) by Andy, on Flickr

IMG_2210 (2) by Andy, on Flickr

IMG_2213 (2) by Andy, on Flickr

IMG_2214 by Andy, on Flickr

So far so good, the bushes line up and the length of 3/4" ground steel bar rotates freely, I hope the armature will line up and revolve freely with it's extended shafts.

Andy

[crueby]

Fascinating project, following along....   

[Chipmaster]

Cheers Crueby and Roger 

I have shortened the extension shafts for the armature to the required lengths and centre drilled the ends.  With the shorter extension I carried on with a thin long series drill right through the centre to allow air to escape and prevent the hydraulic problem I was having.

Here is the armature with it's extension shafts and bronze bearings.

  IMG_2228 by Andy, on Flickr

Over to the lathe, I could now remove the topslide and prepare the cross slide for line boring the dynamo.

Two 30 x 20 x 300mm bright drawn mild steel bars were fastened using two of the 5/16" UNC rear tool post mount threaded holes and the two holes vacated by the top slide mount. the centre drilled 1" precision ground mild steel (PGMS) bar lined up the whole job when supported between centres.

 IMG_2232 by Andy, on Flickr

There are two holes in the base which I will use to hold it down, one is arrowed in this picture.

IMG_2233 by Andy, on Flickr

Ready

IMG_2234 by Andy, on Flickr

Packing was used to raise the dynamo to the required centre height and the cross slide gibs tightened up to keep it in line.

IMG_2236 by Andy, on Flickr

The two bearing pedestals have been removed and I'll convert the one inch PGMS bar into a between centres boring bar tomorrow when I've found a suitable piece of round high speed steel for the tool bit.

IMG_2237 by Andy, on Flickr

Two reels of 0.75mm copper wire for the two field coils were delivered today. These 500g reels equate to approximately 142 metres or 465 feet per reel. That should be enough for at least 300 turns per field coil.
However, I also need to find something that can be adapted for the bobbins on which to wind the coils that will slip over the field coil steel cores.

IMG_2239 by Andy, on Flickr

Andy

[Alyn Foundry]

Hi Andy.

You're set up for what is most likely the trickiest part of the whole job, looking good.

Don't forget that the clearance between the " Pole pieces " to the Armature is but a few Thousandths of an Inch. If you underbore the diameter you can always use some shim Steel and if you overbore well you can take a little off each core.

For the bobbins there are a number of ways. PVC household water waste pipe with discs of plastic glued at either end is one method. Alternatively there are many plastics available in billet form so you could carve out a couple from the solid.

For me it was the " aesthetics " that mattered most. Once the coils were wound we used PVC electrical tape to hold them in place but then rolled on several layers of heavy duty Brown parcel paper to build up the bobbins. We then used White butchers string to " serve " the finishing layer. Boot polish was used to get the colour right and then a couple of coats of Shellac to finish.

The finishing touch was to sleeve the Copper wire with a cloth looking sheath.

Cheers Graham.

[Chipmaster]

Yes Graham, quite tricky, here's some line boring video.

<a href="https://www.youtube.com/watch?v=gqwiIp2joHs" target="_blank">http://www.youtube.com/watch?v=gqwiIp2joHs</a>

When I stopped work for dinner this evening the distance between the poles was two inches. In the picture below you can see how the machining hasn't yet reached the full width of the lower pole piece end nearest the camera but it should be ok when the diameter of the armature 2.376" is reached if my estimate is correct, the machined surface of the upper pole piece is fine.

IMG_2249 by Andy, on Flickr

Andy

[Dave Otto]

Looking good Andy!
Graham, that is a great idea using the butcher paper to even out the coils and make a nice foundation for the cord covering. I have always admired the how nicely the coils were finished on the old dynamos.

Dave

[Alyn Foundry]

Thanks for the " boring " video Andy.... 

A video like that is worth several thousand words of text !

I have only ever done " between centres " boring a couple of times myself, doing the main bearings for Vincent's Retlas engine. My Le Blonde RP has a very long front to the saddle, I simply drilled and tapped 4 holes to suit the base casting and bored away.

Going back to the bobbins I should have mentioned that they could also be printed too.

Your final job after the correct diameter is reached will be to take back/flat off the roughness of the pole pieces. This will ensure the magnetic field is transferred into the armature proper.

Cheers Graham.

[Alyn Foundry]

As Andy plugs away at the pole pieces I'll provide some information for the next stage of operations.

All DC generators will act like a motor if a DC voltage is applied to them. This knowledge will be useful in setting up the machine.

I wanted Vincent to go the whole way with his by fitting wire gauze brushgear. But Vincent didn't want to be messing and carved up the donor Lucas Dynamo for its Carbon brushes and springs. The very early machines all used gauze and used the natural spring in the material to keep them in contact with the commutator. This meant that the gauze had to be placed at a near right angle to the commutator instead of the direct on position of Carbon brushes. The drawing shows a rectangular housing with knurled " pinch screws " that hold the gauze layers in place and another screw to lock the housing to the support pillar.

The design suggests a Negative earth situation so that only one, the Positive brush, needs isolation from the frame.

This machine will be used in a " shunt wound " configuration which means that the Armature will be in parallel to the field coils. We shall have to wait and see if we need to use a shunt field resistance when the time comes.

Cheers Graham.

[Chipmaster]

I continued hacking away at the dynamo pole pieces this afternoon but the job was delayed by having to dig up dahlia tubers because of frost so I still haven't finished. A diameter of 2.3185" was reached by 5.15. About 65 thou left to reach the required diameter. The boring gar is removed periodically to measure the job with a telescopic gauge.

Using speeds of between 50 to 100 rpm with a high feed rate and ten to fifteen thou cuts, the finish is pretty good. With this set up I can leave the dynamo mounted on the cross slide, remove the boring bar and check clearance for the armature by mounting it between the lathe centres. I can also assemble the dynamo with the pedestal bearings to check the armature to pole piece air gap

So far I have guessed the cut  but if I want to increase the cut precisely I loosen the retaining grub screw and advance the tool bit by lightly tapping it from behind. The movement is measured by a dial test indicator.

 IMG_2253 (2) by Andy, on Flickr


Nearly done.

IMG_2256 by Andy, on Flickr

IMG_2260 by Andy, on Flickr

Hi Graham,  "Your final job after the correct diameter is reached will be to take back/flat off the roughness of the pole pieces. This will ensure the magnetic field is transferred into the armature proper."

Does that apply to just the horizontal surfaces such as arrowed in this picture or all over?

IMG_2259 by Andy, on Flickr

Andy
 

 

[Alyn Foundry]

Good morning Andy.

Yes, those are the areas to pay attention to. Just remove as much metal so as to clean up the faces.

As the armature will be in really close proximity to the magnetic flux generated by the field coils you don't need to worry about " air gap " at the sides.

Cheers Graham.

[Jasonb]

Graham, is the direction that the wire is wound in critical on a dynamo, I know it can affect the bi-polar motors?

I cut my bobbins for "lecky" from Delrin but they were quite a bit smaller so Grahams suggestion of tube with glued on ends sounds best.

[Alyn Foundry]

Hi Jason.

Not super critical because the magnetic polarity can be reversed electrically but it would be best if both coils were wound in the same direction.

What is different about the Manchester style is that the frame becomes one pole, either North or South and the top cover becomes the opposite magnetic pole. With this in mind if both poles are wound in the same direction they will both exhibit the same magnetic polarity with the same DC ( Direct Current ) voltage applied to the wires.

Cheers Graham.

[Chipmaster]

This afternoon I finished machining the poles to clear the armature. In this first picture the armature is mounted between the lathe centres with one of the shaft extensions.

IMG_2261 by Andy, on Flickr

The clearance was close, I could hear slight rubbing as I turned it by hand and the thickness of a cigarette paper was enough to jam it.

IMG_2267 by Andy, on Flickr

I advanced the boring tool by 0.0015" to add 0.003" to the diameter then tested the air gap with the armature mounted with the extended shafts running in the pedestal bearings.

IMG_2276 by Andy, on Flickr

The result seems pretty good, you can hear the rubbing sound in the first part of this video.

<a href="https://www.youtube.com/watch?v=ltWfr5HliUE" target="_blank">http://www.youtube.com/watch?v=ltWfr5HliUE</a>

My next jobs will be milling oil chambers in each of the two pedestals and a surface for the armature reaction compensator to rotate on the pedestal adjacent to the commutator. At this stage the bronze bearings are a push fit in the pedestals, I will use a Loctite retainer to keep them in place after the oil chambers are completed. The little holes for returning excess oil to the chamber look challenging, there may not be enough pedestal casting to do that.

Oil chamber by Andy, on Flickr

Andy