Tailstock Tales ?

Alchymist

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If you want to talk about microwave precision - phase matching semi-rigid coax cables at 18 Ghz - by hand trimming. I'll let you do the math - wavelength at 18 Ghz divided by 360 = length in inches per degree. Spec was usually 2-3 deg.
 
Randy, got to agree with you there. Worst challenge I ran into was a set of 2 way splitters (3 input, 6 outputs, + reference cable). All 6 outputs had to be phase matched to the reference cable within 3-4 degrees. Kicker was that they were not all on th same wave. Some were like +630, 720 deg, etc in relation to the reference.

Big thing was, had to have cables with one connector installed, and trim with a dummy connector, have 2nd connector installed, and rematch. And the temperature cycling they went through - many cycles. As to temp vs phase changes, most of the cable sets were installed in close proximity to each other, so they all saw the temp change together. And then some of the devices you run into - magnetic fields used in ways hard to comprehend.

But, guess we have strayed from the subject .......better shut up I guess.
 
Commutator dressing sticks are great but they do not get the Commutator on the armature perfectly round, they will leave it still egg shaped. What they do is mainly seat the brushes to the commutator while cleaning it up. I have a few differnet types of stones, those that just seat the brushes and those that grind off the copper.

I have gone to DCGT insert cutters. Leaves almost no undercutting. the copper comes off in a fine spray.

As for holding the centreless shafts, Bison makes a 3 jaw chuck bearing in it and mounts with a MT shank. different chucks have MT2 MT3 etc. These work much better than the old Jacobs sleeve type chucks which I have as well.

Walter

RandyC link=topic=682.msg3673#msg3673 date=1296598721 said:
I didn't know that the part had to be warmed, I was assuming that the parts that must adhere together would simply have a light coating of shellac applied and then pressed together at the "tacky" stage (which happens rather quickly with shellac). That shellac trick is definitly going to be tried out before the week is over, it beats the tar out of using carpet tape on fragile parts !!!

Another FINE tip that I will not forget: super glue and baking soda ... who would have imagined ? From your photo, I see what you mean about the odd angle of the dressing stone. That is also a good tip, I've turned many motor and generator commutators back in the day (before automobiles had alternators) and using that little Atlas saw to de-burr the copper and undercut the mica was always a pain. (If I still owned that old lathe with the commutator goodies, I would have included photos of those tools in this post - they are pretty clever in their own right.)

Many thanks,
Randy
mumbles link=topic=682.msg3658#msg3658 date=1296593256 said:
Funny how common items like Bees Wax and Shellac come in handy for metal working.
These methods that were used in years past, are nearly lost in these times.

Here are Shellac chucks that came with my Levin lathe.
Some, the faces have concentric circles cut in, some are plain. I dont know if the circles help with holding, or are to help centering the part.
The watch guy would shellac the face of the chuck, then use the alcohol lamp to heat the chuck and set the part.
http://s170.photobucket.com/albums/u265/donsmonarch10ee/?action=view&current=levinlathe-1.jpg

I think this is still on subject.
For holding parts with glue "right now", super glue, that normally does not work on metal, plastics, or in this use, gluing an abrasive stone to a stick.
The way this works is, lay down the glue, toss some baking soda on top, blow off the unstuck soda, more glue and soda. Do this until you have it built up like a weld.
You can actually machine this stuff. Sort of hard to remove however.

This application I am gluing a small piece of an "Ideal Industry" commutator dressing stone to a stick, to dress a commutator on my Monarch lathe.
This is done with the machine powered up. Need to do this to get the stone in the tight area.
Harley guys, this works on your old generators!
The Monarch guys scoffed at this, however it says to do this on the electrical panel on the machine.

What is nice about this, it gets the commutator perfectly true, and does not smear the copper between the bars like cutting in a lathe, no undercutting needed.
http://s170.photobucket.com/albums/...?action=view&current=commutatorstones.jpg

http://s170.photobucket.com/albums/...ction=view&current=commutatordressing.jpg

Several years ago, I took some parts that were a high nickel alloy, they were made a couple thou too thick, and were thin. they needed to be ground.
I used super glue and baking soda to nest them on a ground steel plate, building up the super glue and soda around them.
I had to soak them in a solvent I got at a model airplane shop for a couple of days for them to release.
One word of caution, super glue and soda will stick you to anything instantly!
 
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Randy, I hope people pay special attention to reply#1, 2nd photo and the well written explanation below it.

Seemingly too few people are aware of the "tangent" method of determining or setting up an angle or, on a lathe, a taper.

It is not only accurate but extremely easy.

Thanks for explaining better than I did when I mentioned it in a post about a week ago. Your quality photo is also worth a book of words.
 
Re: Tailstock Tales ? Now armature trueing

Mumbles

My main business is repairing power tools and electric motors.

There are a lot of factors involved, ranging from copper content and hardness of the commutator, the type of brush be it carbon or graphite, or mixed with other ingredients etc and its hardness. Also the Voltage and Current that is passing through the brushes etc.

Comm Stones come in different grits and types, some are cutting stones that will actually remove the copper, others are only dressing stones that seat the brush to the comm.

Depending on how worn the comm is, it can take several thou of cleaning to bring it into a true cylinder. I have seen comms that have had better than 1/16" of dishing. Comms also tend to wear out of round and develop an egg shape.

If you are using a stone to true the comm, and using it freehand, it will grind off the high spots, yes, and it will bring the comm close to round, but will not get it perfect. A true comm can only be obtained by spinning in a lathe with fixed tooling, or by spinning in the motor, if it is large enough, again with a fixed tool that cannot ride up and down with the comm. the idea is that we do not want to have the brushes oscilating up and down in the holders, just slowling being feed into the comm as they wear.

On those 3" comms, it tends to work not bad with the stones, but on a 1" comm in a power tool, where there is not even enough room to get a stone in there, the lathe is the only option.

Walter
 
Nice writeup, as usual (and expected :) ). I can add one small tip to tailstock use. I don't do a lot of small work like many hobby machinists, or model folks, but occasionally I need to turn a small diameter part. I sometimes use a collet on the mill and tool on the table or in the vise, but if I need a center for support because of length, that won't work out. I have a handful of cut off taps that have the center hole in the shank end that I can chuck in the tailstock. I then turn a 60 deg point on a sacrificial length on the end of the part I need to turn. The inverse center in the tap shank provides support for machining. I have used this method down to about 0.020". The advantage is obvious: There is no need to drill a center hole in the work. After finishing the turn, simply cut off the "point" to finished length. It is a dead center, so of course a bit of lube is required. Also, since the workpiece is small, pressure from the tailstock must be carefully regulated.
 
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