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From: stratton@...

So, if someone momentarily forgot that a screw was left-handed and
twisted it the wrong way, with the result that the nut came off and
spilled all the balls, how would that idiot go about reloading it?

Chris

I just went up to my shop, and found the roll of stuff I have been using.
It is 0.35" dia, plastic coated, and has give or take 21 strands. Trying to
cut it is a bear so might be stainless steel! The roll it came on is so
old, that no lables exist anymore so I can't help you there. This is some
stuff that was in the junk box, available and so I tried it! It works.
What with everybody doing CAD today, I'm not sure any of the office supply
houses even carry it anymore. But then I am some what limited in where I
can shop in the small town that I live in. When I went to Engineering
school, they taught me two things (and thats about all I can remember):

-----Original Message-----
From: stratton@... [mailto:stratton@...]
Sent: Thursday, February 24, 2000 10:19 PM
To: cad_cam_Edm_dro@...
Subject: [CAD_CAM_EDM_DRO] Stepper Power


From: stratton@...

I've attempted some calculations on the stepper motor vs power supply
size issue.

I took as an example Microkinetics 34M470, nomivally a 470 oz-in motor
in a Nema 34 frame. I haven't bought one yet, so I'm working entirely
off the data on their web site:



The various wiring voltage/current combinations all indicate that they
rate this motor for just under 15 watts of I^2R type power.

I looked at their graphs for performance with their various drives,
and used 7.4 x 10^-4 as the conversion from oz-in-RPM to mechanical
watts (it seems to be right, can anyone verify?). Their data and my
calculations give results like this:

500 ozin 300 rpm = 111 watts
100 ozin 2300 RPM = 170 watts
125 ozin 2100 RPM = 194 watts (1/4 HP)

These are of course marketing numbers obtained under ideal conditions
with the best drives they make, and quite possible overheating the
motors (the were running at 120% of rated current) But needless to
say, 194 watts is a lot more than 15W (or 21W), and getting this kind
of performance clearly requires a high voltage supply sized for the
larger number.

Working backwards, 300 watts (mechanical, winding heat, switching
losses, etc) at 50 volts requires a supply that can deliver 6 amps. Not
quite the sum of the rated current for the two windings, but only off
by a factor of 2 or 3.

It would thus appear that sizing the chopper drive high voltage supply
current based on the rated motor current results in a large but not
unreasonable safety margin. Obviously this is bad news cost wise, so
I'd be thrilled if anyone can poke holes in my logic...

Chris

From: "A. G. Eckstein" <axtein@...>

Joe,

Lets start from the botto, I also felt the same way when I started this
project. However I am using a "cable" that appears to be plastic coated
multi-strand wire. It is the stuff that is used on a parrallel bar for a
drafting table. Its tough and so far, does not appear to be slipping.

Check the diameter of the shafts on you encoders as mine were advertised at
3/16", but are actually 5mm. Makes a big difference when you order the
drill rod for the shaft and try to stuff it in the hole???

So far, on the two axis that I set up using this with the 5mm shafts (no
diameter reduction), I am getting a consistant 0.000177" resolution for my
units to count by. On the z axis, I am attempting to grouve the shaft to
reduce the diameter so I can get that magical 0.0001 resolution; but will
settle for 0.000125. I am afraid of the slippage problem at such small
diameters along with the possibility of bending the shaft due to tension of
the cable. It appears we are talking physical diameter of the shaft in the
bottom of the grouve on the order of 0.0988" ! But I had to buy a 3'
length of drill rod so I guess I can afford to try as I don't see any
additional projects in the near future that will use 5mm rod for anything
and I use only about 2 1/4" of rod per set of axels.If I start having
problems with this type of wire, may try some of the heavier guitar strings
(don't ask what note, I ain't no musician;_) )as it appears these have a
circular wrap around a central core thus giving the effect of a "tire
track" which would be parallel to the axis of the shaft rather than the
strands that are perpendicular to the the shaft.

Hey, I'm just a country redneck that is doing this for fun and the fact
that the numbers on the computer screen are eaiser to read than the ones on
the dial and I have trouble trying to read a scale even with a loupe! So
even if I am off a thou or so, that is still at least 20-30 times more
accurate than I can do with a scale and a scribe!!!!!

All fun aside, I want it to be as accurate a I can make it. Considering
what I am starting with:

1 An oriental mill/drill which we all know has its problems in the accuracy
department.
2 Acme thread screws that have a ton of backlash in them.

Yes, I desire positional absolute accuracy, but more often than not a
higher desire is to have relative accuracy. For instance, if I want to
mount a motor with a bolt circle fastening pattern, I want the central
mounting hole and the bolt holes to be really accurate. If it is off-center
of the plate I am machining by .050, big deal. In the case of the blocks
being machined for the DRO project, it is important to have consistant
accuracy between the bearing hole and the mounting holes etc. Exactly how
far from the edge of the block is of minor importance.

Another point on the encoders; when I ordered the encoders, I also got some
bearings they had advertised. Well, I ordered 10 and destroyed one of the
motors in trying to see how everything was put together. Got down to the Z
axis, and needed another bearing...Had run out of the loose bearings so I
went to dig the one out of the encoder end of the motor I destroyed. It has
a different OD than the one in the nose of the motor which was the same
size as the loose ones that I ordered. So If you are planning on useing
those bearings, please be aware of this small problem.

Art

At 09:08 PM 02/23/2000 -0800, you wrote:

From: Joe Landau <jrlandau@...>

Art,

I am starting to build a DRO for my mill--have bought motors
and encoders from Goldmine, and am planning the setup. I'm
curious how your wire loop worked out, --what path did you
use, and what kind of wire. I remember reading that Steve
was worried about slippage. Have you experienced any, and
how have you prevented it?

Intuitively, I'd think a steel wire on a very small steel
shaft could slip very easily.

--Joe Landau

OLDER THAN DIRT

Country Bubba

(Actually the inventor of Country and Bubba)

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From: "Murray Leshner" <multi-volti@...>

Hello:

If mounting a big NEMA 42 stepper motor (1125 oz-in) on something other

a factory-made screw-driven table (a direct drive application), what do you
suggest mounting the motor on? (how thick ...1/4", 3/8", 1/2" ?)

Thanks

Murray



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Welcome to CAD_CAM_EDM_DRO@...,an unmoderated list for the

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