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I have my Grizley MiniMill working. I've taken some photos, will post
them to my web site when I get a chance.

For motors I used some NEMA 23 motors about 4" long that I found
surplus- the only speck I have is that they cost $15. They have no label
or makers name. They are the same size as the ones usually listed at
150-180 oz-in. They are 200 steps/rotation, and measure 2.4 ohm per
coil- ignoring the center tap.

I have a slo-syn 430-th driver module, selected because it was $10 at
the MIT flea market. It is capable of 3.5A, so I started runing the
motors with it at full current, but the motors seem to get very hot-
after 20-30 min they were to hot to hold onto. I lowered the current to
about 3 amps and the motors sounded smoother, still run as fast as my
program will drive them, but still get very warm.

So, how do I select a current for a motor when I dont have a spec?

I also note that at certain speeds, while the motor is rampning up to a
long move, the belts will vibrate a lot. They seem to steady out when it
reaches steady speed. I have measured and I am not loosing steps, so I
dont think its a motor resonance problem. Should I worry about this
vibratiopn?

ron

Ron Ginger wrote:

I also note that at certain speeds, while the motor is rampning up to
a
long move, the belts will vibrate a lot. They seem to steady out when
it
reaches steady speed. I have measured and I am not loosing steps, so
I
dont think its a motor resonance problem. Should I worry about this
vibratiopn?

This ocurrs when the length of belt causes it to resonate (like a guitar
string) at the
step frequency. It could cause some wiggles in the cut being made. If
not, I
wouldn't worry about it. There's not much you can do, either. The only
thing
I can think of is to have some springy material that touches the back
side of
the belt, but doesn't interfere with the movement of the carriage. This
would damp
out any vibrations.

Jon

--- In CAD_CAM_EDM_DRO@..., Ron Ginger <ginger@s...> wrote:

I have my Grizley MiniMill working. I've taken some photos, will

post

them to my web site when I get a chance.

For motors I used some NEMA 23 motors about 4" long that I found
surplus- the only speck I have is that they cost $15. They have no

label

or makers name. They are the same size as the ones usually listed at
150-180 oz-in. They are 200 steps/rotation, and measure 2.4 ohm per
coil- ignoring the center tap.

I have a slo-syn 430-th driver module, selected because it was $10

at

the MIT flea market. It is capable of 3.5A, so I started runing the
motors with it at full current, but the motors seem to get very hot-
after 20-30 min they were to hot to hold onto. I lowered the

current to

about 3 amps and the motors sounded smoother, still run as fast as

my

program will drive them, but still get very warm.

So, how do I select a current for a motor when I dont have a spec?

I also note that at certain speeds, while the motor is rampning up

to a

long move, the belts will vibrate a lot. They seem to steady out

when it

reaches steady speed. I have measured and I am not loosing steps,

so I

dont think its a motor resonance problem. Should I worry about this
vibratiopn?

ron

Ron,The docs that comes with dancam and dancad have some information
on how to figure out the courrent neccessary.I've being running my
step motors that are rated at 5v and 1amp max per fase, at
0.300amps/fase and there isn't much difference on the torque.
the motors are double stak and are rated at 120 0z/in at the
maximum volts and amps.They are made by pacific scientific and cost
only $40.00 double shaft.
try to add a tensioner on the belts a see what happens.
step motors run hot specialy when stoped,but not to hot or it will
desmagnatize.If you can't hold it with bare hands than lower the
courrent.
Hope it helps.
Fogassa.

step motors run hot specialy when stoped,but not to hot or it will
desmagnatize.If you can't hold it with bare hands than lower the
courrent.
Hope it helps.
Fogassa.

Using what you can hold with your bare hands as a measure is probably being
very conservative. I just double checked some of the motors I have. The
instructions with a Vexta NEMA 23 says to keep the outer case under 100 deg
Centigrade and if temps are higher to use fans for cooling. The Superior
NEMA 34 with an encoder says the rear end bell of this encoder equipped
motor is not to exceed 100 deg Centigrade and the plate has the temperate
rise marked as 65 deg centigrade so if you are starting at room temp you
will expecting temps around 100 deg Centigrade. No, I don't run any of them
that hot, but my point is most steppers I have seem are rated to a
temperature that I wouldn't even want to touch much less hold. Agreed you
get little reduction in torque if you drop from the maximum amperage, but
the safety margin temperature wise is there.


Tim
[Denver, CO]

timg@... <mailto:timg@...>

Thanks for the notes. I guess the 'hand hold' test is not a good measure
of motor heat. Must be why measuring instruments are used :-)

My driver module has a pin that controls current and a table of R values
to set. I tried lowering the current to 3A, and they still worked fine,
then I lowered it to its lowest possible value- 1.5A I think, and the
motors still runs just fine, and barey get warm after 15 minutes of
operation. Using Maxnc I can drive them at 10" per minute without
loosing steps- plenty fast for a mini mill with a travel of only about 8
inches.

On the suggestion of manual feed, I had planned to do that as well. Even
if used just to setup the table it seems easier than needing software
and comand keys. I plan to just add a simple switchbox with a pot and
push button on each axis.

Tonight I should try to make my first real part on the mini.

ron

--- In CAD_CAM_EDM_DRO@..., "Tim Goldstein" <timg@k...> wrote:

step motors run hot specialy when stoped,but not to hot or it

will

desmagnatize.If you can't hold it with bare hands than lower the
courrent.
Hope it helps.
Fogassa.

Using what you can hold with your bare hands as a measure is

probably being

very conservative. I just double checked some of the motors I have.

The

instructions with a Vexta NEMA 23 says to keep the outer case under

100 deg

Centigrade and if temps are higher to use fans for cooling. The

Superior

NEMA 34 with an encoder says the rear end bell of this encoder

equipped

motor is not to exceed 100 deg Centigrade and the plate has the

temperate

rise marked as 65 deg centigrade so if you are starting at room

temp you

will expecting temps around 100 deg Centigrade. No, I don't run any

of them

that hot, but my point is most steppers I have seem are rated to a
temperature that I wouldn't even want to touch much less hold.

Agreed you

get little reduction in torque if you drop from the maximum

amperage, but

the safety margin temperature wise is there.


Tim
[Denver, CO]

timg@... <mailto:timg@...>

OK!
It was conservative,I just moved to a new apartment,and could not
find the motors data sheet or anything related to my retrofit.Today
I've got some time to do so.
To the motors I've got 109 oz/in the outer surface should not exceed
+ 212F