Using what I have in the junk box together with some high powered stepper
motors and a big 36V linear power supply salvaged from a couple of old
mainframe printers and about $300 in rails and ball screws I think I can
build the mechanical part but what about the drivers and software?

The software candidates are Kcam, TurboCNC and Mach2. Can someone explain
the strenghts and weaknesses?

As to drivers, I have found them from $25 to $200 per axis. What am I
supposed to be looking at?


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Glenn Ashmore wrote:

Using what I have in the junk box together with some high powered stepper
motors and a big 36V linear power supply salvaged from a couple of old
mainframe printers and about $300 in rails and ball screws I think I can
build the mechanical part but what about the drivers and software?

The software candidates are Kcam, TurboCNC and Mach2. Can someone explain
the strenghts and weaknesses?

As to drivers, I have found them from $25 to $200 per axis. What am I
supposed to be looking at?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

I'd recommend Mach3. I just built a small router myself and tried EMC
and Mach2/3. I didn't spend much time testing the other options as EMC
was free and Mach2/3 pretty well blew everything else away. At $150 for
a very generous license it's pretty much a no-brainer.

I'm using the HobbyCNC.com 4AUPC kit with the 200oz steppers. Nice kit,
good price and works well in the 1/8 microstepping mode. I'm using a
beefy 24v power supply from Surpluscenter.com.

Pic in the dropbox: http://www.metalworking.com/DropBox/CNC_Router.JPG

Pete C.

DAMN! That is a really nice rig. What kind of capacity do you have?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Pete C." wrote I'd recommend Mach3. I just built a
small router myself and tried EMC
and Mach2/3. I didn't spend much time testing the other options as EMC
was free and Mach2/3 pretty well blew everything else away. At $150 for
a very generous license it's pretty much a no-brainer.

I'm using the HobbyCNC.com 4AUPC kit with the 200oz steppers. Nice kit,
good price and works well in the 1/8 microstepping mode. I'm using a
beefy 24v power supply from Surpluscenter.com.

Pic in the dropbox: http://www.metalworking.com/DropBox/CNC_Router.JPG

Pete C.

TurboCNC is designed to run in DOS. Works very well on older systems. I am
currently running it on on old Pentium 200 with 64 MB Ram. Runs good on my
homemade machine.

Mach 2 is a windows based program. Need A newer computer to run it although
I am not sure of the exact requirements.

Not familiar with KCAM.

If you have not done so yet, check out cnczone.com for better answers.
These guys are obsessed with Hobby (and some pro) CNC machines and related
software, drivers, etc. Excellent Site.

I am currently running the xylotex 3 axis driver board (149 bucks) with 276
oz steppers (39.00 each new) and a 24v power supply (24.99) from mpja. This
has made a good smooth combination for me. My machine is only getting
about 30 ipm max but I am only using a 1/4-20 threaded rod for a lead screw.
Obviously something a little coarser would be faster.

Check the max rating on the xylotex board. I don't belive it will handle
the big steppers or the 36 v power supply you are thinking of using.

Dan

"Glenn Ashmore" wrote in message
news:wRBge.12147$sy6.7227@lakeread04...
Using what I have in the junk box together with some high powered stepper
motors and a big 36V linear power supply salvaged from a couple of old
mainframe printers and about $300 in rails and ball screws I think I can
build the mechanical part but what about the drivers and software?

The software candidates are Kcam, TurboCNC and Mach2. Can someone explain
the strenghts and weaknesses?

As to drivers, I have found them from $25 to $200 per axis. What am I
supposed to be looking at?


--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

Travels are about 23" x 23" x 10". It's nice enough for my first one,
but I've already got plenty of ideas for improvements and this one isn't
even 100% complete yet. Somehow a welded steel frame looks very
"polished" once you slap some paint on it.

I actually went with welded steel construction because it gives good
rigidity without excess weight (MDF weighs a ton) and it can also be
cheaper since it does not require nearly as many fasteners. The steel
stock averages about $0.50/foot when you buy in full 24' sticks from a
"real" steel supplier, about 1/5 of the cost of HD or Lowe's. The actual
machine probably weighs less than 50#. It uses mostly 1/2", 3/4" and 1"
square 14ga tubing.

One of the things I wanted in the design was the ability to work on
large surfaces. Having a rigid steel frame with an open bottom and
enough Z travel allows me to remove the machine from it's normal
worktable and clamp it directly on top of a large item such as a full
sheet of MDF and work it in 2x2 sections. One of the project ideas I
have for it involves drilling a unique pattern of holes on a 4x8 sheet
of masonite.

The normal worktable has a raised platform to bring the typical work
closer to the gantry for improved rigidity. Even in this configuration
it has a clear through path front to back so I could work a 2'x10' sign
in sections.

I need to add felt wipers for the "ways" to help keep dust from getting
caked on the guide bearings, and an enclosure to keep dust from getting
everywhere else. I'm still learning the whole CAD - post processor - CNC
controller thing, but I'm starting to get the hang of it.

Pete C.


Glenn Ashmore wrote:

DAMN! That is a really nice rig. What kind of capacity do you have?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Pete C." wrote I'd recommend Mach3. I just built a
small router myself and tried EMC
and Mach2/3. I didn't spend much time testing the other options as EMC
was free and Mach2/3 pretty well blew everything else away. At $150 for
a very generous license it's pretty much a no-brainer.

I'm using the HobbyCNC.com 4AUPC kit with the 200oz steppers. Nice kit,
good price and works well in the 1/8 microstepping mode. I'm using a
beefy 24v power supply from Surpluscenter.com.

Pic in the dropbox: http://www.metalworking.com/DropBox/CNC_Router.JPG

Pete C.

Dan wrote:

TurboCNC is designed to run in DOS. Works very well on older systems. I am
currently running it on on old Pentium 200 with 64 MB Ram. Runs good on my
homemade machine.

Mach 2 is a windows based program. Need A newer computer to run it although
I am not sure of the exact requirements.

I'm running Mach3 on a $99 surplus Dell P3/733 with 128mb and W2Kpro
without problems. This is a dedicated machine so there isn't anything
else running on it to conflict. I also added a PCI dual parallel port
card so I have plenty of I/O for machine upgrades.


Not familiar with KCAM.

If you have not done so yet, check out cnczone.com for better answers.
These guys are obsessed with Hobby (and some pro) CNC machines and related
software, drivers, etc. Excellent Site.

I forgot to mention that site, that's what got me started with the CNC
router thing.


I am currently running the xylotex 3 axis driver board (149 bucks) with 276
oz steppers (39.00 each new) and a 24v power supply (24.99) from mpja. This
has made a good smooth combination for me. My machine is only getting
about 30 ipm max but I am only using a 1/4-20 threaded rod for a lead screw.
Obviously something a little coarser would be faster.

Check the max rating on the xylotex board. I don't belive it will handle
the big steppers or the 36 v power supply you are thinking of using.

I'm using 5/16-14 ACME and I can get 70 IPM rapids, but I start to get
screw whip at that speed. I can do decent cuts up to about 50 IPM as
long as the cutting load is reasonable.

Pete C.

In article ,
Dan wrote:
TurboCNC is designed to run in DOS. Works very well on older systems. I am
currently running it on on old Pentium 200 with 64 MB Ram. Runs good on my
homemade machine.

If you aren't scared off by linux, the EMC package (originally
from NIST) is free, and linux (or just about any unix) tends to be a lot
faster on older hardware than Windows. Check out:

http://www.linuxcnc.org/

IIRC, a 500MHz pentium is quite sufficient for the stepper motor
version, which is a bit more CPU-cycle hungry than the servo motor
version -- and this for a pretty busy milling machine keeping track of
positions to 0.001". I don't know what resolution you are after for the
router, or what speeds.

Mach 2 is a windows based program. Need A newer computer to run it although
I am not sure of the exact requirements.

I know that a servo motor powered system run by Windows would
scare me to death. The thought of a BSOD (Blue Screen of Death) just
after a rapid move command was issued, with no system ready to stop it
at the right place is not comforting.

For stepper motors -- if it died, it would stop issuing pulses
to the stepper motors, so you would be fine. (Other than having to
restore your initial position to restart the run. :-)

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

In article , Pete C. wrote:
Dan wrote:

[ ... ]

Check the max rating on the xylotex board. I don't belive it will handle
the big steppers or the 36 v power supply you are thinking of using.

I'm using 5/16-14 ACME and I can get 70 IPM rapids, but I start to get
screw whip at that speed. I can do decent cuts up to about 50 IPM as
long as the cutting load is reasonable.

Hmm ... you might want to consider doing it the way Bridgeport
did on the BOSS-3 through BOSS-6 machines at least.

The Y-axis, being fairly short, was rotated normally.

The X-axis, however, was too long for that, so the anchored one
end of the leadscrew (not-rotating), and instead mounted the nut (a
ball-nut) in a pair of facing tapered roller bearings, and rotated *it*.
Thus, no leadscrew rotation, and no whip.

Also -- the leadscrews were closer to 1" diameter ball screws.
You probably want ball screws and nuts, if you can come up with a way of
keeping the sawdust out, because they are both more precise, and a *lot*
lower friction, so the motors can accomplish more.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

Pete C. wrote:

Glenn Ashmore wrote:

Using what I have in the junk box together with some high powered stepper
motors and a big 36V linear power supply salvaged from a couple of old
mainframe printers and about $300 in rails and ball screws I think I can
build the mechanical part but what about the drivers and software?

The software candidates are Kcam, TurboCNC and Mach2. Can someone explain
the strenghts and weaknesses?

As to drivers, I have found them from $25 to $200 per axis. What am I
supposed to be looking at?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com


I'd recommend Mach3. I just built a small router myself and tried EMC
and Mach2/3. I didn't spend much time testing the other options as EMC
was free and Mach2/3 pretty well blew everything else away. At $150 for
a very generous license it's pretty much a no-brainer.

I'm using the HobbyCNC.com 4AUPC kit with the 200oz steppers. Nice kit,
good price and works well in the 1/8 microstepping mode. I'm using a
beefy 24v power supply from Surpluscenter.com.

Pic in the dropbox: http://www.metalworking.com/DropBox/CNC_Router.JPG

Pete C.
That looks like a massive Z stage! - Nice jog so it seems.

Martin

--
Martin Eastburn
@ home at Lion's Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder

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DoN. Nichols writes:

I know that a servo motor powered system run by Windows would
scare me to death. The thought of a BSOD (Blue Screen of Death) just
after a rapid move command was issued, with no system ready to stop it
at the right place is not comforting.

That's pretty unlikely as the continuing pulses require a running system.

In my limited experience a runaway machine happens far more often due to
operator error (many times) than system problems (once or twice).

Any CNC system needs limit switches and a panic button for such events.

In article ,
Richard J Kinch wrote:
DoN. Nichols writes:

I know that a servo motor powered system run by Windows would
scare me to death. The thought of a BSOD (Blue Screen of Death) just
after a rapid move command was issued, with no system ready to stop it
at the right place is not comforting.

That's pretty unlikely as the continuing pulses require a running system.

Note that I said a *servo* motor powered system. With stepper
motors, you are right. But with a servo, there is a card in the
computer which has a collection of D/A converters. You write to one of
them, and it outputs a voltage. The voltage is proportional to the
desired speed, and is fed into a servo amplifier, which drives the servo
motor at that speed.

Write the speed value to the D/A, and it starts putting out that
voltage, (no need for the CPU to keep remembering to generate pulses),
and continues with that voltage until a new value is written. If it
happens to be rapid move to the position to start a cut, you will likely
have parts of an endmill bouncing off the walls. (That happened to me
once, thanks to programming a rapid move through the workpiece without
remembering to raise the spindle to clear it. And it used to be a solid
carbide end mill. :-)

A servo at top speed can be a *lot* faster than a stepper, which
runs out of steam at high step rates. The machine which I used to use
occasionally at work (a clone of a Bridgeport retrofitted with ball
screws and servo motors by Anilam, the maker of the controller) was
capable of 200 IPM rapid moves. And modern machines are capable of more
than that.

In my limited experience a runaway machine happens far more often due to
operator error (many times) than system problems (once or twice).

Yep -- I can agree with that. But the problems with a servo
system thanks to the computer going non-compos-mentis at the wrong
moment are more severe than with a stepper system.

Any CNC system needs limit switches and a panic button for such events.

The limit switches do shut down the servo amp, and ideally lock
the rotor as well. Whether it does it soon enough at 200 IPS remains to
be seen.

At 200 IPS, by the time you even *think* of reaching for the
panic button, it is all over. :-)

However, if it is a normal cutting speed, the panic switch can
indeed save you.

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"DoN. Nichols" wrote in message
...

The limit switches do shut down the servo amp, and ideally lock
the rotor as well. Whether it does it soon enough at 200 IPS remains to
be seen.

At 200 IPS, by the time you even *think* of reaching for the
panic button, it is all over. :-)

The way that was handled in high-speed servo systems used in old, large disk
drives and impact printers was to have a "dead man timer" on the driver (at
the final output stage, or nearly so). Even after a servo was commanded to
slew at a high rate, it had to be refreshed every (say) five milliseconds to
allow it to continue to slew. If the dead man timer timed out without a
refresh, it braked the servo, and panic'd the system.

LLoyd

The folks that are driving servos from Mach[x] are typically doing it
through Gecko drivers. The geckos make the servos look like steppers to the
controller (ie the gecko takes step and direction signals, then controls the
motor taking feedback from the encoder). The gecko faults if motor hits 128
steps out of position (properly sized they never get anywhere close to
that). So previous posters comment around "no pulses, no movement" was
correct around typical Mach system driving servos. This isn't to say you are
wrong in general, just in the particular. BTW Mach doesn't do closed-loop,
so the _only_ way to driver servos from it is with an external motor driver
doing the same stunt as the Gecko (at least as far as I know, someone will
correct me if I'm wrong on this). I believe that Mach does its actual pulse
generation via a trick hitting the motherboard timer (don't ask me what the
trick is), ie doing an end run around windows. That is how they manage to
get pulse generation (a real-time job, really) done reliably from a patently
non-real time operating system (Windows).

I've been lurking/researching on this for a while, and I've never heard a
single user of either say anything bad about Mach or Gecko.

Regards,

Adam Smith
Midland ON

Having said all of which, I have a dream project of porting EMC or at least
pieces of the NIST stuff to QNX. That is a REAL real time operating system.
Probably never do it, though.

"DoN. Nichols" wrote in message
...
In article ,
Richard J Kinch wrote:
DoN. Nichols writes:

I know that a servo motor powered system run by Windows would
scare me to death. The thought of a BSOD (Blue Screen of Death) just
after a rapid move command was issued, with no system ready to stop it
at the right place is not comforting.

That's pretty unlikely as the continuing pulses require a running system.

Note that I said a *servo* motor powered system. With stepper
motors, you are right. But with a servo, there is a card in the
computer which has a collection of D/A converters. You write to one of
them, and it outputs a voltage. The voltage is proportional to the
desired speed, and is fed into a servo amplifier, which drives the servo
motor at that speed.

Write the speed value to the D/A, and it starts putting out that
voltage, (no need for the CPU to keep remembering to generate pulses),
and continues with that voltage until a new value is written. If it
happens to be rapid move to the position to start a cut, you will likely
have parts of an endmill bouncing off the walls. (That happened to me
once, thanks to programming a rapid move through the workpiece without
remembering to raise the spindle to clear it. And it used to be a solid
carbide end mill. :-)

A servo at top speed can be a *lot* faster than a stepper, which
runs out of steam at high step rates. The machine which I used to use
occasionally at work (a clone of a Bridgeport retrofitted with ball
screws and servo motors by Anilam, the maker of the controller) was
capable of 200 IPM rapid moves. And modern machines are capable of more
than that.

In my limited experience a runaway machine happens far more often due to
operator error (many times) than system problems (once or twice).

Yep -- I can agree with that. But the problems with a servo
system thanks to the computer going non-compos-mentis at the wrong
moment are more severe than with a stepper system.

Any CNC system needs limit switches and a panic button for such events.

The limit switches do shut down the servo amp, and ideally lock
the rotor as well. Whether it does it soon enough at 200 IPS remains to
be seen.

At 200 IPS, by the time you even *think* of reaching for the
panic button, it is all over. :-)

However, if it is a normal cutting speed, the panic switch can
indeed save you.

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"DoN. Nichols" wrote:

In article , Pete C. wrote:
Dan wrote:

[ ... ]

Check the max rating on the xylotex board. I don't belive it will handle
the big steppers or the 36 v power supply you are thinking of using.

I'm using 5/16-14 ACME and I can get 70 IPM rapids, but I start to get
screw whip at that speed. I can do decent cuts up to about 50 IPM as
long as the cutting load is reasonable.

Hmm ... you might want to consider doing it the way Bridgeport
did on the BOSS-3 through BOSS-6 machines at least.

The Y-axis, being fairly short, was rotated normally.

The X-axis, however, was too long for that, so the anchored one
end of the leadscrew (not-rotating), and instead mounted the nut (a
ball-nut) in a pair of facing tapered roller bearings, and rotated *it*.
Thus, no leadscrew rotation, and no whip.

Also -- the leadscrews were closer to 1" diameter ball screws.
You probably want ball screws and nuts, if you can come up with a way of
keeping the sawdust out, because they are both more precise, and a *lot*
lower friction, so the motors can accomplish more.

Actually I'd like to find a cheap used Bridgeport BOSS-x with a dead
control to retrofit. Would be a nice upgrade to the 1J I have now.

For "V2" I'm considering both rotating nut and rack and pinion style
drives. Not sure if I'd go with ballscrews since ACME seems just fine
for this type of machine and is quite a bit cheaper.

The current machine was more or less designed on the fly adopting some
ideas from what I saw on CNCzone and adapting to what I had on hand. I
started with cheap all thread since I wasn't sure how many times I'd
rebuild it. Once it was settled I switched to comparable ACME. My
accuracy target was 1/16" and the ACME rod exceeds that goal by a fair
amount.

Pete C.

"DoN. Nichols" wrote:

In article ,
Richard J Kinch wrote:
DoN. Nichols writes:

I know that a servo motor powered system run by Windows would
scare me to death. The thought of a BSOD (Blue Screen of Death) just
after a rapid move command was issued, with no system ready to stop it
at the right place is not comforting.

That's pretty unlikely as the continuing pulses require a running system.

Note that I said a *servo* motor powered system. With stepper
motors, you are right. But with a servo, there is a card in the
computer which has a collection of D/A converters. You write to one of
them, and it outputs a voltage. The voltage is proportional to the
desired speed, and is fed into a servo amplifier, which drives the servo
motor at that speed.

Write the speed value to the D/A, and it starts putting out that
voltage, (no need for the CPU to keep remembering to generate pulses),
and continues with that voltage until a new value is written. If it
happens to be rapid move to the position to start a cut, you will likely
have parts of an endmill bouncing off the walls. (That happened to me
once, thanks to programming a rapid move through the workpiece without
remembering to raise the spindle to clear it. And it used to be a solid
carbide end mill. :-)

A servo at top speed can be a *lot* faster than a stepper, which
runs out of steam at high step rates. The machine which I used to use
occasionally at work (a clone of a Bridgeport retrofitted with ball
screws and servo motors by Anilam, the maker of the controller) was
capable of 200 IPM rapid moves. And modern machines are capable of more
than that.

In my limited experience a runaway machine happens far more often due to
operator error (many times) than system problems (once or twice).

Yep -- I can agree with that. But the problems with a servo
system thanks to the computer going non-compos-mentis at the wrong
moment are more severe than with a stepper system.

Any CNC system needs limit switches and a panic button for such events.

The limit switches do shut down the servo amp, and ideally lock
the rotor as well. Whether it does it soon enough at 200 IPS remains to
be seen.

At 200 IPS, by the time you even *think* of reaching for the
panic button, it is all over. :-)

However, if it is a normal cutting speed, the panic switch can
indeed save you.

Enjoy,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

I thought that most of those internal servo controller cards had their
own onboard CPU and did not rely on the host machine for processing
power in the servo loop. The onboard CPU would handle the move based on
higher level commands from the host (move to x) vs. requiring the host
to generate a step pulse stream as would be required for an external
step/dir servo drive like the Geckos.

With this type of arrangement, if the host system crashed, the servo
drive would simply complete the commands already in it buffer and stop.

Pete C.

In article , Pete C. wrote:
"DoN. Nichols" wrote:

In article ,
Richard J Kinch wrote:
DoN. Nichols writes:

I know that a servo motor powered system run by Windows would
scare me to death. The thought of a BSOD (Blue Screen of Death) just
after a rapid move command was issued, with no system ready to stop it
at the right place is not comforting.

That's pretty unlikely as the continuing pulses require a running system.

Note that I said a *servo* motor powered system. With stepper
motors, you are right. But with a servo, there is a card in the
computer which has a collection of D/A converters. You write to one of
them, and it outputs a voltage. The voltage is proportional to the
desired speed, and is fed into a servo amplifier, which drives the servo
motor at that speed.

[ ... Most of my description snipped ... ]

I thought that most of those internal servo controller cards had their
own onboard CPU and did not rely on the host machine for processing
power in the servo loop. The onboard CPU would handle the move based on
higher level commands from the host (move to x) vs. requiring the host
to generate a step pulse stream as would be required for an external
step/dir servo drive like the Geckos.

With this type of arrangement, if the host system crashed, the servo
drive would simply complete the commands already in it buffer and stop.

Agreed, it would. But the NIST EMC package (the one which I am
familiar with) uses the Servos-to-go board, which has six D/A
converters, corresponding encoder counters, and lots of digital I/O for
limit switches, command switches, turning on and off things like coolant
pumps and switching motor on/off/reverse, if you are not using a VFD to
drive the spindle.

With that (which costs a *lot* less than a Gallil board with its
own CPU, you can handle the three normal axes, the spindle motor (via a
VFD), and a couple of extra axes for special purposes. (The card
handles eight axes, but the drivers in EMC seem to limit to six.)

Anyway -- this board is more likely to be used with a hobby
conversion than a Gallil, and it can be driven from Windows as well as
the real-time converted linux kernel, so the possibility of a BSOD
runaway does exist.

One reason that Gallil has not been used much for this, is the
difficulty of getting sufficient information from them to enable writing
drivers for a non-Windows system. They will cheerfully sell you
pre-compiled drivers (no source) for Windows, but if you want a
different host OS, you are SOL.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

DoN. Nichols wrote:

In article ,
Richard J Kinch wrote:

DoN. Nichols writes:


I know that a servo motor powered system run by Windows would
scare me to death. The thought of a BSOD (Blue Screen of Death) just
after a rapid move command was issued, with no system ready to stop it
at the right place is not comforting.

That's pretty unlikely as the continuing pulses require a running system.


Note that I said a *servo* motor powered system. With stepper
motors, you are right. But with a servo, there is a card in the
computer which has a collection of D/A converters. You write to one of
them, and it outputs a voltage. The voltage is proportional to the
desired speed, and is fed into a servo amplifier, which drives the servo
motor at that speed.

Write the speed value to the D/A, and it starts putting out that
voltage, (no need for the CPU to keep remembering to generate pulses),
and continues with that voltage until a new value is written. If it
happens to be rapid move to the position to start a cut, you will likely
have parts of an endmill bouncing off the walls. (That happened to me
once, thanks to programming a rapid move through the workpiece without
remembering to raise the spindle to clear it. And it used to be a solid
carbide end mill. :-)

A servo at top speed can be a *lot* faster than a stepper, which
runs out of steam at high step rates. The machine which I used to use
occasionally at work (a clone of a Bridgeport retrofitted with ball
screws and servo motors by Anilam, the maker of the controller) was
capable of 200 IPM rapid moves. And modern machines are capable of more
than that.


In my limited experience a runaway machine happens far more often due to
operator error (many times) than system problems (once or twice).


Yep -- I can agree with that. But the problems with a servo
system thanks to the computer going non-compos-mentis at the wrong
moment are more severe than with a stepper system.


Any CNC system needs limit switches and a panic button for such events.


The limit switches do shut down the servo amp, and ideally lock
the rotor as well. Whether it does it soon enough at 200 IPS remains to
be seen.

At 200 IPS, by the time you even *think* of reaching for the
panic button, it is all over. :-)

However, if it is a normal cutting speed, the panic switch can
indeed save you.

Enjoy,
DoN.
My CNC table can rip 1000 IPS while cutting (have yet to try that foil :-) ) but
I limit the high speed travel to 200 and the cutting speed based on the material,
thickness, the type of head, volume of air and a roll of the bones and anything that
will work.

Martin

--
Martin Eastburn
@ home at Lion's Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder

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