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Art,

And of course that was the problem, thank you. Sometimes when the floodwaters are rising you forget to paddle ;

Frank Carpenter

Excellent news Tom.As from today I am a registered
user.it took along time to choose the software and I`m
sure i landed in the right place.

Thanks
Scot

--- caudlet <thom@...> wrote:

--- In mach1mach2cnc@..., Scot Cameron
<scotxl@y...>
wrote:

Hi Tom,I know where I`m going with it now.Thank

you.

I`ve read in some post`s that there may be a ready
built THC kit coming is this your design.

Scot
UK

Yes. Bob Campbell and the designer of the Sound
Logic breakout card
have partnered with me to offer a version of the
THC. They are going
to provide some additional features that will give
it even greater
functionality. The sensing of the arc current
within the plsama
machine for feedback to the THC was going to be a
problem because
every brand of machine did it differently. They
have worked out a
way to use a low cost AC current sensor that will be
easy to install
and will work with any plasma cutter from 25A to
200A. The units are
several weeks away from being available but will be
worth the wait.

Great care is being taken to maintain total
isolation between the
plasma unit, THC conroller and the PC.

Coupled with MACH2 the THC will offer all of the
features of an
expensive commercial unit ($$$$$) for a fraction of
the cost. You
will need a registered version of MACH2 before you
can use the THC
option.

Tom C

__________________________________
Do you Yahoo!?
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--- In mach1mach2cnc@..., Scot Cameron <scotxl@y...>
wrote:

Hi Tom,I know where I`m going with it now.Thank you.
I`ve read in some post`s that there may be a ready
built THC kit coming is this your design.

Scot
UK

Yes. Bob Campbell and the designer of the Sound Logic breakout card
have partnered with me to offer a version of the THC. They are going
to provide some additional features that will give it even greater
functionality. The sensing of the arc current within the plsama
machine for feedback to the THC was going to be a problem because
every brand of machine did it differently. They have worked out a
way to use a low cost AC current sensor that will be easy to install
and will work with any plasma cutter from 25A to 200A. The units are
several weeks away from being available but will be worth the wait.

Great care is being taken to maintain total isolation between the
plasma unit, THC conroller and the PC.

Coupled with MACH2 the THC will offer all of the features of an
expensive commercial unit ($$$$$) for a fraction of the cost. You
will need a registered version of MACH2 before you can use the THC
option.

Tom C

Gentlemen:

I agree that the limit switches are there to save a crash and should
do two things:

Instantly stop the motors on all axis
Issue an e-stop signal back to the software.

In the best interest of safety the switches should be all wired in
series in a normally closed configuration so that activation of any
switch in the ladder breaks the string and removes power from the
motors. By using a normally closed configuration any wire break would
cause the unit to stop as well. In planning my controller power
supply I made provisions for a totally mechanical limit switch
configuration. The limit switchs are wired in series to ground. The
ground goes to the neg side of a 12VDC control relay. All switches
have to be open (contacts shorted) for the relay to activate. Any
disturbance in the string will cause the relay to fall out and its
contacts to open. Included in the limit string is a front
panel "STOP" switch and a table maounted "PANIC" switch. All of the
DC runs to the motor modules go through a large contactor with a
115VAC coil. For the motors to have power both the front panel RUN
switch AND the control relay contacts have to be activated. Tripping
a limit will cause the control relay to drop out and shut down the DC
to all of the motors. A separate set of contacts on the control
relay will issue an e-stop back to the software. No additional
parallel port pins required.

In my design the Main contactor supplying the DC is wired in
a "latching" configuration so that once it drops out it requires an
activation of a "RUN" momentary button on the front panel to
reactivate. Once a fault or limit has caused the contactor to open
the DC path it requires a manual restart to prevent intermittent
limit conditions from restarting the machine.

There you have it. In building a safe machine it should be designed
so that a failed component results in a no-go condition. In other
words it takes every component in the string to be working properly
before the machine will produce motion.

I like software. I like computers. I don't trust the safety of my
machine or myself to either.

Tom C

Hi Tom,I know where I`m going with it now.Thank you.
I`ve read in some post`s that there may be a ready
built THC kit coming is this your design.

Scot
UK


__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free, easy-to-use web site design software

--- In mach1mach2cnc@..., "scot" <scotxl@y...> wrote:

Hi Tom,i was wondering if i could ask you some questions on the THC
setup,i have decided to modify my machine and add a z-axis,can you
help me on how the z axis is driven and how much travel should i

give

it.Thank you
Scot
UK

The Z axis is normally a leadscrew type drive although you could use
other methods. The axis has to travel a short distance at relatively
slow rates so a stepper type drive direct coupled to a lead screw (5
or 10 TPI) works quite well. I built my large machine to handle a
2HP router as well as a torch sub-assembly (with floating head) so I
wanted torque rather than speed. I used a triple stack 23 frame
motor, a 16MM X 4MM ballscrew and nut, and two Thompson slides. The
motor is driven by a Gecko 201 microstepping motor drive module. The
rest of the table is all servo using Gecko 340's.

You need something that will give you the same basic precision as
your X and Y since you can use it with the THC circuit to get
accurate verticle positions above the work. The stroke need not be
but 3 or 4 inches total. I do most rapids with the head 1/2" above
the material but that can be dangerous if you are not watching
because loose pieces from an internal cut can start to fall out and
jam with one end sticking up, and a rapid over that spot (shear
chance) can cause an ugly situation. A safer rapid height is 1". I
like to raise my head 3" to more easily remove the torch handle and
replace the tip comsummables.

I added a special button to my THC screen layout that is marked "Load
Material" and it rapids the head up and out of the standard work area
so I can load/unload the machine. Since 90% of my cuts are on either
2ft square or 2 X 3 ft pieces I have the table "jigged" up so that
loading and clamping material is quick.

Having a controlled 3rd axis (4th in my case since I run a dual drive
Y axis) has distinct advantages over a fixed, manual adjust or
solinoid type design. Watch E-bay for short THK or Thompson type
linear slides. They typically go pretty cheap for the short ones.
Be sure to buy enough so you can build a spring loaded floating head
design like the one in the Master5 Photo's section under
THC_Project. It makes doing a surface find and Z axis zero a breeze
and it's saved my torch head on several occasions.

Good luck and have fun with your project. Ask any questions you
want. Someone on the list will usually give a quick answer.

Tom C

Hi All,

A warning to anyone using a LM2907/2917 Frequency to Voltage
converter for spindle control. The chip data sheet does not specify
an upper frequency limit, I have found that it is very non linear
above about 13KHz, I did not realize the problem with Mach1 because I
was using a D-FF as a pre-divider, however when I set up Mach2 for a
Kernel speed of 35KHz I found that at above half spindle speed I was
getting very strange results. The answer was to use the second D-FF
on the chip, so there is now a divide by 4 pre-scalar to the FtoV.
This modification should be good for M2 up to a Kernel frequency of
45KHz.

Apologies to Art for any time he wasted on another non M2 problem.

Bernard

Hi Art,

Is it possible to combine the spindle step/dir axis with the rotary A-axis?

The reason is that I'm thinking of using a servo motor as the spindle drive,
but occasionally use it as an axis for threading.

Will it work if I use the same output pins for both axis?

Thanks,

Peter Homann
mailto:Peter.Homann@...
Adacel Technologies Limited,
250 Bay St, BRIGHTON, 3186, AUSTRALIA
<>
Telephone +61 (3) 8530 7777, Facsimile +61 (3) 9596 2960
Mobile 0421-601 667

Hi Tom,i was wondering if i could ask you some questions on the THC
setup,i have decided to modify my machine and add a z-axis,can you
help me on how the z axis is driven and how much travel should i give
it.Thank you
Scot
UK

I have found the same quandry myself. I my experience, the limit
switches should be there to prevent damage to the machine, and in
effect initiate an E-Stop condition. It realy dosen't matter which
switch is actavated, it should prevent movement of the machine and
spin down the motor. The Home switches should be there to position
the unit for initial setup and zeroing of DRO's and should be
positioned inside the envelope of safe machine travel.

Also had a few thoughts about the physical qualties of the
switches ...The limit switches need only to be mechanical in nature
and need only a gross resolution. For the home switches, I've been
playing around with the inexpensive laser diodes (laser pointers)
that can be bought almost anywhere. What I have come up with is the
laser diode powered by a 5v DC "wallwart" transformer and a 220ohm
resistor to limit current and a small NPN transistor on the output of
a photoreceptor. A switch is guaged "accurate" mainly by its
switching speed - so this switch will opperate in the billionth of a
second range and should prove to be very accurate indeed.

As a physical layout, this scheme would require an e-stop,x+,X-,Y+,y-
,Z+ limit switches wired to 1 input. The z+,X+,X-,Y+,Y- home switches
would require their own seperate inputs for a total of 6.

Thoughts?



--- In mach1mach2cnc@..., "capteod" <mfgguru@c...> wrote:

I was wondering if the possibility is available to separate the
limit switches and the home switch. I seriously believe that there
is a serious safety concern when the limit/home function is the

same

contacts.

My experience in equipment is that the limit switches are part of
the E-STOP ladder and the home position is separate and that is to
prevent damage to the equipment. I would think as hobbiests we

need

the protection this would give us. If necessary I think the
activation of LPT2 is an issue to consider.

ART, Thanks for the great product.

Bernard:

Yes, it is necessary to restart after changing frequencies.
This is necessary to restart the engine timer. Also, if you tune the spindle
in 35 Khz and then switch to 25Khz, you have to retune. Any frequency
changes and all motors must be retuned. This is due to calculations
involving your actual timing periods to make everything as accurate as
possible.

The missing pulses you see are probably the bresenham divider in
operation. For exmple 25Khz is one pulse every 40us but 24.9Khz is still one
pulse every 40us one will be missing every 24999 pulses. This can look like
missing pulses.Most step/dir convertors to analogue simply charge caps so
there is no problem with this method, but you may be trying to use a circuit
type not so tolerant of this type of pulse timing. The steppers won't notice
it but your spindle VFD might.

Hope this helps,
Art
www.artofcnc.ca

Art,

I'm gradually trying to sort things out here. When I first noticed
problems I was running the kernel @35Khz, I then switched to 25Khz
and got the figures I gave you. I have now re-started M2 and get
figures much more in line to what is expected, there are still some
anomolies, for example at 3/4 spindle speed there are intermittent
missing pulses, I can see this as I have a D-ff as a pre-scalar and
instead of a regular 1:1 square wave there are random 1:2 pulses,
these correspond to missing pulses in the step train and a lot more
variation in the VFD frequency. Changing the kernel to 35K and I am
back to the original conditions.

This gives rise to 2 questions.

1) It seems necessary to do a program re-start after changing kernel
frequency. Can you confirm?

2) I am running a HP Pavilion 650MHz P3, is this fast enough to run
at 35KHz, what is the symptoms when you run out of steam?, the other
4 axis seem to be working OK. The Diagnostics page give a pulse freq
of 36119 and CPU load = 0%, worst case 0.000158.

Bernard

--- In mach1mach2cnc@..., "capteod" <mfgguru@c...> wrote:

I was wondering if the possibility is available to separate the
limit switches and the home switch. I seriously believe that

there

is a serious safety concern when the limit/home function is the

same

contacts.

My experience in equipment is that the limit switches are part of
the E-STOP ladder and the home position is separate and that is to
prevent damage to the equipment. I would think as hobbiests we

need

the protection this would give us. If necessary I think the
activation of LPT2 is an issue to consider.

<snip>

I would welcome your thoughts on or off list how we could improve
section 4.6 and appendix 4 of the Mach2MillManual. (Rev A1.8 in
Files and download from www.artofcnc.ca) I have found it hard to get
balance of risks and features here.

Thanks, John Prentice

I was wondering if the possibility is available to separate the
limit switches and the home switch. I seriously believe that there
is a serious safety concern when the limit/home function is the same
contacts.

My experience in equipment is that the limit switches are part of
the E-STOP ladder and the home position is separate and that is to
prevent damage to the equipment. I would think as hobbiests we need
the protection this would give us. If necessary I think the
activation of LPT2 is an issue to consider.

ART, Thanks for the great product.

Steve:

Definitely noise on the step pin. When you jog, the DIR pin gets set and
dosent change until you change diretcion, thats why it creeps in the last
direction.

Art
www.artofcnc.ca

On Wed, 06 Aug 2003 15:35:15 -0300, you wrote:

Thansks, I did'nt realize it was lathe that had the problem, will
retroubleshoot. Have already fixed the Mist/Flood thing this morning.
Thatnks for the long outstanding reminder. Severasl other things have been
fixed as well, but I will do spindle now.
I do have a report of Mill not running the VFD properly from step/dir,
your is running OK in Mill, right?

Didn't run it as such, I manually set speed on mill VFD with a pot. I
just disconnected 10V & 0V wires to VFD and checked voltage, but I
will try it tommorrow.

I also have another fault, which is probably mine in that VFD/motor is
inducing steps on X axis causing creeping. Funny thing is if I've
jogged in, it moves slowly in, out, if out. I don't know why it is
only doing it on X, but I have my suspicions that the gecko is faulty.
Motor gets hot on standby even though current reduction is set, but
not on Z. I'm going to swap them over in the morning and see if it
follows the gecko or stays on X. I disconnected the spindle sensor and
it still does it - so not that. I'll try it on mill and see if it does
it there too, before I go altering wiring and let you know what I
find.

--
Steve Blackmore

Thanks Todd:

I'll check it out.

Art
www.artofcnc.ca

Steve:

Thansks, I did'nt realize it was lathe that had the problem, will
retroubleshoot. Have already fixed the Mist/Flood thing this morning.
Thatnks for the long outstanding reminder. Severasl other things have been
fixed as well, but I will do spindle now.
I do have a report of Mill not running the VFD properly from step/dir,
your is running OK in Mill, right?

Thanks,
Art
www.artofcnc.ca

Bernard:

Can you explain this a bit better, Mill seems to be working properly
according to reports. Is is possible that your pulse width is too low for
the circuit? Steve reports proper operation in Mill, just lathe causing
problems.

I'm using spindle Step/Dir with V7.2, just changed from M1 where
spindle was OK, this is mill. Using 25Khz kernel freq, calibrated
FotV at half speed VFD op = 60hz,increase speed to 3/4 output = 83hz,
increase to max output = 87hz. (FtoV has been checked for linearity
using separate function generator).

I don't understand this statement. Do you mean you get 60Hz at half speed
and 87 at full? with 83 at half?

Looking at the ouput of the D-FF pre-scalar at 1/2 speed frequent,
but random, change in output from 80uSec to 50uSec, at 3/4 speed
pulses change from 55uSec to 30uSec, not possible to measure pulse
train at full o/p - too random.

Too random at full speed? This is strange, at full speed, you should be
getting a 25Khz output to the FF from the printer port. Can you verify this?
I am getting 25Khz at full output from the printer port.

The output of the VFD dithers .2 to .3 in the Hz window at all ouput
frequencies.

Sounds like the conversion is not owrking, what are you using to convert
from step pulses to the VFD?

Thanks,
Art

On Wed, 06 Aug 2003 15:39:57 -0000, you wrote:

Have you cut any threads with the latest Mach2?

No, afraid not - impossible until step/direction speed control works
properly.

--
Steve Blackmore