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I have problem with Z steps on my micro mill.
After rechecking and testing everything electrical
and mechanical, found that problem was with backslash
compensation(I'm using TurboCNC). I put zero there
and no lost steps on Z anymore.

Leo

--- In CAD_CAM_EDM_DRO@..., "Raymond Heckert" <jnr@...> wrote:

Check to make sure that the Z-axis isn't binding up somewhere. Also

check

that the timing belt is 'drum-tight', and free of oil, grease, etc.

RayHex

-----Original Message-----
Date: Monday, September 04, 2006 4:01 PM
Subject: [CAD_CAM_EDM_DRO] Re: Can a PC operate a BOSS 5 or 6? (and a
question)


<snip> One problem I've had recently is the Z axis stepper keeps

losing steps. I wrote about a month ago and said it was losing
power (by the way thanks to all who replied, I don't get on here
very often), but a few changes in my acceleration profile, and it
seems to run pretty fast again. However all the adjustments I make
don't seem to fix the step loss problem. It doesn't lose them all
the time either. I'm running a 3d profiling program with about
65,000 lines of code, with the top of the part at Z0, and the bottom
at Z-.150. By the end of the program its usually off by about .050"
but sometimes as much as .200". Also this motor seems a lot hotter
than the Y and X motors, although they are all the same kind of
motor.

I'm considering changing to servos, but don't have any experience
with them. Would I be able to change just the Z axis to a servo and
geck0 3whatever, and leave steppers on x and y? I found what looks
like a good deal on www.homeshopcnc.com and would like to know if
this servo would drive this machine.

Carl Mikkelsen wrote:

Jon,

The large-scale calibration is fairly well covered by the simulated annealing method of estimating the systematic error parameters. This discussion grew out of concerns about quantization, and (I speculate) that quantization will cause a surface roughness on nearly any surface machined with a hexapod.

The quantization-roughness may be far less than the roughness that comes from servo control system errors, vibration, chatter, or other effects.

Have you been looking at EMC for hexapod controls? Do you know if it can generate the transformed actuator commands, independent of the real-time actuator controls?

I'm not an expert in this area, but the general flow is :

G code interpreter
trajectory planner
kinematics
servo control

Since EMC can jog a hexapod in cartesian coordinates once the struts are homed,
I think that basically proves it can already do it.

Jon

rocketscientistnate wrote:

I reread the advert at homeshopcnc.com. Its 850 oz-in PEAK. 170 constant. Its definitly not a pulley slipping, I can watch the end of the motor shaft. I wrote a short program to just move the quill up and down, and watched it. It can go up and down a hundred times and then it just kinda stalls on one move and makes a nasty grinding noise but just creeps a little. When the controller sends it the other way, it takes off and goes fine again for a while. If it was something that happened everytime i did something in particular it would be easy to diagnose.

Hmmm, I wonder if you have a chip in your ballnut? I get these in my machine
every once in a while. My marginal quill motor will sometimes stall on this.
My EMC software is continuously reading the encoder position, and if it lags
more than a little, it will stop on a following error and let me know there is
a problem. What good are servos if it just blindly goes on mis-making the part?
(This is not a big problem here, it happens once every few years.) My ballscrew
is on the front of the quill (a retrofitted manual 1J head) and more prone to
crud getting into it. Yours is pretty hard to get to, so my trick with greasing and
cleaning may be the only way to get chips out of the ballnut or its roller bearings.

Are you using Gecko 320/340 drives? They should fault out when they get behind
by 128 steps.

I don't know if it helps, but everytime I run a program and it does this, it seems to lose steps in the same direction everytime it does it. Like in this program everytime it loses some it will be higher, or the next time I run it they will always be lower. Or say I'm running a 3d part where the x moves back and forth stepping .005 in the y every pass, (z axis making the profile) the whole part will be tapered from the lower to higher y values at a fairly consistent taper. Sometimes it tapers up, sometimes down, and ocasionally it works fine. If instead it lost steps both directions, it would be rough and jagged, but not consistently tapered.

This makes me think it might be an acceleration problem, or possibly something to
do with the timing between step pulses and changes in the direction signal.

Jon

I was thinking to put power on the clips and use a heavy enough gauge copper
to make the resistance much less than the resistance wire.

The control circuit would pump current through the wire and monitor the
voltage drop. Divide to get the resistance, which tracks temperature. If the
temperature drops as you feed material, the controller would compensate with
more power.

Anyway, that's the idea. If you have a PIC controlling it, it would be
pretty easy. So if you're running narrow material, the PIC would measure the
length of the resistance wire while it was still cold by a resistance
measurement.

It would have the advantage of not burning your foam by ever getting too hot
and auto compensate for feed rate to an extent.

You guys may know what I am looking at here. I have a 1985 Bridgeprt
R2G4 Series I with Fanuc 11MA controller. Lots of manuals but little
discription of what I need to know.

Trying to interface with a PC so I can write programs and send to CNC
but everything is so old, I don't even know what I am looking for.

I wish I could find a command on the controller that said, send
program to PC, then I would know I am communicating.

ALso, If I could just punch in Gcode in MDI Mode on controller and
"SAVE AS" I could do some work.

Are there any software updates for this stuff? Easy way to retrofit
up 20 years?

Any other user or owners groups??

thanks Lee

--- In CAD_CAM_EDM_DRO@..., Les Newell <lesnewell@...>
wrote:

If you can easily move the quill up and down you probably don't

have a

problem. Most commercial retrofits use around 400 - 500 oz-in

continuous

torque rated motors. Those motors are 170 oz-in continuous.

Les

I had a spare motor that came with the mill, but I hadn't tested it
yet. I got it out, it ran great so I mounted it on the mill. No
luck, it does the same thing. I turned the belt and the ballscrew
inside the head and it couldn't have been any freeer. (freer? never
spelled that before) I'm pretty confident in the deskcnc control
board and the gecko drives, unless during the series of short moves
(less than .005") they get ahead of the machine, but I don't think
that should happen. I'm wondering if running the combination of all
three drives is somehow depleting the current to that motor, but I
doubt this too. The power supply is just like you (Les) explained
to me a couple years ago. 1 transformer, a bridge rectifier
(actually three in parallel because they were there) and some
capacitors for filters. It seems like it almost has to be in my
acceleration curves, but I can't seem to work it out right.

Thanks
Nathan

--- In CAD_CAM_EDM_DRO@..., "turbulatordude"
<dave_mucha@...> wrote:

I am starting to think that is how it is done. just heat the wire
and watch the cut.

I don't suppose it is anything difficult as I am trying to make it.

I was envisioning using a feedback so the cutting would slow when the
wire cooled, and/or adjust the current automatically.

I used to cut out lots of foam wings for RC airplanes way back yonder,
and I did it exactly like Phil describes. Worked just fine.

Irby

--- In CAD_CAM_EDM_DRO@..., "Phil Mattison"
<mattison20@...> wrote:

I use nichrome wire from the hobby store with spring tension, a 12v
transformer and a light dimmer. I've found that when cutting, the

foam draws

heat from the wire so the temperature (and therefore current) is highly
dependent on foam density, thickness and cutting speed. The wire expands
quite a bit when hot so the spring is needed to maintain tension. Unless
you're setting up a production system where repeatable conditions and
results are needed, it may make more sense just to play it by ear. I

just

turn up the power until the wire starts to glow, back it off a

little, and

start cutting. How much to back it off depends on the thickness and

density

of the foam.
--
Phil Mattison

I am starting to think that is how it is done. just heat the wire and
watch the cut.

I don't suppose it is anything difficult as I am trying to make it.

I was envisioning using a feedback so the cutting would slow when the
wire cooled, and/or adjust the current automatically.

Dave

----- Original Message -----
From: turbulatordude <dave_mucha@...>
To: <CAD_CAM_EDM_DRO@...>
Sent: Tuesday, September 05, 2006 7:36 AM
Subject: [CAD_CAM_EDM_DRO] Re: foam cutting current ?

--- In CAD_CAM_EDM_DRO@..., "Dennis Schmitz"
<denschmitz@> wrote:

The coefficient of resistance wire isn't as linear as platinum

but it's

stable. You can design the current regulator to maintain a set

temperature

once you've calibrated it.

Come to think of it, this will be an average over the length of the

wire, so

if it's not all being used in cutting the foam, the temp wouldn't be
inaccurate. So if you string the wire on a tension mount with

insulators,

then bring the current in with copper wire and clips. Then you

put the

length of the resistance wire doing the cut in the controller,

or the

controller could measure it if it was cold. Should get an even

temperature

across the wire that way.

Just thinking out loud...

If I follow, one could put some sensing leads with alagator clips, and
'store' them on the ends of the wire. for many cuts, measuring that
would be good enough, then on the heavy cuts, one can move them to
the edges of the part....

or, would one put the power on the clips ?

or, does it really matter ?










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Jon,

The large-scale calibration is fairly well covered by the simulated
annealing method of estimating the systematic error parameters. This
discussion grew out of concerns about quantization, and (I speculate)
that quantization will cause a surface roughness on nearly any
surface machined with a hexapod.

The quantization-roughness may be far less than the roughness that
comes from servo control system errors, vibration, chatter, or other effects.

Have you been looking at EMC for hexapod controls? Do you know if it
can generate the transformed actuator commands, independent of the
real-time actuator controls? I don't have a G-code interpreter as
part of my system, which certainly limits how easily I can import
files from other people. Also, if EMC handled the dynamics of
acceleration and setting the cut rate, it would simplify the job ahead of me.

I'm wondering if I should try using spindle load (as measured by the
current consumption or some other means) as a moderator on cutting
speed, or is the key just keeping the tool and work cool and flushing
the chips well.

There is so much about actually machining that I need to learn.

-- Carl

No, 2500 Oz-In would break things. Usually, because steppers lose

so

much of
their (holding) torque when moving, a servo with a much lower

rating can be

used. I'm using a motor with about 150 Oz-In torque on my

Bridgeport quill.

This isn't a BOSS quill, but a manual head with an external

ballscrew

added to
the front. The Bridgeport power feed has an overload clutch that

is to

be set
at 200 Lbs. linear force, so you don't want more than that, anyway.

So, I'm suspecting there is some other problem that is causing

lost steps.

Could a pulley be loose and slipping? I've sure seen this before.

Make sure the lube system is getting to the quill ballscrew, the

lines

or metering
orifices can clog up.

Jon

I reread the advert at homeshopcnc.com. Its 850 oz-in PEAK. 170
constant. Its definitly not a pulley slipping, I can watch the end
of the motor shaft. I wrote a short program to just move the quill
up and down, and watched it. It can go up and down a hundred times
and then it just kinda stalls on one move and makes a nasty grinding
noise but just creeps a little. When the controller sends it the
other way, it takes off and goes fine again for a while. If it was
something that happened everytime i did something in particular it
would be easy to diagnose. I don't know if it helps, but everytime
I run a program and it does this, it seems to lose steps in the same
direction everytime it does it. Like in this program everytime it
loses some it will be higher, or the next time I run it they will
always be lower. Or say I'm running a 3d part where the x moves
back and forth stepping .005 in the y every pass, (z axis making the
profile) the whole part will be tapered from the lower to higher y
values at a fairly consistent taper. Sometimes it tapers up,
sometimes down, and ocasionally it works fine. If instead it lost
steps both directions, it would be rough and jagged, but not
consistently tapered.

Thanks
Nathan

If you can easily move the quill up and down you probably don't have a problem. Most commercial retrofits use around 400 - 500 oz-in continuous torque rated motors. Those motors are 170 oz-in continuous.

Les


rocketscientistnate wrote:

I use nichrome wire from the hobby store with spring tension, a 12v
transformer and a light dimmer. I've found that when cutting, the foam draws
heat from the wire so the temperature (and therefore current) is highly
dependent on foam density, thickness and cutting speed. The wire expands
quite a bit when hot so the spring is needed to maintain tension. Unless
you're setting up a production system where repeatable conditions and
results are needed, it may make more sense just to play it by ear. I just
turn up the power until the wire starts to glow, back it off a little, and
start cutting. How much to back it off depends on the thickness and density
of the foam.
--
Phil Mattison

rocketscientistnate wrote:

There doesn't appear to be that much gummy stuff, and most of it is at the end. When the machine is off, I can turn the motor and move the quill quite easily by turning the position indicator (about 1.5" diameter) mounted on the end of the motor shaft. It moves smoothly and easily all the way up and down. Should the stickiness be something I should be able to feel when doing this?

Yes, if it is binding, then you would be able to feel it.

It won't hurt it to give it a good cleaning and it sounds like the cheapest potential solution. Also are you saying that all motors for this need about 2500 oz-in of torque? Or that servos need 3 times as much as steppers? I think I had read about 900 oz-in for a stepper replacement works good on these.

No, 2500 Oz-In would break things. Usually, because steppers lose so much of
their (holding) torque when moving, a servo with a much lower rating can be
used. I'm using a motor with about 150 Oz-In torque on my Bridgeport quill.
This isn't a BOSS quill, but a manual head with an external ballscrew added to
the front. The Bridgeport power feed has an overload clutch that is to be set
at 200 Lbs. linear force, so you don't want more than that, anyway.

So, I'm suspecting there is some other problem that is causing lost steps.
Could a pulley be loose and slipping? I've sure seen this before.

Make sure the lube system is getting to the quill ballscrew, the lines or metering
orifices can clog up.

Jon

Les Newell wrote:

Hi Nathan,

This a a fairly common problem. After a lot of use the slideway oil tends to leave a gummy deposit where the quill slides in the head. I found that taking the front cover off, cleaning out the oil then pouring in some cellulose (lacquer) thinners and running the quill up and down a few hundred times helped wash out the crap.

My method of freeing a Bridgeport quill that was binding was to extend it fully and
wipe axle grease all over the quill, then retract and work in and out a few times,
then extend fully again. Wipe off the grease PLUS all the grit, chips, etc. that have
stuck to the grease, then repeat. When the grease comes off the quill without little
sparkly bits in it, then you can wipe it off and relube with oil.

Before the purists jump all over me, this is for a quill that is BADLY contaminated
and full of score marks. Don't do this on a shiny and smooth Bridgeport quill, or
you may bind it up even worse. I had to beat the quill out of my head casting
with a large wood block and a sledge hammer. It had been fully retracted and left
in a garage for 15 - 20 years. It is a tribute to Bridgeport's fine machining that it
still works fine after all that. I got LOTS of chips out of the space between the quill
and housing. I assume it was all packed into the score marks, as the quill is still
a VERY snug fit.

Jon

Carl Mikkelsen wrote:

A decent parabola would require a rather large billet to start with, and a lot of material to be removed. I agree that it would be a good test.

The proposed test came out of a discussion of quantization error, which intrinsically prevents a hexapod from cutting a smooth plane, unlike a Cartesian machine which could cut a perfect plane.

What I was curious about is how to measure the small-scale deviations from the desired shape. Isn't this property called surface roughness? What is a simple way to measure surface roughness?

There are instruments that do this, surface roughness indicators.

But, one other way is to do this backwards. Maybe the plane is the easiest, here.
You mount a dial test indicator in the spindle, lock the spindle and sweep the indicator
across the surface by CNC control. The deviation of the indicator tells the error.
Sweeping an indicator across a granite surface plate would sure tell you whether the
machine could move in a straight line.

To bring it up to multiple axes, you could obtain a new bearing ball of the largest size
possible, like maybe 2 or 3" diameter, and sweep the indicator around that surface. You'd
need to make a heavy "nest" to hold the ball so it doesn't move.

Jon

--- In CAD_CAM_EDM_DRO@..., "Dennis Schmitz"
<denschmitz@...> wrote:

The coefficient of resistance wire isn't as linear as platinum but it's
stable. You can design the current regulator to maintain a set

temperature

once you've calibrated it.

Come to think of it, this will be an average over the length of the

wire, so

if it's not all being used in cutting the foam, the temp wouldn't be
inaccurate. So if you string the wire on a tension mount with

insulators,

then bring the current in with copper wire and clips. Then you put the
length of the resistance wire doing the cut in the controller, or the
controller could measure it if it was cold. Should get an even

temperature

across the wire that way.

Just thinking out loud...

If I follow, one could put some sensing leads with alagator clips, and
'store' them on the ends of the wire. for many cuts, measuring that
would be good enough, then on the heavy cuts, one can move them to
the edges of the part....

or, would one put the power on the clips ?

or, does it really matter ?

The coefficient of resistance wire isn't as linear as platinum but it's
stable. You can design the current regulator to maintain a set temperature
once you've calibrated it.

Come to think of it, this will be an average over the length of the wire, so
if it's not all being used in cutting the foam, the temp wouldn't be
inaccurate. So if you string the wire on a tension mount with insulators,
then bring the current in with copper wire and clips. Then you put the
length of the resistance wire doing the cut in the controller, or the
controller could measure it if it was cold. Should get an even temperature
across the wire that way.

Just thinking out loud...

There doesn't appear to be that much gummy stuff, and most of it is
at the end. When the machine is off, I can turn the motor and move
the quill quite easily by turning the position indicator (about 1.5"
diameter) mounted on the end of the motor shaft. It moves smoothly
and easily all the way up and down. Should the stickiness be
something I should be able to feel when doing this? It won't hurt
it to give it a good cleaning and it sounds like the cheapest
potential solution. Also are you saying that all motors for this
need about 2500 oz-in of torque? Or that servos need 3 times as
much as steppers? I think I had read about 900 oz-in for a stepper
replacement works good on these.

Thanks
Nathan Clymer


--- In CAD_CAM_EDM_DRO@..., Les Newell <lesnewell@...>
wrote:

Hi Nathan,

This a a fairly common problem. After a lot of use the slideway

oil

tends to leave a gummy deposit where the quill slides in the head.

I

found that taking the front cover off, cleaning out the oil then

pouring

in some cellulose (lacquer) thinners and running the quill up and

down a

few hundred times helped wash out the crap.

You can change to a servo on the Z without changing the other

axes. That

servo you are looking at hasn't really got enough torque to use as
drop-in replacement. Ideally you need one with 2.5 - 3x the

torque. You

can get around the problem by fitting a smaller pulley on the

motor but

this can be hard work. It is a big job to change the belt. If you

do

this be very careful to make sure the ball nut does not run off

the end

of the screw. According to Bridgeport if you do this you have to

replace

the nut and screw! You may also have to relocate the motor

mounting

holes if the belt does not line up perfectly.

Les

--- In CAD_CAM_EDM_DRO@..., "turbulatordude"
<dave_mucha@...> wrote:

Hi all,

Is there a formula to help select the proper voltage and current for a
foam cutter ?

Any special wire ?

Dave

I don't know of any formulas but power disipated is I^2.R and the R
will be a function of temperature itself so it might be a bit
complicated. I suspect it is a rule of thumb situation.

How long a wire do you need for cutting? A review of RC websites
might give you an idea of the currents, its not more than a few amps.
, lots of people seem to use 12v transformers driven from dimmers. A
current regulated supply might be better.

The best wire is nichrome, it has a high resistance and is very
strong. I do manual cutting with a 0.25mm wire which is rather thin
but reduces my "recast layer" meaning there is no melted surface on
the foam. In CNC I think they tend to use the wire in a non contact
mode so they always have this melted on layer which is fine if weight
is not the issue and it can give a nice finish.

Graham

Hi Nathan,

This a a fairly common problem. After a lot of use the slideway oil tends to leave a gummy deposit where the quill slides in the head. I found that taking the front cover off, cleaning out the oil then pouring in some cellulose (lacquer) thinners and running the quill up and down a few hundred times helped wash out the crap.

You can change to a servo on the Z without changing the other axes. That servo you are looking at hasn't really got enough torque to use as drop-in replacement. Ideally you need one with 2.5 - 3x the torque. You can get around the problem by fitting a smaller pulley on the motor but this can be hard work. It is a big job to change the belt. If you do this be very careful to make sure the ball nut does not run off the end of the screw. According to Bridgeport if you do this you have to replace the nut and screw! You may also have to relocate the motor mounting holes if the belt does not line up perfectly.

Les


rocketscientistnate wrote: