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I've been running a Boss 5 from my pc for over a year now. I use
Deskcnc, which seems to do a great job of running the mill, but I
don't use it much for programming. I've got gecko 201s and they
drive the stock stepper motors pretty well.

Now that i've said it can be done, I have a question for everyone
else. 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.

thanks
Nathan Clymer

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

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:

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

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

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

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:

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

--- 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

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 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.

I had exactly the same problems as you. On top of lost steps I had problems with the Z drive blowing. In the end I changed over to servos and now it performs brilliantly. Rapids are limited to about 100IPM because I used undersized motors and geared them down. However that is more than enough for what I do.

Les

rocketscientistnate wrote:

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

I had exactly the same problems as you. On top of lost steps I had
problems with the Z drive blowing. In the end I changed over to

servos

and now it performs brilliantly. Rapids are limited to about

100IPM

because I used undersized motors and geared them down. However

that is

more than enough for what I do.

Les

I would love to do that. Where is the best place to get the
servos? What size do I need, to gear them down and go undersize, or
to go 1:1. I assume I'll need gecko 320s? What are the possible
hang ups in doing this? With the encoders is it pretty much
guaranteed that if its running the servos are going to be in the
right place? I'm a little anxious as I have customers starting to
breath down my neck. Luckily, the local college lets me use their
Fadal when I'm broken down. :) I had almost decided to try to sell
the whole machine and get a smaller benchtop one, that I could be
sure would work. I thought if I go to servos, its my luck that it
still won't work and then I'll have the same useless machine, and
still be out the money for servos.

Thanks
Nathan

Raymond Heckert 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.

That's a good thought, if the belt is a bit loose, it may try to jump a tooth, and
get hung up.

Jon

Hi Nathan,

I went the cheapskate route and bought some treadmill motors from Surplus Center. They were similar to these: <>. Mine have a short shaft sticking out the back, perfect for an encoder. You would have to ask to find out if these motors also have a shaft sticking out the back.

Surprisingly for a cheap motor they run very smoothly at low speed. The only problem is that they are designed for high revs so you need to gear them down at least 3:1 to work well. My Z axis is about 2:1 if I remember correctly and the motor can get a bit hot if you keep running the Z up and down at rapid speed for a while. In actual use none of the motors get particularly hot.

To get a suitable ratio you need to use different belts. I used 15mm HTD belts on X and Y. You can't easily change the Z axis pulley which is why I couldn't get the ratio I wanted. Be warned belts and pulleys can be expensive!

If you are using the machine for work it is probably not worth spending the effort and time to use these motors. You would be better off finding a more suitable motor even if it is more expensive. As I mentioned before you need somewhere around 30 lb-in (480oz-in) continuous rated torque if you want to re-use the existing pulleys.

As long as you are reasonably careful about screening and use good quality cable on the encoders you are unlikely to lose steps. That is what I really like about my servo setup. I don't have to worry that a stepper may have lost steps somewhere along the line. I use Gecko G320s on the mill and Rutex R990H on my lathe. IMHO the R990s give very slightly better performance but they are more hassle to wire up. Don't sell your Bridgeport. No benchtop machine will compete with it once you have it working correctly.

Les


rocketscientistnate wrote: