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Author Topic: Losing Zero  (Read 5706 times)

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Offline russh

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Re: Losing Zero
« Reply #10 on: November 17, 2015, 02:38:22 PM »
The movement in the X and Y seems smooth, cant feel any grinding or jerking on the table. There is a touch of noise in the Z, I'm tempted to say like a grinding noise, but I wouldn't say its actually grinding.

The motor sound nice, like any electrical hum as the work

Offline russh

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Re: Losing Zero
« Reply #11 on: November 17, 2015, 02:50:18 PM »
I've just ran at 800 mm/m and it seem stable, I measure delta from start Zero of X: 0.0069 Y: 0.01 and Z: 0.09, but this may just be down to measure error. I'm going to keep running this movement programme through a few more times and remeasure

Offline bfgstew

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Re: Losing Zero
« Reply #12 on: November 17, 2015, 03:08:42 PM »
Seems you are getting to the motors sweet spot with the velocity settings. It took me a while as I thought faster was best, how wrong was I, you may find that 600 will suit your Z axis, no harm in trying?

Offline russh

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Re: Losing Zero
« Reply #13 on: November 17, 2015, 03:11:52 PM »
Right, so this low velocity is pretty normal then, I guess it depends on the motor spec?
What I dont understand, if the machine manufacturer states 5m/min for X and Y, and 3m/min for Z, which im way off

I will give 600 a try

Offline russh

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Re: Losing Zero
« Reply #14 on: November 17, 2015, 04:16:12 PM »
Seems I still have a small problem

Now down to 600mm/m

After running a 25 minute program of a repeat set of movement

Y and Z seem stable

X lost roughly 0.3mm

Re: Losing Zero
« Reply #15 on: November 28, 2015, 03:37:19 PM »
Hi russh,
what is the pitch of your lead screws? I use 5 phase Vexta steppers, I wanted the better resolution (500 step per rev verses 200 step per rev for more
common 2 phase steppers) and smoothness at full step. When researching I found the Vexta website handy because they have a graph of motor torque
vs speed. As it turns out a motor rated at say 200 oz.in typically measured at around 100 rpm is likely to be only 20 oz.in at 1000 rpm.
More research has shown that all steppers are broadly similar in that the torque diminishes rapidly at speed. Microstepping makes it worse.
The bottom line is that stepper motors have no grunt at speed, and you will lose steps or stall if you try.
My steppers are fitted with 10:1 low backlash planetary gear reducers, with the reduction even modest steppers produce great torque but very slow. My 'rapids'
I have settled at 600 mm/min with 5mm pitch screws ie the screws at 120 rpm and the steppers therefore at 1200 rpm. When tuning/experimenting I tried a lot faster,
one stage I had rapids of 2100 mm/min ie screws at 420 rpm at steppers at 4200rpm. They ran hot and very unreliably.
As I progressed I found that at 600 mm/min I could back the drivers off a wee bit and still have reliable operation even with 30 kg on the table. At cutting speeds
around 150 mm/min in steel I have 80kgf of thrust so plenty of grunt...
My advice is don't try to run steppers fast, they don't like it and you will break tools like they're going out of fashion.

Craig
My wife left with my best friend...
     and I miss him!

Offline russh

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Re: Losing Zero
« Reply #16 on: November 28, 2015, 03:50:58 PM »
Hey Craig,

Really appreciate that post. I dont know the answers to your questions of pitch and stepper motors, but leave it with me and I will strip the machine back slightly to take a look.

Its interesting cause its mostly the Z axis loosing position the most, and that has the large cast head, spindle and motor all attached, so the motor will need alot more torque than X and Y
Re: Losing Zero
« Reply #17 on: November 28, 2015, 04:47:41 PM »
Hi russh,
sounds like the weight of the z axis will be a challenge. Maybe you could consider a gear reducer, they really improve torque/thrust.
Most of my toolpaths are 2d in the sense that the z axis lowers to to fresh cut of say 2mm and then x-y take over until a fresh cut is to be made.
If my z axis is slow it doesn't matter to much.
Low backlash planetaries are not cheap even second hand but are available for most steppers are pretty easy to fit. The ones I use are 23 size
so a 23 stepper screws directly to the input and the output mounting is 23 size as well so you just stick it in between as it were.
The only time the reduced axis speed is really going to hurt is when you do co-ordinated moves like helical cutting or 3d contouring. Even then you
are likely to be at federate which is so much slower anyway.
I amongst other things engrave circuit boards and particularly when drilling all those little holes with tons of small z moves do I miss fast rapids.

Craig
My wife left with my best friend...
     and I miss him!

Offline russh

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Re: Losing Zero
« Reply #18 on: November 28, 2015, 04:54:14 PM »
What I dont get is this is a purchased machine, not a DIY job, and there are your tube videos of it in operation working pretty fast. I'm wondering if I've been ripped off with cheap stepper alternatives by the manufacturer. I will strip it a little and get some more details.

This is the machine
http://youtu.be/sop3aiFxaws
Re: Losing Zero
« Reply #19 on: November 29, 2015, 12:33:28 AM »
Hi russh,
watched the vid and I'm jealous! Looks the business. I noted that the note that introduced the clip said 2200 W BLDC spindle and
SERVO control. Is that how your machine is fitted out?
Might be worth an email to the manufacturer to clarify what 'servos' were actually demonstrated in the vid and if your machine is the same
spec.

Craig
My wife left with my best friend...
     and I miss him!