Newbie- Is a higher resolution worth it?

[pinjas]

Hello,

I have seen some drivers that seem to have very high stepping. An example of this is made by mdfly model number MDLS556P. It's steps can go as high as 1/128. That seems pretty outstanding. I am in the planning stages of a belt drive (most likely) cnc x (2 steppers) yz plasma table.

Is there any use or reason in having resolution that high?

Does it actually spell out to accuracy or should I just stick with the typical 1/16ths step I see in most drivers?

If you know of any quality drivers that would be ideal for this application I would love to hear about them.

Thanks.

[RotarySMP]

If this is your first machine, and you are going to a parallel port, step direction controller like MACH2 /EMC/ TurboCNC (I know MACH2 and EMC support other protocols as well) then you are limited my the max pulse train a PC can output, which is around 45kHZ with the examples above.

Plasma machines need to cut pretty fast (in thinner material), and you are never going to get accuracy in the tenths, so normal hobby micro stepping drives like the Geckos, at 1/5 or 1/10 steps are going to be plenty to cut down on resonance, but still be fast enough for your machine.

I doubt micro-stepping at those levels is about positioning accuracy. It is probably more about dealing with resonance and damping issues.

Start with Geckos. They are cheap, good, well supported, and easy to wire.

[pinjas]

Originally Posted by RotarySMP If this is your first machine, and you are going to a parallel port, step direction controller like MACH2 /EMC/ TurboCNC (I know MACH2 and EMC support other protocols as well) then you are limited my the max pulse train a PC can output, which is around 45kHZ with the examples above. Plasma machines need to cut pretty fast (in thinner material), and you are never going to get accuracy in the tenths, so normal hobby micro stepping drives like the Geckos, at 1/5 or 1/10 steps are going to be plenty to cut down on resonance, but still be fast enough for your machine. I doubt micro-stepping at those levels is about positioning accuracy. It is probably more about dealing with resonance and damping issues. Start with Geckos. They are cheap, good, well supported, and easy to wire.

I've been trying to wrap my brain around this idea, and I have thought of this many times. I have seen parallel to USB cables online and I often wonder why parallel ports are used at all. It almost sounds like it would be better to use a USB port based on what you typed.
I believe most of the material I am cutting is 1/16ths and 1/8ths inch aluminum on the table I am planning out. Fast cnc cutting speed sounds wonderful to me.
I have looked into gecko but I have trouble telling what is what when looking at their drivers. I have seen some drivers that have relays on them as well, for the plasma torch.
Is there such a thing as a USB driver? Would it be of benefit to use?
This is indeed my first CNC table build, the purpose isn't really for hobby, however. I have aims to use it for fabricating fairly large numbers of various things.

[rowbare]

I am assuming you would be using Mach. I would recommend starting by using the parallel port. Once you have a bit of experience, and if you find you need it, you can get something like a SmoothStepper to allow you to use the USB ports. I wouldn't start with the SS since it adds another layer of complexity and potential frustration. Keep it simple to start with and you will be much better off.

As for microstepping, Mariss, the designer of Gecko drives has stated that more that 10 microsteps isn't terribly useful. I forget the rationale behind it but if you need to know you can do a bit of serious searching in the forums here and find it.

bob

[jimcolt]

The highest resolution will not necessarilly improve accuracy with plasma, but will produce a smoother cut edge. Cogging or stepping from drives can actually be seen in an air or oxygen plasma cut edge. Virtually all industrial machines (read expensive machines) use servos, the best use AC brushless servos that are inertia matched, with low backlash planetary gearboxes and precision racks, sometimes helical racks....to produce best accurace, edge smoothness. You can see the difference, but probably cannot measure the difference in cut accuracy!

Higher resolution and belt reduction drives will help to minimize edge roughness.

Jim Colt Hypertherm

[RotarySMP]

The Parallel port (LPT) is used because:

1/ It is parallel- you can tell different things to do different stuff at the same time.

2/ It is dumb - It is an old protocol which seems to work at a pretty low level in the computor, and you can force the computor to feed it to a certain rythym in real time (about 45KHz). Basically this is a good drummer.

The USB port is serial, one command at a time, so if you want multiple things to do different stuff at the same time, you are out of real time. You are into coding blocks of commands together, then sending them out to some widget which decodes them and does the real time control of the multiple parallel things. Since the USB port is not real time, it doesn't matter if the PC stops talking on it while it inspects its navel, or whatever it is that OS's do when they seem to be doing nothing.

Their are some non-parallel port solutions out there, such as the USB based "smooth stepper", for which there is a Mach 3 driver available. These address the two main weaknesses of LPT based systems:

1/ Future proof - The LPT port is dying out. Not a real problem today, as it has been dying out for about 10 years, and yet there are still new MoBo's which have them, and cheap PCI-LPT cards. For at least the next 10-20 years you will be able to get cheap Pentium III and up used computors with an LPT for a few bucks.

2/ They can offer much higher max frequencies than 45kHz with very stable pulse trains.

You only really need higher frequencies if you need both high resolution and high speed at the same time, whic a plasma cutter doesn't.

For a plasma cutter, the scarf that the torch cuts is not very accurate, so having high positioning resolution is pointless. The moving bits are not very heavy (the torch and support) so you can get very high speeds with a belt drive system , and still have driver resolution an order higher than the needed part resolution, but stay within the 45Khz.

A USB based system would not gain you anything. Start simple.

Geckos vampires are more robust than the normal drives, and they are easy to wire up. There are plenty of LPT breakout boards available to simplify the wiring.

Wiring up a relay is not differcult.

If you hate wiring, buy a Gecko G540, then about half the wiring is done for you.

[James Newton]

Just a quick note... I agree with everything everyone else has said here. Especially the point of starting simple, getting /something/ going, and then moving if you find you need to improve performance in some area.

I would like to add that microstepping does somewhat reduce the massive vibration associated with stepper motors (since the aren't starting and stopping in quite as large a step) and so can help to reduce the nasty mid band resonance issues.

And finally, although Geckos are /excellent/ drives, if you are more the do it yourself type, or you recognize that starting out quite often involves things going wrong so the ability to repair the driver cheaply is important, and if your motors are in the medium small range (up to 2 amps per phase) you might consider the Linistepper. You can replace the drive transistors yourself for $2 if you happen to fry one, and it does allow for very smooth /analog/ stepping while maintaining good high speed power through current regulation.

The Linistepper actually uses an analog drive (it's not a chopper) so it can have a capacitively smoothed "step" that rounds off the corners on each start and stop further reducing vibration and giving you the advantages of more steps, without requiring the higher speed step frequencies that are difficult to produce.

Mariss has even said: "A switching type drive makes sense when the power levels are large. The inefficiency of a linear drive becomes prohibitive at such levels. At 7A and 80V, a classic linear drive dissipates an unacceptable 560 Watts of heat in the power transistors. At the other extreme, say 1A and 24V, the complexity of a switching type drive makes less sense. Heat dissipation then is a manageable 24 Watts and the simplicity and other advantages of a linear amplifier becomes appealing."
http://www.cnczone.com/forums/714433-post28.html

[gandalf1]

I have always understood the parallel port is a true machine control port. I suppose it must cost a bit more for the 25 pin connector than the USB both for computer manufacturers or printer makers so they seem to have stopped fitting them. USB to Parallel cards might work for the basic printers but maybe not much use for a machine control and USB being serial output surely means that instead of X and Y or comes to that Z as well moving simultaneously they must move in sequence.
I'll stay Parallel and used museum piece computers.
John.

[pinjas]

I really appreciate the input guys. I have been reading a lot on various subjects concerning CNC plasma tables but I still feel extremely lost or overwhelmed by the amount of options there are for each individual idea.

I've been considering using Page Title these guys for sourcing parts. They seem to have fantastic pricing.

1. Analog vs digital. I don't seem to see a lot about this subject, if anything at all. But I am looking over this Page Title page. I am a little concerned about the products as at the top of the page the word 'guarunty' is used, however, they make some claims that sound promising and may even make things simple. I know it has been suggested to get the g540, I am not against it and I have seen plenty of positive things about it but I have nothing against wiring at all. In fact, I sort of enjoy wiring things.

Most of my design and ideas are taken straight from http://www.cnczone.com/forums/plasma..._finished.html this thread. This guy uses "KL- 5042 Microstepping Driver". The reason I bring this up is because of the pricing. I am trying to do this as cheaply as possible so long as I don't sacrifice quality in operation.

2. G540 vs something digital vs KL- 5042. What do you guys think? I assume some may lean towards one vs the other.

3. I am pretty lost on what the ideal size steppers are. What size steppers would be best for the x x y z? I am going with a 4 axis setup. x x y z. Some suggest that it is better to have the X driven on both sides, I only assume this is true. I am generally planning on cutting sheets of aluminum at 1/16ths and 1/8ths. The table is to be made out of steel. I haven't settled on the dimensions of the table. I could fit a 4x8, but I am not sure if it is needed or worth it. It seems that, in terms of cost of material, there is no benefit. So I might go with something like 3 by 6 and a half for table dimensions. Like I said, I am trying to do this as economically as possible. Would it be better to have smaller z and y stepper? Or maybe something under 300oz for all 4 axis? I am totally lost on this.

Thanks a ton. Things are starting to form into a reality in my mind.

[vger]

Pinjas,

I recently did a repair job on a router table (Countertop shop) that lost the Y axis drive. The table is 5 ft by 10 ft with a Z of about 6 inches. There were 5 stepper drivers in the machine, 2 for X, 1 for Y, and 2 for Z... Yes... 2 for Z, one for each of the 2 routers. Each of the X and Y motors was belt reduced by 4:1 driving pinion and rack (1" per rev of pinion) for motion. The stepper drives were set at 1/4 step, so the end resolution was 3200 steps per inch. 100 steps for 1/32" is a lot finer than you would need for plasma. Anyway, the steppers were NEMA 34's and the drivers were set at 5 Amps. You can get by with a lot less since the plasma has no cutting forces to contend with.

A USB to parallel adapter (if it emulates the LPT fully) will have serial to parallel and parallel to serial converters in it. A couple of bytes would be sent out the USB for output, and a couple more would be read for input. This requires the USB interface in the computer to convert the parallel data on the buss to serial, send it out the USB to your adapter where it is converted back to parallel, and vice versa. Seems like a lot of converting to get back what you had in the first place.

Good luck with your build, keep us informed.

Steve

[RotarySMP]

None of the standard hobby CNC control software (Mach3, EMC, TurboCNC etc) supports USB, with the exception of the Smoothstepper installation for Mach 3 (as far as I know).

A USB to Parallel port won't work as the software doesn't address the USB port. If you have a computor without a parallel port, buy a PCI -> LPT card.

Don't be a afraid of the parallel port, it is really easy. Mach two tells a pin to turn on, and the pin goes to 5v, so that the relay you implement turns on the widget. EMC tells the pin you define as X step to step 5 times and the motor drive moves the motor 5 micro steps.

You have it easy with a belt driven plasma. No cutting forces, and you can easily change gearing if you need it to run faster, or more accurately.

Just buy any name brand bipolar micro stepping drives ( I would suggest Gecko Vampires, so if you mess up you don't blow the drive), and run Keling 382 or 425 OzIn steppers.

[pinjas]

Thanks for the reply vger, I really appreciate the well thought out responses RotarySMP. Although I haven't really ever said this to any degree, I do have the notion of possibly using a router with the table as well in the future, mostly for carving things in wood for friends and family, gifts or whatever.

I guess that guys Z axis needed a lot of balls.

I certainly don't fear the parallel port. I've done a bit of research on PCI parallel ports, they are cheap, at least compared to the over-all cost of a CNC setup.

Although, I can't really tell the difference between each driver. I can tell the difference in pricing. G203vs seem a bit pricey.

I have a few questions concerning stepper motors.

• What is dual shaft?

• I think I've read that it is better to have an 8 wire stepper over a 4 wire stepper. Is this accurate? I say this because the two steppers suggested by RotarySMP have this difference. HIGH TORQUE STEPPER MOTOR 1203 oz-in, ½” shaft with a key or flat