Messages

681

General Mach Discussion / Re: Need Guru input on an idea: Using Mach as dynamic balancer

« on: May 14, 2010, 09:25:58 AM »

Not sure how an accelerometer would help you.  I believe the way tire balancers typically work is to have strain gauges on the spindle support, which will give you a cyclic strain reading that can be correlated with the angular position of the wheel, to determine the location of the heaviest point, while the magnitude of the strain gives an indication of the amount of imbalance. 

For lower precision, I'd try using a proximity sensor.  If the spindle is mounted on compliant mounts, you should be able to get enough motion through compression of the mounts to get a good reading from the proxiimity sensor.  Since you'll inherently know angular position courtesy of Mach3, and a simple calibration with a few known weights will tell you how to scale the proximity sensor reading, the math to calculate the weight required, and the correct position, should be pretty trivial.  A quadrature setup should give high sensitivity.

Regards,
Ray L.

682

General Mach Discussion / Re: input read frequency?

« on: May 10, 2010, 11:33:21 PM »

Ray

I'm not disputing anything you say. As I've already said, we established this earlier on in the thread.
By dynamic probing routine I mean one that determines at run time what it's next step will be based on previous steps.

But riddle me this. Why doesn't Mach *appear* to work in the same way with regards it's THC UP/DOWN inputs i.e. take a step and then check THC UP/DOWN ?

Cheers

Ian

Because torch height isn't controlled by G31....  It's a completely different, and less accurate, control loop.  ONLY G31 behaves as I described.

Regards,
Ray L.

683

General Mach Discussion / Re: input read frequency?

« on: May 10, 2010, 10:07:18 AM »

I'm probably a bit slow and everyone else already knows this but... Re: probing - this must mean that in order to probe at the best resolution your machine is capable of you MUST probe at less than 10 steps per second right?

Ian

Probing is a completely internal operation, and probe input is sampled at kernel speed.  The 10Hz is the macro-pump rate, which has nothing to do with probing.

Regards,
Ray L.

At this point in the thread maybe so Ray (see my last post above yours) but at the time I posed the question the thread wisdom was that ALL inputs were read at 10Hz.

That said...

Probing is a completely internal operation

generally yes - but not in a dynamic probing routine and then the 10Hz macro rate really bites you in the ar*e.

Cheers

Ian

Ian,

I don't know what you mean by "dynamic probing routine", but if you're using G31, it takes a step, then checks the PROBE input.  The 10Hz rate has nothing to do with it.  Were this not true, it would be absolultely impossible to probe at 50IPM, as I routinely do, and get 0.0001" repeatability.  If you're directly monitoring the PROBE input with any kind of macro, then you ARE subject to the 10Hz rate. 

Regards,
Ray L.

684

General Mach Discussion / Re: input read frequency?

« on: May 09, 2010, 09:09:18 PM »

I'm probably a bit slow and everyone else already knows this but... Re: probing - this must mean that in order to probe at the best resolution your machine is capable of you MUST probe at less than 10 steps per second right?

Ian

Probing is a completely internal operation, and probe input is sampled at kernel speed.  The 10Hz is the macro-pump rate, which has nothing to do with probing.

Regards,
Ray L.

685

General Mach Discussion / Re: Encoder motor control

« on: May 04, 2010, 11:36:36 PM »

Adding an encoder cannot magically "fix" and under-designed drive.  Your problem is your motor is too small for the load you're moving, and/or you're trying to accelerate too quickly, rapid too quickly, or "push" more than the motor is capable of.  The only fix for that is either backing off on what you're expecting the motor to do, or putting in a motor better sized to the load.

Regards,
Ray L.

686

General Mach Discussion / Re: Proper Tool Changes

« on: May 02, 2010, 10:46:12 PM »

If you're doing manual tool changes, unless your knee is CNC'd, don't even bother setting up the tool table - just change the tool, and zero it to the work using the knee, then hit CycleStart.  If your knee is CNC'd, I have a set of macros that I wrote to use the knee for doing tool-length compensation, though this requires using custom macros in your G-code (M843 instead of G43, and M849 instead of G49) for turning tool length compensation on and off, due to limitations in Mach3 (That will be fixed in v4).  I have another set of macros I use for setting up the tool table, using probing.

Regards,
Ray L.

687

General Mach Discussion / Re: mach's rounding of measurements?

« on: April 24, 2010, 11:44:17 PM »

As I said, there are no fractional steps, so a move won't call for 352.7 steps.

Gerry, I worded my question badly.  I meant "if the distance called for scaled to 352.7 steps".  I realize that steps are a quantum measurement.

A move will call for a given distance. Mach3 will send as many steps are needed to reach that distance, without exceeding it, to the nearest full step.

OK, I won't dispute that since you say it is fact and fact is fact.  But I wonder why.  In my professional life I have worked with stepper-driven systems for almost 30 years now (many with relatively coarse timing belt drive) and the controlling firmware's criterion has always been "what step is the closest to the destination?" and not "what step is <= the destination?".  It is just a surprise to me that Mach adopts the latter criterion... [insert shrug emoticon here]

Randy

Why on earth do you care?  In the real world, it makes absolultely no difference whatsoever whether it rounds up, rounds down, truncates or anything else.  In any real machine, the inaccuracies of the machine itself vastly exceed any positioning error due to rounding.  The stepper motors are nowhere near that accurate, especially when micro-stepping, and especially when the machine is actually moving under any load whatsoever.  The flex in the machine, inaccuracies in the screws, runout in the pulleys/gear/whatever, and backlash (which is NEVER zero) will completely swamp any error due to rounding up or down by a single fractional step.  Worrying about this is truly picking the fly poop out of the pepper...

Regards,
Ray L.

688

General Mach Discussion / Re: Aluminium Cutting

« on: April 21, 2010, 09:27:20 PM »

Good Evening to All
Its been quite a while since my last post, just goes to show when you build a good Mach machine nothing really goes wrong, True to a point, since last time I posted anywhere, I have added a 4th axis to the big router, and actually worked out how to use it, still trying to learn how to alter a 3d file but that is a different matter entirely.
Ok enough rambling from me, My next project is to make a 23' Aluminium boat, the panels I am hoping to cut using my CNC router, I can already hear shrieks out there, apparently it can be done. The thickest material will be 6mm and the rest will be 4 and 3.
The machine has a 5HP Fimec motor speed range from 7 to 14.700 rpm and cuts max speed 3000mm/min comfortable, can go a lot faster but scary at high speeds! I don't want to use mist lube on the cutter I have made up a concentrated compressed air fitting to blow onto the cutter, but I don't want oil going all round the joint.
I will probably use either a 3mm or 6mm cutter cut down, smaller the better.
Now the Crunch, What I would like to know What is be best cutter to use? speed/feed rate? rpm? and cut depth?
Has anyone got experience?
Cheers Katoh

I don't see any reason you shouldn't be able to do what you suggest.  I'd probably use a carbide endmill rather than a router bit.  I do my aluminum roughing using a 1/2" carbide 3-flute endmill, 0.125" DOC (~3mm), 6000 RPM, 75 IPM.  It'll do that all day long with just a strong blast of air to keep the chips clear.  In general, with aluminum, if your feed is too slow, you'll find the tool heats up, and chips weld to the tool.  The natural reaction when you see a hot tool, and chip welding, is to slow down, but that's exactly the wrong thing to do.  You want to maintain the heaviest chipload you can get away with (which is a function of your machines stiffness and spindle power), as a thick chip will carry heat away from the tool.  If the machine stiffness prevents running the desired chipload, reduce RPM, reduce feedrate accordingly, and try again.

Regards,
Ray L.

Regards,
Ray L.

689

General Mach Discussion / Re: micromachinng surface finish

« on: April 19, 2010, 09:40:04 PM »

There are soooooooo many things wrong with that paper....  Whoever wrote it does not understand what he's working with.  Perhaps most glaring:

"The low-cost machine has been set-up to use 1/4 stepping for a positional accuracy of 0.0000625 inches (about 1.6 microns). It should be noted that in all cases, the accuracy achieved is dependent on other considerations such as manufacture and assembly processes employed. In addition, spindle run-out is responsible for much of the inaccuracy. Typical spindles have inherent run-out in the region of several microns. However, the accuracies are improving. The low-cost spindle which is being used in this application, shown in figure 3 below, has a low run-out; approximately 0.00024 inches (about 6 microns)."

He confuses resolution with accuracy (two TOTALLY different things!), and makes no allowance for the inaccuracy of the leadscrews, and other purely mechanical factors, such as backlash (which is virtually NEVER zero).

Regards,
Ray L.

690

General Mach Discussion / Re: Is there a VBscript beginners guide?

« on: April 19, 2010, 10:07:48 AM »

Thanks omegasea, wasn't aware of this document. But "Cypress Enable".... does it ALL apply to Mach3 VB scripting as well?

Dan

Cypress Enable is the VB interpreter Mach3 uses, so everything in that manual applies to Mach3.  The Mach3 specific functions are documented here:

http://www.machsupport.com/forum/index.php?action=dlattach;topic=12730.0;attach=18221

Regards,
Ray L.