Messages

6731

General Mach Discussion / Re: Motion controllers - Take me to school

« on: September 07, 2017, 02:57:02 PM »

Hi Mike,
just been scanning around some of the other servo manufacturers and commonly a 400W servo has a rated torque of 1.27Nm which is equivalent to
160 oz.in. A 400W servo seems ridiculously large on Sherline mill.

My mill having gearboxes and so on is unusual and so my recommendation may likewise be way off as well. Do you have a specification for the torque of
the existing Sherline steppers? You know they work so you might say just double the torque and say 'now it'll work better'.

Craig

6732

Mach4 General Discussion / Re: Mach4 V3468 cannot get it to shows Controller Plugins?

« on: September 07, 2017, 02:21:29 PM »

Hi,
I found this to be very useful:
https://www.lua.org/pil/contents.html

Note that it covers LUA, not the Mach API nor does it cover wxLUA but it's a damn good start.

Craig

6733

General Mach Discussion / Re: 2 Axis Dispaly w Encoders

« on: September 07, 2017, 02:13:05 PM »

Hi,
I don't understand:

But your milling machine must have the place to fix the rotary encoder.

Attached? How? It is like some sort of quasi linear encoder?

Craig

6734

General Mach Discussion / Re: Motion controllers - Take me to school

« on: September 07, 2017, 03:27:19 AM »

Hi Mike,
ger21 is right. My servo is set with a following error of 20 encoder counts. It is an 8000 ppr encoder so 20 counts equates to 0.9 degrees, a half-step
of a two phase stepper.

I can set the following error window to be smaller, 4 counts I think is minimum, but then I have to slow everything down otherwise the drive faults out
all the time. I can likewise increase the following error but then there could be a noticeable inaccuracy between where I wanted the part cut and where it
actually gets cut, on the other hand you can push the speed up without running foul of following errors.

Craig

6735

General Mach Discussion / Re: Sherline Lathe 4410 - very new to CNC

« on: September 07, 2017, 12:33:22 AM »

Hi,
I've used Mach3 and Mach4 on my mill. In terms of machining a part there is no differrnce between them,
the part comes out identical in both cases.

Where Mach4 shines is its ability/capacity to be customised.

Craig

6736

General Mach Discussion / Re: Motion controllers - Take me to school

« on: September 06, 2017, 11:29:58 PM »

Hi Mike,
the most powerful 23 size from Clearpath is in the HP series CPM-SDHP-2341S-ELN, 165 oz.in but to get it they
had to drop the rpm back to 1680 rpm and up the price to $631.00

At slow speeds steppers produce a lot of torque, better, considerably better than a servo of the same size. At high speeds
the servo comes into its own but that won't matter a damn if the servo can't accelerate fast enuf to stay within its
following window and it fault out.

If you're really keen on servos you will probably need to go up to 34 size units.

The cheaper alternative is low inductance, high torque steppers with a decent high voltage drive, 68V or better.

On the basis of my previous post I would recommend a continuous torque of at least half my steppers/gearbox,ie
350 oz.in

Keep looking, keep talking, keep comparing, all of these are free, its too bloody late when you've just dropped a grand on the
wrong thing!

Craig

6737

Mach4 General Discussion / Re: Hall Effect for Spindle Speed Feedback

« on: September 06, 2017, 06:05:53 PM »

Hi,
depending on the Hall sensor you may need something like a schmitt trigger or comparator.
Other sensors have logic level outputs, all that's required is a supply.

Carig

6738

Mach4 General Discussion / Re: Hall Effect for Spindle Speed Feedback

« on: September 06, 2017, 02:45:33 PM »

Hi,
Hall effect sensor should be perfect for the job. Are you electronically inclined? Do you have a circuit idea in mind?

Craig

6739

General Mach Discussion / Re: Sherline Lathe 4410 - very new to CNC

« on: September 05, 2017, 03:02:28 PM »

Hi Donnie,
welcome to the forum. Mach and your Sherline lathe will work together.

When Mach was first written and released it communicated to motor drivers using a parallel port. This method still works but requires a computer
with a parallel port or that you put an expansion card in it that has a port on it, they can be had for $20. The computer also had to run a 32 bit
OS like Windows7 32bit or XP. A parallel port can be a bit of a pain, it can go cranky depending on what other software you have on it but it is free.

An ordinary USB to parallel converter won't work, it can't provide the critically timed pulse streams required. There are however motion controllers
that do the same job, they plug into your PC with a USB plug and have a DB25 output plug that would go straight into your Sherline control box.
They cost around $100. Inside them they have either an FPGA or DSP chip and it can take numerical data sent by Mach to it over USB and generate
beautifully timed pulse streams to motor drivers, very very clever little gadgets.

http://www.cncdrive.com/  The UC100 is cheap and cheerful
https://www.pmdx.com/   The PMDX-411 is cheap and cheerful

Both of these companies have been around since the beginning of time and have a great reputation for support and hundreds if not thousands of CNCers
use their products. Beware that a lot of Chinese made stuff can be difficult to get to work, the info they send with it is sketchy and hard to read and often
don't provide my help if you get stuck but it sure is cheap...suppose if you had to throw it away it wouldn't hurt to much!

Craig

6740

General Mach Discussion / Re: Motion controllers - Take me to school

« on: September 05, 2017, 03:03:05 AM »

Hi Mike,
I notice the servo you are looking at has rated torque of 58 oz.in.  Seems very wimpy to me...don't under do it...you'll regret it each time the servo
faults. When a stepper gets pushed it gets hot, starts making noises, push a bit more its starts losing steps and then stalls. An under specified servo
gets hot, starts making noises, push a bit harder and the drive faults 'following error'. If a servo can't keep up and lags behind where its supposed to
be by 20 (programmable) encoder counts it faults out and usually E-stops the machine.

While cutting forces can prevent a servo from keeping up it much more likely because it can't accelerate fast enuf to follow the trajectory you have set it.
Torque= J(moment of inertia) x dW/dt (angular acceleration).... that is without torque there is little or no acceleration and so it will take forever to get to
any speed.

May I suggest an experiment. You say that the Gcode job to machine the item pictured takes several hours to run. Have you tried the 'Simulate Program
Run' button on the toolpath tab? I use it a bit and find it accurate enuf for most purposes. Here's the experiment....edit your motor tuning as if your steppers
can go twice as fast but leaving everything else the same and <Simulate Program Run>, how much did your cycle time improve? Now go back and edit
your motor tuning with your regular speed but double the acceleration setting on all the steppers and <Simulate Program Run>, how much did your cycle
time improve.

There have been a number of posts that talk about the relative merits of speed verses acceleration and most of us vastly underestimate the acceleration
required to achieve fast cycle times.

While my mill is homemade it is cast iron and steel probably not dissimilar to your machine in terms of weight. With the gearboxes on the steppers I have
rated torque of 705 oz.in. I have settled for 0.3g for acceleration, the steppers can handle better than 1g but the whole machine rocks around and has to be
bolted down. I can't help but think 58 oz.in sounds too low.

Craig