Messages

8661

Show"N"Tell ( Your Machines) / Re: New Build 6 axis CNC first timer

« on: April 05, 2009, 07:02:51 AM »

Hi Barry,

My machine here is a 3 axis router. Each axis motor is current limited to 2 Amps and the PSU is rated at 24 Volts, 6 Amps. The driver board gets its 5 Volt from the 24 Volt  PSU. This setup wouldn't work for everybody but it is fine for my needs.

Tweakie.

8662

General Mach Discussion / Re: How to post code in Write wizard?

« on: April 04, 2009, 08:12:23 AM »

Hi,

Something  that is easily overlooked when using the Write Wizard for the first time on a new installation of Mach is to click on one of the direction buttons. If you don't then the only GCode you get on the Mach screen consists of Z moves only, everything else is 0.0000.

Tweakie.

8663

Show"N"Tell ( Your Machines) / Re: New Build 6 axis CNC first timer

« on: April 04, 2009, 03:54:43 AM »

Hi Barry,

I just stuck the box on the back of my router frame where it is out of the way and wired to it. If it didn't work first time I knew I would get it working eventually. But as luck would have it first time and rock'n'Roll.

Tweakie.

8664

Show"N"Tell ( Your Machines) / Re: My soon to be CNC router

« on: April 03, 2009, 11:30:49 AM »

Wow !
I would commit all sorts of sins for a machine like that. Look after it Allyd.

Tweakie.

8665

Show"N"Tell ( Your Machines) / Re: New Build 6 axis CNC first timer

« on: April 03, 2009, 11:26:06 AM »

Hi Barry,

For your wire - used screened cables for everything except the spindle (this will avoid any possible stray pickup problems at a later stage) and earth them at the controller box end only. For bipolar steppers you only need 4 core, for unipolar you need 5 core, not sure if you will be using encoders. Obviously the cores have to be man enough to handle the motor current. Limit switches only need two core but again make it screened cable.

Hope this helps.

Tweakie.

btw. When it comes to earthing - it pays to have one single earth point and earth everything to this single point within your control box. (do not earth the screen of your LPT connection - this is only earthed at the computer end).

8666

General Mach Discussion / Re: New UPDATED Mach3 VB Parameters list added to Member Docs..

« on: April 03, 2009, 11:10:34 AM »

Thank you Scott.

Tweakie.

8667

Third party software and hardware support forums. / Re: Help with Stepper Motor Tuning and Setup

« on: April 03, 2009, 09:53:19 AM »

That's the way to go Prof. 

Tweakie.

8668

Show"N"Tell ( Your Machines) / Re: Laser cross hair tool position.

« on: April 03, 2009, 09:48:17 AM »

Hi Rich,

0.030 inches resolution is no good at all - obviously not all these laser pointers are the same. I shall now consider myself lucky and perhaps buy a lottery ticket this afternoon.

Tweakie.

8669

Third party software and hardware support forums. / Re: Help with Stepper Motor Tuning and Setup

« on: April 03, 2009, 05:48:50 AM »

Hi again Prof,

I fully understand what you are trying to do here, you have explained that well in other postings, but I can’t help thinking that you are ‘re-inventing the wheel’. We have moved on a lot since the early days of CNC and the advent of chips with computing powers have simplified controlling the drive requirements of stepper motors considerably. If we consider a basic CNC machine it all comes down to the need to move an axis from one place to another. Because any axis has mass this then requires a greater force to accelerate and decelerate it than it does to maintain it at a constant speed. Just considering mass and acceleration at the moment and ignoring the many other forces involved, then the greater the mass the greater the force required likewise the greater the acceleration / deceleration the greater the force required. Now steppers have the characteristic of being able to provide high torque (force) at slow speeds and low torque at high speeds which pretty much meets the requirements for moving a CNC axis. When a stepper is stationary, the torque is high so the current through its windings can, within limits, be reduced without compromising its performance (holding torque). So to drive a CNC machine well and efficiently the current through the steppers must vary in accordance with the task. Minds greater than my own have tackled this problem and for example chips, such as the Alegro SLA7024M series for unipolar and the A3982 for bipolar steppers implement the requirements to a tee. There are, of course, many other makers and chips to choose from and I recommend that you proceed in this direction. After all we must learn from and build on others experience because, as others have said, life is just no long enough to make all the mistakes yourself.

Sorry for rambling on a bit but if your ultimate goal is to build a working CNC machine why not concentrate on the mechanicals and purchase Gecko drives for the steppers – it may be a lot cheaper in the long run.

All the best,

Tweakie.

8670

Third party software and hardware support forums. / Re: Help with Stepper Motor Tuning and Setup

« on: April 02, 2009, 12:51:04 PM »

Hi Prof,

18-20 Volts is OK for your steppers, just make sure the 1 Amp current is not exceeded otherwise they will get very hot and may be damaged.

The motor settings are not really applicable to free running mode as everything will change when they are put under load driving a machine.
However, as motor torque reduces as the speed is increased - then increase the speed settings until the motor stalls when driven then back off the speed setting some 10 - 20 %. Set the acceleration to the fastest that will allow the motors to start from stationary.

Hope this helps,

Tweakie.