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Messages - Tweakie.CNC

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7621
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.

7622
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.

7623
Show"N"Tell ( Your Machines) / Re: Laser cross hair tool position.
« on: April 02, 2009, 12:21:39 PM »
Rich,

Is your laser similar to the ones that Dave and I have (with chrome color case) or is it the one with brass color case ?.

Just curious.

Tweakie.

7624
Show"N"Tell ( Your Machines) / Re: Finished my 4th axis
« on: April 02, 2009, 11:36:22 AM »
I am sure it will be quite stunning when it is done. When are you going to make a start on it ?.

Quote
Marcel would have you make one 1" OD with a dinky one just like it free and floating in the center.
What a challenge THAT would be !
Thanks,
RC

I think that Marcel is the one and only person who could make one that small RC.

7625
Show"N"Tell ( Your Machines) / Re: Laser cross hair tool position.
« on: April 02, 2009, 11:26:30 AM »
Sorry to hear that you wasted $5 and that it is no good Rich.

As said in the posting above I have a beam width of less than 0.3mm and this is brilliant for a router but not for a mill perhaps.

Tweakie.

7626
Tutorials / Re: OEM Buttons Description
« on: April 02, 2009, 05:24:43 AM »
For those who follow - Hood has now compiled an .xls file of the OEM codes and this is attached below.

Tweakie.

7627
Show"N"Tell ( Your Machines) / Re: Finished my 4th axis
« on: April 02, 2009, 02:11:11 AM »
Looking forward to seeing the end result Lemo. I think that the final finishing and polishing will take some hours to get anywhere near to the finish on that render.

Tweakie.

7628
Show"N"Tell ( Your Machines) / Re: Laser cross hair tool position.
« on: April 02, 2009, 02:02:58 AM »
Bad joke perhaps but I am glad that somebody looks at my website.  :)

Tweakie.

7629
Show"N"Tell ( Your Machines) / Re: Finished my 4th axis
« on: April 01, 2009, 11:21:44 AM »
Would that have been the 1st April last night ?   ;D

Tweakie.

7630
Show"N"Tell ( Your Machines) / Re: My new CNC mill. JEH Guitars
« on: April 01, 2009, 08:08:58 AM »
That's great Jens - please post more pictures as you proceed.

Tweakie.

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