What is going on with the mini CNC Mill?

[Geoff]

To start with the Mini Mill was out of action for some time as the spindle motor was believed to have been burnt out, but RobB found that it was working just fine after he did a nice job cleaning it:-) A series of tests were run and it looks to be working without fault. Now we have a spare spindle motor in case we really do burn the spindle motor out!

Next the controller was going to be fixed up but it got dismantled ... (I'm going to use some of Andy's “... “ to skip what would be a distraction) so now we (well mainly Ajax who has done a nice job) have put the controller into a good sized box.

The E stop saga continues. Well no, it now switches both the phase and neutral, cutting power to all but the laptop. Thank you to Lachlan who kindly supply the nice E stop and bits:-)  

First tests went well to start with, then we started testing with a fancy pattern draw in Inkscape. Thank you to Bob who showed us how to get Inkscape to generate a cool test pattern:-) 

After running the cool test pattern a number of times it decided to give Ajax some work to do, and it ran of the Y axes. After an hour or two (Ajax had some previous experience with this:-) the bearing and stop was back looking like it should look. 

Michael et al kindly delved into the firmware to find why the limit switch did not stop the bed from running into, and through, the limit. By default the limits are not checked when running a job. A number of changes were made to make the limits kill the job.

Now we currently have the limits killing the job due to noise. It has been tested with the spindle motor off and both the Mill and the laptop plugged into a saturated core isolating transformer. Alas the limits are still killing the job so we are going fix this by changing the limit switch from normal open to normal closed. This means the wire going to the Mega is normal connected to ground and thus very unlikely to have any noise. To make certain, we are going the add opto's and a low pass on the limits just to remove any possibility for any noise on the limits to be an issue.

When will it be ready for me to use? 

We do not know that we have all the bugs fixed yet, as we have only just started with the investigation into the RF and electrical noise. Hoping it to only be weeks for it to be in operation.  

Regards

Ajax and Geoff

[Geoff]

Currently we are still working on the limit switches. The following is an excellent post on "CNC Noise Cures" and well worth a read:

 http://www.cnccookbook.com/CCCNCNoise.html

"Use Shielded or Twisted Pair Cables": Ajax has done a fine job rewiring the limits using shielded cable.

"Wire Home and Limit Circuits Normally Closed": I'm currently working on this with Michael's help:-)

"Use an Opto-Isolated Breakout Board": We now have some nice opto's, if it needs to be done we will add an opto board with a low pass filter!

While testing the limits it has become apparent that another issue exists. Once the limits are fixed we will need to address why the mill is losing it's place. Again this is an intermittent issue.   

Regards
Geoff

[tubular]

Geoff as discussed in person, but not so much in that cnc thread, it might be worth strengthening the pullup resistors first, cos if that works if saves you making other stuff non-standard.  

Do you know whether its relying on internal pullups inside the microcontroller - if so what resistance are these?  Are the pullups enabled?  You can check this by loading across a switch with something like a 10kohm and see what voltage you get, which gives you the current common to the 10k load and the microcontroller pull-up, from which you can then calculate the approximate internal pull-up resistance.  

I have a bag of 3 pin connector sets with pins etc.  Will put them with the mini mill at the space

regards

Lachlan

[Luke Weston]

The RAMPS has no pull-ups or any other protection or interface
components on those endstop signals... which I don't think is optimal.
But then again it is RAMPS board, it's not exactly a great example of
solid engineering for about a hundred different reasons.

So if a mechanical switch or open-collector sensor is used then yes,
it is dependent on the internal pull-ups being enabled in the
ATmega2560, which are 20-50k. (AVRs don't spec that pull-up resistance
any tighter than that, it may vary.)

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[Clifford Heath]

If you can get power near the switches, it would be
a good idea to fit pullup resistors at the switches,
with a smallish C filter. That way you don’t have an
unterminated antenna wire injecting signals that
need to be filtered. By all means load the line at
both ends, but especially at the switch end.

Clifford Heath.

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[Geoff]

Thank you for your posts.

We tried the "Wire Home and Limit Circuits Normally Closed" trick and it has worked well:-) It took a bit of mucking around with the firmware and we had to fix the firmware by changing the hardware:-[

When testing the mill, I found that the Mega with the (RAMPS board on it) totally loses the plot if I turn off and on the light switch (which has a florescent light on it) and needs to be power cycled.

I am thinking the easiest way to go may be to change the light?

Regards

Geoff

[Geoff]

Essentially the Mini Mill is now working, but there are some reliability issues that still remain eg running the spindle from the same supply as used by the motors. This generates a lot of electrical noise that may well interfere with the uC.

We are now working on improving the mills reliability, updating the firmware, and adding a graphic display. This also involves a good bit of documentation. 

On Monday, 29 June 2015 22:46:36 UTC+10, Geoff wrote:

[Rob B]

maybe replace fluro with LED tube also may "fix" /avoid the problem 

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[Michael Wheeler]

I'd have to be a NeoPixel tube

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[Jai]

Colour and intensity varying with tool speed, feed rate, and percentage of job completion.

jai

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[Geoff]

We are having issues with the fluro's interfering with the 3D printers, Mini Mill, and may be they could also be an issue for the big Mill.

The best solution is to fix the interference at the source as RobB has suggested?

Regards

Geoff

[Geoff]

Ok, the issue is that the lighting is on the power circuit.

On Tuesday, 14 July 2015 14:17:46 UTC+10, rbritt wrote:

[Clifford Heath]

Maybe try a ferrite snap-on at the power entry to the light? Reducing the interference close to the source might help more than trying to stop it getting into your hardware. You might also fit a mains-rated suppression cap to the fitting.

Clifford Heath.

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[Geoff]

The Mini Mill has now been rewired, new limit switches, redesigned and installed new brackets for the limit switches. The motors each now have there own plug. This is thanks to Ajax's hard work:-)

To do:

1. The controller needs to be rewired, we now have most of the parts.

2. The firmware is in the process of being updated and the changes documented.

3. We are documenting the new work as we go and when done we hope to have a complete set of documentation to accompany the Mini Mill.

Regards

Ajax & Geoff

On Monday, 29 June 2015 22:46:36 UTC+10, Geoff wrote: