Messages

261

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 27, 2012, 05:53:12 PM »

I've been making progress on the ATC - albeit slowly, due to interruptions.  The basic mechanism is proving quite reliable.  I've let it run random toolchanges for hours on end, running hundreds of toolchanges along the way, and it has never once made a mistake.  And that's running completely open loop!  Next week, I hope to get the sensors mounted, so the control program will be able to confirm that each commanded motion has actually fully completed.  With the sensor feedback, this thing should be pretty darned bullet-proof.

I have two other project I have to complete before I can actually put the ATC into service.  First, I need to complete the new telescoping Y/Z way covers.  The current ones are too wide, and prevent the ATC from going fully into its out-of-the-way park position.  The second is finally installing a spindle sensor, as I need to be able to ensure the spindle has fully stopped before doing a toolchange.  The sheet metal parts for the way covers are all cut and bent, so it's just a matter of about a days work to assemble them, and get them mounted on the machine. 

In the meantime, I've started making the "final" ATC parts, to replace some of the existing ones, which were made specifically as disposable prototypes.  I've re-made the pivot arm, and air cylinder attachments, and they came out beautiful.  The remaining work on the ATC is to re-make a few of the minor parts, mount the "skirt", connect up the door operating cable, and mount the sensors.  That will all take some time, but nothing really hard there.  I expect when it's all done, I'll either powder coat the whole thing, or perhaps just polish the aluminum.

Regards,
Ray L.

262

General Mach Discussion / Re: Mach3 and Tapmatic Tapping Head

« on: October 25, 2012, 11:07:47 AM »

There's no need to take the tapping head apart to understand how it works.  It has clutches in it.  As long as the tap is moving down, the tap will keep turning CW.  When the tap stops, the tap will be dis-engaged, and, shortly after, the 2x reverse gear will be engaged, backing the tap out. 

Regards,
Ray L.

263

General Mach Discussion / Re: grounding your cnc

« on: October 21, 2012, 09:35:57 PM »

There is a difference between grounds from an electrical  and noise point of view.

Earth Ground is Earth Ground is Earth Ground, Earth Ground does not change into something else when being used for noise abatement. While the primary purpose of the ground wire being added to electrical system was safety having a low impedance path to earth (a path which had no current flow from any circuit) was also a perfect place to bleed off electrical noise.

A copper ground rod is for safety - it will do nothing at all for noise.

That is incorrect. Crack open the power supply on your PC, where do all the filter parts get bonded to? The Earth Ground! Why? It is a low impedance path to ground. In the case of a machine like a Plasma Cutting table, Automated TIG welding machine etc, the local ground rod provides a low impedance path to the earth rather than rely on the small gauge ground wire that runs all the way back through the plant to the electrical service entrance. Any local ground rod should be bonded to the buildings electrical ground to prevent a potential shock hazard between the two.

I'm not meaning to sound like a 'know-it-all' here, I just want to dispel myths about grounding. I used to design, install and service automated welding and cutting systems and have had first hand experience with about every type of noise issue there is. I just want to share that experience with others.

Jeff,

Sorry, but I have to disagree.  For small signal stuff, like we're dealing with here, the earth ground is not going to do much of anything to reduce noise - the impedance through that path is orders of magnitude higher than the direct path through the ground conductor, even all the way back to the main panel.  It is quite common to have significant potential difference between the "local" earth ground, and the power panel earth ground, if the two are separated by any significant distance.  This creates a local shock hazard if the machine is connected only to the panel ground through the ground terminal of the circuit.  This IS a safety hazard if, for example, the user is foolish enough to be standing in a  puddle of coolant on the floor, and there is a short somewhere in the machine making some part of the machine "live".  With the machine grounded to a local ground rod, this hazard is eliminated.

The situation, and hazards, with high-current welding equipment are quite different from what folks are dealing with here, and if someone is having problems with, for example, spurious E-stop or limit triggers, tying the machine ground to a local ground rod is exceedingly unlikely to make any difference at all with those problems.

Regards,
Ray L.

264

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 21, 2012, 09:00:30 PM »

HIYA RAY I noticed that something is PUSHING your spindle up and down. You can see movement of the actual spindle during the change.

Just a thought, (;-) TP

Terry,

No, not pushing, the quill is being moved intentionally as part of the process.  When loading a tool, I move the quill down 0.050", to make certain the TTS holder is pushed fully into the spindle, so it will seat properly against the spindle nose when the drawbar is tightened. After the drawbar is tight, I move the quill back to home position.  There is enough compliance designed into the system to accomodate this small motion.

Regards,
Ray L.

265

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 21, 2012, 08:03:25 PM »

Here's a somewhat better video:  http://youtu.be/aDEgRS6PI60

Regards,
Ray L.

266

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 21, 2012, 03:11:50 PM »

Just spent almost two hours running constant, random toolchanges without a single problem!  Now that the mechanics are getting broken in, it's running much smoother, and I see no need to cushion or damp the motion.  I'm very encouraged so far!

Regards,
Ray L.

267

General Mach Discussion / Re: grounding your cnc

« on: October 21, 2012, 11:17:37 AM »

A copper ground rod is for safety - it will do nothing at all for noise.

Regards,
Ray L.

268

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 20, 2012, 08:06:31 PM »

Ray did you give any thoughts to doing a MOTOR drive to swing the arm instead of air. I worry about the constant BANGING at the end of stroke with the air.

Just curious, (;-) TP

Terry,

Yes, but it creates other problems.  It's really not as rough as it looks in the video - I had not done much in the way of "tuning" before I took that.  Now that I've had some time to tweak it, it's a lot smoother.  I will also be adding dampers at the ends of travel, to make the stops more gentle.

I did run the thing for some time yesterday, just swinging out, doing a random toolchange, then swinging back.  I did dozens of them with no "Oopsies".  Once I get all the sensing switches in place, it should work really nicely.

Regards,
Ray L.

269

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 19, 2012, 01:07:37 PM »

Here it is doing a toolchange under computer control for the first time.  It's running *really* slow, because I have long delays between the steps, so I can catch it if something goes wrong.  It's about 20 seconds in the video, and I should easily be able to get that under 10 seconds when it's all done.

P1060662 - YouTube

Regards,
Ray L.

270

General Mach Discussion / Re: BT30 spindle from scratch - with power drawbar and ATC of course

« on: October 18, 2012, 08:00:27 PM »

I got my pneumatic parts today, so tomorrow I'll be working on software to sequence the ATC.  I've the air cylinders plumbed and wired, and under computer control.  I just need to wire up the carousel motor, and start writing code!  No "sensors" yet, but I can easily make it operate without them for now.

Regards,
Ray L.