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Introduction to CNC

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John Stevenson12/08/2011 21:52:53
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Just a heads up, Arceuro are doing an introduction to CNC on Saturday 20th August at their Syston, Leicester depot.
 
Limited to 6 people and I think they have two already , more details on their web site.
 
Link on the right hand side of this notice.
 
John S.
Andrew Johnston12/08/2011 22:42:54
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Interesting, but does it cover what to do when you're 40 minutes into a 3 hour CNC program and the b@*&dy power disappears for a few seconds and everything shuts down, like wot happened this evening?
 
That's the third power cut we've had here in the last two weeks, mumble, mumble, mumble. Every time it rains the power seems to go off. And to add insult to injury E.on have just announced stonking price hikes.

In the end I did what any seasoned machinist would do; I went to the fridge and grabbed a beer.
 
Regards,
 
Andrew
 
Hmmm, I wonder if this off-topic post will get me ex-communicated?

 
 

Edited By Andrew Johnston on 12/08/2011 22:43:18

John Stevenson12/08/2011 23:03:36
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Yes had one a couple of months ago, again raining, big CNC was running and manual lathe was running but not doing anything.
Lights started flicking and manual lathes started growing like a phase down so rushed in and shut the CNC down just as the power went out phase by phase.
 
Turned out to be a damaged cable part way down the road, finished up blowing a big chunk out of the pavement. 3 hours or so later power came back on, went to check the CNC and it was OK, no damage but the manual lathe would only run in low speed and high speed tripped the breakers.
 
Turned out to be a tiny interlock contact block on the main contactors, £8.00 for a new one and a day to fit it by the time the lathe was pulled away from the wall, repaired, put back and re-levelled on all 8 feet.
 
Banged a claim in but they wouldn't entertain it.
 
Signed - Ex-communicated from Nottingham.
Andrew Johnston12/08/2011 23:36:51
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The power here was only off for an instant, enough to badger the CNC mill and the clock on the cooker, but not the clock on the microwave. I suspect all three phases went, as the CNC mill and the computer that runs it are on different phases and they both went off, and I think the house is on the other phase.
 
The time before when the power went off it was out for an hour, came back for 15 minutes and was then out for two hours. We have overhead and underground cables in my steet. I get my feed from the underground cable, but I'm pretty sure the ultimate feeds are overhead on telegraph poles. I live in the country, but I'm hardly in the sticks!
 
At least I don't think it's damaged anything, just that I've lost the zero references for the part I was machining. The XYZ references I can get back, but the 4th axis (A) may be a bit more difficult. I'll give it a go tomorrow morning, otherwise it's bin it and start afresh with a new cast iron blank.
 
Regards,
 
Andrew
ady12/08/2011 23:45:34
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Maybe an Uninterrupted power supply unit would be handy.
 
Would give you time to either shut down or kick start a wee jenny.
Steve Garnett13/08/2011 00:37:19
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I hate to think what a 3-phase UPS big enough to run a lathe or a mill would cost. If you're running, say 3hp plus the computer, that's at least a 2kW-capable box you need to find, for a start. With a bit of improvising, you could probably do this in a relatively straightforward manner for a single phase, but 3 phases? Whilst I'm sure that somebody somewhere must do one, I've never seen one myself.
David Clark 113/08/2011 09:11:20
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Hi Andrew
You just continue where you left off.
You have to figure out where you are in the program, go to a safe start position and continue.
I used to do it all the time, not because of a power cut but because of broken drills.
One job was drilling holes in stainless gas burners, there were about 1200 holes in each burner, all on a fourth axis, all drilled about 5.4mm with a carbide drill.
We just figured out the row and the rotation to get us back to the hole after the one with the broken drill.
 
regards David
 
PS You were ex communicated from 22:43 to 22:44 last night.
Andrew Johnston13/08/2011 11:14:20
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Hi David,
 
Thanks for the advice, but unfortunately as the computer went off as well, so the mill completely lost its marbles and also lost the program, so I have no idea where it got to. It's now running again, as I type , on a new blank. I'm going to make a new blank to replace the one that was partly machined. The roughing cut is programmed to leave 0.2±0.1mm of stock. I don't think I can realign in the A axis to that accuracy as there is nothing to reference against. It'll only take me a few minutes to make another blank, but it is £2 down the drain in material.
 
Steve: I haven't seen a three phase UPS either. As it happens the mill runs on single phase. Eh, what didn't I intimate two phases above? The mill was designed in the US, so the main drives, controls and VFD are intended to run from a 220V supply, ie, 110-0-110. There is a separate, isolated, supply input, normally 110V, to run the computer and with a separate switchable output for things like coolant pumps. The isolated supply is also rated for 220V, so that's what I use for the computer and coolant pump. I was a bit concerned about running the two supplies from different phases, but they have proved to be truly isolated, so everything is fine. I don't think I could afford a UPS(s) with appropriate power ratings. Plus, my experience of UPSs for computers is that they don't work. Several places I have worked have had UPSs fail to do the job when the power goes. The place I'm working at the moment had a big storm a few weeks ago and the power went off for about 8 hours. Not only did the UPS fail to protect the server, it committed hari-kari. There is now a pile of very swollen lead acid batteries on the floor awaiting recycling!
 
Regards,
 
Andrew
David Clark 113/08/2011 11:50:16
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Hi Andrew
That will teach you to save the program before running it.
regards David
 
Andrew Johnston13/08/2011 15:12:19
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I do my CAD/CAM on a computer in the office. Only the computer in the workshop that was driving the CNC mill lost the program. Fortunately I still had a copy on the office computer, and on the pen drive I use to transfer between the two.
 
Regards,
 
Andrew
Raymond Anderson13/08/2011 16:04:22
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For 3 phase ups try this company [be prepared to part with an arm, and a leg as well]
Regards,
Raymond
Steve Garnett13/08/2011 16:57:12
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Posted by Andrew Johnston on 13/08/2011 11:14:20:
 
Plus, my experience of UPSs for computers is that they don't work. Several places I have worked have had UPSs fail to do the job when the power goes. The place I'm working at the moment had a big storm a few weeks ago and the power went off for about 8 hours. Not only did the UPS fail to protect the server, it committed hari-kari. There is now a pile of very swollen lead acid batteries on the floor awaiting recycling!
 

 
I have one UPS on a specific bit of kit, and because of where it's used it gets exercised quite regularly and doesn't give any trouble at all. I think in part it's because it's not a 'cut in' style one, but one that uses a relatively hefty supply that runs everything and float charges the battery, rather than one that's just capable of charging it and relying on the switch-over to work. So effectively it's running the device all the time.
 
As you've observed (and so have I), large storms can take out the control mechanism, and often everything else as well from a UPS just as easily as they can take out anything else that happens to get in the way!
 
I've figured out how it might be possible to convert a 3-phase inverter so that it has a UPS function. All you do is take the 600v DC line in it (worst case, using a star-connected motor) and add some storage to it. 42 car batteries in series should do fine... (apart from potentially a bit of a charge-balancing problem!)
Andrew Johnston14/08/2011 09:50:40
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Raymond; thanks for the link. Took me a while to find a proper spec on the website amongst all the PR bull about IGBTs and DSP. They are certainly some serious bits of kit, but I wouldn't even think about asking for price, and to cap it all batteries are extra!
 
Steve; funny you should mention converting a three phase VFD. The last power converter I designed was three phase in, 600VDC out, with a rating of 50kW. It was bi-directional so putting 600VDC in gave you three phase out. Perhaps I should see if I can sneak one out of the building. I've also designed a number of lead acid battery management systems for experimental electric vehicles, and I whole-hearted agree that you need to monitor each individual battery and include means for balancing so that all cells are at pretty much the same SOC. Otherwise it all gets out of hand pretty quickly and you end up with badgered batteries.
 
Regards,
 
Andrew

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