Managing Long CNC Carving Operations

      Thoughts on how to handle situations when a complicated carving process may run for more hours than your shop is usually open. December 14, 2009

What is the general practice for carvings that take eight plus hours? Do you pause the program and leave everything on overnight and resume in the morning, or do you just make sure there is nothing that can go wrong and let it go overnight?

Forum Responses
(CNC Forum)
From contributor B:
If it were me and I knew it would take eight hours to run then I would start it first thing in the morning and let it run through lunch and breaks. Although I have heard of others leaving it run, I have too much invested in equipment, building, and materials that time saved wouldn't be worth the risk. If a malfunction occurs and a fire starts in the dust collector or a tool breaks etc. someone really needs to babysit the machine. A broken tool could ruin your part or you may have to start over with a fresh tool so no time would be saved. Also, if something messes up you won't know where the error is in your program. You could pause like you said but the power is still to the machine. I can't pause and turn off the air compressor because the machine will fault for lack of air and need to be reset. I can't pause and turn off the vacuum because matter can get under the part when it relaxes and not stay put when turned back on. I'd say it's not a good practice to do.

From the original questioner:
So how would you run a carving that takes well over eight hours?

From contributor B:
Start it as early as possible and stay late if you need to. If you have good software such as I do (Alphacam) you can take some of the fat out of the program and speed up some of the cuts to shorten the cycle time.

From contributor M:
I have left my router on overnight several times. Itís not a real comfortable feeling, but what the heck. I set my part on vacuum pods that pulled from an air venturi vacuum pump (air compressor) and set up a portable dust collector. I didn't want to run the vacuum pumps or the big dust collector. No tool changes, just finish pass with small cutter.

From contributor W:
I do lots of carvings. Some take as long as 24 hours or more. I have a webcam pointed at the machine and can view it from wherever I am. I have never had a problem leaving things to run unattended, except for the rare occasional broken tool, however you can stop the machine, change the tool and then modify the program to start somewhere before the break.

From the original questioner:
Contributor W - what setup are you using to do all that?

From contributor A:
I'm with contributor B. I would not leave the machine unattended if there were any other alternative and there are many easy alternatives. I can't say I have never let the machine run overnight, but that was a long time ago and I have a lot more experience now. I would not consider it again.

Pausing the program is one way to do it, but I prefer to write my code in such a way that no operation takes more than say an hour or two. This helps in a lot of ways. Besides having an opportunity to stop in the middle of something if you need to leave the building, a broken tool only sets you back to the start of the last operation. Large programs usually use small tools and small tools are more delicate. You can nearly always game a convenient spot to break up your operations while you are programming, if you have your mind in that mode. I find it very difficult to predict the run time of a very large program with great accuracy. Opportunities to stop are useful to me.

Fire is a very real risk. A power surge or momentary power failure has the ability to cause a machine to stop in place, leaving the spindle running. The same can happen if a relay inside the machine fails. Now you have a potential fire. Itís rare, but over the years I have also found bits of metal in plywood, MDF and flake. I found a bullet once buried in a piece of solid. None of this is predictable, and without someone hanging around with enough sense to hit the red button in an emergency, you could be out of luck.

From the original questioner:
I'm not actually programming my own carvings, but purchasing them, I guess I will have to pull them up and see if I can manually copy and paste codes into separate programs.

From contributor M:
I agree with contributor B and contributor A. Leaving the machine unattended is a recipe for disaster. I don't care how confident and comfortable you feel about doing it. In contributor W's case viewing it from a webcam is great, but he will never know if a fire starts in his dust collector until it's too late!

How much longer than eight hours are we talking about here? If you are talking about nine or ten hours, have the boss suck it up and pay some overtime or give you the flex option of coming in late or leaving early somewhere in the rest of the week. If you are stretching way past ten hours, can the program be broken into smaller chunks (multiple programs) at logical break points and then continue it the next day?

From the original questioner:
That's what I'm not sure about. Like I mentioned above, I'm purchasing the models and importing the code into my router, so I would have to dive into the code and see if I can figure out how to break it up which I've never done before.

From contributor W:
In case youíre interested I use "Cam Wizard" for the webcams, Mastercam for most of the cad and CimcoEdit to edit the code. I use GoToMyPc to run things remotely. Works for me and the only thing I can't do is load and unload the machine or load new tools. As far as being worried about a fire in the dust collector or a catastrophic event. I do believe that's what insurance is for. I feel ok about leaving the furnace on at home while nobody is home not to mention the heaters in the shop. I trust my programs after I have a look at them in CimcoEdit, make adjustments if and as needed and just don't see the need to worry so much. I guess fire alarms and a fire suppression system helps, and as far as crashing the machine, if it's going to happen because of my lack of checking things before I run them well then I have nobody to blame than myself. Even if I was watching my machine and something went terribly wrong I think that I, like most people would get that deer in headlights look and it would be over faster than you could react. I own my machine a Thermwood Model 42 10x5 table and just don't see the need to worry so much.

Get yourself a good editing program that will show you all the tool moves and you can see where a good place to break programs into pieces if that's what you want to do.

From contributor G:
I am currently carving a life size chess set - 32 pieces 3" thick slices 24" diameter so we are running all day and some evenings. I pause machine and shut down at night.

From contributor M:
I could agree with you more. You company is set up to deal with your overhead. I say let it run over night after checking the code. If something is going to happen itís going to happen. If it doesn't, think of the time you saved instead of "what could of happened" (which is insured anyway).

From contributor K:
I was upstairs in my office while a carving was running, a good size block of MDF. A tool hit a piece of metal imbedded in the MDF, caught some dust on fire and burned through the 1/4" waste board and the 3/4" spoilboard and was burning like hot coals due to the vacuum, kind of like a blacksmith pumping air into his fire. All of this happened in less than a few minutes. Policy since is that if no one is in the shop working, the router is not running. No amount of insurance could ever pay for the grief it would take to rebuild and get back to where we are now.

From contributor T:
We had the same issue as above. We were boring some holes with a compression cutter and it sounded like a good idea at the time, when all of a sudden we smelled smoke, but nothing else. Here we burned at the bottom of one of the through holes and the 20HP forge blower took it from there. We burned through a 3/4" spoilboard and the part with nothing visible at the surface. Had we been watching on a webcam, our shop would be ashes today. Remember with the vacuum running there is no smoke to see, just the smell.
Our policy is the same. No one working, machine off, period! A true no tolerance policy now in effect. Anyone who does otherwise is just playing with fire (no pun intended).

From contributor O:
We've done several long-term carvings, up to 31 hours. Generally the different tools will divide the time into segments that can be handled in a regular day. We do other millwork as well, so we choose days when we aren't using the CNC for regular cutting purposes.

From contributor G:
My fire was less than seven minutes that we were in an office just out of site, a fellow passed the machine and saw a 1/2" burn hole. I was there with an extinguisher in another 90 seconds from that. Two more minutes and it would have been in and on its way past the vacuum pump.

From contributor B:
I would like to say some of you guys have brass ones but reality is that some of you are just plain stupid with your CNC routers. Leaving the machine to run overnight by itself should be illegal. Sure, machines especially in the automation industry are designed to be left alone overnight because they have systems that work out scenarios and fixes for anything that could happen. Most commercial machines aren't designed that way. While they have faults and sensors and proxy switches things can still happen that are otherwise totally expected.

The fact that you would risk losing everything in your shop for a carving is ridiculous. I mean seriously, if you can't comfortably run the situation by your insurance company you shouldn't be doing it. Run the program, if it goes beyond business and even reasonable overtime hours then stop the program at whatever line it is at and restart it the next day from that line at your safe z.

I just don't see the advantage to letting your CNC router run all night, you may get the job done a day or two earlier but is that profit enough to justify risking what you may have spent your life building? I rarely walk away from the CNC router, and if I do I'm within a distance that I could stop it fast enough before something bad happens. I've seen fires started and they are usually because someone isn't watching and listening to the machine. One in particular because the CNC operator decided to let the program run while he unloaded units of plywood from a delivery truck reckless leaving it alone for almost a half hour. The program was wrong (z in the wrong location) and the collet bottomed out on the MDF and started a fire that got sucked into the dust collection system.

Did he really save that much time doing what he did? No. Would have been better to even pause the program with the spindle still on and lock the software than leaving it unattended. Be smart guys. The machine is only as good as the operator/programmer and even that is saying a lot it seems.

From contributor G:
Since our fire I have yet to leave it alone. After all I finally went CNC after sticking my thumb in a table saw twice in one year! So once is hopefully enough here. I have yet to replace the plenum so the smell of the burn still radiates when I turn on the vac.

From contributor S:
I've had a CNC for about seven years now and I have yet to understand how people make money carving things with their machines. I've played around with it but the time consumed is enormous for the product made. Maybe I need to re-look this and see if I can find something that people want in this recession and turn it out on my machine.

From contributor W:
Wow, I can see that from the responses that very few people feel safe running their CNC's with nobody home. But what really surprises me is that I must be the only one that actually takes the few seconds to check the code for any mistakes I may have made prior to sending it off to run the parts. Like min and max X Y Z. Also using router bits to drill holes, is it too much to change tools as needed?

From the comments with the exception of hitting a piece of buried metal, all of the errors, fires etc. would of been prevented had the programmer been prudent and check the code prior to releasing it to run. Now don't get me wrong I totally understand about not running unattended. However even if someone is in the shop and letís say something does get a bit hot if you have your vacuum pump outside or in a sound room and the exhaust it going outside and your dust collector is outside, you would not know there was a fire until you stopped the vacuum (you won't even smell anything while its running) or an alarm in your dust system goes off. You all have your dust collectors sprinklered and alarmed right? It would be just like running unattended.

From contributor W:
Sorry I forgot to mention, using your router bit to drill holes, at what speed was your spindle at?? If you ran a drill bit at 16500 to 18000+ rpm it would also burn. It's all about feeds and speeds and there is plenty of that discussion elsewhere.

From contributor B:
I drill holes from time to time with a spiral cutter but I don't advise it. Spindles and routers aren't designed to have that plunging force on the bearings all the time and it wears them down in the long run. It also makes tool life very short hitting the tip of the tool all the time (why I always ramp when cutting if I can).

But most with a commercial machine use, line boring blocks are usually an accessory added on. They come down with an air cylinder/slide and are pneumatic so you can get the RPMís way down. Some even have the feature of two air cylinders, one a single 5mm and the line block.

From contributor Y:
Hey guys the simple and safe solution is to break up an eight hour job into two smaller, four hour jobs. I use ArtCAM and itís real easy to section off portions of a job and make it into two or more jobs. Itís much safer and there is no need to leave a machine unattended.

From contributor O:
I use ArtCam too, and often split the job into separate tool sections. It works well.

From contributor G:
I use aspire. There are several methods as mentioned above. With winCNC controller I can pause, shutoff the spindle and vac and restart the next day. I have never used any other controller as this is what I have on all three of our CNC's. There is a restart function from any line number in the program and this comes in handy for a variety of reasons.

From contributor W:
A part can shift, causing all subsequent machinings to be off and arrival in the morning with a part that is wrong. I had a horizontal deep pocket mortise that was off bury up to the collet and catch on fire. If I had been away from the machine all the fine chips would have caught like wildfire, the head would have raised, snapped the bit, and knocked the head out of alignment. Our automatic fire suppression system in the dust collector might have gone off after a long time because face it, dust collection isnít all that great on a carving.

After the ceiling sprinklers go off the machine will most likely keep burning, unless you have a very elaborate system in place. If your machine has hydraulic lines of any type, as soon as they are burned through good luck putting out the spewing high pressure flamethrower even if you are on site. Just some things to think about. Just because you have been lucky in the past is no reason to risk ruining a nice machine, insured or not.

From contributor Z:
I have been using a four spindle duplicating machine for twenty one years now, and I have never spent more than five hours on any one carving . I hold a 2/1000th of an inch tolerance from carving to carving and have never considered going to CNC. They are too expensive to program and to purchase. I'm not knocking CNC but I have never had any use for one.

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