Safety and Fire

[james mcgrew]

with the disscussions on rates of feeds and cnc ooperations i thought i would bring an experience here for anyone who has not had this happen yet and for those who have as a reminder

on saturday i was doing a training session with the x3 machine, we were running a file that i had made the mistake of asking a 1/4 inch bit to cut through the material, the bit cut about 10 feet in cut length and snapped, we removed the bit (seemed warm but not hot) and left the vacuum on to hold the material while we went into my office to rework the pass depth on the file.

in just a few minutes one of the guys in the shop said there was a fire, on the way to the fire i still did not know what was burning, i thought first to grab a fire extinguisher (they are located in many places and all corners and entrances as well as passages thru the building) we got real lucky time wise.

while we had removed the bit a small ember had begun to burn, the vacuum gave it wind and direction and no one could see it, about the time someone smelled it it broke throughthe spoil board surface.

i hope all reading this realize size of machine does not matter, they are made up of two things
1) electrical parts
2) parts that create friction

be careful, pay attention. my x3 is a god send and i would be as hard pressed as any to replace it and or pray i do not burn down the building or worse

my hope is this will help the new and old cnc'r

 

[iSign]

Thanks for the heads up.

That reminds me when I put all my new machines online about 10 months ago, I had been given all kinds of advice from every direction & was overwhelmed trying to do everything, do everything correctly, and do everything on time. Overall, the main things seems to get done on time and correctly... but one thing I never did just popped back in my head when reading your post. I was told that I needed to run some kind of wire inside, or wrapped around the outside of my dust collection hose, to prevent against a dust fire, or dust explosion.

I wonder how many people do this & how important others feel that it is.

 

[andy]

Earthing your dust extraction hose is probably a good idea- it's a static elimination system.

Whether you earth or not depends to a large extent what you are cutting- shops which cut loads of MDF are left with huge piles of dust which is easy to ignite and a static discharge could in theory provide the source of ignition. If you are cutting acrylic and polymetal the swarf and chippings aren't likely to go up in smoke so it's probably not essential- none of my extractor hoses are earthed.

I have heard of shops which cut loads of MDF having spindles ignite- this is caused by very poor maintenance which allows a lot of MDF dust to get dragged into the cooling fan on top of the spindle. It is a good idea to blow out your spindle every so often to clear out any dust which has built up inside.

If you don't want to set fire to your machine during cutting the easiest thing to do is make sure your router bits are always sharpy sharp- setting fire to material you are trying to cut is pretty hard to do- unless your cutters have all the sharpness of a carrot.
Carbide cutters are pretty robust- they do get hot during normal cutting but not Red hot. If your cutters do get very hot they are knackered and need to be chucked- if you see slight browning on the bottom of the cutter it's time to wave them good bye.

Carbide cutters need to be run at fast speed rates- they cut better and last longer at a decent feed rate. If you think you are going to save your cutters by running them slow you'll probably find they blunt very quickly,

 

[james mcgrew]

the static of mdf and sign foam are incredible and after we ran copper wire (grounded) from the DC to the dust boot and spindles on both machines it stopped. for the most part (no dust collection is perfect) the dust makes it to the bins, i would suggest multiple fire extinguishers near the machines, good practice in any shop!

i am currently carving a life size chess set and it requires carves in slices of 3" thick each and the material is 1" thick mdf, i have lit the material several times as we are carving 3" deep and a lot of material is still in the cut, page 4 of this pdf by hartlauer is based on onsruds info for feeds and speeds, for the benefit of someone who may be new to cnc we have blown it up and posted page 4 at all three machines.

http://www.hartlauer-bits.com/HartlauerBitsList.pdf

i keep 120 psi air hoses at all machines and blow them off constantly note: do not blow dust directly into an electrical component like a drive or a spindle motor.

 

[james mcgrew]

can you guys see the photo or am i missing something? it is all fuzzy when i expand it?

jim

 

[rcook99]

No they are fuzzy.

 

[james mcgrew]

i will post another pic from the office computer to see why the pics are fuzzy, it should show the copper wire attached to the z and dust foot.

jim

 

[briderx]

Well, I must say.. If your bit is getting hotter than room temperature, you're doing something wrong. A router bit should NOT get hotter than room temp, even while cutting aluminum. The idea of a CNC router is to have the heat buildup in the chip extraction. THOSE should be hot, not the bit. You should be able to stop your job at ANY time during your routing, and touch the bit without it being hotter than your hand. The hotter the bit gets, the easier it is to break. I know this might not necessarily be the problem that started the fire, but someone above said "bits get hot"..

 

[andy]

I run my carbide tools at speeds which generate heat in both chip load and tool because good quality carbide router bits last longer and cuts cleaner at high feed rates.

I've just scored over 250 sheets of ali composite using the same solid carbide cutter- a cutter which was too hot to touch at the end of each sheet.

Maybe I am doing something wrong but one cutter did 250+ sheets and is still in one piece and sharp enough to do many more jobs.

Quality carbide tools are counter intuitive- you want to be gentle to prevent them snapping- in reality they work best at faster feed rates.

I wouldn't know about how to cut metal on CNC routers- we use water jet for all our metal work.

 

[james mcgrew]

dumb me

i might just want an advanced course in work holding as well

jim

 

[briderx]

I run my carbide tools at speeds which generate heat in both chip load and tool because good quality carbide router bits last longer and cuts cleaner at high feed rates.

I've just scored over 250 sheets of ali composite using the same solid carbide cutter- a cutter which was too hot to touch at the end of each sheet.

Maybe I am doing something wrong but one cutter did 250+ sheets and is still in one piece and sharp enough to do many more jobs.

Quality carbide tools are counter intuitive- you want to be gentle to prevent them snapping- in reality they work best at faster feed rates.

I wouldn't know about how to cut metal on CNC routers- we use water jet for all our metal work.

I cannot argue the fact that heat breaks down carbide bits.. It's a fact. Yes, I have had jobs before where the bit was SO HOT that I swear it could have been red.. (it wasn't) BUT you get premature dulling and early breakage when the bit is exposed to high temps.

Keeping your bits at room temp is the only method to keeping your bits sharp for as long as possible. I typically change a bit once a month or so now.. Depending on the jobs and the bit. Again, the heat should be extracted in the chips pulled from the table.

That's awesome you're getting that long of life on that bit, you still may want to rework your formula to check your feeds/speeds. You'd be surprised how fast you can actually go without heating your bit.

I also, every once in a while (usually with new material) is to grab my caliper and measure my chips to see how thick they are.. I compare that data to what I calculated it to and if it matches, I know my sweet spot.

Jim.. Damn dude. Problem after problem, huh? Hang in there..

 

[james mcgrew]

i have three machines and just keep making mistakes, i was once told to just keep falling down up hill!!

jim

 

[Biker Scout]

Good post... I just had my first ember last week, and it happened right in front of me (thankfully) I was cutting some 3/4" maple for our counter top and I'm not too sure what happened, but I heard a funny noise, and went inspect, and saw that the gantry had stalled briefly, and started cutting all crazy. Well, the abrupt change in direction cut into my part and maybe hit a knot in the wood, I dunno, but just as I ran into the router room to hit the emergency stop button I saw the ember beginning to grow. Presumably from the vacuum or spindle breeze.

Turned out all that happened was that a drive belt on the gear reduction drive broke, and I was not getting full X-Axis power. The gantry was twisting into the work.

Anyway, what scared me was the fact that I had walked down to the corner store to get a soda. I had just walked back in when I heard the funny noise and went to inspect.

I know you shouldn't leave them unattended and all that, but being these things are robots and you get complacent when they work as they are supposed to day in and day out... I figured 5 minutes alone couldn't hurt.

See, normally I don't cut a lot of wood here, so, in reality I might have never encountered an issue. But all this talk of exploding dust, and grounded vacuum lines has me re-thinking things. Especially if I ever load wood in there again.

 

[CharliefromTechno]

While it may seem counter intuitive, the faster you cut through your material, the cooler the cut. Occasionally MDF, especially cheap MDF will contain small bits of metal. It only takes a little peice of a staple or screw to ignite a spark which can really spread rapidly if you are creating a nice draft with vacuum hold down. Fortunately most machines are primarily metal which though quite rare, should keep any fire from spreading.

 

[james mcgrew]

thanks for keeping this thread at a fore front of safety, sadly my mistake was stupidity!! i was showing machine and used the visitos file with out checking code, after a few passes bit dove into full thickness and took off by the time i shut it down bit had snapped (vacuum was on) i removed the snapped bit and at that point nothing appeared to be wrong so we went into office to rewrite the file, the ember was below the material and the vacuum inflamed it! i have found you can shave mdf with the right feed and spindle speeds, rule is if it is powder something is wrong

jim

 

[JK driver]

I've had the same thing happen. Don't remember the exact details of why the fire started but the plywood or mdf, whatever was being cut ignited and started the sacrificial mdf on fire and the vacuum pulled it through. Kind of looked like a jet engine! Alot of people think you just load them up and let them go. You really should baby sit them. At least be in ear-shot to hear pitch changes.

By the way, Mr. Mcgrew that figure carving is awesome!

 

[james mcgrew]

thanks we have finished the first set!!

http://www.youtube.com/watch?v=tCrEJ2Ud5YU

jim