PDA

View Full Version : Long swarf = bandsaw blade from finger's perspective



nheng
07-08-2007, 01:46 PM
I had a real close call yesterday while making a large PVC replacement bushing for a Telescope brand deck chair.

While taking the 2" stock down to 1.6" in one shot (plus a finish pass), the swarf was nicely flowing off the carbide insert and heading toward the rear of the machine. When it looked like it might start to pile up, I thought it would be wise to grab it quickly, snap it off and let the broken end fall toward the rear.

When I grabbed it and yanked, it did not break as anticipated, due to the depth of cut and feed yielding tougher swarf than I am used to working plastic. What happened instead is that it wrapped on the piece and rapidly wound onto the piece, pulling up the almost bandsaw like piece thru my fingers.

The index finger got a nice slice about halfway to the bone. Had it been just about any metal, especially SS, I think it would have been to the bone or perhaps severed.

After a bit of blood letting, all is well ... just a warning not to do things you already know are stupid but seem ok at the time :( Den

tattoomike68
07-08-2007, 02:03 PM
Sorry, thats a bummer.

When I machine plastic I even clean all the steel chips out of the machine so if the plasic chips do grab the dont grab up all the steel drill chips and stuff and whip them around too.

wierdscience
07-08-2007, 06:07 PM
Your lucky,that could have been real bad.Plastic strings like that are a lot stronger than you would ever believe.I have seen stuff get sucked up out of the chip pan or off the apron and get flung.

When I am turning plastic I usually go to the mill first and mill a slot down to just above the finished size,that way I get little C's instead of long strings.

Like Mike said cleaning the steel out of the chip tray before is a good idea and so is cleaning the plastic out after.Some hot steel chips on top of plastic shavings can cause a fire,don't ask me how I know:rolleyes:o

Doc Nickel
07-08-2007, 08:09 PM
Yep. That's the only thing that scares me in the shop- long stringy swarf, especially stainless.

Pieces chucked in the lathe, tools in the mill, whirly blades 'o death in the saws and grinders, all of those are dangerous, but predictable. Don't jam your finger into the whirly thingie and chance are you won't get cut.

But the stringy swarf coming off the lathe- and typically whipping around down towards the handwheels- however, is not predictable. You can't tell when that thing's gonna whip around your index finger just as it catches on the chuck and gets wound up like a winch cable.

Aluminum strings- at least the dinky ones my little 3/4HP lathe can generate- are fragile, the delrin strings are almost fluffy, but the stainless cables are sharp, serrated and stronger'n baling wire. I sliced myself a good one last night just cleaning up the cuttings off the chip tray. Didn't want to put my gloves on 'cause my hands were oily.

In fact, the last two or three times I've been cut, have been on stainless swarf.

Doc.

Evan
07-09-2007, 01:57 AM
Like Mike said cleaning the steel out of the chip tray before is a good idea and so is cleaning the plastic out after.

Heck, clean the tray regardless. A couple of years ago I was facing down a round of aluminum using the electric crossfeed and it was making long, stringy swarf. I tend to sit on a stool well to the right side of the machine and out of the path of the whirly bits. Good thing, too. Somehow the swarf reached down into the chip pan and instantly yanked up a big wad of chips and began winding them up and hurling it all over. The problem was worse because the power switch and outlet are on the other side of the chuck from where I sit. I just had to wait for the commotion to die down before switching off.

http://vts.bc.ca/pics2/chell.jpg

BadDog
07-09-2007, 02:52 AM
And did you add a secondary kill switch on the tailstock side after that? ;)

Funny thing, but because of my bad legs, I also sit on a stool at my Rockwell just as you described, and I've had it snatch up stringy chips just as you described, even got a nasty cut from it, and never thought of that till now...

dp
07-09-2007, 02:58 AM
Earlier this year I was turning a 2" bar of CRS with a nice new carbide chip. I'd set the chuck RPM up high and was taking deep cuts. The result was a continuous blue wire that did not curl but ran right straight off the lathe toward the floor. Once in a while I'd cut it with wirecutters because at 6" of turn that was a lot of wire. Somehow the wire found a path to the power strip on my lathe bench and yep - went right into the hot wire hole and created a massive and quite startling blue spark and total darkness. My emergency battery lights lit up right away and I was able to figure out what happened.

As soon as I got the mess cleaned up I relocated that power strip. The wire coming off the turn had snaked through a belt loop of my jeans and bee-lined right for the outlet. The resulting ball o' flame cut my belt loop 90% loose. And I don't let wires persist any more - I stop the cut if I can't see the loose end.

Your Old Dog
07-09-2007, 08:49 AM
The wire coming off the turn had snaked through a belt loop of my jeans and bee-lined right for the outlet. The resulting ball o' flame cut my belt loop 90% loose. And I don't let wires persist any more - I stop the cut if I can't see the loose end.

I'll bet that could never happen to Evan. Maybe you too should consider working ala nude to prevent such near disaster! :D

I don't mind the swarf and long curls. It keeps things interesting in my shop. Bobbing and weaving like a prize fighter makes a simple machining task exhilarating ! :D

Evan
07-09-2007, 09:04 AM
I'll bet that could never happen to Evan.
Hah. I was sitting near the front of my shaper last night to see exactly how it was cutting on a heavy cut. It kept throwing swarf at me even though I placed a small guard to deflect it. This is no small matter as the swarf comes off smoking hot and clanks when it hits the floor. When sweeping it up it sounds like little wind chimes. One piece ended up in my shirt pocket and as I wasn't wearing a tee shirt under it presented a distinct hazard to my left nipple for a bit. :eek:

Scishopguy
07-09-2007, 01:09 PM
The hazards of metal turnings become apparent early on in the game but when turning plastics we don't tend to think that they pose much of a danger to the operator.

Depending on the cut, PVC can be pretty strong and can snatch tools off the pan and throw them at you. As it comes off the tool it is pretty soft and can be stretched to the breaking point easily but as it cools it becomes tough as wire.

The worst thing that I have heard of came from a friend who had a job turning urethane roller skate wheels on his south bend. The stock came in short lengths and had a small hole all the way through. He would part them off and bore the bearing pockets. It was a nice little gravy job but he soon learned how dangerous the chips were. The chip was long and stringy and wrapped around the chuck and stock. He had to stop it and cut the bird nests away with side cutters at regular intervals. You couldn't even rip it loose with pliers. This was an eye opener for me to keep clear of even the plastic chips while the machine was turning. He said that it even yanked the cutters out of his hand when he got too close.

RPM
07-09-2007, 02:22 PM
Talking of emergency kill switches for a lathe, has anyone come across an AC switch that you could set up with a string that could run the length of the lathe, a bit like the old emergency cords in railway/railroad coaches? I'd put one in in a heartbeat if i could find one...
Richard in Los Angeles

Evan
07-09-2007, 03:07 PM
It wouldn't take much fiddling to mount a momentary on toggle switch so that a pin runs through hole in either side of a guard and holds it on. Pull the pin and it's off. Push switch back to on and insert pin and it's rearmed.

http://vts.bc.ca/pics2/estop1.jpg

nheng
07-09-2007, 07:20 PM
Never could understand kill switches being placed to the left of the headstock. Always seemed like a perfect opportunity for an amputation or severe lacerations.

I like Wierdscience's idea for causing little "C"s to be created instead of long turnings.

The other thing I've done when turning polycarbonate plates is to put the shop vac nozzle adjacent to the cutting tool. No cleanup afterwards ... just gotta make sure the whole darned vacuum doesn't get pulled into the spindle ;)

J. R. Williams
07-09-2007, 07:30 PM
The spring loaded toggle switch design is a good one.

I have a large round head push button emergency switch on my shaper. All you have to do is push and it is off. To restart the big button head has to be rotated a few degrees to release and reset the switch. It came of off some surplus equipment.

A lathe can be a handful as I have had my chip pan emptied on my 13" lathe in a couple seconds with all the cuttings being wrapped around the work and chuck. Some materials can be a big problem....

JRW

wierdscience
07-09-2007, 11:14 PM
Talking of emergency kill switches for a lathe, has anyone come across an AC switch that you could set up with a string that could run the length of the lathe, a bit like the old emergency cords in railway/railroad coaches? I'd put one in in a heartbeat if i could find one...
Richard in Los Angeles

Richard,yes I have seen the setup on a large lathe,it had two cables,one at eye level and one at foot level.The lathe was 20' between centers with no traveling clutch or motor controls.

It had a second feature,a brake drum with a DC solenoid.It was designed for a 1 second stop.I believe a 12vdc automotive A/C clutch could be modified to act as a motor brake.