[acannell]

i have a mini mill and the top edge of the enclosure is at chin level, so the operators face is always exposed while operating it

id like to make a transparent shield of some kind so that the machining can always be seen, but is strong enough so in a worst case accident like somehow an entire bt30 tool holder goes flying at 7000 rpm it will stop it

it needs to be something that will not scratch because i dont want to be replacing it and i want to just be able to wipe it off with windex even if it has chips on it, without scratching it up

im thinking some kind of gorilla-glass with wires embedded in it would work

that or gorilla glass with a fabricated "prison bars" shield made over it

or?

[Al_The_Man]

Try an automotive glass supplier, they have tempered glass that's used in locomotive cabs etc.
Al.

[TiagoSantos]

how about polycarbonate (for the projectile resistance..) with transparent film that can be easily peeled off and replaced? I'm thinking about the transparent film they use on sandblasting cabinets.

[louieatienza]

how about polycarbonate (for the projectile resistance..) with transparent film that can be easily peeled off and replaced? I'm thinking about the transparent film they use on sandblasting cabinets.

Whatever it is, if it saves my face I could care less if it scratches! ....

[acannell]

Whatever it is, if it saves my face I could care less if it scratches! ....

the problem is, once its scratched I cant see through it, so sorta defeats the purpose of having it be transparent at that point..might as well just put up a sheet of steel

[acannell]

how about polycarbonate (for the projectile resistance..) with transparent film that can be easily peeled off and replaced? I'm thinking about the transparent film they use on sandblasting cabinets.

i was thinking about this....id be nice if it didnt have any disposable element though..if i can rinse it with flood coolant then wipe it off with a paper towel and windex every day without it losing visibility that would be great.

its not right in the line of fire for chips..really only the odd chip flying up and out into space will get to it..but coolant will definitely get on it and my coolant system isnt exactly reverse osmosis filtered

[underthetire]

Some glass shops will make a glass/polycarb/glass combo. Okuma used the same type for years. Cleans well, but still has protection. Only down side, they will only take 1 hit before the glass cracks.

[wizard]

How about a Magnesium Aluminate Spinel possibly laminated with a polycarbonate? Here is an interesting paper: http://ceramics.org/wp-content/uploa...over-story.pdf. Probably out of your price range.

An economical solution would be laminated ballistic glass. However this stuff gets thick and heavy real fast.

The real question here is what are the realistic risks? This is a mill so you don't have the potential of a significant amount of steel coming loose to wreak distraction upon your face. Yes a BT 30 arbor is nothing to sneeze at but is relatively small in comparison to what might be chucked in a lathe. What ever you do I'd highly suggest backing up the "glass" with a metal grid of substantial strength.

[acannell]

The real question here is what are the realistic risks? This is a mill so you don't have the potential of a significant amount of steel coming loose to wreak distraction upon your face. Yes a BT 30 arbor is nothing to sneeze at but is relatively small in comparison to what might be chucked in a lathe. What ever you do I'd highly suggest backing up the "glass" with a metal grid of substantial strength.

i really dont know...i may actually be in a relatively safe position above the action..but its an older machine so if we assume some worst case scenario like a drawbar failure at 7000 rpm with some fly cutter loaded at the top of Z axis travel who knows what could happen

its okay if its a one-hit shield..it shouldnt normally be exposed to any impact

so i just need a "scratch proof" front surface, and then something behind it that will take the impact like reinforced glass or lexan or whatever

there must be some kind of scratch proof glass treatment film or something

[dholby]

Polycarbonate Makrolon AR2, is hard coated to resist abrasion.
Its used today on most machine guards. Its a little more money the regular Polycarb.

[acannell]

Polycarbonate Makrolon AR2, is hard coated to resist abrasion.
Its used today on most machine guards. Its a little more money the regular Polycarb.

yeah i think thats the winner..i may even have some since i have a sheet that was meant to be used as a house window, so i think its probably scratch resistant!

[underthetire]

Ive seen 3 lbs parts lifted out of vises and thrown around in a steel enclosure. Looked like an alien trying to escape. Quite a bit of hazard in all reality.

[acannell]

Ive seen 3 lbs parts lifted out of vises and thrown around in a steel enclosure. Looked like an alien trying to escape. Quite a bit of hazard in all reality.

id like to hear the rest of this story! tell us more!

especially what the moral of the story is..i.e. why it happened

[underthetire]

Ive seen quite a few major accidents in my life. This shop just bought a brand new (at the time) Mori Seiki SV500. For some reason, the operator didn't check or wasn't trained to check how the parts were being clamped. The material he tried to put in vise jaws was out of parallel so only 2 spots were clamping. 10K rpm with a 1/2 EM sucked it right out in a pocket cycle, helicoptered the part, end mill finally broke and the whole rotating mess made a nice 360 deg sweep through the enclosure. Hit the front of the enclosure first, right by the door. Had to beat the sheet metal back in just to get the door functioning again. If you've ever seen the newer Mori sheet metal, you know this takes some doing, as the stuff is pretty darn thick. High helix endmills can be notorious for this as well. Seen other accidents from parts sucking out of tabs, etc.

Seen retention knobs snap (new ones BTW) throwing CT40 tools out of the spindle at 15K RPM. These were always the center through coolant type, one reason Mori quit using those and went to side through.

6" shell mill came apart at another shop. Always locktite those center bolts.

And my favorite on the older machines that used counterweights, chain snapping. Once those counterweights are no longer attached, its quite surprising how fast those heads come down. Better have an extra pair of shorts in your tool box for that one.

NONE of these compare to some lathe accidents though, some quite gruesome. VTL's still make me cringe a little while im around them.

[acannell]

Ive seen quite a few major accidents in my life. This shop just bought a brand new (at the time) Mori Seiki SV500. For some reason, the operator didn't check or wasn't trained to check how the parts were being clamped. The material he tried to put in vise jaws was out of parallel so only 2 spots were clamping. 10K rpm with a 1/2 EM sucked it right out in a pocket cycle, helicoptered the part, end mill finally broke and the whole rotating mess made a nice 360 deg sweep through the enclosure. Hit the front of the enclosure first, right by the door. Had to beat the sheet metal back in just to get the door functioning again. If you've ever seen the newer Mori sheet metal, you know this takes some doing, as the stuff is pretty darn thick. High helix endmills can be notorious for this as well. Seen other accidents from parts sucking out of tabs, etc.

Seen retention knobs snap (new ones BTW) throwing CT40 tools out of the spindle at 15K RPM. These were always the center through coolant type, one reason Mori quit using those and went to side through.

6" shell mill came apart at another shop. Always locktite those center bolts.

And my favorite on the older machines that used counterweights, chain snapping. Once those counterweights are no longer attached, its quite surprising how fast those heads come down. Better have an extra pair of shorts in your tool box for that one.

NONE of these compare to some lathe accidents though, some quite gruesome. VTL's still make me cringe a little while im around them.

yikes..these stories freak me out but i try to read alot of them because i know it makes me just a _little_ more careful..hopefully

sometimes i ponder the idea that really only some invisible semiconductor quantum electric effect is preventing the drawbar actuator from simply actuating at any random moment...does that make me schrodingers machinist?

[underthetire]

You want a drawbar story?
I have one of those i've shared in the past....

[acannell]

You want a drawbar story?
I have one of those i've shared in the past....

you betcha lets hear it!

[underthetire]

Ok..
I get a call to go to a customers shop. Message was spindle started on its own. So i drive over there...well..then i get the real details. According to the shop manager ( the operator was already at the ER) the operator was changing inserts on a 6" aluminum finishing face mill (ya, the really sharp ones). He removed the tool from the spindle, change inserts, and placed the tool back in to the spindle. Now, according to him, as soon as he hit tool clamp, all 30HP came to life spinning the tool instantly to 8K RPM. I couldn't duplicate it myself(with a blank holder of coarse). Not sure to this day if it just saw a tool clamp signal and took off, or he did something else by mistake. He could no longer use some of his fingers. This was a fairly decent Japanese machine. Ive seen lots of other "import" machines with obvious PLC/safety errors, like being able to manually press tool unclamp while the spindle is turning etc. This was always a concern when a distributor got a new "commodity" machine line. I would do everything i could think of to try and destroy/create problems in those machines. Some got fixed, others we just wouldn't sell.

[acannell]

Ok..
I get a call to go to a customers shop. Message was spindle started on its own. So i drive over there...well..then i get the real details. According to the shop manager ( the operator was already at the ER) the operator was changing inserts on a 6" aluminum finishing face mill (ya, the really sharp ones). He removed the tool from the spindle, change inserts, and placed the tool back in to the spindle. Now, according to him, as soon as he hit tool clamp, all 30HP came to life spinning the tool instantly to 8K RPM. I couldn't duplicate it myself(with a blank holder of coarse). Not sure to this day if it just saw a tool clamp signal and took off, or he did something else by mistake. He could no longer use some of his fingers. This was a fairly decent Japanese machine. Ive seen lots of other "import" machines with obvious PLC/safety errors, like being able to manually press tool unclamp while the spindle is turning etc. This was always a concern when a distributor got a new "commodity" machine line. I would do everything i could think of to try and destroy/create problems in those machines. Some got fixed, others we just wouldn't sell.

wow thats bad...

this is exactly the kind of thing im worried about on my mill..

i dont know how they design safety systems for missile launchers or whatever, but im pretty sure my mill does not meet that standard....who knows what could happen if a couple IC's start failing or something like that..i mean i give them the benefit of the doubt they made some effort and tried to design the electronics so that the failure modes of components end up fail-safe..but i really doubt it was done with any serious analysis and testing..

hence the safety shield

[wizard]

wow thats bad...

this is exactly the kind of thing im worried about on my mill..

It is very reasonable to worry about these things. However good design can greatly reduce the risks.

i dont know how they design safety systems for missile launchers or whatever, but im pretty sure my mill does not meet that standard....who knows what could happen if a couple IC's start failing or something like that..

That should never be a problem on a well designed machine. Simply opening the doors should disable the spindle drive. In any event the NFPA, OSHA and the EU have a bunch of machine safety standards that should be adhered to.

i mean i give them the benefit of the doubt they made some effort and tried to design the electronics so that the failure modes of components end up fail-safe..

You can't be sure if that if the machines come from countries with no standards in place.

but i really doubt it was done with any serious analysis and testing..

Actually if the machine meets EU standards some analysis must be done and documented.

hence the safety shield

Safety shields are good but I don't see them as an answer to every safety issue that comes up. The tool change problem that was described above is an example of where the shield didn't help. However I'd be the first to recommend a a full and substantial enclosure for anything doing something other than trivial machining. The doors should properly interlock the the machine though.