[CNC Viking]

Hi,

Does anyone know the best transparant plastic material for windows for a VMC's protection cage. I have a Feeler FV-800 VMC that need a new window ( it is actually one of the side slide doors). They are made of 10 mm thick material that even withstand cellulose thinner.

[Geof]

I have only ever seen polycarbonate (Lexan or Tuffak) used for machine windows. It is resistant to methanol and regular oils and Varsol, but I do not know what you mean by cellulose thinner.

[One of Many]

Poly Carbonate? Likes of the brand names of Lexan or Hyzod.

DC

[CNC Viking]

I checked a little, and my machine was equipped with Acryl (Plexiglass) windows. The plastic type is PMMA. I believe that this type is more resistant to solvents than Polycarbonate (PC). The cast quality is supposed to be the best, but is maybe harder to come by than extruded.

[Geof]

I checked a little, and my machine was equipped with Acryl (Plexiglass) windows. The plastic type is PMMA. I believe that this type is more resistant to solvents than Polycarbonate (PC). The cast quality is supposed to be the best, but is maybe harder to come by than extruded.

Check much deeper!!!!!!

Acrylic, Plexiglas, Perspex, PMMA (Polymethylmethacrylate if you want the tongue twisting name) Is in no way more resistant to various solvents than polycarbonate AND IS FAR LESS IMPACT RESISTANT than polycarbonate.

It is possible your source of information was wrong, I have found a great many people casually say that all clear plastics are acrylic.

You final sentence is accurate, cast acrylic is far better than extruded, it is less available and is more expensive.

[One of Many]

Check much deeper!!!!!!

Acrylic, Plexiglas, Perspex, PMMA (Polymethylmethacrylate if you want the tongue twisting name) Is in no way more resistant to various solvents than polycarbonate AND IS FAR LESS IMPACT RESISTANT than polycarbonate.

It is possible your source of information was wrong, I have found a great many people casually say that all clear plastics are acrylic.

You final sentence is accurate, cast acrylic is far better than extruded, it is less available and is more expensive.

I placed the Polycarbonate as a question mark, since I don't really know what the OEM material actually is. Most guarding on industrial equipment specified by OSHA is PC. Although, the windows in our Bridgport. Milltronics and Okuma machines seem to be much harder than PC as far as scratch and chemical resistance. So, it wouldn't be any surprize to find it is some form of hard coated cast acrylic with a rubberizing component to increase its impact strength.

Something along the lines of Polycast SAR ?

DC

[Geof]

... the windows in our Bridgport. Milltronics and Okuma machines seem to be much harder than PC as far as scratch and chemical resistance...DC

I am not familiar with the SAR but I know it is possible to get polycarbonate with a very scratch resistant coating; to my knowledge it is used in glazing applications.

But I think this hard coating makes the polycarbonate more brittle. I have done a lot of forming of plain polycarbonate and it cold bends extremeley well, but the abrasion resistant stuff would often crack.

I was also thinking about the resistance to 'cellulose thinner'; the material in CNC Vikings machine could be laminated tempered glass, or even laminated plain glass.

[One of Many]

I am not familiar with the SAR but I know it is possible to get polycarbonate with a very scratch resistant coating; to my knowledge it is used in glazing applications.

But I think this hard coating makes the polycarbonate more brittle. I have done a lot of forming of plain polycarbonate and it cold bends extremeley well, but the abrasion resistant stuff would often crack.

Just tapping on these windows gives a completely different sound than some of the panes we have replaced with PC. The OEM ones do seem harder and as a guess more brittle. The replacements were due to some previous coolant usage degrading their clarity.

My bad experience with PC was well after cold forming and machining pinch guards for tube stretching fixtures I designed. Upon finishing, I cleaned them of oils with some "convenient" brake cleaner I tested to make certain it wouldn't melt the material. I sprayed them down, whiped them clean ready to install. Within 10 minutes, they cracked like baked glass marbles and just fell apart. The replacement batch of 8 were cleaned with a water based cleaner.....lesson learned. Solvents and transparent, thermal formed plastics are a bad combination, not worth the risk, so I no longer take the chance!


DC

[Geof]

...I cleaned them of oils with some "convenient" brake cleaner...DC

Naughty, naughty as you found out.

I learnt a similar lesson. Unfortunately the cracking was delayed by several days during which time we shipped a lot of items to customers. That rresulted in a lot of phone calls, a lot of UPS call tags to pick up the packages and a lot of expense on overnight shipments for the replacements.

[cam1]

Our VMC has double pane tempered glass.....heavy, but resistant to most if not all common chemicals.

regards

[One of Many]

Our VMC has double pane tempered glass.....heavy, but resistant to most if not all common chemicals.

regards

I've seen SAE safety laminated glass in Sand Blaster windows. I am not certain what, if any local regulations allow for in chip producing type machine tools.

Probably best to be penny wise and not pound foolish on the usage and abusage. Environment dependant verse the risk over why it needs replaced this time.

DC

[Geof]

That is a good point about tempered glass where it can be hit by chips. I wonder if the chips would be enough to trigger it shattering?

You do the experiment and report back, okay.

Some crazy things I am willing to do but occasionally I find delegation a good approach.

[CNC Viking]

Check much deeper!!!!!!

Acrylic, Plexiglas, Perspex, PMMA (Polymethylmethacrylate if you want the tongue twisting name) Is in no way more resistant to various solvents than polycarbonate AND IS FAR LESS IMPACT RESISTANT than polycarbonate.

It is possible your source of information was wrong, I have found a great many people casually say that all clear plastics are acrylic.

You final sentence is accurate, cast acrylic is far better than extruded, it is less available and is more expensive.

I checked my service manual's part list and it clearly says that the machine's windows are "Acrylic". And after 12 years, the remaining side door is remarkably free from scratches and the light transmission seems to be "as new". Since the thickness is 10 mm I don't think I need to worry about impact resistance, but nevertheless I will go for 10 mm Plexiglas Resist 75 (TM).

Datasheet:http://www.plexiglas.de/methacrylate...platten_en.pdf

I simply do not trust the PC's resistance against certain solvents ( I know that Makrolon (TM) cracks as you look at it if you use any "wrong but still very common" solvents. I also believe that PMMA has better light transmission over time than PC. And, as far as I have seen, PMMA is cheaper than PC.

[cam1]

That is a good point about tempered glass where it can be hit by chips. I wonder if the chips would be enough to trigger it shattering?

You do the experiment and report back, okay.

Some crazy things I am willing to do but occasionally I find delegation a good approach.

How about your automotive windshield? How about aircraft windshields (they are not all made out of polycarbonate, as they need to be heated) How about spacecraft windows?
The machine I was referring to is a Milltronics VMC. A colleague of mine had an event like that occur(tool failure), and yes it did shatter, however it contained the burst. I've seen many VMC's equipped with "glass", so I don't really consider it to be an experiment. My approach is to go back to the supplier for a quote on a replacement, and then I always have the option to find my own, at my risk.

regards

[Geof]

CNC Viking;
Thank you for that link!!!! I am passing it along to my people to find out if it is avaliable here. I read through everything and noticed it is extruded which in my experience was always negative for acrylic. I wish that stuff had been available thirty years ago, some things I made then would have been much easier.

Cam1;
I guess one reason I am dubious about the tempered laminated glass is one time I touched a window made of this with a screwdriver and it shattered on me. Most of the fragments stayed together but having that happen an inch or so away from yours eyes is a shock.

I shouldn't be such an old stick-in-mud.

[CNC Viking]

[QUOTE=Geof;494458]
Cam1;
I guess one reason I am dubious about the tempered laminated glass is one time I touched a window made of this with a screwdriver and it shattered on me. Most of the fragments stayed together but having that happen an inch or so away from yours eyes is a shock.
QUOTE]


I agree Geof.
I would not risk of having a glass window exploding on me / into the machine / into the shop! If nothing else happens - what a mess to clean up all those microscopic glass fragments.

[Geof]

.... what a mess to clean up all those microscopic glass fragments.

Most of the fragments do stay stuck to the laminate layer so clean-up is not difficult. Some very small fragments do break free but it is a minuscule amount. I think the main reason a became so negative about using tempered glass was that it seemed to break so easy when I only touched it, no banging or hammering.

And I became negative about acrylic when I was badly cut by a piece of broken acrylic.

[Seraph]

Article on Safety windows an machines

It mostly seems to recommend composites based on layers of glass for solvent resistance, polycarbonate for impact resistance and other plastics (i'm assuming to give some flexibility )

[Geof]

Seraph; That is a good link, and I find it interesting that it comes out of Germany and the highly impact resistant acrylic comes from Germany but is not mentioned.

I stole some excerpts from it:

Polycarbonate is particularly well suited for use in vision panels. Polycarbonate sheets 8-mm thick fall into the same resistance classes as 3-mm Fe P01 or S235JR steel sheet. Because of its poor ductility, however, polymethylmethacrylate, does not meet impact resistance requirements specified in the different resistance classes. The same is true for vision panels made entirely of safety glass, which, because of its reduced ability to absorb energy, does not offer satisfactory protection.

Whenever thicker and thinner sheets are used together, the thicker sheet should always face the machine's working-zone side.

Laminated safety glass (in this case 24-mm thick) can fail catastrophically when used as a machine guard. Impact energy was 380 J.

When using transparent screens, employing several thin screens instead of one thick screen increases overall impact resistance. Our tests showed that two 6-mm polycarbonate screens, placed close together, withstand a maximum cutting speed of 10,200 m/min, while a single 12-mm polycarbonate screen has a maximum impact resistance of only 9000 m/min.




EDIT: I should have looked more closely. The article is from 2000, probably the high impact did not even exist then.

[cam1]

Good link Seraph:
As usual, there is a convergence of agreement, that glass/plastic laminates provide the best all around protection, when all factors are considered. I think I'll affix some 1/4polycarbonate panes on the exterior of my VMV tempered glass windows

regards