Need Help!- Lexan Clearity!

[truckmann4x4]

I need to Mill lexan but I need a finish of visible clearity.
Ive tried several facing tools and varying speeds and feeds but the finish is foggy.
Please let me know if there is a way to get the finish I need.[/B]

[One of Many]

Most of what I have had experience with is a propane torch on the egde to return the clarity.

There is a theoretical process called "controlled heat polishing" on glass. If there was some way a heat source(heat gun or torch) could be attached to a CNC mill, you might get some clarity to return, but perfection is doubtful. The idea is to reflow the surface without soaking too much heat into the base that could start to boil any moisture absorbtion. Little bubbles will show up at that point.

Possibly glazing with a clear acrylic paint or polyurethane may help?

DC

[BYTHEBOOKBOB]

Dear Truckmann,

There is a process known as "vapor polishing" that uses the heated vapors of methelyne chloride to polish acrylic and lexan surfaces. The Methylene chloride is quite flammable so care needs to be taken to heat it below the flash point. The vapors are best applied to the desired surfaces of the part via a teflon or silicone rubber tube. The vapors cause the outer layer of the plastic to disolve slightly and become "wet". When the vapors are removed the surface quickly dries but retains the wet or polished appearance.

Good luck and be careful!

BTBB

[guru_florida]

I thought some people used Novus polishing creams to return the clearness. Maybe some cream polishing before heating might help the heating process work better?

[Geof]

Originally Posted by guru_florida I thought some people used Novus polishing creams to return the clearness. Maybe some cream polishing before heating might help the heating process work better?

The Novus polish works well on acrylic but I have never had success on polycarbonate.

Vapor polishing works with polycarbonate and with care it is also possible to get a good improvement just using a hot air gun. But polycarbonate is much more difficult to work with than acrylic and a great deal of care must be taken to avoid overheating because this will cause bubbles from the water that is present in the surface of polycarbonate.

[One of Many]

Vapor polishing is more of a production method and not one that can be done at home at least. The process also needs some post heat soak time to stress relieve the surface, as the chemical exposure will induce surface cracks. The surface improvement is 0nly about 5-10microns. Which means it must be a nice surface to start with, but that may also be true of heat polishing. It will make tool marks clear, but does not remove them.

PC is strange to work with considering its properties of tough but still soft enough that it doesn't take well to friction polish or cutting compounds. Half the time, I think the friction heating does more to reflow the surface than the compound actually removing material like harder acrylics.

Baking the PC at 100-140deg for a few days can help reduce the moisture bubbling effects. Depends how old the stock is and the storage environment.

I have had some luck using Tetra Hydro Furan to desolve the surface back to a semi-optical calrity. Some evaporation can fog the surface, but now I wonder if attempting a heat polish after would help.

The part size is going to limit what can be experimented with.

DC

[stevehuckss396]

Try good old elbow grease. use sand paper down to 2000 grit and then buff it with a clean cotton rag. Once it is very clean, wave a propane torch accross the surface a few times and it will be crystal clear.