Tuesday, November 13, 2007

More 'Cutting Remarks'

Since posting thoughts earlier about ‘Cutting Plastic’ back in September, Skippy and Buzz have had a number of side discussions and have some additional inputs.

Skippy: Hey Buzz – Back on the idea of cutting plastics, someone suggested using a standard or carbide blade for cutting slightly abrasive PVC and Acrylic plastics but installing the blade ‘backwards’; any thoughts?

Buzz: The concept of 'blade in backwards' is a confirmation that a negative rake or tilt to the blade teeth imparts slicing versus gouging action in some plastic saw blade designs. This 'using of a blade improperly' is a bad idea all around – especially with carbide inserted blades – the carbide pieces are joined to the blade body, but are designed to push and cut into the product while cutting, not be pushed against backwards while trying to “exit” a product to be cut. Having the carbide pieces come loose and or be knocked off and slung at the high foot per minute speeds that saw blades run at is a potentially dangerous outcome. These blades just aren’t designed to be used that way. We are agreeing with negative rake in general for plastics along with the right tooth configurations, disagree with using wrong blades 'creatively'. Just buy the right kind of blade to start. Yes, PVC is slightly abrasive, generally due to the loading of talc or calcium carbonate or other fillers - sometimes they are in color and UV packages. While on the subject of abrasiveness, do your production folks a favor - remind them to remove jewelry while handling these plastic articles - particularly gold and silver rings while handling the slightly abrasive PVC - you know those grey marks they leave on the PVC? (come'on you want to test it right? Just rub a ring on the surface . . .) - yup, thats GOLD and SILVER being worn away - puts a new spin on the phrase 'value added' - eh?

Skippy: A few reminders again about safety. The sawn material removed will generally be larger than dust and can be airborne. Inexpensive paper dust masks to filter out the chips (which won't be much if you put together an inexpensive 'catch box' behind the chip path to catch 80% of the chips) and just as importantly, eye protection are always a good idea in a shop environment when using cutting and grinding tools. It may be that you also need a "Lock-Out, Tag-Out" procedure to disconnect all sources of danger when installing blades, doing set-up, and servicing the equipment.

Buzz: eventually someone recommends putting a lubricant on the blades as well. Recommendation - do not put petroleum products on PVC or other plastics in general - depending on the application, the by-products in the can (aerosol propellants etc) can create a variety of problems including UV and color fastness failures, and negative interaction with mating parts (not previously mentioned). If your final installation (what ever this does) needs to be warranted by you, not a good idea to create a future problem.

Skippy: what about ‘Silicone’ spray?

Buzz: Ah yes, good old "silly-cone" spray; next to ‘WD-40’ and Duct Tape, another of the great ‘cure alls’ - falls in line with the 'Bash to fit, Crush to assemble, Paint to hide' axiom - this is generally not a good material to be used in a shop environment as it will get into (and onto) everything eventually (worst is the floors and assembly counter surfaces) - again, if used on and impregnated into PVC can cause other problems - especially if you later want to use any adhesives with gaskets, tapes, labels etc. From a warranty standpoint, it is not a good idea to spray, coat or otherwise inject other stuff into your base compound; bare minimum it is likely to VOID the warranty from your profile supplier as well as their raw material manufacturer.

Skippy: So in general, a user of saw blades to cut plastics is looking to key in on

a) Correct blade design; differs per material; and correct equipment set up and use
b) Correct Cutting speeds (often measured in foot per minute surface speeds)
c) Adequate product support during cutting operations
d) Personal protection correctly applied and used at all times

Buzz: that's right Skip, hopefully you have already used the information to acquire the correct blades and are producing satisfactory results.

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