It has been my experience that PVC doesn't hold up around hot metal, but will, along with other plastics, hold up in a dust collection system if used downstream from the heat source. If you're serious about dust you need to step up to 6- or 8-inch size piping. The little 2.5 inch shopvac size isn't sufficient to handle it. They move a relatively small volume of air fast. You want to move a large volume.
I use some typical 8-inch steel fittings ala hardware store/Home Depot to collect and initially transport the hot grindings. Then I use 8-inch steel-wire reinforced plastic flexi tube to transport it to big gate valves (both available from MSC, but not cheap).
I don't remember the exact specs on my dust collector, but it's a 55-gallon drum-head type. 2-hp. 3,600 rpm Delta with a gaint puff-up final filter bag. It pulls enough CFM to do the job. If you aren't careful, it will suck a rag right out of your hand without the slightest difficulty. I would like a surplus Torit industrial unit, but have had a hard time finding one tht isn't really huge that can perform equal to my Delta. I think I paid $200 on Ebay for it.
The advantage of going with larger CFM and bigger plumbing is that it creates a much greater 'gravitational-like field' pulling in more grinding debris. The smaller dust systems will collect fine, but only the stuff that's shot right into it.
Here is a link to a picture on my site that will give you an idea of the material I use for my plumbed dust collection.
http://www.caswellstudios.com/SwordPages/BodyPages/tools/SurfaceGrinder.html
For open wheel belt grinders, (Bader, KMG, countless homemade units, etc.), you will likely find plumbed dust collection systems inadequate. These grinders shoot the bulk of the grindings down, but fixing a dust-collection scoop under there is darned inconvenient. Also, these open wheel machines produce a lot of fine debris that will never be sucked into a static system.
I ran into a good solution at Bill Herndon's shop. You get one of those big, belt driven whole house fans with exterior louvers (38 inches or so). Stick that baby in the wall preferably right behind or next to your grinder and blow all that stuff right on out. The heavy grindings just stack up on the ground and you sweep 'em up, but all that little stuff just goes right out. This is also good to run when forging, welding (other than TIG), running hydraulic equipment that may fume oil vapor, using misters for coolant, are cleaning off anything with compressed air, or if it's just too hot in the shop. You want to use a belt-drive unit (preferabbly with a sealed motor) because the type with the typical non-sealed motor in the center will not appreciate all that fine metal dust in it's works (poof/zap!)
Sorry for the lengthy epistle.
Hope it helps.
But still what the collector takes out will be enough to start.
