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kasey_jones
02-09-2007, 06:48 PM
I've been reading (alot) of the posts dealing with the whole vacuum issue. It's starting to make sense (I think).

About the only thing I’m sure of is using the Fein Turbo III and a grid like David Buchsbaum designed in his “Introducing…F16” post.

I plan to cut mostly lithophanes with my bot, so getting the table as flat as possible (and keeping it flat) is a must. I'm struggling with the decision of what material to use as my support and vac grid.

I started to go into the pros and cons of all the different material discussed, but this post began to look like a novel, so I’ll just ask if price wasn’t a problem (even though it always is), could I just get a thick piece (1 to 1.5 inches) of Komacel, UHMW, Phenolic, etc (whatever), and use it as my support and vac grid? Or maybe... Is there such a thing as a permanate table (by table I mean support and vac grid) that would require only surfacing the spoilboard when needed.


Thanks,
Kasey

hines
02-09-2007, 08:31 PM
Kasey, if you're going to be cutting small lithophanes you may want to check out making a vacuum puck, also called vacuum clamp.
http://www.joewoodworker.com/veneering/vacuumclamping.htm

If you do a search for vacuum clamp you should find some examples on the board.

billp
02-09-2007, 10:52 PM
Kasey,
If you primarily intend to do lithophanes, make a "Lithopod". It's a designated pod/puck, in this case 1"PVC(first picture).
You can then use gasket tape from All Star Adhesive to alter the actual vacuum area you need to cover (picture 2). This allows you to use a small, rotary vane type vacuum pump with a switch, etc. and you'll never have a piece of plastic/solid surface move on you at all. PLUS this kind of vac table never needs to be resurfaced (unless you make a disatrous error in setting your initial Z height)..
7940
7941

kasey_jones
02-10-2007, 06:01 AM
Dave / Bill - Good ideals.

Bill - Why not just use the 1" PVC as the material for my table? What are the pros and cons of using PVC vice plywood/MDF?

Thanks - Kasey

ed_lang
02-10-2007, 09:07 AM
Kasey,
What size machine do you have?
I have a 4'x 8' machine and if I were going to run a lot of the lithos, I would do exactly as Bill P. showed above. In fact, that is how I started with my machine for everything I did. It works great!!
I used a scrap or Corian and made a larger "puck" and then used plexi for the vacuum mask. The masks were made for each job I ran. Quick, cheap and held real tight.

Now I have a full size vacuum table and two Feins. I still cut vacuum masks for smaller jobs and use gasketing.

So, as you can see, it all depends on what type or types of jobs you will be cutting. You might find that the Feins and the entire table serving as a vacuum table will not be best for you.

If you plan to cut sheets of material, then the full size vac table is best I feel. I used two 3/4" ply sheets for mine. One bolted to the cross members of the steel table and the second one glued to the first. I then cut my vacuum grid into the second 3/4" sheet of ply. On top of that one I have a sheet of MDF that was surfaced on the side that goes down FIRST before glueing. Now that the MDF spoilboard is getting thin, after many times of surfacing, I am rethinking my choices. I like the "Bradyvac" system a LOT. I also will be using Trupan Ultralight in place of the MDF this time. If it were not for the fact that I cut 4'X8' sheets, I would only use the smaller high vacuum pucks.

If money is not a problem, then the 1" PVC would be fantastic! Make sure you use a glue that will sitck to it as well as the spoilboard!!

billp
02-10-2007, 11:36 AM
Kasey,
Ed is right, PVC is pricey, but stable. It is also pretty heavy in full sheets at that thickness. But it would seem to solve a lot of the standard complaints we read about here on the Forum:
it won't absorb moisture and turn into a large rice krispie
it won't bleed vacuum through it's surface or sides,SO
this would make it a good base for running vacuum ports, or the Brady vac moveable plenum/spoilboards because there wouldn't be any need to seal edges, etc.
it WILL accept threading, and hold down screws or other mechanical fasteners
it "fly cuts" very nicely so getting it flat initially shouldn't be an issue
you could have a few ports scattered around the table surface and simply use gasket tape to designate the "jig du jour" you need at that moment for one off jobs
I think you can find full sheets from places like McMaster Carr, or possibly even Grainger. A good plastic supply house might also be a place to search, but I think pricing in plastics varies considerably from one geographic region to another.

billp
02-10-2007, 11:45 AM
I just checked the McMaster page, and a full sheet of 1" thick PVC "flame retardant" ( a nice concept) , "weather resistant" ( for marginal work areas?) will run you -$718.73 (each.....) Maybe THIS is why we don't ALL have PVC tables...

bill.young
02-10-2007, 12:13 PM
I don't know if this is true for PVC but some plastics absorb a lot of moisture and shrink and swell considerably...if we have to use a bushing between a propellor and the propellor shaft, the propellor guys recommend nylon because it swells so much when it gets wet.

Also this might be completely different stuff but the PVC sheets that they sell to make house trim out of is awfully noodly and can be much more easily bent than the same thickness of plywood. Even at 1" thick I'd worry about it sagging between the supports without some sort of "underlayment".

Bill

Brady Watson
02-10-2007, 01:14 PM
.75 to 1" expanded PVC sheet would be economical to use, but an 'underlayment' as Bill pointed out is imperative...The only way you are going to get it flat is to GLUE it down to those underlying layers. Komatex, Sintra, Celtec (and others) expand and contract with the weather. Gluing it to your sub-structure (not the steel, people) stabilizes it to a reasonable level. Adding a Trupan bleeder to the top of the PVC grid allows you to hold down full 4X8 sheets.

The original question was to hold down lithophanes...and I guess for many, this poses a bit of a conundrum...Do I make a big full-size vac grid? ...or do I make a small accessory grid that I can add or remove to the top of my table when I want to do lithophanes? The answer for me, was BOTH! You can do both...and have it all.

For smaller accessory vacuum jigs/plenums, you can use any number of materials. I've had really good success with corian epoxied together to make a plenum box for doing small parts. You don't need a special vacuum pump to effectively hold down lithophanes or small parts. You do need an air-tight box though. If you need it to be dead flat, put a piece of Trupan on top (that can be removed). This way you can screw the whole thing down, and just CR (like you would your 4X8 bed) and get things nice & flat. Then put whatever you want on top to cut. It works out pretty well.

With all of this vacuum stuff, don't be afraid to experiment with your own ideas, theories and setups. You will quickly figure out what does and doesn't work. Try to use up some of the scrap materials in your shop for experimenting and do things on a small scale before going nuts with all kinds of valves, zones and exotic setups.

-B

kasey_jones
02-11-2007, 05:54 AM
Thanks everyone for your advice. I spent most of yesterday, throwing it all around in my head. It appears other than price, using a piece of PVC would give me more of the permanate solution I was looking for. I'll post pics if I decided to do the PVC sheet.

Thanks again.
Kasey

beacon14
02-11-2007, 02:45 PM
A big concern I'd have with PVC as Brady alluded to is that it changes size with temperature. Unless your shop stays relatively constant temperature year-round, you may want to use slots instead of holes to bolt the PVC to the table so it can move a little.

kasey_jones
02-11-2007, 04:04 PM
David

I was under the impression PVC (solid kind) would not be affected by the weather, but expanded PVC would. Brady - did you mean ALL PVC or just the expanded kind?
I have a local supplier, so I will stop by and price it out tomorrow.

Thanks again
Kasey

Brady Watson
02-11-2007, 07:14 PM
Expanded. If you are going to do a big 4X8 grid, then scuff the back with 60 grit paper and gorilla glue it down to the support board. No need for screws whatsoever. If the bleeder gets tweaked...just flatten it with your spoilboard bit.

-B

davidallen
02-12-2007, 09:48 PM
Would one of those plastic grids used as light diffusers be useful for a vacuum support?

da

Brady Watson
02-12-2007, 11:28 PM
David,
Probably not. You're close enough to take a ride down to my shop one day & I'll show you what I run here.

-B

bcammack
02-13-2007, 07:40 AM
Solid PVC sheets, bonded to the table surface are a hot item on big CNC mills such as we use for routing stone countertops. Vacuum seal to a pod is never questionable and the machine runs so much quieter.

Yes, it is expensive.

nappy1
02-13-2007, 07:30 PM
Ok, I held back long enough. I have 36" x 48" pieces of 1" thick PVC in stock. If anyone is interested, e mail me.