Bleeder board and gasketing

[gabepari]

Since the machine is down for a few days (maintenance and slow time for our customers) I am going to change the way the bleeder is attached to the plenum. If I was the only one using the machine, I would opt for a system like Brady's, but I need to be able to have someone that can barely remember righty-tighty lefty-loosy (NO, not me
), be able to change the configuration of the vacuum table quickly between jobs.

So I cut some grooves in the plenum, built up some walls and added a few more zones to accomodate 4x8 sheets on the 5x10 table without masking. Very simple mod for those who used the standard 4 zone grid and don't want to replace the entire plenum.

Anyway, I am going to cut some o-ring grooves in the plenum and install threaded inserts, so I can bolt the bleeder down with plastic or fiberglass bolts (I'm tired of scraping the goo off the plenum when changing spoilers and I don't like the idea of gluing the bleeder to the plenum, I like to be able to take things apart). What gasketing material should I use between the bleeder and plenum. As I can cut any groove I want, I imagine the size isn't as important as the durometer.

I would like it to bottom out, so the bleeder is flat against the plenum without a whole lot of upward pressure from the gasket, but enough so that is seals well. Also, I'm worried about the gasket retaining a memory and not bouncing back when I pull the old spoiler off, maybe just put some new gasket in each time I change boards??

Thanks for any help,

Gabe Pari
www.socalteardrops.com (http://www.socalteardrops.com)

[Brady Watson]

Try the 1/4" gasket tape from AllStar. It's @ 1/16" thick, high durometer. Just make sure that whatever you do on the perimeter of the sheet you also do in the center of the sheet...otherwise it will cup.

Another option for you is to use no gasketing between the sheets at all & just run some AL tape around the perimeter of the sheets. It will both seal off the edge of the sheets & act as a gasket/air barrier. I use this method all the time since I often remove my bleeder from the table.

-B

[Gary Campbell]

Gabe....
we do something very similar to what Brady describes above. We use AllStar CR 2525 adhesive backed material around the perimeter of our 4 Plenum zones. .250 groove .1875 deep. Radius corners. We then use our 2.5" surfacer to cut a 1.5" wide .030 deep path around the outside of each zone spoilboard. Then a quick coat of contact in the recess and edges and then put on the tin tape, which covers the recess and edge. Its probably overkill, but seems to work. Spoilboard doesnt seem to cup till under 1/4" thick. I am not sure if its our method or just the 80-90+% humidity here.

3167
Gary

[bstern]

I tried the All-star gasket material with no luck.
The corners did not pull down all all the way during surfacing. I did a radius similar to whats pictured above and followed All-star's instruction's on groove depth to a T. Maybe a larger radius would work better.

I removed the gasket and used silicon caulk. works great but I have not had to change the bleeder yet.

I was thinking of when the bleeder gets down to about 1/4 to 1/8 thick I would try just putting another piece of trupan on top and seal the edges.

Has anyone tried this?
Any thoughts on if it would work well?

[gabepari]

I just ended up getting some 1/4" gasketing material from McMaster Carr, $17 for 100'. Bolted the bleeder down with fiberglass 1/4"-20 bolts. Works like a charm.

This time I did not surface the face that sits against the plenum and I used a full 25mm thick Trupan. It works much better than before. I get about 3-4" when all zones are open and no material on the table. It seems that the leaks created by the cut paths don't matter as much with the thicker bleeder. I notice a small delay when I close the valves, confirming that there is alot more air in the 25mm that needs to be sucked out before pulling vacuum.

So far I'm happy. Next I'm going to try using an 1/8" spoiler just placed on top of the bleeder, so I don't have to cut into my $100 piece of Trupan


I'll try to get some pics up tonight.

Gabe

[Gary Campbell]

Gabe..
What numbers did you get with the old spoilboard, all valves open and nothing on the table? What material was it?
Gary

[gabepari]

Before we were using 18mm Trupan, surfaced both sides. All valves open, nothing on the table, 2-3". I thought that the skin on the bottom of the bleeder would make a bigger difference. But that Trupan seems to be pretty porous on the surface, so really no reason to cut off the nice smooth side before putting it on the plenum.

Gabe

[Gary Campbell]

Gabe..
the difference between the 2 is what you are losing with the thicker material.. not a great loss if you have some to spare. Thanks for the info. I am considering going to 3/4 from 1/2 Trupan.
Gary

[gpari]

What amazes me is the reduction in pressure loss from tool path leakage. A file that would usually drop to about 6-7" by the end of the file, is now at 11" by the end.

Gary, what kind of pump are you running?

I've got the roots 15hp 14" 330cfm, that was supplied by shopbot, running 3 phase.

Gabe

[Gary Campbell]

Gabe..
You have the pump I wish I had. I definately have 3 phase envy. We are using 4 vac motors. only 7" Hg. Hope to find a single phase unit it the near future, after I get the center leg set in and the rest of the E chain installed. Sounds like a thicker spoilboard is in order tho.
Gary

[gpari]

So far I'm sold on the thicker board. I will however probably get a larger vacuum when we move our shop, maybe even spring for a PRS as well


I've got wire chain on then x-axis, haven't installed the y-axis chain yet. Also have center legs/braces and z-axis braces (with trammel bolts) that I need to install.

Gabe