vacuum hold down

[matney_models]

I need more help about my vacuum hold down. I have 2 Fien turbo 3 vac, with LMDF about 5/8" thick, cut a 3/16" v cut about 3/4" apart. With a 1 1/4" air camber lines in the bottom board

[matney_models]

This cut into the bottom of the LMDF.
to help it out. I'm still not getting the holding power I think I should have.
The vac sound like you have your hand over the hose. They are pulling that hard.

[loriny]

do you have a gauge to check the amount of vacuum you have with and without a sheet of material on the table?

[ken_rychlik]

Post a picture of your vac plenum before putting the top sheet on.

It sounds like you may not have enough air flow. I use a 1/2 inch ball nose to cut mine and the cuts are 3/8 of an inch deep.

I don't have any cuts in my top spoilboard. Some do that, but unless they line up with your other holes it won't help much.

Did you seal the plenum? Oh and did you cut out the holes where the vacuum is hooked up?

Need more info to help.

Kenneth

[jerry_stanek]

You maybe loosing vacuum through all of your spoil . I have my grid cut into a piece of mdf that is over my plywood table then I just surface the LMDF one side and flip it over and glue the surfaced side down to the grid. Once the glue is dry I cut a1/4 inch groove all the way trough the spoil board down the center and across the center to separate the zones. I glue a piece of 6 mm sintra in the groove. I then surface the top and I am ready to go. I found I was loosing to much vacuum through the whole spoil board if I didn't do this.

[dana_swift]

Ideally a vacuum system would have no-flow, so the "hand over the hose" pressure would be available everywhere. The real world is not so nice, "flow happens". The biggest culprit is around the edge of the bleeder board. Be sure the bleeder board is sealed at the edges. There are many posts on how to do that.

For a quick vacuum test, wax paper will seal the top as if a part were being held down. Then check the vacuum with a gauge at the blower. The wax paper should hold tight to the bleeder board. If there is any leaking at the edges tape it off with masking tape.

Then test with a sheet of material. The difference is the quality of seal on the new material and the flow through the material. Note that the MDF family of materials are very porous, and wont vacuum hold because the flow is almost the same as the bleeder board alone.

It takes a while to get the hang of vacuum, which is very flexible, and "can be" very effective. It can be frustrating also.

In every vacuum system I have seen operational there is a gauge the operator can monitor. From experience I know when my part is likely to be getting ready to shift. Then I put a quick clamp on the edge somewhere to help out. Install a gauge and watch it while cutting.

It also helps to order the toolpaths so things that cut through are done last.

Good luck-

D

[zeykr]

I can't tell from the picture: Did you surface both sides of your spoilboard to remove the outer 1/32 of material or so besides cutting grooves in the bottom?

[matney_models]

Yes I surface both sides. And cut 1 side like the pic is the 2 post. And ever thinned it some like down to .600"

[erik_f]

Have you used your vacs for cleaning up MDF ever? If so your filters are most likely clogged all to hell. If your edges are not sealed you will lose a ton of vac. The plenum needs to be as free flowing as possible and the bleeder board needs to be surfaced on both sides to avoid it cupping and for better air flow. Your vacs should (as others have said) sound like they are plugged when you have your work material on top. Over all vacuum was pretty simple for me once I got one concept: You are not trying to suck the material down, rather, remove the pressure under your work piece and increase the amount of atmosphere pushing down on top of your work piece.

[harryball]

are you 110% SURE you got ultra light MDF? If you use medium or regular MDF the results will not be as good as the UL. I've found suppliers are very lax about giving you the right MDF. Dixie ply tried to load me up with regular MDF rather than Trupan UL.

I use a similar setup. 2x fein III's with 4 zones, 2" pvc plumbing and ball valves. I get ample holding power on a full sheet and enough holding power on a single zone to trap a guy in place.

I use shellac on the edges to prevent leaks. I also glue my board down.

FYI
Photos show a spoil board surfaced down to about .2" thick (which is glued to the base grid) and marked showing each zone. I then added glue along the zone lines with some globs in the middle to keep the centers of the zones from bucking. Once that was done I placed the new spoilboard (with help) on the top then wrapped with plastic and turned on the vacs. I left that about an hour. Works very well for me.

[carlcnc]

ULDF and LDF will have substantial bleed horizontally,in effect you never really get optimal "isolated" flow thru 1 zone.
I had to cut the spoil board into pieces for each zone, then used a liberal amount of titebond to glue them edge-edge.
That way each zone is sealed from the next.
The last ,maybe best improvement I did was glue the spoilboard directly to my plenum board. I figure when I have to replace it my router is accurate enough to skim cut the old glue off without taking more than a few thou off of my plenum board.


Carl