Vac/spoilboard trouble

[mgranato]

I use 2 Fien vacs on my 10 zone 96x60 table. I've never been able to find Trupan, but have had good results with Sierra Pine UL. I tack glue the spoilboard to the plenum that's painted with epoxy paint. My normal procedure is to use the 3/4 UL done to +-1/8 then surface it down to the plenum, re-glue and start over. That's the history, now the problem...

My most recent UL replacement is not letting much air at all through. I've tried 6 different pieces, I've tried 1/2, and I've even laid different grades and thickness of plywood on the table, but no matter what I try the gauge reads 4-5 inches with nothing on top of the spoilboard. I've flushed the plumbing and cleaned the vacs. Most of my work is on the 2x2 sections of the plenum, so I've got two vacs pulling on 1 section of 2x2 getting nearly 5 in with just UL on the table.

I'm not sure why this method has quit working all the sudden, but I'm running out of things to try. Anyone else experience anything like this or have any advice would be a huge help.

[beacon14]

So, you got a new batch of MDF and it doesn't work as well? Does it look and feel like the same material? There are a lot of grades and brands of MDF. Did you ask the supplier if it's the same stuff as last time?

[chuckster]

I have had the exact same problem this last spoilboard replacement. I planed both sides as usual and it seems there really isn't as much vacuum as normal. I have always used .75 MDF. I really never even thought it could be the MDF! Perhaps next time I will try LDF, and hope it's a bit better. David, do you seperate the zones with wood strips?

[mgranato]

I tried the stock I had left from my original buy that were the same sheets that had been working just fine, but don't now. I also bought new sheets which were the same (at least by name and appearance) as the originals. With all zones open, the vacs pull 2.5 in, but when I shrink down to 1 zone I'm just not able to get any flow through. I even planed one of the sheets (bought at the same time as the originals) down to 1/8" and still got 4+ in.

[richards]

The glues used in MDF make some brands (and some batches) of material unsuitable for use as a bleeder spoil-board.

For my bleeder spoil-board, I've switched from regular MDF to ultra-light MDF with excellent results. (Trupan is not available in Salt Lake City, so ultra-light MDF is my only practical choice.)

[mgranato]

UL is what I've been using and trying to use now. I've also tried regular and different plys but regardless of the material/thickness the gauge is reading the same number.

[bleeth]

Mike: Have you checked your guage?

[mgranato]

I replaced it this morning, but unfortunately the results are the same.

[beacon14]

With all zones open, the vacs pull 2.5 in, but when I shrink down to 1 zone I'm just not able to get any flow through. I even planed one of the sheets (bought at the same time as the originals) down to 1/8" and still got 4+ in.

That's really odd. Forgive me for asking the obvious, but have you checked the plumbing for obstructions and checked the filters on the vacs?

Chuck, I have the zones separated in the plenum layer with a strip of PVC edgebanding between the quadrants, but my spoilboard is a full sheet with no separation between zones.

[mgranato]

Believe me, I've been racking my brain looking for the obvious :-) I checked and flushed the plumbing. I cleaned the vac filters which only had the faintest of dust on them to begin with. It's the craziest thing, it's like I'm trying to pull through hardiboard no matter what material I put on the table.

[chuckster]

Ok David, I just thought you were the one I was talking to about that at Camp ShopBot in Marion this last time. I did try it with a 1/4" deep x 1/4" wide wood strips in the spoilboard to seperate the zones a bit better. It actually worked well until I replaced the spoilboard a week ago and now get crappy results! I am going to check out the plumbing in the a.m. just to make sure the issue isn't something that simple!

[letterman7]

To spin off what Mike said, only MDF made with formaldehyde glues will work for a pull-through spoilboard. Other glues are too dense. Weird, huh? But I have no idea how you can check that unless you can get an MSD sheet for your brand of MDF.

[chuckster]

I have decided to give LDF a try. I am just concerned that it may be TOO porous. I'll post the results as soon as I complete the job!

[mgranato]

I've tried everything I could think of, and my ultimate (hopefully temporary solution) was to drill/perf the spoilboard. My suction is back up were it was prior, but I'm not too sure how good of a long term solution this will be.