Spoilboard idea...

[geneb]

After reading about Mike's issues with his spoilboard and the last post mentioning drilling holes in it, I got to wondering...

How effective would it be to take say a 3/4" sheet of good plywood, surface it and then fill it with 1/8" holes on 1/2" centers across the whole board?

The only downsides I can think of is that you'd need to filter the vac source to keep sawdust out of a dedicated vac motor. (I use a pair of Fein Turbo III's so that wouldn't apply to my case)

You'd also have to mask the table to cover any open holes if you're not using a full sheet of material, but that's no big deal.

The spoil board could even be drilled with 1/8" on 1/2" centers and 1/16" on 1/4" centers, but that may be overkill.

While maintenance of this set up would be higher than Trupan or Ultralight MDF (unblocking holes), is it a reasonable solution?

I ask because I can't even get Ultralight where I'm at unless I take a day off work and do some traveling. (I'm a hobbyist user of the 'bot)

g.

[frank134]

why not use 1/4" peg broad. do you think that will work? you could also put a piece of that black landscape material between the peg broad and the vacuum board which hopefully will act like a filter for the saw dust.

[gabepari]

As soon as just one of those little holes is exposed by your toolpath you will loose a bunch of vacuum.

You will need to onion skin all your parts.

Gabe

[geneb]

I like the peg board idea. I wonder how well it would take to being surfaced?


Can't hurt to try it I suppose.

g.

[Gary Campbell]

Gene...
Using pegboard or any perforated sheet will lose vacuum very quickly if one or more of the holes falls into the path of the bit. Also your cutting dust will be vacuumed into the plenum. Those are the simple reasons.

Here are the more technical reasons not to do this:
Vacuum is negative pressure per square inch. Therefore your holddown will be the total area of sealed area times the negative pressure. In order to make is work, you would have to gasket around the part and seal all the other holes.

As far as flow goes, our Trupan spoilboard reads about 1.5 to 2 inHg without a mask. This according to the Ametek performance charts is the flow equivalent of a 1 1/4" orifice.

Fully masked off, we have about 9 inHg which is the equivalent of a 1/4" orifice.

Hold down fails around 3.5-4 inHg which is the equivalent of a 3/4" orifice.

This tells us that if 6 of the 1/4" pegboard holes flow vacuum, hold down will fail.

One of the "magic" things about a porous spoilboard is that it resists flow where you have leaks.
Gary

[mgranato]

I'm all for a better solution than perfing the spoilboard, but if you can't get Trupan and the UL mdf is reading 4.5" on a unmasked 2x2 section with 2 Feins pulling on it my vac system is useless. I would love a better solution than what I'm doing now.

[geneb]

Mike, if it's any consolation, mine is pulling about 3.5 with no masking at all on a 4x8 spoilboard. I'm using BORG MDF that's been surfaced down to a bit under 1/2".

If I get a chance I'm going to try the pegboard on Saturday.

g.

[mgranato]

Gene, I feel ya. I'm a bit bummed by the whole thing. Things were great with my last SB, it was as easy to get through as a Big 12 defense. Now I'm in the 2-2.5 neighborhood over a 4x8 with no masking, where as before it would barely read.

Where are you located, and how far would you have to go to get the Trupan?

[gabepari]

Having a very low reading on your gauge with nothing on your table isn't always a good thing. The more porous your spoiler, the more it leaks. Meaning when you do start cutting, the air will leak faster through the exposed areas.

Granted, I use Trupan, BUT I use 1" and don't surface the bottom of the spoiler. That way the board resists leaking when I cut through my part. I usually replace when the board hits about 1/2" or so.

Also, I'm running a 15hp Roots pump, a little more grunt than 2 Feins.

Gabe

[Gary Campbell]

Mike...
Even tho you may have a different starting vacuum point, what is more important is, what is the difference in readings with the spoilboard covered with a sheet or fully masked. What is your highest vac readings?
Gary

[beacon14]

Gabe,

Maybe I can buy your 1/2" thick Trupan leftovers.

[geneb]

Mike I'm in Graham, WA. I know of no Trupan supplier within reasonable driving distance.

The vac difference between material loaded and not loaded isn't much, but it's enough to keep full sheets from scooting around while I cut. I mostly cut OSB and 1/2" MDF with 1/4 or 1/8" down shear cutter. (Centurion Tools are *awesome* :D )

g.

[mgranato]

Gary, with a full sheet (5x8) of mel on the table I drew 5" with a starting point of under 1". Now I get just a bit under 5, but I start at 2.5. My full sheet cuts are usually large enough to not matter. The problem is when I drop down to one 2x2 zone. My old starting point was under 1 and went to 5.5 with a 2x2 jig covering the whole zone. Now (without perfs) I'm starting at 4 and then goes to 5 with the same setup. With perfs I start a 2.5 and go to 5.

David, you beat me to it :-)

[carlcnc]

I am surprised noone has mentioned using industtrial particle board, 49x97 3/4 works great for me. it is not usually available from Lowes or the Orange box,
so in a pinch I have used 1/2 underlayment grade.
both seem much more porous than mdf
nice thing is you only have to surface the top for Z accuracy,
Carl