MDF Bleeder/Spoil Board - Ultra Light vs. Standard

[80grit]

I was hoping to use 1/2" UL MDF for by bleeder/spoil board, but I am having a hard time finding UL MDF in my area. Then, I got to thinking about how standard MDF looks on the edge.

When you look at 3/4" MDF on the edge, you can see how the density appears to get thicker close to the surface. So, I was wondering if I fly cut 1/8" or from each surface, would that leave me with a lighter , more porous 1/2" piece of MDF than the same brand factory 1/2" material?

[Kyle Stapleton]

You will have to fly cut both side on MDF or LDF.
What are you using for a vac?

[bleeth]

Just skin it enough to get rid of the entire surface. Lots of folks use regular MDF. It's not as good but works fine.
Your nearest supplier of ULDF or Trupan is probably Baton Rouge.

[80grit]

I conducted an experiment using 1/2" and 3/4" MDF from the same store. I planed down a piece of the 3/4" to 1/2" (removing 1/8" from each face), cut them to equal length and width, and weighed them. The 3/4" piece planed to 1/2" was 11% lighter than the factory 1/2". I found that interesting.

I will be using LH motors in a box. 2 motors for now. 2 more when I can afford it.

[jamesburrus]

I Know that UL mdf works well 3/4"

[Ajcoholic]

When I was researching this stuff, I read in more than one place that you would "think" that the thinner the bleeder/spoilboard is, the better the holding would be since the air would be easier to move through the sheet. However they said that this isnt the case and that a thicker bleeder actually works better.

I have not tested this, and have found my board (starting with a 3/4" sheet of standard cabinet grade MDF, skimmed about 30 thousandths off each face) works fine, and I have taken it down to just under 1/2" before I started with a new sheet.

I have also tested placing a second sheet of 1/4" MDF on top of the bleeder, in between the parts being cut and the bleeder/spoilboard, and it worked fine as well. My thought was to leave the bleeder alone and not have to surface it so often, but I still end up surfacing the 1/4" so time savings isnt there.

I would still like to test a sheet of the light weight MDF if I ever get a chance. However, I dont see any better holding power as my bleeder gets thinner from resurfacing, at least not for the stuff I cut.

I just cut some pcs of 1/2" Baltic birch where my smallest part was only about 8 square inches, and out of a dozen parts I had two come loose. Thats on standard MDF.

I guess you could measure the force to slide a pc of material held down on 3/4", then surface it down to 1/2" and measure the force to move the same pc. If it gets harder to move, then you're on to something. If not, then you know it doesnt matter.

[Plyoboxwarehouse]

I've been using a vacuum hold down for several months and have cut several hundred sheets of plywood and MDF on it. I initially started out using regular 3/4" MDF and got pretty good holding power. Once that board was done, I thought I would switch to Trupan Ultralight and get better performance, but found out that it was about the same. I have a vacuum gauge installed on the manifold under the table. I actually noticed that the more the spoil board was exposed during perimeter cutting that my vacuum went down more on Trupan than with regular MDF. The regular MDF is a more dense and seems to me that it helps distribute the vacuum more evenly, the Ultralight Trupan is more porous so the vacuum wants to escape more in areas that are not covered (i.e. perimeter cuts). I actually have to switch some zones off when cutting clears a zone to increase the vacuum in the other zones that still have cutting to do. I'm switching back to regular MDF - it's cheaper anyway.

To 80Grit's post about the density of the 3/4" planed down to 1/2". The center of MDF is slightly less dense than the outer areas. This would explain why he found the center 1/2" of the 3/4" MDF to be less dense than the full 1/2" MDF. That's what my supplier told me anyways.

[MogulTx]

(Curiousity question): I am buying 3/4" MDF in a 5 x 10 for spoil board. Price seems "reasonable" at $68+ incl tax on a single-sheet-purchase basis. (It's probably worth that just from the handling aspects. That stuff is HEAVY in that big of a sheet!!!!!) What are you seeing in your local areas for regular MDF?

[dlcw]

I use 3/4" skimmed both sides as the main spoil board. I then purchase 1/8" MDF sacrificial board and skim it both sides and place my material to be cut on top of the sacrificial board.

At the start of each cutting project (cabinets) I surface the main spoil board. Then place the plywood on the 1/8" board and start cutting. When cutting is done, I slide the sacrificial board off the a roll around table for part labeling and sorting. Before I start labeling and sorting, I put a new 1/8" board on the CNC, load up another sheet of plywood and start the cutting, then go back and start sorting and labeling.

This approach allows me to process more sheets per hour and I don't have to resurface my spoil board. When the next large project comes in, I do a skim on the spoil just to make sure it is flat and level and use the 1/8" boards.

My spoil board lasts for a couple of years easily this way. The 1/8" MDF is about $3.50 per sheet in my area. well worth the cost and time to skim both sides if I don't have to keep surfacing my spoil board.

For a standard 60 - 70 sheet cabinet project, I will purchase 6 or 7 of the 1/8" boards and surface them while I'm working on something else and have them ready when the next project starts.

[Curtisminor]

Hi guys,
I am Curtis Minor. i am building a shopbot vacuum table from make magazen. can any one help me on this topic?