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fasteddy
21-11-2010, 08:05 AM
Hi all..

A few years ago, I went to the NEC to drool over some ready made CNC machines.. On one of them a vacuum bed was being shown with a MDF waste board mounted on the bed.. When I asked, I was told that the MDF was a 'special' type that was porous and allowed the vacuum to grip boards through it..

My local supplier thinks I had a too many sherbets that day and that such a thing does not exist.. Anyone out there share my hallucination and know what this MDF is called?

Thanks..
Steve..

ptjw7uk
21-11-2010, 03:06 PM
Not sure I understand where the 'porous MDF' is coming from as you would not be able to seal away from the object being clamped.
Vacuum clamps usually have valves and seals to limit the area under vacuum.
I think they may have been pulling you leg a bit!

Peter

AdCNC
21-11-2010, 10:20 PM
As far as i am aware all they do to the mdf is take the surfaces off the mdf making it less sealed.

fasteddy
22-11-2010, 07:15 PM
Definitely saw it demoed at the exhibition.. I was more wowed by that than the cnc..
Thanks AdCNC, easy enough to test.. Will machine the surface off a bit tomorrow and try it.. If the workpiece flies off the table, back to the drawing board..!

Steve..

fasteddy
22-11-2010, 07:19 PM
Ptjw7uk.. If I remember right, the mdf was placed on top of the vacuum table, but allowed the air to pass through it.. The cnc was machining kitchen units out of 8' x 4' boards.. I do remember being told that the mdf was available off the shelf but as I said, cant seem to find it now I am looking..

Steve..

ptjw7uk
22-11-2010, 08:06 PM
I wish you well but I would caution you to be careful as you could leave to much open surface and loose most of the vacuum.
Most vacuum systems are designed for specific jobs ie mass production etc and care has to be taken or it will fail.
The other possibility is if you have a high throughput pump then it could withstand a fair amount of leakage etc.
edit - just had another thought after rereading post, If the 8x4 was on a 8x4 mdf and the vac table was 8x4 then there would only be leakage when you cut through.

Peter

kevinb
23-11-2010, 04:44 AM
hi was it not the peg board type of stuff? http://www.panel.com/pegboard,-hardboard,-mdf--hdf-10/
mine has a vacbed the waste board according to the instruction book is made out of normal 6mm mdf, no metion of porus mdf,
its cut to the right size then theres a program to cut the holes in the right places, this is then attached to the vacbed with a few bits of double sided tape to secure it,
the work piece is put on the bed, and any surplus holes coverd with off cuts to get a better hold,


3398
kevin

Toddy
23-11-2010, 12:58 PM
He was pulling your leg as mdf is non porous as such that it would let you vac through it to hold your job,(joiner to trade) lol

AdCNC
23-11-2010, 03:09 PM
He was pulling your leg as mdf is non porous as such that it would let you vac through it to hold your job,(joiner to trade) lol


MDF is quite the opposite to none porous, unless i must be buying "special" MDF lol

Jonathan
23-11-2010, 03:51 PM
Is there such thing as LDF (i.e low density..), that would surepy be more porous?

Couldn't you mask off the open areas of the bed with bits of paper. Just have a stack of A4 paper and distribute it to cover the gaps.

TheChunk
23-11-2010, 11:25 PM
I found a video showing this, I'm amazed that it works.

http://www.nemi.com/flow_thru_vacuum_demonstration.htm

One on YouTube as well.

http://www.youtube.com/watch?v=Egw6lSHcSZc&feature=related

fasteddy
24-11-2010, 08:03 AM
Thats it TheChunk..!!!

I remember the bit about taping up the edges now.. Well found..! Just pulled apart my cnc for another upgrade so cant try it this week, but will definately give it a go next week.. Thanks dude..

Steve..

tumutbound
25-11-2010, 02:51 AM
Using MDF as a spoil board on top of a vacuum table is quite common (check out cnczone.com (http://cnczone.com) or woodworkforums.com (http://www.woodworkforums.com/f170/)).
I seem to recall a recommendation of sealing the edge of the spoil board with paint.

Standard MDF is certainly porous.

quickcut
25-11-2010, 06:24 PM
A wrap door machine uses vacuum to pull the pvc covering over the door . mdf is indeed porous. not sure about hdf though

kevinb
29-11-2010, 03:33 AM
just came across this while browsing

http://www.cncroutershop.com/product/texon-sacrificial-sheet/

Troop
22-03-2016, 02:23 PM
I don't exactly know if this has been resolved however as Toddy said about MDF being non porous i believe he has had the sherbets.
I use 6mm and 4mm MDF and this is perfect for Vac pump.
I am currently looking for a different material that is more porous as using VillMill material is a good extra for any wasteboard.