how much do i need

[spoolin_20b]

Hello

How much suction do I need to be able to sufficiently hold an object down by suction thought 3mm MDF?

I want to use 3MM MDF as a packer between the object to be CNC milled and the bed but I would like to be able to use suction to hold it there like the new commercial wood working CNC machines do


Cheers
Shane J

[mxtras]

Quite obviously, there are a lot of variables.

In a nut shell, for normal cutting of wood products being held to a vacuum table, about 8-10" H2o column is sufficient and for light cutting of Aluminum sheet, 12" seems to be about the minimum (depending, of course on what you are doing). There are ways to cheat - such as mounting your part to a larger base mechanically - increasing the effective area that the vacuum has to work against.

But - as I said, there are a lot of variables and this is not an easy question to answer without seeing what you are working with.

Scott

[ger21]

The smaller the part, the more vacuum you'll need. Also, if you're drawing through a spoilboard, you'll need a lot of volume. Vacuum pumps on commercial machines usually run $5-$10K. What did you plan on using for a pump?

[mxtras]

It's all about surface area - like GER mentions.

A real life example - at one time, I used to cut 3.5"X3.5" samples of material by the hundreds. This material's cutting resistance is similar to cutting 1/4" Luan plywood - maybe just a bit more. I was running a 2 flute, 1/4" cutter at 25Krpm, climb milling at 45-55 FPM and I had an MDF table top. I quickly found that when the table pressure dropped below about 8", the parts would begin to shift.

Of course, these numbers on a different table may not cause the same reaction - there really are a lot of variables.

Scott

[spoolin_20b]

i unsure wat to use as a pump i looked on ebay and saw these i dont know if they would do the job tho

http://cgi.ebay.com.au/Vacuum-pump-Oil-less-single-head-piston-Brand-New_W0QQitemZ190086296439QQihZ009QQcategoryZ105818QQrdZ1QQcmdZViewItem

http://cgi.ebay.com.au/VACUUM-PUMP-A...QQcmdZViewItem

[ger21]

Those will work, but they won't suck through the mdf.They will work, however, if you make a jig with a foam seal to contain the vacuum. Here's an example. http://www.joewoodworker.com/veneeri...umclamping.htm