Vacuum box advice

[Bredmond]

Hey all,

So I've put my new vacuum box in use, but I'm having some issues with losing too much suction during cutting.

I've got a roughly 24 x 24 vacuum box, about 1.25 inches in internal height, with cross members to prevent table sag.

My holes are 1/4 inch, spaced 3/4 inch apart on center. That makes about 32 rows and columns.

When I cover all the holes with 1/8 inch plywood I get good suction, but as I cut out my design I start getting the bit (which is a 1/16 in end mill, uncut) pulling up the material and the suction eventually decreases to the point where the material can move freely. I'm cutting out a design from MakeCNC, one of their puzzles so the lines are pretty small.

Any suggestions or pointers on the vacuum box (or references to other good sources) would be much appreciated. I don't know if I have too small of holes, to many, to close, etc.

BTW, I am using a small shop vac to drive the vacuum.

Thanks in advance.

Bill.

[4DThinker]

I simply would cut all the way through except for a 1/64" or less. That way the suction can remain, and you can separate your parts easily with a band saw or utility knife, then clean up with a little sanding or a flush trim bit in a table mounted or handheld trim router.

[cjablonski]

Although a bit late to the topic I've done some research and have discovered some different ways to approach this, to which I intend to tackle shortly. ..

1) most larger (dare I say high end home or industrial machines) employ zoned vacuum areas. This allows only the specific area you intend to hold down the greatest vacuum application to the piece. This is where the decision as to the zone size becomes much more subjective as you need to know what you cut most often based around size to determine the number of zones you would need.
2) Maximizing vacuum means the reduction of ports for the vacuum to operate efficiency while still offering the vacuum maximum surface area to "adhere " to. Zoning helps achieve this .

So here how I intend to approach this based on some research I've done. ...

Locate a supplier of HDF ( not mdf fault due to porosity ) in 3/4 in thickness, 4 by 8 sheet.
Cut 2 pieces 25v25 (maximum machining area of my hd)
Clamp flat to the shark and skim 1 face of both parts flat.
This is where the subjectivity comes to play. For my purposes 4 unequal zones will suit me ( mostly a case by case decision independent, any number of zones can be achieved )
The number of zones will determine the number of channels cut into the milled faces of the hdf. For my purpose I intend to utilize 4 zones, therefore 4 channels will be cut into the hdf, all starting from the same corner, independent of each other, not connected and cut using a 3/8" ball nose bit. Both halves will have channels in matching pairs on the face of each of them.
glue both halves together making sure the channels match on both pieces.
Clamp the entire assembly into the shark.
Using a 1/2" end mill, machine 1"x1" squares in the face of the part. Ensure that at least 4 squares per zone (preferably in an "x" or box configuration ) will be within the channel patterns for each zone. I also intend to make the vacuum surface area 2'x2' leaving me all 4 corners as profiles, allowing me to have a preset and consistent X and y zero point
Using the shark, within those 4 squares per zone, drill into the channels to allow vacuum flow.
Machine .125 off the tops of each of those squares using the .250 end mill and switch to a v bit.
Chamfer the outer edge of each of the squares using said v bit, allowing better vacuum flow between squares.
Cut a cross pattern on each of the squares that contain holes to the vacuum channels to allow better vacuum distribution.
Once complete with the top machining, tap the holes where the channels exit the HDF to accept valves to control the vacuum to each zone independently . All 4 could be used at once, but my zones will be of varying sizes. This affords me maximum vacuum pressure for small parts utilizing the smallest zone, yet allows the use of all 4 zones for large parts, and anything in between.
run tubing between all the valves to allow vacuum to be applied to each of them .
run the tubing to a HVAC vacuum pump (easily available online for less than 100 bucks).
In between each of the "zones" I will place compressible tubing style gasket material that will stand proud of the top surface by around an eighth of an inch. This will allow the vacuum the compress this material and reduce or eliminate the loss of vacuum by sucking down the part, and separate each zone. This will be placed in the slots cut in between the 1x1 squares.


Once I've completed making this I will post pictures and offer the vector files to anyone whom may be interested. Hope once completed it will help guide you to a near clamp less future


Best,
C

[jimbob45]

Sounds very interesting. I will be watching for your pictures.
Cheers

[cjablonski]

Slight change to the plan. Will be utilizing concentric circles instead of squares yet maintaining grid style vacuum ports for the benifit of cutting circles while still maintaining vacuum.