Grid Vacuum Table

[fumopuc]

Hi everybody,
retirement is good to do some experiments.
Since a long time I am watching these videos about hobby vacuum clamping at YT.
Mostly it is done there for CNC router and wooden applications.
I know, that these little Chinese pumps, offered all over the world, mostly used for car and other air condition maintenance are not the best choice here.
These do use oil in it, which creates some smoke and a not so nice smell also.
The recommendation of the industrial and hobby suppliers for a grid vacuum table 200x120 mm is a volume flow of:
Min 1 m³/h or 16,7 l/min or 0,59 CFM, I know in the meantime this is not enough for a small work piece to keep it at the place where it should be.
Better as a regular available volume flow is 8 m³/h or 133,3 l/h or 4,7 CFM, recommended by all of them.
This higher volume can be provided by a industrial pump only, which means cost at about EUR 600 to 700 or even higher for a new one.
To much for my hobby budget and so no further action until a couple of days ago.
I have seen a video of a German guy who has done some experiments also, ending in hanging himself at two printed vacuum pads at the roof of his shop.
The vacuum was created by a Chinese 12V "toy" vacuum pump. These pumps are worldwide available for EUR 15 to 20, also.
A 3D printer is available and EUR 17,00 from the hobby budget also.
So my decision was to start some own experiment too.
A double sided vacuum pad was designed and printed.
Dimensions 150x150 mm, a grid of 17 mm and a slot width of 6 mm for a 6 mm cellular rubber cord.
For the power supply a 12V switching power supply for EUR 8 was also purchased.
The result could be seen here in the video.

The vacuum is able to keep the big plate, with the big surface to the pad and the pad to the table, but everything is still movable.
This will be fine as a work holding strategy for a metal sheet or a piece of wood for manual grinding and similar jobs, but not for any milling.
I did not try it, but I am sure it will be possible to keep it in position if somebody with 90 kg will try to hang at two of these.
But it does absolutely not like any shear force as normal at milling preparation.
And as bigger the surface as better the force, which seems to be logical. This will be the only way to increase, because the vacuum pressure can not increase.
Experiments to try it with a small piece of aluminum 70x70x20 mm failed completely.
The printed surface is to rough.
The grid is to big.
The 6 mm cord is to soft and to big.
But the general conclusion was, may be if these above parameters will be increased the results will be better.
So it was time again to have a detailed look to the industrial suppliers of this tables, how they do it.

[Kim]

Some interesting experiments there, Achim! 
Looking forward to where you'll go with this next.
Kim

[Jasonb]

Would it be better if you only had the grid on the top surface and printed some lugs around the edge so that the table can be secured solidly to the mill table? Not sure if it would increase holding power but you would eliminate some of the movement from the lower seal rolling and compressing.

[fumopuc]

Hi Kim, thanks for watching. Experiments are ongoing.

Would it be better if you only had the grid on the top surface and printed some lugs around the edge so that the table can be secured solidly to the mill table? Not sure if it would increase holding power but you would eliminate some of the movement from the lower seal rolling and compressing.

Hi Jason, yes that will be the right way.

After seen the offers of industrial  supplier for a small grid table, I have recognized that my list for increasing above is the way to go.
A small table with 200 x 120 mm has a grid of 12,5 mm there and a slot width of 4 mm for 4 mm cord.
So I made my own design for a small grid table, suitable for my little CNC mill table.
The raw part has been prepared with the conventional mill, due to size.
At the drawing the over all dimension should be visible.
Here a small video of the CNC mill doing this grid job. A 3 mm VHM cutter, at the very first beginning I have had a very optimistic feed rate, due to an operator failure.
From an other CNC job that day the feed rate in the CNC controller was over written by the hand wheel with nearly 100%, but I have been quick enough to stop it and the cutter survived.
I have been very happy that the computer has done this chamfering job in a really very short time.
<a href="https://www.youtube.com/watch?v=eI-_Pa9Z1xc" target="_blank">http://www.youtube.com/watch?v=eI-_Pa9Z1xc</a>
Next tests in using it will follow.

[Jasonb]

That looks good, I like the provision for stops and also tucking the vacuum outlet out of the way.

How deep did you make the 4mm grooves?

Also on the second 3D image you show 5 of the squares with holes, is there a purpose for these, maybe to take something to stop very thin work sagging

[fumopuc]

That looks good, I like the provision for stops and also tucking the vacuum outlet out of the way.

How deep did you make the 4mm grooves?

Also on the second 3D image you show 5 of the squares with holes, is there a purpose for these, maybe to take something to stop very thin work sagging

Hi Jason,
the additional 5 holes, it is M 5, are the result of a longer learning curve.
I will explain it soon.
The grooves a 3 mm deep, dimension was missing at the drawing.
Here the clamping test with a 70X70X20 mm aluminium block and with a bigger plate also.

All these testing has been done with the small Chinese "toy" 12 V vacuum pump.
And I have been very surprised by the results.
The 70x70x20 mm can not been machined with this clamping force, but the bigger plate should be very close.
Aluminium to Aluminium with its flat surfaces are not the best pairing, even if there are some rest of the cooling fluid at the parts.
So I took a small pieces of the brown stuff and made some further experiments.

With the rough surface of the multiplex plate no chance for any movement.
I could move the mill and the work bench, but not the plate anymore.
Here was the point to decide how to go ahead now.
It was clear for any kind of increasing the clamping force another vacuum pump was necessary.
The recommendation was 8 m³/h, so I have started a search for anything used in the net.

[fumopuc]

Hi Everybody.
At ebay I have found an used industrial vacuum pump which seems to be reasonable.
A Thomas 2660CHI39-367, I have heard this could be used in a dentist chair before.
The volume flow is about 120 l/min or 7,2 m³/h or 4,3 CFM.
Theoretically very close to the recommended values.
The price was EUR 100 and 2 days later it was in my shop.
The big plate of aluminium was not possible to move a bit anymore.
The smaller block with 70x70 mm was still not 100% clamped.
So we are coming to the extra holes in my table which Jason mentioned already.
I have seen these holes in industrial tables also, mostly with a steel insert and set in grid of 100 mm.
In the meantime I recognize the reason for it.
To work against the very last little movement of a small work piece like the 70x70 mm block I have made some ex center discs in 3 different sizes.
I hope these will help now.
But what is If I want to mill through a work piece ?
I have heard this should be possible with a grid table too.
The key word here is soft PVC.
Some pieces are ordered.
In the meantime the small Chinese toy vacuum pump has got a housing and can be used mobile now, together with the printed pad, may be at the garden table in summer time also.

[Admiral_dk]

Interesting addition to hold small pieces in a sideways fashion 

[fumopuc]

Per, thanks for watching.


Next experiment, 3 mm soft PVC between the work piece and the grid table.
This should give the right conditions for any through drilling or milling.
A drawing was printed to used as a pattern.
A hollow punch for some holes.
The two wholes above left hand side are the only ones in operation here.
Switched the vacuum pump on and the 70x70 mm alumium block is not movable anymore, the mill and the bench a bit.
I have been surprised.
I do under stand that the vacuum power will be the same, due to the atmospheric pressure is the same, but there is much more friction between the table, the PVC and the work piece.
I have ordered some 3 mm brass plates to start with the first parts for the IHC Titan engine.
Plan is do it with this grid table and there the first drill through should be tested and of course the over all clamping and edge seaming.
 
The Thomas pump has got its final place under the bench now.
Also a fixed installation of a gage and the couplers with ball valves were made between my mills.

[fumopuc]

Hi everybody,
yesterday und this morning I have made the first real parts with the grid table.
These are brass plates for the IHC Titan.
May be this short video will show how easy it is to work with the grid table.

For those how are interested in cutting data:
5 mm VHM cutter 3 flutes
18.000 U/min
feed rate 1500 mm/min
fz 0,2777 mm
ap 3,2 mm
ae 0,5 mm
the brass needle chips are sharp like a knife and do fly nearly 1 meter if not stopped.
First a 2D adaptive cleaning with 0,1 mm remaining stock
Followed by a 2D contour two times around for final cleaning.
I am very happy about the result.

[kvom]

I took the easy way out and purchased a vacuum plate from Pierson Workholding a few years ago.  I used it to machine most of the aluminum parts for the hummingbird project.

[Jasonb]

That looks to be working well and good to see that the PVC will allow you to drill through provided hole is not too large.