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Ken Frantz
03-04-2003, 3:41 PM
When I had the cabinet shop, we had a mica laminated offeed top behind the tablesaw that was 4 ft by 8 ft. When cutting 4 X 8 sheets of material it was hard sometimes to push the material, especially "CORIAN" for one, on the table. (had gotten weaker in later years)and have often thought of building a reversable down draft/ updraft table. In the downdraft confiuration it could be used as a sanding table. Reversing the air flow it would float the material on the table just like a puck on an air hockey table. By the way---has anyone built an air hockey table????

Since I am retire, I think of all of the things that I would have liked in a shop to make things easier, but never took the time to think about building stuff like this. Spent the time trying to make a living.

NOW has something ever crossed your mind about a project like this???? Or is my mind just wondering about these ideas and liable to get lost and can't find its way back!!!! HI HI HI

"WHEN YOU LOOSE YOUR MIND, YOU JUST AS WELL FORGET IT!!

Ted Shrader
03-04-2003, 5:12 PM
Interesting idea. But what about the hole size. On a hockey table the holes are relatively small, on a sanding table they are several times again larger. Would need the larger hole size for dust flow. Unless you come up with an adjustable aperture ....hmmm..... lots of moving parts there.

Would also require adjustable airflow. Mostly so the sheets goods would not blow away if they are light weight. Or more air for the heavier ones.

Ted

John Sanford
03-04-2003, 8:55 PM
I've never even considered building an "air table", BUT, I wouldn't be at all surprised if a design cropped up in Popular Mechanics sometime during the last 50 years.

Something you can consider is simply having two tops. The outfeed doesn't HAVE to be 4x8, it only has to be large enough to support a sheet of plywood, which means about 30+" wide x 50" long. Smaller tops would make switching them much simpler. You'd have to come up with some sort of cam/toggle mechanism to draw the tops tight against a seal in order to avoid excess leakage, and quite possibly some means of controlling the airflow (pressure/suction) to account for a) different sizes/weights of floating material, and b) the potentially different requirements for the downdraft. Its even possible that you could use the downdraft table as a vacuum hold down.

Dude, you could have the ultimate in gaseous tools for your workshop.

Ken Frantz
03-04-2003, 9:36 PM
Ted:
I had this all written up and made the mistake trying to
correct the preview instead the “sheet” I was working on and
lost it all. This time I will use WORD PERFECT so I can use the
spell checker. And then paste it. I hope I can remember what
I wrote!!!
The top could be made in three layers, the top, bottom
with the hole size for use when it is used for a sanding table
and the center as a slide with two sets of holes a) a set with
the large holes b) a set with the small holes. The holes that
would be spaced far enough apart to change the hole size
when the slide is moved back and forth between the top and
bottom.
The air flow could be adjusted by 1) a variable speed
motor/ fan and would be reversible. 2) using 2 or 3 fan
units and just run the ones that would be required to keep the
material just about “floating” or turned off the fans if you are
using light material such as mica laminate, 1/8 or 1/4 inch
material in the case of using the saw table being used. When
using it as a sanding table, reverse the fans ( 1, 2, or 3) for
the downdraft mode and use the big holes.
Here are some of the problems that I foresee:
1) saw dust jamming the slide
2) If the fans were not reversible, a way of changing the flow
of the air would have to be designed along with the reversible
filtering system.
When I had the shop, 90% of the cutting on the table saw was ˝, 5/8, 3/4 inch MDF, plywood, particle board and a real
small amount of CORIAN etc and 1 & 1 1/4 inch particle board
5' by 10' sheets when we built mica laminated restroom stalls
(this is where the floating action would be really needed!!!)
DANG THAT STUFF IS HEAVY!!!!!!!! Takes 2 good men and a
boy to get that on the saw!!!!!!! So if this stuff was going to
blow off, I would be heading for the house anyway. HI HI HI
After thoughts: Since the hockey pucks are small as compared
to a ˝ sheet of board, could the hole be bigger and spaced
further apart than on a hockey table???? If so, could the bigger
holes be use without trying to reduce the small hole with the
slide and use one size hole for both operations ??? Simpler,
construction wise.
All- in- all if a person had the space for both kind of units, that
would simpler yet!!!!!!!
I guess I will throw out the bone and see if anyone else want
to chew on this idea for a while.
JUST KEN RUMBLING IN THE RAMBLE SEAT OR IS IT
RAMBLING IN THE RUMBLE SEAT OF LIFE.
PS: How many of you know what a rumble seat is???
2nd PS: You jumped in before i could get this rewritten----so good evenig to you!!! I see you alread had the bone for a while!!! HI HI HI

Ken Frantz
03-04-2003, 9:42 PM
Sorry John---I should have us your name instead "you" in the 2nd PS!!!!!

Ted Shrader
03-04-2003, 9:53 PM
from Ken Frantz

After thoughts: Since the hockey pucks are small as compared to a ˝ sheet of board, could the hole be bigger and spaced further apart than on a hockey table???? If so, could the bigger holes be use without trying to reduce the small hole with the slide and use one size hole for both operations ??? Simpler,
construction wise.

Ken -

I see you had already thought of the things I did. Does that mean great minds think alike? :)

Regarding your after thoughts:
--------------------
On a down draft sanding table, I think a lot of the efficiency comes with the air velocity over the localized areas of the table. If you start spacing the holes too far apart or too big in diameter, you might loose that. I agree the holes could be farther apart than an air hockey table for the outfeed function due to the relative size of the "puck". In this case 4'x8' most likely.

I think the most restrictive items in the design is the hole spacing for the down draft sanding table. Once that is determined/optimized, only variable left is the CFM of air. That would be controlled by, as you say, they use of more (or fewer) fans.

So, yes, I think the same surface could serve both functions if air flow can be adjusted. Only problem is, when sanding, the saw could not be used.


Let's see if anybody else has any other ideas.

Regards,
Ted

Lee Schierer
03-05-2003, 10:05 AM
In a down draft table you are interested in moving the most amount of cfm around the work piece to suck in all the dust.

In air hockey you need psi to carry the weight. Since the "puck" is light weight, you need low psi. If you want to move something heavy like corian or ply wood, then you will need slightly greater air presure per square inch than what the material weighs to make it float. To get psi, you're going to need a powerful air source, otherwise you will just block the holes that are covered and increase the flow throught he remaining holes. If you put a coffee mug on an air hockey table it will just sit there and not move at all.

Another thought is what about all the dust your air table is going to kick up into the air.

John Sanford
03-05-2003, 1:00 PM
Originally posted by Lee Schierer
Another thought is what about all the dust your air table is going to kick up into the air.

NOT directed at Lee, simply a response to the issue he raises:

Theoretically, there won't be much dust to worry about while using the "air table." The table will be used in conjunction with the tablesaw, and as such it will be a minimum of 6" behind the BACK of the blade. As we know, the vast majority of the dust action takes place at the front of the blade.

I'd like to add to what I said about the sizing of the table, with the issue of "air diversion" in mind. You only need a table that is large enough to keep the workpiece from falling to the floor. That means it must support just over 50% of the length and/or width. Supporting a 4x8 sheet with a 4x8 table is nuts. Not only do you greatly increase your surface area, and therefore friction area, but you also have the vast majority of your "hockey holes" doing nothing except acting as overflows, as Lee warned. A smaller table gives you a passel of advantages. It takes up a whole lot less space in the shop. It handles SMALLER pieces far better. It has far fewer air holes exposed when the workpiece is coming onto the table. Fewer air holes means higher potential PSI at each hole, which means you don't need nearly as large of a air mover.

The monstrous saw work stations in cabinet shops are as much a function of using the station as an assembly table as they are outfeeds. Is there really a need to set up multiple cabinets on the station at a time?

Dan Cameron
03-05-2003, 2:49 PM
Just a couple of thoughts....

Covering an outfeed with a few strips of UHMW tape will have a dramatic effect on the friction. Strips must be parallel to feed direction.

I have considered building a downdraft table using pegboard. My idea is to use sheets face-to-face. By sliding one sheet slightly with respect to the other the effective hole size can be adjusted.
Perhaps the top sheet could be in several pieces so that different size "active zones" could be created.

The engineer in me feels obliged to point out that you do not necessarily need high PSI to levitate a heavy object if the AREA over which that pressure is applied is large.

Dave Anderson NH
03-05-2003, 3:17 PM
In the diemaking trade where steel rule dies are made from sheets of veneer core maple and baltic birch super grade plywoods, air tables are common for the larger die saws. A die saw is essentially a scroll saw on steroids. As an example, our saw in our in-house die shop is considered small with a table measuring 32" square and it has a 48" throat opening. Sandvik makes considerably larger die saws up to a 96" throat with a table over 4' x8'. These large saws REQUIRE an air table so that the diemaker can precisely cut large sheets of die board as he moves them past the reciprocating blade. A 5 foot square sheet of dieboard has too much friction to slide easily and without a lot of force. Literally these sheets have to be moved by finger pressure alone for the cuts to remain accurate. I would suggest going to the Sandvik website or contacting a dealer to get the specs on the larger machines. These should include the cfm, blower size and horsepower, and most other information. As for practicality, industry wouldn't use them if there wasn't a tangible economic and productivity benefit.

Lee Schierer
03-05-2003, 3:43 PM
Originally posted by Dan Cameron
Just a couple of thoughts....

The engineer in me feels obliged to point out that you do not necessarily need high PSI to levitate a heavy object if the AREA over which that pressure is applied is large.

Your insticncts are working correctly. Bear in mind that the weight of the object per unit of area also factors in. That's why I cited the example of the coffee mug on the air hockey table. Approximately the same size as the puck but much heavier. It needs more psi air to move it.

Scott in Douglassville, PA
03-05-2003, 3:49 PM
Thinking too hard folks. How about hooking up the inlet of the DC when using the single top as a downdraft table, and the outlet of the DC when using it as the air table? Put some kind of adjustable, settable blast gate between the hose and the table hook-up to fine tune the amount of air for the table, and you should be good.

Or am I <i>under</i>thinking?

Ken Frantz
03-06-2003, 10:22 AM
Good morning from Central Florida!!!

Going over the post I started and I will try to sumerize all the ideas and throw out some others.

First I would like to say that the “print page option is great!!!”
I printed this post and high lighted the ideas that were presented so I could make some kind of order in this summary

John your are right about the 4 by 8 table being to big. The only reason for that big of table in the shop is that a lots of times a pieces had to be cut oversize in order to flip the pieces around to
trim the factory edge. Keep in mind that this was a production shop. When I would cut the stock for the wall cabinets, say 11 inches wide, I would set the saw at 12 inches and cut one side and then turn it around and cut the other side and set the pieces on the right of the fence (had room to stack up to 26 inches wide). After cutting 5 or so sheets, I would set the saw at 11 inches and then cut the factory edge off along with cutting the remaining ˝ sheets. But since I am not in production type operation, yes a smaller table could be used. But since I will have space in my home shop, I will use the same size table. In fact, one of my buddys had a 8 X 10 behind his saw!!!!

Ted stated that (4 X 8) a big table with all of those holes would be not nessary and would require a lots more air flow. I agree on that point. Just having the holes about where most of the “traffic”
would be is the only place to have the holes.

Now to figure out how far apart to make the holes and their size.

Ted, your statement “Does that mean great minds think alike?” Could mean the great minds could get into trouble if their thinking doesn’t work out!!! HI HI HI

Back to the topic:

An idea popped into my mind this morning as I way waking up and after I read the post again, Dan’s phrase, kindled the thought of “active zones” along with Scott’s idea of reversing the intake and outlet from a “DC” for the table.

If someone would build a table deep enough to support the material as it came off of the saw and the “active zone” (behind the blade) wide enough to float the material. Then for the “active zone on the left side of the table be used for the down draft section for the sanding operation. Now the down draft would be used as the intake of the fans and the exhaust would be the “floating” side. The fans could be place between the two sections with the dust filters on the side of the down draft section, thus doing double duty and not have to worry about reversing the fans. A way might have to be devised to divert the air to the side of the cabinet so that the “floating air” will not raise dust on the top. Also maybe the same on the down draft side if by chance a sheet of material would cover some of the inlet holes.

Dave said about the air table (haven’t checked out his “story” yet) is all that is needed for the air pressure is just to relieve some of the weight of the material so it can be moved easier.

Thanks fella, now I will throw the bone back it the ring and let the gang rechew the input and see what comes out!!!!!

Trying to think of the first part of a verse ________ is the mother of inventions.

I will see you around the corner!!!!!!!!!!!!!!!

Lynn Kasdorf
03-10-2003, 4:25 PM
How about rollers or UHMW tape on a table surface?

On an air table, I think that the large panel would not get levitated until, say 2/3 of the panel was on the table. When the first foot or so is there, all the air would go through the uncovered holes.

I suspect it would provide lift just when you don't need it anymore.

An array of rollers would work much better, IMHO.

Howard Rosenberg
03-14-2003, 6:04 PM
Hi Ken - I've seen those tables you're referring to. The German Engineering company, Homag AG sells those with their beam saws.

No zones, no nothing - they rely on little sleeved ball-bearings that push down when a heavy object is passed over them. When they're pushed down, there's a tiny gap that allows the air out which is what creates the "air cushion". I've seen those bearings at supply houses - all you'd need to do is create a six-sided box with supports under the top and what appears to be MILLIONS of holes and bearings.

Do you have a major bookstore chain in your area? Our national answer to Barnes & Noble is Chapters. Different branches get in some pretty esoteric UK ww mags and there's a UK company called Trend that sells a home-made vac-clamp kit with these bearings. If you looked at these mags or checked Trend's website, you might get some ideas.

Hope this helps. Howard