Vacuum table (using shop vac) for AR8pro

[buildswithbrian]

Fean,
I feel like I have to respond to this...
I don't this I or anyone else has not been "nice" in this thread,
that being said, I or anyone else that has done any research into vacuum tables know that Gary is correct
in that a vacuum table does not necessarily "need" the holes in the top surface, dependent on the correctly
"configured" design.
I am, and continue to be skeptical however, that it will work with such a simple and inexpensive design such
as the one I (and many others) have built, and are using quite satisfactorily.

Perhaps I am wrong, until someone builds it (my table using a shop vac.) we can can only theorize.
there is more than one way to skin a cat, or build a vac table.
maybe I will try it sometime in the future... It would be nice to not have to drill 1000+ holes

my only issue with Gary's comments are that he presented his way as the "only" way,
and that is obviously not true, and the rest of us are "lost sheep" (sorry I took some offense to that)

Gary's table he linked to (while admittedly superior) would probably cost upwards of $1000 to build, not to mention the
"ability & knowledge" involved with constructing his design.
Gary is apparently an expert in the design/construction of commercial type vac tables, and obviously a very
intelligent person, and I am glad he shares his info/knowledge in the appropriate places, where people that
need it can find and make use of it, just don't shove "your" way down my throat and not expect me to choke on it.

Build my table design, build CNCnutz's design, build Gary's design, hell.. build your own design based on your own research and situation,
I just presented an option, specific to the Axiom AR8, make of it what you choose, but just don't flat out
tell me I am wrong when it works. (meaning Gary here)

can we please get back to opinions. criticisms, whatever, pertinent to the original post?

[Deleted]

I've presented links that demonstrate what Gary is talking about. It is not theory, it is fact, even if you haven't done the experiment.

[johnb]

Dec 9, 2018 21:48:02 GMT -5 buildswithbrian said:

Ok Gary,
You sound like a politician with all the round about talk,
Why Don’t you put you’re money where your mouth is and make a video
With specific dimensioned plans Showing exactly how to build a table with your bleeder board design for less than $100 dollars
Don’t give me bs about specs on motors, don’t give me bs about all the classes you teach or your theories about what a vacuum table should be.
Show me the money
We the sheep are waiting to be enlightened

Are you for real, dude?  What Gary did was point anyone who has any interest to real information, not "theories".  A "theory" is no longer a theory when it has been proven. There's plenty of proof of what he said, and he provided exactly that.  Gary has plenty of videos (72 on YouTube as of today).

It would be pointless and a waste of time to provide "specific dimensioned plans" or, for that matter, specific recommendations on what motor/vacuum or whatever to use. If you bothered to look, you'd see that his work transcends a single manufacturer...every machine of the same size would be different. When you stop to consider that varying table sizes create different requirements for vacuum power, then the permutations and combinations would become endless and virtually incalculable, rendering said "plans" useless for anything other than the single machine for which they are targeted.

What he DID do was point out how to make your inexpensive vacuum table even more inexpensive...by eliminating the un-needed holes, holes that take time, electricity & bit life to produce.

I, for one, value Gary's contributions...on this and other forums.  He's a tremendous resource. Don't view his silence following your "calling out" as anything other than washing his hands of the abuse that followed his well-reasoned and supported advice.  I doubt that he will post again on any of "your" threads, Brian.

[gerry]

I agree..... +1.

[johnb]

There's really great information in this thread. I am particularly fond of Brian's (brilliant) solution of "one long T-Nut" as a hold down. Fean's post of CNCNutz' epiphany on the porosity of MDF is very enlightening. Pay particular attention to the part of the second video where he talks about "how not to burn up the shop vac".

My machine is still awaiting delivery. As soon as possible after I get it, I plan to build a vacuum table that closely follows Brian's build in his video, with the following modifications:

1) Everything other than the top and the inner supports will be built from 3/4" melamine to prevent bleed. The melamine will face "inward". Any place a glued butt joint exists, a "light dado" will be cut through the melamine in order to provide for adhesion.


2) The top will be Trupan with the "bottom surface" lightly fly cut prior to assembly.


3) I will plan to use sheet plastic (heavy dropcloth or Visqueen-type material to occlude the portions of the board that are uncovered when sucking down smaller parts.


4) Since the top will serve as a sacrificial spoilboard as well as a bleederboard, I plan to fly cut as necessary as it becomes scored. Eventually it will require replacement. This can be done by either milling all the way down or simply fly cutting it and then fly cutting the bottom of an overlay board and bonding it to that surface with a sufficient number of "glue dots" and then sealing the seam and the edges of the overlay board.


3) The top will be lightly fly cut after assembly, but no holes will be drilled. All raw wood edges will be sealed.


I don't plan to do a video of the construction, but I might do one showing the result in action. In any case, I'll let y'all know how it works out.


Brian- You could incorporate a part of this into your already-constructed vacuum box by cutting a sheet of Trupan, sealing the edges, then fly cutting the bottom and laying it over your existing top. Whether or not you do this, you'd probably increase your suction capability by sealing all of the exterior surfaces of your "box" except for the top itself.


I do have one question about your original build...Since the pockets for the support posts and the dado slots for the support rails are presumably pretty close, why did you cut the support posts and then glue and drill them separately on the CNC instead of going to the drill press (like you did for the support rails themselves)?

[buildswithbrian]

Dec 15, 2018 18:56:19 GMT -5 @fean said:

I've presented links that demonstrate what Gary is talking about. It is not theory, it is fact, even if you haven't done the experiment.

Sorry fean, but is a theory and not a fact until the experiment is concluded
It has been proven to work in other circumstances but not this one (yet)
If you are presenting CNutz 2 videos, one of which shows mdf leaks some air as concrete evidence you must not have watched the whole video.
His table is essentially the same as mine, and I of course watched his videos before I built mine, the only thing he did was sealed around the edge of his table and bottom, both of which I have done of course even mentioned in the description of my video that that was the only step I didn’t show.
What exactly is your problem with having holes in the top, why is there only one way to do it, ?? when the holes obviously work what could possibly be your issue with it. ?
Did you even read my previous post?

[buildswithbrian]

John, I have quoted your comments/questions in quotes, my replies are following the **** this board won't let me color or otherwise distinguish them.

"My machine is still awaiting delivery. As soon as possible after I get it, I plan to build a vacuum table that closely follows Brian's build in his video, with the following modifications:"

"1) Everything other than the top and the inner supports will be built from 3/4" melamine to prevent bleed. The melamine will face "inward". Any place a glued butt joint exists, a "light dado" will be cut through the melamine in order to provide for adhesion."

**** sounds like a good idea, It will eliminate the need to paint or seal the mdf sides, edges, bottom.
**** I only choose MDF at the time because it's what I had on hand, so I paint sealed my table


"2) The top will be Trupan with the "bottom surface" lightly fly cut prior to assembly."

**** absolutely, from what I have also read this is highly recommended for best performance.


"3) I will plan to use sheet plastic (heavy dropcloth or Visqueen-type material to occlude the portions of the board that are uncovered when sucking down smaller parts."

**** yep, this is called "air damming" and is 100% necessary for my table "peg-board" design, I use scrap sheets of 1/8" ABS plastic myself.
**** not sure if it is needed with the ULMDF though ? sure it couldn't hurt.


"4) Since the top will serve as a sacrificial spoilboard as well as a bleederboard, I plan to fly cut as necessary as it becomes scored. Eventually it will require replacement. This can be done by either milling all the way down or simply fly cutting it and then fly cutting the bottom of an overlay board and bonding it to that surface with a sufficient number of "glue dots" and then sealing the seam and the edges of the overlay board."

**** makes sense to me, unless you build a separate plenum and use the gasket material to seal

"3) The top will be lightly fly cut after assembly, but no holes will be drilled. All raw wood edges will be sealed."

**** my table's spoilboard edges were paint sealed with the rest of the table, just in case.


"I don't plan to do a video of the construction, but I might do one showing the result in action. In any case, I'll let y'all know how it works out."

**** please do share, I am looking forward to see if it works"


"Brian- You could incorporate a part of this into your already-constructed vacuum box by cutting a sheet of Trupan, sealing the edges, then fly cutting the bottom and laying it over your existing top. Whether or not you do this, you'd probably increase your suction capability by sealing all of the exterior surfaces of your "box" except for the top itself."

**** no immediate plans to try this just yet, If I do in the future however, I will build a new base as well. as I mentioned in a previous post, I am a bit skeptical of my shop vac's
**** power to pull sufficient flow thru. to hold with the same force as the peg-board design"
**** as mentioned before, I sealed my tables bottom, sides and edge with paint (I noted in the video description box, that I did not show this step)
**** the video was already long enough, no one needs to watch such a simple step.

"I do have one question about your original build...Since the pockets for the support posts and the dado slots for the support rails are presumably pretty close, why did you cut the support posts and then glue and drill them separately on the CNC instead of going to the drill press (like you did for the support rails themselves)?"
**** you must have only skimmed through the video, the holes in the mdf "rib" were only pilot holes for the screws to hold them in place until the glue set. no accuracy was needed there.
**** the holes for the support blocks however, need to be accurate and are aligned precisely over the slots in the table. I don't see any advantage to drilling them on the drill press.
**** I already had their holes locations programed in the cnc, was quick and easy (and repeatable) to just run the drill file.

**** I have a question for you John, What do you intend to use to pull the vacuum for your table? a shop vac, or will you buy a dedicated vac-motor?
**** please post updates to your tables progress,
**** Brian

[johnb]

Brian-
I'm still pondering the motor and leaning toward one of the Lighthouse units that go for a couple of hundred bucks (although I'm a little put off by the notion of non-replaceable brushes...read that "1,500 hours (maybe) then throw it away"). My machine is a 4x4 so I'm unsure if I'd get adequate suction out of a shop vac for that amount of area (or what kind of life to expect from the shop vac motor being "intentionally abused" by choking it down and running it for hours on end). All that being said, you could still buy 6 Lighthouse motors for the cost of the mid-size Black Box (which is what is called for with the 4 x 4).

Lighthouse insists that you need a 1/4" inlet hole of "free air" to the motor to provide cooling. I'm unclear on how much unblocked bleeder board it would take to provide that equivalent. Obviously it's a factor of (changing) board thickness, board type (read that "permeability"), and other factors such as humidity and phase of the moon. Clearly, if covering the whole box with a sheet of something, you'd need a hole somewhere (whether using a bleeder board or a top with holes in it.)

I get where you're coming from on the support blocks which raises another question... Can you not chuck a (longer) standard twist drill bit into the machine collet for "just" the drilling part of the program? I get that you'd likely have to also modify the file to "peck drill" the holes and change the feed and spindle rate, but my question is more aimed at situations where you might have a LOT of thicker parts to drill through and/or you are in a situation where the appearance of the object is important and you don't want a glue line.

And...for the record, I watched your video carefully (three times) but will admit to neglecting to read the "liner notes" on that album

Some type of inlet filter would be required for the Lighthouse unit when using a drilled top to keep the chuff that ends up getting sucked into the holes from getting to the motor. The same holds true if you just "drill a hole somewhere"(when using a bleeder board).

My vacuum will be piped straight through the wall to the cnc machine and will reside in the purpose-built room that I'm using to house my main dust collector. It wouldn't be any trick at all to pipe a clean air feed into that room that could be shut off. That room will be sealed and soundproofed and vented to the outdoors mostly (I'll rig a way to return the air to the shop through a filter for those days when I don't wish to be pulling 1,000 cfm of cold air into the shop to replace what's being exhausted...In South Texas, there aren't that many of those kind of days).

[buildswithbrian]

John,
Sounds like you are doing your homework :-)
I wish I could offer you some valuable input on the vacuum motor choice
But I have no personal experience with that type of motor and wouldn’t feel right giving you advice on it.
Especially not knowing how much You plan on running it.
1500 hours is a lot of time for a hobbyist, but not very much time using it in a commercial level
running it for six or even eight hours a day.
As far as drill bits go in a CNC router, the only input I can offer is to be careful.
I talked extensively with A cnc tools salesman and also the tech guy
At CamMaster about using regular twist drills and was told it’s not a good idea.
I was hoping to put a drill chuck on the router or spindle and was told that the speed is too Fast. Long story short I was told you need a special drill chuck that is precision balanced , And boy are they expensive. I was looking into this because I sometimes need to drill a bunch of small odd size holes,
Where it wouldn’t be practical to buy the special CNC drill bits with quarter inch or 1/8 inch shanks That will fit in an er20 collet.

Good luck with your project
And your new machine 👍
Brian

[grg]

Dec 17, 2018 20:36:21 GMT -5 buildswithbrian said:

John,
Sounds like you are doing your homework :-)
I wish I could offer you some valuable input on the vacuum motor choice
But I have no personal experience with that type of motor and wouldn’t feel right giving you advice on it.
Especially not knowing how much You plan on running it.
1500 hours is a lot of time for a hobbyist, but not very much time using it in a commercial level
running it for six or even eight hours a day.
As far as drill bits go in a CNC router, the only input I can offer is to be careful.
I talked extensively with A cnc tools salesman and also the tech guy
At CamMaster about using regular twist drills and was told it’s not a good idea.
I was hoping to put a drill chuck on the router or spindle and was told that the speed is too Fast. Long story short I was told you need a special drill chuck that is precision balanced , And boy are they expensive. I was looking into this because I sometimes need to drill a bunch of small odd size holes,
Where it wouldn’t be practical to buy the special CNC drill bits with quarter inch or 1/8 inch shanks That will fit in an er20 collet.

Good luck with your project
And your new machine 👍
Brian

If you are just relying on that lighthouse website, be sure to poke around a little.  I spoke with the owner of the CentralVacuumMotor.com company a few weeks ago and he pointed me at a completely different vacuum motor that was much better to use as a vacuum source for a CNC table (he kinda treated me like a fool).  I bought one with the intent of building a unit that can house three of them but haven't had a chance to get to it yet (business has been booming!).  He says one of these is more than enough to power my 2'x4' axiom and three would do a 4x8' table.

122178-18 Ametek Vacuum motor p/n 122178-18 w/gasket
www.centralvacuummotor.com/Ametek/122178-18.htm

That said, man you guys are getting worked up in a vacuum (lol).

The math is pretty simple.  Hold down force is directly related to the surface area that the vacuum contacts (and is sealed) to the object being held (there are other friction factors but they're linear in relation to the vacuum so we'll ignore them for the most part).  In broad generalities and assuming the vacuum is perfectly sealed, is steady state, and therefore there is no air flow; A 1" circle has an area of 3.14in^2.  Apply -10psi to something that blocks that circle and you are going to get 31.4lbs of force trying to pull that object in toward the hole.  Keep adding holes, keep getting more hold down force.  The advantage of the porous MDF substrate is that the "holes" are so tiny and spread out so vastly, that you can consider the entire surface of the MDF as a "hole" and use the surface area of the MDF in your hold down calculation.  A piece of pegboard (presuming the fibrous material is NOT porous beyond the drilled holes) has, what?, perhaps 15% of it's available surface area as holes?  Basically, with the pegboard, you are achieving only 15% of what you might be able to get with an MDF surface.

That said, the MDF surface being more porous is more leaky, slower to flow, and requires a more robust vacuum source.  however, the MDF does make an easily replaceable, resurface-able spoil board.  There are other elements that enough air flow is needed to generate enough air flow to overcome any slight leaks and still maintain a reasonably high enough vacuum...which in turn helps to pull the part to the table and seal off leaks.  Use MDF without a good enough vacuum source and it could well be a failure.

Shopvacs are also not designed to have 0 airflow and they need air to cool the motor and bearings.  They are also designed specifically for air flow and not necessarily max achievable vacuum.  That said, if the pegboard and a shopvac works, it works.  Easy enough.  I have no doubt that it does work.  It won't work as well as a $1,000 vacuum motor setup using MDF as a surface but that really shouldn't be a surprise to anybody.

[johnb]

grg-

That is exactly the website I was looking at as well as the motor. They have a link (on the left of their site) to "Shopbot Vacuum Motors", most of which are the Lighthouse line. www.centralvacuummotor.com/shopbot.htm I actually found this link in conjunction with the thread here (probably through something Gary posted).

I didn't realize that I was looking at two Amtek motors at the top of this page (it's somewhat confusing that they list Amtek part numbers and Lighthouse part numbers side by side in columnar form for all the other motors). Clearly there's not an equivalency there.

In going back, I also noted in the product bulletin that this motor needs "clean dry filtered air" (for the separated motor cooling). It's not using any air being drawn through the vacuum table for that purpose, and therefor doesn't require a "leak hole". What it WOULD require (in my planned installation) would be a "containment box" within my dust collector room with a clean dry air source from another area. That would be a simple matter. I want it in there because 1) It's immediately adjacent to where I plan to put the Axiom and 2) The more noise I can keep out of the working area of the shop the happier I will be. My (large upright) air compressor will be in an adjacent "closet" and likewise sealed off from the shop. That one's on the outside wall, so it's no problem to put an inlet vent down low and a thermostatic fan outlet (with shutters) up high to keep the compressor heat out of the shop. The ceiling in the area is 10', so I'll duct the "outside waste air" from the dust collector over a lower ceiling in the air compressor closet and vent it out the same outside wall (except when in "recirculate mode").


I'd be happier if I could locate a motor with replaceable brushes. I just have an inborn revulsion at buying things that "can't be fixed". I still use a (Very) old Rockwell 315 hand circular saw that I've replaced brushes AND bearings in more than once. Try that with the plastic-geared crap that everybody sells these days. Maybe I should just revise my way of thinking about what constitutes a "consumable".

[stevem]

Will a vacuum pump from Harbor Freight work for this size vac table?. I'm talkint a table size of 2x2 or 2x3.

[buildswithbrian]

Guys, something to think about....
so a (regular) MDF top that has 1010 1/4" holes AND with the top fly cut (as it will be once surfaced off) is essentially the same as an
MDF top with NO holes, skimmed both sides

My (possibly faulty) logic is as follows,
so the bottom is not skimmed, however it does have 1010 1/4" dia. gateways for the air to flow from the bottom (vacuum source) up into
the interior of the MDF where it can flow sideways making its way toward the top (the only exit path)
so in essence, we are pulling vacuum through the open 1/4" holes AS WELL AS through the skimmed surface of the MDF.

keeping in mind of course the entire surface of the table is covered so as not to lose air flow through open holes,
which is of course how you are supposed to use the vac. table (air damming open holes)

All this being said, I agree with all concerns about overloading or not cooling the shop vac's motor.
I have used the my table for 3 hours non-stop with ALL holes totally covered (no bleeder holes to cool motor)
and also have used it leaving a few holes uncovered.
totally blocked the motor pitch is different, but it just keeps chugging along, and the vac has not cooked (yet)
perhaps my Rigid shop vac is more robust than others... time will tell.
It would be great to not have to worry about this, and have a "regenerative" blower type of motor that doesn't need
air flow for cooling. I do have an old one I pulled out of a dumpster on a job-site many years ago (works fine)
and I have hooked it up to my table as a test, it worked the same as the shop vac.
I haven't hooked it up permanently because I will need to fabricated a mounting bracket and hose coupler.
The Shop vac. is just simpler to hook up (for now)

I like John's idea of having the motor in a seperate enclosed and sound-proofed area.
the shop vac is pretty darn loud

Any thoughts on this ?

[grg]

Dec 21, 2018 16:52:43 GMT -5 stevem said:

Will a vacuum pump from Harbor Freight work for this size vac table?. I'm talkint a table size of 2x2 or 2x3.

If you are talking about one of the 2.5 or 3cfm pumps they have, I really don't think so.  I have one of those types of pumps that I use for vacuum bagging composites but I don't think it has nearly enough air flow to hold down material on any of the typical CNC hold down tables. If you were using suction cups or something with a very sealed perimeter on a material that is smooth and seals well, yes, probably.

[buildswithbrian]

Dec 22, 2018 8:58:59 GMT -5 grg said:

Dec 21, 2018 16:52:43 GMT -5 stevem said:

Will a vacuum pump from Harbor Freight work for this size vac table?. I'm talkint a table size of 2x2 or 2x3.

If you are talking about one of the 2.5 or 3cfm pumps they have, I really don't think so.  I have one of those types of pumps that I use for vacuum bagging composites but I don't think it has nearly enough air flow to hold down material on any of the typical CNC hold down tables. If you were using suction cups or something with a very sealed perimeter on a material that is smooth and seals well, yes, probably.

Depends on how the table was built, if it’s the totally sealed type with gasket material then I don’t see why it wouldn’t work but it is a different type of vacuum system which pulls close to 22 inches of mercury
There are two totally separate types of vacuum tables.
One type uses high flow low vacuum And relies on that high flow to compensate for any leakage therefore they have less holding capacity and then there’s the type that uses a true vacuum pump and must be gasketed and sealed and cannot compensate for leakage because there is not enough flow , These are the true vacuum tables and have incredible holding force up to the theoretical 14.7 pounds per square inch of air pressure
Vacuum powered Veneer presses use the true vacuum pump such as the One you were referring to from Harbor freight
While admittedly the harbor freight one is most likely lower quality than say a pump from “Gast” it should still pull a good vacuum It just takes longer to evacuate the volume, But once it’s pulling say 20 to 22 inches of mercury and you have no leaks that thing hold up the world, of course again it’s based on square inches Of surface area of the part.
Also keep in mind if designing a true vacuum table, the structure of the table itself must be designed to withstand up to 14.7 pounds per square inch pressure or it could collapse or bow, bend or otherwise fail.
I only point this Out so we all are on the same page regarding what type of vacuum system you are building or talking about.

[zaxis4]

Dec 8, 2018 23:24:13 GMT -5 Gary Campbell said:

Ty...
No problem... I was talking about zero holes, not less. The MDF is porous. Here is some more info:

www.camheads.org/showthread.php?t=5186

www.camheads.org/showthread.php?t=8558

So you are saying using this design a shop vac can pull enough air through .75 mdf to hold down parts? All you really need to do then is put a sheet on top and mill it flat? That is amazing....I would not think that would be possible.

[zaxis4]

Dec 13, 2018 10:34:44 GMT -5 @fean said:

Dec 12, 2018 13:55:54 GMT -5 stevem said:

The super glue and tape idea works quite well. As an alternative, try using double sided tape where you would put the glue! No fuss, no muss and it works really good. Holding power is quite high and easier to remove the part without any glue residue to worry about.

I also see that since buildswithbrian called out Gary there has been no response.

Be nice, Gary's information is not only completely correct, he's provided great resources of information on the subject. While low density board is likely superior to MDF, I know several commercial shops that use 3/4" MDF with no holes, they just throw it on and surface both sides to increase the air flow. When it gets to thin, they replace the board the same way. For outhosey who want a YouTube reference, you can watch these two, especially the second one where he is correcting his errors and demonstrates exactly what Gary is talking about.

There are 2 sets of holes in this plan also.....It is not sucking air through solid mdf?? I am confused also

[zaxis4]

Would it be useful to run a Y off of ones dust collection system to a vacuum table? It could be set up with a blast gate. Maybe not enough volume....just wondering??

[buildswithbrian]

Dec 22, 2018 18:24:01 GMT -5 zaxis4 said:

Would it be useful to run a Y off of ones dust collection system to a vacuum table? It could be set up with a blast gate. Maybe not enough volume....just wondering??

Wouldn’t think it would work
There is high CFM with a good dust collector but not that much suction
I think compared to a shop vac even

[johnb]

Dec 22, 2018 6:54:09 GMT -5 buildswithbrian said:

Guys, something to think about....
so a (regular) MDF top that has 1010 1/4" holes AND with the top fly cut (as it will be once surfaced off) is essentially the same as an
MDF top with NO holes, skimmed both sides

My (possibly faulty) logic is as follows,
so the bottom is not skimmed, however it does have 1010 1/4" dia. gateways for the air to flow from the bottom (vacuum source) up into
the interior of the MDF where it can flow sideways making its way toward the top (the only exit path)
so in essence, we are pulling vacuum through the open 1/4" holes AS WELL AS through the skimmed surface of the MDF.

keeping in mind of course the entire surface of the table is covered so as not to lose air flow through open holes,
which is of course how you are supposed to use the vac. table (air damming open holes)

All this being said, I agree with all concerns about overloading or not cooling the shop vac's motor.
I have used the my table for 3 hours non-stop with ALL holes totally covered (no bleeder holes to cool motor)
and also have used it leaving a few holes uncovered.
totally blocked the motor pitch is different, but it just keeps chugging along, and the vac has not cooked (yet)
perhaps my Rigid shop vac is more robust than others... time will tell.
It would be great to not have to worry about this, and have a "regenerative" blower type of motor that doesn't need
air flow for cooling. I do have an old one I pulled out of a dumpster on a job-site many years ago (works fine)
and I have hooked it up to my table as a test, it worked the same as the shop vac.
I haven't hooked it up permanently because I will need to fabricated a mounting bracket and hose coupler.
The Shop vac. is just simpler to hook up (for now)

I like John's idea of having the motor in a seperate enclosed and sound-proofed area.
the shop vac is pretty darn loud

Any thoughts on this ?

I would suspect that the "side bleed" through the open holes would exist with the bottom of the board un-skimmed as the suction draws the air out of the board itself and whatever air lies between the board and the object being held (plus the damming so that the board is entirely covered).



I follow your logic, but you have the explanation backwards. The air flows DOWN through the holes toward the vacuum source on its way to the only exit path (the vacuum). As for the damming...watch the CNCNutz video where he demonstrates that he's providing substantial damming with nothing more than a sheet of newspaper (the paper itself being less permeable than the board). I suspect that the greater suction through the holes would provide less damming with newspaper because the vacuum would be concentrated more where the paper meets the hole, "opening up" the pores in the paper (and maybe even tearing it)



I would posit that, with a totally impermeable sheet of something (like aluminum) covering the entire board, there would be no difference in the amount of holding force of a board that has holes versus one without, provided that both sides of the board have been skimmed. I would likewise posit that, provided the sides of the plenum were sealed, you could gasket the top edge of the sides of the plenum itself and get equal holding force against the impermeable object...up until the point at which it flexes enough to break the seal on its way toward being sucked into the plenum. In all cases where a "perfect seal" is attained, I would think that your motor pitch would be the same once the air is drawn out of the board.

[zaxis4]

Dec 22, 2018 21:21:26 GMT -5 buildswithbrian said:

Dec 22, 2018 18:24:01 GMT -5 zaxis4 said:

Would it be useful to run a Y off of ones dust collection system to a vacuum table? It could be set up with a blast gate. Maybe not enough volume....just wondering??

Wouldn’t think it would work
There is high CFM with a good dust collector but not that much suction
I think compared to a shop vac even

So Brian...I for one really appreciate your post and your outstanding effort to enlighten us all about building a vacuum table. Until your post I had never really considered using one, let alone building one. I am amazed at the power that can be generated with something as simple as a shop vac. Not knowing anything about such things I assumed it was something best left to a manufacture who knows all about such things. I am a hobbyist so your plan really got me thinking about building a table. Your video and drawings are superb and generous of you to share. The Axiom machines sort of dictate that the vacuum supply must enter from the side, rather than the bottom, like many designs that I have researched, since your post. I was wondering if the ( i hope my terminology is right) plenum cut into the bottom plate similar to the CNCnut video, with the vacuum attached from the top, would increase the holding power because of the smaller volume of space beneath the spoil board. It seems that could also simplify the design a little. However there is probably some mathematical formulas to calculate the design of the tool path or the configuration of the partitions. I think you are really on to something in your design. I say that because there are a lot of CNC users out there like me that are not into production and could use something like this to hold small projects. A lot of us do not need to hold down large sheets. I would think that a good design like yours that could be made with simple materials and powered with a shop vac could almost be marketed. You have really motivated me to build your table. Right now I only have a lot of "what if's" in my head but you really have me thinking...Thank you.

[johnb]

zaxis4

If there are no "leaks" in the plenum (other than the surface board with or without holes) then hold down force won't be affected by the thickness of the plenum...only the amount of time it takes to evacuate the air from the larger space (which probably couldn't even be measured). If your entire workroom was tightly sealed and the vacuum placed outside of it, you could (theoretically) attain the same level of vacuum within your entire shop (from the same vacuum source) that would exist with the same motor being used in any sized box. The reason that more motors are called for in larger vacuum boxes is due to the inherent leakage (when the damming isn't complete and/or the object itself bleeds air along with leakage where through-cuts are made in the course of cutting out parts) as well as the desire to be able to "zone" the vacuum. I believe that if you covered your entire board with "Visqueen" or something similar and only cut out the area of whatever you're holding down, it would not matter how big the box itself is (length, width, height) for a given vacuum source. Where you'd get into trouble is with a small piece with a vacuum that's too small to provide adequate holding force for the aggregate size of what's being held down.

What IS affected by the thicker box, however, is the thickness of the object you are capable of milling because of the reduced space between the bit at maximum gantry height and the top of your material. Since this box likely won't be used for 3-D carving of thick pieces of wood (clamps would be preferable), this wouldn't pose a problem. If thickness IS a concern, you could always make your box long enough to overhang the "far end" of the table and poke your hose in there from the bottom. Obviously, the "unused part" of the box would be sealed up (just like the sides & bottom) and not drilled or skinned.

[zaxis4]

OK thanks John....good to know. How critical is it that the air flow through the mdf spoil board which ,would be much more constricted without holes, could cause the vacuum to labor or overheat. Maybe the air pumps mentioned in the other posts can deal with that better. I am also getting that small pieces do not hold as well because of surface area so the extra surface not being used needs to be covered. Is that right?

[johnb]

With or without holes, if the board is completely covered with project and damming, the only flow through the board will be where you've made through-cuts and are actually getting airflow through the vacuum, otherwise the flow is completely occluded in all situations.

Something not previously discussed: If you have holes in the board, then any holes "uncovered" by through cuts will clearly allow air to flow more freely than that which must pass through the board. This is going to lessen the suction on the remainder of whatever is occluding the board (damming and project).

Definitely you need to cover the unused surface of the board to provide adequate suction to the small pieces. Even that may not be enough (depending on what your vacuum is capable of). Think of the suction as "negative psi". The force of the perfect vacuum (which you cannot attain) is the weight of the atmosphere on the other side of the piece (assuming the piece itself is not permeable). This force, in "pounds per square inch" is applied over every square inch of the piece. The smaller the piece, the fewer square inches and the lesser the total force applied to the piece. Think of it this way...if you place a weight of 144 lbs in the form of a 12"x12" piece of steel on a sheet of plywood that's 12" x 12", you have a downward force of 1 psi and the total force required to shift that piece of plywood is 144 lbs. (ignoring the weight of the plywood and disregarding friction for the time being).

If you quadruple the size of the plywood and also the weight, you still have a force of 1 psi on the piece, but you have to move a total of 576# to get it to shift sideways. Your vacuum board (prior to any through cuts of the piece) is going to have the same number of "negative psi" applied to each square inch of the piece, no matter how big it is, but the bigger the piece, the more it will resist sideways movement (which is, of course, what you're mainly interested in). Of course, you also get the benefit of more weight in plywood and more friction in the larger piece.

[buildswithbrian]

Posted by Zaxis4....
"So Brian...I for one really appreciate your post < snipped > I would think that a good design like yours that could be made with simple materials and powered with a shop vac could almost be marketed. You have really motivated me to build your table. Right now I only have a lot of "what if's" in my head but you really have me thinking...Thank you." end quote

Zaxis3, thank you I appreciate your kind comments
please keep in mind though that my design is predicated from the work of many others, I simply adapted it to work for my situation and machine, and I have posted the
video and general instruction as an attempt to help others like yourself in the same situation.
A lot of us hobbyists need to improvise and make do with somethings that professionals find less than perfect, sometimes it works out, sometimes it doesn't.
but we have to keep moving forward and experimenting, and hopefully sharing our successes (and failures) so we all learn as a group.
That is what is so great about the internet and forums like this one.
Speaking as someone that grew up (before the internet) I truly appreciate this incredible technology that can bring us all together to
create, share and otherwise connect with like-minded people.

This thread has been great... I appreciate all the comments and criticisms (good and bad) that it has generated.
looking forward to a new year of experimenting, learning and sharing.

Merry Christmas all.
Brian

[buildswithbrian]

A note to all following this thread...
There is a minor correction I need to make on the attached PDF drawing accompanying my table...
I built my table with only 2 layers (3/4" MDF) of support blocks but in my PDF drawing I show 3 layers.
this was pointed out to me by one of the members of this group that built my table (thank you Mike)
this doesn't affect the function of the table in any way, but will lessen the thickness of what you can cut on it (z-axis height)
I'm not sure how I did this (brain fart i guess, it was a couple months later I made the drawing)

I will be correcting the drawing when I get time and will re-post it here.

[zaxis4]

Brian, What would happen if a .25 piece of MDF were placed on top of the spoil with the holes in it? If it still has the suction then it solves the replacement issue also? Just wondering.....

[buildswithbrian]

Dec 28, 2018 17:07:30 GMT -5 zaxis4 said:

Brian, What would happen if a .25 piece of MDF were placed on top of the spoil with the holes in it? If it still has the suction then it solves the replacement issue also? Just wondering.....

I honestly don't know, haven't tried it...
I am fairly sure you would need the ULMDF to even attempt this, and I
have not yet acquired any to try it.
my guess is (as mentioned in previous posts) is my shop-vac won't have the power
to pull enough flow to work, but who knows??

I may give it a try if I can order a sheet thru my commercial supplier when
I order a sheet of bamboo plywood (which is in short supply) for another project.

if I do I will post the results

If anyone else gives it a go... please post.

[zaxis4]

www.solutionsforwood.com/_docs/profiles/TP-Vacuum-hold-down-strength-CNC.pdf

I ran across this about using 2 spoil boards....may be of interest for those seeking information on their vacuum builds 

Brian, the way you built the box seems like the only viable way to attach vacuum because of the way the Axioms are set up with the T tracks. I am sure you already thought all of that through though. It would be nice to come in from the bottom or top like most builds out there. Seems like the only way to keep it thin. I have found out that the lDF is scarce and expensive around Denver

[jcwoodworking]

Brian's way is not the only way. You can do it with a plenum and bleeder board like Gary suggested (with no holes). That is the route I went. Works fantastic. I used a lighthouse vac motor for the suction though.

_