Vac Table Top Surface

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joejinky
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Re: Vac Table Top Surface

Post by joejinky »

I've been on the computer all night, playing with ideas. I think I have come up with a solution! I got the idea from the crawl space side vents around my home. I will start on this project very soon, and post photos (maybe) of the results.

Joe
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Re: Vac Table Top Surface

Post by Mikehell »

joejinky wrote:
Tue Mar 10, 2020 4:30 am
]

Thanks! I will add WEDGE capability to the table surface. I had not thought of that. By drilling holes into the top material but not penetrating completely through, I should be able to put pegs into the holes, and then use wedges to secure the smaller pieces. THANKS!

Joe
Pegs may not work. You can try using threaded inserts and plastic bolts. Just be sure to get the inserts deep enough so a resurface of the table won't hit them. I can't see pegs holding up in soft MDF for any amount of time.

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Re: Vac Table Top Surface

Post by tomgardiner »

With a 5 x 12 you will need something like 20 hp of vacuum. Typically two 10 hp pumps. If they are regenerative pumps double the hp required. I recommend separating the table into zone with there own valves.

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Re: Vac Table Top Surface

Post by joejinky »

tomgardiner wrote:
Tue Mar 10, 2020 12:16 pm
With a 5 x 12 you will need something like 20 hp of vacuum. Typically two 10 hp pumps. If they are regenerative pumps double the hp required. I recommend separating the table into zone with there own valves.
The table is 5x10. I can't imagine trying to maintain suction over a 5x10 (50 sq. ft.) area simultaneously. I would never route anything that large anyway.

I am going a different route. I am creating an array of vac ports on the table surface that can be opened or closed individually. In that way, I will only be pulling air through those ports that are beneath the material to be routed. The rest of the table surface will essentially be solid. I don't know if this will work, but I am willing to dump a thousand dollars into a working model to test it.

Joe
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Re: Vac Table Top Surface

Post by adze_cnc »

joejinky wrote:
Tue Mar 10, 2020 3:50 pm
I can't imagine trying to maintain suction over a 5x10 (50 sq. ft.) area simultaneously.
I once had six sheets of 3/4" MDF temporarily stacked on our 5x9 machine (which already had a 3/4" spoilboard). For amusement's sake I turned on our 10HP Becker pump. The pump reasonable well still held down a further 4x4 sheet of 1/4" MDF through all the other MDF.

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Re: Vac Table Top Surface

Post by joejinky »

adze_cnc wrote:
Tue Mar 10, 2020 4:53 pm
joejinky wrote:
Tue Mar 10, 2020 3:50 pm
I can't imagine trying to maintain suction over a 5x10 (50 sq. ft.) area simultaneously.
I once had six sheets of 3/4" MDF temporarily stacked on our 5x9 machine (which already had a 3/4" spoilboard). For amusement's sake I turned on our 10HP Becker pump. The pump reasonable well still held down a further 4x4 sheet of 1/4" MDF through all the other MDF.
Wow. Were these 3/4 MDF sheets modified (pressed surfaces removed?) or were they fresh out of Home Depot 3/4" MDF sheets?

I might have to go look for a STRONG vac pump!

Thanks!

Joe
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adze_cnc
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Re: Vac Table Top Surface

Post by adze_cnc »

joejinky wrote:
Tue Mar 10, 2020 4:56 pm
Wow. Were these 3/4 MDF sheets modified (pressed surfaces removed?) or were they fresh out of Home Depot 3/4" MDF sheets?
De-skinning 6 sheets (12 sides) of MDF seems like a really tedious job. That's 8 to 10 hours of my time I'd like to keep to myself. :D

Just your average 1 lb per sq ft per 1/4" thickness MDF.

Steven

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Re: Vac Table Top Surface

Post by joejinky »

So ... I don't know a thing about love ... er ... VACUUM PUMPS!

I am looking at them on Amazon. Do they have duty cycles, or can I turn one on and leave it running unattended for five or ten hours at a time without worrying about fires and other disasters?

Can you point me to a good pump? I prefer "Made in 'Merica!" over the Chinese models, even though they are more expensive.

120VAC preferred, but I do have 240 VAC in my shop if that is necessary.

My budget ... Under $1,000.00 would be nice.

I am preparing to build my experimental vac port table top. I *THINK* it will work well, but that is a lot of work to make this with no guarantee that it WILL work. I am only running on good ol' redneck engineering here.

I guess I will have to look at redesigning the top to have independent regions that can be turned on or off. I don't want to mess with O-Ring gaskets if possible.

Will a vac table work if I place material directly onto say ... 1/2" holes in an array? Or do I need some air space between the material and the support to create a chamber of negative air pressure?

If the holes are conical shaped, does that make a difference? I am reminded of the TV vacuum commercial where they use a funnel shaped fitting on a shop vac hose to life a 16 lb. bowling ball. I SUSPECT that the conical shape was crucial for the lift. Maybe it is a #/sq.in. thing?

Always learning ...

Joe
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Re: Vac Table Top Surface

Post by joejinky »

adze_cnc wrote:
Tue Mar 10, 2020 5:08 pm
joejinky wrote:
Tue Mar 10, 2020 4:56 pm
Wow. Were these 3/4 MDF sheets modified (pressed surfaces removed?) or were they fresh out of Home Depot 3/4" MDF sheets?
De-skinning 6 sheets (12 sides) of MDF seems like a really tedious job. That's 8 to 10 hours of my time I'd like to keep to myself. :D

Just your average 1 lb per sq ft per 1/4" thickness MDF.

Steven
Wait ... you first wrote 3/4", but now they were 1/4"? I don't care about typos, but that does make a big difference.

Joe
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Re: Vac Table Top Surface

Post by Rcnewcomb »

If you are mostly cutting full sheets of material a vacuum table (with optional locator pins) is great. This is sometimes referred to as a universal system.

If you are cutting mostly hardwood and/or odd shapes and sizes then you need to adjust your strategy. It is sometimes referred to as a conventional system. This is where gasket material is a game-changer.

A bit more information for your reference: Total Guide to Router Vacuum Tables for CNC & DIY

And from the CAMaster site:
Understanding Vacuum Hold-Down For CNC Cutting
Whether you’re investing in a brand-new CNC router, or simply looking to get the most out of one you already own, it’s the perfect time to look into vacuum hold-down. Aided by an industrial vacuum motor, many manufacturers today are achieving a touch-free, powerful clamp on the products they craft. If you hope to play on a level field, vacuum hold-down is something that merits strong consideration.

Why Vacuum Hold-Down?
All manufacturers need some method of securing their substrate material firmly in place. The traditional choice is the manual one – namely, clamps and screws – but this can be frustratingly difficult to set up (not to mention the potential these metal bits have to scuff or otherwise damage your product). Furthermore, using clamps means designating sections of material to be used as contact tabs, which must later be cut and/or sanded away – this means wasted time and materials. Vacuum systems are the answer, providing a potent holding force with the simple flick of a switch.

Types of Hold-Down Systems
There are two primary methods of vacuum hold-down:

Conventional systems form seals around only the relevant regions of the material. This method is an energy-saver when compared to full-surface vacuum seals, but does require the creation of a product-specific template. As such, conventional systems are best used when cutting smaller, repetitive parts (for which a template will see enough use to justify its creation).

Universal systems, by contrast, are typically full-table setups that apply a full seal to the entire substrate. Simply place your material down – no templates required. This does require additional airflow in comparison to conventional systems, but if your cutting needs are expected to shift continually, this may be worth the savings on template creation.
- Randall Newcomb
10 fingers in, 10 fingers out
another good day in the shop

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Re: Vac Table Top Surface

Post by joejinky »

That is very helpful. Thank you!

Joe
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adze_cnc
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Re: Vac Table Top Surface

Post by adze_cnc »

joejinky wrote:
Tue Mar 10, 2020 5:17 pm
Wait ... you first wrote 3/4", but now they were 1/4"? I don't care about typos, but that does make a big difference.
No typos at all. Just an observation that a 12" by 12" by 1/4" square of regular MDF is about 1 pound.

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Re: Vac Table Top Surface

Post by tomgardiner »

Re: vacuum pump manufacturers.
There are a handful of brands that you see again and again in industrial settings. I don't know all of their countries of origin.
Perske, Becker, Travani, Buusch, Decker, are all good brands. There are others I am sure.
They are made to run all day everyday. Dry vane pumps have a service life before required replacement of seals. That rebuild can be expensive. Be aware of that if you buy used. I bought a used oil type pump that is quiet and good flow from 7 1/2"hp.
My advice is don't reinvent the wheel. Have a look at the bases of machines online. The gridded pattern in mine is cut with a big bullnose. The zones are separated by grooves with 1/4" neoprene foam gaskets. The plumbing is 1 1/2" white schedule 40 drain pipe to each zone and 3" main to the pump.
The last bit of advice is that too little vacuum is useless. If this a machine meant for production invest in a large enough pump (look at the specs of similar machine sizes). There are ways to make a cnc work when you have limited vacuum but it is more labour intensive and time consuming.

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Re: Vac Table Top Surface

Post by ger21 »

Your vacuum pumps have a LOT to do with your end results. If you are using vacuum cleaner motors for your pumps, you need to use Trupan, as it flows better.
With big industrial rotary vane pumps, regular MDF works fine. We have two 10HP Becker pumps on a 5x12 table.
Gerry - http://www.thecncwoodworker.com

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Re: Vac Table Top Surface

Post by joejinky »

I have built the base for the vac table out of oak planks on edge, with 1/2" plywood over the top. I will construct a frame on top of that which will create a cavity that the vac pump will suck the air out of. On top of that, a series of adjustable circular vents that can be individually opened or closed. They will be distributed over 14 panels that can be replaced when necessary. Try as I may, I know the router bit will occasionally carve into the top of these panels.

The whole thing will be fly cut to be level with the rails, so there is hopefully no variation in the cut depth from one end of the table to the other. I don't know. I may fail at this, but I'm going to give it a try anyway. :roll:

Joe
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