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Old 07-10-2018, 06:16 PM
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Default Vacuum table design

It doesn't make sense to me to pull the vacuum thru the MDF. It seems like a far better idea to section the table off, cut grooves and add a vacuum port to each section with gate valves to close off those that aren't being used. Is there a reason that this isn't done?
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Old 07-10-2018, 06:22 PM
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might not make sense but i have been doing it for years !
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Old 07-10-2018, 07:06 PM
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When you say: "It doesn't make sense to me to pull the vacuum thru the MDF."

Vacuum, especially general purpose vac systems that use an MDF spoilboard are one of the least understood items associated with CNC router tables. You are in the majority. That said, you don't have to understand it to use it.
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Old 07-10-2018, 07:23 PM
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While I hope that I too may one day have an income from this, right now it's just for personal use and I want to do all that I can to keep monthly expenses down. It just seems like it would be far more efficient to apply vacuum directly to the workpiece rather than thru the MDF and likely require a smaller vacuum as well.
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Old 07-10-2018, 09:24 PM
Rlee1972 Rlee1972 is offline
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I think Jim Becker has recently built something along the lines (possibly) of what you are searching for. If you will look him or his recent posts up, you will see with lots of details and pictures provided. As for vacuum experience, I have none. Our first arrives next week.
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Old 07-10-2018, 09:40 PM
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Using Zones on larger tables to optimize vacuum isn't uncommon, but the lightweight MDF spoilboard still sorta needs to hang around if you don't want to destroy your vacuum table. It's a sacrificial element.

But for doing smaller pieces, what Ron mentions is something to consider...fixtures designed for the workpiece. Some of them are custom to a specific workpiece and others are a mini version of the larger vacuum table where you can move and change the gasket setup to suit the job at hand. But in general, I don't believe you'd want to be making through cuts with that kind of setup for obvious reasons. For "cutout"s, you'll want an onion skin to preserve the fixture, for example. Etc.

You can set things up for however it works best for you and that often means having multiple ways, depending on the work you're doing in the present.
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Old 07-10-2018, 09:42 PM
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Thanks I'll do that.
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Old 07-11-2018, 07:08 AM
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Quote:
It doesn't make sense to me to pull the vacuum thru the MDF. It seems like a far better idea to section the table off, cut grooves and add a vacuum port to each section with gate valves to close off those that aren't being used. Is there a reason that this isn't done?

It is done, all the time.
There are many different types of vacuum systems, and different types of pumps used with the different systems.



A sealed system like you are describing usually uses a high vacuum low CFM pump, while pulling through the spoilboard requires very high CFM pumps.
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Old 07-15-2018, 09:30 AM
The real JP The real JP is offline
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I didn't understand why the vacuum was made to pull through a sheet of mdf either. It seems crazy...... but it works well.

The plenum is sectioned and gated almost exactly like you said so why isn't the spoilboard sectioned? Right?

The answer I came up with is that it doesn't have to be. The vacuum is strong enough to hold down through the mdf without it being sectioned. That way you have a flat smooth easy to machine sealing surface for the material you are holding down.

If there are some gaps it won't matter as much because the mdf diffuses the vacuum. So basically you have a large flat vac area that doesn't have to be sealed off very well, it can have some leaks and still work well.

If there were actual holes for the vacuum to work through. Debris would get in there and any leaks would severely effect your hold down strength.
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Old 07-16-2018, 01:13 AM
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Quote:
Originally Posted by The real JP View Post
I didn't understand why the vacuum was made to pull through a sheet of mdf either. It seems crazy...... but it works well.

The plenum is sectioned and gated almost exactly like you said so why isn't the spoilboard sectioned? Right?

The answer I came up with is that it doesn't have to be. The vacuum is strong enough to hold down through the mdf without it being sectioned. That way you have a flat smooth easy to machine sealing surface for the material you are holding down.

If there are some gaps it won't matter as much because the mdf diffuses the vacuum. So basically you have a large flat vac area that doesn't have to be sealed off very well, it can have some leaks and still work well.

If there were actual holes for the vacuum to work through. Debris would get in there and any leaks would severely effect your hold down strength.
While I understand that it works I just don't like the idea of paying for the electricity that it takes to pull a vacuum thru mdf if there is a cheaper way to do it. I have a hvac vacuum pump and a larger freon recovery vac that I want to try first for smaller parts. I'm far from the first to try this and if it works for them why not this one too.
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Last edited by Options; 07-16-2018 at 01:39 AM. Reason: New info
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