![]() DIY CNC Router Vacuum Tablesīuilding a vacuum table for your CNC Router (or Mill) is pretty straightforward. If the up-force is enough, the part could even be flung across the table. If the part is lifted even a little, perhaps not enough you can see, you’ll leak vacuum and unless your vacuum pump has a lot of capacity, the part will soon pop off as vacuum drops. The up-force needed to overcome the holding force is just a function of the weight of the part plus the hold-down force due to vacuum. Most of the time, the coefficient of friction will be such that it takes at least twice the force to move the part sideways as it does to lift the part. Be sure the vacuum table surface is not too slippery to provide holding against side force. Side force is a function of friction between the part and what it is laying on. One is side-force and the other is up-force. The last thing to know is that there are two forces trying to upset the part on the vacuum table. Just as MDF can be used to spread the vacuum, your part may leak vacuum if it is made of anything permeable (foam board, MDF, that sort of thing) or if you introduce too many through holes into it during the machining. This works well, but it does require a vacuum pump that can pull a greater volume of air through because the MDF will leak wherever there’s not something lying on it. MDF is porous, so vacuum goes everywhere. Most CNC Router Vacuum Tables avoid this problem by using an MDF board atop the vacuum table to spread the vacuum. In that case, it is the surface area of the chambers and not the surface area of the part that will determine the hold-down force, and that’s much less than the surface area of the part. We may not get much vacuum anywhere except where the chambers are. Now in order to keep the part flat, and not bowed, we want it to sit flat on the vacuum table. Consider a vacuum system built out of aluminum with small vacuum chambers underneath. It’s important to be aware of that difference.Īnother way force can be limited is you may not be able to apply the vacuum to the entire bottom surface of the part. Meanwhile, small parts have much less force holding them down. A 10″ x 10″ square part potentially has 100 square inches times 14.7 lbs per square inch or almost 1500 lbs of holding force! ![]() A large area on a large part can have significant force. The hold-down force is proportional to that pressure difference and the surface area exposed to the difference. Every square inch of area exposed to that difference can have a force as much as 14.7 lbs pushing down on it (the difference between 0 and sea level air pressure). ![]() ![]() Vacuum Tables generate hold-down force because of the difference between a vacuum under the part and atmospheric pressure pushing down from above. Note: If you’re looking for information on Vacuum Chucks and Fixtures for VMC’s, we have a page for that too. Vacuum tables can be set up with zones that can be turned on and off with valves as well. Granted, unless you have a lot of vacuum available, you may want to seal part of the spoil board so the area receiving the vacuum is limited. You can lay an MDF spoilboard right on top of a vacuum table and it’s porous enough to still pull a vacuum. Vacuum Tables are often the best solution for the flat sheet work often being done on CNC Routers. Vacuum Table with zoned sub-plenum plumbing. Total Guide to Router Vacuum Tables for CNC & DIY Introduction
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