Vacuum Hold Down Problems

[Spencer_CNC_NOOB]

Hello, I have a router table that is 5' x 13' but is currently roped off to a 4'x12' area with a MDF 3/4 spoil board that has been cut on both sides to open it up (surfaced it)
I am cutting 2 inch foam that has aluminum skin on each side, they are all through cuts.
I am having 2 problems with this machine, first I am not getting enough vacuum to hold down parts, the vacuum pump is a Becker VTLF 2.250 https://beckerpumps.com/products/vac...es/vtlf-2-250/.
No matter what I do I have a hard time holding parts well enough I can't just pull them up with my hand.

Do I have enough vacuum?
Is the CFM too low?
Is my spoil board too dense?

Thank you form any help you can provide.

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[routalot]

I would suspect the flow rate isn't sufficient to get ahead of the leakage.Things you might check are if the spoilboard has a clean seating on the machine,leaks in the plumbing,blockage in the filters and pipes and the presence of holes in the spoilboard.I have known people to varnish or shellac the edges of the MDF to reduce leakage too.If the table has a zoned vacuum grid and you have a gauge,could you determine the level of vacuum in each zone?You could then compare it with the vacuum at t he pump to see if any one branch has a leak.The spec of the pump indicates that it ought to deliver a high enough level of vacuum and if it is meeting that figure at the outlet,the problem is leakage or insufficient capacity.For most machines,flow volume is more important than absolute vacuum,in fact there are lots of machines with a vacuum relief valve in the system.You almost certainly won't be able to listen for leaks if the pump is inside the building as the things are so noisy.

[Spencer_CNC_NOOB]

Thank you for your suggestions I have checked and there are no leaks in the vacuum lines and the spoil board has a clean seating, it is looking like it might be insufficient capacity. What would be the best way to go about fixing this?

[ger21]

What size are your foam sheets? Make sure the vacuum is restricted to the area of the sheets only.
Is there a vacuum gauge that tells what you are getting?

[routalot]

Thank you for your suggestions I have checked and there are no leaks in the vacuum lines and the spoil board has a clean seating, it is looking like it might be insufficient capacity. What would be the best way to go about fixing this?

As I posted earlier,you might begin by applying a coat of shellac or varnish to the edges of your spoilboard to limit the leakage there.Depending on the anatomy of your machine it might be feasible to plumb in valves to prevent the vacuum being applied to regions that don't have a portion of the job over them.Failing that,a plastic sheet over the empty area can do much to help.The final and most expensive option is to add more pump capacity.

[ger21]

On our old machine, we had two of those Backer's on a 5x12 table. When cutting 4x8 sheets, we'd lose a lot of vacuum, and it was rarely practical to block off the table.We now have a new Morbidelli X200, with 16 automatic vacuum zones, and our hold down has doubled, by directing all the vacuum to the areas in use.

Also, some materials just do not hold down well with vacuum, if they are not rigid enough.