Vaccum pump

[bertterbo]

I've got one of the cheap Amazon vacuum pumps, 0.8pa, 3 CFM. It works great, and gets a vacuum of at least -29inHg, which secures pieces to my wood turning vacuum chuck just great.

However ... when the piece has tiny air gaps in the grain, a good suction cannot be formed, and I only get about -10inHg, which isn't enough to turn with.

If I upgraded to a 9cfm or even a 12cfm pump, how much of a difference do you think I would see?

 

[ps.harris80]

If you can't get a good suction with a 3cfm pump because of air gaps in the grain I would suspect you will get the same issue regardless of how much suck you apply, to a vacuum pump a leak is a leak, the bigger CFM pump will just show the leak quicker.

 

[bertterbo]

If you can't get a good suction with a 3cfm pump because of air gaps in the grain I would suspect you will get the same issue regardless of how much suck you apply, to a vacuum pump a leak is a leak, the bigger CFM pump will just show the leak quicker.

I was thinking that a higher CFM could hold a better vacuum even with a leak. As its removing more air quicker (than a lower cfm) than being lost due to the leak.

 

[ps.harris80]

I suppose the only way to find out is buy a bigger pump and see. Good job they are a lot cheaper than they used to be, I used to do refrigeration work in the 90's and the vac pump I used was over £300 then, now they can be found well under £100.

Your thinking may well be valid. Let us know how it goes with the bigger pump.

 

[Yojevol]

A bigger capacity pump is not the answer. The tiny flow through your seal is insignificant compared with the free flow rating of the pump, be it large or small. A larger pump may well pull less vacuum than your present one. A higher quality pump may improve the suction but that could be an expensive solution.
What you need to do is improve the seal. I would suggest filling the grain where the chuck makes contact.
Brian

 

[bertterbo]

I suppose the only way to find out is buy a bigger pump and see. Good job they are a lot cheaper than they used to be, I used to do refrigeration work in the 90's and the vac pump I used was over £300 then, now they can be found well under £100.

Your thinking may well be valid. Let us know how it goes with the bigger pump.

Well, a higher CFM is around £120 for a cheap one and upwards of £300 for a better quality one. So risky

 

[bertterbo]

A bigger capacity pump is not the answer. The tiny flow through your seal is insignificant compared with the free flow rating of the pump, be it large or small. A larger pump may well pull less vacuum than your present one. A higher quality pump may improve the suction but that could be an expensive solution.
What you need to do is improve the seal. I would suggest filling the grain where the chuck makes contact.
Brian

Can't really fill the grain as I'd be cutting away the material being filled.

 

[Tris]

Random thought but if the work is porous and on a vacuum chuck, why not slap a coat of sanding sealer on and let the vacuum pull it into the wood. Hopefully it will seal deeply enough to allow you to keep turning

 

[Yojevol]

Can't really fill the grain as I'd be cutting away the material being filled.

Seal the whole surface that is subject to the vacuum suck. With luck the sealant will hold if it's well cured.