Hold Fast v810 Vacuum Generator Question

[Kyle Young]

I acquired most of the parts for this Hold Fast v810 vacuum generator. It has the generator, hose and headstock insert. I also has an optional PSI gage for the compressed air input. From what I can tell, it just lacks the cup chuck. Before I make or buy one, I decided to make sure the generator worked. So, I hooked up my little compressor and carefully put my thumb over the end of the rod. Meh. I've never done this before but I assumed it would give me my first thumb hickey. I've uploaded a video of the test.

I just cant imagine this will hold a piece of cardboard onto my lathe, let alone a bowl. Input? What's wrong?

 

[Dwayne Watt]

Vacuum holding force is a function of the area of the chuck. Anything smaller than roughly 4 inch diameter isn't going to create much holding force. At 15 mm Hg, your 1/4" tube has less than 1/2 pound force holding effect while a 4 inch chuck will have 88 pound force hold against the chuck. A decent vacuum pump should maintain around 25 mm Hg or 12 psi which is 150 pound force on that same 4 inch chuck. So, in a sense you are correct, that tube won't hold much but vacuum (negative pressure) can hold or even fracture a wood piece on the lathe with a proper size vacuum chuck.

 

[Tom Gall]

Kyle, I agree with what @Dwayne Watt has said. It should work fine for most applications - depending on the porosity of the wood, etc.. However, I think your "thumb" test should pull near maximum vacuum (at your elevation above sea level) ... I would check all your fittings for leaks. The big downside of this type of system (venturi) is that you need a compressor!!! A lot of juice (larger hp. motor) and noise. Most vacuum pumps use a fractional hp. motor (mine is 1/4hp.) and can run for hours on end ... I wouldn't want to run my compressor like that. Of course, it depends on your usage and you won't have to buy/source a vac pump. Just my 2¢.

 

[Kyle Young]

Thank you @Dwayne Watt and @Tom Gall for the response. I am at 4600 ft above sea level so the venturi is going to struggle a bit. I already had the compressor and this was "free". I will primarily use it for turning off tenons on larger bowls so it shouldn't be for hours on end. Ill check the hoses and give it a run on a blank and my Powermatic cage in place and give it a little stress. Then stand back.

 

[Gary W Miller]

Kyle, I agree with what @Dwayne Watt has said. It should work fine for most applications - depending on the porosity of the wood, etc.. However, I think your "thumb" test should pull near maximum vacuum (at your elevation above sea level) ... I would check all your fittings for leaks. The big downside of this type of system (venturi) is that you need a compressor!!! A lot of juice (larger hp. motor) and noise. Most vacuum pumps use a fractional hp. motor (mine is 1/4hp.) and can run for hours on end ... I wouldn't want to run my compressor like that. Of course, it depends on your usage and you won't have to buy/source a vac pump. Just my 2¢.

Well said.

Gary