Vacuum Pump Availability *LINK*

Re: Vacuum Pump Availability

Ralph Lindberg

I've been using a very similar appearing rotary type for about 10 years now with no issues.

HOWEVER

This put a fine oil mist in the air. What I do is wrap a paper towel around that port and let it soak up the oil

A friend built a bypass that collects the oil into a container

Re: Vacuum Pump Availability

Bill Blasic

I highly recommend Doc's book, so much good info. I have been lucky enough to have met Doc and have his autograph on my book.

Re: Vacuum Pump Availability

John C Lucas

My first pump was an automotive compressor and it really spit oil out of the exhaust. I made a sort of muffler out of pipe filled with steel wool and it worked perfectly. I eventu� lly upgraded to a GHast pump.

I highly recommend his book also I have a copy

Re: Vacuum Pump Availability

Cyril Griesbach

Doc, that looks VERY similar to the one I have which is made for servicing the refrigeration industry but cost LOTS more.

And, yes, your book is great.

Re: Vacuum Pump Availability

Roger Chandler

Bill, may I ask where Doc's book is available, or how one might obtain a copy if you know? Perhaps if you do not know, then maybe Doc will let us know. I have a vacuum pump like the one mentioned, and have some parts gathered, but there are some questions I have before I set out on making my own system. At present I use a Holdfast system with my compressor, but want a dedicated system with a pump. Lots of great info on the oil exhaust here........much appreciation, to all who posted info!

Re: Vacuum Pump Availability

rch

amazon

Fixtures & Chucks Amazon *LINK*

Doc Green

On Amazon, you can "Look inside the book" and get a good idea of what it's all about. Unfortunately, they didn't include but a couple of pages from the chapters on vacuum systems.

You can find the Table of Contents on my website:

http://www.docgreenwoodturner.com

Good Luck, ~Doc


Doc's Book on Amazon

Re: Vacuum Pump Availability

Ralph Lindberg

The one I have is intended for servicing vehicle A/C units, but it works well for me.

Other things I've done...

Ralph Lindberg

I also added a filter system between the vacuum chuck and pump (Harbor Freight #68247).

This helps keep the sawdust out of the pump (you should have seen the filter after the DW chucked up a bowl that was leaking sawdust through some cracks)

I'm also in the process of building a "vacuum reserve" tank, to give me a couple seconds to bring some support up for -when- we lose power -again- while I have something on the vacuum chuck.

I'm building this out of 4-inch PVC #40 pipe, it's about 2 ft long.

Re: Vacuum Pump Availability

Bob Verne

Doc, the label on the vacuum pump shown in the link says "Ultimate Vacuum 5Pa". Converting, 5Pa = .0015 inHg, way low for a vacuum chuck. Am I missing something?

Bob

Vacuum vs Pressure

Doc Green

The 5 Pa is the "absolute pressure" inside the vacuum chamber at the limit of the pump, and as you note, 5 Pa is a very small pressure.

The "inches of mercury" measure of a vacuum is "Relative" to atmospheric pressure, or, it's how much less the pressure inside the chamber is than atmospheric pressure, which is 30 in Hg.

Absolute Pressure = Atmospheric - Vacuum

For example, if a pump can pull a vacuum of 26 in Hg, the pressure inside the chamber is 4 in Hg. If a better pump pulls 28 in Hg, the pressure would be 2 in Hg.

If a vacuum pump could remove all the air so the absolute pressure inside the chamber is zero, the vacuum would be 30 in Hg.

So, the pump in question can remove almost all the air, leaving behind only enough to produce a pressure of 5 Pa. This would correspond to a vacuum of almost 30 in Hg.

Hope this makes sense. ~Doc

Re: Vacuum vs Pressure

Bob Verne

Thanks, Doc. Makes sense. Great explanation.

Bob

Re: Vacuum vs Pressure

Robert Edington

Doc. I read and reread your response trying to get my head around it. I want to get a vacuum system. I don't want to buy the wrong thing. Based on the specs, will this pump do the job? It seems like, based on your response to Mr Verne, that it will.

Thanks for taking time to deal with those who move a bit slower.

RP

Re: Vacuum vs Pressure

john lucas

Robert I ain't no mathemetician. In fact I really had trouble understanding what Doc just said. That's why he writes a book and I haven't

In reality using a vacuum system for turning bowls you don't need maximum values. The only time you need a really high vacuum is with items that have a really small footprint that the vacuum acts upon. Vacuum works by the number of square inches on your vacuum chuck. I find with larger pieces using my 8" vacuum chuck that I can turn the vacuum pretty far below it's maximum of 26" and still have a really strong hold. On the other hand my 4" chuck needs most of that to turn a bowl. I can put a mirror on there where you don't have much leverage and be pretty aggressive in my cutting. When I have a bowl held by the 4" and your turning near the outside rim if you get aggressive you can pop it off.

Re: Vacuum vs Pressure

Doc Green

Yes, I think the pump that I referenced in my original post will work just fine. The best feature of the pump is its capacity of 7 cubic feet per minute. It will be ideal for a leaky system, like a bowl with worm holes in it.

Another way to look at the different ways of measuring a vacuum (or pressure) is to view the absolute pressure as the air left in the system when the vacuum pump has maxed out. The vacuum in inches of mercury relates to the air that has been removed.

The Gast pumps that were favored earlier for vacuum chucks will pull a maximum of 26 in. Hg. That's 26 out of 30 in. Hg. So, 4 in. Hg of pressure would remain in the system.

The pump under discussion will pull a maximum vacuum of "just a hair" under 30 in. Hg. That means "just a hair" of pressure remains, which is to say the pump is almost perfect, but not quite.

In numbers, one atmosphere is 101,325 Pa. The pump will remove all the air but only 5 Pa worth. 5 out of 101,325 is hardly enough to mention.

What makes this confusing are the crazy units and the fact that the two scales are upside down from each other.

Re: Vacuum vs Pressure

John K Jordan

It is easy, in fact, to collapse a thin turning with too much vacuum (DAMHIKT), the reason bleeder valves are built into the system.

"Stronger" vacuums may be more useful for applications other than woodturning, such as vacuum clamps on a milling machine, vacuum presses in some applications, or perhaps stabilizing wood. (BTW, I used one years ago when potting uranium-bearing reactor element samples for polishing and microscopic examination.)

JKJ