Vacuum Question

[oldgriz]

Has anyone used a venturi vacuum systems for bowl turning...
I was looking at this link: http://www.coleparmer.com/catalog/p...&cls=6906&par=&cat=&sch=552&pfx=&lstBool=true

I have a compressor and would really like to have a system without spending an additional $300 on a vacuum pump...

 

[Wilford Bickel]

I have used water based venturi vacuums in the chemical labs for years. The water ones will have major changes in vacuum if the flow of water changes just a little - I would expect the same with the air ones. You will need a large compressor to make sure you can maintain an adequate airflow over a long period. Most of these types of vacuums are meant for vacuum filtration in labs where holding a set vacuum does not matter.

I only gave $70 on ebay for a good Gast rotary vane vacuum pump. It has worked like a dream. It was a 220 volt but that was not a problem to wire up in my shop. Have you looked to see if you can find a used Gast pump?

Wilford

 

[Mark Mandell]

Tom,

The venturi deals are, I think, sold more for veneer press application than anything else. Consider also that they are (usually) quite loud, and net, net expensive since you've got this big compressor running.

If you want the cheapest solution, go to several home appliance repair shops and snag 1 or 2 FREE compressors that have been removed from dehumidifiers. After the shop removes the freon, the units are just so much scrap metal and they're usually glad to give you the compressors for free. It's then pretty simple to wire them up and do a bit of flare-fitting plumbing to hook them up to your lathe. I use 2 such units on my Stubby. They'll pull 27-28" of Hg. and move about 5-6 CFM in free-flow mode.

Note of caution: Also snag one of the fans from the units to use as a cooling fan for the compressor (s). These things have an internal thermal overload and will shut down without warning if not kept reasonably cool. The little fans in the appliance work just fine for this and, like the "pump" are free, and the thing will run almost silently all day long.

Mark Mandell

 

[Steve Worcester]

I have used a venturi system and they do work. I got rid of it though because it uses alot of air, and is very noisy. With my 3.5HP compressor, it would run only a couple of minutes and then the compressor would kick back on.

I have also used a motor driven auto air-conditioning compressor (cost $40 + 3/4HP motor) and then when to a rotary pump. Each worked well, and I only kept changing to get the noise level down.

That venturi was real expensive too, and if you are looking at $100 ceiling, you should be able to do this with a dedicated vacuum pump.

If you need some sources, let me know.

 

[Andrew]

Tom,

I looked into doing the same thing with the venturi vac but all of the advice I found and was offered was pretty much the same as what you see here.

Fortunately, just a short time later, I had a GAST 1/4hp vac unit fall into my lap for $125. I couldn't pass it up although I might have found one for a bit less if I tried and waited. I got it from John Jordan and I think he got several of them, used, from a laboratory. It was pretty much ready to go with just minor plumbing to fit it to a hose and some wiring. I'm very very happy with it and it can run all day long. A little noisy and can get warm but not bad at all. More information on it here.

 

[hockenbery]

cheap alternative

If your lathe has an outboard spindle and you have a shop vac, you can make an inexpensive vacuum system that works in a few minutes. Use a block of non-porous hardwood like maple and turn a fitting to connect your shop vac hose to the outboard spindle of the lathe.

This fitting needs:
1. a through hole about the same size as the hole in the spindle
2. a hole the diameter and depth of the spindle on one end
(this is a loose fit since the spindle threads must turn freely inside but not leak too much)
3 the other end is turned to fit inside the shop vac hose with a slight taper.


This adapter fitting should sit against the spindle nut and or the end of the spindle tightly enough when the vacuum is on so it won’t leak too much so those surfaces have to be smoothly cut.


To use this system secure the shop Vac hose to the adapter with duct tape. Slide the adapter over the out board spindle and hold it in place by either taping it to the head stock or clamping or taping the hose to something so that the fitting can’t fall off.

Put a drum chuck on the inboard side, center you work piece on the drum chuck and turn on the shop vac. Test to see if you can pull the work off. If there s a good fit to the drum chuck it should be quite a struggle to pull the work free and you may not be able to.

This system is only as quiet as your shop vac and has no adjustment, but it works fine for bowls. It is an easy way to use vacuum with out much expense. Don't try this or any vacuum system on any thin walled pieces until you have some experience with vaccuum. It is very easy to crack pieces with walls less than 1/4 inch and certainly possible to crack much thicker ones.

I learned this trick from Liam O'neil many years ago and have used in several classes I've taught instead of lugging my vacum system around.


happy turning,
Al