Vacuum

"Moray" wrote: (clip) the holdfast system which produces 19hg. A used pump I have seen

^^^^^^^^^^^^^^^^^^^^^^ The difference between 19 and 22 inches will hardly be noticed. ^^^^^^^^^^^^^^^^^^^^^ (clip) up to what size/weight bowls can it handle. ^^^^^^^^^^^^^^^^^^^^^ Turn the question around--*DOWN* to what size will it handle. The risk of knocking a piece off the chuck is greater for small bowls. I can't think of any way to predict exactly when you will lose your grip, but for a given article, 19" will hold 86% as well. Or, putting it another way, the Holdfast system will have the same strength as the 21" setup at 93% of the diameter. (because the area goes as the square of the diameter.)

What you need to compare for the two pumps is their relative pumping volume. A pump that handles larger volume will deal with leakage better--you won't have to worry as much about the seal, or the possible porosity in the wood. Again, it is difficult to put numbers on it, but it is good to have a capacity of 3 cfm or so to work worry free.

The holdfast never made sense to me.. why stick a tube through a perfectly good hollow spindle?

Talk to Bill Noble about used pumps and how to build your own system, or have him build some of the parts, like the rotary valve..

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I concur. Bill Noble helped me a lot when I was building my system. I ended up with a rotary vane pump that I picked up off of Craig's list and a bunch of face plates from Bill upon which I mounted various sizes of PVC pipe for my chucks. I use adhesive backed foam from the craft store for gaskets.

I never could see why one would want to run a big air compressor to do the job of a 1/2 HP vacuum pump that will pull more cfm than a venturi. That cfm is important when you are dealing with a bowl that has warped.

Being married to a "down-easter, Scot" for almost 46 years it wears off on one ;-) .

What I did, and it works great, was to buy/obtain the following:

1. used 230v Gast pump from the Surplus Center
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   2. 24" solid 3/8 brake line from my local auto parts store
2. four foot of 3/8 rubber gas line from the same auto parts store
3. a sealed bearing with a 3/8" center diameter.
4. a vacuum filter from Harbor Freight
5. a 6" face plate from Harbor Freight
6. a 24" wide sheet of heavy cork from Hobby Lobby
7. a disk of 3/4" plywood (cut to fit the swing of the lathe)

I use the a switch on the wall to control the pump.

I cut the solid brake line about 3" longer than the length of the headstock and epoxy the flared end of the solid brake line to the 3/4" plywood, after drilling a hole (with a recess to handle the flare) in the center of the disk and mounting the disk to the face plate.

Contact cement the cork to the plywood disk and clean out the center to allow air passage down the tube. I used hot glue to seal the edges of the cork so I would not get cork being drawn into the pump.

Turn a cylinder 3/8" larger than your bearing and drill out a recess in it to accept the bearing. Then drill a hole through the center of the block to align with the center of the bearing. Epoxy a short pieces of the brake tube in the block and center of the bearing. Epoxy the outer race of the bearing into the block. (this gives you your slip bearing to isolate the rotation of the lathe )

Mount the filter on the wall and connect the output side of the bearing block to one side and the other to the input of the pump.

Bingo, for just over $100.00 you are up and running with a system that has plenty of vacuum for any size bowl.

Deb