Ever use both the Oneway and Holdfast chucks

[Raul McCai]

Hold fast is polymer
Oneway is all alum'
Had a chance to compare and contrast?

I've never seen either in person.
How about heir rotary adaptors heat ? Leaks? seizing?

 

[Odie]

I have three of the Oneway Stronghold chucks.....and none of them are aluminum......

Has something changed with their production?

 

[Raul McCai]

Vacuum chucks, I failed to provide the context.

 

[Tom Gall]

Hold fast is polymer
Oneway is all alum'
Had a chance to compare and contrast?

I've never seen either in person.
How about heir rotary adaptors heat ? Leaks? seizing?

The Oneways are beautiful chucks … I have two. But they are very expensive and probably overkill in most situations. I have at least a dozen homemade chucks (various diameters and lengths) made from PVC fittings and/or pipe (both Sched. 40) mounted to MDF or PVC sheet material. Best to use a dedicated faceplate for the chuck.

Re: rotary adaptors …… never had a problem. It may get a little warm with extended use (several hours), but nothing to worry about. Never heard of one seizing up! I purchased my first rotary adaptor (only one available back in 1994) and used it for about 20 years (still works). Then I made one (cocobolo) using a larger bearing and have been using it ever since.

PS - I know you have the equipment and machinists knowledge (I've seen your hollowing rig) to make your own that will be as good, or better, as anything purchased.

 

[Raul McCai]

PS - I know you have the equipment and machinists knowledge (I've seen your hollowing rig) to make your own that will be as good, or better, as anything purchased.

Awww shucks, you may have shamed me into doing it,
I'll use the $$ I save toward a California Toold compressor
There, I feel better already.

 

[Bill Boehme]

If you decide to roll your own rotary adapter, use at least two bearings and use shaft seals to prevent the grease from being sucked out of the bearings. Precision machining is critical and after all is said and done, you can go to JT Turning tools and buy a rotary adapter made to work specifically for your lathe Powermatic 3520 for a reasonable price. I have built several of my own rotary adapters and there is an expensive learning curve based on doing things the wrong way and gradually learning what is the right way.

 

[Fred Belknap]

Have the HoldFast 6" and 3". As they come from factory the will leave compression rings in the bottom of you bowls which is hard to get rid of. I tried the Rubber Chucky thing and they don't fit very good and glue doesn't stick to the rubber very well. The stick foam from Walmart does a good job but doesn't last very long. I have the JT Turning adapter and it has worked great for several years.

 

[Raul McCai]

to prevent the grease from being sucked out of the bearings

For that to happen would not the bearing need to be in the direct line of a high flow rate of atmosphere? My vacuum pump won't draw fast enough to move grease unless I establish a vacuum and then pop the seal upstream of the greased bearing The inrush on such an event may move some grease but not much and especially not on a sealed bearing. I can't see any other way.

I can see the wisdom of two bearings an inch or so apart. That would be useful to take up the moment arm of load (angular loading on a torque arm) that the plumbing and valve (and especially when the operator cranked the valve) might generate.

 

[Bill Boehme]

For that to happen would not the bearing need to be in the direct line of a high flow rate of atmosphere?

Incorrect assumption. There will be a vacuum on one side of the bearings and atmospheric pressure on the other. The rubber labyrinth seal on each side of the bearing does not hermetically seal the bearing ... not even close. The grease will be sucked out in short order. If you don't know what shaft seals are, they are disc seals that have a coil spring to hold the seal tightly around a shaft. They go on the high pressure side of a bearing to block the loss of grease. Of course, if you have a NASA budget you could get aerospace greaseless bearings.

You need at least two bearings because there is a radial load on the hollow axle that connects to the vacuum line. That load translates into a force that twists the inner and outer bearing races out of alignment and also forces open the labyrinth seals. Even without loss of grease this would lead to early failure of the bearing. Beware of low cost rotary adaptors on the market. I have seen some that have only one bearing.

You mentioned the low flow rate of your vacuum pump which indicates it may not be suitable for this application. Ideally, your vacuum pump should pull a blocked port vacuum of 26 inches of mercury or better (that's approximately-13 PSI) and have an open port flow rate of 4.5 CFM or better. A vacuum pump that can pull a blocked port vacuum of 20 in-Hg and an open port flow rate of 3 CFM should be adequate in almost all situations. The reason for the high flow rate requirement is that vacuum chucking involves lots of leaks. Air leaks between the chuck seal and the wood, most of the leaking is air flowing directly through the wood (wood is porous), there is some leakage between the vacuum chuck and the spindle nose, there is some leakage around and through the rotary adaptor, and there is a bleed valve that is necessary to regulate the vacuum applied to the turning (we don't want to implode a thin walled piece). Each of these leaks will reduce the maximum vacuum that your pump is able to pull.

 

[hockenbery]

Got to remember it the whole earth pushing on the outside?

 

[Bill Boehme]

When it comes to picking a lip seal for your vacuum chuck, you are faced with satisfying conflicting requirements. A thick soft seal will work better to seal bowls that have warped slightly, but as vacuum is increased, the bowl will invariably squirm out of alignment and give you fits in getting it aligned as you want it. A thin firm seal solves the squirming problem, but is unable to establish a seal if there is any warping. I have found a compromise that is satisfactory for my needs. It is a door seal with a hollow teardrop cross section. It forms a fairly firm seat that doesn't squirm and for oval shapes it forms a flap seal which I believe is much better than trying to get a compression seal. The bad news is I haven't been able to find the same door seals recently.

 

[hockenbery]

The hold vs the turn well also extends to chuck material.
I have several vacuum chucks made from sona tube the cardboard concrete forms and from cardboard fabric rolls. These also make terrific shipping containers when double boxed.

The cardboard flexes a bit to accommodate oval shapes. It also flexes a bit under a heavy cut so light cuts are required.

 

[Tom Gall]

For that to happen would not the bearing need to be in the direct line of a high flow rate of atmosphere? My vacuum pump won't draw fast enough to move grease unless I establish a vacuum and then pop the seal upstream of the greased bearing The inrush on such an event may move some grease but not much and especially not on a sealed bearing. I can't see any other way.

I can see the wisdom of two bearings an inch or so apart. That would be useful to take up the moment arm of load (angular loading on a torque arm) that the plumbing and valve (and especially when the operator cranked the valve) might generate.

I don't think that two bearings is necessary……might be nice, but not totally necessary. My first rotary union (the E-Z Vacuum Adaptor - still available from Packard Woodworks, I believe) only had one bearing and the two I've made since only have one sealed bearing. Never had a problem with the grease being sucked out because the vacuum is being pulled through the ID of the bearing with attached fitting. However, I would recommend a support for your hose (piping, whatever), even if it's just a string tied to the ceiling or a support from the floor to avoid any downward pressure on the inner race of the bearing.

See pg. 7 of Carl Ford's PDF (below) for info on making your own rotary union as well as some other useful information.

BTW - don't use the full length of lamp rod through your spindle….that's just a pain in the neck. All you need is about 3" of rod protruding - covered with some plastic tubing (⅜" ID I think - the braided reinforced type works well). Just insert into the spindle from the outboard side. You may have to add some tape to increase the diameter a little to fit your spindle.

http://mkmk.com/swiwt/PDF/Vacuum_Chucks_Demo2.pdf

 

[Raul McCai]

here will be a vacuum on one side of the bearings and atmospheric pressure on the other. T

Yah but, pressure Atmospheric pressure is not the same thing as rate of flow. To move anything one would need a high flow rate. Can't get that with a small pump. I'm drawing on my years spent managing an ultra high vacuum physics laboratory here when I think that merely having air moving across the lubricated surfaces at the very slow flow rate that a vacuum pump is capable of generating won't dislodge much of anything. I'd pump a chamber down to a near perfect vacuum and then start going after the molecules floating inside. After the conventional pumps down to about -760 Torr. We'd use diffusion pumps, Coldfingers and turbomolecular pumps pumping for hoiurs to get to regimes like 3 or 4 times 10 to the negative power of 14 Torr (it's all in BAR now) and believe me there was never a rush of air. Not at the beginning not at the end.

Now if we were talking about putting a bearing in the path of the DC flow rate that'd be another fish.
Well, I believe I shall find out in real time. Bearings are cheap.

 

[Bill Boehme]

I understand your need to verify what they say about electric fences. I have done thr same thing myself.

The flow through the bearing depends on how well it is sealed which is why I recommended shaft seals.

The E-Z Vacuum adapter takes a different approach by making it part of the chuck body. That means each chuck would need it's own rotary adapter. Based on my experience of building a similar system as my first vacuum chuck, hooking it up is more time consuming than the quick plug-and-play separate rotary adapter that just slides into the spindle hole on the handwheel side of the headstock.

Keep us posted.

 

[Raul McCai]

slides into the spindle hole on the handwheel side of the headstock

That's the approach I intend - - after I confirm that my head stock spindle doesn't have any holes in it. Can't see why it would, but ~ ~ ~
I may drill and tap a couple holes in the hand wheel to fix the adapter in place. I'm tempted to make it from Acetal and not aluminum. I love how acetel machines.

 

[Bill Boehme]

If your lathe is a Powermatic 3520 then the spindle is all one piece. My first lathe, a Delta 1440, had a two piece spindle o I had to have lamp rod. To carry the vacuum connection across.