Rotary vacuum adapter for vacuum chuck setup

[Bill Boehme]

Larry, very nice design. Tell us more about the shaft seal please!

Shaft seals are a necessity to stop leakage and to prevent the grease from being sucked out of the bearing. They are disk shaped rubber seals with a spring that provides a tight seal around the shaft. They go on the high pressure side of the bearing. Also a rotary coupler needs at least two bearings to prevent deflection between inner and outer races. The JT rotary coupler meets these requirements. From their description, I would guess that the Craft Supplies unit doesn't ... their description says bearing which sounds like one bearing to me.

[Larry Copas]

DSCF9025.JPG

Running at 1,000 rpm on my General 260-20.

Rotary shaft seals are commonly available that will hold 10 psi at the speeds we would be turning with a vacuum chuck installed. Heavy duty seals are available that will hold 50 psi. The problem is finding the right size at reasonable cost.

Anybody might note the hose ring is a 1/2" pex fitting which works great on 3/8" braided vinyl hose. Lots better than a hose clamp and I think it looks professional.

[David C. Roseman]

DSCF9025.JPG

Running at 1,000 rpm on my General 260-20.

Rotary shaft seals are commonly available that will hold 10 psi at the speeds we would be turning with a vacuum chuck installed. Heavy duty seals are available that will hold 50 psi. The problem is finding the right size at reasonable cost.

Anybody might note the hose ring is a 1/2" pex fitting which works great on 3/8" braided vinyl hose. Lots better than a hose clamp and I think it looks professional.

Larry, thanks for the followup pic; pls disregard my earlier questions. I see now how your setup is assembled and mounted, using the OEM handwheel. Very nice job.

[Alan Heffernan]

Larry,
I am familiar with oil and grease seals used on shafts. Does the one you use require lubrication to avoid premature wear? Is it a "lip seal"?

[Bob Bouis]

Also a rotary coupler needs at least two bearings to prevent deflection between inner and outer races.

From the weight of the vacuum hose? Usually people say they use two bearings because it reduces air leakage through the bearings.

[Larry Copas]

Larry,
I am familiar with oil and grease seals used on shafts. Does the one you use require lubrication to avoid premature wear? Is it a "lip seal"?

It is called a lip seal I think. According to Parker a seal without lubrication will fail in a few hours. I packed the recess of the seal with grease. No idea if it will work but plan to pull it apart after running it for a substantial time to check for wear. Since both of my bearings are also sealed the extra seal may not have any or little effect on operation of the adapter.

[Alan Heffernan]

I am putting together a vacuum chuck system for my PM3520A and have a Gast vacuum pump on order. I am now trying to decide which rotary vacuum adapter I should get.

Is the rotary vacuum adapter sold by Craft Supplies that they call "Precision Machine Rotary Vacuum Chuck Adapter" the same as sold by JT Turning Tools? Here are a couple of photos of the Craft Supplies offering.
Attachment 343418Attachment 343419

After the great responses and shared experience here, it is obvious the adapters sold by JT Turning Tools and Craft Supplies are not the same. Your responses have helped me dig deeper into this hardware and the differences in offerings and options out there.

From the suppliers descriptions:
1. JT turning Tools uses two separate sealed ball bearings and it is "assembled with a special, proprietary sealing system installed between the bearings".
2. The Craft Supplies unit uses one double row, dual thrust sealed bearing. (This is effectively two sets of bearings in one housing).

In terms of seals, beit bearing or shaft seals, they need lubrication. The seals on the bearings in question get it from the lubrication that they come with from the factory. Seals are used to keep the lube in and debris out. As we know, seal failure is what typically kills a bearing. The seals go, the lube is lost and/or they get debris inside.

I spoke to a knowledgeable engineer and he reminded me that the seals on a bearing have some capability to resist pressure and encouraged me to dig into the specs on the specific bearing used. He owns several high vacuum systems for his R&D and prototype development work. Of course his systems are very expensive, often have multiple pumps and require far more attention than what's needed to provide my hope to spin a piece of wood. But it is interesting to talk to him and ponder this topic.

Of course I do not have the specifics as to the actual bearings being used in the Craft Supply unit, other than it's a double row, dual thrust bearing.

So that leads me to my current assumptions. I assume that the seals on the double throw, dual thrust bearing that the Craft Supply unit uses can handle a fraction of one atmosphere of external pressure. From the photos on the Craft Supplies site, the effective surface area of the outboard seal does appear to be relatively quite small and therefore would suffer less deflection due to the external pressure created by the partial vacuum. I have no idea what the inboard seal looks like.

Bottomline, the relative simplicity and low cost of the Craft Supply unit make it attractive to me for a trial. When I lay hands on one and time allowing, it will be fun to dig deeper into the specs on the actual bearing used.

[Jeramie Johnson]

Jeramie, Tom has a good setup for the G0766. I think the first G0766 he made one for was mine last year. Here's the review I did then, with pics. http://www.sawmillcreek.org/showthre...6-(and-others)

Thank you for redirecting me to your review. Very much appreciated.