Help Setting Up a Vacum Chuck on a PowerMatic 3520C?

[Aaron Harris]

Greetings-Though it has been and remains an enlightening part of my wood-turning journey to learn a variety of reverse-holding solutions for finishing bowl bottoms, platters and lidded boxes, etc., (Longworth chuck, various home-made friction drives and jamb chucks), I have an order of very nice brushed copper signature medallions with my logo coming to add a touch of class to my bowl and platter bottoms. (If you saw my chicken-scratch efforts with archival ink or pyrography, you would applaud this move lol! And don’t even start me ranting about the cheap Chinese branding iron I got from Etsy!). Anyway, for that to work, I obviously require unimpeded access to bottoms with the tail-stock out of the way to turn the recess for the medallion as a last step, which means a vacuum chuck.


That said, I have never set up anything like this before and don’t have the extensive shop and fabrication experience to know my way around all the component parts like many of you. I have perused websites including this one, and YouTube videos quite a bit, but I’m still confused and unsure how to proceed. I know many of you are old PowerMatic hands, and no doubt some of you have rigged up vacuum systems for the various 3520 models.

I would be grateful for any advice and links regarding components needed for the set-up, assuming I know next to nothing about all of this.

1. Vacuum Pump: I already have an older RobinAir Vacum Master Model 15400 vacuum pump that is rated 1/3hp and 4cfs that I took in trade for stabilizing small blanks that I haven’t gotten around to using(pic attached), as well as a California Air Tools air compressor that is rated at 3.10 CFM at 40 PSI and 2.20 CFM at 90 PSI (so possibly not enough?). I assume if I go with the RobinAir that it needs an intake filter and one for the oily exhaust coming out of the handle hole? Where do I get those? And this may be a stupid question, but does the line from the manifold assembly on the lathe connect to that intake? It generates suction when turned on.
2. Vacum chuck cup: I know I need the actual vacuum cup. I am inclined to spend a bit more for an aluminum/metal model because I hear they run truer with less vibration? If I only have the money to start with one, should I get one about 4-5 inches in diameter? The majority of my bowls and platters are probably between 7 to 13 inches in diameter.
3. Reverse Centering: I know I need an adaptor to flip the chuck around for re-centering. What is the best option for this?
4. Manifold/lathe interface: I know/am pretty sure I need a manifold kit that attaches to the hand-wheel tube with a valve and vacuum gauge.How does it attach, and can I retain the handwheel (which I like and use a lot)? I see what looks like a complete kit on https://www.frugalvacuumchuck.com/home.html. Is this what I need, and does it contain everything needed to attach on both ends?
5. What kind of line and fittings do I need between the pump and the manifold? (Maybe this is all contained in #2 if I just buy the whole kit?).

What else am I not thinking about? I’m sorry for all the questions, but I really have zero experience setting up something like this. As for how much I can spend, I definitely believe in the adage “Buy once, cry once,” though I would also love to economize where possible. I know I can expand cup sizes later if needed.

Thanks in advance for your expertise! My 1st spring craft shows are in March, and I would LOVE to have some nicely-finished bottoms with my copper medallion ready for my table with your help! Aaron

 

[Bob Slocum]

You may already be aware of this.. Robust has a complete kit for the PM.

Vacuum Systems – Robust Tools

 

[Aaron Harris]

You may already be aware of this.. Robust has a complete kit for the PM.

Vacuum Systems – Robust Tools

Thanks, Bob-I was NOT aware of this! I guess I just assumed that Robust accessories were for their lathes. I wonder if I could just call them and order what I need from that menu ala carte without the pump?

 

[Mike Selser]

Thanks, Bob-I was NOT aware of this! I guess I just assumed that Robust accessories were for their lathes. I wonder if I could just call them and order what I need from that menu ala carte without the pump?

It looks like the vacuum adaptor and vacuum hardware kit (plus whatever chuck you want) will get you in business. Any fittings and tubing needed can be picked up at your local hardware store. I would add an inline fuel filter from your auto parts store between the pump and the adaptor. As far as the outlet of the pump I just throw a shop towel over the handle to keep the oil mist from spreading around the shop.

 

[Dave Landers]

Vacuum Pump

You'll want to use your vac pump, not an air compressor. You can get a device to generate vac with a compressor, but its pretty inefficient and since you have a pump....
You can go to the auto parts store and get a fuel filter that'll fit your hose - it's going to be plenty to filter out sawdust. Get a clear one so you can see if it gets clogged.
If your vac pump spits out oil, you might want a filter on that side to control mess.

And yes, you hook up your chuck to the sucking side.

Reverse Centering: I know I need an adaptor to flip the chuck around for re-centering. What is the best option for this?

Live center. When you turn the tenon, leave the mark from the live center - use that to center the bowl on the vac chuck.
You can also get an adapter between your live center (Oneway/Powermatic/Jet style with 3/4x10 threads) and 1-1/4x8 for the chuck. I have one, but rarely use it as the live center point is easy and usually good enough.

Manifold/lathe interface / Fittings

Most folks have a thing with o-rings and bearings that shoves into the hand-wheel side of the spindle. That then relies on the spindle and vac chuck to transmit the vacuum to your bowl.

Between the pump and lathe, you'll want some pipe/tube/hose (obviously).

You'll need a pressure release valve (ball valve - with a quarter-turn handle). Not to shut off the vacuum, but to let it out - so a valve tee'd off the hose going to nowhere. So when the valve is shut the vacuum sucks on your bowl. When the valve is open, it lets air out (and releases your bowl). Feathering the valve lets you control the suckage for adjusting your bowl to center it up or whatever.

A vacuum gauge is handy. Doesn't have to be accurate, just enough that you can glance at it and know if things are good or leaking.
The valve and gauge should be mounted/positioned where you can see the gauge for assurance as your turning, and the valve can be operated conveniently when you're mounting the bowl.

---

For myself, I use the gear from Frugal Vacuum Chuck. Bob avoids the fittings in the spindle and simply passes a tube thru the spindle. I made my vacuum chucks from the bearings he sells - tube goes thru the bearings to get the vacuum in the chuck, without relying on connections to the spindle. All my vacuum chucks are just MDF (or something) and PVC fittings (PVC is easy to true up). So I have several and they[re cheap and easy to make. On the bowl end of the PVC are seals from Rubber Chucky. The thing I like is my vacuum chucks mount in my 4-jaw chucks (don't screw on the spindle) and I've turned several tenons in each (for various jaws) so I can generally just use whatever chuck is already there.

 

[Dean Center]

Dave has given you excellent recommendations. Several additional thoughts:
1. If you can get a brass thingy (?manifold) with 4 male ends, you can connect your relief valve to one, your pressure gauge to a second, your adapter/lathe to a third, and the vacuum pump to the fourth. Neat and complete.
2. You have to decide where in the set up to put your inline filter. Between adapter/lathe and manifold, or between manifold and pump. Both have pros and cons. When deciding, keep in mind that the pressure relief valve can suck in airborne debris. I improved this situation by putting a 4 ' extension tube on the valve, so the air it brings in is farther from the lathe/saw sources of airborne smuck.
3. I use an inexpensive auto fuel filter with the right size jam in connections for the size poly tubing I use (probably 3/8", but could be 1/4") Buy an extra one, because eventually the filter will collect enough debris that you will have to replace it, and have the right one on hand. Clear plastic, as Dave suggested.
4. If you're thinking of commercially made vacuum chucks, look at the Odd Not system. It does not require a separate, potentially expensive adapter, but has a means of connecting to vacuum without one. (I have not used, so this is based on promotional materials)

 

[Dave Landers]

FWIW - this is my valve/gauge assembly (from the back side). It's on the strut channel above the lathe so I can easily reach the valve and see the gauge.


It's gas pipe fittings because that's what was in the junk drawer. The vacuum from (to?) the pump is copper because it made it fit neater on the strut. The other end of the hose is clipped to the strut when not in use.

This is the pump. It's up high on the wall (near the end of the strut) so its out of the way.


And my vacuum chucks look like this.

Several tenons for various chucks. That pipe goes thru the base of the chuck and into a bearing that lets things spin.


The other end of the pipe (handwheel side of the headstock) just pushes into the hose from the valve/gauge assembly.

 

[Jim Reynolds]

I find Doc Green’s explanation of how to build a vacuum chucking setup in his book helpful.

He also has a website with many informative articles.

 

[Jim Reynolds]

If you're thinking of commercially made vacuum chucks, look at the Odd Not system. It does not require a separate, potentially expensive adapter, but has a means of connecting to vacuum without one. (I have not used, so this is based on promotional materials)

Odd Not uses the same technique Dave showed above. Tube friction fit inside a bearing.