Vacuum Chuck holding

[William Rogers]

I have never used a vacuum chuck, but decided to build a system as I had a Thomas pump. I rebuilt the pump and it pulls 29" Hg stand alone. My lathe is a PM 90 and there are no off the shelf chucks. Long story short my system pulls 19" Hg when I have a flat 8-9" board mounted on my 4" pvc style chuck. I think this is about 500 lbs force. It seems to hold well and I did run the lathe at 800 rpm with no problem, but no tool to the wood. I can only speculate the leakage my be through the bearing. Cheap bearing from supply house. My questions are how much vacuum is necessary and should I be looking at better bearings? Bearing suggestions? Since it is homemade I can see a design improvement, but if leaking through the bearing no help.

Thanks, Bill

Edit: I am using 2" hard maple for my chuck and rotary adapter. Should I be using different material?

 

[hockenbery]

You system will probably hold most bowls for finishing the bottoms this is light turning.
You can use tailstock support for a while then turn off the last bit,which is almost no pressure on the work.

Not enough vacuum to hold a ball for hollowing which puts a lot of force on the ball.

Some woods are going to leak a lot.

Too much vacuum is going to break thin turnings.
I don't watch the gauge on bowls but increase vacuum until the bowl pulls away from the tailstock about a 1/16". Then I try pulling on it as test.

Be sure your chuck is not leaking.

The pvc chucks I have, I made by turning a slight concave in 2" stock to make a tight fit with the rim of a faceplate. Mount the faceplate with screws run in halfway use pilot holes.
Remove faceplate put two circles of hotmelt glue on the faceplate one inside the screwholes one outside. Press in place a run in the screws. I use a dab of hotmelt overe each screw and around the edge of the faceplate. True the wood, drill a hole, seat the pvc in a grove made with a parting tool. Seal the outside and inside edge of the groove and pvc with hotmelt.
True the edge of the pvc. Rounding the outside edge will make it take longer to cut through the foam I use.
The edge of the wood should be sealed too. Duct tape is quick, effective, and slightly ugly.

 

[hockenbery]

Also oneway makes a rotary vavum adpter that will fit the outboard sof your lathe.
I have one I use on a General that has 1 1/8 x 8

 

[Dwight R Rutherford]

I have never used a vacuum chuck, but decided to build a system as I had a Thomas pump. I rebuilt the pump and it pulls 29" Hg stand alone. My lathe is a PM 90 and there are no off the shelf chucks. Long story short my system pulls 19" Hg when I have a flat 8-9" board mounted on my 4" pvc style chuck. I think this is about 500 lbs force. It seems to hold well and I did run the lathe at 800 rpm with no problem, but no tool to the wood. I can only speculate the leakage my be through the bearing. Cheap bearing from supply house. My questions are how much vacuum is necessary and should I be looking at better bearings? Bearing suggestions? Since it is homemade I can see a design improvement, but if leaking through the bearing no help.

Thanks, Bill

Edit: I am using 2" hard maple for my chuck and rotary adapter. Should I be using different material?

Here is a graph that will help determine holding force.

 

[Leo Van Der Loo]

The Oneway vacuum chucks do come with a taper lock adaptor like their regular chucks, so they would have one for your PM90

 

[William Rogers]

Dwight, thanks for the graph. For some reason I divided the psi conversion into the in. Hg. So the real holding force is 117 lbs. for a 4" chuck at 19 in. Hg. However looking at the graph there is a significant increase in force with a 6" chuck. I'll most likely build that in addition to the 4".

Hockenbery, Leo. I didn't know Oneway had chucks and adapters to fit my lathe. However I am going to see if I can get better performance. I can isolate the adaptor and check if that is where the majority of the leakage is. I know I can make improvement in that area. If I can save money and then I can buy more Thompson and D-Way tools that I would like to have. If I can't make a decent chuck or adaptor, then I will have to go the Oneway route. I'll do some work today and post later. My target of 24" in. Hg. seems reasonable giving me a 150 lbs force for a 4" chuck.

 

[Vern Crandell]

Just a couple of things William. A perfect vacuum at sea level is about 29 inches of Hg and that decreases as you go up in elevation, so you may not be able to achieve the 24 inches you are looking for. I run the Oneway system on my lathe at 20 inches on a 3 inch or 5 inch drum and have had no problems with things moving if you take light cuts. Also, remember to cut more towards the headstock, that is, try not to cut at 90 degrees to the ways as the piece can slide on the chuck if too much sideways pressure is exerted.

 

[Bill Boehme]

Yes, there can be considerable leakage through the bearing(s) in the rotary adapter especially if there is only a single bearing. Ideally, the rotary adapter should have at least two bearings with shaft seals on the high pressure side of each bearing.

With a single bearing adapter, the other problem that you will have besides considerable leakage is loss of grease in the bearing.

You will also discover that there will be a considerable amount of air flowing through the wood, especially on ring porous species. The other source of leakage is the seal on the lip of the vacuum chuck.depending on your design there could also be leakage between the chuck and headstock spindle. It would be a good idea to include a bleed valve as an intentional leakage when turning thinner pieces.

Always keep the tailstock against the bottom as long as possible.

 

[hockenbery]

Hockenbery, Leo. I didn't know Oneway had chucks and adapters to fit my lathe. However I am going to see if I can get better performance. I can isolate the adaptor and check if that is where the majority of the leakage is. I know I can make improvement in that area. If I can save money and then I can buy more Thompson and D-Way tools that I would like to have. If I can't make a decent chuck or adaptor, then I will have to go the Oneway route. I'll do some work today and post later. My target of 24" in. Hg. seems reasonable giving me a 150 lbs force for a 4" chuck.

Check the loss from the headstock without a chuck on the spindle.
Put something over the spindle that will seal it. (A little foam on a small square of plywood.)
I do that to check the plumbing which includes the rotary adapter.


I make all of my own chucks.

 

[William Rogers]

Bill. That is where I am headed. I bought two bearings, but only used one. I am using a threaded rod between the chuck and rotary adapter. Initially I terminated inside the faceplate I am using. I am now going to terminate inside the chuck. I'll seal the wood with sanding sealer from the outside under vacuum and then also seal the inside. If things work where I can get a decent vacuum I'll post pictures, else Oneway.

 

[Tom Gall]

Bill. That is where I am headed. I bought two bearings, but only used one. I am using a threaded rod between the chuck and rotary adapter. Initially I terminated inside the faceplate I am using. I am now going to terminate inside the chuck. I'll seal the wood with sanding sealer from the outside under vacuum and then also seal the inside. If things work where I can get a decent vacuum I'll post pictures, else Oneway.

William, as a test for leakage of your rotary adaptor just put the palm of your hand over your spindle. Take a reading on your gauge. Or, just put your thumb over the opening on your adaptor while it’s not mounted on your lathe. To test your chuck - take your piece of wood out of the equation. Use any non-porous surface such as a piece of acrylic or a plastic dinner plate, or whatever. The difference in the gauge reading should inform you if there is a problem with leakage in the chuck. If it’s only a nominal amount that would be acceptable in most cases.

I would recommend eliminating the cumbersome lamp rod tube between chuck and adaptor (unless you have a hole somewhere in your spindle – most lathes don’t). Put a short piece of lamp rod (2-3”) on your adaptor – cover with a piece of 3/8” ID vinyl tubing (the reinforced tubing with embedded nylon threads works well) – and just slide this into the outboard end of the spindle. You can fine-tune the fit by adding a little tape (if too small) or some judicial sanding if too tight. Easy in ~ easy out! BTW – if you don’t want to make your own rotary adaptor check out Craft Supplies – they now have an adaptor that uses O-rings that works in the same manner as above for about $65, as I recall.

I have been using vacuum chucking for 23 years now and all my adaptors have only had one bearing.

 

[William Rogers]

Well, it is the wood leaking. I tried the duct tape and saw a 1-2" rise to about 21", telling me there was some leakage through the wood. I redid my rotary seal wood block and without the bearings I started pulling a vacuum and again reached 19". So I mixed a 50/50 shellac and started applying to the wood with the vacuum still running. There were two areas where it seemed to dry immediately. After a few coats the vacuum pump started loading more and it went to 28". Turned the vacuum off and there was shellac in the cavity. It pulled the shellac through the hard maple 2 1/2". I would have never thought I was loosing 30% of my vacuum through the wood. I also my sealed my chuck wood the same way.

Tom, thanks for the suggestion. I was going to redo the lamp rod, but now that I have identified the major source of the problem I will try without. I have an extra outboard faceplate to use for my rotary adapter. The only new source of leakage would be the threads of the faceplate of the chuck. I could always put a plastic washer on the spindle for that. Lot simpler without the rod. I will seal and glue everything together tonight and run a test tomorrow.

This tells me I may need to wrap or seal hollow forms when putting on the vacuum chuck. What do you all do?

 

[Bob Ballard]

I have two early (1660s) powermatic 90 and both have a thru hole in the spindle where a woodruff key slot was cut.I believe its the key for the spindle lock

 

[William Rogers]

Thanks Bob, mine is a '73. I'll check tomorrow before installing the chuck. I don't think the parts list will tell me anything. I may need the rod.

Edit: well the parts diagram doesn't show one. Easy check tomorrow.

Thanks

Bill

 

[Bill Boehme]

I have two early (1660s) powermatic 90 and both have a thru hole in the spindle where a woodruff key slot was cut.I believe its the key for the spindle lock

Wow, I didn't know that Powermatic made lathes back then. Surely you don't mean that a key slot was cut on the inside of the hole through the spindle ... or, do you? I have never seen a Powermatic 90 in person so I am just guessing.

 

[Leo Van Der Loo]

Well, it is the wood leaking. I tried the duct tape and saw a 1-2" rise to about 21", telling me there was some leakage through the wood. I redid my rotary seal wood block and without the bearings I started pulling a vacuum and again reached 19". So I mixed a 50/50 shellac and started applying to the wood with the vacuum still running. There were two areas where it seemed to dry immediately. After a few coats the vacuum pump started loading more and it went to 28". Turned the vacuum off and there was shellac in the cavity. It pulled the shellac through the hard maple 2 1/2". I would have never thought I was loosing 30% of my vacuum through the wood. I also my sealed my chuck wood the same way.

Tom, thanks for the suggestion. I was going to redo the lamp rod, but now that I have identified the major source of the problem I will try without. I have an extra outboard faceplate to use for my rotary adapter. The only new source of leakage would be the threads of the faceplate of the chuck. I could always put a plastic washer on the spindle for that. Lot simpler without the rod. I will seal and glue everything together tonight and run a test tomorrow.

This tells me I may need to wrap or seal hollow forms when putting on the vacuum chuck. What do you all do?

Bill watch putting sealers on the wood or anything else while running the Pump, you do not want sanding sealer or shellac or anything else you put on, in your pump.

 

[Bill Boehme]

Bill watch putting sealers on the wood or anything else while running the Pump, you do not want sanding sealer or shellac or anything else you put on, in your pump.

Not to mention that it will also gum up the inline filter that is keeping the wood dust that is being sucked through the wood from getting into the vacuum pump. I'm glad that you mentioned that, Leo. On the positive side, it's a great science experiment to see things coming through what we think of as a solid. There's also other stuff in the wood like water and sap and whatnot that the filter is keeping out of the pump.

 

[Bob Ballard]

Bill, The slot is cut on the outside with a circular cutter.The woodruff key is 1/2 moon shaped.approximately 1/3 of the circular slot is thru cut to the inside.

 

[Bill Boehme]

Bill, The slot is cut on the outside with a circular cutter.The woodruff key is 1/2 moon shaped.approximately 1/3 of the circular slot is thru cut to the inside.

Thanks for clearing that up for me.

 

[Leo Van Der Loo]

Bill, The slot is cut on the outside with a circular cutter.The woodruff key is 1/2 moon shaped.approximately 1/3 of the circular slot is thru cut to the inside.

I bet using loctite you can glue the woodruff key in and make it airtight in that manner

 

[William Rogers]

A quick check and the spindle is not air tight. I didn't look, but I speculate Bob is correct in the slot being through the spindle. So back to plan A.
Leo and Bill, I was careful when applying the sanding sealer. I had a piece of clear sacrificial tubing to monitor any sign of shellac going to the pump. The whole process was less than a minute.
I checked the rotary bearing assembly and it was sealed with no leakage. However first try with the chuck and no improvement. The leakage was where the threaded rod went through inside the chuck. The final solution was to put a piece of foam gasket held in place with a fender washer drilled for a tight fit to the threaded rod and held in place with a nut. I then was able to get 28" Hg with a piece of plexiglass. I'm not going to much better than that. I'll just use a new gasket each time. I can make 50 from one sheet of foam. Now I can get back to turning.

 

[Fred Belknap]

I recently did a bowl with 3/16" worm holes in the bottom. I put duct tape on the inside and then plugged the holes with silly putty. Worked good, when I got the bottom done I blew the silly putty out with air pressure.

 

[Bill Boehme]

I bet using loctite you can glue the woodruff key in and make it airtight in that manner

As long as you don't ever need to remove it. I suppose that it is holding the pulley

 

[Leo Van Der Loo]

I don’t remember if the bearing has to go over that part of the spindle, I don’t think so, but I’m not sure of that, for the pulley the key just has to sit tight into the slot, the pulley can be removed or installed that way.

But if removal of the key ever was needed, with some heat that would be easy to do.

 

[Bob Ballard]

Leo, That Sounds like a good idea.When I change bearings,I will give it a try.

 

[William Rogers]

Leo, I looked at that and maybe when/if I need to change bearings I might try it. It will introduce more points for leakage such as the spindle and tailstock threads. The key is holding the spindle lock ring on the spindle and to access it you need to remove the rear reeves and speed dial. Not major, but some work. Using the lamp rod is not that big of deal for me. I have an extra outboard faceplate that the rotary assembly will remain on. Setting up is really no more than threading the lamp nut at the chuck. This is a picture of the rotary adapter and chuck. The wooden MT 2 is just to keep the lamp rod centered. The seal on the chuck is cut from toilet plunger. Seems to work for a 4" chuck. I looked at a 6" size chuck and that seemed way to big. I'll see how just the 4" works for now before making any more. Maybe a 5" and 3". Also in the picture is the extra outboard faceplate. Right now I have a ball valve shut- off, but may need to get a needle valve. The system will pull 28" with a piece of plexiglass on the chuck. I know this will drop because of wood leakage in use, but it will be because of the turning chucked and not the system.

 

[Leo Van Der Loo]

Leo, I looked at that and maybe when/if I need to change bearings I might try it. It will introduce more points for leakage such as the spindle and tailstock threads. The key is holding the spindle lock ring on the spindle and to access it you need to remove the rear reeves and speed dial. Not major, but some work. Using the lamp rod is not that big of deal for me. I have an extra outboard faceplate that the rotary assembly will remain on. Setting up is really no more than threading the lamp nut at the chuck. This is a picture of the rotary adapter and chuck. The wooden MT 2 is just to keep the lamp rod centered. The seal on the chuck is cut from toilet plunger. Seems to work for a 4" chuck. I looked at a 6" size chuck and that seemed way to big. I'll see how just the 4" works for now before making any more. Maybe a 5" and 3". Also in the picture is the extra outboard faceplate. Right now I have a ball valve shut- off, but may need to get a needle valve. The system will pull 28" with a piece of plexiglass on the chuck. I know this will drop because of wood leakage in use, but it will be because of the turning chucked and not the system.

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Whatever works for you is the way to go William, most turners use a very thin foamy as a seal, as thicker seals introduce wobble and give the project the ability to move around because of the flexible seal.

 

[William Rogers]

Leo, I didn't think about movement of the turning with the thicker rubber seal. I'll use the thin foam instead of the rubber.

Thanks

 

[Dwight R Rutherford]

William,
I may have missed it in your posts but do you have a bleeder valve in your set up? Important as you can have a thin turning implode. Not pretty but here are chucks made with PVC and closed cell seals.