Vacuum chucking, advice request

[Jon Murphy]

I would like to set up a vacuum chucking system on my midi lathe, but I have limitations on space, finances and noise. I have done my research, but I'm still confused. As I'm of a basically disorganized mind I'll give my background and current set-up in "choppy" paragraphs.

Apparently the Aussies use a high volume/low speed system which uses a shop vac for the vacuum source, whereas in NA we tend to use the low volume/high speed of a vacuum pump. I'm aware of the "bleed" requirement of the shop vac system. Most vacuum systems use a connection to the outboard end (the handwheel) of the lathe spindle, but I've seen pictures (not at vendors) of a vacuum attachment at the inboard end of the spindle (although I can't picture how that works).

My lathe is a PSI Turncrafter Commander 12" swing (by 18" spindle capacity). I believe that the hollow spindle is "solid" and would take the vacuum, the hollow is 3/8" and the spindle is 1" x 8 tpi. My floor space is fully occupied (band saw, drill press, work bench, slow/wet grinder, shop vac, dust collector (rolling platform, 25" x 15" footprint), belt/disc sander and VS 6" grinder (both on pedestal mounts), and cabinets and storage boxes under the lathe and work bench. As this shop is in my bedroom (12" x 15"), and I need half of the bedroom to live in, I'm pretty much at the limit in adding equipment. BTW, for those interested there is an article in the April 2010 (I think) issue of the on-line Highland Woodworking news with pictures on my Bedroom Shop.

My work is bowls and hollow forms, with the hollow forms (a la Ellsworth) being my specialty. Most of my work is with small diameter pieces - although I do turn bowls of up to 10" in heavy wood. I have no problem remounting them, I'm doing fine with jam chucks and extension jaws. (Actually not true jam chucks, I use padding and the support of the tail stock). I also turn "large" hollow forms, up to about 8". Oops, got to insert a point here. I'm 75 and have a prosthetic leg - that means that most of my work is with the smaller forms as it easier for me to collect that wood, the lathe is capable, and I'm willing, but the flesh is weak.

Given that last, I'm putting most of my efforts to small hollow forms - I'm not quite down to David E's one inch "spirit forms", but I'm down to an inch and a half with a half inch "hole". And this is why I'm looking into vacuum chucking. On a large form the slight wobble in the reversing to clean the base with a jam chuck and tail stock is not much of a problem, the vagaries can be sanded off without much change in the wall thickness. But in the very small forms with thin walls the wobble is a problem, the same absolute wobble is a greater percentage of the piece. I realize that there is a problem with aligning with a vacuum chuck - but with the jam chuck one is adjusting two parameters - the form in the chuck and the placement of the tail stock center. I think it would be easier to get accuracy with the single "support".

My ideal would be to have a vacuum chucking system that would run off my shop vac (5 HP with 1 1/4" ID hose), or off my dust collector (850 cfm through a 4" hose, which I can reduce with connectors). It would be nice if it could hold larger pieces, but not important. The basic goal is to hold small forms with thin walls (and I'm aware of the problem of porosity with thin walls). A side issue, I make my jam chucks from layers of wood (some dried maple, some 3/4 5 ply) and tap them for the 1 x 8 spindle. I would expect to the the same with vacuum chucks (but not using the ply). Any thoughts welcome.I am aware of the venturi type vacuum systems, but as I don't have an air compressor I left that out as an option. I have no other need for an air compressor, so if I were to go the route of adding a "machine" I'd probably add the vacuum pump instead, but at about $400 for the pump I'd really like to avoid that.

OK, that was a long one - but what can you expect from someone whose domain name is MurphSays Perhaps a budget vacuum system would be impractical for me, and if so please tell me. Joe, of Veneer Supplies, has kits for the vacuum connections - and it was he that suggested I come to this site when I asked him the same set of questions. I picture a system with a connection at the outboard end of the spindle, a pressure gauge and a bleed valve, and connected to either the shop vac or the dust collector. The standard measures of vacuum, inches of mercury, etc., may not apply in the same way to the capture of veneer, the holding of a large piece, and the holding of a small form - but then again they may.

Best, Jon

[Jon Murphy]

Oops, somehow in editing I ended up sending the HTML version which is nearly unreadable. I'll ask the adminstrator if this can be reformatted to be readable.

Best, Jon (Murphy)

[Tim Thiebaut]

I read through it ok Jon, just took me a few minutes, I know nothing about this myself, but am very interested to hear the input you get from others, I have a small lathe and would like to look into a system for my Jet 1220vs at some point to, its on the list of things to do along with many other things...so any info collected here is of interest to me as well.

[John Keeton]

It seems to me that you just need to build a pump style vacuum system and then design some chucks that are unique to your work. Getting the vacuum to the headstock is a pretty universal need - it is the ability to adapt the vacuum source to the type of pieces you do that is the issue. There are multiple threads on the creek on vacuum systems, but chucking for your needs seems to be just a Beall tap for your spindle size (1" x 8tpi?) and some scrap wood and foam seal.

Keep in mind that the holding power of the vacuum is related to surface area. There would be very minimal holding power for an article only 1.5" in diameter - even with non-porous walls. I suspect nearly every form with walls less than 1/8" will leak some unless heavily sealed.

From what you have related, I would think some form of mechanical mounting might be preferable to vacuum.

As for being able to use your DC system or shop vac, I can't answer that, but doubt it would work. I think the DC system relies on volume of air - the shop vac, not sure on that one.

[Alan Zenreich]

A very interesting shop you have there. By the way is was April 2009 newsletter (http://www.highlandwoodworking.com/woodnews/2009april/bedroom.html)where you showed your shop.

[Alan Zenreich]

Jon,

I agree with John, using a vacuum with small pieces can get tricky.

This is one of the cases where a shopvac type setup works better than a vacuum pump, but I'm not sure.

I tried using my Gast pump setup as an attempt to remount 1" solid sphere the other day, but there wasn't enough "grab" to make it viable for remounting.

Jon, if you find your way north (I'm near Paramus) and want to try your style on my configuration, it would be my pleasure to have you visit.

[James Combs]

Jon, I found a vacuum pump at a local pawn shop and put together my own system. You might take a look at this thread and see if helps. http://www.sawmillcreek.org/showthread.php?162882-My-New-Vacuum-Chuck&highlight=

I tried you use stuff I had laying around so my investment was probably less then $150 with a $100 of it being the pump.

As to using your shop vac or shop dust collector be advised that the vacuum pressure for either of these devices is measured more in inches of water then inches of mercury meaning they have considerably less vacuum then a vacuum pump. For your small items you will need as much vacuum as you can get. Most of us get by with something around 18" to 26" of mercury vacuum but you will probably need to be in the high 20's to hold those small pieces.

[Russell Badders]

I use a system I put together from JT Turning. Works well on my small Jet and on my larger Powermatic.

[Jon Murphy]

First may I thank John Keeton for cleaning up my HTML mess - I'm curious as to my goof in editing out the typos that resulted in that mess. I used the "preview" then edited in that page, then saved.

I thank you all for your help, I think I've gotten the "word" that the shop vac/DC solution isn't a good one - although the Aussies seem to like it. Alan's comment on "grabbing" a 1" solid ball emphasizes the need for a strong vacuum for a small piece, something I was aware of. I mentioned that David Ellsworth is my "guru", although we have never met (he is quite kind in answering emails - I have his book and videos). I say this as he says that the vacuum chuck is needed for his "spirit forms". But John Keeton suggests I may be better off using a mechanical mounting, and I must confess that since I wrote I've done a successful small (2" diameter, 1/2" hole) hollow form using the tail stock and a padded jam chuck. The change I made that enabled me to get a better alignment on the reverse chucking was to use a blunt tip on the tail stock - that allowed me to make small adjustments with a light tail stock pressure still applied. I had been using a "pin and ring" center, which involved backing off and reseating the pin - which threw off the other alignment. I was able to take out the "wobble" effects at the transition with 220 paper, far better than the harsh sanding I'd had to use before.

BTW, may I advertise a product. The Craft Supplies Apprentice revolving center is a reasonable price and has several blunt tips as well as the pointed ones (and "ring and point). I'd throw away my old centers (except the big cone) except that I can use them when I don't care if I mess up the tip (putting pressure on a buffing mandrel, etc.).

James, I thank you for the pawn shop suggestion, I'll start looking at flea markets and such - and if I can get a decent pump for $100 or so I can then look at the rest of the system. Russell, I've looked at the JT site - I'll look again if I find a cheap pump.

Alan, thank you for the invite - I'd love to see your shop. I don't travel much, being a leg amputee, but know Paramus well (about an hour and a bit from here). I also would be happy to have a local correspondent on wood turning topics (finding wood, outlets for products, etc.). I'll put my email in this post (I'm not concerned about it getting out), drop me a line. jon@murphsays.com. And should you be my way you might be interested in my shop (it has been improved since that article, and thanks for making the effort to find it when I was off by a year).

Finally, and for John K., I saw your ambrosia maple bowl on another thread. I recently was given a dried board of about 1/4" thick - wondered what to do with it. My 5" saucer/sake dish hasn't the form of yours, but I had limits in the shaping of the curve as it ended up 1" deep. Lovely wood to play with, the "bug holes" enhance it.


Again I beg your pardon for the long message, but I think I'll become a regular on this forum when I get used to how to handle it.

Best, Jon

[Bob Hamilton]

Hi, Jon:
The key to vacuum chucking is surface area for the differential pressure to act on. Small pieces don't have very much surface area. The amount of differential pressure directly affects how much surface area will be needed to develop an adequate hold.

A dust collector is typically just a centrifugal blower with the piping hooked up to the intake side. They can move a lot of air but do it at relatively low speed and do not develop much differential pressure. Plugging the system by closing all the blast gates simply stops the air moving and the blower doesn't really care.

A shop vac moves a smaller volume of air but at a considerably higher velocity than the dust collector, and the shop vac is more "determined" to keep that air moving. It can develop a significantly higher differential pressure than a dust collector. That allows it to be used for vacuum chucking as long as the piece being chucked has enough surface area for the air pressure to act on. In practice I find that the smallest piece that will be held well enough to do any work on is about 6" in diameter.

A vacuum pump system will develop a much higher differential pressure than the shop vacuum even though it is moving a relatively small amount of air. On a perfectly sealed system the theoretical maximum differential pressure is about 14.7 lbs./sq. in. since that is the difference between atmospheric pressure (at sea level) and a perfect vacuum. That means that on this hypothetical perfectly sealed system a 10" diameter bowl mounted on a 10" diameter chuck would be held on by over 1100 lbs. of air pressure (pi x radius squared x 14.7 psi) Unfortunately, since the surface area is directly related to the square of the radius, the holding forces drop off rapidly as the diameter goes down. A 5" diameter bowl would only be held by a total force of 288 lbs. That is still plenty for doing useful work but look how much change there is by cutting the diameter in half. A 1" diameter piece would only be held by 11.5 lbs. of force under the absolute best ideal conditions. That is really not enough to do much useful work.

Take care
Bob

[Roger Chandler]

Bob Hamilton...........thank you for that post........that is the best practical explanation I have ever heard or seen for a vacuum chuck application..........appreciate your posting this info!

[Harry Robinette]

I used a Fein II vac for about 5 years with no problem these vac's have two fans one for vac and one for cooling . I now use an old Craftsman all-in-one compressor hooked up backwards. What you need is a small compressor that has a threaded EXHAUST HOLE just thread your tubing connector into this and now you have vacuum. Been using this system for about 4 years now and it works great.
Like Bob H just explained the size makes all the difference in the hold.

[David E Keller]

I can't help you with the vacuum chuck, but I've done a number of smallish HFs in the 1.5 to 2 inch range. I've reversed them a number of ways, but lately, I've been using a jam chuck with good success. I haven't been using the tailstock at all for these pieces, but I do have to fiddle with them a little to get them running true. Thanks for starting the thread... I've learned quite a bit just from reading the responses.

[Jeff Fagen]

IMHO a vacuum chuck is a cool gadget that a person thinks he needs but is not necessary for most turning.I have come up with systems for anything I turn to chuck or reverse chuck.

[Thom Sturgill]

I have, and have used both a venturi type system and a pump system using a small vacuum pump. Much quieter and works well. However, I have cracked bowls with both the vacuum system and with 'donut' rings when the bowls were too thin. Bob was absolutely spot on concerning the diameter issues. I have seen several interesting jamb chuck arrangements that use a long threaded rod that has had one end ground to be a morris taper or somehow mounted to a morris taper, and have a cone shaped piece threaded on and a pad threaded on the end. The idea is that the cone supports the rim to keep it steady while the pad supports the inside bottom. The tailstock pushes against the bottom and there is no pressure on the side walls.


At least one vendor sells cast foam cones, but I think those would be easy to turn out of wood and cover with craft foam.

[Alan Zenreich]

Just to avoid some confusion, it's "Morse", not Morris taper.

[John Keeton]

This may be similar to what Thom is thinking of -

http://www.woodturnerscatalog.com/woodturners/Images/products/large/woodchucker-mandrel_l.jpg

[Paul Williams]

Thanks for the photo John. That looks like an easily made tool that will work well for me.

[Paul Merrill]

Jon, check your PM (personal messages), I've got a few questions for you on your equipment. Thanks!

[Jon Murphy]

Bob, I nominate you for the Murphy prize for clarity (Nobel and Pulitzer don't have that category). I am a bit embarrassed, as I'm writing a book on musical strings and one of the criteria is understanding the volume versus the cross section. (The vibrating mass is a cubic measure, the tensile strength a square one - the string material has density (cubic) and gauge (square), and the instrument has length (fixed for guitar, variable for harp). Not an exact comparison, but like the matter of holding force with a vacuum there is a counter intuitive aspect. A string of a given length (VL) has a breaking pitch, given the material. My harpist friends keep trying to tune higher with a thinner string (same length), doesn't work.

OK, got off on a tangent - but your description has me thinking of the math. I suggest that you are wrong on one thing. David Ellsworth, the guru of "spirit forms", says that he can only do them with vacuum chucking, and some of them are less than one inch diameter. That suggests to me that your math is correct, but that David has such a gentle touch that he can finish the base with 11.5 lbs force, or less.

I do not have that gentle touch, I shall continue as I'm doing - and save a few bucks.

Best, Jon

[Jon Murphy]

David, you say thanks for starting the thread - and I say I'm thankful for starting it. A bit difficult to keep up with the format, but I'll get the hang of it soon.

I gather that the "jam" chucks you are using are specific to the piece and that you actually "jam" the piece on it. I use my formed jam chucks with half inch foam padding to provide friction - but that also reduces grip. Since writing the opening of the thread I've been using "blunt" tailstock centers and been getting a good concentric reversal.

It would seem to me that the thin walls (I turn to about 1/16th) would not support the "jam" without the pressure of the tail stock. A soft "hold" pressure, admittedly, but still the pressure of the tail stock.

Best, Jon

[David E Keller]

Jon, I don't think I've done any as thin as 1/16"... If I did, it was unintentional!:eek::D

I've reversed little forms a number of ways... Sometimes I hollow out a piece of scrap to insert the reversed piece into, and other times, I use a small dowel or something similar to insert through the opening and rest against the bottom of the form. Lately, I've been doing more of the 1st scenario because it gives me total access to the bottom. I do use the tailstock with a small wooden insert replacing the normal metallic pin, but I remove it at the end for final cuts and sanding. If you turn a very small cone in the bottom of the jam chuck, it will help center the piece when reversing... Doing so introduces a whole new bit of fiddling since the cone has to be just the right size to work and not prevent the piece from sticking in the jam chuck.

I'm surprised that Ellsworth suggested that he could 'only do them with a vacuum chuck'... A man of his talents and creativity could likely do it a number of ways. I'm no Ellsworth, so if I can do it, I'll bet he could do it blindfolded.

[John Giem]

Hi, Jon:
The key to vacuum chucking is surface area for the differential pressure to act on. Small pieces don't have very much surface area. The amount of differential pressure directly affects how much surface area will be needed to develop an adequate hold.

A dust collector is typically just a centrifugal blower with the piping hooked up to the intake side. They can move a lot of air but do it at relatively low speed and do not develop much differential pressure. Plugging the system by closing all the blast gates simply stops the air moving and the blower doesn't really care.

A shop vac moves a smaller volume of air but at a considerably higher velocity than the dust collector, and the shop vac is more "determined" to keep that air moving. It can develop a significantly higher differential pressure than a dust collector. That allows it to be used for vacuum chucking as long as the piece being chucked has enough surface area for the air pressure to act on. In practice I find that the smallest piece that will be held well enough to do any work on is about 6" in diameter.

A vacuum pump system will develop a much higher differential pressure than the shop vacuum even though it is moving a relatively small amount of air. On a perfectly sealed system the theoretical maximum differential pressure is about 14.7 lbs./sq. in. since that is the difference between atmospheric pressure (at sea level) and a perfect vacuum. That means that on this hypothetical perfectly sealed system a 10" diameter bowl mounted on a 10" diameter chuck would be held on by over 1100 lbs. of air pressure (pi x radius squared x 14.7 psi) Unfortunately, since the surface area is directly related to the square of the radius, the holding forces drop off rapidly as the diameter goes down. A 5" diameter bowl would only be held by a total force of 288 lbs. That is still plenty for doing useful work but look how much change there is by cutting the diameter in half. A 1" diameter piece would only be held by 11.5 lbs. of force under the absolute best ideal conditions. That is really not enough to do much useful work.

Take care
Bob

Bob,
You are correct that the force holding the object on the chuck is the product of the pressure differential times the area. This is a problem for small items and in a few other cases. Since we are limited in the vacuum we can create, to increase the holding force the area must be increased. Yes, this is possible. I have developed what I call a Compliant Vacuum Chuck that addresses these limitations. (article to be published in the American Woodturner in early 2012.) The Compliant Vacuum Chuck breaks the barriers of small size, odd shapes, leakage of the wood, perforations and does not require cutting or penetrating your blank inorder to mount it. An explaination of how I can do this 'magic' is too long for this posting so if you are interested go to the AAW Forums, www.aawforum.org (http://www.aawforum.org), and look for the thread 'Update on Vacuum Chucking Systems'. There are a couple of other strings there on vacuum systems that address some of the questions in this and other threads. The AAW Forum is free and does not require registration to read the posts.
Let me know if you have questions. BTW, I wrote the article 'Understanding - and Improving - Vacuum Chucking Systems' in the February 2011 issue of the American Woodturner.

John Giem