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Thread: Vacuum clamping

  1. #1
    Registered User John Bertotti's Avatar
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    Default Vacuum clamping

    I am curious if anyone here is using vacuum clamping in their shop? I can picture some uses for it but wonder how good it really is. Thanks!
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  2. #2
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    Default Re: Vacuum clamping

    Some years back, the late Jim Grainger ordered a vacuum clamping system for guitar bridges. IIRC, he got it from LMI. He wasn't satisfied with it and decided to return it after only a few uses.
    I don't know of anyone else who has tried it.

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  4. #3
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    Default Re: Vacuum clamping

    Gerry Rosa uses one, see his video: https://m.youtube.com/watch?v=vBiQxTg5mL4
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  6. #4

    Default Re: Vacuum clamping

    Titebond wood glue works best with a clamping pressure of 100-200PSI (depending on the wood density and porosity).

    Any screw-type clamp can exert a force relative to the screw pitch (mechanical advantage) and the amount of effort you put into tightening it. Screw-type clamps can easily apply more than 1000PSI, especially ones with small circular contact pads. That gets spread out over the whole glue joint, sort of. But the point is, with normal clamps, we have plenty of force to work with, in normal woodworking joints.

    Try to clamp a normal panel glue-up, though, with vacuum, and it gets tricky. Not only does it not apply force in the correct direction for a panel glue-up, it can only provide whatever you can achieve as a drop relative to your barometric pressure. Let's say 14.5 PSI (1 bar) as absolute maximum, though it's usually about 10% less than that, realistically speaking.

    Long story short, vacuum works great where you have lots of surface area, and don't need to maximize structure of the glue joint. Lamination is one example, bracing is another example. In those cases, the benefits of even clamping pressure and workflow yield a good enough result. Technically, bracing would be attached to the top more reliably with higher clamping pressure. But in practice, it has generally been considered good enough to use vacuum clamping for bridges, bridge plates, and top bracing.

    For something like a skateboard, though, vacuum really isn't enough. In that case, you're talking about hydraulic jacks and a welded frame to push against. Like a really badass go-bar deck, basically. Which is what more and more luthiers are using for their side lamination and other applications, too.

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  8. #5
    Registered User John Bertotti's Avatar
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    Default Re: Vacuum clamping

    That’s good to know. I doubt I would use it on instruments. I do way more cabinet and tables an engraving than instrument work. My intention is more for holding items in place as I work on them. I’ll need to dig deeper before I commit any fund to this tool. Thanks guys I appreciate the great answer you have given me!
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    Default Re: Vacuum clamping

    Quote Originally Posted by Marty Jacobson View Post
    Long story short, vacuum works great where you have lots of surface area, and don't need to maximize structure of the glue joint.
    My thoughts exactly. I've used vacuum bag exclusively for fancy veneer layups (marquetry and such). For veneer layups on sheet substrates, using cauls and a vacuum bag works better than any other method I've used. I would not dream of using vacuum to make glue ups on hollow objects such as musical instruments. No need to exert force over the entire area, and could cause some damage doing so IMO
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  11. #7

    Default Re: Vacuum clamping

    If John’s asking about vacuum hold-downs, that’s a different thing. Woodworkers use vacuum tables when working on (mostly flat) parts where clamps would get in the way. Useful especially on thin stock. Some make their own tables and shutters to close uncovered holes. An example would be in using a SafTplaner in a drill press for thicknessing a panel.
    I’ll bet that someone once put a hollow instrument in a vacuum bag….once.

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    Registered User amowry's Avatar
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    Default Re: Vacuum clamping

    I use vacuum hold-downs for lots of parts on my CNC, and it works great for that. I've never used it for glue-ups, though I can certainly see how it would be useful in a production environment for things like guitar bracing, bridges, and laminations.

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  15. #9
    Registered User John Bertotti's Avatar
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    Default Re: Vacuum clamping

    Guys yes vacuum hold downs is exactly what I was thinking of using them for. I like Festool but the price is at the top of the range I think. I’m considering the excel5 which gets great reviews and seems to perform better than the Festool pump at a much lower cost. Thanks again!
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    Default Re: Vacuum clamping

    I have a massive vacuum setup that I mostly use for double basses & solidbody instruments. It gets used to re-arch collapsed tops and I also use it for much of my new build process. They don't have much use with the small mandolin processes. I've always been fearful of using a vacuum clamp on the lathe.

    When I worked at the original Breedlove factory, they had vacuum clamps on a lot of workbenches. Every time the power would go out, you would hear about $100k worth of guitars hitting the floor!

    All of the ribs for my guitars and double basses are vacuum laminated. I also use it to make my own laminated tops and backs for the basses (unless they are fully carved). Like everything, there is a learning curve, but once you get it figured out, it is an incredible tool in the shop and does what nothing else will very easily.

    There is an upcoming big article in American Lutherie magazine where I show off the whole vacuum process in use in my shop and all of the test results. I did about 50 different glue ups trying to problem solve things- different woods, carbon, kevlar, and about six different types of glue and then stress tested them all to failure. The results were quite varied in terms of adhesion, structure, and tone.

    It is not an easy process. You need a substantial investment in the vacuum system and bags and such and then you also need to fabricate very specific moulds and forms. Some I have made here in the shop and I had the giant bass moulds digitally scanned and very accurately cnc carved which took multiple tries to get correct.

    I also have several different size go bar decks; they serve a different purpose.

    Here is a heavily damaged old Kay getting a new inside layer added in the vacuum press (in an older bag that is no longer with us), then a different old bass getting a belly patch graft on the go bar deck, and a set of brand new C bouts made from padauk and red spruce (getting the corner blocks added), and a new set of Brazilian rosewood laminated guitar ribs:
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    Last edited by j. condino; Jul-18-2022 at 1:02pm.

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  18. #11
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    Default Re: Vacuum clamping

    Quote Originally Posted by j. condino View Post
    I have a massive vacuum setup that I mostly use for double basses & solidbody instruments. It gets used to re-arch collapsed tops and I also use it for much of my new build process. They don't have much use with the small mandolin processes. I've always been fearful of using a vacuum clamp on the lathe.

    When I worked at the original Breedlove factory, they had vacuum clamps on a lot of workbenches. Every time the power would go out, you would hear about $100k worth of guitars hitting the floor!

    All of the ribs for my guitars and double basses are vacuum laminated. I also use it to make my own laminated tops and backs for the basses (unless they are fully carved). Like everything, there is a learning curve, but once you get it figured out, it is an incredible tool in the shop and does what nothing else will very easily.

    There is an upcoming big article in American Lutherie magazine where I show off the whole vacuum process in use in my shop and all of the test results. I did about 50 different glue ups trying to problem solve things- different woods, carbon, kevlar, and about six different types of glue and then stress tested them all to failure. The results were quite varied in terms of adhesion, structure, and tone.

    It is not an easy process. You need a substantial investment in the vacuum system and bags and such and then you also need to fabricate very specific moulds and forms. Some I have made here in the shop and I had the giant bass moulds digitally scanned and very accurately cnc carved which took multiple tries to get correct.

    I also have several different size go bar decks; they serve a different purpose.

    Here is a heavily damaged old Kay getting a new inside layer added in the vacuum press (in an older bag that is no longer with us), then a different old bass getting a belly patch graft on the go bar deck, and a set of brand new C bouts made from padauk and red spruce (getting the corner blocks added):

    That looks great! My desire is an easier way to hold items I am using a shaper origin to engrave and for hand planning and sanding. Some is quite thin. I have used double sided tape but it isn’t cheap either.
    My avatar is of my OldWave Oval A

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  19. #12

    Default Re: Vacuum clamping

    Nigel Forster uses these for these types of things, John.... https://www.ebay.com/itm/283301596626

    I'd say draw it up and make something similar for yourself using your Shaper Origin.

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  21. #13
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    Default Re: Vacuum clamping

    Quote Originally Posted by Marty Jacobson View Post
    Nigel Forster uses these for these types of things, John.... https://www.ebay.com/itm/283301596626

    I'd say draw it up and make something similar for yourself using your Shaper Origin.
    I actually already checked McMaster care for sheets of UHMW! I have been giving this serious thought a few days now. Reading all I can. Hurt my back this weekend so I’m kind of down hard for a few day. Good time to research! Thanks!
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  22. #14
    Registered User John Bertotti's Avatar
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    Default Re: Vacuum clamping

    Quote Originally Posted by j. condino View Post
    I have a massive vacuum setup that I mostly use for double basses & solidbody instruments. It gets used to re-arch collapsed tops and I also use it for much of my new build process. They don't have much use with the small mandolin processes. I've always been fearful of using a vacuum clamp on the lathe.

    When I worked at the original Breedlove factory, they had vacuum clamps on a lot of workbenches. Every time the power would go out, you would hear about $100k worth of guitars hitting the floor!

    All of the ribs for my guitars and double basses are vacuum laminated. I also use it to make my own laminated tops and backs for the basses (unless they are fully carved). Like everything, there is a learning curve, but once you get it figured out, it is an incredible tool in the shop and does what nothing else will very easily.

    There is an upcoming big article in American Lutherie magazine where I show off the whole vacuum process in use in my shop and all of the test results. I did about 50 different glue ups trying to problem solve things- different woods, carbon, kevlar, and about six different types of glue and then stress tested them all to failure. The results were quite varied in terms of adhesion, structure, and tone.

    It is not an easy process. You need a substantial investment in the vacuum system and bags and such and then you also need to fabricate very specific moulds and forms. Some I have made here in the shop and I had the giant bass moulds digitally scanned and very accurately cnc carved which took multiple tries to get correct.

    I also have several different size go bar decks; they serve a different purpose.

    Here is a heavily damaged old Kay getting a new inside layer added in the vacuum press (in an older bag that is no longer with us), then a different old bass getting a belly patch graft on the go bar deck, and a set of brand new C bouts made from padauk and red spruce (getting the corner blocks added), and a new set of Brazilian rosewood laminated guitar ribs:
    Do you use a wicking mesh of some sort to help evacuate the air out more evenly? I didn’t notice any in the picture.
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  23. #15

    Default Re: Vacuum clamping

    There is absolutely no need for a high vacuum pump for clamping, and in fact, a very good reason not to. With (impossible, or really difficult sealing - remember, wood is porous in all directions), all you could possibly get is a maximum of around 15 psi. Don’t need 99.999% of that: half will do fine, and that’s probably better than you’ll see.
    The other reasons are: cfm matters if there’s leakage, and a high vacuum pump is low, compared with, say, a blower, and the pump will also get destroyed by whatever it sucks up from the wood or leakage paths. And if you think a Festool pump is pricy, you wouldn’t want to price a high vacuum inlet filter.

    So, your small vac table will be three layers: thin plywood or Masonite top, and a thicker middle that is riddled with large holes in both directions, and has a hose port on the side. I mention Masonite because you can buy it as pegboard, already full of holes about the right size. A shop vac would be your vacuum source. If you want to be fancy, put a gauge on the device.. So, if you could seal to about half an atmosphere, and you have a workpiece of about 1 sq.ft., you have 144 sq. inches with about 7 lbs/sq. inch, or half a ton holding the piece down! So even if you can only get a fraction of one atm., you’ve got lots of pressure. You use pieces of any flat stock, even plastic, to mask off the holes where the workpiece isn’t, and go to work!

    Anyway, about small fractional hp oil bath vacuum pumps, in case somebody needs one for other purposes: These used to be expensive as industrial parts, but the ones designed and sold as refrigeration units are much, much cheaper, even if they may not survive years of continuous running. The mostly Asian models are down around $100 for, say 1/2 hp. The difference in price is more than 10:1. I couldn’t get away with using one on my product systems, but was tempted.

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    Default Re: Vacuum clamping

    Quote Originally Posted by John Bertotti View Post
    Do you use a wicking mesh of some sort to help evacuate the air out more evenly? I didnít notice any in the picture.

    When it is not for photo purposes, they always get some kind of "breather mesh".
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  27. #17
    Registered User John Bertotti's Avatar
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    Default Re: Vacuum clamping

    Quote Originally Posted by j. condino View Post
    When it is not for photo purposes, they always get some kind of "breather mesh".

    I figured there would be but had to ask. I didn't realize that was a glamour shot!
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  28. #18
    Registered User John Bertotti's Avatar
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    Default Re: Vacuum clamping

    The little pump I was looking at is only 5cfm. I need to pull up the specs on my shop vac and compare them. The pump is an excel5 my vac is a ct26 older but running great. Wow I found the vac specs it is capable of 138cfm with 96Ē static water. Sadly when the tool runs it is connected to the vac which leaves the table without. I still need to try this first.
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    Default Re: Vacuum clamping

    I built a central vacuum system for my shop, basically the opposite of an air compressor. A Gast laboratory pump pulls vacuum on a repurposed air tank, and a vacuum switch shuts it off when the adjusted point is reached. It's plumbed throughout the shop through 3/8" plastic lines. For workholding, a foot pedal turns the vacuum on and off at the job. (The actual "not-compressor" sits in an insulated mechanical closet so you don't have to listen to it.) I got the idea for my system from joewoodworker.com. There's also a very good article on vacuum workholding by Charles Fox in American Lutherie #88.

    You can make all the fixtures you needs from UHMW polyethylene or Trex "plastic lumber," machining channels for the appropriate thickness of foam tape, boring the vacuum channels, and using standard barbed fittings. Some of the things I've done include bench-mounted instrument body holders; workholding in my fingerboard radiusing machine; and some general workholding pucks that go in bench dog holes.

    If you try to use a Shop Vac to supply vacuum, you will burn it up almost immediately. It's not the same. The pumps I use are expensive, but I got them for free from a pal who horse-trades in laboratory equipment. Vacuum pumps for HVAC applications are cheaper but perform similarly. The pump needs to be designed to run continuously for long periods.

    That said, sometimes there's nothing better than good old double-sided paper tape from Eagle America.

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  31. #20
    Registered User John Bertotti's Avatar
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    Default Re: Vacuum clamping

    The double sided tape I have works great but it is not cheap. I have mostly used a combination of tape and clamping. I saw the pump I was thinking about online as well at joewoodworker. I’ll go look at the set up as well. Thanks!

    I should mention I was hoping to have something that would eventually work with some bags in the future.
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  32. #21
    Registered User j. condino's Avatar
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    Default Re: Vacuum clamping

    The joewoodworker site is a good one for everything vacuum related.

    Small hobby sized vacuum pumps tend to be around 1/8 hp. They burn out very fast if you don't have something like a mac valve that measures the pressure, shuts off the main power, and then cycles it back on only when needed. With a good seal, the pump only turns on for about 7 seconds once every ten minutes, rather than continuous backpressure on the pump.

    I also have a big 3 gallon polished aluminum tank (from a Lowrider custom shop!) that evacuates the air rapidly from the larger bags during the initial stage, before the regular pump pressure activates.

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  34. #22
    Registered User John Bertotti's Avatar
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    Default Re: Vacuum clamping

    Quote Originally Posted by j. condino View Post
    The joewoodworker site is a good one for everything vacuum related.

    Small hobby sized vacuum pumps tend to be around 1/8 hp. They burn out very fast if you don't have something like a mac valve that measures the pressure, shuts off the main power, and then cycles it back on only when needed. With a good seal, the pump only turns on for about 7 seconds once every ten minutes, rather than continuous backpressure on the pump.

    I also have a big 3 gallon polished aluminum tank (from a Lowrider custom shop!) that evacuates the air rapidly from the larger bags during the initial stage, before the regular pump pressure activates.
    Their excel5 pump is the one I am contemplating. Some of the equipment I work on at work uses Venturi evacuation but I don’t want to go that route. Did you use one of their kits or build your own? Thanks!
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    Default Re: Vacuum clamping

    One additional note on making vacuum workholding fixtures. A good source for gasketing tapes and related materials is All Star Adhesives (allstaradhesives.com). They used to sell what they called the ShopBot Starter Kit assortment, which included a number of different-sized profiles and was reasonably inexpensive. I bought one probably nine years ago, and still have a lot of the package left. It allows you to make good clamping fixtures without having to hunt down gasket material every time.

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  37. #24
    Registered User John Bertotti's Avatar
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    Default Re: Vacuum clamping

    Thanks you everyone for your input. For better or worse I am going to order the excel 5 kit and go from there. I already have some ideas on how it will help me out. Thanks again!
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