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Thread: Looking for Better way to hold down work - Vacuum Pods?

  1. #1
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    Looking for Better way to hold down work - Vacuum Pods?

    I own a Camaster Signpro, it has a phenolic top on which I have glued a ULDF top on it and have a Hurricane vacuum attached.

    Quite often, I do 3D carvings and just cannot run the vacuum for 6 - 10 hours straight... Instead I've been using the masking tape and superglue method. This works fairly well, but often it is very difficult to get the completed piece off of the table. So I have been looking into possibly attaching vacuum pods to the top maybe by putting a piece of melamine on top of the ULDF and attaching the pods to it. I'll lose some height, but I have 8" of Z height and most of the carvings are 1 - 3"

    Something along the line of what greenbvc.com sells.

    I was just wondering if anyone has any experience with these or other vacuum pods. I've seen some that are alum, but those worry me with the bits hitting them.

    Anyone have thoughts on how to attach them to they can be swapped out when I do sheet work.


    Any thoughts would be great.

    Thanks, Tony

  2. #2
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    Pods may be a very good idea for your application because you can run a smaller, fit for purpose vacuum pump. I would think that fastening them to your phenolic table could be easily done through the use of embedded nuts in the table (I'd use brass just in case...) and either steel or nylon bolts. The pucks would just need to be mounted to a thin sheet that mates up with the embedded fasteners. You may want to post this question at Camheads in the Vacuum/work-holding area as someone may have already setup a system for this.

    I've only experimented with the technique to-date as I have a small Gast pump from my lathe and for veneer work, so I can't provide much in the way of practical experience.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  3. #3
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    I do carvings as well, and have built around 20 or so pods for short runs of material other than carvings. I would not suggest pods for carvings for a few reasons.
    1. I have a small Becker pump for the pods (4.5cfm). On a long day of running the pump gets quite hot and I don't think it would be great for the pump. I know it is rated for this type of use, but I still am not a fan.
    2. The more important potential problem will depend on the stock thickness. Pods only provide great support where they are located. Between the pods the stock is elevated and if your stock is say less than 1" or it is a deep carving where the material stiffness lessens during the machining, you will see small movement of the stock. I figured this out the hard way for other projects.
    3. If you try to use a number of pods to avoid stock movement during carving, your stock needs to be virtually perfect. I know that seems straight forward, but even the slightest twist or bow in thick stock makes it difficult to achieve a good seal that cannot be broken during machining. I am sure you have already discovered that with your current methods. Trust me I have fought with many pieces over this when I try to use 6 or more pods. These little pumps do not have the cfm to keep up with even small leaks.
    4. Attaching pods to the ULDF top will not work very well since you will lose vacuum. If you are wanting to use small pods, you will need to achieve 20" - 25" of Hg to get enough hold down. That will be difficult if they are placed on top of anything that allows flow below.

    I have ran carvings that took up to 3days. I always fasten with clamps, screws, composite nails... It only takes about 15min or so to clean up the little remainder when done, so I do not follow the advantage of pods for this. If you do not have any t slots, or cannot find a suitable spot for some screws, I would likely use your main vacuum and a large sheet of melamine (perfectly flat, cheap, and great seal) that you can screw parts too. That will be about the quickest changeover. Admittedly, my changeover time between sheet stock and carvings is a bit slow.

    On the topic of tapes, I have found the Allstar tapes (http://allstaradhesives.com/cart/pro...ig_tape_400/44) and the fastcap speed tape (https://www.fastcap.com/product/speedtape) both work very well, are very thin and come in widths that can be more useful for us. The trick is figuring out how much to apply so it is not a pain to get off after it has been on the table for a while.

    DEER_MANTLE_A-04_EDIT.jpg
    PetersTemp-01_01.jpg
    Last edited by Brad Shipton; 11-05-2019 at 1:39 PM.

  4. #4
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    Tony,
    As you probably already know, hold down is one of the biggest challenges with CNC & depending on what you are cutting, your needs will change.

    Vacuum, in my opinion, isn't the right method for holding down 3D reliefs that take several hours or more to cut; especially if you are using LDF or ULMDF. This is because the vacuum will both 'boil out' any moisture contained in the porous matrix of the MDF material and make it change dimension and if the negative pressure of the vacuum source is great enough (let's say >10Hg"), over several hours will actually cause the MDF to crush down and shrink. This will cause your 3D relief to be somewhat wedge shaped as it progressively 'sinks' during an incremental raster finishing pass. I've thrown out or hung on the 'wall of shame' reliefs held with vacuum over the course of 12-18hrs that I refused to put my name on & had to re-machine. Yep...school of hard knocks still in session.

    There are lots of other options out there for hold down for your parts. For instance, a few little dollops of wood glue is often more than enough to hold down most 3D reliefs while they are being machined. Just a quick dink with a mallet and it's off the table, but it does tend to take some spoilboard with it...so what. It's made to get spoiled. If the material has a tendency to cup, you'll also need some mechanical means. You can clamp them down any number of ways. You can screw them down - although I would strongly discourage the use of drywall screws on your machine - ever. (Kreg screws are great) You can even toe clamp the parts down in some cases where there is no other practical way such as deep reliefs - like the attached pics show.

    I've never been a fan of using super glue as a hold down. My preferred method for 'quick & dirty' hold down is carpet tape. Specifically, carpet tape that has a plain fiberglass square weave (so you can get it off), but NOT the stuff that looks like gauze/cloth. The Duck brand 286373 is what you want. Warm up the tape in cold climates before sticking it to your material. J-roll it down. Stick it and clamp it for a minute or two to give it a good bond. It's way easier and better than messing with liquid adhesives.

    If you have your heart set on a vacuum pod system, Google 'BradyVac' and have a look at my BradyVac and BradyVac II system. You may also find my VacuumFilm Technique useful at some point.

    Practice part in HDU & one of the real parts in Sapele...No dowels were used. 4-sides lined up for machining using only pencil marks. Toe clamps were 3D printed.
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  5. #5
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    Brady,

    Thanks for the information on the vacuum pods. Was planning on using a piece of melamine over the top so the pods can "Stick" properly.

    Interesting on the actual vacuum. I have been doing some research and it appears that many people have issues with the pumps overheating when run for the length of times that 3D carving takes. Even saw a video where someone was putting their pump in ice to keep it cool...

    Regarding double sided tape. I use the Masking Tape / Super Glue method currently. I.e. Put masking tape on the spoilboard, then another piece on the wood to be carved. Spread some superglue on the tape stuck to the spoilboard and spray some accelerant on the tape attached to the wood and press them together. Works well and quite a bit cheaper, but just has hard to get off as double sided tape...

    Guess gonna have to work up some custom hold downs that can be attached / removed quickly.

  6. #6
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    Anthony,
    Do you have any example pics of the reliefs you need to hold down?

    Regarding vacuum pumps and not those hurricane type vacuum cleaner motor sources - a real vacuum pump is designed to operate for hours on end without overheating. If you crank up the wick too much (set the blow off valve too high) and the pump cavitates, that's when the problems start. Quite often it wipes out the bearings.

    The carpet tape is way easier to use and remove than superglue. However, it is not a production solution.

    You can most likely hold down several of your parts on a custom low profile jig using one of those replacement vacuum motors (via Lighthouse et al) with no problem. I wouldn't use any vac source that pulls less than 8Hg" since you don't have a lot of surface area there. You most likely don't even need gasketing. Have a look at my BradyVac II. You would most likely want to hang the 'pod' off the table with the intake port pointing at the floor. Then have that feed the grid and open part areas, as shown in the BradyVac II write up.

    In case you haven't discovered this yet, 'vacuum air' directly against the back of the part being machined will hold a lot better than vacuum delivered via a bleeder board with vacuum suction being equal.

    Don't go buying vac pucks...The guy who makes them most likely doesn't have anything different than you. Make your own.

    I've made plenty of jigs like this over the years. Here's one from the archives - profiling 2" poplar balusters using a shopvac and jig made from scrap. Intake hole pointing at floor overhanging table, machined in for vac hose friction fit. Sawdust created on first pass functions as a self-sealing gasket to maintain vacuum. These days I connect a hose to my table manifold port (like a vacuum take off) and plug a hose into this type of jig the same way. My Becker pump will pull 25.5Hg" and surprisingly doesn't collapse shopvac hose!



    Jig (Large).jpeg
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  7. #7
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    If you do not have a temp gauge on your vacuum, you should. The single phase vacuums run hot. The guys posting videos like suggested are not paying attention. I was concerned with my temp readings when I first started using my vacuum, and asked Lighthouse (common supplier for many single phase options) what was okay. I was told, "They can run up to 180 degrees and you will get around 900 hours"

    I agree it is easy to make your own pods.
    The simplest ones I have made were left over plastic, thru hole, air hose connector, and 1/32" gasket top and bottom. 20min. That said, the BVC pods are a great design for commercial shops so you can replace the top if you ever nick it. The NEMI pods are built to a ridiculous tolerance for machining something other than what we do.

  8. #8
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    FYI - All of the single phase vacuum cleaner powered units on the market today (Hurricane and other Lighthouse motor variants) are a result of yours truly's research. Many years ago I started an Open Source Vacuum thread on the ShopBot forum for guys that were just starting out - aka couldn't afford a commercial 3-phase vacuum pump (and converter if needed) - so they could make money during the short term while they saved for a real vacuum pump they could rely on. Those high RPM (20k+) 'screamin demons' were never meant to be run for hours on end...so keep that in mind if you're a lurker reading this...
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  9. #9
    Does the carving you do have a flat surface on one side when you are done? I do some sculpting and the carvings I do must stand by themselves on the bottom. I usually make the wood a lot longer than the finished carving so I can put it in a woodworking vice to carve. Once done I cut off the excess. I recently finished a large statue where I attached a piece of 3/4" plywood to a 4x4 and screwed it to the bottom of the carving.

  10. #10
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    Brad, I absolutely love the old man, very well done. Can you point me to the model?
    Please help support the Creek.

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  11. #11
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    Thanks Bruce. I am taking an Art class to improve my painting. I sent you a PM.

  12. #12
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    Joe Woodworker (https://www.joewoodworker.com/veneer...pingmatrix.htm) describes the vacuum pump and clamps needed to clamp flat things to a flat surfact for machining. His pump "build it yourself" vacuum pump design has a vacuum reservoir and pressure sensors so the vacuum pump runs only when needed. You can buy parts and build everything yourself. His web site is a little hard to find things - calling him will be much quicker to see if this will work for you.

    JKJ

  13. #13
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    Joe Woodworker is great to deal with. Lots of good info and the 'right parts' for low CFM, high suction vacuum pumps.

    However...the size & type of pumps sold and used for lamination and vacuum bagging are not appropriate for holding down most lumber, unless some provisions are made to mitigate vacuum leakage through the actual material. This is where you need a pump that can move a lot of air to buffer the leakage brought on from the porous nature of wood itself. In many cases, those little pumps will not move enough air to counteract air being sucked through the material at a rate greater than the pump is capable of delivering. You either need to seal the wood or come up with some other way around it.

    If you are cutting non-porous material and using gasketing of the proper durometer (pretty much required with those little pumps), they work well.
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  14. #14
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    I agree with Brady here...as I noted previously, I did try a little fixturing with the Gast pump I have for my lathe and for vacuum bag veneer work and it wasn't really all that up to the task.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  15. #15
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    Saw a Youtube Video where a CNC Guy used two pieces of wide blue painters tape on each piece with fast acting glue between. When done the tape releases pretty easy.
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