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Thread: Hold down techniques and jigs - please share!

  1. #11
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    I find vacuum hold down is good for some things. Try cutting a sheet of formica without using a vacuum! How about a sheet of veneer or 1/8" acrylic. Vacuum makes these cuts simple and error free. I rarely use vacuum for anything that is stiff though. I'd rather use a combination of scrap boards and T-track clamps. I've never put a screw into my spoilboard. I can always find a better way.
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  2. #12
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    Agreed Cory. I cut a variety of material and having the flexibility of having a vacuum is great for a lot of sheet goods.

    Brian:

    For the stuff that I can't vacuum I'll often make a "carrier board" where I'll use a plywood sheet with t track or clamps on it and then I'll vacuum that carrier board down.

    This way I can hold down off material like hardwood but I can remove the jig in seconds.

    Using this method had made it so I never put a fastener in my spoil board now.

  3. #13
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    Apr 2007
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    Gene...
    Good job on the wedge sticks. Before the air cylinders went in, I used the same method on a machine I setup as a "Louvre Groover" on the island of Nevis in the Caribbean.


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  4. #14
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    My first try at surfacing a slab



    I had some scrap 1/2 plywood on the table already, so I just made a bunch of these that are 4" circles, then 6" and 8" ovals and fit them into the sides, and took small amounts off each pass, I think I did .1" each pass and it was a total of .5" difference from one side to the other. Maybe could have been more aggressive with pass depth but first time didn't want to risk it.
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    Daniel E.
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  5. #15
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    Why is it very time I see a post from Joe my stomach tightens a bit because I KNOW he is going to find fault with what ever was posted. So he doesn't like or use vacuum hold downs. We've heard that from him umteen thousand times. For his purposes that is probably fine but for some of the rest of us, vacuum is the BEST and most efficient method to use. A very talented guy in his element but that does not mean he is the know-it-all for the rest of us doing other things. Sorry for the rant. He just gets old after a while. Give it a rest Joe. Your way isn't always the best way for everyone at all times.

  6. #16
    Join Date
    Jun 2004
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    Springfield Mo
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    805

    Default pull down

    I laid out a grid of 17/ 64 holes on 5-1/2 centers through the “high spots” in the vacuum plenum. This goes all the way through Trupan top and out of the bottom of the 3/4” plywood base.

    At the bottom of the hole is a 1/4 inch threaded T- nut which can be used to secure the hold down clamps.

    Sometimes I will use a lag screw coming up from the bottom to hold the work-piece using “pull down.” ... you have to miss the lag screw ... nylon screws will work...

    Works great, I cover the bottom holes with heavy tape when not in use, vacuum still works fine.
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  7. #17
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    I don't have one with duct tape, but this one uses a ratchet strap.



    I can only hope that Joe's first foray with a lady didn't turn out the same as his first with vacuum. There are few failures in life, only wins and lessons. Unless of course, you give up too early and toss everything in a dumpster. The fact that Joe couldn't get vacuum to work says much more about him than the power of vacuum.
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  8. #18
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    Quote Originally Posted by tri4sale View Post
    My first try at surfacing a slab
    I think of hold down in the exact same way as forms for concrete. Too little and there's a disaster. Too much and a lot of time is wasted setting them up and taking them down. The "Goldilocks Zone" is where the material won't move with the forces involved with the least amount of effort expended.

    I've surfaced numerous slabs and one thing I've found that's a constant. Very little, and I mean VERY little, hold down is required. Here's why:

    1. The machine is placing insignificant forces into the material.
    2. The workpiece is heavy and has a lot of friction on the table.
    3. The action is strictly to remove material from the top.
    4. The penalty for movement is nil.

    For a slab like that, I would have had a couple of scrap boards just touching it with minimum force. The key is stopping the "activation energy". If the slab is going to move, then it's only going to take a lot of energy to get it to move. All you need to do is stop that initial movement and the piece will stay put. If you don't believe me, try doing your next slab with no hold down on the first pass. Carefully hold it with your hand and feel the amount of force the machine is exerting against the slab. You can probably keep it from moving with a single finger, or none at all.
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  9. #19
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    Jan 2004
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    Gary,

    Thanks for the well wishes and suggestions.

    I'm not against vacuum's. They do an excellent job on light weight flat stock as did the one I built. My issue is this. Most of us can get along without one. All my large commercial routing services have massive vacuum's housed in a special room to manage the noise and heat. They need this level of equipment. But us little guys have been able to manage without the trouble.

    Why have Vac. pucks fallen out of favor. Our former Guru, Bill was strong on them. Seems like a good idea.

    Thanks again Gary for your kind thoughts.

    Joe

  10. #20
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    First vacuum....then parts flipped up on edge to tighten up corners, aligned and clamped.

    Vac pod/puck designed for vacuum to directly contact the back of the lumber for maximum hold down. You do NOT want a bleeder board when doing lumber. The jig was held down to existing vacuum table (with it off) using only a few dabs of wood glue. After it was weighted down and cured, it took only light prying to get it off. Vacuum hose was plugged into the jig (3D Printed fitting) - and the other end plugged into main vacuum manifold using an adapter to jack it into my vacuum relief valve (2" PVC).

    After profile cutting was done, each was flipped up on edge, and aligned using a dial indicator to verify alignment in the Y and the Z. Corners sharpened from the side with an end mill, crotches done with 72 deg V bit. Flipped over & repeated. IIRC, these were 2" thick poplar.

    I know vacuum is 'only good for lightweight stuff'...but I defy the laws physics in my shop on a daily basis.
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