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Thread: Work holding systems

  1. #1
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    Work holding systems

    I have looked at your photos of holding your projects to the CNC table for milling and see and read about different systems. Then Brent pointed out he is copying Jason's holding system. So some discussion is in order.

    Dan and Bill seem to be screwing the workpiece directly to the table. Think I have seen that also on Leo's posts. I am not clear about Jason's x-system. I have to decide on what I want to do with mine. Let's talk, guys.
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  2. #2
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    I've also seen people route t-slots into the spoil board and use hold downs.

    I liked the look of Jasons, so decided to copy what he has done. Seems to make sense to me.

    Here's the link to Jason's video on the 'X'

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  3. #3
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    ok, the question for me is, with the t track in the sacrificial board, how would you go about through cutting profiles? only thing i can think of (after posting this, naturally), is that the t track is well below the surface of the sacrificial board.
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  4. #4
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    The X is pretty handy. It covers most of my workholding needs for smaller projects. I use these Shop Fox side clamps for parts that go on the table directly:

    http://www.amazon.com/Shop-Fox-D3347.../dp/B00012XE0A

    A pair of those and a pair of aluminum blocks with a bolt through them (for the cam clamps to push against on the opposite edge of the workpiece) seem to work for a good deal of operations. For cuts that don't go through the piece (3D, engraving, etc) the side clamps and direct mounting to the table top are all I need.

    For cuts that go through, it depends on the size of the part. In some cases, I side clamp a spoil board of some scrap plywood usually using the same method, then screw the part to that. For larger parts, I have a 28x72 scrap of 1/2" baltic birch ply that has seen a lot of miles on it. I screw that directly to the table (the only screw holes in the main table) and then screw parts to that spoil board. I don't need to do that very often ... usually for larger pieces like the Longworth chucks I did.

    For metalworking projects, I used the machine to mill a very shallow pocket in the intersection of the X track. This gives me a locating position for a screwless vise to hold brass or aluminum parts for more precision operations.

    The main goal for me is to never have stuff sticking up very far above the surface of the work. My dust shoe design stays the same distance from the top of the workpiece (it never moves with the router) to keep the dust collection optimal (and works amazingly, i have to say). Because of that, though, having things stick up is a tricky proposition for me. I have a bunch of those pivot-type clamp things - you know the bent things with the bolt through the middle that pivot on the end to hold the part down -- they just stick up too far most of the time and get in the way.

    When I don't have a choice, like when the work just has to be clamped with something other than the side clamps (thin stuff bows easily, sometimes double stick tape doesn't work, etc) I can pull the dust shoe off and just "go bare" and get dust all over the place.

    Finally, on the guitar, for the inlay on the headstock, I toyed with vacuum clamping and it worked pretty well. I had to hold down a 1/16" thick sheet of plastic and cut into it without going through - vacuum was the only way because double stick tape would've destroyed the final part (anything that dissolved my tape adhesive also dissolved the plastic!)

    Ultimately, workholding is, in my view, never a 'system' so much as it is a solution for the need at the time. LOTS of factors go into what works best. Sometimes the solution is to top-clamp and use the machine to drill a few holes that you use to screw the part down. Other times it's double stick tape or side clamps, or whatever it takes.
    Jason Beam
    Sacramento, CA

  5. #5
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    Quote Originally Posted by Dan Noren View Post
    ok, the question for me is, with the t track in the sacrificial board, how would you go about through cutting profiles? only thing i can think of (after posting this, naturally), is that the t track is well below the surface of the sacrificial board.

    The track is recessed, but i never cut into that table top - i did make it replaceable but i do all i can to avoid cutting into it. It saves me from having to re-cut those giant wedge shaped things (though, it's possible to get the machine to do it for me)
    Jason Beam
    Sacramento, CA

  6. #6
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    I see a road trip to Sacramento in my future.
    ++++++

    Some say the land of milk and honey; others say the land of fruits and nuts. All together my sort of heaven.

    Power is not taken. It is given. Who have you given yours to? Hmmmm?

    Carol Reed

  7. #7
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    Quote Originally Posted by Carol Reed View Post
    ... Dan and Bill seem to be screwing the workpiece directly to the table. Think I have seen that also on Leo's posts. ...
    Actually, I don't screw a work piece directly to the table. If it needs a through cut, I screw it to a sacrificial piece of 1/2" ply or mdf, then clamp the sacrificial piece to my table. I installed six 1/4-20 threaded inserts in the table for some strips I cut out of some oak and cherry for clamping. If I'm doing a surface etching, I'll clamp the piece directly to my table.

    Sometime soon, I'll replace the two pieces of 3/4" mdf that make up my table with a single piece. Having seen Jason's X system, I might have to take a look at that option. Right now, the support under my mdf table is a series of four 20mm by 20mm extrusions that run the length of the table (1500mm) that make it pretty stable, so we'll see what happens.
    Bill Arnold
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  8. #8
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    So, looking at it like sandwich. The bottom is the frame of the machine, in my case 8040 aluminum extrusion.

    Then a layer of say 3/4" MDF.

    On top of than another MDF or plywood layer with Jason's x cross tee-slots.

    For non-through cuts, fasten the work-piece to the tee-slot systems with the hold downs Jason mention with attention to height interferences.

    For through cuts, fasten a waste layer over the tee-slot layer via screwing into tee-nuts.

    Screw work-piece to the waste layer and cut away, mindful of the piece loose of the holding screws. Tab cutting I think they call that.

    Comments?
    ++++++

    Some say the land of milk and honey; others say the land of fruits and nuts. All together my sort of heaven.

    Power is not taken. It is given. Who have you given yours to? Hmmmm?

    Carol Reed

  9. #9
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    That's basically my method of operation most of the time, yeah.

    The tabs work and so does an "onion skin" method where you leave .005-.010" of material left on the bottom of the work to hold it - it's actually very strong. Another strategy i do is cut a profile about 2/3 the thickness of the piece (1/2" deep for a 3/4" thick part) then cut it free on the bandsaw and flush trim ... not an optimal method just from a time standpoint but it truly doesn't take that long to do. If i were in a production run of a given part, I'd build a fixture to eliminate as many ops as possible, though.

    the side clamping thing works great on anything 1/2" thick and above unless i'ts real long -- then the side forces can bow the piece up too much. Sometimes a little double stick tape between it and the main table is fine, other times, I just go the spoil board route and screw it down.
    Jason Beam
    Sacramento, CA

  10. #10
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    Quote Originally Posted by Carol Reed View Post
    So, looking at it like sandwich. The bottom is the frame of the machine, in my case 8040 aluminum extrusion.

    Then a layer of say 3/4" MDF.

    On top of than another MDF or plywood layer with Jason's x cross tee-slots.

    For non-through cuts, fasten the work-piece to the tee-slot systems with the hold downs Jason mention with attention to height interferences.

    For through cuts, fasten a waste layer over the tee-slot layer via screwing into tee-nuts.

    Screw work-piece to the waste layer and cut away, mindful of the piece loose of the holding screws. Tab cutting I think they call that.

    Comments?
    That's pretty much my plan exactly.
    Programmer - An organism that turns coffee into software.
    If all your friends are exactly like you, What an un-interesting life it must be.
    "A door is what a dog is perpetually on the wrong side of" Ogden Nash


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