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Thread: Holding the Workpiece

  1. #16
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    Quote Originally Posted by Jim Becker View Post
    Many folks use that concept, albeit implemented differently. It's not unusual for someone to have a grid of threaded inserts in a CNC cable that can be used for work holding purposes. The surface is usually made of something like MDF because you feel a heck of a lot less unhappy if you hit it with a cutter than you would with an aluminum surface. Nylon bolts add a safety measure there, too, although metal fasteners also get used. While some folks do this on larger machines, it's more typical on smaller, desktop machines from what I've seen. There is nice value on a regular grid of embedded fasteners for work holding AND alignment...not unlike the value of the grid on a Festool MFT.

    An alternative on some machines is an actual aluminum bed made of strips that can not only hold an MDF spoilboard, but are spaced such that you can slide a nut/bolt anywhere along the length of the slot. And as you know from my machine, I have some embedded channels for holding clamps using bolts and nuts.
    Aluminum is ok, but running into steel isn't.

    Exactly, the value is in repeatable placement. I installed one on my mortiser for similar purpose.
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  2. #17
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    Quote Originally Posted by David Buchhauser View Post
    Small fixture plate on a cnc router.

    Attachment 419592
    That's a really nice setup!
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  3. #18
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    Quote Originally Posted by Brian Holcombe View Post
    Aluminum is ok, but running into steel isn't.
    Yes, steel is to be avoided for sure! But running a cutter into aluminum with more of a bite than normal still results in potentially breaking costly tooling...and an unsightly and permanent scaring of the beautiful aluminum. So an aluminum fixture still has to be very carefully designed to avoid that as much as possible.
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  4. #19
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    I Am So New To This.....that I squeak when I walk!!!! My machine is now moving around and I did the Hello World job with the Sharpie pen. All is well so far except for tweaking the X axis drag chain. Now, I have to figure out "how" to hold my work pieces down. Way too many choices to choose from and I don't have time right now to study each one. Keep in mind of where I live....where you can't buy much of anything locally. If there are some I can make on the CNC, I'd like the SVG file so I can give it a try. Right now, I'm opting for 2" painters tape, CA glue, and Accelerator....at least to do my very first cut or two. I'm also trying to figure out dust collection for the machine. But that can come in a different thread.
    Thanks & Happy Wood Chips,
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  5. #20
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    Dennis, I've seen a lot of folks put a grid of embedded threaded nuts into the table for small machines so they can have a very flexible clamping setup without losing height like they might by embedding T-track. I only use the painter's tape and super glue thing for thin materials for the most part, but it's definitely the thing for many kinds of tasks.
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  6. #21
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    I've ordered t-nuts, screws and washers off Amazon and I've found some SVG files for clamps and one for a spoil board for t-nuts. I'm hoping to be "up and running" by very early next week.
    Thanks & Happy Wood Chips,
    Dennis -
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  7. #22
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    Sounds like a plan, Dennis! BTW, I'm liking the clamps I made from straight grained oak the best so far...about .375" thick with just enough flex to clamp down really securely with out breaking.
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  8. #23
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    Dennis,
    Several years ago (on my first cnc router build) I made the mistake of installing threaded inserts into the top of my 3/4" MDF spoilboard/top. I discovered that with the clamps I was using the pressure was too much and some of them started pulling out and bulging up the flat surface of the MDF.

    Threaded Inserts.jpg

    If I were to do it over again, I would install T-nuts from the bottom of the table instead. I assume that you have ordered something similar and are doing the same sort of installation from the underside of the table.

    T-Nuts.jpg

    David

  9. #24
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    That's a really good point, David. The amount of force that can be exerted when tightening down clamps properly can be quite high and as you note, completely blow through MDF with just a threaded insert. I should have noted that.
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  10. #25
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    David,
    Yes....I've ordered T-Nuts, screws, and washers. My plan is to secure a secondary waste board on top of the factory supplied waste board and machine the t-nuts and holes in that piece without chewing up the factory board. I don't need a lot of height on my machine currently, but I'm already planning for a 2nd machine in the future that will give me more rigidity, Z height, and performance.
    Thanks & Happy Wood Chips,
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  11. #26
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    I just did the threaded nuts coming from bottom up on the spoilboard. I really don't like the setup. There are several issues. Holes aren't in right place. Clamps are above the work (Yeah, I thought it wouldn't matter a lot, but it does} you DO need more than side pressure as it won't hold work DOWN.
    But the main issue is PULLING YOUR SPOILBOARD AND THE WORK UP! How? use a bolt that goes down into the nut and hits the lower board. You then are pushing the upper board and the work UP and distorting the work. ARGH.
    You might think this is hard to do, but I've found it isn't. You must be careful with this setup. And as My work has varied from quarter inch to 1 inch height, I have to have different length bolts to use clamps... A real PITA!

    Next time I do this, I'm going with two y parallel and one x parallel track and spoilboard between. that way I can do bolts the correct length ALWAYS.
    And I just bought a bunch of painter's tape and CA glue. I tried that the other day and it worked well. Probably go to that for a while also.
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  12. #27
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    John, if putting in the bolts deflect your spoilboard because they come in contact with the machine top below...either the bolts need to be shorter or you need to put holes in the machine table to provide relief for the ends of the bolts.

    You are correct that when clamping it's necessary to account for both lateral and vertical forces. the design of the clamps can help with that...flat clamps with lips will support the material in both lateral and vertical axis at the same time. You can see what I mean in this thread.... https://sawmillcreek.org/showthread....ghlight=clamps I later made more of these using straight-grained oak and prefer them over the scrap plywood versions. What's good about this design is that it can be scaled to be optimal for different thicknesses.
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  13. #28
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    I installed a 3/4" thick plywood base first and then put MDF on top so I always have the plywood to hold screws tight.
    My MDF spoil board is just about as thin as it can get now and needs to be replaced soon. I have mentioned before that I am going to use PVC sheet on top of my plywood for the next round and see how that works. I have on occasion installed a temporary PVC sheet on top of my MDF for several jobs so I could machine recessed areas for special jobs in the past. This worked well and I am pretty sure that a PVC spoil board with be the hot setup. I will still need to keep a smooth PVC sheet available for the times when I need to print paper templates with my CNC. I do this quite often for chisel letter installs.

  14. #29
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    Jim, sure, but it is still a guess, is it tight because I'm hitting bottom, or just because it's getting tight. T tracks next time..... I sure thought about it, and should have done it.
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  15. #30
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    I am not a fan of the tapped holes/threaded insert method. I have about 250 5/16-18 threaded inserts I will sell at a really good price....

    My issue with that idea is that the tapped holes can and do fill up with chips. The other issue can be the amount of "reach" the clamps have. Ideally the bolt for the clamp should be closer to the work than it is to the spacer block. In fact, the closer you get to the work the better the holding power. Simple physics. I have seen quite a few pics and vids where the placement of the tapped holes cause the user to clamp closer to the spacer block.

    After I tried it and got tired of cleaning those holes I switched to t-track. No, I do not route a groove in the spoiler board for the t-tracks. Instead they are fixed to the sub table permanently. Since they are only .5 thick it is an easy matter to rip strips out of 3/4 inch material to fit between them. That leaves 1/4 inch for surfacing flat. Much easier to pass the vacuum along the length of the t-track and presto, it is ready to go.

    The threaded insert method is a PITA when the spoil board wears out. Go get a new one, drill and counter bore a gagillion holes, remove all the inserts (a pita all by itself), then reinstall them.

    What I do like the idea of is a pallet board that is threaded and can be added when needed. May have to go to the junk yard and see about a piece of 3/4 thick aluminum.

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