CNC Hold Down Methods

Hi everyone! I wanted to share a new video I did on my CNC hold down methods. I use a lot of these techniques in my videos, but i thought it would be good to catalog them in one spot, and discuss some of the pluses and minuses about various options.

I’m interested to hear what other techniques you guys have for hold down. Let me know!

Excellent video, Corbin!

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Great video, I commend you on your open delivery and sharing. I am surprised you did not mention JIGS. Jigs are your friend for any kind of repeat cuts. I use dogs every time for orientation. Use them to orient jigs as well. I also use threaded inserts vs tracks, I know some don’t like them but for me they are great, I use them in my jigs too. Perhaps a new idea, I make blocks with domino or biscuit in the side then match that to the side of a work piece where I can afford the slot for a zero clearance hold down. This allows you to use a lesser Z movement which increases cut speed significantly. I’ll try and post a picture.


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That’s a good point - I didn’t even think about mentioning jigs! I do use them, but mainly for alignment.

Whoa, that is definitely a new idea that I haven’t seen before! I can imagine that you could offset the mortise slightly to allow it to have more down pressure (sort of like draw boring). I might have to experiment with this idea for some of my projects. Thanks for sharing!

Corbin

Biscuits, that’s a new one and a great idea.
Thank you, Corbin for your great video and the stimulus to more discussion!

I have a Domino cutter and about the only thing I use it for anymore is cutting slots for clamping on the CNC.

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Cool Rich! This seems like a great way to do a production run. Thanks for sharing the photo.

@corbin everything you do is amazing. So thankful to have you in our community!

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@Rich-in-SLO , did you really put a plastic nose and glasses on your dust boot mustache (at the top of your picture)? Hah! What fun.

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I tried an Omer composite nail gun to hold down 1" thick 5’x5’ sheets of Baltic birch plywood. Either 1) the gun didn’t have enough power to shoot the nails through the 1" dense veneers and glue and into the spoilboard, or 2) after the composite nail penetrated the plywood, it “bounced” off the MDF spoilboard before re-penetrating, creating a gap btwn the plywood and the spoilboard. Clamps won’t work as the sheets are too big for clamps to reach. I end up using regular nails and a hammer.

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Whoa, that is surprising! I was thinking I wanted to get one at some point, in lieu of a vacuum table, but now I am wondering if they are strong enough.

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It would be good to hear from other composite gun users; they might have better experience or tips. The problem could also be the Baltic birch itself - so much glue, really dense vs. normal plywood, plus I’m using 1" rather than 3/4" thick stock. If clamps could reach all the way around to hold the ply tight to the spoilboard before nailing, the Omer would likely work fine. However, if the plywood is at all convex-cupped, no hold-downs, tape, or clamps will work; only normal (steel) nails or screws will.

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I have had the exact same issue with the ohmer nailer, even with mdf. I have to overdo it quite a bit because it is a 50/50 shot if the brad actually goes into the spoilboard. I have reverted to just using screws or t-track clamps for 1" or thinner stock.

I recently made a t-track table like corbin’s, and its fantastic. I normally work with 3-4" stock and double ops, so I use a hand router to cut divots in the side of stock and crank it down with t-track clamps:

@greg.obj Sticking the clamps in side slots is a good idea! Kind of like the biscuit/domino technique mentioned above.

Works great. I would love to machine aluminum ones with a slim tip that can fit in holes cut with a biscuit joiner, mine is just collecting dust as well.

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I use the Spotnailer 15 ga composite nailer for my MDF sheet work. My air is about 125 PSI at the gun. Anything less than that produces poor results. I use some birch plywood as well and it seems to be fine. I use a lot of work boards (fixtures). Some of them have t-track in the work board and I use the Armor self-adjusting clamps when possible. They make quick work of swapping parts during a production run.