Easy Hold Down Table

discussion of design changes / improvements / suggestions

Easy Hold Down Table

Postby edwardrford » Tue Dec 04, 2012 11:02 pm

Something i've been struggling with since day 1 is how to hold down materials when milling. I've tried a variety of things, but ultimately I resort to using screws. For lots of materials (like plexi, or any sort of wood) this requires drilling pilot holes through the material before trying to screw it down to the work surface. One of the many downsides of this is that your worksurface gets destroyed rather quickly as one tends to hold down material in the same position in their machine, and because of the nature of wood screws and MDF (tears it apart!).

I've been working with t-tracks, which I like quite a bit, but they require access to one end of the track in order to slide the t-bolt into. In some circumstances, this can work on shapeoko. I'm using this setup now actually with my upgraded (open front/back) style machine.

However, last week a discussion about something else came up over here, and Frank and I started talking about a captive nut hold down method. Shortly after, I had a prototype made and tested. Here's a picture:
proto_table.jpg (144.34 KiB) Viewed 11791 times

It's a scrap piece of 3/4" MDF I had laying around. And by scrap I mean *crap*. It's about 10 years old and really dried out. It did however get the job done. I milled 6 holes, each with a pocket to keep the bottom of the t-nut flush with the bottom of the MDF. This process can be done with Shapeoko. To mount the MDF to the existing waste board, that comes with the kit, I think either gorilla glue OR just some wood screws from the bottom of the waste board into the bottom of the MDF will work perfectly. Or both :-)

The t-nuts are only 7/16" from bottom to top, so there should be enough clearance (~1/4") to allow for mistakes to be made in depth of cut without running the risk of slamming into one of the captive nuts!

Then I quickly drew up and milled out some 'clamps' These are 1/4" aspen, not the best material as it's pretty soft, with a .0625" step and a 0.125" step towards the tip.
proto_clamps.jpg (140.84 KiB) Viewed 11791 times

proto_clamps2.JPG (124.06 KiB) Viewed 11791 times

Once I was happy with the way it worked (very well!) I went ahead and picked up a piece of 12" x 12" x 3/4" MDF from work along with the t-nuts to use as the captive nuts. These are 6 prong t-nuts, which are better suited for MDF.
finished_layout.jpg (119.92 KiB) Viewed 11791 times

The final-final layout will actually use up to 20 of the t-nuts (they come in 10 packs, and I wanted 12 so I bought 2 packs...). i found with my experienting (laying things out in 3D) that the more hold down locations you have, the better!

I'll make the final hold downs out of this 1/4" UHMW that I have laying around. I'm thinking a combination of straight pieces, to use as stops, and longer and shorter stepper clamps will work out really well.
finished_clamp_material.JPG (112.71 KiB) Viewed 11791 times

All in all I'm REALLY excited about this! I'll post back here with any updates. I'm planning to release the entire project along with instructional video in the next few days. Open to suggestions at this point, just let me know if you have a design improvement!

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Re: Easy Hold Down Table

Postby jsbannis » Tue Dec 04, 2012 11:54 pm

This was one of the ideas I had thought about for hold down when I first was building everything. Those T-nuts are surprisingly hard to find in hardware stores or online from places with a decent shipping price for small items. I have 4 of them sitting around, since it seems to work well I'll have to try it. I'm gathering stuff for PCB milling and 4 hold down points should work well since it seems I'll probably be using 2"x3" boards for a while. Thanks for being the guinea pig ;)
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Re: Easy Hold Down Table

Postby nfortosis » Wed Dec 05, 2012 12:19 am

I got these a couple weeks ago from amazon. Shipping costs more than the product, but you are still under $10 total for 50 of them. It may be worth checking Parts Express own website to see if its cheaper.

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Re: Easy Hold Down Table

Postby cvoinescu » Wed Dec 05, 2012 12:23 am

I'm glad there's one thing that's easier to find in the UK than in the US! Those nuts are cheap and easily available here. Also, these may also work. I've always wanted table for my ShapeOko, but never got around to doing it...
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Re: Easy Hold Down Table

Postby edwardrford » Wed Dec 05, 2012 12:52 am

It's interesting. I think lots of us are in the same boat here we started using our machines, found feeble work around for holding the materials and thought "ill get to it later" and/or that a proper gold down system wouldn't be worth the time/energy to implement it.

As the official tether of the project I can tell you with certainty IT'S TOTALLY worth it! Ill never go back to screwing materials down. Save the special scenario where it makes sense :)

Glad I'm not the only one excited about this one!

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Re: Easy Hold Down Table

Postby madmike88 » Wed Dec 05, 2012 4:40 am

Very cool, I had just ordered the HF Table you recommended with a 20% off coupon. Now I will have to do this too.

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Re: Easy Hold Down Table

Postby deejayspinz » Wed Dec 05, 2012 10:38 am

Did the same thing for my 1000mm base.

Edit: re-sized image down since we don't need to see what molecular structure MDF is made of! Sorry, thought I already did this during my last edit!
HOLDDOWNS.jpg (59.72 KiB) Viewed 11706 times
Last edited by deejayspinz on Wed Dec 05, 2012 4:18 pm, edited 1 time in total.
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Re: Easy Hold Down Table

Postby kf4mot » Wed Dec 05, 2012 3:43 pm

Where can we get some steel clamps like that? I'm not even sure what to google
Slot clamp maybe??
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Re: Easy Hold Down Table

Postby edwardrford » Wed Dec 05, 2012 4:10 pm

Which steel clamps? Something like this:
hold_down_clamp.jpg (11.86 KiB) Viewed 11712 times

If so, those are called either 'toggle clamps' or simply 'hold down clamps'.

We're selling them now through inventables: https://www.inventables.com/technologies/hold-down-clamp or you can google for them.

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Re: Easy Hold Down Table

Postby Sinktank » Mon Dec 17, 2012 8:04 pm


Instead of captive nuts, would it be possible to extend the life of your MDF holes by drilling a large diameter hole, say 12mm, fill it with epoxy resin, then drill and tap a 6mm hole in the hardened epoxy? Rinse and repeat if/when the thread wears out.

Mind you, the epoxy might cost more than just getting a new MDF off-cut from the wood shop...
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