Clamping for spoilboard

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MDHunt
Posts: 31
Joined: Sun Dec 04, 2016 8:34 pm

Clamping for spoilboard

Post by MDHunt »

I finally got my system set up and when I ran my first project, the wood shifted when the bit changed direction. I had it clamped with two clamps and tightened it after the first slip. It slipped again.
I am wondering what you all can offer for help with clamping wood to an MDG spoil board.
Thanks

Rando
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Location: Boise, ID
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Re: Clamping for spoilboard

Post by Rando »

If the board is moving even though clamped reasonably tight, then it's more normally a too-fast feedrate, and you're actually seeing the cutting forces being transmitted to the piece, overpowering the clamps. Just as a test, try sliding the feedrate slider in the control panel down to like 50% or 25% and testing the run. If it doesn't move, or moves less, then it's likely that. You can reduce cutting forces by either taking more-shallow cuts (lower "axial engagement"), or by slowing down the progress through the material. If you take that second approach, you'll probably want to slow down the router/spindle bit about 1/2 as much as you lowered the feedrate.

One way that can add just a little friction is to take a small piece of thin, say 220+ grit sandpaper. Fold it in half to the grit sides are out, and put that under the MDF under where it's clamped. That'll hold 'er! You can also do things like put a very light coat of spray-on adhesive on the bottom of the spoil board, letting it dry completely (you want the rubber, not the sticky). That also will provide greater stiction (yes, it's a thing https://www.merriam-webster.com/dictionary/stiction ;-). Other ways of keeping it from moving include HARD bolting down solid blocks as registration surfaces/points.

Beyond that, torque them clamps! But, don't ruin the t-slots, I suppose :D. Also, remember that those aluminum, bent-arm clamps can only hold "down". If you have it coming onto the wood from the side, significant forces perpendicular to that direction isn't properly handled. So, when you clamp, try using four clamps, two on each end, all going along the bed length, one in each corner, with each clamp coming in from the end, not the side. Okay, that's confusing...a picture....
4-18-2017 8-26-29 PM.jpg
Bottom line, more is better, until you hit one of them with the bit ;-)

Workholding is a very broad category, to be sure. You'll find the ways that work for you. Honestly, if it were me, I'd get rid of the MDF, and just go with a 50-pound machining vise....oh, wait...that IS what I did :D Okay, maybe YOU don't want to:
20170415_213849.jpg
Regards,

Thom
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