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Old 05-21-2017, 06:43 PM
Moulder Moulder is offline
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Default $350 cnc plywood router

I just saw this on youtube and thought some here might find it interesting. This might be a cheap way to make your own plywood bucks at home.

https://youtu.be/y60q6U7NjTQ
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Old 05-21-2017, 07:45 PM
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Plywood can still be cut quite nicely with a scrollsaw or bandsaw. Bucks have been made for more than a hundred years.
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Old 05-21-2017, 08:23 PM
Moulder Moulder is offline
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That is absolutely true. When life finally allows me enough free time to get serious about metal shaping, a hand constructed buck will be the method I choose. There is more than one way to skin a cat. Some prefer technology to old school/world methods. It is an interesting take on a cnc machine. Maybe they are out there but I've never seen one that uses gravity like this
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Old 05-21-2017, 09:37 PM
Marc Bourget Marc Bourget is offline
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That's because this requires a higher order of math.

The reason the accuracy differs from one area to another is that they haven't allowed for the Catenary Curve of the chains.

In physics and geometry, a catenary is the curve that an idealized hanging chain or cable assumes under its own weight.

In the lower right corner the right hand chain will be more vertical and the catenary will be very low.

Just the opposite with the left hand chain, it's weight would cause it to droop and the + x position would be less than what the stepper motor is telling the controller.

FWIW
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Old 05-21-2017, 10:10 PM
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Kerry Pinkerton Kerry Pinkerton is offline
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Dang Marc, that's good stuff right there. I have seen that behavior exhibited in 'stuff' before but never thought through why.

This site continually amazes me with the skills and knowledge of the group.
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Old 05-21-2017, 10:16 PM
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Kerry Pinkerton Kerry Pinkerton is offline
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To follow up on what Richard said, some years back when MM was doing the Sultan's Bugatti design (which was sadly all lost in the backup fiasco), I asked Gene Olsen to make me printouts for a cycle car size (8' long roadster version of the body. He printed them full size on an antique Hewlett-Packard pen plotter and sent the drawings for all the ribs and spars to me.

I purchased a few sheets of 7 ply marine 1/2" plywood, glued the drawings to the plywood with spray contact cement. In about a day, I had cut out the entire buck for the body. He later sent me the drawings for the fenders but I have never got around to making the buck because I lost interest in the project when I started on my roadster. The buck is up in the attic of my shop.

My point is that the buck is probably within 1/16 of the drawings and that is about as close as I'm ever going to work a buck to anyway. Final smoothing will always be creating fair curves from panel to panel...buck be damned.
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Old 05-21-2017, 11:15 PM
bobadame bobadame is online now
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I think if they used a carbon fiber strand over a spool to drive the encoders they could get very close to their .015 tolerance. Still use the roller chain to drive the router but feed back it's position through a lighter, stiffer system.

Even as a 4' X 8' pen plotter, this machine would be useful to create full scale patterns for buck stations.
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Old 05-22-2017, 01:19 AM
steve.murphy steve.murphy is offline
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Might be a cost effective way to make up body sweeps.
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Old 05-22-2017, 08:28 AM
toreadorxlt toreadorxlt is offline
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I hang out at wrays shop quite a bit and help him with scanning. Last year, we went from Scan to CAD on a 34 quarter panel ready for routering in less than an hour. It's easy to dismiss technology when you haven't used it.
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