Official Luthiers Forum!

Well thanks to a few on this website (you know who you are) I have been inspired to get a CNC router for my shop. After looking into purchasing a machine I quickly ruled this option out due to cost so 6 months ago I start collecting various new and used parts with the idea of building one. So after finially getting in figured out (kind of) I have most of what I need and now it is time to start building. The first picture shows a general rendering of the router. The machine will be a 36 x 24 x 8" gantry style machine. Each axis is driven by servo motors which if all goes well should be capable of around 500 ipm rapids (in theory?!?). I will be controling the servo's using Gecko 320 drives and Linux EMC2 control software.

Here is a Solidmodel of the router. The x axis will be driven by a single motor from below via a timing belt. The rendering shows the motor and right angle gearbox inside the table but not the belt. The x, y, & z axis are linear actuators that use either HTD belt drives (x axis) or ball screws (y & z).


Here is picture of the controls. (3) Gecko 320 drives, (3) 68V power supplies, and CNC4PC breakout board. All mounted in a PC server case. Still much to do but it is a start in the right direction.


Thanks for looking. I will post more as I move along.

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Brad
Avon, OH

Awesome Brad!! Well beyond me!! Looking forward to seeing it at work! I am sure that the others will post in on the technical issues. Make sure that you have a mechanism to adjust the belt tension. I am just about to adjust mine, it probably has never been done in the ten years of the machines life and I have to take the front rail off to do it. They are a little loose!

Good luck

Shane

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Canada

How much belt tension is the right amount? I have been wondering about this.

How is your setup coming along?

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Brad
Avon, OH

Guys, I don't think you should need tension adjustment on a timing (cogged) belt.
The center to center distance of the shafts is determined by a formula that supposedly places the belt at the right tension.
But then I guess that backlash would increase if the belt did stretch over time.
Hmm. Other thoughts?
Nelson

I think if it is a short belt, you probably don't need a tensioner. The longer the belt gets the more prone it would be to stretching to the point that it could disengage from the sheave.

My K2 uses timing belts without tensioners

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http://www.PeakeGuitars.com

My Precix has a small adjustment for the belts. It is a bit of an ordeal (that I may even tackle tonight) as you have to remove the front rail to get at the adjusting machine screws. The manual for my machine says that the belts should be replaced about once per year but when when I called the manufacturer they said that really they will easily last 10 to 15 years or longer but that they should be snug. Mine have a bit of slop in them and I don't think that they have ever been adjusted (judging by the placement of the adjustment now).

Brad, I have everything here now to run the machine. All of the software, the new spindle nut and collets. All I need now is to get over the fear!! And turn it on! I have used the controller and moved the axises around and used the controller to start and stop the spindle. My table is fairly large 50 x 60 inches or so, and is set up with three vacuums to hold things to the table. I want to add inserts into the table so I can attach (bolt) fixtures for the various small luthiery items I want to machine so I need to build a program so that the machine will drill the holes in itself and then I can use the same program for drill the holes in the fixture bases. I figure it will be few months before I have any clue what I am doing. But the potential is tremendous! I am looking forward to seeing your rig up and running.

Shane

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Canada

Shane...have you considered making a fixture "sub-table" that would have inserts that would sit on top of your vacuum table and be held in place with your vacuum? I always thought it would a great setup to use the vacuum to hold the fixuture and the fixture to hold the workpiece (assuming the workpiece could not be held via vacuum). This would make changing from fixture to fixture very quick.

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Brad
Avon, OH

I've yet to find any wooden guitar part that can't be held down with vacuum, though fixture design is certainly more challenging on some. I have considered making a pallet system that held down the pallets with vacuum, but I've never had a part with both the numbers and short cycle time to justify the time making it.

The table on my Fadal is drilled out for dowel pins like the ones at Taylor, so all my fixtures index back in the same place every time I put them on. Kevin Ryan uses something similar; he has an aluminum plate mounted to his table that has indexing pins and tapped holes. If you use index pins to lay down your fixtures, sometimes you need to plan how you'll get them off the pins once they're flush to the table!

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services