Official Luthiers Forum!

I thought I should add some new content since I haven't done that for a while. I am also hoping that sometime before the summer I will post a new "processing tops" thread as I have some changes in mind for the process. Anyway, I just made a couple of dishes and took some pictures of the process. Prior to just over a year ago I made the dishes with a router, sleds and my rim sander. This is how I now do it on the CNC machine. I will have to show this in two posts as the pictures won't fit on just one.

First thing I do is make a "virtual dish" in Rhino. The completed dishes are 2 - 3/4" layers of MDF. The glued joint retains stability of the board while one surface is being milled (which builds stress in a single piece and will cause it to warp). So the first thing to do is to draw a 24" diamtre, 1.5" thick disc...Like this:



Once I have the disc I need to add a ball the diametre of the dish. This one is a custom 50' dish. In the following picture you can see the dish WAYYYY down at the bottom of the ball in the centre of the picture.



Next, we need to separate the ball from the disc and a bit of the disc where the ball was, creating a dish...ya still with me, cause I nearly lost myself there!?! Anyway, so here we have the dish with a surface applied:



And the last thing that is development related is to apply the tool path. I use a Rhino plug-in called MADcam for that (thanks to Michael Turner for the help when I started all of this and for suggesting MADcam..). So the final file looks like this:



I will show the machining process in the next post.

Shane

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Canada

OK, so once we have the computer work done we get to the wood work. The parts I am not showing are sawing a sheet (or sheets) of MDF into 24.125" squares on the table saw. Then I layout and drill a 3/8" diametre hole in the middle. That helps me align the blanks and also allows you to add things like a post if you want! Then I cut 3/4" discs out on the CNC...not shown here. Once I have these pieces, I glue them up with eight clamps around the edges and a bolt in the middle:



Once I have these made up, I place them on the CNC and hold them in place with a centre dowel and vacuum and start the program and rout them out, like this:



So now I have a dish (69 minutes on the CNC to get to this point!). The next steps are to clean them up, so I place them on my motorized rim sander and clean up the edges and remove the fine tool marks from the CNC.



Once they are all cleaned up I finish the sanding process by sprucing (pun intended!) up the back with a bit of sanding:



Once I have brushed all of the loose dust off of the dishes I apply a label that denotes the radius of the dish:



Then I apply two coats of waterbased varathane:



And once dry the dish is finished!



On my dishes I apply a piece 80 grit pressure adhesive sandpaper so the dish can be used for sanding or for use on the go bar deck. When I use the dish on the go bar deck I just cover the sandpaper with the paper I peeled off the back of the sandpaper when I applied it to the dish. That protects the wood being pressed in the go bar deck.

Anyway, I thought some of you might find this of some interest!

Thanks
Shane

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Canada

Thanks Shane, looks good.

Just curious but, would MADcam allow you to create a spiral tool path starting from the center (centre for you Canadians)?

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Shane, not to derail your thread, but just wondering if anyone has used the flip side of a radius dish as a disc sander.
I believe some folks may machine another radius on the back side to have both on one dish.
I realize that the rpm on a motorized dish is very slow but a large flat sandpapered surface is handy even for manual sanding.
Nelson

Hey Andy, Yup, MADcam has that function but the file size almost triples and I would have to network in my computer to deal with a file that size. I have tried it but don't really see the advantage. With this 3D profile 2 Axis' are always on the move and the third is stationary. In a spiral rout it would the same, just a different pair so I have elected to keep it like this. It is very accurate and works great for me. The spiral tool path also requires an initial plunge cut to the depth of the dish. This 50' dish is only .120" in the centre but a 10' dish is .602" in the middle so the initial plunge is nearly 5/8" deep! My stepovers are only .030 with a 1" Amana ballnose insert cutter (Thanks Nelson!)

Nelson, I have made lots of double sided dishes, there is even one in Italy! As for the sander, one could easily use a flat sanding surface if one needed one. My sander turns at about 120 rpm.

Thanks
Shane

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Canada

HI Shane,

May I comment on Madcam a bit?
Yes you can do a spiral cut as well as the cut like Shane used. In addition, you can also do a roughing cut that will take all the material less whatever you care to leave for the finishing pass. The new (v5) of Madcam will allowyou to pick where tool bit enters the work part. For anyone considering cam for Rhino, give Madcam a uninhibited 30 trial. The offer allows the user to cut real world parts for 30 days while learning something about the software and deciding if this is the direction you want to go.

Mike

I don't know if my dish was CNC'd or routed but I will say it is a great product and reasonably priced. Keep the good stuff coming Shane

Fred

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Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

Cool Mike! Is this the 3 axis version or the 5? Maybe I will e-mail Joakim and see if I should be looking for an upgrade! It really os a great little program, easy to use and powerful!

Thanks
Shane

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Canada

People have been asking about prices.

The dishes are $75 each but on March 1st the price will be increasing to $87.50 (the price hasn't changed in over 5 years!). Shipping is a bit high for these as they weigh in at 17 pounds. But the dishes are complete once you get them, no need to "laminate them to a second surface" as is suggested by some other vendors, as I have done that before the dish was made. So shipping is as follows:

1 dish to California - $39
2 dishes to California - $60

1 dish to NY - $46
2 dishes to NY - $78

Shipping is actual costs plus $2 to $3 for packaging.

Thanks

Shane

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Canada