Official Luthiers Forum!

Well,

I finally have all of the belts changed on my CNC machine and run it all over the place with the controller. I have a bunch of orders for sanding dishes which it typically make on my shopbuilt rim sander. But I thought maybe the cnc machine would be a good option to do these in future and also may be a good way to used to the machine. So I was playing around in my version of Rhino 4 and can make the cylinder real easy but am having trouble making a dish in the top. Anybody have any tips on doing that?

Thanks

Shane

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Canada

Shane what radius of the dish and what diam of the edge and depth?

Mike

Shane think of it as a revolve. Draw your curve in side view,include the side and bottom lines too, and spin it on its center. If you need geometry I could easily create it for you in Solidworks tomorrow in a couple minutes. I export in IGES, STEP, STL, whatever you need. And if you want multiple profiles I can do that too, let me know I would be glad to help.

Or email me and we can get on the phone and I could walk you through it.
mctracz@yahoo.com

Oh and if you need help with surfacing/creating models (necks, bodies, molds, jigs, etc.) in 3D I can help you out there too. I build in Solidworks everyday, as an Industrial Designer. Usually injection molded objects like medical devices, consumer electronics, packaging, housewares, and even juvenile products. Its fun stuff!

_Mike

Ps. Have you found any Weissenborn tops in your stash?

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_Mike Tracz
MCT Guitars
https://www.instagram.com/mustcreatethings/
https://www.youtube.com/mustcreatethings

Man I love this place!! Mike (turmite), the dishes I make are double laminated 3/4 mdf so they start out at 1.5 inches thick by 24 inch diametre. The radii I have as stock is 10', 12', 15', 20', 28', 30' and 45'. I am hoping that with the cnc I can make any specified radius without having to make new ramp rails for the router ( ).

Mike (mtracz), that is a SUPER offer!! And maybe we should talk offline about some of that (and I do have some weiss sets ready now as well, and some Mahogany back and side weiss sets as well!). I purchased Rhino 4 and really want to figure this out. The problem is I always have a thousand things on my plate and I never find the time to spend a week learning a new program or process, so I am looking for a short cut ( I should apologize for that). I am sure that once I start using the program and get shown a few basics I will be able to make adjustments for other needs. So, I am going to try your suggestion and see how that works. Also, I just read through part of the manual a bit and I may be able to start with a cylinder and use "loft" and "extrude" commands to get the shape I need. I did a bunch of math last night and have the offsets (the dish depths) for all of the radii I mentioned, for example, a 25' radius dish 24" wide will have a reduced depth in the middle of 0.24".

Mike, I am REALLY interested in learning how to model and surface necks, bridges and every other thing guitar related. I am sure that once I learn something like a neck I should be able to apply those processes to modeling bridges, electric guitar bodies, etc. I am quite excited and anxious to actually finally produce something on this CNC machine, I have had it for a few months now and now that it is all together, I want to make things!

Thanks you guys! AWESOME!

Shane

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Canada

Hi Shane,

Attached, I hope is a zip file with a Rhino tutorial in it I made for you. Follow the steps and read the text block in the top view!

I could have modeled all the dishes faster than I made the tut, but it will help you tremendously to do this exercise and learn from it.

You resemble me 4 years ago.....problem is, I am still in the same boat. Too many things to do to sit down and really study Rhino, and I know it would same me tons of money if I would!

Mike

ps...wow, they won't allow extensions with zip!

pm me your email address

Thanks Mike and Mike...you guys are getting me there!

Shane

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Canada

Yes... Thanks for emailing me the Rhino tutorial. Just opened it up in Rhino now.

Looks Great!!!

Thanks Mike

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Rick Hubka
Chemainus BC Canada

Just to confirm....WHAT A GREAT COMMUNITY!! The two Mike's jumped in and offered help right away. Mike Turner did up a tutorial and e-mailed it to me, I was confused (not difficult to do!) so I called him. I had drawn the dishes in a slightly different format than he had presented (I did a bunch of math first which apparently isn't needed but just worked better for my mind) but couldn't get the dishes finished (I had a huge ball sitting on a 24" cylinder and needed the ball taken away from everywhere except from on top of the cylinder and then I needed the cylinder's "lid" replaced with the outline of the ball). So, within literally 10 seconds on the phone, I was done! Here is a 25' dish. I can draw any radius dish now in about 20 seconds or so.



Mike (and Mike), thanks again for all of the very quick and accurate help!

Shane

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Canada

I think what you've done is similar to what I do: boolean subtract the ball from the base. If so, then run the 'shrink trimmed surfaces' command once you're done with the modelling. It turns the concave surface into just what you see rather than a trimmed spherical surface (it makes a difference to the software, even though the geometry is identical). You can end up with some funny errors in CAM or massive file sizes if you skip this one (and how!).

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

DONE! Thanks Bob.

Now I am drawing out a vacuum hold down for the dishes so that I can just place these dishes on the jig and get to work!

I will post pictures of the operation once I have it all done (might be a week or two)!

Thanks

Shane

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Canada

Bob can you explain why it makes a difference to the software. I too am a little like Shane, and explainations sure help me to understand.

The funny errors I understand, but can you explain the file size difference. Is this something that can be verified by camming the same surface twice, once without the "shrink trimmed surfaces" and once with?

I love Rhino, but man is there ever so much stuff to learn!!!

Mike

ps Shane,......you're welcome.

In the case of this dish (made with a boolean), the software will keep the whole sphere used to make the top surface in memory. So, depending on what you're doing, it's still keeping track of a giant surface that you don't need. Shrinking the trimmed surface 'deletes' the unused part of the large surface and rebuilds it to keep only the used portion.

It might not make any difference in Rhino, as they might have some sort of algorithm in place to ignore the unused portions until they're called for, but I know that it can make a big difference when you export to other file formats. The first time I really noticed the effect was, I believe, when I exported to an IGES file and opened it in MasterCAM. Rotating the model was -really- laggy for such a small surface, and I narrowed down the problem to untrimmed surfaces (and the issue went away when I shrunk them and re-exported).

If you consider that some objects (let's say you made a bridge or even a mold or something more complex using a lot of booleans) could have a load of extra junk in memory, the performance hit could be huge in some cases.

On the flip side, having the untrimmed surfaces in memory does allow you a bit more room to 'step backward' through your design at a later date and make changes by untrimming those surfaces. That said, I'd rather just use the incremental save command in Rhino or use something like Solidworks and be able to really go backwards in my design if changes need to be made.

I hope that was at least as clear as pond-water on where shrinking trimmed surfaces can make a difference

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services