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scordatura

CNC Making Discussion

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The software part of Don’s post needs a lot of emphasis. A user must learn how to design in CAD. Then, the CAM part is no easy thing either. As Don noted doing 3D can be daunting. If you enjoy figuring things out, you’ll love CNC. However, it will take time away from making in the beginning, but put you on warp speed later.

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1 hour ago, Michael_Molnar said:

If you enjoy figuring things out, you’ll love CNC. However, it will take time away from making in the beginning, but put you on warp speed later.

I hope my "later" comes sooner.  Running on impulse drive is painfully slow.

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Yes I would describe my CNC efforts so far as fits and starts. Excitement and effort followed by...this is daunting...renewed interest...what have I gotten myself into!  Oh just hone the gouge and have at it old school. :)

I am in the CAM phase now. Figuring out tool paths. Deciding if I should do the CAM and G code in Fusion 360 or use VCarve Pro for the CAM and G code. 

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3 hours ago, scordatura said:

I am in the CAM phase now. Figuring out tool paths. Deciding if I should do the CAM and G code in Fusion 360 or use VCarve Pro for the CAM and G code. 

Folks on a CNC users' group seemed to be fairly unanimous that Fusion360 has the best CAM package.  Although I haven't ever used anything else, it does seem to be relatively user-friendly as well as powerful.  I feel more comfortable with the CAM than the CAD, oddly enough.

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I spent the bulk of my career working at Alias / Autodesk. I even worked with the fusion team for a bit on the rendering software. Benefit of Fusion is that the CAD and CAM are integrated into a single package and for personal use it is free. For folks in our industry looking at CAM -- you couldn't do any better. If you want to experiment with generative design, it is also worth having a look at Rhino / Grasshopper.

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1 hour ago, Urban Luthier said:

I spent the bulk of my career working at Alias / Autodesk. I even worked with the fusion team for a bit on the rendering software. Benefit of Fusion is that the CAD and CAM are integrated into a single package and for personal use it is free. For folks in our industry looking at CAM -- you couldn't do any better. If you want to experiment with generative design, it is also worth having a look at Rhino / Grasshopper.

Agreed.

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As an alternative to using CNC machinery have any of you seen the wood router offered by Gemini? Looks like a great option for those wishing to avoid the high initial investment of laser scanning along with having a lot less to go wrong. I work with lots of laser scanning and high end 3D printing in a dental laboratory along with some experience with CNC machinery in producing custom components for cars. Feel free to pick my brain if anyone needs help with figuring out how to export and edit STL files. 

Here's a demo of it. Not too bad for $3200. 

 

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Doing all of the operations in Fusion 360 makes sense. For those who do not know, both Fusion 360 and VCarve Pro can be had for free. The VCarve Pro is a trial that does not have limited functionality or a time period. VCarve Pro is Windows only where Fusion 360 is both Mac and PC. 

I thought I might share that when I was doing the outline of the plates, I suspected I might save time by converting a .tif in Illustrator to a .svg file. It imports into Fusion 360 very nicely but when it renders the outline, I had to do quite a bit of work to close the outline that Fusion 360 created from the .svg file. It required zooming in on the points and manually closing them up. Not sure why that happened but it was probably as much work as creating the outline in Fusion 360 using an image file to guide your lines (serve as the canvas). It also created too many different elements to render the outline.

I prefer a high res .tif file to work with if possible. That means when you scan a Strad poster or other pattern source, save it as high a resolution .tif that you can. Also if your desire is to create a symmetrical outline or arching, you can do one half and "mirror" it to the other side.

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1 hour ago, NCLuthierWyatt said:

As an alternative to using CNC machinery have any of you seen the wood router offered by Gemini? Looks like a great option for those wishing to avoid the high initial investment of laser scanning along with having a lot less to go wrong. I work with lots of laser scanning and high end 3D printing in a dental laboratory along with some experience with CNC machinery in producing custom components for cars. Feel free to pick my brain if anyone needs help with figuring out how to export and edit STL files. 

Here's a demo of it. Not too bad for $3200. 

I thought about going that route. I even bought plans to create your own duplicating router but never went farther when CNC got less expensive. 

As far as scanning laser or a probe to get the .svg file, I would think that some makers would just design it in software from plans. At one point I thought that I might do some plates in a wood like basswood (easy to carve) and then use a probe on a CNC to generate the "mesh" rather than design in the Fusion 360 software. I looked into laser scanning but found it too expensive. In addition if you are going from an older instrument you have to correct for arching distortion and other asymmetries. While not impossible it involves decisions and knowledge how string pressure and sound post distortion affects arching. 

The medical community uses software to go from CT scans to stl files. https://www.embodi3d.com/blogs/entry/345-a-ridiculously-easy-way-to-convert-ct-scans-to-3d-printable-bone-stl-models-for-free-in-minutes/. The problem is getting a CT scan file. I think that the Library of Congress used to have CT scan files but they have disappeared from the interwebs. I tried to contact the curator at the LOC regarding this but got...crickets. Aren't the instruments and assets there the property of the "people"? Oh well. Ct scan files are also VERY large!

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Trouble with 3d printing from CT scans (CT->STL) is the accuracy of the resin print. S&Z ran into issues with this with the Tuscan Strad publication. They simply couldn't get the accuracy they were looking for + - .3mm was considered too great a margin of error. 

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1 hour ago, Urban Luthier said:

Trouble with 3d printing from CT scans (CT->STL) is the accuracy of the resin print. S&Z ran into issues with this with the Tuscan Strad publication. They simply couldn't get the accuracy they were looking for + - .3mm was considered too great a margin of error. 

 

I did this instead from 3D scans, I cut 356 printscreens and then cut 356 slices in 1mm balsa wood. Adjusted then the numbers of sliced to match the overall length (to accomodate margin error in wood thkness). All slices are centred with 2 prick holes from printscreens to wood cut. Fishing thread through the prick holes and cyano glue to glue them all together.

I don’t reach neither a .3mm precision, but the result gives a good idea of the curves of the plates. The attached picture is the back being glued altogether (the sleigh frame is to tension the fishing threads).

Maybe someone could further develop this for CNC further template.

cheers,

Sug

85DCE784-47A6-48C4-ADCC-7ADE5E733064.jpeg

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Not all CT scans are equal. Most common CT scanners have resolution of 1mm cube per voxel. The mewer CT scanners can go far more precise. I've worked with 1mm res CT scans and you can get quite decent results even from that but it requires manual work on the slices. Most any automated process will create too many random defects in the surface.

The LOC CT scans were published few years ago and I think someone managed to download them before they pulled them, at least the Betts scan was posted here on MN later... I would love to get my hands on some of those too.

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6 hours ago, Urban Luthier said:

Trouble with 3d printing from CT scans (CT->STL) is the accuracy of the resin print. S&Z ran into issues with this with the Tuscan Strad publication. They simply couldn't get the accuracy they were looking for + - .3mm was considered too great a margin of error. 

Who is S&Z (Sam Z?) Could you elaborate more on the Tuscan Strad pub you are referring to?

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I don't think the complete raw micro-CT scan is included on the DVD. Just pictures and analyses are mentioned...

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15 hours ago, sug said:

https://www.scrollavezza-zanre.com/en/1690-tuscan-antonio-stradivari-violin/

For the complete CT scans, you need to order the DVD. They are definitely more than 1mm accurate - for the exact accuracy you may want to ask them directly.

Sug

Yes this is what i was referring to above. The CT data is super accurate! However S&Z were unable to produce an + - .3mm accurate resin based copy from the data (they were using an additive fabrication process with resin not CNC). When I spoke to Andrea, he wasn't 100% satisfied with the results and decided to cancel the 3d print option originally offered with the book.

It is too bad -- even at these tolerances, I would have been happy. It is near impossible for amateurs to get a hold of plaster casts for study purposes. 

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1 hour ago, Urban Luthier said:

It is near impossible for amateurs to get a hold of plaster casts for study purposes

Yes. I am envious when I see casts of important instruments. I remember seeing a cast at the LOC for arching corrections and/or sound post patch that Rene Morel made. I thought how much I would like to make a positive mold of that!

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Following this discussion makes me wonder what people are trying to achieve with CNC machines.

It seems to me that they might be a great labor saving way of producing a generic sort of arching shape which could be finished by hand. But why try to replicate old, known violins with all the programming and accuracy problems that involves.

CT scans clearly show the arching shape characteristics of the early makers. And my venture into making arching templates has given me an understanding of how those characteristics can be replicated with a high level of accuracy.

Whether that could be applied using CNC machines I don't know, but I hope not. It's a case of what floats your boat I suppose.

 

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Accurately duplicating the geometry of great instruments is not very helpful for getting great results unless their wood properties are also closely duplicated.

I value multiple duplicity.

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I really don't subscribe to the theory that some examples of early violins are in some way far superior to what can be made today. But I do think that the early makers worked to a well thought out, practical method of construction which produced very well crafted instruments which were arched in a fairly common way. And I think that, from what I can see, they used good quality wood, especially the spruce of the Alpine variety which had consistent attributes.

 

 

 

 

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3 hours ago, Dennis J said:

Following this discussion makes me wonder what people are trying to achieve with CNC machines.

Everyone has a different goal.  

While I AM very interested to learn all I can about great instruments, I'm fairly convinced that slavish duplication of dimensions won't get the same result as the original, and duplicating wood properties is not very feasible.  I'd rather build something different, but equally good (or better, whatever that is).  My goals:  1) Reducing the work required of my damaged joints 2) More productivity 3) Make things closer to what I want than my skills (and patience) are capable of producing. 4) Playing with high-tech toys.

There are some capabilities of CNC that are really helpful... like making very accurate tooling and forms.  I'm at just the next stage, using the machine to establish the outline, purfling groove, lowpoint of the channel, and the long arch along the centerline.  That saves a lot of tedious work for me.  I will eventually do the 3D rough arching, but for now I don't really know exactly what I want on the crossarch, so I'll use my usual method of carving mostly by eye.

All of the surfaces will be carved and scraped to the final shape, so I don't think it will be too obvious that CNC was the apprentice who worked on it.

1050761961_violaplate.jpg.2ad08205487537679f4e146175d0e010.jpg

I'm really liking the vacuum holding base.  It's repeatable and accurate enough to pull the plate off, check the purfling groove depth, slap it back on and take a deeper cut.  

One downside of CNC's is that one goofed setting can trash a plate instantly.

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8 hours ago, HoGo said:

I don't think the complete raw micro-CT scan is included on the DVD. Just pictures and analyses are mentioned...

Yes, a full CT scan video is included in the DVD. 

 

Sug

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6 hours ago, scordatura said:

Yes. I am envious when I see casts of important instruments. I remember seeing a cast at the LOC for arching corrections and/or sound post patch that Rene Morel made. I thought how much I would like to make a positive mold of that!

You can try the slice manufacturing method above. It gives good result for the eye training on the shape of the plate. Then you may finetune with real instrument observation, etc.

 

cheers,

Sug

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4 hours ago, Don Noon said:

I'm really liking the vacuum holding base.

So am I. Could you show what you are using to create the vacuum?  How did you create  the seal?

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4 hours ago, sug said:

Yes, a full CT scan video is included in the DVD.

Full CT scan is not a video. It's lots of data in very special format (DICOM or such) that can be viewed or evaluated by special software (that you see at your doc looking into monitor). Is such raw data included as well?

Video created out of the crossections is much less valuable, nice pictures but it would require some creative hard work to re-create 3D model out of that versus original RAW data.

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