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Thread: laser scan vs. probe scan?

  1. #1
    Join Date
    Jun 2017
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    Default laser scan vs. probe scan?

    Hello,
    Has anyone imported a 3D laser scan of a part to cut. I build archtop instruments and have been using the probe to copy carved tops and backs. The accuracy of the cuts is not good enough. They require lots of time adjusting to only get a part that I still have hours working on to be able to use. I realize that my being a newbee is probably a lot of my problem. Just thinking about sending a finished top or back out to be laser scaned. Is it any better than the probe?
    Thank you, Graham

  2. #2
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    Laser scanning is the only way to go for precise work. The worst cases scenario with laser scanning (in my lab anyway) is that you will collect data 100x finer than the touch probe is able to resolve. More resolution is possible, but at that point picking up unwanted woodgrain texture becomes an issue later on...unless your design intent is to preserve the woodgrain texture. I get requests for both.

    The probe is OK for decorative things but really doesn't do well when precise replication is required. First, it mechanically has too much hysteresis in it - isn't triggered as linearly as you want it to and at the end, all of the data is offset 1/2 the probe diameter, which means you now need to a do a 2D (for vectors) or 3D (for reliefs) offset to get close to the actual size of the part. So yes - by far - laser scanning is WAY better than the touch probe. I've probed well over 150 million points with the SB probe early on & it was 'fun' and OK for some decorative work, but it fell short for tight, precise projects where I needed more resolution and accuracy.

    Collecting the data at a higher resolution is only one part of the job, depending on your own skill set. For instance, many instrument makers are brilliant at what they do day to day but simply lack the skills required to fully follow through on machining their parts successfully. (There's no shame in that...BTW) I do offer 3D scanner services where you can pay a fee and receive a file ready to be imported into CAD/CAM. However, in order to machine the body (or neck) properly, it should be defeatured (remove all pockets etc and digitally fill + 2D vector digitize their original locations for optimal 2D machining). If you are not certain how to toolpath the data, I can create sample toolpaths using your data and bit specs (either mine or yours) and finally, show you the entire process in a video that you can follow step by step (specifically using YOUR data in VCP v8+ or Aspire). It is all a la carte - so you can buy only what you need, but most importantly - get what you want finally in a very short amount of time.

    The attached pics show an example of a body scanned (right off the scanner), the body defeatured and 2D vectors placed in original locations, and finally everything toolpathed and simulated in Aspire. One thing that may not be readily apparent is that the body is scanned from all sides, so you get a perfect marriage of the front, back and sides without any alignment issues to worry about - It truly is 'Full 3D'. I've done many mandolins, guitars, violins, bodies & necks, plus other instruments over the years.

    Feel free to contact me off-list if you wish to inquire about scanning services. The easiest is to email me from the website: www.IBILD.com or send me a PM.

    -B
    Attached Images Attached Images
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

  3. #3
    Join Date
    Jan 2015
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    Wilson, NC
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    Default

    Wow, nice scan Brady. The SB probe couldn’t touch that kind of resolution. It’s like an old Atari vs. a new Xbox One.

    Graham, it is not just because you are new. It is because you are seeing how primitive the SB probe results are. There is no magic button that “fixes it up” as you have noticed.

    My own SB probe experience made me realize it is an absolute waste of time it is. Hours setting up to scan and MANY hours of trying to dump gallons of turd polish on that scan to no effect.

    This is not a slight against SB, it is just that the probe has limits. Unfortunately, the limits are so low, it is easier to work with a tape measure and a photo.

  4. #4
    Join Date
    Sep 2014
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    Poughkeepsie, NY
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    Graham,
    Send your part to Brady. I just had him do some laser scanning and toolpathing on a quatrefoil plinth block. Excellent service and quick turnaround time. One of the best things was he'll send you a video of your part with what he did to it. The video is so good it should be on the Vectric website.

  5. #5
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    Jan 2015
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    Wilson, NC
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    Brady, how difficult is it get a scan transformed from a point cloud to splines or vectors? Do you have a software package to handle that?

    For example, that guitar body could have 100k vertexes as an STL, but maybe 50 splines as a Rhino file.

  6. #6
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    Let me jump in with one quick thought on duplicating items in general. If you want to make exact copies of a particular item then getting Brady to laser scan it at the highest resolution is definitely the way to go. You'll get a precise copy and great bang for your buck. If you plan on making any mods or cleaning it up, though, extremely high resolution may be counter-productive.

    I was a boat carpenter and boatbuilder in a previous life and can guarantee that no boat that I ever built or worked on was symmetrical from side to side. Differences in the way planks bent, time spend fairing and sanding, variations in the setup of the frames made small but measurable differences in the two sides. An accurate scan of the hull would give you an precise copy of an imprecise thing.

    If however you wanted to build a boat like the original design, you would at least try to make it symmetrical and all that extra precision would make your job harder. A scan with the minimum number of control points to define the shape is what you need, so that you can find and fix the deviations.

    So if you want to make exact copies of that specific guitar then more is better when it comes to data points, but if like boats there may be some "anomalies" that you want to smooth out in software, maybe less resolution is better.

    Bill

  7. #7
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    First, thanks for the kind words. I strive for perfection in my work, particularly scanning. A point of clarification - yes it is possible to video your part with intelligent instruction in Vectric software, but this is an additional cost to scanning your part.

    Bill - Very good point. This is something that can be a real pain on models/parts that are warped, twisted or 'off spec' for one reason or another. You certainly would not need and probably couldn't, work with a 5GB scan of a hull...or your kitchen layout. This would be akin to using a 1/32" end mill to pocket out a large sign, when a 1/2" tool will do the job perfectly. One thing important to note is that the method of data collection and the equipment vary greatly depending on the intended use of the data. More on this later.

    Will,
    That is a good question and one that comes up from time to time. I am going to apoligize first in case this gets long winded...but I hope that it is informative and worth the read.

    I get requests from time to time from customers asking if they can get their scan data in IGES, SolidWorks, STP or other 'solid' format. The short answer is 'no' because of the way that data is collected, it does not immediately translate into these formats without human interaction. Furthermore, before a model/part is scanned, I ask the customer their intentions with the data. Will it be machined? Will it be 3D printed? Are you intending on modifying it in software, if so, what software? etc - as this can affect the workflow down stream. The truth is, there isn't a scanner on the planet that will go from scan to solid/spline type data without some human interaction - but it's also important to recognize that not all models lend themselves to those types of formats either.

    Generally speaking, there are 2 types of models I run into. First, there are organic reliefs, decorative carvings, sculpture and natural designs like flowers, leaves, bones etc. None of these things lend themselves to being readily converted into platonic solids - that is to say, large portions of the relief are not comprised of planes, cones, spheres or cylinders. It may be possible that small areas are portions of these things, but this would equate to thousands of solid slivers in order to define an organic shape. Now it is possible to drape over the relief and create a surface & output it as such, but it falls under non-parametric 'dumb' surfaces and solids. It will get you the file format for compatibility sake, but not be dynamic like a true solid or parametric design.

    The second type is a mechanical/engineering type model. A cylinder head, piston, machined castings, power tool cases & shrouds etc. These parts do lend themselves to being converted to solids more easily than organic models because vast portions of the model can be made up of planes, cones or conic sections, spheres or spherical sections and cylinders. In these cases the data is used as a reference to create clean geometry without sand casting marks or blemishes. This is called retopology. The data is used to extract cross sections for sweeps and/or the software is intuitive enough to search/sense where there are solids present and automatically extract those areas as platonic shapes. Again, the intended use of the data will dictate what software is best for this operation.

    Of course if the intention is to only collect curves/spline data for further development or if the subject is conducive to it, the choice of equipment becomes important. Just like making the choice to capture a 2D outline vs a 3D surface with the SB probe, the same holds true when it comes to selecting the right hardware. If the customer has a tubular frame or boat hull shape that needs to be digitized (let's say for aftermarket accessory fitment analysis, or bulkhead sections), the right choice would be a digitizing arm with intelligent interaction (3-point circles, splines etc) compared to a full 3D laser scan that will just capture everything as a big mesh, which may not be what you want.

    Converting to a solid format is a moot point for many who just machine the data on a 3 axis or rotary setup. 99% of the time, the CAM software (unless a plugin for a solid CAD program) will readily take in an STL and toolpath it. This is certainly the case for any wood cutting CNC. There are times however when it is worth extracting some cross sections, in a program like Rhino (and don't forget that Aspire can do this stuff too!), and use that to do some retopology or modifications. For instance, an STL can be pulled into Rhino, cross sections extracted and rail swept, extruded or spun to create a smooth 'blueprinted' surface. Mechanical features like bosses or screw holes can be also added as solids, by themselves to enhance the original model or as part of a complete retopology. Here's the interesting thing....most of the time, if your intention is to machine or 3D print the part, you're going to go right back to an STL mesh again, converting your solids to meshes in order to machine or print them...so the solid format itself doesn't often hold up when it comes to manufacturing methods within the grasp of those readiing this here, but it IS a helpful format during the modification/retopology stage because unlike a mesh, you can transform it freely without things getting really complex (like when a mesh gets twisted or is no longer manifold etc).

    My goal has always been to collect data so clean and true that retopology isn't necessary for most parts. This means going from scan data right to CAM without any fuss in between. It doesn't always work out this smoothly depending on the part, especially dirty ones or with dried paint stuck in it or if the part has been degraded by the weather etc (like bent, twisted or warped) - but most of the time it does. I've always avoided using the canned 'smooth everything' smoothing tool because it degrades the data and rounds off sharp corners. Instead, a few swipes with the sculpting tools usually clean up dirt or paint left behind by the customer or other areas you wouldn't want in a production run part.

    Attached is an example of some retopology in Rhino. The goal here was to remove the handle and make the body straight so that it can be mounted without the handle getting in the way. The new parts were created using the scan data as a reference and were then 3D printed. They fit perfectly the first time, which still impresses me every time I do these things, since my earlier attempts with older equipment, software and skills often felt short. It is now possible to collect data so accurate that it works out perfectly as-is. It truly is amazing.

    -B
    Attached Images Attached Images
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

  8. #8
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    Thanks guys. Brady, I will finish down a part to be exactly what I want and then talk with you. Probably leave it about .010-.015 thicker to allow for voicing. It will take a little while due to the fact that I am trying to finish a mandolin in progress. Mandolins are what I build.
    Graham

  9. #9
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    Will,
    Good to know the turd polish comes in gallons.

  10. #10
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    Graham,
    No problem. Contact me whenever you are ready.

    I thought I'd point out one more quick example while we were discussing this stuff...and that is, sometimes scan data can be incredibly useful for building complementary geometry around the scanned model.

    Attached is a pic of a Lighthouse motor scanned and pulled into Rhino for fitting an enclosure. The data is used as a reference for fasteners, stand offs, machined plates etc required for creating an enclosure. This is challenging, but not impossible, to do any other way.

    Doing it with this method gives the added benefit of trying out standard fastener lengths, available stand offs and other off the shelf parts, avoiding the need for everything to be made custom. The ability to fully visualize the part from any angle is incredibly powerful for this type of work.

    Colored geometry was derived in part from the grey scan reference data.

    -B

    This motor is actually one of THE original motors that started it all...the '9-15' -The predecessor to every Lighthouse vacuum based implementation done on a CNC hold down system...
    Attached Images Attached Images
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

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