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  #11  
Old 08-17-2019, 03:09 PM
Terry Williams Terry Williams is offline
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Awesome!

How long did it take to get it done, did you do it with a handheld scanner?

I have scanned some large objects with my scanner in handheld mode, but it takes a while - especially if it's hi-resolution. I have to use a powder spray (like Spotcheck) and markers to get a scan result that good on dark objects like oiled brass.

Great Job!

This is a pretty cool project - I'm an an old Machinist Mate (USS Enterprise CVAN-65 1969-1975) so I can appreciate it.

Thanks!
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  #12  
Old Today, 08:34 AM
BradyWatson BradyWatson is offline
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Terry,
Thank you for your service & your kind words.

No, this was not done with a handheld scanner for various reasons - but mostly because handhelds (for the most part) would require hundreds of registration markers all over the model to match up overlapping scans and to track the handheld in 3D space...The other thing about handhelds is that it takes an incredible amount of hand/eye coordination in order to keep the scanner in the 'sweet spot' where measuring is most accurate and linear - using in the center of the depth of field range. If you don't maintain the proper working distance from the model being scanned you will either have problems matching up adjacent scans or the data just won't be good...the list goes on.

The only prep to the bell I did was to add a bit of talc to the black shiny lettering to reduce reflectivity and to bring up the signal strength in comparison to the surrounding areas.

In this case, since the bell was outside, I brought a 12x12' black enclosure with me to block out the sun and give me enough working space around the bell. I had to move it a few times. It did a pretty good job of blocking the sun, but there was still more light than I anticipated so I had to do some fancy footwork to get the results I wanted. As you can imagine, it got wicked hot in there...so I had to pop out and cool off from time to time. It took me about 2hrs to setup, scan and break everything down after I verified I had full coverage of the bell.

Incidentally, someone else had tried to 'scan' the bell using photogrammetry - where a series of photos are taken (100+) and then stitched together to create a 3D model. The problem is, that doesn't work so well on models that are large with fine detail, such as the lettering and date on the bell, which had a hand-punched texture and max depth of only about 1/8" or so. Furthermore, the lettering was all done by hand back in 1905/1906 so it isn't like you are going to match the font. Even if you unwrap the bell and attempt to create them from a photo (digitize/trace then subtract in Aspire etc) you are up against compound rotary or spherical distortion, that bends things in ways you really can't account for in software...Studying that sort of thing is an interesting 'case study' for those interested in rotary type work and the effects of rotary/spherical distortion.

Once I had the data back in the office, I was able to analyse it and clean it up. The raw scan data was somewhere in the 2GB range, so that had to be decimated to a more reasonable size on disk so that it could be used for 3D printing. Rather than use the data as-is for the top nut/yoke where the bell is suspended from, I rebuilt those portions in CAD and added it to the rest of the bell. The original parts were rusted and had paint/rust flaking off so they were pretty ugly in real life.

It was interesting for me to see just how far off my measurements were using photos and creating the bell from cross sections etc compared to the 'true to form' measurements from the scanner. Even though I've been doing this type of work for 2 decades, every project has an opportunity to learn something new or to try out new things.

-B
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File Type: jpg 3DBellWithVectors.jpg (61.3 KB, 7 views)
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