Large DIY spheres

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nfaino
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Large DIY spheres

Post by nfaino » Fri Nov 10, 2017 6:43 pm

I was scanning a large, fairly flat outdoor scene and didn't want to jump my small spheres and scanning positions in such small increments. So I tried making my own large spheres...They've actually worked out quite well, so I thought I'd post some images to hopefully help out others.

I looked around all over the place (online) for a large sphere. It was mentioned on a forum post to use large ornaments, which in July were really expensive when I did find them. I also thought about a beach ball since it would be easily transported, but I'm not sure how spherical they are and I couldn't find reasonably priced plain white ones either. In the end, I went with outdoor lamp globes. They were readily available at Lowes and were relatively inexpensive.

In order to close up the bottom of the globes, and to give a base to mount them to stuff, I picked up some 6" magnetic parts holders from Harbor Freight. They were the perfect size and shape (the only downside, I realized later on, is that the magnets are not strong enough to hold the spheres in any orientation except up).

Other items that were needed were large washers and nuts (1/4"-20) which were added to the base so that the spheres could be threaded onto a tripod, white paint to remove the gloss from the plastic (not sure if it was needed, but I just assumed that it would be), and liquid nails to glue things together (I ended up having to weld some parts as described below).

In total, here is everything that I needed:
IMG_0906.JPG
- 12" diameter lamp globe (purchased at Lowes)
- FlexiDip white rubber coating spray (purchased at Lowes, I think they have similar at Harbor Freight)
- 6" magnetic parts holder (purchased at Harbor Freight)
- Liquid Nails (purchased at Lowes, I think they have similar at Harbor Freight)
- 1/4-20 nut (for securing to camera tripod)
- Large washers (I had a variety of sizes on hand, so I don't know a specific size needed)
- (optional) Welder (I ended up having to do some welding when the liquid nails failed)

Here are some photos of the items:
IMG_0908.JPG
IMG_0910.JPG
IMG_0911.JPG

The steps:
First, I glued the globes to the magnetic parts trays, which were a perfect fit
IMG_0912.JPG
In order to place compression while gluing, I used a Home Depot bucket and jug of water as weight:
IMG_0914.JPG
IMG_0915.JPG
Then, at first, I glued the nuts and washers together and to the magnetic base. The nut was inset in the washer so that the washer would be a nice flat surface to rest on the tripod base or something else flat.
IMG_0920.JPG
I might not have waited for the glue to cure long enough, but the nut and washer ended up popping off, so I had to weld them together.
IMG_0925.JPG
In the end the larger spheres really help space out the scan positions. Below is a photo of the large sphere (farther away on the tripod) and the smaller spheres on the ground.
IMG_0928.jpg
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tadol
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Re: Large DIY spheres

Post by tadol » Tue Nov 14, 2017 5:23 pm

I hesitate to post too much, but I would like to add a few comments -

You should paint the interior of the spheres, preferably in a dark color - that will help with getting more points as well as minimizing sphere “glow” when used in the sun. Glass globes are extremely fragile, and one mis-step on a job could bring the whole job down, shattering a target or two. Larger target spheres are a bit more expensive, but if you do these types of jobs even semi-occasionally, you should be able to expense a set or two of larger spheres pretty easily - they are almost unbreakable, and should last for years. 250mm are nice, but you could probably get away with a set of 200mm for that job, and 6 of those can be had pretty reasonably (call me - ;) ) and then if anything does happen to a target, you can easily replace it or just get repair parts quickly and easily. If you don’t do these jobs very often, consider renting targets - I think a fair number of locations do keep targets on hand for training as well as for rentals, so check around. Its a good business for shops that offer scanners and survey equipment. I rent larger targets, as most people dont regularly need 250 or even 380mm spheres, but shipping costs from CA could make that unreasonable. And if you rent them, you don’t need to find more storage space -

Lots of creative ways to make sphere targets, but (my personal feeling is) you’d probably be better off and ultimately make more money putting that energy into business development and marketing, But I do understand the appeal of creative problem solving!
http://www.KoppaTargets.com
Inexpensive Laser Scanning Targets & Accessories
for Architecture, Engineering, & Forensics
Now Available thru the FARO product catalog

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nfaino
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Re: Large DIY spheres

Post by nfaino » Tue Nov 14, 2017 10:28 pm

Thanks for the input, tadol.

I like the idea of painting the inside of the spheres, that could be helpful if they were too translucent.

I have a set of six 200 mm Koppa spheres, but like I said, this was a very large job that I was scanning (not just the one photo that was posted). I did use the 200 mm (~8" diameter) spheres, also, but the large (12" diameter) homemade ones were used in conjunction and spaced farther apart.

The large spheres that I have posted here are 12" diameter acrylic (not glass, which would be a bad idea since mine have fallen many times) lighting globes (Newport Lighting model 7791-12W, $20 from Home Depot). I did spray them with the rubberized, matte coating to reduce reflectivity which seemed to work since FARO Scene didn't have a time finding them.

For me, the cost of materials was very inexpensive and definitely eases the heartache of seeing one fall from a fence post down into a loading dock (which surprisingly didn't break it).

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