Bruce Charles DesignsSpinning Top Base 3.93” (100 mm) Diameter - Double Concave Fused Silica Glass Optical Lens - Spin Top Glass Base Surface (Parent) 100mm 680599201066

I'm an avid collector of precision spin tops, and I've purchased a couple dozen glass spin lenses over the past few years to service the hobby. What initially caught my eye when I heard about this new Bruce Charles Designs spin top lens was the very affordable price of $17.95... three or four times less than I've typically spent for a spin lens.So... it's one thing to gauge the quality of a spin top, but how do you gauge the quality of a spin lens given that, in-the-hand, they often look and feel very similar. For me, that's easy... you compare the spin times you've achieved with the same top on different lenses that have about the same specs... which is exactly where the 100 mm (roughly 4 inches) Bruce Charles Designs fused silica lens really distinguishes itself. In the past few weeks, I have conducted spin testing with 12 of my favorite tops (ranging in weight from 18 to 65 grams) on my Bruce Charles lens and compared the spin times I achieved to my previous spin times on other lenses. Get this... I've set new personal best spin times for 9 of the 12 tops. Additional spin time has ranged from ~20 seconds to more than 2 minutes and has averaged just over a minute. That may not sound like a statistically relevant difference, but from years of spinning experience I can assure you, beating a personal best by a minute is a very big accomplishment. I don't know what's physically different about the BCD lens (and maybe it's just harder), but the difference seems to better preserve the inertia developed by the torque generated at launch, resulting in significantly longer spin times... and that's a metric we all seek in our spinning experience.Bottom line: I could not ask for more than a glass spinning top lens that is very affordable AND that allows me to achieve longer spin times. I bought three of these lenses sight unseen on the price alone, but the longer spin times give these lenses bona fide added value and allow me to highly recommend them to any spin top enthusiast. A truly superior lens for spinning tops!!

This helps me get over 6 minutes of spin time

My name is Spinning Scotty Dodge,and I’d like tosay this has a perfectly shaped surface for spinning! The top gradually moves towards dead center! Hard scratch resistant glass that looks crystal clear! If you have a top/s you need a spinning disk! One day I’ll have a top spinning room! Good job Bruce you outdid yourself! I can spin the top anywhere I can place the disk! I love to decompress!

Very nice piece of glass for the price. It appears optical quality when you look thru it and I was unable to spot any imperfections on my version that arrived 11.2020. I have a prometheus lamba top with ruby tip that spins perfectly on it. This is obviously perfect for the desk, office or dresser. The only thing that limits my spin time is my ability to control a spin onto the roughly 4" surface. I have to back off somewhat or the top goes flying off the side. I get longer spins on my quartz kitchen countertops because I can go all-out without worrying about where the top goes. It all depends on your technique and I'm certainly not a pro. I guess the solution is to get the bigger one (about 6"). But this thing is awesome if you need a compact size and I'll probably hand some out as gifts this holiday season.

In the long run, the spinning stage that works best at providing you with long spin times for your tops is likely to vary with your spin techniques and, curiously, sometimes for the top design itself. The latter is a tough one to really know the "why?" of, especially if you have two tops of similar design, weight and size, with the same type spin bearing. But, I've seen it happen, one top nearly identical to the other, actually spinning longer on a cheap mirror than on premium glass such as this lens. Regardless, this lens from Bruce Charles Designs have proven so far to provide the longest spins for any top I've tried on it, and could control well enough to keep it on the smaller diameter, open edge stage, than any of my other spin bases, and believe me, I've got plenty that run the range from 3X mirrors to cheap science lenses in various sizes & focal lengths, to K9 and BK7 borosilicate glass lenses up to a 6" diameter. With the very shallow concave surface, keeping a top on the lens can be a challenge relative to your spin launch skills, but you'll be rewarded with great spins once you master the technique needed by a particular top. If all else fails, a "spin control ring" large enough to encircle the lens and stand maybe a half-inch above it, will help, and those can be 3D-printed, made from wood, fashioned from a strip of plastic or thick paper taped into a loop, etc....numerous possibilities.Now having 4 of these Bruce Charles Designs lenses and two bases, I can confirm that at least the currently shipping lenses as of Feb. 2020 are of a different design than specified in the details. They remain at 100mm diameter but measure 10.5mm thick and have a 1000mm focal length for each side. The weight is less, consistent with the lens being a little thinner, at 175g. Overall, for my preferences this is a better design but again, some may favor a deeper concavity for potentially easier spinning.