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Author Topic: Does it make sense to switch to "spherical" (convex) hard wheels?  (Read 992 times)

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R.U. Sirius

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As I am slowly refurbishing a couple of arbors, the time has now come to decide what wheels to put on. I noticed several suppliers offering spherical wheels for grinding.

These are from ukam.com (my preferred supplier of diamond tools in my professional life as a scientist, though I never tried their lapidary products):


...and this is by Crystalite, available from Arrowhead Lapidary:


How versatile are these? My gut feeling is that you could use them to shape the cab preforms just like with ordinary wheels, but with the added benefit of better visibility of the contact point AND of course creating concave features more easily. I would also expect them to wear out somewhat unevenly, depending on my technique.

Are there any reasons not to use these exclusively on cabbing machines? What kinds of wheels would be best for sanding stages if grinding was done on spherical wheels (expanding drums with offset belts to access concave edges)?

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kent

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Re: Does it make sense to switch to "spherical" (convex) hard wheels?
« Reply #1 on: November 02, 2021, 03:09:58 PM »

I purchase three curved  diamond 6" wheels of varying grits for the sole purpose of creating shapes with an inside curve for a series of my "Unity" boxes
IMG_8435b.jpg
*IMG_8435b.jpg (47.62 kB . 600x588 - viewed 145 times)

The travertine  "petals" on the top of the box had to be first ground at the underside to match the curvature of the box lid and match the changing curve at the  different angles of the petals. I was also trying to get uniformity of the inside curve When the stone is held at 90 degrees on the wheel I could get the curve (6" radius) however if you change the angle, the inside radius changes. So what this feels like is similar to using the edge of a wheel to form your shape. You work harder to get a fair cut (uniform) because the piece is no longer in full contact with the wheel. So what os necessary to have a steady hand and cut (grind) evenly at each pass. To mess things up even more, I had to go from 6" wheels to my 8" expando to finish off.

So I got a tad frustrated and haven't used the wheels since. They were good for the curvature of these petals.  I form pendants primarily and I like the flat grinder surfaces (and expando) as it allows me better control in grinding even and fair cuts.
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irockhound

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Re: Does it make sense to switch to "spherical" (convex) hard wheels?
« Reply #2 on: November 02, 2021, 10:32:23 PM »

I agree, because it is a compound radius there is not a flat surface in any direction.  For doing things like the bevel around the edge of a cab you will be fighting one curved surface or another and in normal cab cutting I could see a lot of flaws in the surface.  Granted a skilled cutter can adapt and work to get what they want with anything, it would be just easier to not have to adapt and overcome the hurdles of the curved wheels.  When it comes to inside curves on the side of a stone, (I love doing negatives and positive cuts on the same stone) I can see a benefit because the edge of the wheel is rough on things but works and the radius you can get on an 8" wheel is too big for the size of cabs most people do but the tight radius across the wheel width is super tight and is great to get those inside curves knocked out.  I would still rather go with std. wheels personally and use the edge for tight radii and have the benefit of a flat surface to do my bevels with.
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Slabbercabber

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Re: Does it make sense to switch to "spherical" (convex) hard wheels?
« Reply #3 on: November 03, 2021, 12:05:13 PM »

I have a convex diamond wheel that I use for knife handles due to the inside curves required.  When I am no grinding a knife handle it goes back in the box.  It is a major pain for anything other than inside radius grinds.
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lithicbeads

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Re: Does it make sense to switch to "spherical" (convex) hard wheels?
« Reply #4 on: November 03, 2021, 02:38:41 PM »

Not much of a contact point means very slow grinding relative to a regular wheel. Get a sintered wheel one grade coarser than you are used to working and it will be many years of happy grinding. One grade coarser in sintered will give you  the same grinding performance of a plated new wheel  a grade finer  for a very long time.
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R.U. Sirius

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Re: Does it make sense to switch to "spherical" (convex) hard wheels?
« Reply #5 on: November 03, 2021, 04:27:11 PM »

Thank you, all! I've decided to go with standard wheels. Now just keeping my fingers crossed that no pandemics, wars, or alien invasions stop me from making it to the U.S. in December! Lapidary resellers in Canada are few and far in between, and price the products accordingly. Shipping into Canada is not any better, with all the postage, import duties, and brokerage fees.

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irockhound

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Re: Does it make sense to switch to "spherical" (convex) hard wheels?
« Reply #6 on: November 03, 2021, 07:32:32 PM »

A few months back I tried to get a backup set of 8" wheels and had problems finding the coarse wheels in stock.  Looks like it is better right now and I only see the 60 grit out but other suppliers may have that back in stock by now.  Crazy how things are so hard to come by now.
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