1 year, 9 months ago-
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Hi, Mark. I’d be interested in other responses to this. From what I’ve seen, there’s no general agreement on the subject. There’s the obvious factor that higher speed should mean faster cutting, and there is the “hydroplaning” consideration at high speeds.
I have seen specific recommendations, even by lap manufacturers, and it would be interesting to know the reasoning behind them.
I use a 1640 RPM motor with a 4 step pulley. I use the smallest step for polishing, I’m guesstimating about 250 rpm. I use the next to largest step for cutting, guesstimating 850 rpm? Somewhere in my tool pile I have an optical timing light (for measuring rpm on diesel motors), as soon as I find it I will update with accurate speeds.
Still on hold for the optical timing light. Haven’t used it for several years, but it’s around here somewhere. Can’t even blame this one on the wife. She likes to move my stuff from wherever I left it to a more ideal location. She then develops amnesia when I ask where she put it.
I use speed as a complement to what I want to accomplish. Speed to me is a reason for me to do it faster, to accomplish more in less time than I want to give in time. I sweep different to to get the effect of the speed to gain efficiency in my cut to flat and meet.
What is optical timing light, please?
tucsonbear may be using the meter I have used. you would place a small piece of aluminum tape on you target. bring your target to speed. point the gage at the target, the gage will read every time the target passes the gage and will display the rpm. I do not know the brand name.
These devices are relatively inexpensive. Look for them listed as “non-contact tachometer”, “optical tachometer”, or “photo tachometer”. Amazon has a wide selection.
I have an optical tachometer. I checked the speed on my facetron. I wanted to have an idea of actual RPM, not just a mark on the dial. Mine was made in 2001. Doesn’t go as fast as the rated speed. I read in a couple different places that low speeds are best for polish. When I’m polishing the dial is usually set between 150 & 375 RPM. I usually use a Diamatrix lap for final polish.
well guys i’ve been faceting for 53 yrs and now at 78 i teach it to, even to other oldtimers my ways, actualy any speed for the cutting is fine on my ultra tec i dial half way up, most time about 1000rpm, low speed takes to long and high speed yes you start hydro’ing but i set my drip to just enough to flush cutting not a flood. but right here we change to polish, i dont do what everyone else does. i use a very slowww speed and i use a NONE scored TIN lap with 50,000 grit diamond powder. i use a VERY SLOWWW drip of water enough to make a mud/slur of the diamond. we polish better than 90%+ stones this way with different hardness’s, we need no other lap and works fast if you have a machine with an ac motor using belts/pulleys get rid of the system and get an universal ac/dc perm magnet motor and a speed control. i get speed controls from china about $15-$25 that work great. also one said sweeping back and forth but i’m hoping he finishes aimed straight at the center. just in case there could be a little worpe to the lap. if you have questions email me. gemmakermz@cs.com
hi i think i have jeff theesfeld (historian for usfg) using my polishing method some what now, he was here at my place for a visit and i showed him. he did seem to like it better, i’m hoping, and was using it. i was surprised he had an unused crystalite tin lap and i gave him a sample of my 50k diamond powder to use. you might ask him if he likes and using it and my method.
Rpm is just what the spindle turns per minute.what you need is the surface feet per minute for a better understanding on what to use for polishing. For example: if you run at 250Rpm on a 8” Lap and you polish at the 7” dia the surface feet would be 458 sf/m.
If you polish at the 4” dia, the sf/m is 262. So you can see there is a large difference of sf/m but you are at a constant 250Rpm. Does this make sense?now 81 and still at it. yup jeff is polishing my way now and happy. and have many more using my method. i now am making a limited number of 6″ 98+ pure tin laps. the softer tin holds the diamond better and charges into it, very similar to the early tin laps made by crystalite. but not soft enough to change surface. the machining of surface to be as flat as possible is the only scoring needed. best to use a sweeping action on any lap for polishing as any surface texture can be worked into stone surface if held in only one spot— move it.
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