RocknCritter
spending too much on rocks
Member since November 2008
Posts: 489
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Post by RocknCritter on Jan 29, 2010 13:37:37 GMT -5
I've been considering building a lapidary machine and have been following the thread on Motor Sources. There is a lot of good information there. However, I like having a variable speed motor. From what I can tell so far, there are a lot of variable speed DC motors and some AC motors over 1 HP. It's also possible (?) to wire an AC motor below 1 HP using a bridge rectifier. Below is a crude electrical schematic based on some second hand info from a friend. So......... #1 Is this schematic correct? #2 Are the electrical parts such as the rectifier, rotary switch, fuse, fuse holder and cord readily available, over-the-counter parts? If so, what's a good source? #3 Can any 1/3 or 1/2 HP AC motor being used for this? #4 I noticed in the Rio Grande catalog they're selling a 1/3 HP 1725 rpm motor. In the description, it states the "Maximum wheel size is 6". Is this a result of the rotation speed being wrong for an 8" lap? #5 If a motor is advertised with having an rpm range from 2300 to 3600, is it possible to slow it down to say 1200-3000 rpm's? Any other advice is appreciated!
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chromenut
fully equipped rock polisher
Member since December 2009
Posts: 1,971
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Post by chromenut on Jan 29, 2010 14:04:19 GMT -5
pictures so small I think I burst a blood vessel trying to read it...
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Post by akansan on Jan 29, 2010 15:44:37 GMT -5
Not sure on the electical parts of the question, but I don't see why the 1/3 HP motor couldn't be used on a 8" machine. The rotation speed can be adjusted using pulleys quite easily. It might be more the mass, rather than the speed. The GP-8 came with a 1/2 HP and the Titan uses a 3/4 HP. So I guess it would depend on how many wheels, what type of wheels, length of shaft, etc.
Which brings up an interesting question - I might be looking for too small a motor for my own unit. Hmmm.
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blessed
spending too much on rocks
Member since January 2010
Posts: 329
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Post by blessed on Jan 29, 2010 16:23:44 GMT -5
Howdy Rockncritter It don't look right to me. The black wire is your hot and white is common. Switches and other stuff is usually on the hot. Someone will set us right. As far as the switches, motor, and other stuff Grainger has them. That is where I buy some of the things for building tumblers and chop saw.
Blessed
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blessed
spending too much on rocks
Member since January 2010
Posts: 329
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Post by blessed on Jan 29, 2010 17:48:05 GMT -5
Forget Grainger...Speed control for universal type AC/DC motors, use only with 115v ac/dc universal brush-type motors. This came straight from Grangers catalog. 2009-2010
Blessed
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Post by johnjsgems on Jan 29, 2010 22:04:01 GMT -5
The 1/3 hp motor is likely too light for most 8" machines. Variable speed is generally by use of a dc motor run through a rectifier to plug into ac. Brush type motors are sometimes run with rheostats but in continuous use it will cause a loss of power, motor overheating and shortened life. Best to use a three step pulley if you want multiple speeds. A straight 1725 rpm works for pretty much everything.
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RocknCritter
spending too much on rocks
Member since November 2008
Posts: 489
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Post by RocknCritter on Jan 30, 2010 10:00:37 GMT -5
Pulleys won't work. This is a flat lap design. So how are faceting machines wired? What motor do they use?
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Post by Rockoonz on Jan 30, 2010 13:28:13 GMT -5
Use a belt drive on your flat lap instead of direct drive. A motor under a tub of water isn't safe. If you insist on variable speed use a DC motor with controller, if you use AC your torque will drop off faster than your RPM.
Lee
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wb0zrd
off to a rocking start
Member since January 2010
Posts: 3
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Post by wb0zrd on Jan 31, 2010 12:43:13 GMT -5
RocknCritter,
An AC motor will not work on DC...if you wire it up the way your schematic shows you will have smoke. There are ways to vary the speed of an AC motor.
Only a month at rock tumbling...30 years as an electrical engineer.
Cheers, Paul in Colorado
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RocknCritter
spending too much on rocks
Member since November 2008
Posts: 489
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Post by RocknCritter on Jan 31, 2010 16:01:17 GMT -5
Hi Paul,
I just sent you a PM.
I talked to someone else last night and he mentioned the same thing. It's possible, just not way in the schematic. Most faceting machines, some flat laps and the machines from 3M have variable speed motors. So I'm hoping to achieve the same thing.
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Post by johnjsgems on Jan 31, 2010 22:29:32 GMT -5
I think you'll find all you mention are dc motors.
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Saskrock
fully equipped rock polisher
Member since October 2007
Posts: 1,852
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Post by Saskrock on Feb 5, 2010 2:04:24 GMT -5
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RocknCritter
spending too much on rocks
Member since November 2008
Posts: 489
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Post by RocknCritter on Feb 9, 2010 10:49:34 GMT -5
Thanks Sasrock for the tip.
How do you tell if a motor is a brush type universal motor instead of an induction, shaded pole, soft/slow start, or brushless type motor? I have asked a few electric motor vendors and haven't received an answer. I don't want to buy the wrong type motor.
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Daniel Green
off to a rocking start
Member since April 2009
Posts: 19
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Post by Daniel Green on Feb 9, 2010 15:12:45 GMT -5
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idrockman
starting to shine!
Member since September 2006
Posts: 25
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Post by idrockman on Feb 11, 2010 11:11:19 GMT -5
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