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Thread: Is It Possible to Slow Down a Grinder's Speed?

  1. #31
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    Well, the water soluble oil is specifically made as a coolant for machining operations. The CNC and Machining instructor also used a similar oil for grinding opertions including lathe cutters (tool steel). Supposedly it draws the heat away bettter. It also won't rust your tools.

    Again, I try to do my grinding with a very light touch when I approach the fine edge of the tool.

    My question is why would you want a fast quench, won[t that make the edge brittle?

  2. #32
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    You want a fast quench if your cutting tool suddenly gets too hot! No oil quenches as fast as water. Water by itself is hard on machines,so they found ways to slow down the corrosiveness of water.

    Unless you get the tool up to red hot,cooling it fast will not make it brittle. It's too late to save the temper by then anyway.

  3. #33
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    Quote Originally Posted by Frank Drew View Post
    5,280 ft., no?
    Yes... Typo or brain fart... Either is not surprising! lol!

  4. #34
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    The water soluble oil is actually mixed about one or two parts oil to to ten parts water, So it really is not strictly an oil coolant. My apologies for not making that distinction clear. I can certainly see why water would be a better quench or coolant than pure oil!
    No, the sky is not falling - just chunks of it are.

  5. #35
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    Since I started this thread, I should say that I went to Woodcraft and purchased a slow speed 8" grinder (on sale). Took it home and it hums beautifully. It even comes with 2 friable wheels so I don't have to buy new ones initially to replace the gray ones.

  6. #36
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    If it only HUMS,it will soon burn out!!!

  7. #37
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    By the way, it is possible to slow down a single-speed permanent magnet, split-phase or other single-phase motor with a modern VFD. They work by slowing the 60 Hz frequency of the AC power and keeping the voltage constant. Here is an example (the GS1 model):

    http://www.automationdirect.com/adc/...Catalog/Drives

    The more tradtional way of doing this is with a gear motor, though the addition of a transmission makes a gear motor considerably more expensive.

  8. #38
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    I do not think that they will operate 1 phase motors,David.

  9. #39
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    Yeah, my bad - that was a poor example. But you can get VFDs that are 3ph in, 3 ph out, 1 ph in, 3 ph out, and 1 ph in, 1 ph out. Here's a better example:

    http://www.anaconsystems.com/text/opti_e2.html

  10. #40
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    Now,this is some useful information. Are these something new? I might get one for my 1 phase Oliver wood lathe,minimum speed is 500 RPM. Need it to go slower.

  11. #41
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    Quote Originally Posted by george wilson View Post
    Now,this is some useful information. Are these something new? I might get one for my 1 phase Oliver wood lathe,minimum speed is 500 RPM. Need it to go slower.
    Yeah, they're fairly new, at least at relatively low prices. The electronics used to be really expensive because the small semiconductors couldn't take the power/current. But with the advent of high-power integrated circuits, they've gotten a lot cheaper.

    But I would think that a person with the skills that you have might prefer a mechanical gear-down of your lathe. I would think it would be simpler, and my personal preference is "simpler=better", despite being an engineer that loves playing with high-tech toys.

  12. #42
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    My lathe has the motor connected to the spindle with 2 variable diameter pulleys only. One on the motor and one on the spindle. I'd replace the motor with 3 phase,but it is a special shaft motor,I think. The low speed on these type lathes is never low enough 500-3000 RPM. If I really had to do a large outboard spindle turning,I could do it on my 16" metal lathe. I've got it rigged to do 30 RPM. However,it is not collected too the dust collector,and not in an area I want to get dust all over. I try to keep my precision machine tool area(for metals) clean as possible of dust.
    Last edited by george wilson; 02-03-2013 at 10:49 AM.

  13. #43
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    Well, how about replacing one of the variable diameter pulleys with a larger diameter one? I've bought such things from McMaster/Grainer/MSC before to change the rotational speed on HVAC units.

  14. #44
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    Then I'd lose some top speed. VFD is an easier solution. I do a lot more small work than large,and don't want to lose top speed.

  15. #45
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    Since I started this thread, I'd like to say that I went ahead and purchases a slow speed 8" grinder (on sale at a large tool store). It even came with 2 friable wheels so I don't have to purchase replacements. Turned it on and it runs very smoothly. Thanks for everyone's input.

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