Bench Grinder Problems with CBN

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raar25

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Mar 29, 2011
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So I upgraded to a CBN wheel and it is awesome. I was able to get 3 scary sharp tool in just a few minutes. The problem is my 3/4 hp HF bench grinder (3 months old with very little use) has a very hard time starting due to the extra mass of the metal wheel. It worked fine with 2 Al-Ox wheels. Has anyone else run into this and what grinder did you find worked? For now I take one wheel off when I want to use the grinder.

Thanks,
Ray
 
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Fay Prozora

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I've seen posts about this on another forum and they say the same about turning it by hand and the flip the switch. I want to upgrade too but the cost is out of my reach so will have to look for sales or save my pennies.. LOL! Hope you have good luck with your upgrade.. Fay
 

jttheclockman

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There are reasons that HF tools are cheaper and you are finding out one of them. Motor quality is something you pay for. You spent good$$$ on the wheels so it maybe time to upgrade the workhorse. Use that one for polishing or rough grinding. Or do as others have suggested spin by hand before hitting the switch but remember to remove hand before you hit the switch.
 
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raar25

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Well nice to know I am not alone in this problem. I have tried starting it spinning by hand and it doesnt work. The electric pulses on the armature are actually slowing it down when I hit the switch. I am reluctant to buy another 3/4 hp grinder for more $$ only to have it do the same thing. Does anyone have a recommendation of a strong performer?
 

monophoto

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The issue is that the motor is that the torque developed by the motor is only marginally able to accelerate the higher mass of the metal CBN wheel. Motor torque is closely related to its horsepower rating.

If you've shopped for a lawnmower or snowblower in the US recently, you may have noticed that they are rated in terms of engine displacement rather than horsepower. The reason for this is that manufacturers were playing games with the way the determined the horsepower ratings, with the result that consumers were being mislead into believing that they were purchasing a machine that was more powerful than it actually was. Changing the ratings to engine displacement rather than horsepower forced manufacturers to use a parameter that was less susceptible to manipulation and misrepresentation.

A similar thing took place in the high-end sound system business many years ago - manufacturers were manipulating the power rating assigned to speakers and amplifiers.

It would not surprise me to learn that if one were to actually test a brand-X Chinese motor sold by HF with a "3/4 horsepower" rating in accordance with NEMA MG-2 standard for motors, the results might show that the true rating is less than 3/4 horsepower.
 

jttheclockman

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The issue is that the motor is that the torque developed by the motor is only marginally able to accelerate the higher mass of the metal CBN wheel. Motor torque is closely related to its horsepower rating.

If you've shopped for a lawnmower or snowblower in the US recently, you may have noticed that they are rated in terms of engine displacement rather than horsepower. The reason for this is that manufacturers were playing games with the way the determined the horsepower ratings, with the result that consumers were being mislead into believing that they were purchasing a machine that was more powerful than it actually was. Changing the ratings to engine displacement rather than horsepower forced manufacturers to use a parameter that was less susceptible to manipulation and misrepresentation.

A similar thing took place in the high-end sound system business many years ago - manufacturers were manipulating the power rating assigned to speakers and amplifiers.

It would not surprise me to learn that if one were to actually test a brand-X Chinese motor sold by HF with a "3/4 horsepower" rating in accordance with NEMA MG-2 standard for motors, the results might show that the true rating is less than 3/4 horsepower.


They have been doing this with electric motors for years and still do it.
 

raar25

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Mar 29, 2011
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Glastonbury CT
Interesting I took a look at a HP and amp chart recently and most companies are calling 5 amp motors 3/4 HP, however based on the chart I saw, this is just slightly above 1/2 HP. HF also has another 3/4 HP motor that draws 9 amps. You could say it was much less efficient or it could be that a higher energy output causes the high draw of current. I will probably give that one a try and if it doesnt work, bring it back.
 

raar25

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Glastonbury CT
So I searched craigs list for something and came up short of two deltas that were sold out from under me. So I end up back at Horror Fright and buy another grinder like I already have. Sure enough it is all about quality (or lack there of). The new machine runs smooth and quiet and does the job just fine. So I guess the old one is going to be a buffer as someone suggested. But I had to try for $40.
 

Fay Prozora

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Great going. Those new CBN wheels do look heavier than the big white ones like the ones I have. I like my grinder but the thing is a heavy one but it is a slow speed grinder. If I should ever have to upgrade I will use this one as a buffing system and the upgrade for the grinding of tools and such... Later in the future tho... Fay
 
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