Grinder Options - confusing for a Nube

[Cushing H.]

I searched the forum on this ... and did not quite find the answer to my specific question... I am looking at the Ameribrade grinder, and one of the options is the drive wheel. 7" or 4". I guess the 4" is more suitable for lower HP motors ... but this one is 2HP ... so likely the 7" is the better choice?

I am stymied by the Bore dimension: either 5/8? or 7/8 inch. does this really make a difference on available torque? with the 2HP motor, it 7/8" a better choice???

 

[12345678910]

I searched the forum on this ... and did not quite find the answer to my specific question... I am looking at the Ameribrade grinder, and one of the options is the drive wheel. 7" or 4". I guess the 4" is more suitable for lower HP motors ... but this one is 2HP ... so likely the 7" is the better choice?

I am stymied by the Bore dimension: either 5/8? or 7/8 inch. does this really make a difference on available torque? with the 2HP motor, it 7/8" a better choice???

You pick the bore that fits the shaft of the motor.
Probably 5/8" for you.

 

[Cushing H.]

ou pick the bore that fits the shaft of the motor.

thats kind of what I figured - but their website does not specify the motor shaft size ... its kind of like you get to choose both at the same time. So my question really amounts to is there an inherent benefit trade-off in shaft size (oh ... I only have 110V, so their variable speed motor will run at 1.5 HP, not 2...

 

[Drew Riley]

FYI, all of the motors you'd consider using for a grinder will have a NEMA frame number/designation. This means that certain dimensions (including shaft diameter) are always going to be the same for that given frame number. You can find charts online that give the various specs per frame, but the most commonly used frame size in the 1 to 3 HP range is going to be a 56 frame motor which has a 5/8" shaft diameter. If there's a "C" after the number, that means it's face mountable, though IIRC, the Ameribrade uses a foot mount framed motor. Most C face motors have a removable foot/base for mounting either way.

That said, you may find a better deal on a 143 or 145 frame motor, which has a 7/8" diameter shaft. As for shaft size vs. torque, it's negligible at this HP range. 5/8" will be plenty for a 1.5 to 2 hp motor.

As for a 4" vs 7" drive wheel, that has more to do with the SFPM (surface feet per minute) you want to get out of your belts, though, yes, a 1hp will have a slightly easier time running a 4" than a 7" wheel. A 7" will give you a higher SFPM, however, which some makers prefer, who use a lot of ceramic belts which really need to be run at a higher SFPM to get the most out of them. Some guys get the smaller drive wheel and double the speed on their VFDs. Other makers get the larger wheel and STILL double the speed on their VFDs.

Personally, I use a 5" wheel, but if the choice was between 4" and 7" with a VFD, I'd probably lean toward the 7". I'd say you're still going to do most of your grinding at slower speeds anyway (especially finish grinding with higher grits), but it's nice to have that extra SFPM when you're hogging, and a larger drive wheel can still be slowed down plenty with a properly set VFD.

 

[Cushing H.]

So, is it fair to say that i am better off getting the 7” wheel for the occasional need for high SFPM, and relying on the VDF to give me generally much lower speeds most of the time? I am likely to place my order tomorrow...​

 

[Storm W]

So, is it fair to say that i am better off getting the 7” wheel for the occasional need for high SFPM, and relying on the VDF to give me generally much lower speeds most of the time? I am likely to place my order tomorrow...​

You have probably done your shopping and made your decision at this point. I choose a esteem and it's a great grinder as probably is the one you are choosing. If I had to do it again I would probably get a tw90. Some of the features like the east of going horizontal and its tooling rest as well as some of the attachments would be extremely helpful with the direction I have gone with blade making.

 

[Ken H>]

Well, you might have placed your order by now, but the large drive wheel size isn't all that important on a VFD. If you're getting a 1725 rpm motor, then you'll want to double the RPM with the VFD, and a 4" drive wheel will give you 4,000 SFPM with that. Just as important as the high speed is the low speed which you'll use MUCH slower than you ever imagined when you are working with fine grits, and perhaps when you start sharpening knives on the 2X72 grinder running in reverse. Reverse is pretty important on the grinder.

Anyway, as you've placed your order by now I'll stop now - I can get pretty long winded sometimes {g}

 

[Cushing H.]

I did place the order, but i am sure it is not too late. I AM counting on the VFD for slow speeds, but was pretty much told you canget pretty darn slow with the 7” drive wheel. Is that an incorrect belief?? If there is truly a tradeoff, i would rather target higher precision/slower speed (i am a hobbyist, not volume producer). Please advise if there is truly such a tradeoff?

 

[Drew Riley]

Every maker is different, but it's rare anymore that I go all the way down to "zero" on my VFD, with a 5" wheel. However, there are plenty of times I peg it out to 100%, and I do notice a difference on the ceramic belts. Full disclosure, I also have an 1800 rpm motor set to 2x speed on my VFD.

On the bright side, if you feel like 7" is too fast, 4" drive wheels are only about $40 or so.

 

[Cushing H.]

On the bright side, if you feel like 7" is too fast, 4" drive wheels are only about $40 or so.

LOL. Kind of what I was thinking. Thanks for the input ... I will stick with the 7" for now and see how it goes. Hopefully I will get the thing in relatively short time (gotta make a bench for it though ... not sure what size - but that is a different thread!)

 

[Ocelot85]

I have the same grinder, the 7 inch wheel is a better choice. I had a single speed motor with 4 inch wheel before, but upgraded to the VFD and 7 inch wheel. With the VFD I can still run the belts at a crawl if I want to, so the 7 inch wheel is no issue there so I doubt you'd think it was too fast.