Grinder electrical question

So Im on my way, got a deal on a open box balder 2hp on ebay and jumped on it, im down to a few last decisions and I have a question about wheel sets. On a budget build is there anything wrong with poly/plastic style wheels? Just wondering if there is a performance gap between them and solid aluminum wheels? Additionally though I understand the difference and reasons behind different drive wheel sizes im not sure about the following...
-For wheels at the platen, some go 2 diff size wheel such as a 2” and a 3”, what is the advantage if any for this?
- i see options for tracking wheel size, what is the benefit of a 4” vs. 3” or vice versa?
Thanks
 
Not really sure about the tracking wheel but the different size platen wheels give you different sizes of radius you can grind built into the grinder. Good feature.
 
Thank you all for your help and education, I have another question, Im about to pull the trigger on a Ameribrade grinder, I will be using a baldor 2hp 1750rpm motor running 220. I will also be running a vfd capable of 120hz, my 2 choices of drive wheel sizes from them are 4” and 7”,
With the 7” my belt speed at 60hz is 3200, 120hz 6k plus and at 30hz it will be 1600, my question is would 1600 be slow enough for detail and fine sanding for wood handle and such? I think 4 is too small but just wondering if I should source a 6” wheel from elsewhere or is 1600 slow enough for delicate work?? Cant thank you guys enough.
 
You might be overthinking this. With a VFD, you are not limited to 1,600 ft/min, you can adjust the speed down to your liking. I have a KBAC-27D on a DIY grinder with a 7" Ameribrade drive wheel and an 1,800 rpm motor and I can adjust it to very slow speed. The Ameribrade wheel is very nicely made and the company was great to deal with, very promptly answered my questions.

I don't want to cause any confusion, but here are some more details. The drive wheel size will obviously control the belt speed for a given frequency. Once you pick your wheel size and maximum frequency, the top speed is set. If you set your top speed way higher than you ever need, you lose resolution on your speed control dial. But you can still reach all the same slow speeds you can reach with a lower top end speed. So, the choice of drive wheel size is not all that critical as long as the wheel is big enough.

With a VFD where the maximum frequency is fully programmable, you can program the VFD to give you the same top belt speed whether you have a 6" or 7" wheel. With the KBAC-27D drive, that is not the case because there are some limitations on the maximum frequency. The KBAC-27D drive has a 1X/2X setting and a separate max. speed adjustment from 0.7x-1.1x, and the two adjustments can be used in combination. That means you can adjust your top end frequency from 42-132Hz, with a gap between 66-84Hz. So, the useful top end range is essentially from 84-132 Hz. For the 7" wheel, you get a top speed range of approx. 4,500 ft/min to 7,050 ft/min and for a 6" wheel you would get 3,800 ft/min to 6,050 ft/min. I think around 5,000 ft/min is a good top speed to aim for and both sizes can achieve that. That's all personal preference, though, and to figure out what you like, you just have to get a bit of experience. But it is not a big deal if you get a 7" wheel and then figure out you never want to grind above 4,000 ft/min. You are just losing around 10% of you adjustment range, I doubt you will ever even notice the difference in practice.
 
Ok.. I wasnt as concerned with the potential top speeds as I felt the were easily achieved. I was more concerned about the lowest speed I coupd achieve and If it would be useful. I think this is where I got confused... the calculator for SFM I used only had 30hz to 120hz to choose from for input so in my haste instead of realizing the vfd would go lower than the parameters of the calculator.
Thanks for the reassurance.
 
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