craigbladeworks
Well-Known Member
I have a lot to rethink on this build. Thank you gentlemen. I appreciate the input and help.
may as well keep going with this. here is basic wheel set, 4"drive,3"idle,2ea 2"contact($120 delivered) http://www.ebay.com/itm/Belt-Grinde...208?pt=LH_DefaultDomain_0&hash=item3aa2c15078
i would source 1 1/2" square tube or square stock and aluminum plate local as shipping costs as much as the material. you can get a 240vac VFD for the same price as the 110vac one, just need to have access to either dryer or range outlet.
I can across a 1725 1.5hp 3ph for half the motor I was looking at. With a 2year warranty too. But not sure what the overall benefit is of the lower rpm?Well, it depends on which you want, and how much money you're prepared to spend. I went with 3450 RPM motor due to cost restraints. Either one will work just fine.
The 1725 RPM will require a larger drive wheel, OR - pushing the motor to 100% overspeed to get required SFPM. One thing about 1725, you can do the 100% overspeed and still only be at 3450 RPM. "IF" I had both sitting there at same price - I'd go with 1725 RPM motor with maybe a 5" drive wheel.
Ken
What's the reasoning for choosing a 1725 over a 3450? I don't doubt your right just wasn't sure what the reasoning isIf you're using a VFD, you want the 1725 motor. You will still be able to go from 0 to 3600 rpm with that motor, this is the right motor. There's no reason in the world you would ever go faster than that. All the VFD's I've used over the years will run the motor at twice it's rated speed. The motor doesn't care. Don't by a 3600 rpm motor if you're using a VFD!
So I'd be looking at greater low speed torque? That sounds great.The idea of using the 1725 rpm motor is the vfd will run up to 120hz. At 60 hz, (line freq) the motor will run at name tag RPM, say 1725 rpm. By overspeeding the motor to 120 hz you 1725 motor will be spinning at 3450 RPM. The advantage of using the 1725 rpm motor, the torque at 60 hz is at a max say at 1800 SFPM belt speed. A 3450 rpm motor running at 50% hz speed 1800 SFPM will be at reduced torque. Of course, at slower belt speeds a lot of torque is not normally required while max torque is more desired at full belt speed of 4000 SFPM - boy you can throw some sparks there.
Got to go - more later unless someone else chimes in to finish.
Ken H>
So if I get a 5 inch wheel @ 60hz spinning 1725 I'd be getting 2258 sfm. So I'd have to run my motor at 100% over just to reach 4500 sfm.I'm now back - had to take wife out to dinner tonight.... small price to pay for clean socks.
Yes, the 1725 rpm motor will give more low speed torque than would a 3450 rpm motor. Remember, for 1800 SFPM (with 4" drive wheel) belt speed, the 1725 rpm motor will be running about 100%, while a 3450 rpm motor would be only 50%, and torque will be similar. BUT - here is the real kicker, at that low speed, you really don't need much torque. You need the torque at high speed where you're doing real hogging of metal. I have a 3450 RPM motor, it was about $50 less expensive than a 1725 rpm motor.
Some folks talk about running at 6,000 SFPM for hogging - hard for me to imagine running that speed. 4K SFPM is pretty fast for me, and that cuts pretty fast.
My thinking (at the time) was the 3450 rpm motor with a 4" drive wheel would give me belt speeds from 4,000 SFPM on high at only a very slight overspeed of motor. At the lower end the 3450 RPM motor will give 800 SFPM belt speed at 25% of motor, and there is still plenty of torque for low speed grinding - a delicate touch is normally used at such low speeds. At times when grinding mammoth ivory I've even slowed down to 500 SFPM speed for "touching" the scale.
When I wish to go hog metal, crank it up to max at 70 hz to give the 4,000 SFPM belt speed.
Again, at same price (maybe even a sight extra) I would go with 1725 rpm.... I think {grinning}
Ken H<>