Hey guys I have just about finished my no weld grinder and am about to purchase a motor. I'm using the four step pulley system from usa knifemaker. My question is without getting into too much of the complicated calculations for belt speed,which would be a better choice a motor that turns at 1440 rpm, or a motor that turns at 2800 rpm?
motor for no weld grinder
- Thread starter elasmonut
- Start date
Wayne Coe
Forum Owner - Moderator
Tracy and I have differing openions on this. The slower motor is a better motor. It has more posts (contacts and because of this the slower motor is generally a few bucks cheaper) in the motor and has better torque. You get plenty of speed out of a 1440 (1800) RPM motor when in the fast speed. Also, when running in the slower speed setting the 1800 rpm motor will cool better.
Last edited:
Elasmonut,
Glad to hear about your grinder project, and I hope it's coming along well.
I consider myself the ultimate dummy on electric motors, but I do realize motors are available in all sorts of RPM. For our purposes, the most common seem to be 1700-1800 on the low end, and 3400-3600 on the high end.
Is there a reason you have selected the 1440/2800?
My reason for asking is this: Once you select a specific RPM and become used to working with those particular speeds, it's usually desirable to be able to easily find the same speed range should the motor ever need to be replaced.
Considering the spread on a 4-step pulley, a few hundred RPM difference at the motor can have a large impact on differences in final belt speed.
Once I replaced a 1100 RPM motor with a 1750 (the 1100 was harder to find and much more $$).
It was almost like having to learn the machine all over again. Mistakes were made, material was scrapped, and money was lost until I readjusted myself to it.
Just sayin' that use of a commonly available RPM window might be worth considering if motor replacement is ever needed.
This may not even bother some people, but it sure frustrated me. Sorta like a baseball player performing well as long as he uses the same glove. Get him a new glove, and he has to get used to it before he performs like he used to.
If you're truly set on the 1440/2800, either can work.
But with the faster motor (2800), you will probably be best off avoiding use of the highest step-up drive ratio (5" pulley at motor connected to 2" pulley at the driveshaft). It's not that you can't make good use of the high surface speed at the grinding belt, but rather that precision of the drivetrain becomes critical at those speeds.
I know you wanted to avoid the calculations, so I'll simply give you end results of such a combination (2800 RPM motor with your 4-step pulleys and 4" drive wheel) so you can see what I'm talking about.
1. Your motor spins at 2800 RPM. At the highest step-up ratio, the 5" pulley on the motor speeds up the 2" pulley on the driveshaft.
2. This will have the driveshaft spinning at 7600 RPM. At that speed, a 4" drive wheel will give the grinding belt an approximate surface speed of just under 8000 SFPM.
8000 SFPM is screamin' for sure! If the motor is powerful enough (1.5+ HP), slap a ceramic belt on it and you'll hog away metal like there's no tomorrow. Now we're gettin' some work done!
BUT, notice that your driveshaft is spinning at 7600 RPM to move the belt that fast! This is where the precision becomes critical.
Now we're talkin' "better" bearings ($$) and a tight fit of the driveshaft to those bearings to minimize runout. The bearings must be precisely aligned- no sloppy mounting here. The straightness of the driveshaft becomes more critical. Balancing becomes an issue with not only the driveshaft, but also the pulley connected to it (by the way, is the pulley you're using rated for those speeds?).
So basically, to make life easier, using the high speed motor means not being able to use your highest step-up ratio.
But the benefit of the 4-step pulley is that any ratio change applicable to the step-up (high end) also applies to the reduction (low end).
What that means is you can still have a slower speed than available with the 3-step pulleys. That in itself can be very valuable, especially to someone initially learning the machine.
With your current 4-step pulleys and 4" drive wheel, here are final approximate belt surface speeds for the two motors you have mentioned.
Slow (1440) motor: 555, 1106, 2056, 4092
Fast (2800) motor: 1080, 2150, 3998, 7959
Notice with the slow motor, you can (naturally) obtain very low belt speeds. Maybe slower than most people would normally want in a machine, but it provides excellent control on more delicate materials while definitely being faster than working it by hand.
For fast metal hogging, speed (with plenty of motor power) is the objective. But for the reasons mentioned above, we are better off not using the highest ratio with the fast motor. So when using the fast motor, we are for all practical purposes making it three ratios instead of four.
We'll call each step ratio a "gear" for purposes of familiarity.:biggrin:
The slow motor in "4th gear" provides close to the same belt speed that the fast motor provides in "3rd gear"! Either motor is giving you close to 4000 SFPM in "high gear".
Weigh it over, then choose what you think is best for your needs. If you're getting a super deal on a fast motor, by all means take advantage of it.
Plenty of people get lucky enough to run the blazing speeds without the worry/expense of the added precision, and they do just fine. I'm not one of them. I was one of the unlucky ones who had to spend time contacting the engineers at Maska (pulleys) and KML (bearings) to figure things out. (Machine did not run smooth, and I kept going through bearings, pulleys, and drive belts.)
Just a reminder to consider choosing a common RPM (1800/3600) for the reason mentioned above. I don't know where you're located, but a thought that just occurred to me is that perhaps where you're located the 1440/2800 is the standard, rather than the 1800/3600.
Hope it helps without being too confusing.
Good Luck,
Rob
Glad to hear about your grinder project, and I hope it's coming along well.
I consider myself the ultimate dummy on electric motors, but I do realize motors are available in all sorts of RPM. For our purposes, the most common seem to be 1700-1800 on the low end, and 3400-3600 on the high end.
Is there a reason you have selected the 1440/2800?
My reason for asking is this: Once you select a specific RPM and become used to working with those particular speeds, it's usually desirable to be able to easily find the same speed range should the motor ever need to be replaced.
Considering the spread on a 4-step pulley, a few hundred RPM difference at the motor can have a large impact on differences in final belt speed.
Once I replaced a 1100 RPM motor with a 1750 (the 1100 was harder to find and much more $$).
It was almost like having to learn the machine all over again. Mistakes were made, material was scrapped, and money was lost until I readjusted myself to it.
Just sayin' that use of a commonly available RPM window might be worth considering if motor replacement is ever needed.
This may not even bother some people, but it sure frustrated me. Sorta like a baseball player performing well as long as he uses the same glove. Get him a new glove, and he has to get used to it before he performs like he used to.
If you're truly set on the 1440/2800, either can work.
But with the faster motor (2800), you will probably be best off avoiding use of the highest step-up drive ratio (5" pulley at motor connected to 2" pulley at the driveshaft). It's not that you can't make good use of the high surface speed at the grinding belt, but rather that precision of the drivetrain becomes critical at those speeds.
I know you wanted to avoid the calculations, so I'll simply give you end results of such a combination (2800 RPM motor with your 4-step pulleys and 4" drive wheel) so you can see what I'm talking about.
1. Your motor spins at 2800 RPM. At the highest step-up ratio, the 5" pulley on the motor speeds up the 2" pulley on the driveshaft.
2. This will have the driveshaft spinning at 7600 RPM. At that speed, a 4" drive wheel will give the grinding belt an approximate surface speed of just under 8000 SFPM.
8000 SFPM is screamin' for sure! If the motor is powerful enough (1.5+ HP), slap a ceramic belt on it and you'll hog away metal like there's no tomorrow. Now we're gettin' some work done!
BUT, notice that your driveshaft is spinning at 7600 RPM to move the belt that fast! This is where the precision becomes critical.
Now we're talkin' "better" bearings ($$) and a tight fit of the driveshaft to those bearings to minimize runout. The bearings must be precisely aligned- no sloppy mounting here. The straightness of the driveshaft becomes more critical. Balancing becomes an issue with not only the driveshaft, but also the pulley connected to it (by the way, is the pulley you're using rated for those speeds?).
So basically, to make life easier, using the high speed motor means not being able to use your highest step-up ratio.
But the benefit of the 4-step pulley is that any ratio change applicable to the step-up (high end) also applies to the reduction (low end).
What that means is you can still have a slower speed than available with the 3-step pulleys. That in itself can be very valuable, especially to someone initially learning the machine.
With your current 4-step pulleys and 4" drive wheel, here are final approximate belt surface speeds for the two motors you have mentioned.
Slow (1440) motor: 555, 1106, 2056, 4092
Fast (2800) motor: 1080, 2150, 3998, 7959
Notice with the slow motor, you can (naturally) obtain very low belt speeds. Maybe slower than most people would normally want in a machine, but it provides excellent control on more delicate materials while definitely being faster than working it by hand.
For fast metal hogging, speed (with plenty of motor power) is the objective. But for the reasons mentioned above, we are better off not using the highest ratio with the fast motor. So when using the fast motor, we are for all practical purposes making it three ratios instead of four.
We'll call each step ratio a "gear" for purposes of familiarity.:biggrin:
The slow motor in "4th gear" provides close to the same belt speed that the fast motor provides in "3rd gear"! Either motor is giving you close to 4000 SFPM in "high gear".
Weigh it over, then choose what you think is best for your needs. If you're getting a super deal on a fast motor, by all means take advantage of it.
Plenty of people get lucky enough to run the blazing speeds without the worry/expense of the added precision, and they do just fine. I'm not one of them. I was one of the unlucky ones who had to spend time contacting the engineers at Maska (pulleys) and KML (bearings) to figure things out. (Machine did not run smooth, and I kept going through bearings, pulleys, and drive belts.)
Just a reminder to consider choosing a common RPM (1800/3600) for the reason mentioned above. I don't know where you're located, but a thought that just occurred to me is that perhaps where you're located the 1440/2800 is the standard, rather than the 1800/3600.
Hope it helps without being too confusing.
Good Luck,
Rob
Thanks guys, if it wasn't for forums like this I'd still be usin' files and sandpaper. Rob45 your explanation has really cleared things up thank you for taking the time. For what I want and my level of skill I think I'll go with the lower speed. As for if 1440/2800 are the standard? not sure but here in Oz it seems to be, but I really don't know much about this and am on a pretty steep learning curve right now.
rhinoknives
Well-Known Member
Rob45 Has spelled it out better than I ever could!
My Vote is go with the slow motor for all the reasons listed! Fast to me does mean going thru bearing's etc and with my Coote grinder I had the fast and didn't know not to use fourth gear! The rubber started to separate from my 8" contact wheel. I sent it back to Norman Coote and he tuned up and replaced the wheel on the grinder for inexpensive and explained all of this mumbo jumbo about belt speeds to me.
That was about 13 plus years ago and the longer I make knives, the more I realize that slower is better in all of my machines!!
Laurence
www.westsidesharpening.com/
My Vote is go with the slow motor for all the reasons listed! Fast to me does mean going thru bearing's etc and with my Coote grinder I had the fast and didn't know not to use fourth gear! The rubber started to separate from my 8" contact wheel. I sent it back to Norman Coote and he tuned up and replaced the wheel on the grinder for inexpensive and explained all of this mumbo jumbo about belt speeds to me.
That was about 13 plus years ago and the longer I make knives, the more I realize that slower is better in all of my machines!!
Laurence
www.westsidesharpening.com/
Good point, Ken.
Like I said, I'm not very smart when it comes to the electrical side of things.
The main concern is to have a motor commonly available to you (wherever the location) so as to avoid unintended changes.
The motor I mentioned replacing earlier was the original 3-phase industrial motor replaced by a single-phase "farm duty" motor. When I closed the shop down and moved the machine to my house, I checked into the expense of getting electrical hooked up.
That's why the motor was changed out. But it definitely made a difference, especially at high speed.
Thanks for pointing it out.
Rob
Like I said, I'm not very smart when it comes to the electrical side of things.
The main concern is to have a motor commonly available to you (wherever the location) so as to avoid unintended changes.
The motor I mentioned replacing earlier was the original 3-phase industrial motor replaced by a single-phase "farm duty" motor. When I closed the shop down and moved the machine to my house, I checked into the expense of getting electrical hooked up.
That's why the motor was changed out. But it definitely made a difference, especially at high speed.
Thanks for pointing it out.
Rob
Adam Vigil
Well-Known Member
I went with Waynes 1.5hp 1725 rpm motor for my GIB build with step pulleys and could not be happier. As explained above the slower motor has more torque and runs cooler