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Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by BelnapCustomKnives, Apr 6, 2018.
Thanks. This post made the conversation much more interesting and informative for me.
Belnap, using a calculator online for hp to torque conversions a 24000 rpm 3hp motor would put out .7 torque in foot pounds, to compare a leeson 3hp motor at 3600rpm would give 4.4 torque and 1750 would give 9. Some interesting numbers and that goes along with my understanding of woodworking equipment, take a look at most router motors like what you are using that are rated for high speed and hp but what they aren’t telling you is you are getting substantially lower torque than a standard motor, but those motors normally are spinning small objects at high speeds where you don’t need a lot of torque, and I’m not saying your grinder doesn’t work because it clearly does from the video you posted but I can hear the motors speed changing in the video so it wouldn’t surprise me to see a big drop in speed when pressure is applied. Not trying to start a argument just more or less thinking out loud
After reading some more based on your explanation it seems that the little motor is operating in its normal power ratios which would be straight torque line and climbing HP line until it reaches 24,000 rpm/400hz and the two lines meet and deliver max rated power, speed, and torque at exactly where you need it for heavy removals. Vs. what the conventional sander drive is doing which it maxing out at 60hz then trading torque for rpm so at top rpm it is operating at a significantly reduced power/torque when you actually need it most and when you slow down it develops max power when you really do not need it.
Have you looked at automationdirect? I only ask because you are comparing the cheapest spindle motor direct from a supplier to a mid range quality motor from a "middle-man" company.
Could not find the Leeson on that sight. I was meaning to compare to a popularly used motor by other sander manufactures such as the one I referenced. There appear to be inexpensive motors on that sight but I have not seen anyone mention they use those particular ones on their machines.
Lots of folks are using the Iron Horse 3 ph motors on grinders and other things. They work just fine and are a good bit less expensive than the normal 3 ph motor.
Hello Gents, my 2Cents is that I always have a 90 Durometer rubber wheel on my Grinders for the Drive, and of course any contact wheel. After my Coote machine which is 8” Belt driven grinder I bought a Hardcore 2 x 72” and even bought an extra Rubber wheel for my Tag 101... I’ve found they reduce slippage, improve tracking and help keep sound & vibration down!! Which helps reduce fatigue which grinding out a stack of blades..............................It’s worth it! I won’t use a plain Aluminum drive or any other than a Idler wheel and even those track better & quieter with a rubber contact coating...
Those are really affordably priced motors
Laurence you like 90duro to grind on as well? Have you tried the 70duro? Always thought a softer wheel would be more pleasing to grind on and have better traction as a drive ala grippier
Thanks for spotting that! Typo, mine are 70 durometer just like my contact wheels!...
Hi, I messed with a similar calculator online and got similar torque number for the 24,000 motor. Which probably accurate because it is using a drive wheel diameter of 1" to achieve 7000 sfpm. The rpm numbers mentioned for the other motors would require a bigger drive wheel to achieve 7000 sfpm. The drive wheel diameter would need to be considered to get actual torque delivered to the belt because of the increased arm of the larger drive wheel. Might still be higher than the little motor. I am not saying the little motor is producing more torque because it is not a torque motor. The small amount of torque it does produce has proven in real world testing so far to be more than enough to perform all grinding functions I have tried so far very well.
At 1750 with double speed jumper the motor would be running 3500 rpm and require a 7-8" drive wheel to achieve 7000 sfpm. Once this motor goes over 1750 per the chart JTknives shared the motor begins to loose torque with rpm increase. Then after that there is torque lose due to large diameter drive wheel. I have not worked it all out and it still may be a higher number than the spindle motor at that belt speed. Same would go for the 3500 motor if it was jumped for double speed and a 4 inch drive wheel to reach 7000 rpm. I have a KBAC29 vfd and might go ahead and buy an Iron Horse 3hp and do some side by side comparison.
Belnap it would definitely be neat to see a comparison of the two, we could crunch numbers all day long and would probably be suprised at how close a lot of it would come out with everything figured in, I think as long as you can get from point a to b and nothing blows up in the process then that’s all that matters. Definitely a interesting thread to follow.
You forget in your calculation this ......................
When I turn power off , this little 2x42 monster continue to spin half minute ......
2hp 380V 3 phase motor and 2820 RPM , drive wheel / flywheel / is 22cm.dia , 6400 SFPM . Be my guest and try to stop this ......................
380 Volts... Sweet! I want to see it running.
Thanks for the idea. I have reversed it on accident when starting but not deliberately for an period. I will do that and see. This is my first VFD and I am still in a one direction frame of mind because I am not used to having the option of reverse.
You should read this ...................... https://www.bladeforums.com/threads/its-good-to-read-it.1569678/
OK , I will join the club You win ! Definitely I will use this one for my CNC belt grinder .And I had so nice cohabitation till now with my neighbors
Can't wait to see your CNC grinder. I have thought about doing that but only thoughts no action. I don't have any CNC skills yet. Is this an air cooled motor?