- Joined
- Jul 2, 2014
- Messages
- 7,594
I need to rough and finish grind some carbide hand scraper inserts. For rough grinding I will be using my HF Baldor clone carbide grinder at high speed with a 300 (Edit: 150 grit) grit resin bond diamond face wheel. That should work fine, with a simple jig to hold the scraper handle for grinding the correct radii.
For finish honing/lapping, I bought a 6" (150mm) diameter, 1mm thick import steel plate, with a 600 grit plated diamond coating, and plan to use my surface grinder for the slow speed work, because it has a VFD. I had to open up the mounting hole in the lapping plate from 1/2" to 1 1/4" and then mounted it on a wheel adapter and installed it on my 1946 B & S model 2L surface grinder. The runout is minimal, and I want the capability of running the grinder at very low rpm's to do the lapping. Previously, I had the VFD set for 15-60 hertz, which allowed a measured 3266 rpm at the high end, and jogging at low speed to get the ISO 2 oil circulating in the plain bearing spindle. It also allows slow acceleration and deceleration to keep the wheels from slipping on the adapters and going out of balance. I want now to also get the maximum wheel rpm up to 3600 rpm, which is the rated limit of 7" surface grinding wheels (makes the wheels act harder when desired.)
So, tonight I reset the VFD for a range of 5-65 hz, which gets me up to just under 3600 rpm, and down to about 160 rpm, and infinitely variable between those limits. My question is about the low speed operation. The grinder has a 1946 1.5 hp GE 3 phase motor, which is running smoothly. I don't imagine that 65 hz is going to hurt anything, my concern is running as low as 5 hz for short periods of time, 5-10 minutes max, light loading. I really do not think the big old motor will overheat under those conditions for that period of time, but wonder if the VFD might add additional strain on the old motor that I should be concerned about.
For finish honing/lapping, I bought a 6" (150mm) diameter, 1mm thick import steel plate, with a 600 grit plated diamond coating, and plan to use my surface grinder for the slow speed work, because it has a VFD. I had to open up the mounting hole in the lapping plate from 1/2" to 1 1/4" and then mounted it on a wheel adapter and installed it on my 1946 B & S model 2L surface grinder. The runout is minimal, and I want the capability of running the grinder at very low rpm's to do the lapping. Previously, I had the VFD set for 15-60 hertz, which allowed a measured 3266 rpm at the high end, and jogging at low speed to get the ISO 2 oil circulating in the plain bearing spindle. It also allows slow acceleration and deceleration to keep the wheels from slipping on the adapters and going out of balance. I want now to also get the maximum wheel rpm up to 3600 rpm, which is the rated limit of 7" surface grinding wheels (makes the wheels act harder when desired.)
So, tonight I reset the VFD for a range of 5-65 hz, which gets me up to just under 3600 rpm, and down to about 160 rpm, and infinitely variable between those limits. My question is about the low speed operation. The grinder has a 1946 1.5 hp GE 3 phase motor, which is running smoothly. I don't imagine that 65 hz is going to hurt anything, my concern is running as low as 5 hz for short periods of time, 5-10 minutes max, light loading. I really do not think the big old motor will overheat under those conditions for that period of time, but wonder if the VFD might add additional strain on the old motor that I should be concerned about.
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