ballen
Diamond
- Joined
- Sep 25, 2011
- Location
- Garbsen, Germany
A few months ago I bought a cylindrical grinder: a 1960s era Studer RHU-450. Another thread in this forum describes some of the work I have done to fix it up. Now I'm starting to learn how to use it. My experience so far is limited to two test pieces. One is a piece of 16mm (5/8") steel from the scrap drawer, and the second is a scrap of 12mm (1/2") diameter stainless. The first I did between centers, and the second with a collet.
The finish is not as good as I had expected, and I want to track down why. I'd be grateful for advice from the experts here. It's probably technique or the wheel, but I am not sure. I also have a J&S 540 surface grinder and can get mirror finishes from that without trying very hard.
First off, here is the wheel that came with the machine. This is 300 x 30 x 127mm (12" x 1 1/4" x 5"). I am not experienced at reading the codes, but I think 81A is aluminium oxide, 80 is the grain size, I don't know what the -4 means, G is the hardness (on the softer side) 13 is a very open bond. M is not a bond type that I could identify, perhaps the V means vitrified bond. I removed it from the hub, ring tested it, reinstalled, balanced, trued, and balanced again.
Wheel surface speed is about 28m/s = 92 feet per second = 5500 feet/minute. I am using the recommended pulleys for this wheel.
I am dressing the wheel using the tailstock mounted diamond point that came with the machine. It's about a half-carat made in Germany diamond, looks in good shape to my inexperienced eye.
I am grinding wet, using the same synthetic grinding coolant as on my surface grinder. I did clean out the coolant sump, which has "3 level" system of weirs to trap grit, but is not as extensive a filtering system as on the J&S 540. I don't have any kind of paper or other filter.
Here is the grind on the 16mm (5/8") steel rod. I spun this at various speeds from 50 to 500 rpm. It didn't make any real difference in the finish. I also tried various feed rates from inches per minute to inches per second. I had dressed the wheel with a fairly quick pass, intended to leave it open, the same that gives me good finishes on my J&S surface grinder.
Here is the grind on a 12mm (1/2") diameter bit of stainless (just the part to the right was sticking out from the collet). In this case the finish is better than before, because I experimented dressing the wheel with a very slow pass rather than a quick one as before. I mounted this in a collet in the work-head, and spun it around 400 rpm.
You can see this rod lying next to a piece of flat steel (under the dial indicator) which I have surface ground. The surface ground steel is a mirror surface, whereas the stainless has a more "frosted" appearance. If I run my fingernail along it, I can "feel" the texture.
Here are some possible reasons for this not-very-good finish:
(a) wrong wheel
(b) wrong dress
(c) wrong feed/speed
Potentially
(d) lack of a solid base, the machine is still on a pallet
(e) problems with the (solid-bearing) spindle
The spindle is perfectly smooth and quiet, and the runout is at the micron level (0.00004"). But I have not taken the spindle apart or gone through the procedure for setting the spindle end-play and runout, because I didn't think it was needed. When it runs it gets up to temperatures of about 37C = 100 Farenheit, pleasantly warm
I'd be grateful for advice about what to try or experiment with to get a better finish.
Cheers,
Bruce
PS: here is the wheel side of the coolant nozzle. I don't know why there is this little hole. Also, it seems that most of the coolant just bounces off the air around the wheel. But this looks like the stock nozzle shown in the manual...
The finish is not as good as I had expected, and I want to track down why. I'd be grateful for advice from the experts here. It's probably technique or the wheel, but I am not sure. I also have a J&S 540 surface grinder and can get mirror finishes from that without trying very hard.
First off, here is the wheel that came with the machine. This is 300 x 30 x 127mm (12" x 1 1/4" x 5"). I am not experienced at reading the codes, but I think 81A is aluminium oxide, 80 is the grain size, I don't know what the -4 means, G is the hardness (on the softer side) 13 is a very open bond. M is not a bond type that I could identify, perhaps the V means vitrified bond. I removed it from the hub, ring tested it, reinstalled, balanced, trued, and balanced again.
Wheel surface speed is about 28m/s = 92 feet per second = 5500 feet/minute. I am using the recommended pulleys for this wheel.
I am dressing the wheel using the tailstock mounted diamond point that came with the machine. It's about a half-carat made in Germany diamond, looks in good shape to my inexperienced eye.
I am grinding wet, using the same synthetic grinding coolant as on my surface grinder. I did clean out the coolant sump, which has "3 level" system of weirs to trap grit, but is not as extensive a filtering system as on the J&S 540. I don't have any kind of paper or other filter.
Here is the grind on the 16mm (5/8") steel rod. I spun this at various speeds from 50 to 500 rpm. It didn't make any real difference in the finish. I also tried various feed rates from inches per minute to inches per second. I had dressed the wheel with a fairly quick pass, intended to leave it open, the same that gives me good finishes on my J&S surface grinder.
Here is the grind on a 12mm (1/2") diameter bit of stainless (just the part to the right was sticking out from the collet). In this case the finish is better than before, because I experimented dressing the wheel with a very slow pass rather than a quick one as before. I mounted this in a collet in the work-head, and spun it around 400 rpm.
You can see this rod lying next to a piece of flat steel (under the dial indicator) which I have surface ground. The surface ground steel is a mirror surface, whereas the stainless has a more "frosted" appearance. If I run my fingernail along it, I can "feel" the texture.
Here are some possible reasons for this not-very-good finish:
(a) wrong wheel
(b) wrong dress
(c) wrong feed/speed
Potentially
(d) lack of a solid base, the machine is still on a pallet
(e) problems with the (solid-bearing) spindle
The spindle is perfectly smooth and quiet, and the runout is at the micron level (0.00004"). But I have not taken the spindle apart or gone through the procedure for setting the spindle end-play and runout, because I didn't think it was needed. When it runs it gets up to temperatures of about 37C = 100 Farenheit, pleasantly warm
I'd be grateful for advice about what to try or experiment with to get a better finish.
Cheers,
Bruce
PS: here is the wheel side of the coolant nozzle. I don't know why there is this little hole. Also, it seems that most of the coolant just bounces off the air around the wheel. But this looks like the stock nozzle shown in the manual...