AlfaGTA
Diamond
- Joined
- Dec 13, 2002
- Location
- Benicia California USA
I went into work on Saturday to run a little job. I needed to use the "C" axis of my Universal "Tool makers" table to cut some splines using the horizontal spindle on the FP4NC (a subject for another posting)
As part of the setup i needed to indicate in the part and make it run concentric with the built in rotary table (C). Well now i have had this table for over 10 years having purchased it from FPS in Germany. They sold it to me "rebuilt" (the only way they would sell it) and they re-surfaced the top of the table with the correct planned surface and checked the rotary encoder for correct operation.
Well as i indicated in my part having to rotate the table through multi turns , i noticed that the reading on the control was changeing on every rotation. When i got to the "0" point of the table rotation as verified by the built in indicator, the angle readout was getting smaller with every full rotation...Yikes can't make splines unless i can get a real reading. Now you have to remember that the universal table has only a protractor around the base of the table that is graduated in single degrees, and since the handwheel connects to the table rotation via a 3 speed gearbox a conventional dividing plate or degree collar is out.
Well of course i suspected the electronics. Went immediately to the "NZP" board that controls the display from the "C". On the Dialog controls all the axis use the same board and you set DIP switches to configure the board to the axis it is serving. Well i checked the swithches 4 times and the board was set correctly, no problem. So i swapped the board from the "C" with the "Z" and tested the table again, but there was no change...the readout was loosing numbers with every turn.
So now what. I did a bit more checking and the result was strange! If i rotated the table in the + direction, there was no value loss as long as i did not rotate further than about 300 degrees. I could return to the mechanical zero and everything was fine. If i went further than 300 degrees the trouble appeared. If i went in the "-" direction all was fine until i got around minus 50 degrees and then the values started differing from the actual table position. The ovious answer is that something was wrong with the rotary encoder. Possibly a dirty scale and missing counts. I had to get to the bottom of this and quickly as i needed the job done.
Well having no parts drawing for the table or manual i was shooting in the dark. I looked at the bottom of the table where the cable to the control came out...the encoder must be close i reasoned.
Removing the steel ring from the base of the table through hole did nothing to disclose the encoder location.
I decided to remove the table. The top of the table has 6 allen bolt heads showing at the bottom of the "T" slots and it seemed a fair bet that removing them might give access to the parts below.
I removed the bolts and the 4 nuts that provide the clamping to secure the table rotation. I tried to turn the table to see if it was loose , but it did not move. I then tried to lift the table off and with a bit of coaxing it came free.
With the table lifted you can see the outer bering surface..part of the casting and fitted with 2 grooves to carry oil supplied from a front mounted pressure gun fitting. Also the 4 holes for the clamp bolts can be seen. The inner disc with the holes tapped into it is where the table bolts. This disc is steel and is the rotating part, connected to the worm wheel. You might also notice the peg sticking up. This peg is in effect a dowell that locates the table to the disc and is the reason that the table would not turn free even when the bolts were out.
You might also be able to make out the tip of the "zero" indicator sticking proud of the outer casting surface , just a bit past the front.
The green piece in the center is a steel cover ,not sheet metal, but rather a heavy steel forming.
Ok so i got to the encoder and the photo shown is not quite accurate. When i opened up the cover i noticed that there were two complete reading heads, along with two lamps. I carefully cleaned the encoder scale (glass disc with lines engraved on its surface) using Isopropyl Alcohol and lint free lens cleaning tissues. I turned the power on and tried the tabel rotation again...but the trouble was still there. With the power on i noticed that both lamps were on. This seemed funny to me as i sort of remembered that the extra reader and lamp were there in case one burned out. But having never seen one of these before i reasoned that perhaps two readers were used to error check or increase accuracy...
Several additional cleanings of the scale did not help with my problem.
I looked at the DIP switch block and by switching #3 or #4 i was able to turn off either of the lamps. With only one lit i tried the rotary again and to my surprise the readout was correct
Now the srange thing is that i can't explain why the error only happens in one sector of the table rotation , but with both lamps lit the error returns on cue.
Now this table was never apart in my ownership. The problem must have been present since i have owned it and i never noticed the trouble because i was never making full rotations. I would by luck make plus moves (less than 300 degrees) and go back the way i went to zero i suppose. But the maddening thing is it came this way from folks that should know better......
Showing the under side of the table, the bolts to clamp the table rotation and the holes for holding the table to the rotary plate. Can also make out the dowell hole with a steel hardened bushing pressed in. Also the ramp notch of the "zero" indicator setup.
I replaced the table and secured it to the base with the allens. I used RTV sealant on the bolt shanks to prevent coolant from getting into the base of the table.
Additional view of the encoder. The glass scale is visible with two concentric rings of engravings for the scales.
Cheers Ross
[ 04-16-2007, 10:56 AM: Message edited by: AlfaGTA ]
As part of the setup i needed to indicate in the part and make it run concentric with the built in rotary table (C). Well now i have had this table for over 10 years having purchased it from FPS in Germany. They sold it to me "rebuilt" (the only way they would sell it) and they re-surfaced the top of the table with the correct planned surface and checked the rotary encoder for correct operation.
Well as i indicated in my part having to rotate the table through multi turns , i noticed that the reading on the control was changeing on every rotation. When i got to the "0" point of the table rotation as verified by the built in indicator, the angle readout was getting smaller with every full rotation...Yikes can't make splines unless i can get a real reading. Now you have to remember that the universal table has only a protractor around the base of the table that is graduated in single degrees, and since the handwheel connects to the table rotation via a 3 speed gearbox a conventional dividing plate or degree collar is out.
Well of course i suspected the electronics. Went immediately to the "NZP" board that controls the display from the "C". On the Dialog controls all the axis use the same board and you set DIP switches to configure the board to the axis it is serving. Well i checked the swithches 4 times and the board was set correctly, no problem. So i swapped the board from the "C" with the "Z" and tested the table again, but there was no change...the readout was loosing numbers with every turn.
So now what. I did a bit more checking and the result was strange! If i rotated the table in the + direction, there was no value loss as long as i did not rotate further than about 300 degrees. I could return to the mechanical zero and everything was fine. If i went further than 300 degrees the trouble appeared. If i went in the "-" direction all was fine until i got around minus 50 degrees and then the values started differing from the actual table position. The ovious answer is that something was wrong with the rotary encoder. Possibly a dirty scale and missing counts. I had to get to the bottom of this and quickly as i needed the job done.
Well having no parts drawing for the table or manual i was shooting in the dark. I looked at the bottom of the table where the cable to the control came out...the encoder must be close i reasoned.
Removing the steel ring from the base of the table through hole did nothing to disclose the encoder location.
I decided to remove the table. The top of the table has 6 allen bolt heads showing at the bottom of the "T" slots and it seemed a fair bet that removing them might give access to the parts below.
I removed the bolts and the 4 nuts that provide the clamping to secure the table rotation. I tried to turn the table to see if it was loose , but it did not move. I then tried to lift the table off and with a bit of coaxing it came free.
With the table lifted you can see the outer bering surface..part of the casting and fitted with 2 grooves to carry oil supplied from a front mounted pressure gun fitting. Also the 4 holes for the clamp bolts can be seen. The inner disc with the holes tapped into it is where the table bolts. This disc is steel and is the rotating part, connected to the worm wheel. You might also notice the peg sticking up. This peg is in effect a dowell that locates the table to the disc and is the reason that the table would not turn free even when the bolts were out.
You might also be able to make out the tip of the "zero" indicator sticking proud of the outer casting surface , just a bit past the front.
The green piece in the center is a steel cover ,not sheet metal, but rather a heavy steel forming.
Ok so i got to the encoder and the photo shown is not quite accurate. When i opened up the cover i noticed that there were two complete reading heads, along with two lamps. I carefully cleaned the encoder scale (glass disc with lines engraved on its surface) using Isopropyl Alcohol and lint free lens cleaning tissues. I turned the power on and tried the tabel rotation again...but the trouble was still there. With the power on i noticed that both lamps were on. This seemed funny to me as i sort of remembered that the extra reader and lamp were there in case one burned out. But having never seen one of these before i reasoned that perhaps two readers were used to error check or increase accuracy...
Several additional cleanings of the scale did not help with my problem.
I looked at the DIP switch block and by switching #3 or #4 i was able to turn off either of the lamps. With only one lit i tried the rotary again and to my surprise the readout was correct
Now the srange thing is that i can't explain why the error only happens in one sector of the table rotation , but with both lamps lit the error returns on cue.
Now this table was never apart in my ownership. The problem must have been present since i have owned it and i never noticed the trouble because i was never making full rotations. I would by luck make plus moves (less than 300 degrees) and go back the way i went to zero i suppose. But the maddening thing is it came this way from folks that should know better......
Showing the under side of the table, the bolts to clamp the table rotation and the holes for holding the table to the rotary plate. Can also make out the dowell hole with a steel hardened bushing pressed in. Also the ramp notch of the "zero" indicator setup.
I replaced the table and secured it to the base with the allens. I used RTV sealant on the bolt shanks to prevent coolant from getting into the base of the table.
Additional view of the encoder. The glass scale is visible with two concentric rings of engravings for the scales.
Cheers Ross
[ 04-16-2007, 10:56 AM: Message edited by: AlfaGTA ]