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- Jun 10, 2019
- Messages
- 534
I have an MK Products rotary positioner that is supposed to be compatible with HF welding processes. I only recently welded aluminum on it for the first time and hit a problem: the positioner's RPM would drop significantly when welding. For example, I was set to 1 RPM, but during welding it dropped to about 0.3 RPM. The effect seems to correspond to the current. When backing off the pedal, the RPM would be less affected (though still very noticeable).
I dug into it and I ended up also finding two speed-control issues (#1 and #2 below) which occur as-is (just the machine itself, w/o any welding). My questions:
1. The documented speed range does not match the RPM readout
*I think this may be a typo in the manual. There is an identical looking, newer revision machine and its manual says 1-10 for high. This seems more logical.
2. The machine's readout does not match reality when in High range only
Low Range
High Range (deviates more as the RPM setting increases)
Notes
The positioner is directly connected to the + lug on the welder (as it normally should be for TIG; DCEN) with a high-quality cable. The positioner is plugged into its own 120v circuit.
DC welding doesn't change RPM. My welder doesn't have selectable HF so I cannot rule out A/C vs. HF. Positioner can handle up to 300a weld current; I'm welding at far less than that.
My positioner's chuck has blackened jaws. Seems to conduct the weld current fine, but will be testing with a jumper to the turntable. I also want to try at different RPMs and both speed ranges.
The jog button spins the table at 9.8 RPM (indicated, I have not measured). Its not documented what it should jog at, but assuming that ~10RPM is the jog speed, then I suppose the speed control issue may just be the pot...though I'm not sure why only High would be affected?
The potentiometer's scale is 0-10. It doesn't do anything until position 2 in either range setting. At the #2 position is when you hear the transformer hum and get movement. Position 0 does show a readout of 0 RPM, so I suppose its OK, figured I'd point that out.
MK can/will take the machine for diagnosis and repair. I just wanted to have a bit of a go myself because I'm curious. And cheap. But mostly curious. I have a little bit of DIY EE and tools and am tempted to poke around.
Manual for my machine (has a high-level schematic): link
I dug into it and I ended up also finding two speed-control issues (#1 and #2 below) which occur as-is (just the machine itself, w/o any welding). My questions:
- Could the 2 speed control issues be the same root cause as the HF problem?
- If not: then regarding HF only - how are these devices generally isolated from HF? And are there things I can do to further isolate the issue or diagnose? e.g. change where the positioner is plugged in, inspect in the positioner's guts (possible an internal electrical ground lead fell off?), or do anything else?
1. The documented speed range does not match the RPM readout
Per Manual | Per Machine Readout Display | |
Low Range RPM | 0.5 - 3 | 0.3 - 2.3 |
High Range RPM | 0.5 - 10* | 1 - 7.4 |
2. The machine's readout does not match reality when in High range only
Low Range
Readout RPM | Actual (Measured) RPM |
0.3 | 0.225 |
1.0 | 1.0 |
2.0 | 2.0 |
High Range (deviates more as the RPM setting increases)
Readout RPM | Actual (Measured) RPM |
1.0 | 1.5 |
3.0 | 2.875 |
5.0 | 4.6 |
7.0 | 6.25 |
Notes
The positioner is directly connected to the + lug on the welder (as it normally should be for TIG; DCEN) with a high-quality cable. The positioner is plugged into its own 120v circuit.
DC welding doesn't change RPM. My welder doesn't have selectable HF so I cannot rule out A/C vs. HF. Positioner can handle up to 300a weld current; I'm welding at far less than that.
My positioner's chuck has blackened jaws. Seems to conduct the weld current fine, but will be testing with a jumper to the turntable. I also want to try at different RPMs and both speed ranges.
The jog button spins the table at 9.8 RPM (indicated, I have not measured). Its not documented what it should jog at, but assuming that ~10RPM is the jog speed, then I suppose the speed control issue may just be the pot...though I'm not sure why only High would be affected?
The potentiometer's scale is 0-10. It doesn't do anything until position 2 in either range setting. At the #2 position is when you hear the transformer hum and get movement. Position 0 does show a readout of 0 RPM, so I suppose its OK, figured I'd point that out.
MK can/will take the machine for diagnosis and repair. I just wanted to have a bit of a go myself because I'm curious. And cheap. But mostly curious. I have a little bit of DIY EE and tools and am tempted to poke around.
Manual for my machine (has a high-level schematic): link
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