Member postings for Les Jones 1

45 m/ sec is 45 x 60 metres per minute = 2700 m/min. One revolution of you grinding wheel is the diameter (D) In metres times π. (π is about 3.142 in case you have forgotten it from when you were at school.)

So the surface speed will π x D x RPM (In metres/min)
So rearranging this RPM = surface speed./(π x D)
So RPM =2700/(π x D)

Les.

I would NOT advise adjusting any of the potentiometers. Have you got the correct horsepower resistor to match the power rating of the motor on your lathe ? If the value of this resistor is too high it will limit the current (And hence the torque.) to too low a value. I am surprised the board works as well as it does after such a fault.

Les.

I don't think just replacing the resistor is a good idea. From the way it has been destroyed I think the fault current was much more than a stalled motor would cause. I also think it is VERY likely that the diodes and SCRs that form the controlled bridge rectifier will have been damaged. It is also likely that the LM324 IC has been damaged. I suggest that you first test the diodes D13 and D14 and the SCRs. When first testing it with power applied I suggest connecting a 100 watt incandescent lamp in series with the mains input to limit the current. Also disconnect the motor from the control board and connect a small (Say 15 watt.) mains voltage bulb in it's place. Don't be tempted to fault find using an oscilloscope UNLESS YOU USE AN ISOLATING TRANSFORMER TO SUPPLY THE BOARD. This is because the common negative line will NOT BE AT GROUND POTENTIAL.

Les.

I think the component WAS a ceramic resistor that is used to sense the motor current. I think the output connections to the motor must have been shorted out putting the full rectified mains voltage across it to cause it to fail in the way it has.

I think the board is a KBLC speed controller board and the resistor that has failed is R21.

This is a link to information on the board.
http://andysmachines.weebly.com/variable-speed-controls.html

Les.

Edited By Les Jones 1 on 14/02/2022 22:50:45

As the SCRs and diodes have the L suffix they do not need to be insulated from the heatsink.. So that is one of the possible problems eliminated.

Don't worry about P1 and P3 being reversed. That would just swap over the low and high speed ends of the potentiometer. I would expect a reading of about 10 volts between these two points. The voltage on P2 With respect to P1 or P3 should change as the potentiometer is rotated,

Les.

Remove the two metal links on the motor. (leave the wires from inside the motor on the original terminals.)

This should do what you want,

If forward and reverse are the wrong way round swap over the wires to terminals U2 and W2

Les.

Although your switch looks similar to the one in the video the connections may not be the same. The first step will be to test the way the switch behaves. If there are no markings on the connections mark them with numbers or letters to identify them. Then create a table showing connectivity between the connections in all three positions. (Off, forward, reverse.). When you have done this post the results so can give you a digram of how to connect it,

Les.

I realised after re reading you first post that I assumed it was a shunt wound motor with you mentioning field connections. It is useful to know it is definitely a permanent magnet motor. What is the information on the plate on the motor. (Voltage, current wattage , horsepower.)
I had assumed that the motor did not run at all when connected to the controller. Is this assumption correct ?
Can you post the circuit of exactly you have wired it up. (This is with it wired outside the machine to simplify things.
You are correct in connecting a permanent magnet motor to the A+ and A- terminals.
What is the part numbers of the original diodes and thyristors and the one you fitted as a replacement ? I ask this as some devices have insulated tabs and some have the tab connected to one of the terminals. Depending on the type just an insulating pad between the device and the heatsink may not be enough to insulate it from the heatsink. The fixing screw could connect the tab on the device to the heatsink. A photograph showing the diodes and thyristors in YOUR unit would help to clarify this potential problem.
Can you measure the voltage between the potentiometer connections P1 and P3. Then measure the voltage between P1 and P2, first with the potentiometer fully anticlockwise then about half way and then fully clockwise.

Les.

You have not answered the question of which connections measured 110 volts (Field connections or armature connections.)
You start by saying "This link" but you do not give any details for the link.
Two of the diodes and the two SCRs form a phase controlled bridge rectifier. This output will be to the armature and the average voltage output is controlled by how much delay there is between the zero crossing point of the AC waveform ant the point at which the SCRs are triggered.
The 3rd diode provides a half wave rectified of a constant voltage for the motor field winding.
As the motor only has two wires coming out of it you will need to dismantle it to bring out the field and armature connections separately.

Les.

Hi John,
I asked for information on the motor in case it is not a shunt wound motor. It is possible that it is a series wound motor that someone has attempted to use as a shunt connected motor.

Les.

The controller should have two outputs to the motor. The one that goes to the field winding will be a fixed voltage. The one that connects to the brushes will be controlled by the speed potentiometer. Which connection did you get a constant reading of 110 volts ? I have not been able to find the schematic online for your speed controller But I do have a schematic of the KBIC 240D controller. If yours is a similar design it would explain why you get a reading of 110 volts rather than about 240. The 240D uses half wave rectification for the field supply so you will be reading the average voltage of half wave rectified 240 volts. I suggest that you measure the voltage to the armature and see if that is present and varies with the speed potentiometer setting. It would be helpful if you could provide a link to the information on your controller and any information on the motor.

Les.

Most motors have a diagram stuck to the cover plate on the terminal box showing how to reverse it.

My guess would be that the red and black wires connected to terminals A and Z are the main winding. If I am right then swapping them over so that the black wire goes to Z and the red wire to A should work. To find out properly you would have to partly disassemble the motor to trace the wires and do some resistance tests.

Les.

Hi Chris,
Here is a link to a program that will do the calculation for you. You give it a list of the change wheels you have, the leadscrew pitch and the pitch you want to cut. It tries all combinations and tells you the percentage error for each suggested combination.

Edit. I've just tried the link on that page to "Nthreadp.exe" but it does not seem to work. I have a copy of the program which I could email to you or if you post a list of the change wheels that you have I will run it and give you the results.

Les.

Edited By Les Jones 1 on 23/12/2021 16:18:11

I order my prescription online. I then log in after a day or 2 and check that it has been approved. (I assume this is approval by the doctor.) This seems to work very well.

Les.

You also get people posting a question and they get a number of helpful replies. They do not post again to say that their problem was solved. (Or even to say that none of the replies helped with their problem.)

Les.

This is one source from ebay. (But you will probably find more as I only spent a few minutes searching.)

**LINK**

Nitrile seems to be a good choice for propane or butane.

Les

As you have not given any dimensions of your O ring I estimate from your picture that it is about 6mm ID and about 2mm cross section.
If this is a correct estimate then this is one possible source.

**LINK**

Les.

After looking at the pictures in your album I am not convinced that it is an NVR switch. Start the lathe in the forward direction. Switch the power supply off to the lathe. Did the switch return to the centre off position ? Restore the power to the lathe. Does the motor start as soon as the power was restored ? These tests will show if it is an NVR switch.

Les.

It is not recommended to do any switching on the output of most VFDs. I suggest that you check with the manual for the VFD that you have. You normally have the forward ,reverse and stop controls together with the speed control potentiometer mounted in a convenient position away from the VFD. The wiring between the controls and the VFD is only low voltage and current so thin multicore wire is used. It is probably possible use the old forward/reverse/stop controls connected to the control inputs of the VFD. using the old controls in this way may give problems as sometimes the contacts oxidise when there is no cleaning action that occurs when switching high voltages.

Les.

There should be nothing other than a length of 4 core (3 phases + earth.) screened cable between the VFD and motor. There should be no contactors or switches between them.

Les.