G0752z Potentiometer-Garbage

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WilsonFlyer

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If you have a 'z' model lathe from Grizzly, you are probably acutely aware of the ridiculous and unpredictable behavior of the potentiometer Grizzly decided to source with these models. It is maddening to say the least. Ten complete revolutions with absolutely no predictability of where you are along the way at all when changing speeds. :mad:

Contrarily, my LMS mill is as predictable as the hands on a clock (relatively speaking, of course). I can reach up and turn it without even looking and be predictably within 25-50 RPM every single time. It doesn't even go one complete revolution, yet it works amazingly well. I want this on my lathe. The question is, "Is that too much to ask?"

I have searched relentlessly for a suitable replacement mostly to no avail. I did finally run across a gentleman on YT who had basically taken control of the programming of the phase converter and installed a keypad to the front with a built-in potentiometer. Apparently, he could then disable the off-board potentiometer (by one very simple program element of the phase converter) in lieu of making the one on the control board the functioning one and disabling the outboard one. The one on the control panel functions almost identically to the one on my mill, which is exactly what I want.

Evidently, when a heavy chuck installed and the lathe is spun down too quickly, it acts like a generator throwing current back at the system which generates an immediate shutdown condition in the phase converter and shuts down the lathe. This is apparently why Grizzly chose the 10 revolution potentiometer. To slow us down. LOL The REAL fix was to add an electronic brake resistor (necessary to use his solution) which would have increased the production cost by about $40US. Sigh. And here we are. The brake is easily sourced as in the control panel and the connecting cable

This guy's solution was really elegant. I don't think I can post links because I haven't posted enough here yet probably, but if you search YT for "Grizzly G0752 Lathe: Install digital keypad and brake resistor - Part 1," you will quickly find it. There are 2 parts to the video series and they are fairly short and straight forward.

I would settle for his solution, but I'm imagining an even more elegant solution, though it may not be possible. I'm good for installing the brake, but is it possible to then just replace the existing potentiometer with one now more appropriate since the brake is installed? Seems simple and easily done to me, though I'm no electronics engineer by any stretch. The question is, how do I source such a replacement and how would I know how to wire it in once I had one in my hands? I bet one is available that has exactly the same wiring as the one that's in there now, save only being a one revolution potentiometer.

Does my question make any sense? Surely, I'm not the only one that's been down this rabbit hole. Well, me and that one guy on YT. LOL

I bet someone here has already done this. Can anybody help a brother out or am I just mad? LOL
 
I have the 752Z. The pot is annoying, but there's a speed readout and it works, so I'm not sure what your issue is besides convenience. If you don't turn the pot and turn off the lathe and turn it on again it runs at the same speed. I'm usually fiddling with speed due to different operations, so it doesn't seem to bother me, at least not to the point of springing into action.

The speed readout is actually pretty good. My ELS measures the speed independently using a rotary encoder and it matches the native readout rather closely.

Are you just wanting a 1 turn pot vs a multi turn? Or something else?
 
The G0752 pot is a 4.7K 2W. Any potentiometer that is close to that value will work and any elect5ronic supply house like DigiKey or Mouser will have a single turn replacement. I would expect that the 2W rating is vast overkill as the usual function is as a simple voltage divider. For durability, I would suggest a wirewound pot as opposed to a carbon film or ceramic resistance element.

Wiring is simple. The pot has three terminals as does the OEM. Wire the new pot in the same configuration.

I have a G0602 and have converted to a brushed DC motor with speed control through a single turn pot. That has more than enough resolution for my purposes.
 
First off it is very common for manufactures to use 10 turn speed pots, even in my knee mill the factory digital head has a 10 turn pot. If you change the speed to quickly then it will cause a fault, typically on deceleration it is a buss over voltage error. Dangerous on a lathe if one needs to stop quickly. Most of the stock potentiometers on these cheap lathes are crap anyway. No real reason to have a remote display, but some VFD's have a removable display, others you can add one. His way of pulling the wires through is quite sloppy, if one is going to do electrical do a clean installation.

If you want a 1 or 3 turn speed pot then just install one, it is a linear 5K pot. I use ETI 3 turn, but can also use a single turn. NO reason to add a keypad in the video unless you plan to do remote programming.
Clarostat Honeywell 53C35K 22mm Linear Taper Potentiometer 5K Ohm 2 Watt 10%
www.ebay.com

Clarostat Honeywell 53C35K 22mm Linear Taper Potentiometer 5K Ohm 2 Watt 10% | eBay

Honeywell 53C35K.
www.ebay.com

The VFD is a Delta MS300 which is very common, get a braking resistor for $26 with 12" leads, pull the leads out the bottom to mount it or mount it in the cabinet. Connect the wires to B1 and B2. About as simple as it gets.
JP100J220RJ
 
Thank you all SO much. That is all very helpful! Exactly what I needed to know.

WobblyHand: I guess I dislike it most because it's not what I'm accustomed to. Could I live with it? Sure I could. And do. But if a solution that satisfies an itch is as easy as mksj says it is, I'm going to do it. I intend to add James' ELS. I just have to order the components not sourced by him. It's one of the 'next things' on my list. I'm more of a tinkerer than a maker, and little projects like these make me just as happy as turning a perfect magic cylinder. ;-)

The worst thing that could happen, I suppose, is that I lose a couple of hours that I actually enjoyed modifying it and end up putting it back like it was. Won't be the first time that's ever happened. Thanks for the advice...

to all of you!
 
mksj said:
First off it is very common for manufactures to use 10 turn speed pots, even in my knee mill the factory digital head has a 10 turn pot. If you change the speed to quickly then it will cause a fault, typically on deceleration it is a buss over voltage error. Dangerous on a lathe if one needs to stop quickly. Most of the stock potentiometers on these cheap lathes are crap anyway. No real reason to have a remote display, but some VFD's have a removable display, others you can add one. His way of pulling the wires through is quite sloppy, if one is going to do electrical do a clean installation.

If you want a 1 or 3 turn speed pot then just install one, it is a linear 5K pot. I use ETI 3 turn, but can also use a single turn. NO reason to add a keypad in the video unless you plan to do remote programming.
Clarostat Honeywell 53C35K 22mm Linear Taper Potentiometer 5K Ohm 2 Watt 10%
www.ebay.com

Clarostat Honeywell 53C35K 22mm Linear Taper Potentiometer 5K Ohm 2 Watt 10% | eBay

Honeywell 53C35K.
www.ebay.com

The VFD is a Delta MS300 which is very common, get a braking resistor for $26 with 12" leads, pull the leads out the bottom to mount it or mount it in the cabinet. Connect the wires to B1 and B2. About as simple as it gets.
JP100J220RJ
Click to expand...

Stupid question, if I may. Is that a one revolution or a three revolution pot? I don't know how to look at the specs and tell. I really want a single rev one. Thanks again!
 
You need to understand the speed range and how fast you can adjust the speed. When you purchase a lathe with a VFD installed, in general it will be 2 or 3 speed and you are requiring the motor to cover a wide speed range, so maybe 20-200 Hz, if you add a VFD to a lathe with multiple mechanical speeds then the speed pot is maybe asked to cover 20-80 Hz, so that is the reason for multi-turn speed pots. It is fine if you want a single turn but when adjusting the speed while it is running just don't crank on it quickly. The two speeds pots I referenced, the first one by ETI is a 3 turn which is a nice balance, and the second one is a single turn (300 degree). These both take 3/8" hole to mount and you need to check behind the front panel to see if there are any clearance problems. If the stock one is a 10 turn then there should be sufficient room behind it. If you do not know how to wire it, there are 3 wires which are the 0V, sweep or variable, and typically the +10V. The connections should be the same on your current speed pot.

When choosing a single turn speed pot you want the resistance to be linear which is most common not log, in addition you do not want the terminals on the back (i.e. SP22G-5K) of the pot as these are typically continuous rotation 360 degrees with no stops, you want a 3200-320 degree rotation with stops. So for the ETI single turn I would use the SP22E-5K which is an excellent single turn speed pot. Terminal 1 is 0V, terminal 2 is the sweep, and terminal 3 is the +10v. The one your ordered CMU5021E will also work fine, the ETI ones will last much longer.


Potentiometer for VFD speed control.jpg
 

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