# G4003g, new motor and Machtach: Speeds?



## Splat (Mar 4, 2019)

I upgraded my g4003g motor and went with Hitachi vfd setup. Thanks Mksj for all the help!  I finally got my Machtach installed. I'm amazed how far off the speeds are compared to the gear/rpm chart sticker on my lathe. The upper speeds are really off. Anyone else seeing the same on their g4003g?


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## darkzero (Mar 4, 2019)

The listed RPMs must be in metric. 

I have a PM1236 and my speeds are off also. Same for my mill & my old mini lathe. My actual speeds are faster than listed. Measured with a Monarch Pocket-Tach 100.


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## pdentrem (Mar 4, 2019)

50 vs 60 hertz. Example per the chart - 78/65=1.2, 60 hertz/50 =1.2.



			https://www.oaktreeproducts.com/img/product/description/List%20of%20Worldwide%20AC%20Voltages.pdf


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## darkzero (Mar 4, 2019)

pdentrem said:


> 50 vs 60 hertz. Example per the chart - 78/65=1.2, 60 hertz/50 =1.2.
> 
> 
> 
> https://www.oaktreeproducts.com/img/product/description/List%20of%20Worldwide%20AC%20Voltages.pdf



Could have been an error between 50hz & 60hz. Motor on my lathe is listed as 60hz. On my mill the chart lists speeds for both 50hz & 60hz. My measured speeds are still faster than the speeds listed for 60hz. Not that I really care, just saying.


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## Splat (Mar 4, 2019)

Per Machtach I'm getting speeds slower than what the sticker shows on my lathe for the faster gearing. Interesting.


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## Splat (Mar 5, 2019)

Actually, I just found the section in the manual (pa-lease...manuals..who reads them?!   )  about adjusting/calibrating the Hall sensor via the pot on the Machtach board. I didn't do that but wonder if it'll make that much a difference. I'm more worried about the Hall sensor I got from Amazon not being fast enough for the higher speeds to read correctly. Gotta look that up later.


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## darkzero (Mar 5, 2019)

HF & Amazon sell inexpensive optical tachometers if you want to dial in your machtach. Should be good enough for that purpose.


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## Splat (Mar 5, 2019)

I have one Will but I just gotta get the time to get to it. I think I may drop from 4 magnets to 2.  I got pretty darn accurate spacing when I epoxied the magnets but one is just a hair off, maybe a 1/32", and may be causing a problem with faster speeds. Also, the mags are about 3/8" diameter so maybe a tad big for the G4003G spindle. Slowest reading would be 17rpm with 2 mags so that should be fine. Gonna see hopefully tomorrow morning.


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## Splat (Mar 6, 2019)

OK. Checked everything out and all appears correct. I used my RPM gun and confirmed the MachTach's readings. I honestly don't recall using the higher >1K speeds before but this is bugging me. In the "1400" gearing I'm only getting about 1100. The drive belt is tight. I wonder if I need to go back to two belts. I'm using a link type belt and it's definitely past its break-in period.


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## mksj (Mar 6, 2019)

My experience with the MachTach, Tachulator and most the cheaper ones on eBay is that they either work, or do not work. The Tach Hall sensors you buy on eBay are rated to something like 9999 RPM with a single magnet. If you take the barrel off you will find a small IC hall sensor at the tip, a resistor and a LED.  Spacing of magnets or on optical sensor reflective material can cause errors. The MachTach and Tachulator both can accommodate multiple marks/pulses per revolution, this only effects the lowest RPM and not the accuracy.

On the MachTach when I use shielded wire and grounded one end, it picked up all the VFD noise. I have not had this issue with the cheaper tachs. Both the MachTach and Tachulator you can set the pulse sensitivity which looks at on/off voltages, this is sometimes an issue when switching types of sensors.  In the case of noise contamination/sensor sensitivity, typically the numbers jump all over the place. I have done a few custom tach/hall sensor installs, and I do occasionally have issue with decreased RPM reading at the higher speeds (typically more erratic readings). I find that the sensor sensitivity  goes down when the sensor is embedded in metal and some hall sensors are more axis directional.

Unlikely to be the belt(s), you would see a drop in RPM when turning if they were slipping. If you are not the original machine owner it is possible that the motor pulley was changed. Many people have used the linked belts on the G4003 series to diminished  the vibration issues with the surface finish, I have mixed feelings on them vs. getting a better belts. Single or double belt should make no difference if not loaded.


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## Splat (Mar 6, 2019)

Hey Mark. I did check the voltage on the MT board and was getting very good low/on and high/off. The speed reading is pretty solid and does match my RPM gun when I tried this morning. I used clear epoxy to mount the magnets on the spindle. One thing I noticed this morning is the motor pulley gets hot after running at the higher speeds for only a minute or two. Link belt tension was about 3/8"-7/16" deflection. I've read a lot, if not most, of those posts about surface finishes and IIRC most were related to the crap single phase motors this lathe came with. Adding the rubber isolators helped. Yes, the motor pulley is original. The original owner bought this new from Grizzly and put very few hours on it.  Idk...maybe I will try a V belt.


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