# Grizzly G4000 Lathe RPM



## chip maker (Jan 17, 2014)

Hi All and maybe someone has an answer to this. I installed a MackTach digital tachometer on my lathe and to my surprise the rpm is not correct. I have a MackTach also on my Grizzly G8689 so I switched the units and they both read the same on the lathe. If I set the belts to 300rpm the tach reads 349 if at 600 the tach reads 650. I contacted the maker of the MachTach who to me is one hell of a nice guy and he said he has a Grizzly lathe a bit bigger than mine and he has the same issue with his as well that the lathe plate isn't true to what the rpms really are. I was just wondering if anyone has seen this with their lathes as well.


----------



## darkzero (Jan 17, 2014)

I don't think that to be abnormal. I used my Monarch tach to measure the spindle speeds on my PM lathe & mill, the RPMs aren't exact to what is on their name plates and the difference varies with each speed so it's not a percentage that is off. I did not expect them to be either. I trust my tach over what the nameplate values are. There are other factors that can affect the reading too.


----------



## coolidge (Jan 17, 2014)

darkzero said:


> I don't think that to be abnormal. I used my Monarch tach to measure the spindle speeds on my PM lathe & mill, the RPMs aren't exact to what is on their name plates and the difference varies with each speed so it's not a percentage that is off. I did not expect them to be either. I trust my tach over what the nameplate values are. There are other factors that can affect the reading too.



That's interesting, I assumed stated RPM should be just that. Also your avatar is giving me chuck envy.


----------



## mick-h (Jan 22, 2014)

I have experienced much the same thing! 
I was given a Tachometer (a Smiths Instruments Venture Hand Tachometer - ATH4) the same as this one (HERE).
I tested it on my Chester MF42B Lathe (same as the Grizzly G4015Z), the stated speeds on the lathe were ok up to around 300 - 500 rpm, but after that, the tacho was reading higher speeds than was stated on the lathe!
Until reading this thread I thought I had been given a dud tacho, but it now seems that it is probably the stated lathe speeds that are wrong and not my (free )) tacho.
ATB,
Mick


----------

