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PM 45/932, CNC and Similar Mill Oil Change

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Ray C

H-M Supporter - Sustaining Member
Staff member
H-M Supporter - Sustaining Member
Nov 16, 2012

It was time to change the oil on the PM45 CNC machine. The 932 and 45 are the same machine and that pattern of mill is very popular so, the instructions here on changing oil should be fairly universal. Generally speaking, a brand new machine should get an oil change after (roughly) the first 20-40 hours of operation.

Worth mentioning again, the oil I use is ISO 32 or 68 hydraulic fluid. ISO 68 is best for really warm climates and 32 otherwise. Also, if you have a machine with the 3000 RPM variable speed option, just use the ISO 32. All these machines require approximately 3.5 quarts of oil.

First, behind the spindle, there should be a metal plate held on with 4 allen screws. Depending on how old your machine is, it may not have this plate. Remove it if it exists.


Underneath that plate, you'll find a drain plug. Usually, it's a 6mm allen hex but, it could be a different size on the older machines. You'll need a drain pan that holds at least 1 gallon of fluid. Before draining the oil, run the machine at top speed for a few minutes to get any/all grit and particles suspended. Stop the machine and remove the plug and drain the fluid.

I like to put a little Teflon sealing tape on the threads before reinstalling the drain plug. Be careful not to cross thread it on the way in. You don't need excessive torque when tightening.


Up at the top, remove the metal plate thats held with 4 screws. Again, older machines will not have the metal plate. In the photo, I'm pointing to the fill plug. You can also see the plastic vent tube which equalizes air pressure when the oil warms up. Without it, it will blow oil past the seals.
...Remove the oil fill plug, use a funnel and fill with oil. When you get to about 3 quarts, start watching the sight glass on the side and fill to the mid-way level on the glass. Naturally, reinstall the drain plug and the metal lid.


One little tip here... I prefer to tack the nut on the drawbar with a spot of weld. The nut is pinned with a roll pin and if you ever get a stuck tool in the spindle, that roll pin can snap -and if it does, you will have no way to loosen the drawbar. Tacking the nut to the drawbar will prevent you from getting into this situation (ask me how I know).


And finally, write the date of your oil change where you can see it. On my manual machines, I change oil every 2 years. The CNC will be changed more frequently...


And that's that...




Registered Member
Mar 10, 2014
Thanks Ray, appreciate the photos and the info. I know it will help me when my machine is do for its first oil change.



Active Member
Active Member
Dec 25, 2015
Good tip on the tack weld, Ray. Any reason to just do a tack and not a more continuous weld? Would there ever be a need to remove the nut for some reason and hence the tack? Sorry for the newbie question!
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