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Cincinnati No. 6 Vertical Mill - lube oil help

Mark Kramer

May 24, 2023
Hello Everyone,
We are resurrecting a Cincinnati No. 6 vertical mill. We believe it was built late 1960's.

We are having an issue shifting gears and we are actively looking for the correct oil to replace the CMMCo. No. P-38 oil.
According to the tech manual - the P-38 will be used for Column gears, bearings, hydraulic pump, etc. (See section 17 in the attachment).

We rebuilt the oil pump so we are getting flow to all areas of the machine.
When we start the end mill - our oil pressure is ~200 as it warms up = we drop to around ~150.
To shift gears the tech manual states we need to be around ~200.

The prior oil was contaminated and removed. The current oil is Mobil DTE 24. We believe the oil is not correct.
Possible Mobile Oil is Mobile DTE light if we want to stay in the 15 - 20W class or Mobile DTE Medium Heavy if we want to stay in the 75W class.
We also have Lubriplate HO-1 which is 20W.

Required viscosity 145-160 @ 100F or 40C per the P-38 spec and is ISO 32.
To convert Mobile Kinematic cSt to SUS - formula cSt XXX x 4.63 = SUS XXX
Mobile DTE Light = Kinematic (cSt) 31 x 4.63 = SUS 143.53
Mobile DTE Medium Heavy = (cSt) 65.1 x 4.63 = SUS 301.43
Lubriplate = 196.2 @ 100F

Attached are all the supporting documents.
With the age of the machine - we are attempting to make a best replacement.
Mobile DTE Light viscosity 143.53 ISO 32 or Lubriplate viscosity 196.2 at SAE-20 (due to the age of the end mill).

Any help will be appreciated!
Mark K


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Mark Kramer

May 24, 2023
Hello Everyone,
Attached is the Cincinnati Machine Lubrication Manual which gives cross-references!
Happy Hunting!
Mark K


  • Cincinnati Machine Lubrication Cross Reference.jpg
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Sep 4, 2016
Hello Everyone,
Attached is the Cincinnati Machine Lubrication Manual which gives cross-references!
Happy Hunting!
Mark K
Welcome to the forum.
This is a deep subject.
You have done your homework and have plenty of information to call an oil supplier and ask for modern crossreferences for what you need.
There are members here that have are knowledgable on what modern oils are needed for certain older machines. Yours is not common. Thanks for the lubrication manual. Ill post that on Vintage Machinery.org.

You may find other useful manuals for your mill on this website. Just about any machine you might have should be listed in the Manufacture's Index.

Long list

Thats a monster mill.
Your 50psi loss in pressure is the oil heating up. Wrong oil
Someone may have an answer for you but I would talk to a distributer.
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Feb 23, 2016
Houston, TX
Hi Mark. I edited the title and the first sentence. Just an FYI, the machine is a vertical mill. An end mill is a tool this machine can use.

A No. 6 would be a true monster. I'd be curious to see some pics of the data plate of serial number. Also curious what hp the motor is to power it.

From the pub reprints that M-Lud linked, I randomly picked a 1955 brochure. Page 6 has a pic of something like yours:

The pdf, again page 6:

With serial number we can sort out what year, and maybe more specific pubs.


Apr 30, 2010
Redmond, WA
We have a Cincinnatti HD vertical #5, 20hp and are using any brand hydraulic oils in AW32, 46, and 68 depending on which sump the viscosity is spec'd. I have a decent #4-5-6 vertical manual from ebay which we used to translate the specs. RPM and feeds shift ok, but the spindle creeps but does not stop when disengaged. I reset main sump pressure to the high end of spec but that didn't help as well as no joy from two changes of spindle oil and one of main sump. My guess from the machine wear is slop in worn clutches, and fixing them is off scale relative to worth of the machine. One reason we didn't go OCD for the spec oils. Might consider a new X leadscrew since there is 0.125" of backlash :( . Any thoughts about where to get one?

btw if you want to see what this machine can do, check out Fireball tool on youtube. His ?? maroon painted 50hp HD #5 in mild steel. That machine looks pristine.
face mill video
giant insert mill
(7" LOC x 1.5" DOC)

our #5 max so far is drilling 2.25" unpilotted holes in 4140 with an AMEC Co insert drill.


Mark Kramer

May 24, 2023
Hello Grant,
Best wishes on taming the beast! Leadscrews and nuts - you might look into Apex. If you need a leadscrew due to wear, you might check the 1/2 nut for just as much or worse wear. Apex may not have your machine information so you may have to provide with you specs.
Apex: https://apexleadscrew.com/
Mark K


Jan 25, 2005
Victoria, Texas, USA
Best bet is buying leadscrew material and making a new nut. I doubt anyone is going to have a nut long enough and or massive as the one's used on these old mills. They may be a split nut type, too. Let us know how it comes out.