MILL gearbox oil vs grease?

[Trebleplink]

I've posed this question in the Smithy forum (Information On The Smithy 1240 CNC Bed Mill?)
without any opinions from mech engineering types. I'm an experienced electronics guy but just above novice machinist. Below are photos of the Smithy CNC ready mill. The odd thing is that other mills of this type seem to use an oil bath in the gearbox, and Smithy uses grease "applied with a putty knife". Is this a good plan? Is this adequate? I'm considering the idea of installing a zirc fitting on the gasketted cover plate and pressure filling the gearbox with grease that way, but I know very little about the finer points of lubrication for this kind of service.

Here is a link to a picture of the gearbox with gasketted coverplate open:

http://www.scott-inc.com/1240/lubeplat.jpg


Other pics:


http://www.scott-inc.com/1240/1240.jpg

Showing z linear rails with grease fittings:

http://www.scott-inc.com/1240/linear-z.jpg

Showing lube grooves in x ways

http://www.scott-inc.com/1240/oiler.jpg

Built-in motor mounts:

http://www.scott-inc.com/1240/xdrive.jpg

http://www.scott-inc.com/1240/ydrive.jpg

And limit switch bracketts on all axis:

http://www.scott-inc.com/1240/zlimit.jpg


Opinions are welcome.

[tenmetalman]

Hi,
I can't believe that the gear box you've shown in your thread is lubricated with grease. There must be some sort of error. If your sure theres no filler port. I would drill and tap the cover to a 3/4" pipe thread about 1/3 the way down from the top of the cover. Install a street elbow with a threaded plug in the elbow with it pointing up with the cover installed. I'd use 80/140 grade gear lube. I'd put a quart in the gear case loosely install the plug and turn the spindle on and look for leaks. If none are found I think I would put about a total of 3 quarts of the gear lube in the gear case and call it good. checking for leaks and fixing as required.
Paul tenmetalman

[Trebleplink]

Well, thats the problem: it doesn't hold oil at all. I initially rotated the head 90 degrees, removed the gasketted cover plate, and filled it with medium oil. It immediately started running out around the top of the spindle. I'm thinking "how can it operate with the head tilted if the top of the spindle doesn't seal?" I quickly replaced the plate and rotated it to vertical. I soon had a lot of oil on the shop floor - looking up into the bottom of the gearbox, you can clearly see the balls of the the gearshaft bearings. So, it positively WON'T hold oil.

[NC Cams]

Lubriplate made a "clinging grease" that was specifically designed for use in exposed gear trains.

Ball bearings are "lubed for life" with grease, typically 25%-30% of the exposed cavity.

Until or unless you find a way to seal up the gearbox, the factory method of "schmearing grease all over everything" will have to suffice.

Personal opinion: a rather primitive way to do it but it worked like a charm for many years in many gearboxes until spray/pressurzed/drip fed lube systems became developed.

[Adobe Machine]

Try anti-seize..This stuff will not come off anything ! Best "open Gear" lubricant I've ever used. We repaired / rebuilt large gearboxes ( mine crushers) that had up to 250 electric horse-power and open gear boxes, you can understand the large forces involved trying to rip teeth off the gears, and the wear factor. We were able to extend the live of the gears by a lot using anti-sieze..I have inspected gears we built years later, and the anti-sieze was still there, in the pressure zone. Of course getting it off your hands and clothes is fun .Had an employees lady friend threaten me with death due to her getting anti-sieze where it should not have been in/on her body..not my fault, she was just mad..

Adobe (old as dirt)

[Al_The_Man]

Many of these spindle gear boxes have gone over to using transmission fluid from 90 gear oil, My Excello's have.
Al.

[NC Cams]

I won't argue with my esteemed colleague regarding anti-sieze (essentially oil carrier with a pulverized nickel powder) on mining gears.

However, gear lubrication is dependant on force AND speed. The higher the speed (as in sliding velocity between part A and B) the more critical the shear viscosity of the lube. Moreover, the involute on the gear results in a "moon walk" effect that has to be dealt with.

This is why "clinging grease for exposed gear trains" was created. Primarily, to lubricate under the sliding/high pressure/ "moon walking" conditions endemic to gear trains.

Another issue involves centrifugal force - high speed gears want to centrifuge off the lubricant. This is where "clinging" grease is critical.

Something you have to consider about anti-sieze and or ANY metallic lubricant is its affect on OTHER parts. Rolling bearings don't always like metallic lubes - bushings, especially babbit and some bronze bearings aren't particularly fond of it either.

Be ESPECIALLY careful with MoS2 fortified lubes. Although they are dynamite for EP lubrication, they are not always well tolerated by non-hardened shafts, especially shafts used in bushed applications. Ugly lesson learned with that escapade.

For experiemntation, anti-sieze would be an interesting experiment. However, I'd still be more inclined to use a lubricant either recommended by the manufacturer or a high performance alternative that was specifically formulated for exposed gear trains.

BTW, high load/low speed gear trains see a much different NET loading condition than a high speed/moderate load gear box. Lube requirements are affected by the peak surface footage speed of the gear pitch that the smallest tooth count/highest loaded gear will encounter.

[Willbird]

I recall My dad watching with glee as some inbred circle track pilots went thru a series of transmissions because they decided STP oil additive was the miracle replacement for 90 wt. gear lube like the box was designed to use, not sure if they ever figured it out, they may have finally decided chevy was junk and switched to Fords over it :-).

Bill

[Trebleplink]

Thank guys for all of the suggestions. I've lubed it with "Red & Tacky" grease and have installed a grease fitting in the coverplate. As I earlier mentioned, there are visible balls in the shaft bearings as viewed from underneath. One poster indicated only a portion of the airspace was occupied by grease in permanently lubed bearings - I'm thinking thats to avoid constant grease displacement during operation.

I could conceivably fill the box with grease via the pressure port, to the point extra would squish out through the gaps in the bottom bearings. Then the initial turn of the gears may displace some grease, but then they would remain in very close proximity to a bunch of reserve. Otherwise, I'll have to constantly remove the plate an manually re-lube.

[Adobe Machine]

NC Cams: Your correct, and I might add that I hardley ever reccomend "off lable " use of petroleum products, as over the years I have learned to respect the petroleum engineers opinion( except some ATF's,they work real good in a lot of applications not labled for ) . The anti-sieze was suggested by a petroleum engineer, ex minning engineer that had done some wear / longivity tests and concluded open gearing might benifit. If the rpm exceeds 1500 rpm or so , then the lube Trebleplink has picked will do a good job..any lube is better than none in an emergancy situation.
O'God, STP ?

Adobe (old as dirt)