Lathe Spindle Questions

[Doug W]

I have some general questions about lathe spindle bearing design and lubrication. First let me state that I have little experience in machine tool repair. However, I have extensive experience with automotive transmissions and axles etc.

In the near future I will be replacing the spindle bearings in my Logan 14”. The spindle design I guess is somewhat typical for a lathe of the 1950s. The spindle bearings at the chuck end are two opposing angular contact bearings with a spacer separating the outside races. A nut on the spindle adjusts bearing preload by forcing the inner races together. The bearings are of the factory greased sealed type with a labyrinth type seal mounted at the chuck end of the spindle. At the other end of the spindle is supported by 2 smaller sealed angular contact bearings. The lathe has a single gear keyed to the spindle, which is engaged only when the lathe is in back gear. This gear’s teeth are always in contact with a shallow oil bath in the headstock. The oil is not used to lubricate the spindle bearings only the gears. Max rpm of the spindle is 2000 rpms.

From my automotive experience I find this design very unusual. I am considering replacing the bearings with open cage (easier and much cheaper to find in precision classes) and mounting a trough to divert oil from the gear that slings oil to the spindle bearings. Since I don’t have much knowledge of other lathes headstock/spindle designs I have several questions.

1. I have read that oil at relatively low rpms is superior to grease for lubrication and cooling. What lathes use oil in a similar design?
2. Is there any reason for a Labyrinth seal in this application? A typical rubber garter spring seal would retain the oil and keep out the crud better. I know eventually the spindle (or wear sleeve) would get grooved.
3. Is there any concern for metal from gear wear being pumped through the spindle bearings? As mentioned the gears are only engaged in back gear.
4. Any other potential problems I am overlooking?

Doug W

 

[JRIowa]

Doug,

1. Most of the "modern" engine lathes run some sort of oil bath/splash system for bearing lubrication. Many of the cheaper engine lathes only run a 3 bearing spindle! A 14" lathe in most makes would probably run ISO 32 hydraulic oil for spindle lube at that RPM (that's what my Clausing takes).

2. Labyrinth seals are used 'cause chips are a nasty thing and tend to get everywhere you don't want them. On our newer CNC lathes, the labyrinth design is pretty exotic and have drain holes for the liquid to escape. There is always a neoprene seal on the front and rear bearing to hold the oil in.

3. Only when you chew up the gears! Like I mentioned earlier, most of the newer lathes do it already.

4. How are you going to meter the oil flow to the bearings? 2000 rpm is not to bad, but you can't "flood" an angular contact bearing at high speeds because it cannot displace the oil fast enough and will run hot. Is the headstock equipped with a sight glass and a way to drain the oil?

JR

 

[Doug W]

JR thanks for the quick response.

"4. How are you going to meter the oil flow to the bearings?"

The Logan has a flat removable top cover so it makes it easy to see what is going on. Up to 200 or so rpm the oil doesn't even fling off the gear and out of the case. I am thinking of placing a temporary clear plastic cover on to observe the process.

About 1.5 inches below the cover is the part of the headstock casting that houses the two large bearings (chuck end). The casting in this area is horizontally cylindrical. One idea is to drill an oil passage through the casting and the bearing spacer at the righthand side. This would be slightly left of the righthand bearing. Oil would flow down to the spinning spindle and lube the bearings. Excess oil would exit out the left bearing and drain back to the sump. The left bearing's cage is completely open and visable. The oil level currently is about 1 inch below the bottom of bearings. If the oil passage is drilled at the top of the cylindrical area I think excess oil would simply drain off the high point of the casting and flow back to the sump rather than flood a 1/8" or so hole. I could thread the the entrance of the oil passage to insert orifaces of diameters or place a small cup or reservoir. A flip cap oiler could be placed directly over the reservoir in the cover to provide manual oiling if it was needed.

What do you think? Is this similar to other lathes?

Doug W

 

[Forrest Addy]

I'd retrain the original design but I'd replace the bearings only if they can be shown to be duds. It's amazing how a thorough cleaning can quiet bearings that have been used around people who abuse airhoses.

If it was me, I'd lubricate the spindle bearings with short fiber bearing grease. In this application grease lubrication is suitable for 3000 - 5000 RPM depending on preload.

One of the functions of an angine lathe is to turn ROUND diameters. That's why they put expensive bearings on cheap lathes - so a diameter machined on it comes out round.

Generally speaking the spindle bearings have to generate an axis of revolution about 4 times as precisely as that expected of the finest work you'd perfomr. If you ever wish to machine fits for ball bearing races the work size tolerence is 0.0005" total size, cylindricity, and concentricity error.

Substituting ABEC Grade 1 general purpose bearings for precision bearing will render your lathe useless for any precision class more refined than the roughest sort of mechanical work. You won't even be able to turn starter motor commutators or brake drums to commercial standards.

Do it right. The future will reward you with accuratly machines diameters and fits.

[This message has been edited by Forrest Addy (edited 10-28-2003).]

 

[AlfaGTA]

Doug: Forrest is correct! There is nothing wrong with the original design. After all it was built in the 50's and it is still around. I will bet it will still turn a part round! I would stay with the original grease packed bearings. I have a modern engine lathe (less than 10 years old that swings 21". It is a Mori Seki (very high Quality Import) It has grease packed spindle bearings, and pressure lubed gears in the headstock (gear head). Works fine and i wouldn't change their design. ps. i also have 2 15" Colchesters that have pressure oil to the spindle bearings...They work fine as well. The point is that your lathe was engineered as a complete package, and there seems no reason to change it. Replace the bearings with the same precision as original if there is a problem with the spindle, but i would keep the grease and spend my time making parts. Cheers Ross

 

[J Tiers]

I suppose you have considered talking to Logan about it?

They had bearings for my 10".

No need to go to the bearing shop and/or redesign the system if you can get the right ones from Logan...if you actually need them.

 

[Doug W]

A few answers and a few questions.

Unfortunatley the existing bearings are pitted/stained from I assume coolant getting past the Labyrinth seal.
I also believe a previous owner replaced the sealed bearings with incorrect open bearings.
One of the main reasons for considering and oil lubed design is the availability of high quality Abec 5 and 7 open cage bearings in matched sets on Ebay. I rarely see sealed types, in the size I need anyway.
I could also use grease in a open bearing. I would just have to ensure that the oil in the headstock would not wash it out.

The questions. How do you clean and repack sealed bearings? My experince is that seal is pretty fragile.
Forrest could you please specify a brand and grade of the grease you recommend.
Doug W

 

[J Tiers]

Logan page of available bearings. The 14" are listed at bottom right of the page.

http://lathe.safeshopper.com/31/cat31.htm?296

If it won't go directly there for some reason, www.loganact.com go to "lathe dept" and select their secure ordering website.

If the bearings were replaced, it is possible the P.O. "butchered" (modified) the headstock to fit new ones of a different size. In that case you might have to get something different.

But, appropriate bearings are probably right there at Logan waiting for you............

A call to Logan (talk to Scott Logan) would no doubt determine if the Logan bearings can still be installed in your machine.

 

[Doug W]

J Tiers
The lathe is unaltered with the exception of the replacement of sealed bearings with open type.
The significant reason for looking at open cage bearings is the cost.
The standard bearings Logan sells are ABEC 3. I believe the total for the 4 required bearings is about $500.
I recently won a matched pair of SNR ABEC 7 bearings from Ebay for $57. I still need the 2 smaller bearings. It is debateable if the spindle and housing are machined to be able to fully utilize the tolerances of a ABEC 7 bearing but at 1/6 the cost of ABEC 3 I would like to try.