Thread: Adjusting or replacing babbit bearings in a Mars Great Scot lathe (brisbane)

Do you have much clearance in the Bearings ( Not longitudinally but Vertically).

If you have more than about .002" clearance you may want to try a 68 grade oil.

If your clearance is less you may want to try a 46 grade oil,both of these oils would be hydraulic.

Others will probably advise on a more correct oil,but if cost is a factor either of the 2 listed are available in small litre sizes.

The reason for the slightly higher viscosity oil is just to try and keep a film on your bearings for a little longer than the 46.

In regards to drip rate this could also depend on bearing clearance and if whether or not there is a oil groove or small sump in the bearing houseings.

Also the drip rate could depend on how long you are planning on using the lathe for each time its used.

Generally the drip rate would be set and forget but if the clearances are excessive you may need a faster flow.

I have seen some of the Oilers from RDG they are ok but not great,but they do work.

You may find that they wont shut off properly/completely,that the metering/nedle valve can be a bit dicky.

Probably as a rough start point,you could use a measure to see the capacity of the bearing houseings,once you have worked out the capacity run the lathe,see how long it takes for the oil to dissapear from the filler or the hole on top of your houseing,(not just from the top but until you cant see any more oil in the filler hole.

After you have timed this you can adjust the drip to give 1 or 2 drips over the time it took the oil to dissapear,eg if it took 3 mins to drain from the filler then adjust so you had 1/2 drips every 3 mins,you might end up with there being a quicker flow but dont make it slower.

If possable try and remember to shut them off after use.

Evening Chris, Peter. I use Grahame Collins recommendation of the Chain-n-bar oil - comes in 1 ltr packs SAE20. Not too sure Peter what the hydraulic 46 is about - is this high/lower viscosity than SAE20? I'd be interested in your view.

Chris - my settings on the oiler are as per Peter's advice. Make sure you shut off, or have a mop-up the next day! Mark

I use the 46 hydraulic on the Hercus plain bearing spindle,gearbox,carriage.

The 68 is slightly thicker,which should in theory take up a bit of clearance on the spindle bearings if present.

The higher the number the thicker the oil.

The Chain bar oil has additives to make it sticky (thicker),as a guess I would say it has the consistency of 90 grade gearbox oil.

Many thanks for everyone's ongoing advice.

Waggling the chuck up and down (scientific waggling of course!) while watching a dial indicator, I measure .06mm vertical movement in the spindle (about .0023"), so I presume that equates to between one and two thou clearance?

Tested with compressor oil (what I had about) the RDG oilers seem to resist dripping any slower than about 4 drops/min.

I'm not sure I understand your drip rate instructions. I would count how many drips D the oilshaft above the bearing holds, then how many minutes M it takes a running spindle to drink it all. Then I'd aim for a drip rate comfortably faster than D/M drips per minute. Is that the same as what you said?

Picture of the fitted oilers added to the flickr set linked upthread.

Source: Viscosity Information

In regards to the Drip rate it seems similar to what I was saying
You wont need the oil ports full all the time,but you should aim for oil on the bearings all the time.
Cant think of the correct name for this type of lub set up,so I'll just call it flow through.
At the end of the day having to much oil is better than too little,hopefully your oilers have enough capacity to last a couple of days if not longer before refilling.

Originally Posted by pipeclay

Cant think of the correct name for this type of lub set up,so I'll just call it flow through.
.

Total Loss? lol
bollie7

Thankyou.

Thank you all. I'm at a total loss with these oilers. (pauses for groans)

One of them adjusts between steady flow and about 6 drops a minute, the other one seems to have no appreciable movement in the needle valve, and drips at about 10 drips a minute no matter what I do. They empty out in under half an hour. RDG have supplied me with two oilers having the same product code, but different boxes and slightly different shapes, for added aggravation.

(Still using compressor oil, which I suspect is too thin, and does not admit to being any recognizable grade on the bottle). BTW, thank you very much for for the viscosity chart, Bryan, very helpful when comparing ISO to SAE.

Anyway, the oil shafts hold about 30 drips, and take about ten minutes to drain with the spindle at 300rpm, so a ballpark drip rate of 3 drips per minute seems to be what I need. I'm going to have to go get some proper ISO68 hydraulic oil on the weekend, redo the consumption test, and see if the oilers behave any better.

I tracked down some Castrol Hyspin 68 spindle oil.

Still no control over oiler drip rate, so I stripped down the oilers and worked out the problem.

The needle valve barrel hadn't been deburred at the bottom end, and wasnt screwed fully into the valve seat. This meant the body of the oiler was too long, and the needle would not fully enter the seat even with the adjustment screwed all the way down. I filed about 1mm off the barrel length, and cleaned up the rough ends, allowing the needle to seat fully.

I get controllable drip rate now, though adjustment is still very hair trigger. The finish on the needle and seat was rather rough, I suspect I should strip them down again and clean that up.

The next problem is drip formation---when reassembled I got a good view of drip formation through the sight glass, then after a few minutes dripping stopped and oil wicked down the inside of the glass instead. The oilers are still delivering oil, but its impossible to tell how much without removing them from the headstock entirely. I had the same problem originally with one of them, before I dissassembled them. I suspect this is a finish problem on the bottom of the needle seat, where it forms the top of the sight chamber.

I wonder what shape it /should/ be for good drip formation.

Here's a picture of the disassembled oiler, although it doesnt show the bottom of the seat/top of sight chamber.

I would think you need to provide a lip for the drop to form on. Can you turn a groove to relieve the outlet a bit, except for right around the hole?

Originally Posted by Bryan

I would think you need to provide a lip for the drop to form on. Can you turn a groove to relieve the outlet a bit, except for right around the hole?

Hmmn, I will have to strip one down and take some more pics of the bottom of the valve seat, but I think that would work. Holding the sucker while turning it shouldn't be too hard--can use the barrel of the needle valve as a mandrel, gripping it at the unthreaded part.

Hi guys,
Which part are you guys talking about?
Wouldnt a short taper on this part make the dip form there?

Stuart

The part pointed to by the arrow (which I have been calling the barrel) screws into the large part above and to the right, which contains the conical needle seat. The glass windows in that part are the area for sighting drips, as they form on the underside of the seat.

The needle with it's conical tip engages with the needle seat, and the closeness of engagement (via spring and top screw collar) controls speed of drip.

I will post a disassembled picture of the seat-and-sight-glass part tomorrow.