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View Full Version : Crazy Idea! (oh well what else is new)



wierdscience
02-10-2004, 10:34 PM
Okay,I have this old Seneca falls lathe that I have been debating on how to fix the old spindle bearings on.There never were any,just plain cast iron bores(stupid way to build a lathe)I though about bronze sleeves,timken bearings,and needle rollers,but no satifaction,finally it hit me,what if I took and line bored the head and ground the spindle,then made up a set of hard bronze sleeves and pressure lubed the bearings ala-automotive? It already has oil control return cups I could just tap the castings for copper tube fittings and install a small gear pump direct drive off the motor shaft,since It has a clutch anyway I could have oil pressure before I spin the spindle,I could even use an inline filter to clean the oil on its way to the bearings.Plus I should be able to make better speed,What do you guys think on this one?

Bruce Griffing
02-10-2004, 10:41 PM
I think it would work well - but how would you handle the thrust?

G.A. Ewen
02-10-2004, 11:07 PM
Should work, If it doesn't you can always try one of your other ideas. Once you've line bored the head your on your way. Let us know how it works out. Better still, take photos of each stage and if the lathe works to your satisfaction after the fix write it up and send it to Neil. I think that it would be of interest to many readers.

wierdscience
02-10-2004, 11:16 PM
Thrust no problem,It believe it or not has a ball thrust bearing!Nothing on the mains,but balls on the thrust,go figure http://bbs.homeshopmachinist.net//biggrin.gif

Evan
02-10-2004, 11:51 PM
Same as the South Bend lathes.

darryl
02-11-2004, 12:13 AM
Weird, I'm just a little concerned about how you would go about line boring the head. I'm trying to imagine the setup and I'm having a problem visualizing it. Could you elaborate somewhat?

Carl
02-11-2004, 12:23 AM
How about using automotive insert bearing shells with your pressure lube system?

WJHartson
02-11-2004, 12:52 AM
That should work fine. You will have to control the pressure some way so you don't push the spindel against the top of the bearing. You only need to lift the spindel. You could have an oil groove all the way around the bearing in the center to help control the oil. Temperature and oil viscosity will also play a part.

Good luck with the project. Take pictures.

Joe

Thrud
02-11-2004, 02:23 AM
Darin
The Myford Super 7+ have a tapered cone scraped bearing for the main head bearing (3000rpm max) - pretty spiffy.

spkrman15
02-11-2004, 09:38 AM
Ok, but why not use Roller bearings? I always figured Roller bearings were better then any bushing type bearing. Am i wrong? Note i am not a Jedi yet and have alot to learn

Rob http://bbs.homeshopmachinist.net//smile.gif

wierdscience
02-11-2004, 09:57 AM
Well some back ground,the front spindle bearing is long,Its only 1-9/16"od but its nearly 3" long,the back one is 1-1/2"od and about 2" long so there kinda narrow,the reason for the delema is there isn't enough room to bore it out for a roller or ball bearing.

For the oil control problem they made it easy,each bearing was supplied with dipper rings and either side there is a oilcatch cast into the headstock that returns to a oil well under the bearing,my plan is to bore just the bearing section and not the oil catch,I figure if I run about 10-20 psi on a really small gear pump I should get a full film,and not a gyser,we'll see.

Line boring I plan to do at work,I could do it on the ways by building a contraption to do it,but work is to easy,I have got one saving grace in the fact that the spindle still fits tight in the bearings,its just to scared up to run without heating badly,So I'll make a boring bar to pass through both bearings and fit sleeves the same as the bearing bores to use as an aligment tool to set the headstock up in our big horizontal mill then remove the bushings and bore both bearings in one setup.Should come out perfect,if it doesn't I can shave the tailstock to compensate.

Cass
02-11-2004, 11:58 AM
I think you should look into using the high tech plastic bearing sleeves that Igus makes. You can press those in and then oil them with a drip cup similar to SB. The bearings used in automotive applications are referred to as "hydrodynamic" meaning that the supporting oil film is established by the rotating shaft pulling oil under itself due to the rotation of the shaft in the journal. You get no lift at zero speed and therefore this condition is referred to as having no load capacity at zero rpm. Oil "hydrostatic" bearings use external pumps to generate the pressure in the film and therefore do have full load capacity at zero rpm. Hydrodynamic bearings are relatively simple and low cost compared to hydrostatic and that is understatement. Both bearings must leak to work so you have to be concerned with having seals to contain the oil and return it to some sump and reservoir with a filter. The gear pump must have a relief valve. The oil is introduced at the top of the journal and not at the bottom where the very large hydrodynamically produced pressure is. All this is messy and complicated in machine tools. I know from personal experience. The new polyamide plastic bearings are pretty fantastic and have all the performance you need on a small lathe. You get more repeatability, more reliability, lower cost, cleaner operation, faster implimentation and boring the holes out a little to give clearance for the plastic bushings should be pretty straight forward.

wierdscience
02-11-2004, 08:03 PM
Cass,AADD kicking in? http://bbs.homeshopmachinist.net//biggrin.gif yes I know about the polymide bearings,heat is the enemy there.

I also know about the need for an oil pump and relief as mentioned above.The lathe is already equiped with a means of oil control and recovery.Plus the only way to oil these bearings is through the top of the cap anyway.

Since I have to plumb the thing and mount an oil pump anyway I'm going to do that first before I bore the headstock and grind the spindle.

Cass
02-12-2004, 01:04 AM
I think you will find that the right plastic bushing will handle the heat with no problem. And especially if you oil it. Take a look into that. Of course pumping oil will keep you occupied if that is more interesting.

BillH
02-12-2004, 11:58 AM
So the lathe heats up too much in use? How bad are the bearings really? I would get any rough spots out, use proper spindle oil, adjust the shims, and try using it as is. As Evan said, its just like a South Bend, I think the simplest approach is allways the best if it works.

This type of bearing is very accurate,and lasts almost forever given that it is properly lubed. Railroads called this a friction bearing, and they got "Hot Boxes" probably due to no lubrication.

[This message has been edited by BillH (edited 02-12-2004).]

wierdscience
02-12-2004, 09:47 PM
I scrapped,fitted,adjusted lubed etc etc,the previous owner seized the bearings,lots of galling both in the bores and on the hard spindle,If I could fix it that way I would have years ago,The only reason I'm fixing it is becuase the damage was done early in is life and the ways,apron,tailstock etc are perfect.