Thread: Plain versus roller bearing headstocks

You would in my opinion generally say yes to both questions.

Most definately higher speeds.

The axial loading probably yes,but then you would be limited to the amount of load depending on Hp of the motor,Belt condition/Adjustment.

The Geared head models would take a heavier axial load.

If you were trying to workout whether it would be beneficial to change a plain bearing machine to a Roller bearing machine it would depend on what you wanted to do with it.

If you were making a lot of Small parts under 1"/25mm most of the time the Roller would probably be better,especially if you were using Carbide.

If you were working with material mostly larger than 1"/25 mm probably not much difference between the 2.

If the Headstock bearing surfaces and bearing journals of a plain head were good you can get a better finish than the roller.

Sometimes the roller will have wear in the bearings and this can cause vibration which can leave its mark in the surface finish.

Generally if there is clearance on the spindle with the plain bearing it can be adjusted quickly and easily by the shims.

The roller needs the preload or possably the bearings replaced if there is a problem not a hard job but can be expensive depending on the class of bearing.

Plain bearings are better from a finish point of view.... Roller bearings are better from a speed point of view...

At least in the 260's Hercus only used non precision bearings (as opposed to cl3 or better) in the spindle

Thanks for the informative replies . I was under the impression that plain bearings are a more tricky job to replace - they are high precision things that need to be reamed or bored to a good finish . Are replacement plain bearings available? I would like to pull down the Sheraton headstock and check the roller bearings out . It does have some vibration evident at the higher speeds , this may be down to the base being on a uneven floor . I have rubber strips under the feet, but that doesn't seem to help . Any suggestions welcome . Mike

Is it a plain bearing machine,or is it a rollerbearing machine wwith just standard tapered roller bearings.

Originally Posted by pipeclay

Is it a plain bearing machine,or is it a rollerbearing machine wwith just standard tapered roller bearings.

It's a roller bearing headstock with tapered rollers I presume . Don't know what grade bearings Sheraton used , but I'd suggest high grade ones.

Have you checked to see if theres any axial or latteral play,check to see if you can get any lift out of the spindle.
Have you placed a screw driver or similar against the bearing housing and checked for excessive noise.

Your lathe must NOT stand on uneven ground! It must be levelled (with leveling screws or double wedges. If it has any warp in it, over time it WILL settle to a warped shape and never be accurate again. Cast iron is a weird material - the molecules can and will move significantly in relation to each other. Typically - even on very large machines, a bent table can be straightened by supporting it for a few weeks under the low spott (off the machine) and it will straighten.... hard to imagine but true.
Joe

Originally Posted by jhovel

Your lathe must NOT stand on uneven ground! It must be levelled (with leveling screws or double wedges. If it has any warp in it, over time it WILL settle to a warped shape and never be accurate again. Cast iron is a weird material - the molecules can and will move significantly in relation to each other. Typically - even on very large machines, a bent table can be straightened by supporting it for a few weeks under the low spott (off the machine) and it will straighten.... hard to imagine but true.
Joe

I believe what you say joe.

I read about grey cast iron, and it's got graphite in it which makes it self lubricating ( which is why its used for engine blocks ) . The graphite is a by product of the manufacturing process . It's also porous to some degree and oil will make its way through the cast iron , amazing but true.

My lathe sits on concrete , but has a slight wobble in the base . I can see or feel the base oscillate slightly at a certain frequency when its operating . It's only very slight, but it is there.

thanks for the advice

Mike

Originally Posted by .RC.

Plain bearings are better from a finish point of view.... Roller bearings are better from a speed point of view...

At least in the 260's Hercus only used non precision bearings (as opposed to cl3 or better) in the spindle

On the 260, higher precision taper roller bearings were an option that was offered along with lathe alignment to one half of the standard error. Cost for this option back in 1988 was only $350. If one was to buy today a set of taper roller bearings in abec7 precision (same as P3 precision on metric bearings) it would cost almost $1000 . Just for the two bare bearings that is. They are not-so-common imperial sizes.

I do not know if this option had a code stamped in the serial number, probably not. So the only way to tell if fitted, is to take the spindle out: abec7 (or P3) bearings have a serial number stamped onto the face of inner and outer race (this is so because inner and outer race are matched and must not be mixed). Standard automotive grade bearings do not have any serial numbers stamped at all, but just the bearing size code is stamped to one race only.

High precision bearings run quiter. In bearing language, the words "noise" and "runout" and "precision" are interchangeable, as they all describe the very same feature.

Chris