Cast iron bearings (running speeds)

[David S Newman]

I have just purchased a sensitive 0-1/4 drilling machine with no makers name, but looks to be good quality and fairly old. The spindle runs in split for adjustment cast iron bearings. The pulley arrangement, which looks original will give speeds up to 4000 rpm, would like to know if this type of bearing is ok to run at this speed ? The spindle is unhardened and appears unworn. David

[tattoomike68]

Are you sure they are cast iron and not ceramic?

[David S Newman]

Are you sure they are cast iron and not ceramic?

Definately cast iron, all part of the casting. David

[topct]

Although the rest of my 65 year old SB9 shows some wear everywhere else, the grinding marks on the spindle have only been very nicely polished. If I don't hold the mike to long I think I could measure the wear.

What is the diameter of the spindle?

Steel and cast iron make for a very sturdy bearing. The diameter and clearance will determine the max speed.

[Evan]

4000 rpm sounds rather high. What diameter is the spindle? The South Bend 9 was available in a 12 speed version with hardened spindle and had a maximum of 1200 rpm. Faster was not recommended. It will depend on the SFM of the spindle bearing surface vs the load, known as the PV Factor (Pressure-Velocity).

[garyphansen]

Evan: I believe that a drill could be safely run at higher speeds than a lathe because on a lathe the oli film is taking a load at right angles to the bearing. Gary P. Hansen

[David S Newman]

Although the rest of my 65 year old SB9 shows some wear everywhere else, the grinding marks on the spindle have only been very nicely polished. If I don't hold the mike to long I think I could measure the wear.

What is the diameter of the spindle?

Steel and cast iron make for a very sturdy bearing. The diameter and clearance will determine the max speed.

The diameter of the spindle is 1/2 inch and appears to be made from steel with a ground finish.
I would think this machine is several decades old.

[oldtiffie]

Deleted/erased-out

[Allan Waterfall]

If this helps....

A lot of model aero engines have used cast iron main bearings without problems,revs probably up to around 12,000 without problems although there is a constant flow of lubricant from the fuel used.

Allan

[David S Newman]

Might sound a silly question but when a bore warms up does it expand inwards or outwards ? Tried running the drill at 4000 rpm for ten minutes the bearings warm up slightly and no sign of a seize, looks like the high speed will be OK. Thanks for your input. David