Setting bearing preload.

Martin,

You are bang on the money regarding the expansion minefield! The common assumption is the expansion is the same as it is all heated up and is the same sort of material. This is always incorrect as the heat is generated at the bearing locations and sometimes from the work holding (depending on how carried away you get with the tool)which provides localised expansion from thermal differences due to the large areas of the machine loosing the heat to the environment. If you do the math's, you might be surprised to find out the relative dimensional changes in the assembled head stock. This is the reason machine spindles have the supporting bearings close together at one end and a sliding or floating bearing at the other - this is not done for fun but out of necessity.

Mark

I have a No 4 Issue of the Myford News which was published in 1990 in it are two articles detailing the servicing of the Counter Shaft and the Spindle of the Super 7 or ML7-R, the spindle article gives the procedure for the bearing adjustment with good illustration's.

I have the articles on PDF files if they are of use to anyone PM a E- mail address and I can send them on.

Mike.

Thanks Ken. I may not be the worlds greatest engineer but always keen to learn from others and improve my equipment where I can (so not a Myford owner afraid to tamper with originality). It sounds like I may have got the bearing setting right. There's negligible heat expansion where the two taper rollers are concerned and since the combination robustly resist any reasonable thrust that's headed their way, I'm very happy with the modification.

My Atlas has Timken tapered roller bearings from new and is only slightly bigger and a similar design to a Myford.

The official procedure is as follows:

Run the lathe for 30 min to one hour to warm up the spindle. Loosen the thrust nut and then tighten until the end play just disappears. Tighten a further 1/16 th of a turn and lock.

The thread on the spindle is 20 tpi so 1/16 th turn corresponds to about 3 thou.

Russell

A slight digression [given that the question raised by Chris seems happily resolved]

It is perfectly possible to build a useful spindle using one Taper Roller Bearing, and 'whatever' at the other end. ... The TRB then acts in way similar to the bronze bearing at the front of the Myford S7 [or the Mega Adept] Headstock, but without the need to pre-set a critical 'oil-film' clearance.

... This may have some merit for heavy duty drilling spindles.

MichaelG.

I used to be a Toolmaker at British Timken (RIP).

Counting turns will vary with the thread pitch. The proper procedure is to measure the static torque via a spring balance on an arm.

The shortcut is to nip it until there is the faintest drag when turning by hand. Lock it there or if you have a castle nut then back off to the first split pin slot.

More sophisticated set-ups may have spring shims.