Some background/intro: I knew that there would be a need for scraping the front bronze bearings because I had taken a look at them and seen the majority were worn smooth and probably had minimal- or less than optimal contact, especially in front. Some radial wear "grooves"/lines also. Clearly in need of refurbishment!
My goal is obtain a structure with good contact area and distribution of scraping marks to allow for proper lubrication of spindle, which ensures longevity, and of course to make an accurate (and rigid) bearing
Having read about multiple (3- or 4-contact) area bearing, which should make the bearing stiffer, I wanted to try this also. At least on one bearing.
The way I would do this is to first finish scrape it complete, then relieve the sections axially. However, there is no evidence that Myford did this and I may (only) try one or two this way..
To avoid oil leaking out in front the front (and rear) of the bearing it may also be OK to try to have a consistent high spot around the periphery. We will see how it goes.
Design: Myford changed headstock design with different oil feed systems, first version with oil reservoir on top and gravity feed through 3 holes and 1 or 3 axial grooves.
This was later changed to wick feed (through cup oiler and smaller reservoir feeding into wick), inclined some degrees from central position below bearing, an only one oil hole and axial groove
The groves doesn't extend all the way back and front to avoid oil seeping out
Tools: triangular and/or "spoon" scraper. Triangular scraper tends to dig in (faster), but is OK. Resting on the rear edge for sturdier handling (I tried masking tape to avoid scratching the surface, but too much hassle for possible minimal results)
Grinding scraper using either "manual stoning" or machine. Latter is best, especially the one with angle setting possibilities. Spoon scraper can be ground to negative (scraping) angle, which makes it easier to handle. Resting the motor onto the end so the grinding disc is horizontal is nice (better control)
Setup considerations: mounted on firm base allowing rotation of workpiece (headstock). In my case I tried a simpler "direct to vice" method, but concluded that you need to be able to rotate the headstock to conveniently (read accurately) scrape the cylindrical/tapered bearing. I then looked for a way to mimic Nick Müller's setup using a rotating table, and thought a perfect way would be my Saacke grinder's dividing head. It has an ISO40 taper, but should be easy to make an adapter. However, some "fool" had broken a tap or screw in the head locking mechanism, and it proved to be worse to undo, hence I had to rethink to get things moving.. Came up with the simplest of the simple, just whacked a piece of bored- out- to fit aluminium bolt onto a stud which formed part of the mounting plate for the headstock (used 3 of 4 bolts to secure the headstock). Then I took 2 blocks of wood, clamped together and drilled a suitable hole through their centerline. Plugged the alu bolt in this hole and voila.. I can loosen and firmly tighten the headstock in "any position".
For radial positioning of spindle when testing, I mounted a couple of the old thrust bearings as they normally would be sitting, ie, facing one another with a distance ring and tightened using the pair of castellated nuts front/back.
28 сен 2024
