Hello:
I make the belts for my U3 from ? 5mm green textured PU, material I found on Aliexpress.
Works fine and slips much less since I turned a new spindle pulley in Al to replace the lousy plastic OEM pulley.
First thing I did when I purchased it (a year ago or so), after a thorough cleaning and taking stock of what was what, was to replace spindle bearings which were shot and install a new 24V/200W PWM regulated motor, later upgraded to a 400W one.
From then on, the U3 slowly has morphed into a project in itself as I am still adjusting issues that kept cropping up every time I started to do something.
eg: carriage, tailstock and headstock alignment, saddle/carriage gibs, new carriage leadscrew, new carriage handwheel arrangement and so on.
Not unexpected from a 43 year old unit with an evident lack of maintenance and an unknown number of previous owners.
Had I known ...
But I digress.
While taking spindle runout readings I noticed that the belt (on or off) had a marked influence on the spindle, albeit noticeable only with the dial in place.
I assume (?) that the Bellville washers fitted along with the bearings are directly related to this axial movement, their being some sort of protection for the bearings/tool if and when the tool would decide to dig into the material being turned.
Not that something of the sort would ever happen to me ...? 8^¡ã
Refecting on this, a couple of questions popped up:
1.
I have seen photos/videos of other round belt driven lathes where they actually seem to be loose.
Just how tight does the spindle belt have to be on the U3?
How can this tightness be measured?
There is no provision to regulate it, has anyone ever found a way to do it in a simple and efficient manner?
2.
Do the Bellville suffer material fatigue? ie: would they need replacing after many years' use?
Thanks in advance.
Best,
JHM
