Someone moaned about the amount of politics and calendars:-
I may have let slip (to the point of monotony) that I have been rebuilding an Ebay basket case Hardinge HLV for the last 18 months.
At the start of March I started to work on improving the removable, hardened dovetail way bed. Having removed the bed, I measured its thickness in a number of places. The micrometer showed that there was at least 3.7 thou of wear. At least, because the micrometer doesn't measure to the bottom of the roughness.
I could have sent the bed away to be reground. Trouble is that I'm cheap. That's why I didn't just wait for a lathe to turn up in better condition to start with...
I reasoned that I might be able to grind the bed on my £75 J&S 1400 grinder.
Because the bed is38" long and the table travel on the grinder is only 24", the bed had to be ground in two sections. I got a bit of a visible furrow at the point where the table stopped at the end of the cut in the middle of the bed, but even after the roughing cuts, the bed thickness is now even to within a couple of tenths outside of that narrow furrow, which the carriage will ignore. I had to remove 6 thou to get rid of all of the wear marks.
Ok. That did for the thickness of the bed. Now I can think about the dovetails. The dovetails have a 1/8" wide, unmachined, vertical section at the top. I assume that I can measure from that to the dovetail on the opposite side to get an indication of the wear.
While thinking of that, it was assumed that the way to grind the dovetails would be to make a sine table. The old 6"x12" Humphrey's electromagnetic chuck that I inherited off father could be pressed into use for that. A 15" long bit of 1 1/4" square bar was milled into angle iron on the Myford and hinge pins turned on the ends. A couple of lengths of 2" square were milled and ground into L shapes for the sides. Holes could be bored in these for the hinge pins before final grinding to get the height of the side at the exact level of the bottom of the hinge pin. Something like this:-
|-----------------------------------| | | | |---| | |-------|_______________________|___|_| | /-\ | |/-\| | \_/ |________________________\_/___ | | |______________________________________|
Boring the holes means that the boring head that I got some years ago needed an adapter to fit the Myford headstock mandrel. Did that, got a set of taps from RDG to finish the internal threads, having had problems with getting these right before.
In the meantime, the junction box on the mag chuck needs sorting.The screws holding it to the chuck have waled out heads and one of the screws holding the cover on was sheared off before I was born by the look of it. No problem. Bit of 3/8" silver steel for the cap head screws and 3/8" brass for the countersunk screws. drill out the busted screw and run a 5/32"BSW tap down all the holes to clean them up..
A jig had to be made to hold a tenths dial gauge at a variable, fixed height and slide along the bed, measuring the variations in width. Just a bit of sawing, milling, grinding, drilling, tapping and Loctiting. Job done.
The jig shows that the vertical bits at the top of the dovetails seem to be parallel within a tenth, but that the dovetails have a reasonably steady 12 thou slope compared to the vertical bit. Bugger. The jig needs modifying so that it can measure one dovetail against the opposite dovetail. If I make a push tool to fit the boring head, I can use it with the Myford dividing head to make a ball turning tool and make some ball ended pins to go on the jig to bear against the dovetails. Haven't got any 1/2" round HSS. Never mind, make a
3/8" to 1/2" adapter to hold the 3/8" HSS that I've got.To cut off the bit of round HSS to the right length, I can use one of the thin cut off disks I got for the grinder. Bugger, the wheel arbours won't grip something that thin. Never mind. Slice off a bit of 95mm bar and turn up a spacer to fit the wheel arbour.
Now, What was it that I was trying to do...
Mark Rand RTFM