The Craftmans Shop > New from Old
Making-A-Taper-Gauge
awemawson:
Not much done today as it's Easter Sunday and apparently I have other things to do :scratch:
But I did manage to centre up the plate that I've ground flat on the underside, select the taper arbor that I want to use, and drill out the central hole to 21 mm. This gives lots of room for boring to size.
The selected arbor is the type that remains parallel on the bearing surface as the internal taper expands the sleeve. At 1/3 travel it opens to about 24 mm and at mid travel is about 24.5 mm, so I will aim to bore out the hole using a boring head tomorrow to about 24.25 mm .
awemawson:
I got set up to bore the hole for the turning and grinding mandrel this morning.
I'd forgotten how satisfying boring precision holes is when it all goes smoothly - which for a change it did. Producing nice curly swarf and a hole that admitted the expanding mandrel just as far as I wanted.
To celebrate I cleaned up the second side of the plate, this time having to remove 11 thou to get though the surface muck and bullets.
NormanV:
Surface grinding is a mystery to me. I once made an iron casting for a 12"x10" surface plate. I took it to a local engineering college and they surface ground it for me. I was puzzled by the fact that they could grind across the 10" width with no appreciable wear on the grinding wheel. How is that?
awemawson:
As you feed across the work, the theory goes that, the leading edge of the wheel wears (very slightly), but the remainder of the width of the wheel remains at the diameter to which it was dressed so the ground surface becomes flat (or as flat as the grinder!)
Remember that feeds are exceedingly small on finish passes, measured in tenths. I was fairly gulping that plate in 2 thou bites as this isn't the finished thickness of the part yet - I just wanted it flat enough to get a bore true to the surface.
I started turning the plate into a true disk on the manual lathe. Firstly pressing the arbor firmly home using the arbor press, then placing of a 'soft centre' turned in place in the 3 jaw to avoid changing chucks etc.
This wasn't satisfactory, as the intermittent cut was pounding the soft centre and slowly putting it out of true.
So I mounted up a hard centre in the spindle bushing, and used the catch plate. A process rather delayed by seeking the catch plate -WHY was it in the cupboard with all the Bridgeport bits, NOT the cupboard for the Colchester bits :scratch: Oh well it only took an hour to find it !
Haven't finished turning it yet as I've been called away for canine supervisory duties :bugeye:
awemawson:
I managed to get back out to the workshop for half an hour and have at last finished the intermittent cut phase of the operation. It's now a true cylinder of 110.8 mm diameter.
End target is 106.358 mm so a generous 4 mm to play with - I will approximate to the 7 degree 7 minute 30 second angle on the top slide and taper the side to that but leaving it well over size for final tapering on the cylindrical grinder where the angle can be set far more accurately (I hope! )
Still at least I've got to where I'd hoped for today
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