I finally had my machinist friend machine a new bronze spindle bush for my Graziano SAG 180 lathe. This guy has extensive experience making and fitting tapered prop shafts to propellors including hand scraping the tapers to fit as well as making bronze bushes including those for large ocean going vessels.
The original bush had seized on the spindle due to someone bypassing the oil supply probably to "fix" an oil leak :nutter: as shown in the third photo. The original also had the threads broken off from someone hammering on the fragile cast phosphor bronze, my attempts to silver solder steel threaded sections failed and resulted in the bushing curling into a three leaf clover profile as internal stresses relaxed. The new bush is made from LG2 bronze or red brass which is softer but has better embedment of particles and is less prone to seizing than phosphor bronze.
Once the continuous cast blank was bored to the same size as the spindle shaft (it's adjustable over and under size with the combination of the tapered socket and wedge key) it was fitted to a centre ground steel mandrel with a milled pocket below where the key socket will be milled. The mandel was centred and the outside of the bush skimmed parallel (to 0.001mm!) and concentric to the mandrel so as to provide convenient reference surfaces. The Colchester Master has enough compound travel to machine the entire taper without resorting to fitting the taper attachment to the lathe. It took many trial fits and blueing to get the the angle correct and the rear surface of the cast iron socket only mated for a narrow ring and a small area top and bottom: this was found to be due to someone doing some gouging of the iron socket and making it slightly oval for reasons known only to them.
At that point the decision was made to lap the bush taper and iron socket with 900 grit silicon carbide for a better fit. Oil galleries were plugged (They are all straight through holes so wire and cleaning cloth can be poked through later to clean them) and the two were lapped together. Each time the bronze showed mating with the two x one inch wide rings of the cast iron socket, a new taper would be machined to true up the bronze surface and the fit checked with blueing. The machining had the effect of moving the taper a little further along the bush towards the position of the final surface in the middle of the bush. I was surprised at how little iron was removed with each "wet" of carbide and most of the wear was on the bronze taper which meant it had to be remachined often after plenty of washing and scrubbing to remove carbide grit.
It took six lapping sessions and truings of the taper to get 270 degrees of good contact for the rear surface with nearly complete contact for the front surface. The iron socket shows the dodgy oil gallery bypass someone gouged in the iron from the pressurised oil gallery to the oil drain hole. The gouge had to be drilled to key in the epoxy and shows the epoxy patch and the drain hole back to the headstock.
The last photo shows the milling of the final split down the middle of the keyway, the continuous cast bronze sprung shut slightly and through pure luck measures only a tiny bit of distortion towards the rear of the bush and which the key can pull back to an accurate circle with very little force (finger tight keyway bolts). We fitted a left over digital angle display I once manufactured years ago as a jury rigged angle readout to allow the milling of the 15 degree sides of the keyway with a straight endmill, it was very handy in the role!. The photo of the new bush alongside the old one show a bit of the bronze's crystalline structure which was revealed by using razor sharp, diamond honed, positive rake carbide tooling. In other shots it looks like galvanised iron in appearance.
I'm thinking of fitting a small external 5 micron cartridge diesel fuel filter assembly after the pump and before the bush as the bush is the only thing the pump feeds after I found a few lumps of black casting sand coming loose inside the headstock and originally painted over by the manufacturer.
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The original bush had seized on the spindle due to someone bypassing the oil supply probably to "fix" an oil leak :nutter: as shown in the third photo. The original also had the threads broken off from someone hammering on the fragile cast phosphor bronze, my attempts to silver solder steel threaded sections failed and resulted in the bushing curling into a three leaf clover profile as internal stresses relaxed. The new bush is made from LG2 bronze or red brass which is softer but has better embedment of particles and is less prone to seizing than phosphor bronze.
Once the continuous cast blank was bored to the same size as the spindle shaft (it's adjustable over and under size with the combination of the tapered socket and wedge key) it was fitted to a centre ground steel mandrel with a milled pocket below where the key socket will be milled. The mandel was centred and the outside of the bush skimmed parallel (to 0.001mm!) and concentric to the mandrel so as to provide convenient reference surfaces. The Colchester Master has enough compound travel to machine the entire taper without resorting to fitting the taper attachment to the lathe. It took many trial fits and blueing to get the the angle correct and the rear surface of the cast iron socket only mated for a narrow ring and a small area top and bottom: this was found to be due to someone doing some gouging of the iron socket and making it slightly oval for reasons known only to them.
At that point the decision was made to lap the bush taper and iron socket with 900 grit silicon carbide for a better fit. Oil galleries were plugged (They are all straight through holes so wire and cleaning cloth can be poked through later to clean them) and the two were lapped together. Each time the bronze showed mating with the two x one inch wide rings of the cast iron socket, a new taper would be machined to true up the bronze surface and the fit checked with blueing. The machining had the effect of moving the taper a little further along the bush towards the position of the final surface in the middle of the bush. I was surprised at how little iron was removed with each "wet" of carbide and most of the wear was on the bronze taper which meant it had to be remachined often after plenty of washing and scrubbing to remove carbide grit.
It took six lapping sessions and truings of the taper to get 270 degrees of good contact for the rear surface with nearly complete contact for the front surface. The iron socket shows the dodgy oil gallery bypass someone gouged in the iron from the pressurised oil gallery to the oil drain hole. The gouge had to be drilled to key in the epoxy and shows the epoxy patch and the drain hole back to the headstock.
The last photo shows the milling of the final split down the middle of the keyway, the continuous cast bronze sprung shut slightly and through pure luck measures only a tiny bit of distortion towards the rear of the bush and which the key can pull back to an accurate circle with very little force (finger tight keyway bolts). We fitted a left over digital angle display I once manufactured years ago as a jury rigged angle readout to allow the milling of the 15 degree sides of the keyway with a straight endmill, it was very handy in the role!. The photo of the new bush alongside the old one show a bit of the bronze's crystalline structure which was revealed by using razor sharp, diamond honed, positive rake carbide tooling. In other shots it looks like galvanised iron in appearance.
I'm thinking of fitting a small external 5 micron cartridge diesel fuel filter assembly after the pump and before the bush as the bush is the only thing the pump feeds after I found a few lumps of black casting sand coming loose inside the headstock and originally painted over by the manufacturer.
