The Craftmans Shop > New from Old
Making-A-Taper-Gauge
awemawson:
Not been able to get a lot done over the past few days due to other commitments, but I HAVE managed to set up the 1300 and do a test grind for parallel.
Just a bit of 32 mm hot rolled bar from the scrap bin, faced and centred at both ends, and set up in the cylindrical grinder to test for parallel grinding. First go produced a difference end to end of 5 thou over the seven and a half inches of the bar.
Now many years ago I produced a crib sheet for removing tapers in the grinding as it gets quite tricky working out what needs rotating and how much. The 'top table' of the grinder swivels on the travelling table, the pivot being in the centre. By knowing how much the part tapers and over what length, and which end is bigger my crib sheet tells me how much to move the end of the table. In this case the 5 thou taper 'should' be eliminated by 10 thou movement which I of course then applied. This has reduced the taper to five tenths of a thou over seven and a half inches. A bit of persistence would get rid of that but it's quite near enough for what I'm doing.
I was pleased with the ground finish considering the grotty but of steel that it was !
May get a bit more time tomorrow.
awemawson:
Of course I couldn't leave it at that - I had to get that last bit of non-parallelism out. A couple more iterations and it was gone to the limit of my measuring capability :thumbup:
However while doing it there were ominous growlings from the work head - a bearing not sounding too good. I eventually tracked it down to the front motor bearing on the work head - the grease had dried out. However getting at it involved rotating the entire work head on it's swivelling base thus loosing my parallel setting :bugeye:
Now the base is graduated and the graduations are on a good diameter so you can get it back close to where it was but never exactly the same place! OK another round of grinding that bar and I eventually got it back spot on where we were a couple of hours ago. The reason for the dried up grease - one of the grease nipples was blocked and not actually passing grease to the bearing - nipples both changed and the bearing seems no worse for wear.
Now years back I had made a big test bar to aid setting this machine up - just a 3-1/2" bar accurately centred and ground, I've even made a nice wooden box for it, but when I recently got it out of the cupboard I noticed a couple of small spots of corrosion despite having been sprayed with preservative.
So as I type this it is having a thou taken off back to a fair finish (I hope!)
A machine like this grinder has too many degrees of freedom. The work head can swivel, the grinding head can swivel and raise and lower, and of course the main upper table can swivel - all these movements make setting up great fun, and also as you slide the tailstock up and down the ways it will be pointing ever so slightly in a different direction ! Even clamping the upper table results in a very small angular movement - it's tiny but when trying to split tenths of a thou tiny counts !
WeldingRod:
How are you driving that test bar?
Sent from my SM-G892A using Tapatalk
awemawson:
There is a 1/4" Whitworth tapped hole in the driving end with a cap screw in it that engages a tab on the rotating bit. (Tab held in a left hand threaded 3/8" Whit bolt that had me puzzled until I remembered it's handedness (original J&S feature)
awemawson:
Wanting to press on with this gauge today I dug out my metric slip gauges and their accessory set, and made up a 'snap gauge' 5 thou larger than the maximum limit on the fat end of the chuck taper.
This being 106.371 mm I assembled slips to the tune of 106.498 leaving 5 thou for tweakng when I was happy with the measurement method. Sorry about the mixed units, but the grinder is Imperially calibrated.
Once there and happy with the process I dug out an Imperial micrometer of suitable range, re-adjusted the snap gauge to finished size, and also leaving projections to use for zero setting the micrometer zeroed it, so it is only being used as a 'distance to go' meter not absolute measurement.
The parallel section of the gauge was then quite quickly brought to finished size, and this being the upper limit will leave me some wiggle room when finally I remove the chuck and use it's recess as a standard to blue it to.
I've layout blued the gauge, so that when grinding the taper I can see it progressing across the width of the gauge to give me an estimate of depth of the taper. This will be ultimately adjusted to the chuck recess when removed (remember that crane !)
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