How order of operations and tapers are very confusing to some .

[mmcmdl]

In my apprentice days , I had the task of grinding some large ID tapers for the nuclear subs down in Virginia . These parts were approximately 16" long , with 2 degree locking tapers 8" or so in diameter . The supplied taper plug gage had to have 80% contact thruout the bore . With X amount of pressure on the plugs , the stickout of the gage had to be held to +/_ .015 .

Our estimating crew sees the .030 tolerance on stickout as a wide open dimension , and bids the job accordingly . There order of operations were as followed .

1- cut the stock
2- drill and rough bore for grinding
3- face overall final length
4- heat treat part
5- grind finish tapered bore to print dimensions .

This job cost the company their arse . Not only is a taper darn near impossible to achieve an 80% blue transfer , but to hold that taper and hold that wide open .030 tolerance stick out was just as close to impossible . An increase on the tapered diameter of .001 dropped that plug gage into the bore a mile and a half it seemed ! You figure it out with trig , and see what it works out to .

The order of ops should have been .

1- cut the stock
2- drill and rough bore
3- face length oversize leaving 1/4" extra
4- heat treat part
5- grind tapered bore to angle and near depth with plug gage .
6- Finish grind overall length of both ends to bring in stick out requirements .

Sometimes it's these little details you miss that end up beating you if not noted .

 

[jbobb1]

When I read the 3rd operation (actual attempt) my jaw hit the floor! Done a ton of taper work (not quite that large), but the obvious is obvious!