Post by springcrocus on Aug 22, 2016 18:29:47 GMT
It's been a strange week just gone; some disappointment, fixing my 3-jaw chuck and a touch of woodturning. I was setting up to do the last but one operation on my valve sleeves and something didn't feel right. So I clocked them up and found that I had three thou runout between the O/D and the I/D. Definitely not acceptable, they've got to meet in the middle of the cylinder casting and be dead in line. I can polish the odd thou to align them but not this much. I considered rotating to equal wall thickness and pushing them in this way but the bore was skewed on the axis. In the end, I decided to bin them and start again.
The problem occured because my mandrel moved in the chuck after final sizing and this was because my chuck jaws were noticably bell-mouthed. Although the workpieces were loaded to the mandrel a number of times, the problem wasn't spotted earlier because of how I work. I automatically mark the mandrel with a loading orientation and always mark and load each workpiece to the same position. This minimises the chance of errors but backfires in a situation like mine where the mandrel moves after final positioning. This chuck has had a lot of abuse in the past, having spent over fifteen years in an industrial environment, and it really should be tossed out but I decided to re-machine the hard jaws and give them a new lease of life. The first picture shows, looking at the outer jaws, how they have been machined or linished back over the years and the centre jaw has had the side angles restored.
Although the jaws are hardened and can't be filed, they can be machined with carbide tooling and here I am using a 10mm solid carbide endmill to remove the material. The vice is set at a thirty degree angle, I used conventional milling at half-cutter width and taking, on average, seven thou depth of cut.
Once all three jaws were cut back they were reloaded to the chuck, which was scrupulously cleaned and mounted, and were set up as shown below. The held billets are tee-slot nuts from the mill and are as close to the front of the jaws as I can get to mimic normal workholding conditions.
Then they were bored with a small boring bar holding a carbide insert, taking just enough to get a full cleanup on all three jaws. They won't be as accurate as using a toolpost grinder but, so far, test-bars are going in with no more than a couple of thou runout which I find acceptable.
Let's hope this week can be a bit more productive.
Steve
The problem occured because my mandrel moved in the chuck after final sizing and this was because my chuck jaws were noticably bell-mouthed. Although the workpieces were loaded to the mandrel a number of times, the problem wasn't spotted earlier because of how I work. I automatically mark the mandrel with a loading orientation and always mark and load each workpiece to the same position. This minimises the chance of errors but backfires in a situation like mine where the mandrel moves after final positioning. This chuck has had a lot of abuse in the past, having spent over fifteen years in an industrial environment, and it really should be tossed out but I decided to re-machine the hard jaws and give them a new lease of life. The first picture shows, looking at the outer jaws, how they have been machined or linished back over the years and the centre jaw has had the side angles restored.
Although the jaws are hardened and can't be filed, they can be machined with carbide tooling and here I am using a 10mm solid carbide endmill to remove the material. The vice is set at a thirty degree angle, I used conventional milling at half-cutter width and taking, on average, seven thou depth of cut.
Once all three jaws were cut back they were reloaded to the chuck, which was scrupulously cleaned and mounted, and were set up as shown below. The held billets are tee-slot nuts from the mill and are as close to the front of the jaws as I can get to mimic normal workholding conditions.
Then they were bored with a small boring bar holding a carbide insert, taking just enough to get a full cleanup on all three jaws. They won't be as accurate as using a toolpost grinder but, so far, test-bars are going in with no more than a couple of thou runout which I find acceptable.
Let's hope this week can be a bit more productive.
Steve
