Andy, little would you believe it, I prefer someone to correct me when I am wrong. I don't profess to know everything, but what I do know should be correct, as I do pass over a lot of information. If that incorrect info can be corrected, then I am very grateful.
So please, don't be afraid to tell me I am wrong (just don't go out alone in the dark, the Boggy man will getcha).
Anyway, we are now at the last part of this project.
Again, it is a highly abridged version, because most things have been shown before, but if there is anything you don't really understand, then shout up and I will try to explain the process
I left the last post awaiting threads to be cut.
They have now been completed using the offset single point technique.
The threads are 1.5mm pitch, and this is the first metric thread I have cut on this machine since I purchased it over a year ago. Everything went very smoothly.
I had purchased a ball raced nose nut specifically for this job, and it screwed on and fitted perfectly
Now we get to the tricky bit, cutting the taper for the collets to fit into.
The standard taper for an ER collet is 16 degrees inclusive, so that means the topslide (compound) needs to be set over by 8 degrees.
This was duly done, but you have to remember that the taper is critical for correct operation, and this is only a very rough setting. A little later, things are tweaked to get the taper exact.
This shot shows what the setup looks like.
The topslide is set over, a boring bar is in the toolpost, set as though it would be boring a normal hole, and the saddle locked up.
All cutting is done using the topslide feed handle, so you need to get your technique sorted, whereby you use both hands in a swapover motion so that you get a steady and constant feed with no 'jerkiness' between changeover. This ensures you have a nice smooth surface for the collets to slide on.
I cut about 2/3rds of the required meat removal and then blued up the internal surface with Engineers blue, NOT layout blue. Engineers blue doesn't set and go dry, and so can transfer itself onto anything it comes into contact with. I usually have to give the whole area a good clean down afterwards, as the stuff seems to jump from here to there all by itself.
Taking the smallest and largest collets from the set (to allow for the different springiness) the collets were gently pushed into the blued up hole and even more gently, rotated. You want to make sure that your actions don't compress the collet at all, otherwise you may get a false reading. That was the reason for using the two collets, just to make sure I wasn't pressing in too hard and I was getting a consistent result.
The two lines at the tops of the collets are the top one is how far it goes into a normal collet chuck, and the bottom, how far they penetrated into the taper I had cut.
As you can see, the blue has only transferred onto the bottom part of the collet tapered face. This shows me that the angle that I am cutting is too large.
I slackened off the topslide bolts very gently, and tapped the topslide with the plastic end of a small screwdriver to reduce the angle by a minute amount.
Things were tightened up again, and a skimming cut done so that the old taper was only just cleaned up. You don't have a lot to play with, so while you are fine tuning, you take off the minimum material to do the job. I found the sweet spot first time, you might take a couple of 'taps' to get it spot on.
The new taper was blued up and rechecked again with cleaned down collets.
This is the result of my 'adjustment'. I have blue showing from top to bottom of the taper. The uneveness is caused by the rough finish on the taper, but as long as it is as shown, then the finish will be tidied up at the final stage. I have my taper now spot on.
The next stage is to get the taper to the correct diameter. So after the collets were cleaned up with spirits, they were place in my normal chuck and the depth marking was put on. This shows how much deeper it still needs to go. It looks a lot, but when dealing with tapers like this, even a tiny skim is a lot.
When I got to the final skim, I really slowed down the hand feed, and speeded up the chuck.
I was considering breaking out the toolpost grinder for a final lick over, but the results I got by hand feeding will be just fine.
The collet now sat at the correct depth.
So now the moment of truth.
I grabbed a 16mm collet and a new tungsten cutter, and by mounting the cutter in the wrong way around, I had a reasonably accurate test bar.
A quick check with a high precision DTI showed I had a TIR of 0.0001".
A fly farting as it went past could have caused that, so that'll do me.
So onto the mill, and using the newly made RT adapter and a woodruff cutter, I made some slots for the C spanner to fit into, just so I can get the thing off wherever it is mounted onto. I actually had to chisel it off the lathe fitting, but the first cut with the woodruff took the gouge mark out.
That completes the set of parts to make my dream of interchangeable tooling come true.
I can now interchange either 3 and 4 jaw self centring chucks, an ER32 collet chuck or a small faceplate between my lathe and the RT on my mill.
A super happy Bogs.
