Stew doesn't know I am posting this, but I suppose he will soon.
This is a good example of how not to get someone to do you a favour.
Stew had asked me to machine up a backplate for his spindexer, as I have a very accurate 5c collet chuck, whereas he had no real way of holding it that would guarantee it's accuracy.
Anyway, Stew calls around early last week with the backplate. Where's the chuck says I. The first
Friday comes along and he drops the chuck off, luckily just before my afternoon power nap, 15 mins later and he would have got a real good welcoming reception
So this morning, I started, and this might show you how I do my lathe backplates. You will need to imagine this is the plate fixed to your lathe nose.
A near enough measure up was done on the chuck recess.
The face was skimmed up to leave just a little more than what had been measured. By doing it this way, you can go wild with the cutting for a while, before you have to settle down to some serious stuff.
I set the saddle stop and pushed the saddle against it, then set the depth of cut to 0.100" (2.5mm)
Then it was a matter of rough plunge cutting until I reached the spigot I had just cut on the face.
I then did a couple of thou cleanup of both faces. The recess was then more accurately measured up.
And the spigot was gently reduced in diameter until it was about 0.005" (0.025mm) larger than the recess measurement. No further measurements are carried out.
The front corner of the spigot had a tiny chamfer filed on the front. This is only a mock up, I used both hands for the job.
I totally disregard all the buls**t and wives tales about freezing the flange and heating up the chuck, doing it that way will set up all sorts of stresses you don't want, and besides you may want to take the chuck off at sometime for cleaning.
I very gently skimmed down until the chuck is a nice wringing fit on the spigot.
If you balls it up and go too small, there is still usually enough meat on the backplate for you to have a lot more goes until you get it right (on this one at least 4 or 5).
After that, I skimmed the outer edge of the backplate. You should never clock up off the chuck, as that can be almost any shape, so this skimmed face will be an accurate datum face to clock from. I also skimmed the front across, just in case that needs clocking at some time.
Now for the next part, getting the two joined together. Unfortunately, there are no thru holes, so they are transferred from the back flange. I will be using the RT on the mill to do that job.
Now I need to fix the chuck to the RT, no chuck key supplied, and I don't have one that will fit. The second
So a quickie grind up of a bolt got me a temporary one that will do the job.
Using the super duper chuck key, I tightened the chuck onto my Myford threaded adapter.
The RT was set at 0 degrees, and the mill table was moved about until a drill that would just go down the threaded hole fed into the hole in the back of the chuck. This was tried again in the other holes by rotating the RT by 120 degs each time, once a nice balance between all 3 was found, the mill table was locked up.
A chuck was fitted to the RT and the backplate mounted up. Each position was given a good centre drilling.
Followed down with an 8.5mm drill.
I use an oversized drill because sometimes the actual mounting holes in the chuck are not always accurately drilled on some of these cheapo ones, and because they are only bolting holes, they can be way oversized if needs be and within reason.
That quirky thing came out and bit me on the bum. No matter which way I turned the backplate, one hole was definitely out of line. All backplate holes lined up perfectly with the other two, so it wasn't my drilling.
So I relieved one hole with a file until the bolt fitted. Unfortunately, no bolts supplied, so I had to modify a few. The third
Because the backplate is now made to fit one way only, it needed to be marked up as such.
Stew had already made a datum mark because it is most probably been set up for another backplate. I just marked up this backplate for it to line up with.
I set it up on my lathe again and checked the runout. 0.0015" (0.0381mm). Methinks that will do, with it being so far away from the spindle, and a self centring chuck as well.
I just hope Stew is happy, if he has remembered where he has left it
Bogs
