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View Full Version : Herbert Mill spindle R8 conversion.



Peter.
04-06-2009, 06:59 PM
Since my old Herbert mill uses a collet particular to the machine, and since it was made in 1952 and came with just 6 imperial collets, I decided to take the opportunity whilst the spindle was out to convert it to a more commonly-available taper fitting so I could use a wider range of tooling. R8 was the most obvious choice since it is highly available and very close to the Herbert collet dimensionally. I decided to ask John Stevenson for his advice and help.

I measured up the spindle and sent the dims off to Sir John who drew the collets overlaid on each other in CAD.

http://peterrimmer.myby.co.uk/images/colletcompare.gif

The tapers are very close, so I sent the spindle off to John to sort. He bored out the hardened end of the spindle and shrunk a piece of EN36 in the end and machined that for the R8 taper. He also bored the shank and made me a new drawbar. I told him I didn't need a hardened end for the light & infrequent use my mill would see.

When I got the spindle back from John I was very impressed. I stuck the spindle in the mill and it did have a tiny runout (which we were expecting). I set-about truing the runout like this.

Set the angle of the head by putting a dial gauge mounted on the table onto the taper and raising/lowering the knee until I had the dial moving just .001" with .400" travel (the most I could lift the knee before the dial gauge fouled the spindle). I figure 1:400 was close enough, so I ground & polished a HSS tool and mounted that in my lathe toolpost, which I held in my vice on the table.

http://peterrimmer.myby.co.uk/images/truespindle03.jpg

http://peterrimmer.myby.co.uk/images/truespindle02.jpg

I then simply used the knee to lift the cutter and shave .001" off the taper to remove the runout. There's plenty of meat on the end of the slug to shorten it to accommodate the wider taper if needs be.

The result - less that a ten-thousandth of runout. The dial graduations are .01mm. Video shows 4 turns of the spindle:

http://peterrimmer.myby.co.uk/vids/norunout.wmv

I'd just like to add my great thanks to Sir John for his help and excellent work. I don't have the skill nor the tooling to machine the hardened end of the spindle but he did a great job on it for me - thanks John!

John Stevenson
04-07-2009, 06:42 AM
Not a problem Peter and that was the best way to get the error out.
Don't matter how good you clock the spindle for boring you have no way of checking that the spindle is lying along the central axis of the machine, even using soft jaws and over the length of an R8 it's enough to throw a few tenths off.

Running in it's own bearings is the only acceptable way.

Nice to do something interesting besides those damn electric motors.

.

rockrat
04-07-2009, 08:36 AM
Nice job gents. I have to admit, taking a spindle out and cutting on it is a daunting task. It looks as though things went about perfect.

I like the truing up while in the machine. I agree that its own bearings are the only way to go when making the "final" surface. And a soft spindle means you don't have to grind.

Fantastic work thanks for sharing.

rock~