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Unfamiliar Boring Head Shank add-on: What do I have?

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  • Unfamiliar Boring Head Shank add-on: What do I have?

    This is a recent eBay purchase. I thought when I got it in-hand I'd be able to figure it out, but I can't. The boring head is a standard 2" Criterion, the shank a straight .750 Criterion. The part in between? It has an index mark on the top flange, a scale 0-30 in the middle and a lock screw on the bottom. With the lock screw loose, the center band rotates smoothly 360 deg. but doesn't seem to do anything! When I get home I'll make a pin-wrench to take the thing apart, but 'till then is it familiar to anyone?


    Above: The assembly

    Above: The 'top' view (shank side)

    Last edited by chipmaker4130; 05-23-2011, 11:55 PM.

  • #2
    Thats a Tenths ring, it has a total of .003 offset adjustment. (each graduation on the tenths ring equals .0002 bore dia. increase)
    With just .003 total movement, it's very difficult to detect that anything is happening when the ring is turned.
    It has to be fit to the specific boring head so the index mark on the shank flange matches the adjustment axis of the boring head.
    Last edited by dfw5914; 05-24-2011, 12:56 AM.


    • #3
      Hey thanks. That sounds very useful! If the total offset is only .003, that explains why I didn't see it with a quick spin.


      • #4
        That is pretty cool. I have never seen one before.

        At EASTEC last week Wohlhaupter was showing off their new (to me) "DigiBore" boring head system. Very very cool. Here is a Youtube video that explains it way better than I can:


        See if you can spot the "mistake".

        Which got me thinking that it should be possible to make a simple knockoff. Even 0.0005" inch accuracy would be a huge help.



        • #5
          That is a very useful addition to a boring head. I made something that used a similar principle to provide a fine adjustment for between centres boring. There is a double eccentric inside and to adjust you turn the centre via the flats. I have modified it a bit since this photo was taken.



          • #6
            Interesting looking tool, Bill. How does one 'bore' between centers? I've done a lot of simple turning between centers but that's it.


            • #7
              One way to "bore between centers" is to mount the boring bar between centers, the bar is driven by a dog at the spindle. The work is mounted on the cross slide or compound. The cutter is a piece of HSS (or your material of choice) mounted in the center of the boring bar. If you have a copy of How to Run a Lathe there is a description with pictures in there somewhere.

              I don't know if that is what willmac meant with the tool he is showing. I am hoping he will tell us more :hint: :hint:



              • #8
                Yes, Void has it right.

                The big advantage of boring between centres is that you will end up with a parallel bore unless you do something seriously wrong. Normally you set the cut by advancing the tool within the bar, typically using some kind of screw arrangement.

                To get a finer adjustment, you can offset either of the centres. Often this is done by offsetting the tailstock but this means that you have to get it aligned again afterwards. Another approach is to use a centre mounted in a boring head in the tailstock. This is OK, but you need a suitable sized boring head, set up correctly. In either case a bell centre drill is used to get a centre hole that can be offset angularly a little without interference.

                See below for a between centres boring setup. This is an extreme example of using a Myford lathe way beyond its normal limits.

                Note that in this case I did not use my eccentric offset tool, because there was not enough room to get the full length of the cut.

                My tool uses the same principle of fine adjustment that the OP has in his boring head.

                Hope that is clear, if not please ask.