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  • A "heads up"

    Originally posted by hitnmiss
    12 pages of "Mines bigger than yours"


    I don't know what's sadder, the fact that you guys wrote 12 pages or that I read them!
    Thanks hitnmiss.

    Good "get back to reality" post.

    Served me right for being a "smart-ar*e" and a "big-noter"/"skite".

    I guess I deserved and needed that.

    So - how to do it with stuff that can be found in many/most HSM shops?

    It took a bit of looking around for tools and materials and then getting back to first principles and re-focusing on the job at hand - checking the taper reasonably accurately.

    Here we go.

    There are too may pics to post in one go - even with multiple successive posts, so I will do it in one post using direct links to the pics and readers can "click" them (or not) to suit themselves.

    The principles here were and are sound but far too expensive for may HSM shops:

    I will use my HF-45 mill and 2 rotary tables - "Rotabs" - (6" and 8"). The 6" has a 7 1/2" lathe face-plate that I modified to suit my lathe and rotabs.

    Both rotabs are calibrated to read to 5 minutes direct and at least 2 by interpolation. The test sheets show a maximum error of 1 arc minute.

    The 8" has a 10" face-plate that is part of the rotab package.

    My basic idea was to set the MT sleeve and an MT with a chuck "Jarno" taper up to be suspended/fixed between centres in a rotab.

    The centres were made from spare 18mm (3/4") Cold-rolled steel rod that I had. I set them up in the lathe to less than 0.0002" (2 "tenths") Total Indicated Run-out (TIR) with my TDI which is calibrated to 0.01mm (0.0004") and turned the 60 degree tapers. So maximum "run-out" as measured was 0.0001"

    The rotab was set to indicate zero run-out with/along the 20mm centres OD's with the TDI at centre height.

    The work-pieces were to be fitted between the centres to be a light turning fit with no "slack" or "end-float" .
    The rotab reading was to be recorded at that setting (setting 1).

    The rotab was to be rotated until there was zero deflection on the TDI as it was run along the taper by using the mill table "X" lead-screw. This setting was recorded (setting 2).

    The difference/s between the settings was the taper of the work-piece (ie half the included angle) as in the sketches in the first link.

    This worked very well. No clamps were needed. I could have used small bags filled with lead shot over the centres to hold them.

    Checking concentricity and/or run-out was very easy as well.

    In retrospect, I would have done better with the centres made from 2" CR stock - mainly for centre height and weight (for stability).

    The next method was a variation on the first. I used 2 vee blocks (matched set) on the rotab table. The vee blocks were aligned by dropping either a straight round bar or a piece of straight extruded brass angle stock into the vee blocks. The alignment was excellent.

    The centres were placed in the vee blocks and the work was suspended easily without clamping. The blocks did not move on the rotab either. If they had, I would have used paper between the blocks and the rotab table.

    This too worked very well.

    The next pic is a variation on the previous pic. but is set up on the 6" rotab using the brass angle to both keep the vee blocks in alignment as well as providing a very successful extension of the "V" to rest the centres in/on to support the work piece.

    The next pic is another variation making use of the larger (7 1/2") angle plate on the 6" rotab without the brass angle.

    The next pic is a variation of the previous pic except that the brass angle is used.

    The next pic is of using the centres in the top of the "T" slots in the mill table. It was surprisingly accurate and would work as/for a quick check for concentricity for anything that could be held between centres.

    I hope this helps.