Qctp build ?s

Discussion in 'Tools' started by Naiveambition, Mar 15, 2019.

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  1. Mar 15, 2019 #1

    Naiveambition

    Naiveambition

    Naiveambition

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    ive been building a quick change toolpost for my Southbend and my 7x10. I picked up a rough set of free plans on the net. The 7x10 is made to plans, and with the SB ,I increased the cam rod inside and outside diameters to offer more area to tighten on the bottom flange, made a little taller, and sized the top nut so I can use my tail stock wrench to tighten. I think it's the only tool that's always in it place lol.

    Anyways what's a common clearance for the holders . I have .037 when tightened with a pushrod style cam.
    And is their a optimum angle the cam should be to offer more holding force , or not?
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  2. Mar 18, 2019 at 4:38 AM #2

    Wizard69

    Wizard69

    Wizard69

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    I’m not sure which clearance you are talking about but if you are talking dovetails I’d keep them as tight as reasonable. You want to avoid large gaps that would allow the tool holders to rock. A couple of thousands might be a good target. Basically tally a good sliding fit.

    Note that this is for plunger type tool posts. Systems that use tapered dovetail licks obviously can accommodate greater allowances.
     
  3. Mar 19, 2019 at 4:19 AM #3

    velocette

    velocette

    velocette

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    There is a shelf full of tool holders in my shop plus a couple of QCTP's . The Eccentric cam has a lift of 2 mm on a 50 diameter with the clearance dovetails varies a bit from 0.1 mm to 0.4 mm measured on the taper not with the plunger extended The taper on the cam is self locking to a Bronze plunger. Mark the position of the cam at it's lowest point with corresponding mark on the toolpost. I found this out the hard way. A 60 Degree taper on the bottom of the dovetail will push the plunger back.
     
  4. Mar 22, 2019 at 6:20 AM #4

    Naiveambition

    Naiveambition

    Naiveambition

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    thanks for the replies, I was able to finish all the peices.
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    I did remake the dovetails to a pretty close fit using the block as a guage when cutting holders dovetail. I have maybe a 1/4 of a turn and It locks nicely I think it measured somewhere around .025 fully locked.
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    I also increased the contact area of the plunger and located it in-line with the lathe center height. At the time I made the plunger, there was now way to remove it after swarf etc. accumalated so I created a small slot to aid in removal. Later after redoing the holders, the plunger can now be removed simply by turning the cam a full rotation.
    I have never seen or used a qctp in real life so I have yet to know their pros and cons. I did try some alum real quick with acceptable results , stainless and the crappy steel I seem to find will be the next test.
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