Backplate runout
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  1. #1
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    Default Backplate runout

    I've been workin on cleaning up my import backplates , I have the one for the 6" 3 jaw down to .0015 . am I chasing my tail
    trying to get it better then that for a 9A late ?
    tks
    animal

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    how are you checking it?
    (with what, how are you turning the spindle, ect)

    is it always in the same place no matter what?

    sometimes even a hard spot can cause the tool to not quite cut the same as the rest and look like runout.

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    I've been usin a hand crank I made that goes in the outboard spindle & have a indicator mounted on the compound with the saddle locked & the cross & compound gib's tight.
    am I doing this right ? if not please let me know what to change
    tks
    animal

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    i wouldnt say youre doing anything wrong.
    its just .0015 is really that small and seemingly insignificant things add up.

    for giggles try it under power in the slowest backgear speed just to see if its the same.

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    You SHOULD make your measurements under power. The reason is that a layer of oil forms between the spindle and the bearings (give it a couple of seconds to stabilize when you power on). Turning the spindle by hand doesn't give the oil enough time to distribute evenly, giving you poor readings.

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    ok , got my homework . will check tomorrow under power
    tks
    animal

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    so I ran it last nite, warmed it up for @ 10 minute's & ended up with @ .0012 , that was with a .001 dial indicator & a B&S 7030-5 test indicator . was done in back gear with bearing cap temp's of 53 F on the chuck side & 55 F on the outboard side .
    tks
    animal

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    what do you see on the spindle itself?

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    on the end of the spindle nose I read <0.0005
    animal

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    Quote Originally Posted by animal12 View Post
    on the end of the spindle nose I read <0.0005
    animal
    Do NOT put an indicator on the backplate under power.

    I am imagining the following that you are doing, correct me if anything is wrong:

    1) you remove the backplate from the chuck, and thread the backplate on the spindle.
    It nees to seat fully on the register diameter and bottom on the spindle. There should
    be no light visible under the joint.

    2) you take a thin facing cut off the front of the backplate. Possibly a skim cut on the OD.

    3) you stop the lathe and put an dial indicator on the face, and rotate the spindle by hand, looking
    at the total runout after the facing cut. This should be zero within a few ten thousanths depending
    on the surface roughness.

    4) most lathes are set up to face somewhat concave.

    Let me know if the series of events is what you are seeing.

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    I have made gauges that had to be down in the sub microns and have honed, compounded, lapped and polished them to near zero. taking a tenth off a part is not difficult. Even .0015 is possible.
    But for anything that has to come off and back on one should map the error... then remount and map it again.
    I would use a very sharp positive top rake bit or insert and try to skim off 001...but after I reinstalled and mapped it...this to see if it takes from the high place.

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    Might be a defective backplate?
    I had to send one back to Shars that was terrible...
    Threads were not cut perpendicular to the backplate. It would not seat properly on the register. Wobbled like a drunken sailor when I screwed it onto the spindle.

    Wondering if it might help to screw the backplate on "backwards"- true the register that seats on the spindle first, then flip it around to face the usual surfaces?

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    Quote Originally Posted by tobnpr View Post
    Might be a defective backplate?
    I had to send one back to Shars that was terrible...
    Threads were not cut perpendicular to the backplate. It would not seat properly on the register. Wobbled like a drunken sailor when I screwed it onto the spindle.

    Wondering if it might help to screw the backplate on "backwards"- true the register that seats on the spindle first, then flip it around to face the usual surfaces?
    I' ve done that in the past - the reversed backplate to true and bore as needed.

    1) not sure from the description if this is called for here, and

    2) when this is done, a spacer ring needs to be made up to account for the lack of counterbore on the front of the plate - and that ring ideally
    needs to be made in one operation without being un-chucked, with the front surface faced and then cut off clean, so front and back
    are dead parallel.

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    Defective back side might show up by bluing up the back side and lightly run it up to register to see the witness in the blue up.. a few sharpie lines may be better than blue.

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    Quote Originally Posted by tobnpr View Post
    Might be a defective backplate?
    I had to send one back to Shars that was terrible...
    Threads were not cut perpendicular to the backplate. It would not seat properly on the register. Wobbled like a drunken sailor when I screwed it onto the spindle.

    Wondering if it might help to screw the backplate on "backwards"- true the register that seats on the spindle first, then flip it around to face the usual surfaces?
    Yep I would try that for sure. Then flip it back over and see what happens.

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    For the ring for the backwards mount, use a bearing race off an old bearing. More parallel than anything I can cut.

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    Considering the quality of your chuck you may find the chuck error and the backplate error cancel out the error. Like iwananew10K said .0015 is not that much. Rotating the chuck on the back plate to find the sweet spot and adding a line up mark may be the better/Ok plan. likely looking to reduce wobble as the adjust true will reduce run out.
    If you have .0005 error in your spindle register it will be very difficult to get the backplate better than .001 run-out with truing the back plate register off a .0005 error because of going from a diameter of about 3" to one about 6".
    *Still good to check that the BP thread is true to the BP register. failing that could cause chatter and all kinds of problems...You could turn an interference thread and check the BP register off that. it would be like a lathe mandrel but having a thread on a very slight taper. Yes, good only one time use if made out of a chuck. Made between centers you can use it again.

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    Finding the BP thread square to the spindle register and wishing to rid the .0015 you might shim with BOPP/cellophane (cigarette) clear film placed in just the right place to error-map the take off from the high place...and take a face skim cut.

    BOPP is about 18um or .0008..likely just enough to rid .0015 going from 3" to 6" dia.

    I used to use it for grinding when a thin boost was needed...also used .001 and .0015 to rig .0005

    Likely you could hand hone .0008 from the BP at one side face of the BP register.
    Likely you could hand hone true the spindle nose register if it is .0005 or whatever out.

    Putting your compound at 1* or 2* you can advance to take only tenths off a facing cut. 1* is about .017 per inch angle so a 1/32 in-feed is only about .0005 toward the face cut. You back out the cross dial and crank in the compound dial..and the use the cross feed to take the cut.

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    Quote Originally Posted by wheels17 View Post
    For the ring for the backwards mount, use a bearing race off an old bearing. More parallel than anything I can cut.
    Nice! I may use this sometime...

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    I had made a couple of rings for the backwards mount , but they must be scared of daylight , cause I sure can't see them anywhere now that I'm lookin for them . I like the bearing idea . I have had problems with backplates fitting one way but when ya turn them around they wont go on . I tried to put the 4 jaw on today from my old Seneca Falls Star Lathe & I can't even get it on a full turn , but it fits on the old lathe just fine. same spindle thread . these china imports have got to be made of cast iron with styrofoam thrown in during the casting process judging from the look of the threads .I was able to get a ok finish using a braised carbide bit with a small radius but still looks likek it needs bondo.
    animal


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