Harrison M300 center lathe taper turning
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  1. #1
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    Default Harrison M300 center lathe taper turning

    The Harrison M300 lathe at work is fitted with the correct taper turning attachment and it has been for some years.
    However, nobody has ever had much reason to use it so it has been sitting connected to the machine dormant for a number of years.
    I have been tasked with setting it up for use to cut a 1.5deg angle on steel.
    While I have set the machine as well as I can to do this, it doesn't seem to be cutting right.

    I am unable to get a flat surface and even when I get close, the surface finish leaves a lot to be desired.

    I have made sure that all the surfaces are cleaned and lubricated correctly and that it moves relatively freely when being turned without feed on.

    Is there any pinch bolts or something I might be missing? Nobody on site seems to have any recollection.

    the machine cuts parallel diameters fine with reasonably high accuracy.

    Thanks in advance
    Marshall

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    For 1.5 degrees can’t you just offset the tail stock?

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    I probably could do for this angle, but it would be useful to know for future reference and steeper angles

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    Which way are you cutting the taper, from small to large, or large to small?

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    I'm cutting it from small to large

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    Have you taken out the backlash? Does the taper finish on o/d? If yes what tool are you using,home made or insert? Is the tool on centre?

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    I have taken out the backlash, yes
    The trial taper I have been cutting finishes clear of the job
    I using an insert cutter that I know to work well when parallel turning
    and
    Yes, the tool is on centre

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    The factory manual has no real information about how to operate the lathe. Just exploded parts diagrams and a lube chart.
    It can be found online if wanted.

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    Quote Originally Posted by MarshallCAV View Post
    I'm cutting it from small to large
    Try large to small, that way all the forces are in one direction.

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    Quote Originally Posted by Bill D View Post
    The factory manual has no real information about how to operate the lathe. Just exploded parts diagrams and a lube chart.
    It can be found online if wanted.
    That's the problem I have been finding, despite a long time of looking!

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    You need to take the backlash out the opposite way that you would think.
    IOW, overshoot your mark (smaller), then dial back to it.

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    Quote Originally Posted by Booze Daily View Post
    You need to take the backlash out the opposite way that you would think.
    IOW, overshoot your mark (smaller), then dial back to it.
    That has made an improvement, but it still isn't quite right.

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    Quote Originally Posted by Booze Daily View Post
    You need to take the backlash out the opposite way that you would think.
    IOW, overshoot your mark (smaller), then dial back to it.
    Is this always the case, or just for tapers? I cut some tapers last weekend taking the backlash out going towards the work, and it worked just fine. More taper work this coming weekend, so if I'm doing it wrong, I'll try the other way. Could be tricky at the knee of a mid piece taper change.

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    At the start of the taper cutting process you should see a demonstration of how the DOC affects surface finish. When you start making the taper the DOC will be very thin at the big end, and the surface finish will be poor. As you progress towards the small end, the DOC increases, and the surface finish improves.

    Don't rough the whole section to the large OD and then try to add the taper or you'll never get a decent finish at the large end.

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    Quote Originally Posted by NRDock View Post
    Is this always the case, or just for tapers? I cut some tapers last weekend taking the backlash out going towards the work, and it worked just fine. More taper work this coming weekend, so if I'm doing it wrong, I'll try the other way. Could be tricky at the knee of a mid piece taper change.

    The taper attachment pushes the cross slide toward you, so I always take the backlash out toward me. I also lock the compound down.

    I’ve only used a taper attachment a few times, so this is the best I can remember.

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    If the taper turning attachment has sat for many years without being used it needs stripping, cleaning, re-lubrication and careful re-assembly with proper attention to setting the gibs correctly. These are precision devices and its unreasonable to expect them to work just like that after years of neglect. I'm always amazed by the amount of time people will spend fiddling and fidgeting with something that clearly isn't working properly rather than simply servicing it and setting it up so it has a chance.

    Your reported symptoms are classic for a unit of this type not moving freely.

    As you know the Harrison taper turning unit hangs of the back of the saddle and works via a stacked pair of plates. The upper, parallel sided, plate swivels to set the taper with a shoe running on it to shift the cross slide. The lower, dovetail sided, plate runs in a carrier fixed to the back of the saddle with matching dovetails. A stout rod runs back to a fitting clamped on the bed to hold the lower plate still when taper turning. Clearly any friction due to lack of lubrication or poor alignment will try to twist the saddle. Being overhung from the back of the saddle the taper turning attachment has considerable leverage so if things aren't moving smoothly there will be a stick-shift balance between the cutting forces and any momentary increase in resistance to movement of the taper turning unit leading to poor finish.

    Besides servicing the taper turning attachment it would be wise to clean off the underside of the bed where the anti lift keeper gibs run and verify proper setting of these. Ideally the keepers should be removed and cleaned too but I'm fairly sure thats a right pain and may be a job too far. Generally they are never looked at and rarely lubricated. Its common to find considerable old oil varnish and general grunge on both bed and strips.

    Do verify that the telescopic feedscrew is working correctly and moving freely. Its important that the shoe running along the taper guide bar moves smoothly and without shake both vertically and horizontally both on the bar and in the carrier.

    When you put it back together make sure the tie rod connection to the bed clamp is correctly adjusted so the rod sits level and parallel to the dovetail carrier on the saddle. If you think that carrier has been taken off or is not an original factory fit best to check that the dovetails actually are parallel to the bed both horizontally and vertically. If they are not it will never run freely.

    If the unit is really sticky the twisting forces may even be sufficient to alter the taper angle. I have seen this particular effect with a late model toolroom SouthBend Heavy 10 having a similar style of taper turning unit using two dovetail plates rather than one dovetail and one parallel. A bad design as clearly the slightest misalignment in any plane will lead to considerable friction. The SouthBend has no keeper bearings or gibs under the front of the saddle so any excess friction in the taper turning unit could easily and visibly twist the saddle. That particular unit had been removed and refitted by a person who didn't quite understand how it all went together with some fairly subtle mistakes under the obvious errors. I took me most of a day to get it behaving itself. Worth it in the end as it proved capable of cutting morse tapers with essentially no error detectable by ordinary bluing test methods.

    Clive
    Last edited by Clive603; 10-03-2019 at 01:03 PM.

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    Was the lathe cutting well on non-taper work before you started?
    Bill D

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    Quote Originally Posted by Bill D View Post
    Was the lathe cutting well on non-taper work before you started?
    Bill D
    Yes it was, and it has done since


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