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Thread: AL960B level and alignment
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3rd Oct 2018, 09:11 PM #16Most Valued Member
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.......... assuming your test bar is perfect.
Taiwanese lathes are OK. I'm not sure what my very well looked after Chipmaster would show on a test bar 12" out from the spindle. One tiny bruise could throw it out more than that.
Get a chunk of aluminium round bar around 32-40mm diameter, grip it in a decent (ie not bell-mouthed) chuck and take a cut over it with a nice sharp tool to clean it up. Then take another cut of say 0.5mm. Mike it 25mm from the chuck jaws and 200mm from the chuck jaws. Tell us what you get. That'll tell you if it's turning parallel.
If you want to chase down rabbit holes WRT the accuracy (or otherwise) of your headstock spindle Morse taper socket, have at it, but IMO it's pretty pointless. I've NEVER put anything in mine in many, many years, not even a dead centre (and if I did the first thing I'd do is take a cut over it to true it anyway).
PDW
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3rd Oct 2018, 09:14 PM #17Novice
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I considered that and wiped it well each time before re-inserting the PTB. I tried giving it some gentle persuasion that Shed suggested, but the .0015 was the best I could get making sure it was home in the taper with a rubber mallet. I'll try again to be sure.
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3rd Oct 2018, 09:20 PM #18Novice
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G'day PDW. I'm not sure I understand properly. Is this test different to the first I did at the start of the thread?
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3rd Oct 2018, 09:27 PM #19
Hi Guys,
If I could get one and a half thou at 12 inches out on my Myford, I would be very happy !Best Regards:
Baron J.
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3rd Oct 2018, 09:31 PM #20Most Valued Member
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I wouldnt sweat .001 in 12 inches on a light taiwanese lathe, i dont think it, or any other even fancy lathe of the same size would reliably hold much better than that over long term thermal cycling and use. I would start using the machine and when a use case comes up that you need less taper than that, tweak it in on a case by case basis.
Spend your precious time making good parts.
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3rd Oct 2018, 09:35 PM #21Most Valued Member
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Not necessarily, my guess is that all this is telling you is that there is a very slight difference in the angle of the tapers.
I am not very good at explaining what I am thinking so bare with me.
Now bring the high spot around and stick your thumb beside the DTI on the test bar and give it a little push, you need to split the difference that you have there, so if you have 2 thou run out give the bar a bit of a shove until the DTI shows 1 thou, spin it around and see what you have, do it again if you need to.
This might sound a bit rough but you won't bend the bar and given that (in my mind) the tapers are unlikely to be EXACTLY the same you can get a bit of movement, this method has worked for me.
cheers, shed
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3rd Oct 2018, 09:40 PM #22Most Valued Member
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3rd Oct 2018, 09:55 PM #23Novice
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Thanks guys. Sounds like I was expecting too much. I thought tests on a parallel test bar in the spindle taper should definitely fall within tolerance specs from the manufacturer, otherwise what’s the point of using a PTB. Fells like a waste of money now.... lol. Shed, thanks again, I’ll retry seating the PTB lightly.
All else failing, I’ll align the headstock simply using the 2 collar method?
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3rd Oct 2018, 10:04 PM #24
Hi Dennis,
I think a lot of the specifications that come with Chinese/Taiwanese machines is a little artificial. I can't see those people spending any more time than they have to, checking every single machine. As you are finding out, it takes a good deal of care and a lot of time to do the tests needed to verify even the most basic parameters.Best Regards:
Baron J.
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3rd Oct 2018, 11:15 PM #25Most Valued Member
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the real value of the test bar comes in the first case when you need to check tailstock alignment. also its always good to have something you know to be cylindrical.
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6th Oct 2018, 09:18 AM #26Novice
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Gday Shed, thanks so much for your advice on PTB setup. Worked a treat.
https://youtu.be/_slWpYhAXis
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6th Oct 2018, 10:18 AM #27Novice
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I ended up severely reducing the error in the head stock alignment, via a DTI, simply by loosening and re-tightening the head stock mounting bolts. I didn’t have to touch the adjusting screws. I wonder if the error was due to some tension that might have been induced all the time the machine had been moved after factory setup.
I’ll try the 2 collar test again now and see where it’s at.
https://youtu.be/TytjLaYxdmQ
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6th Oct 2018, 11:17 AM #28Most Valued Member
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Somewhere I recall reading about so-called 'torque alignment' which I think basically came down to, the HS wasn't scrape mated to the bed and by selectively tightening the bolts you could tweak it into alignment.
Needless to say this is highly subject to problems but if it's worked for you - bonus. Don't touch it, hope it doesn't shift over time and that nothing else changes either......
PDW
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6th Oct 2018, 12:17 PM #29Novice
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After The adjustment, the first 2 collar test was 0.0009”. Using RDM with only slight tweaks to the tailstock front foot, my 4th pass gave 0.00000” difference. So happy now. Thank you all for your good advice.
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6th Oct 2018, 07:57 PM #30Most Valued Member
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Don't tell your mrs or else you won't have an excuse to buy a cylindrical grinder.
cheers, shed
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