Two collar test - how close is close enough?

Tony Wells said:
BTW, these tests are done with spindle stopped.
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LOL! I think my brain was still asleep when I read your reply this morning... I couldn't, for the life of me, follow what you were telling me. I reread it later in the morning and understood it fine.
 
Thank you all for the help! The answers Holescreek and Tony gave led me to some tests that reassured me the main was not badly worn. The answer JR 49 gave led me to try adjusting the front foot. I gave it a half dozen cranks and took another cut. When I measured that y ime, t he unsupported end was smaller so I knew I had gone too far and adjusted back the other way.

My micrometer is accurate to .001 but has .0005 marks. I now have the difference down to less than .0005 over 6"
 
Skelso, Thanks for saying that my answer helped. As a total beginner, this is the first time I have been able to answer a machining question. I would like to thank all the "pros" on this forum, because, the little bit of machining know-how I have learned, was ALL from this great forum. Thanks to all, and happy New Year, JR49
 
I never do test collars/diametrs with unsupported ends.
for true readings must be done between centers(not a chuck and a center)
center tailstock to spindle first
 
To answer the question I shoot for a difference of 0.
usually the test bar unsupported will show the alignment of the headstock. the larger end at the tailstock end indicates the headstock 'aimed" away from the operator. If you try to "fix" a missalignment with jack screws, you are only jacking the lathe around unless it is bolted down at the center point on both ends them you can address a twisted bed.
usully lathe missalignment is at the head or tail stocks and not to hard to fix, unless its badly worn.
this is my personal findings with my Voest (my big lathe) and my clausing 1236vs (small lathe) your milage may vary
 
rick9345 said:
I never do test collars/diametrs with unsupported ends.
for true readings must be done between centers(not a chuck and a center)
center tailstock to spindle first
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I would think that you're penalizing yourself unnecessarily by adding yet another variable to be considered. Is the error due to headstock misalignment ? Bed wear ? Tailstock alignment ? Any combination or all ? It's admirable if one can deal with all of that but I'll stick with a simpler model - no tailstock center - to minimize the number of problems I need to think about.

After obtaining satisfactory results, the two-collar test bar can be carefully bored for centers and then used for tailstock alignment.
 
randyc said:
I would think that you're penalizing yourself unnecessarily by adding yet another variable to be considered. Is the error due to headstock misalignment ? Bed wear ? Tailstock alignment ? Any combination or all ? It's admirable if one can deal with all of that but I'll stick with a simpler model - no tailstock center - to minimize the number of problems I need to think about.

After obtaining satisfactory results, the two-collar test bar can be carefully bored for centers and then used for tailstock alignment.
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I was answering for the bed leveling/twist.
I use a hardendened/ground bar DTI both at chuck and out 6 in , then run DTI horizantally both side and top to check headstock. I have had success algining tailstock with DTI mounted on/at chuck. The ground bar(mine is 2 in) can be extended out 12 in and with DTI on bar outer end one can visually watch twist as feet are adjusted. Finialized with 2 collar test.

I agree I skipped a step. Thanks you caught it.
The important thing is to devlope a repeatable method that gets one to their desired level of accuracy. There are many methods. Equipment at hand kinda dictates the method.
 
I collected enough parts to actually measure my ways with a DTI, that round bar on the inverted V is cast iron that I chucked up in the mill, its a copy of the King way alignment tool. I used a .0005 DTI, but I also have a .0001 that seemed to jump around a lot when I rolled it along the ways. I found that a light coat of oil also stopped the chatter when using the tool. Tim
http://www.hobby-machinist.com/attachments/front-way-jpg.72188/
 
astjp2 said:
I collected enough parts to actually measure my ways with a DTI, that round bar on the inverted V is cast iron that I chucked up in the mill, its a copy of the King way alignment tool. I used a .0005 DTI, but I also have a .0001 that seemed to jump around a lot when I rolled it along the ways. I found that a light coat of oil also stopped the chatter when using the tool. Tim
http://www.hobby-machinist.com/attachments/front-way-jpg.72188/
Click to expand...

That is a neat tool and very ingenious. If you're referring to Richard King (KingWay), I'm proud to claim him as an acquaintance if not as a friend. Can you provide a link to Rich's tool, I'd very much like to see it !

Very nice work, nice setup and a good suggestion regarding the oil coating ! I'll be interested in your future findings :)
 
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