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Thread: lathe test bar
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7th July 2014, 01:26 PM #31GOLD MEMBER
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Of course it matters, even if its "just a ball park". Unless you're saying there is no difference between "about a thou" and "about a 1/10th"
For what its worth they are, if you can be bothered looking up the table.
What?
Stuart
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7th July 2014 01:26 PM # ADSGoogle Adsense Advertisement
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7th July 2014, 02:58 PM #32SENIOR MEMBER
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Thank you Stuart, I hadn't posted on the forum for a long time and thought I'd test the waters by again contributing. Your post was a great reminder as to why I stopped.
While I'm loath to have "Google Experts" waste more of my time, here are two references to what I was referring to. The first from Blake, not that I'd expect they would know anything about co-axial indicators. Note the 5th paragraph ie co-axial indicators are centring devices and are NOT intended for measuring Blake Manufacturing Co.
The Blake CO-AX INDICATOR is a centering device. It requires a reading of both sides of the bore or boss, in each axis, to arrive at the center. It's sole function is to find center. It is NEVER to be used as a measuring instrument.
The end of this article deals with corrections to be made with using different contact point lengths. For what it's worth (ie 9/10ths of sweet FA as it was just a comment in passing) I meant to write shorter contact point but had longer on my mind as I'm buying some longer ones to increase their reach. I'm sure that error made somebody's day
The Point Of Error-Free Measurements : Modern Machine Shop
With that I've had some work cancelled so I'm off to put my nose back in front of a machine. Something I can highly recommend some do a little more of!
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7th July 2014, 06:33 PM #33GOLD MEMBER
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My pleasure, and here was I thinking I was playing nice.
As always a nice little attack at anyone that questions one of your posts. I own one, do you?
Oh I dont know, they might.
Who said anything about using it for anything other than a centering device?
If you dont have at least a "ball park" of what the needle movement means then its a bit of a waste of time. You cant say whether the part is centered within 1mm, 0.01mm or 0.1mm. Now with the blake the greatest error is about 3 times the reading. But if you want the corrections, here they are to the nearest 0.00001"
Blake Manufacturing Co.
Which is why I asked. Yes Swapping to a longer contact point decreases sensitivity, I notice you even picked up on it in the third edit of this post.
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7th July 2014, 06:56 PM #34SENIOR MEMBER
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Whatever Stuart. You clearly have nothing better to do that hover over your computer and count how many times people edit their posts. That's your life to waste and your business.
I thought I'd put up some posts that may help others here. I'm done, you win. I tried.
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7th July 2014, 09:01 PM #35Pink 10EE owner
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I started writing a long essay on lathe alignment, but it all got far too complicated for me to explain... I know how to do it and why you do it but putting it into words that does not bore people senseless is not easy...
So I will just say this...
I have used a handful of lathes... No doubt many here have used a lot more then me... I have used clapped out machines and new machines...
I have found that for 99% of what I do, when I need to turn something parallel, it is only for a very short distance, say for a bearing fit.. Might be 10mm long.. Seldom would have to turn something completely parallel more then 50mm
I have also found when I need to work to high accuracy, I have to tweak the machine to get it there, even on the new ones.. A lathe is just not a very good machine design for making long non tapered cylinders, you seem to have so much working against you... They are a PITA to make them on...
I have noticed in reading magazines and such some commentators go overboard saying my lathe can cut straight 0.00001mm in 300mm... Yea OK, it probably can... Now unclamp the tailstock, move the tailstock barrel to a different position, reclamp and show me your 0.00001mm... You will not see that sort of straightness again until you spend another two days of tweaking...
Sit down and take a realistic look at what tolerances you require over what distance and go from there.. Level the lathe and take test cuts and adjust it to suit..
Know that should something come along that requires some tighter tolerance then usual, keep in mind you will probably have to adjust something to get it done..
There are a lot of traps out there, and remember turning between centres is not something to be left in the last century.. Do not be afraid to do it... Plenty of times I have chucked up a piece, centre drilled, put in the tailstock, turned it, remove the tailstock and "spring"... the workpiece springs to some new shape...
I am only self taught, so take the above at your own risk...Light red, the colour of choice for the discerning man.
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7th July 2014, 10:44 PM #36Philomath in training
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Getting back to the original topic, attached is a PDF from Schlesinger where he discusses test bars. As he points out (and as Phil - Machtool - agrees (so it must be right)) a proper test bar should be hollow otherwise it will droop under self weight.
A centreless ground bar may do in a pinch but as has already been mentioned there are issues with that due to how it is produced.
schlesinger.jpgschlesinger.pdf
Michael
(PS - my test bar is solid but one day...)
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8th July 2014, 03:31 AM #37
No idea how good they are, Lathe Alignment Test Bars
I'm not in the market for one at present, but then again, I'm not rebuilding any lathes at the moment...
Ray
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8th July 2014, 10:03 AM #38Cba
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Michael,
I personally believe it is a matter of scale. Georg Schlesinger lists test bars from MT 15 down to MT 2. Now I like to think, that the smaller test bars like MT2 to MT4 do not really need to be hollow.
The low cost China made test bars ($60 to $150 for MT2...4) that are offered for home shop use are definitely just plain steel. I do not think that anyone could justify the expense of a hollow test bar just for home shop use. Such test bar is typically only needed once when repairing or restoring a lathe or mill, to properly re-assemble. Thereafter it may be used once or twice a year, but only for convenience - there are other ways to verify accuracy that do not require ownership of a test bar.
Of course some people reading this own much larger machines, and will see this differently.
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8th July 2014, 10:05 AM #39Cba
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Michael,
I personally believe it is a matter of scale. Georg Schlesinger lists test bars from MT 15 down to MT 2. Now I like to think, that the smaller test bars like MT2 to MT4 do not really need to be hollow.
The low cost China made test bars ($60 to $150 for MT2...4) that are offered for home shop use are definitely just plain steel. I do not think that anyone could justify the expense of a hollow test bar just for home shop use. Such test bar is typically only needed once when repairing or restoring a lathe or mill, to properly re-assemble. Thereafter it may be used once or twice a year, but only for convenience - there are other ways to verify accuracy that do not require ownership of a test bar.
Of course some people reading this own much larger machines, and will see this differently.
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8th July 2014, 11:04 AM #40
Is the world as we know it, changing in ways we cannot comprehend. Chris just put up 2 copies of the one post. This happened to me yesterday I think it was. Then it starts to get weird. Yesterday I made a phone call to my wife, who was at home when my phone was sitting in my shirt pocket at work, untouched. Even weirder. Last Friday I got a phone call from my wife's mobile phone. It was at the time, in her handbag, turned off, at home in a mobile non-sevice area. I know she was at home because I was talking to her about this on the land line. Someone is playing with my mind!
The low cost China made test bars ($60 to $150 for MT2...4) that are offered for home shop use are definitely just plain steel. I do not think that anyone could justify the expense of a hollow test bar just for home shop use. Such test bar is typically only needed once when repairing or restoring a lathe or mill, to properly re-assemble. Thereafter it may be used once or twice a year, but only for convenience - there are other ways to verify accuracy that do not require ownership of a test bar.
Of course some people reading this own much larger machines, and will see this differently.
Dean
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10th July 2014, 08:31 PM #41SENIOR MEMBER
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I wonder if ground linear rods are any good as cheaper test bars to check headstock/chuck alignment? I noticed some on ebay a few days ago with runout about the same as cheap lathe test bars. They are a lot cheaper than test bars - but no morse taper. I figured these could be a reference point?
SF25 600mm 25mm Hardened Round Shaft Linear Rail ROD Slide Bearing CNC Router | eBay
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