Thread: AL-320G Tailstock high

Originally Posted by Oldneweng

Tested by Chris, inspected by Jack. Sounds fishy to me. Those stamps are just providing a name. There is no signature. Under our laws, that document would be worthless. It could be printed and stamped by anyone.
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Dean

I have a Southbend 10K inspection record before me. three pages long. Signed at the bottom with a rubber stamp reading "Inspector No. 1". The first page has model, serial number, size and date on it. Of course, South Bend was a reputable and large maker. But according to your criteria, it would be equally worthless under our laws?

Here the inspection record from an Australian made lathe:

Hercus_4935.jpg

It has a signature and date, but no place (except for the address in the header). Does that make it worthless under our laws?


I am no lawyer, but believe the point is this:

An inspection certificate is not required to be a legal document. It can be in certain cases, for example if it is included in the purchase contract of a large machine tool, that gets installed by the maker on site, and the inspection record is filled in by both the supplier and the customer and signed by both. Usually this signature would also trigger the start of the warranty period and realease of full payment.

If talking basic bench lathes or rotary tables, the inspection record is only worth exactly as much, as you trust the manufacturer. If you do not trust the manufacturer, then having or not having an inspection record is irrelevant, is it? One may then ask however, why would one in the first place buy a new machine from a maker that one has no trust in???

Originally Posted by cba_melbourne

I do it all the time. But I clamp my DTI directly into a spindle mounted chuck, to avoid any gravity droop. And I run the DTI tip directly on the inside of the tailstock taper, thus avoiding arbor imperfections. Taht is the setup I also use to return the TS after having it offset for taper turning.

The OP probably only had a DI at his disposal. I agree the setup he came up with has quite a big overhang from the spindle and may be somewhat affected by gravity. It would indeed make the TS seem high, maybe by 0.01 or 0.02mm.

You may well do it all the time, but that doesn't make it any more correct. You also cannot "avoid" gravity by doing it the way you do it, it's just that the effects of gravity are reduced. The shorter and more rigid the setup, the less the effects of the droop, nevertheless any setup will still droop somewhat as it's swung around the bore. Hence the appropriate way to check tailstock height is to measure off a test bar at the HS and TS ends and compare the two

Originally Posted by Pete F

You may well do it all the time, but that doesn't make it any more correct. You also cannot "avoid" gravity by doing it the way you do it, it's just that the effects of gravity are reduced. The shorter and more rigid the setup, the less the effects of the droop, nevertheless any setup will still droop somewhat as it's swung around the bore. Hence the appropriate way to check tailstock height is to measure off a test bar at the HS and TS ends and compare the two

Pete, is that so? I just put my DTI on a scale. Including the stubby shaft to clamp it in a chuck. It weighs 52 grams all up.

1.jpg2.jpg

Here a pic of the setup I have always used to test TS alignment. Do you think the 52 grams would make it droop enough to change its reading? I somehow struggle to believe that.

BTW, I use an old shaving mirror to read the DTI when the face is against the splash guard, as in the second picture.

Sorry for the late reply re test certificate for my AL-320G lathe. I am away travelling the back blocks and don't always have access to the internet due to no Telstra mobile phone coverage where I am camped.
I don't believe that there was any test certificate supplied with my lathe, the only paperwork included being a manual in Chinglish. I took delivery of the lathe in its crate direct from H & F, therefore I assume that there never was a test certificate for it. I can't check in my records as at the moment I'm on the other side of Oz to my workshop.

Alan

Originally Posted by cba_melbourne

Pete, is that so? I just put my DTI on a scale. Including the stubby shaft to clamp it in a chuck. It weighs 52 grams all up.

Here a pic of the setup I have always used to test TS alignment. Do you think the 52 grams would make it droop enough to change its reading? I somehow struggle to believe that.

As I mentioned, just because you do it all the time doesn't make it correct Chris. As I also mentioned the more rigid the setup, the less the indication will be affected by the droop, and what you're doing there is indeed extremely rigid. But yes, it is so Chris. It will still droop. You can't fight physics. Put a more sensitive DTI on there if you don't believe me.

Now it may well be that the variation between the two will be within your personal limits, or even a lathe of this class, and that's fine. It may also be an excellent way to get a ballpark idea of where the tailstock may be sitting. However the "correct" way to accurately indicate tailstock height is as I described, although I don't claim any particular brilliance in that area, and the process has now been replicated here many times over the past few days as people post pictures of their lathe test certificates. Guess what, it shows tailstock height being tested by sweeping along the top of a test bar between centres. As pioneered by Da Man himself, Schlesinger.

Originally Posted by cba_melbourne

I have a Southbend 10K inspection record before me. three pages long. Signed at the bottom with a rubber stamp reading "Inspector No. 1". The first page has model, serial number, size and date on it. Of course, South Bend was a reputable and large maker. But according to your criteria, it would be equally worthless under our laws?

Here the inspection record from an Australian made lathe:

Hercus_4935.jpg

It has a signature and date, but no place (except for the address in the header). Does that make it worthless under our laws?


I am no lawyer, but believe the point is this:

An inspection certificate is not required to be a legal document. It can be in certain cases, for example if it is included in the purchase contract of a large machine tool, that gets installed by the maker on site, and the inspection record is filled in by both the supplier and the customer and signed by both. Usually this signature would also trigger the start of the warranty period and realease of full payment.

If talking basic bench lathes or rotary tables, the inspection record is only worth exactly as much, as you trust the manufacturer. If you do not trust the manufacturer, then having or not having an inspection record is irrelevant, is it? One may then ask however, why would one in the first place buy a new machine from a maker that one has no trust in???

With all due respect, this was just a friendly discussion. Count me out. Go play games with someone else.

Dean

Originally Posted by Pete F

As I mentioned, just because you do it all the time doesn't make it correct Chris.

Look, the "correct" method to align the TS depends on circumstances.

to completely test a TS using Georg Schlesinger's setup you need to make 5 measurements using 3 setups and two different test bars:
- a between centers test bar
- a morse taper test bar to suit your TS

The two test bars should be of high quality, otherwise these would introduce additional errors. See below the relevant extracts from Schlesinger's book "testing machine tools".

TS_SCHLESINGER_1.gifTS_SCHLESINGER_2.gif

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With the method that I proposed, the same alignments can be done in one single setup, and using no test bars at all. It is the method of choice for those of us that do not own test bars, but still want a more accurate alignment than the "razor blade" method. I am confident that the minuscule error introduced by gravity is for all practical purposes negligible. Taking all the measurements for a complete TS test will take somewhat longer though. It is necessary to sweep with the DTI first around and along the outside of the TS Barrel, then sweep around the taper inside the barrel at two different depths a known distance apart.

1.jpg



******************************************************


In the case an older lathe with bed wear is tested, one needs to be aware of following:

- Using the chuck mounted DTI methol, you measure the tailstock close to the spindle, where bed wear is greatest. This may be of advantage for tasks like precision drilling small holes, but may be of disadvantage for tasks like turning long items between centres.
- Using Schlesinger's method, the opposite will apply.

Gkd. I knew this thread was going to become painful long aftrr the OP questions were answered!

Originally Posted by cba_melbourne

Look, the "correct" method to align the TS depends on circumstances.

to completely test a TS using Georg Schlesinger's setup you need to make 5 measurements using 3 setups and two different test bars:
- a between centers test bar
- a morse taper test bar to suit your TS

The two test bars should be of high quality, otherwise these would introduce additional errors. See below the relevant extracts from Schlesinger's book "testing machine tools"

With the method that I proposed, the same alignments can be done in one single setup, and using no test bars at all. It is the method of choice for those of us that do not own test bars, but still want a more accurate alignment than the "razor blade" method.

In the case an older lathe with bed wear is tested, one needs to be aware of following:

- Using the chuck mounted DTI methol, you measure the tailstock close to the spindle, where bed wear is greatest. This may be of advantage for tasks like precision drilling small holes, but may be of disadvantage for tasks like turning long items between centres.
- Using Schlesinger's method, the opposite will apply.

Chris I don't even know why you're arguing about this. By your own admission the indicator will droop, if you don't own a more sensitive indicator you may not be able to see it for yourself, in which case you'll just have to take my, and Isaac Newton's word for it, but trust us, it will droop. You are not Robinson Crusoe I'm afraid, and many of us witness first hand the droop. I also normally use the sweep method to align lateral tailstock offset, and obviously sweep through top and bottom. If the setup is rigid, the droop won't be much, but it will still droop. Wait am I repeating myself here? Why you would want to use a method that is known to be inaccurate I'm at a complete loss to understand. I have already offered a way where a commercial test bar isn't needed if a bar is instead flipped end for end.

The test for tailstock HEIGHT ie what is being discussed here, does not require 5 measurements and 3 setups as you suggest, it is just one setup. The other tests measure completely different aspects of the tailstock alignment and condition. You are apparently confusing what may happen if they are not in tolerance. The appropriate test for HEIGHT is diagram 12 you supplied.

Sorry Chris but your final comment about how far the measurements are from the headstock is complete and utter rubbish, and with due respect I'm left to conclude that you've never progressed past Googling any of this. In the diagrams, the test bar is shown as quite a long bar, however for the purpose of checking TS height it doesn't need to be, and it can be virtually any length you choose (until it gets stupidly short). The only purpose of the test bar is to transfer the height of the centre to a point where it can be accurately measured. That is why the "cheat" I suggested for using a shop-made "test bar" is still accurate, as it serves only to transfer that two centre heights, those if the HS and the TS.

Originally Posted by Pete F

Chris I don't even know why you're arguing about this. By your own admission the indicator will droop, ................................

Ok Pete, you seem really hypnotized by this gravity droop. Let's put some figures about how much a DTI droops under its own weight. A little experiment:


20140721_162259.jpg

Same setup for measuring tailstock height. Left the 0.01mm resolution DTI in the lathe chuck. It weighs 55g with the stem. Right a 0.002mm resolution DTI, its scale zeroed onto the left DTI.

now lets add a weight that simulates gravity. I just had this 44g weight handy. To simulate the effect of gravity, I would only need be half the 55g, as the DTI is cantilevered in the chuck.

20140721_162328.jpg

The "droop" is a ridiculously small 0.002mm. It is absolutely irrelevant in the context of tailstock height adjustment. Even if one owned a Schaublin or a Hardinge HLV and were turning/drilling parts for an electron microscope, nobody would care about 0.002mm when setting tailstock height.

Originally Posted by Pete F

As I mentioned, just because you do it all the time doesn't make it correct Chris. As I also mentioned the more rigid the setup, the less the indication will be affected by the droop, and what you're doing there is indeed extremely rigid. But yes, it is so Chris. It will still droop. You can't fight physics. Put a more sensitive DTI on there if you don't believe me.

Now it may well be that the variation between the two will be within your personal limits, or even a lathe of this class, and that's fine. It may also be an excellent way to get a ballpark idea of where the tailstock may be sitting. However the "correct" way to accurately indicate tailstock height is as I described, although I don't claim any particular brilliance in that area, and the process has now been replicated here many times over the past few days as people post pictures of their lathe test certificates. Guess what, it shows tailstock height being tested by sweeping along the top of a test bar between centres. As pioneered by Da Man himself, Schlesinger.

Chris I am not "hypnotised" by physics, and this could go on forever, so to shortcut the process, perhaps you could just advise what you don't understand in the above statement? I'd like to bold the part where I stated that the more rigid the setup the less it will droop etc, but I'm away and using my ipad so don't know how to do whole paragraphs.

It seems that you accept that the indicator will droop, as you've gone to great lengths to prove that. It seems that you accept that the correct method of measuring tailstock height is with a test bar, as you again went to great lengths to publish the actual Schlesinger process to do so. So I'm completely perplexed as to the purpose of your post. Do you honestly believe the likes of Schlesinger hadn't thought of sweeping the bore and checking vertical displacement that way? Or none if us since him?

From what I could see from the picture I'd suggest much if the OPs "problem" with his lathe in the first instance was due to sweeping the bore, exactly as you described, but with a much less rigid setup. That's the issue with advocating methods that are just plain wrong. You may be able to minimise the errors by an extremely rigid setup, but the errors are still there by the simple fact if the process. Along comes another person who doesn't understand the importance of maximising the rigidity to minimise those errors and next thing he's taking an angle grinder to his tailstock to "fix the problem". The reasons for using the sweeping method are also just plain wrong. To do the process the correct way a test bar is needed but it need not be a super accurate test bar if it is reversed with the reading. Either way it eliminates the very errors that you so carefully measured.

Text book bit of metrology there. Stylus hitting at about 11 o'clock and not top dead centre. Pissy little journal, and a flat at that. What would happen if you bumped the chuck, whilst you were putting the weight on? Have you consideered what an angular change, would be, when you rotate a flat like that.

Try it again, but on a known concentric journal.

Originally Posted by Pete F

............. It seems that you accept that the correct method of measuring tailstock height is with a test bar, as you again went to great lengths to publish the actual Schlesinger process to do so...........

Hi Pete. This will interest you. Just a few pages further down in Georg Schlesingers book "Testing Machine Tools" the master shows he tests turret lathes. Have a good look at figure 6, 7 and 8 .. Isnt that the same setup, that you claim suffers from gravitational sag? I take this to mean, that the two methods are interchangeable - there is no right or wrong method, both do the job equally well.

Schlesinger_Turret.jpg

Oh FFS, Chris, let it go!

I'm not "claiming" there will be indicator sag. There WILL be indicator sag. You know that, you measured that, you posted that.

As far as why there is a difference in the measuring process between these two types of lathes, I'll let you figure that one out for yourself. But here's a hint, one is a centre lathe, the other is a turret lathe.

I'm sorry but I don't mean to be rude, however I've posted the correct way to measure tailstock height for this type of lathe. You copied and pasted from Schlesinger the correct way to measure tailstock height. If you want to do it another way because you think you know better than the rest of the world, then knock yourself out, but please don't address any further arguments to me on the topic as I've wasted enough of my time on those who will not listen to what is being said.