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Alignment - yay or nay?
- Thread starter Jaqkar
- Start date
That seems pretty decent to me (0.00047" over ~7.1"). You are in the range where cutting tool / surface finish are as significant if not more.
This might open up a dam of lathe alignment discussion, but I think when the bar has tail stock (TS) support, the readings are more indicative of alignment of both TS & HS at the points of material contact. In other words, your spindle axis may actually be off by a smidge, but the TS center is 'forcing' alignment. Think of it like when we consciously try to cut taper with the offset TS method (although that is between centers vs held on one side by HS chuck). Don't get me wrong, your HS-TS alignment is a great thing. As long as it was the final alignment step after HS alignment to bed was verified.
If you removed the TS support & the bar was cantilevered & cutting yielded equal diameters, that would prove spindle alignment. But of course now we have material deflection issue to contend with. The cutting tool will deflect the bar more at the unsupported TS end vs the supported HS end, TS diameter will read bigger & we have a false reading. The simplest & practical way I know of to independently check HS alignment is with a test bar in the MT socket. Mine is MT3 which fits in MT5 spindle socket. The bar can similarly be used in MT3 tailstock quill.
This might open up a dam of lathe alignment discussion, but I think when the bar has tail stock (TS) support, the readings are more indicative of alignment of both TS & HS at the points of material contact. In other words, your spindle axis may actually be off by a smidge, but the TS center is 'forcing' alignment. Think of it like when we consciously try to cut taper with the offset TS method (although that is between centers vs held on one side by HS chuck). Don't get me wrong, your HS-TS alignment is a great thing. As long as it was the final alignment step after HS alignment to bed was verified.
If you removed the TS support & the bar was cantilevered & cutting yielded equal diameters, that would prove spindle alignment. But of course now we have material deflection issue to contend with. The cutting tool will deflect the bar more at the unsupported TS end vs the supported HS end, TS diameter will read bigger & we have a false reading. The simplest & practical way I know of to independently check HS alignment is with a test bar in the MT socket. Mine is MT3 which fits in MT5 spindle socket. The bar can similarly be used in MT3 tailstock quill.
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The bars are quite reasonably priced on Ebay. Check the reviews beforehand, some make them others 'distribute' them which may or may not be a bad thing like out of spec? For some reason most bars come out of India which is usually <yeesh> quality, but they are as accurate as anything I can measure in my shop. Also parallel bars are available.
The bars are quite reasonably priced on Ebay. Check the reviews beforehand, some make them others 'distribute' them which may or may not be a bad thing like out of spec? For some reason most bars come out of India which is usually <yeesh> quality, but they are as accurate as anything I can measure in my shop. Also parallel bars are available.
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Your latest result doesn't necessarily mean your headstock alignment is bad. Don't expect to install work in a chuck and it to be perfectly in line with the spindle (regardless of the quality of the chuck) -- that's pretty unlikely. If the end is smaller by .055 mm it's quite possible the end of your rod was wobbling as it turned. You need to use a DTI to measure and a soft mallet to bump the rod into alignment BEFORE you do your test cuts. Or use RDM.
Also, .055mm is a hair over .002". Depending on your lathe, .002" over 7" may meet or beat the manufacturer's specification for your model.
Also, .055mm is a hair over .002". Depending on your lathe, .002" over 7" may meet or beat the manufacturer's specification for your model.
Yup, you are likely seeing some deflection related cutting harmonics which is unrelated to alignment. This is the very reason for the rule-o-thumb: tail stock support recommended when stock exceeds 2-3 x Diameter. At least I think that's the recommendation. This might even be a steel based guideline which is generally stiffer than aluminum. Also, when this happens in real life mode, change the feed rate & it will have the effect of clipping off the hill tops as opposed to following & exaggerating within the tire tracks so to speak.
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It's not too likely the tailstock is right on, so I would check it first. Then spindle run out, then how level the ways are.
Then I would use a 4 jaw chuck with a 10" long , 1 1/2 to 2" diameter steel rod and make test cuts (without the tail stock)using something like a vbgt 221 or 331. Plus everthing said in previous posts.Monarch used 2" diameter when they tested their lathes.
Then I would use a 4 jaw chuck with a 10" long , 1 1/2 to 2" diameter steel rod and make test cuts (without the tail stock)using something like a vbgt 221 or 331. Plus everthing said in previous posts.Monarch used 2" diameter when they tested their lathes.
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Jackar, what are you trying to accomplish? It appears you are attempting to do a 2-collar test, which is usually done to finalize leveling of the lathe. A 2-collar test is done without tailstock support and a sharp HSS tool is usually used to limit deflection. What you are actually doing here is just a first operation turning and the acceptability of the results can only be determined by you.
If you are trying to accurize your lathe then test cuts and test bars cut on your lathe are the best way to do that. However, you should use a sharp, well-ground HSS tool for these tests to limit deflection. The reason for this is that the nose radius on inserted carbide tooling will deflect excessively when taking very light depths of cut due to excessive radial cutting forces so you cannot tell if the lathe is off or if the cutter is responsible.
If you are trying to accurize your lathe then test cuts and test bars cut on your lathe are the best way to do that. However, you should use a sharp, well-ground HSS tool for these tests to limit deflection. The reason for this is that the nose radius on inserted carbide tooling will deflect excessively when taking very light depths of cut due to excessive radial cutting forces so you cannot tell if the lathe is off or if the cutter is responsible.