Tail alignment and gear handle play

[AjohnwParticipant @ajohnw51620]

If your looking for a lot of accuracy it's best to be sure what is out and where. The where aspect can be difficult. There is a simple check on the head that takes out that the morse taper might be out. Chuck some mild steel and turn it with say 100mm sticking out of the chuck making sure there is plenty in the chuck. The bar will bend a bit even with a light cut so run the same cut several times until nothing comes off it at all. Then mic it. If parallel then the axis of the head is ok. This doesn't say anything about which way it's out unfortunately but has a positive attitude – assumes it will be ok. You never know it might be.

The morse taper can be checked by sticking a centre etc in it and testing for run out but that isn't a very sensitive test. It's ok for checking between centre accuracy at that end. A test bar with a mores taper on it is far better as the run out can be checked much further way from the lathe spindle. That can also be used to see where the error is with a bit of thought. The problem is that when a dti is run along it the reading will only remain as it is if it travels exactly along the centre line of the test bar.

A home made between centre test bar can be useful made out of silver steel. It can be checked for straightness by having a bit of thin feeler gauge stock under each end pressed against the inverted V of a prismatic bed. Then check with a feeler guage in the centre against the V. It will be a firmish fit that doesn't change when the bar is rotated if it's straight – and if the bed is straight. There are some NVG methods of making them about. The best way especially on small lathes is to grip little in a 4 jaw at one end and have the fixed steady at the other end and get both ends running dead true. Then face, chamfer, turn a bit of a recess and lightly centre the end of the bar. Reverse and do the same again. You might think that the centre wont be correct if the tail stock is out but they are rigid enough to cut on one side so it will be central. The reason for gripping little in the 4 jaw and no more tightly than needed is to avoid bending the bar via headstock errors. If the headstock centre had low run out this can be used to check a centre in the tailstock. Even varying it's projection to see if it runs parallel to the bed.

The same sort of turning test can be done between centres. Some people turn up a shaft and leave a couple of collars on it and then take light cuts on the collar but because things move it's still best to repeat the cut and there isn't much point in even doing that unless the slides are set correctly or locked. The shape of bar usually shown has a very exaggerated shape when really the reduced dia between the collars just has to clear any errors that are there.

I don't know if these lathes have a tail stock that can be offset. If so I wonder why they don't make any error low so that it can be shimmed up. Frankly I feel anything that claims to be a lathe should have a tailstock that can be offset or great effort should be made to make them truly accurate. Maybe if fixed a decent one could be made from 2. I notice that there is a projection on the casting that looks like it is adjustable but perhaps that's a spoof?

John

–

Edited By John W1 on 27/06/2015 15:37:34

[Neil WyattModerator @neilwyatt]

Hi John. The tailstock is offsetable. The bottom of the tailstock is, like the headstock, ground to mate with the inverted-V bed. That's why I have suggested a bit of attention to the fit between the two parts of the tailstock.

Neil

[AjohnwParticipant @ajohnw51620]

Sounds sane to me Neil. Shimming the head would be tricky given that rest on a V too.

I had to google "puppitast" appears to be a DTI but that leaves me no idea how these measurements are being taken. I feel that a test bar is essential at the levels mentioned and with a simple DTI set up only the height of the tailstock relative to the headstock can be measured – by using the cross slide to pick up the high points. That takes out side to side errors. If there is zero error in height at several points along the bar then running the DTI along the side makes some sense. If there is variation in height i doesn't with a simple set up.

Best thing to do with a lathe to check it initially is to use it. Work just sticking out of the chuck and also between centres or in chuck and long with a centre in it. Then look at the causes for any problems. Minor errors can be taken out with an offset tailstock but the end result is work that isn't round.

John

–

[Nitai LeviParticipant @nitailevi73768]

OK, I re-did some of the tests to double check… well more like hextuple check

First, the lathe is not super aligned with a level. It is sitting on a strong steel table with a wood block on top (sitting on the wood). It's not bolted to it. This is all necessary so any accuracy in the bed is only as good as these conditions allow.

I did the Rollie spindle alignment test. I used a tool steel rod that is very accurate and I double checked with a micrometer that the two places where I measured – one near the chuck, the other just past half the bed length – are the same diameter down to about 0.002mm.

I got variable results depending on how the rod was sitting in the chuck… which is strange since it's not supposed to matter. I tried to rock the rod while tightening the chuck to get it to hold as accurately as I could.
So in Rollie's method I got a difference of about 0.015mm (about half a thousand inch) in about 25cm distance from the end of the spindle.
For whatever reason if the rod was held slightly differently in the chuck I sometimes got up to double that amount for the same distance and same measuring spots… not sure why.
I also noticed that even slight downward pressure on the chuck while turning it will change the measurements…

I checked the spindle itself in many places, the bore, back of the chuck, side, etc. Everything there is accurate to somehwere between 0.002mm and 0.007mm, depending on where I measure. It all seems acceptable to me.

John W1, re the tail measurements, I've done it by holding the puppitast in the head spindle and checking both the bore of the quill and a dead center held in the quill, all around, when retracted and extracted.

Neil, I scraped all the high spots and now I get barely any contact showing on the front (head end) of the tail top half bottom. I also checked with a 0.01mm feeler gauge and it seems like it's just barely touching at on spot and more or less sitting mainly on the back (tail end). This didn't really affect the height problem I had at all.

When you say "wet and dry" did you mean emery cloth? I have a bunch of those too and a few different types of sand papers, but we use different terms here so not sure.
I think I will light and slowly lap and check for any improvement or issues as a result and go from there.

Thank you

Edited By Nitai Levi on 28/06/2015 06:18:23

[HopperParticipant @hopper]

It may be you are overthinking things a tad for a home hobby lathe.

Many good quality lathes of the past were made deliberately with the tailstock a few thousandths of an inch higher than the headstock spindle. This was to allow for wear on the bed and the the tailstock as it was slid back and forth in use. So your tailstock may in fact be not critically out of line.

There really is no point in setting up the tailstock to tight tolerances before you bolt the lathe to the bench.The lathe base needs to be mounted to steel, not wood. Wood can move with changes in temperature, humidity and over time. When the lathe is sat on the steel bench, you should check all four "feet" and make sure there is no gap under any of them. If there is a small gap that a feeler gauge can slide into, a shim of that thickness must be inserted before bolting the lathe down. This ensures the bolting down does not distort the lathe bed to fit the not-so-flat bench.

Once the lathe is bolted down, put a piece of, say, 25mm diameter bar by at least 180mm long in the lathe between centres. It must be between centres, not held in the chuck. Then by taking fine cuts along the length of the bar, you can measure it and determine if it is turning parallel within reasonable limits. If the test piece comes out parallel within limits (say, .001" or less) there is no need to adjust anything any further.

If it does not come out within limits, then the first thing to do is to check the bed for twist using a precision level. There are several threads on here about that topic that can be referenced.

If after levelling the bed, the lathe still turns a taper, then it is time to adjust the tailstock. Even with your tailstock .005" high, you can adjust the sideways offset to make the lathe turn parallel and compensate for it. Always take your tailstock measurements with the tailstock clamped down as hard as in normal use.

Although, I think if you scrape/file the highspots off the tailstock mating surfaces, you should get the tailstock down to .002" above the headstock spindle, which is perfectly fine. That way you can keep the tailstock sideways offset correct.

Edited By Hopper on 28/06/2015 08:25:30

Edited By Hopper on 28/06/2015 08:34:05

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Nitai Levi on 28/06/2015 06:16:20:

I scraped all the high spots and now I get barely any contact showing on the front (head end) of the tail top half bottom. I also checked with a 0.01mm feeler gauge and it seems like it's just barely touching at on spot and more or less sitting mainly on the back (tail end). This didn't really affect the height problem I had at all.

.

Nitai,

This looks like excellent progress … But, for the next stage of 'fitting' I think you should now start using a much thinner layer of Blue: You need to be able to identify high-spots within the area that currently appears to be flat.

MichaelG.

[Neil WyattModerator @neilwyatt]

Hopper,

With mini-lathes there is considerable debate about the benefits of rigid mounting. The best solution I have come across is rigidly fixing the headstock to a solid bench while allowing the tailstock to 'float' with resilient mountings.

In all honesty, I have still to bother putting fixing bolts through the holes under my lathe

Nitai,

The flex you notice may mean that headstock bearings are slightly loose, Make sure they are properly adjusted as if the spindle droops under the weight of the chuck the tailstock will appear higher than it really is.

(see HERE for guidance for setting taper bearings).

Hopper concludes with an excellent point – I suggest you settle on a sensible 'target' of about 0.002"/0.05mm high and aim for that. If you overshoot a little you won't end up with a tailstock that is too low and the attendant bother.

Wet and dry in the UK has become a generic term fro waterproof backed slicon carbide papers which are generally to a much closer tolerance than sandpaper.

Neil

[AjohnwParticipant @ajohnw51620]

I always mount my lathes on jacks / levelling screws. Just needs bolts of a suitable length. First thing to do is bolt these to what ever the lathe is being mounted on, threads pointing up. Then fit nuts A followed by a penny washer, then put the lathe in place and further nuts B and washers. A further lock nut can be added under A if required.

Nut A can be used to level the lathe and support it evenly. The lock nut if fitted can be used to lock it in place. Nut B is then used to hold the lathe down.

People can also make posh ones. Drill and tap the lathe mounting points, make a "flat mushroom" shaped bush to screw into the mounting points on the lathe. These are then used to level the lathe and fixing bolts pass through them.

People can also add rubber to this sort of set up. Washers effectively or maybe some suitable car parts – rubber blocks with threaded sections sticking out of each end. Personally i don't hold lathes down tightly at all. Finger tight on the final fixing nuts does for me. Not convinced that resilient mounting adds anything useful either.

The main reason lathes are rigidly mounted on something else that is also very rigid is to allow final setting up. This is done by warping the bed with the fixing screws. The technique really dates back to when lathe cabinets where made of cast iron and really were rigid. I feel it's a dubious thing to do these days as once set up the cabinets will settle over time and the bed will go back to more or less where it was. The reason it was done like this is that it's rather difficult to adjust the tailstock offset by extremely small amounts. Warping the end of the bed is exactly the same as adjusting tailstock offsets. A DTI can help make fine adjustments to all sorts of things.

Sounds to me that the OP will persist in doing what they have read on the web what ever any one else says. Often the case. Must tell lathe manufacturers that they don't need their test bars and also that users don't need to check via actually turning – many do as fully checking with a DTI has it's problems.

I will clear one thing up though. Rocking the bar while a 3 jaw is closing on it is more likely to make problems worse. Initially if some one hasn't done much of this position a jaw central at the top. As the jaws are closing on the work rotate it by hand, doesn't need much. With a bit of practice this ensures that the chuck doesn't clamp down firmly on the high spots it happens to be in contact with because the work isn't on it's axis. Large work might need the ends tapping true before the chuck is firmly tightened but that usually happens when the work is too heavy to support easily.

Also as some one has mentioned and going a bit further in many cases blue has to be used so thinly that it can hardly be seen.

If some one wants to lap something flat and hasn't something truly flat around the cheapest source is probably a piece of thick float glass placed on a decently flat surface. Rather than putting wet and dry on it, a water proof paper backed abrasive sheet, 3M make lapping and finishing sheets that are adhesively backed. It can be found on ebay. A piece larger than the work is needed so that it can be moved around without the work passing over the edge. Best use plenty of light oil to prevent the abrasive clogging up which ever it is.

If some one isn't used to using a scraper and wants to mate 2 parts diamond lapping sticks are probably a better answer. Arceuro sell some decent ones but they will work a lot more quickly with oil or better still honing oil on them, which unfortunately I think they have stopped selling. The problem with mating 2 parts is knowing which one is out. The chances of finishing up with flat surfaces are slim. A bit of lapping on a flat surface will sort out just where the errors are. Or if 3 surfaces are all scraped and checked against each other it's possible to work out where the errors are – eventually.

Leaves me wondering if these parts have been ground?

John

–

[Neil WyattModerator @neilwyatt]

For clarity this is more or less the arrangement Nitai is looking at.

This is the upper part of the tailstock (as standard the slot is narrower and the cap-head is a grub screw):

Although the base of the casting appears to be ground on my lathe, the slot isn't – note I have milled another 1/8" off the left hand side here.

The finish of the base looks like it has been crudely milled and ground, but not enough to remove the machining marks. Note stray paint… Bear in mind this is an early-ish machine, my impression is that SEIG QC has improved since 1998!

Much easier to adjust side to side with that brass gib instead of a grub screw bearing on the side of the tenon!

Neil

[AjohnwParticipant @ajohnw51620]

It's interesting to read the Arceuro set up instructions. Peatol throw in another step but they do make the parts very precisely. When the slides are all off and cleaned up mix kitchen cream and a light oil, 3in1 is ok, kitchen cream – CIF in the uk. The mix makes a very fine lapping paste. Coat the part that is to be lapped in and push back and forth by hand. The same thing can be done with slides that have gib strips, just adjust and tighten so that they can be move fairly easily by hand lead screws out. Tighten a touch as the paste distributes evenly and again later etc.. Done with a bit of care it can give very smooth slides but it wont cure even minor errors. When happy, clean it all off and lubricate as usual. Slideway oil is very good and doesn't need putting on that often, only a few drops are needed or rub it liberally all over the running surfaces as some do. Personally I always set gibs so that there is very slight drag when pushed by hand. It's easy to set them too tight if it's done via the lead screws and just wears the nuts out more quickly.

John

–

[Nitai LeviParticipant @nitailevi73768]

Posted by John W1 on 28/06/2015 11:04:47:

Sounds to me that the OP will persist in doing what they have read on the web what ever any one else says. Often the case.

Whether I shim the head or scrape/lap the tail… either way I go with it's what I read on the web
In the case of bolting the lathe… I'm not going by what I read on the web…

I did try to follow some of Neil's and your suggestions. I scraped a bit off the tail top part, especially a few obvious high spots in the the front side (i.e. the right side in Neil's second photo). The paint is thin enough that after lightly scraping a few high spots I can't even see contact on the paint on the front side, only the back side.

Now that I can adjust side alignment accurately and I'm happy with all other measurements, I think I'll just carefully lap a bit more and check and measure often that I'm not ruining any other alignment. If I see something is starting to move in the wrong direction I'll just stop and check.

Neil, yes that is the same exactly as my lathe. That brass gib is a good idea, I might add something like that at some point. I thought of adding a screw from the side, but I'd probably never want to move it out of alignment so only open it if it moves out of alignment to correct it.
It's hard to tell from photos but eventhough my lathe is pretty new, the surfaces the tail contacts don't look significantly better than on yours.

Thanks again for all the help.

Edited By Nitai Levi on 28/06/2015 15:51:09

Edited By Nitai Levi on 28/06/2015 15:51:28

[HopperParticipant @hopper]

Interesting about the "bolting down" debate. Never come across that one before, but I am not a minilathe owner.

Just browsing my "Machine Tool Reconditioning" book by Conolly and what he has to say about aligning the tailstock.

He makes no mention at all of using a dial indicator attached to the headstock spindle to measure tailstock alignment. Possibly because this method is prone to inaccuracy due to headstock bearing slack and movement of the dial indicator rig under gravity as it is rotated.

Instead, he recommends that one use a piece of test bar between centres. Turn the bar (or the two larger diameters at the ends) to a fine finish. Measure with a micrometer and adjust the sideways movement of the tailstock until the next fine cut turns parallel.

Once you have turned the test bar parallel, then mount a dial indicator on the carriage with the button resting on top of the turned bar. Traverse the carriage back and forth and observe the dial indicator readings. If the tailstock vertical height setting is correct, There should be zero runout from one end to the other. (Or maybe up to .002" to allow for future wear.)

He recommends that if the tailstock is too high, scraping of the surface between the two halves of the tailstock body, as Neil has recommended, is the way to do it.

Also, on going back an reading your earlier posts, if you are getting a total indicated runout of .005" when mouinting the dial indicator on the headstock spindle, that is double the actual misalignment. So your actual misalignment would be .0025" which I think would be just about perfect. I'm not sure though if you were giving us the total runout or the misalignment figure.

 

Edited By Hopper on 29/06/2015 10:26:11

[Neil WyattModerator @neilwyatt]

When I made my bar between centres, I reversed it between taking the final skim off each collar so that both final cuts were taken at the same end of the lathe. This gave me collars that are the same diameter to less than 0.0005".

This approach doesn't require the lathe to be set dead right, and is much less effort than usual method of using trial cuts and adjusting until he test bar is the same at each end. Naturally once you have the test bar, setting the lathe to turn parallel become much easier.

Neil

P.S. the great pragmatist, LBSC, knew many of his readers wouldn't have a micrometer so suggested turning the test bar until you felt the same drag on a calliper pulled over each end, slightly tight.

[Nitai LeviParticipant @nitailevi73768]

Hi Hopper

Sorry, I know I tend to be too long in some posts…
I'll clarify.

The tail is high by approximately 0.14mm which is 0.0055".
The indicator showed runout of double that, 0.28mm or 0.011".
I made a very solid and stocky puppitast holder to minimze the gravity issue you mentioned.

I posted the corrected height difference on another forum, where I was previously suggested to shim the head… and again was suggested to shim the head…

Considering all the (somewhat contrary) recommendations, I decided to lightly scrape and even more carefully lap. I've done a bit and will later check if there's any improvement (because I've done so little maybe not enough to show much).

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 29/06/2015 11:48:03:

P.S. the great pragmatist, LBSC, knew many of his readers wouldn't have a micrometer so suggested turning the test bar until you felt the same drag on a calliper pulled over each end, slightly tight.

.

Neil,

No disrespect to LBSC … I wouldn't dare, around here … but that's not exactly a novel approach: it's how callipers were meant to be used.

MichaelG.

[Nitai LeviParticipant @nitailevi73768]

So after some very careful scraping and lapping… I got it down to about 0.11mm high. This will take a while so I'll continue and see how it goes.

Thanks again

[HopperParticipant @hopper]

Posted by Nitai Levi on 29/06/2015 16:57:53:

So after some very careful scraping and lapping… I got it down to about 0.11mm high. This will take a while so I'll continue and see how it goes.

Thanks again

Yes, 'tis the nature of scraping to take a while!

But I think, like Neil says, you are much better to spend some time scraping down the tailstock than disturbing the headstock alignment.

Have fun!

[HopperParticipant @hopper]

Posted by Michael Gilligan on 29/06/2015 13:36:51:

Posted by Neil Wyatt on 29/06/2015 11:48:03:

P.S. the great pragmatist, LBSC, knew many of his readers wouldn't have a micrometer so suggested turning the test bar until you felt the same drag on a calliper pulled over each end, slightly tight.

.

Neil,

No disrespect to LBSC … I wouldn't dare, around here … but that's not exactly a novel approach: it's how callipers were meant to be used.

MichaelG.

My old man always used calipers. I guess that is the way they used to do it in the old days. Each piece was made to fit its mating part rather than to an exact size, clearances done by "feel" and so forth. "Feel" was considered an essential part of being a good tradesman. Something that has been lost in the CNC age.

[EugeneParticipant @eugene]

"When Whitworth was working on The Standard Inch, he devised his "millionth machine" to compare different standard bars.

 

It 's accuracy depended on the feel of a scraped disc passing between the scraped surfaces of the sample bar and that of a facing piece. Whitworth claimed a skilled operator could indeed detect a difference of one millionth of an inch between "standards". 

Link to the free E-book description **LINK**

Eug

Edited By Eugene Molloy on 30/06/2015 09:24:57

[BowberParticipant @bowber]

Posted by Hopper on 30/06/2015 01:31:55:

My old man always used calipers. I guess that is the way they used to do it in the old days. Each piece was made to fit its mating part rather than to an exact size, clearances done by "feel" and so forth. "Feel" was considered an essential part of being a good tradesman. Something that has been lost in the CNC age.

Yes but there's nothing like being able to get 2 parts for the same vehicle and they both fit.

Steve

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Eugene Molloy on 30/06/2015 09:19:26:

Link to the free E-book description **LINK**

.

Eurgene,

Good to see someone else referencing Whitworth's work.

Unfortunately; Google seems to have 'done the dirty' on this e-book

…. An alternative provider is available.

MichaelG.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Hopper on 28/06/2015 08:17:48:

Once the lathe is bolted down, put a piece of, say, 25mm diameter bar by at least 180mm long in the lathe between centres. It must be between centres, not held in the chuck. Then by taking fine cuts along the length of the bar, you can measure it and determine if it is turning parallel within reasonable limits. If the test piece comes out parallel within limits (say, .001" or less) there is no need to adjust anything any further.

Err.. I think you have that the wrong way round. You need to turn work held in the chuck to test for bed twist.

Russell.

[HopperParticipant @hopper]

Posted by Russell Eberhardt on 30/06/2015 10:39:08:

Posted by Hopper on 28/06/2015 08:17:48:

Once the lathe is bolted down, put a piece of, say, 25mm diameter bar by at least 180mm long in the lathe between centres. It must be between centres, not held in the chuck. Then by taking fine cuts along the length of the bar, you can measure it and determine if it is turning parallel within reasonable limits. If the test piece comes out parallel within limits (say, .001" or less) there is no need to adjust anything any further.

Err.. I think you have that the wrong way round. You need to turn work held in the chuck to test for bed twist.

Russell.

We are not checking for bed twist. We are checking for tailstock alignment.

Bed twist is best checked with a precision level.

Holding a long test piece in the chuck is mostly used to check for headstock mandrel alignment with the lathe axis.

Turning a test piece between centres is often regarded as the best way to check for tailstock alignment. Unlike tests with dial indicators, it tests the lathe under working conditions with cutting forces applying pressure to the various parts.

But as with most things, there is more than one way to skin a cat I am sure.

[HopperParticipant @hopper]

Posted by Hopper on 30/06/2015 13:04:31:

Posted by Russell Eberhardt on 30/06/2015 10:39:08:

Posted by Hopper on 28/06/2015 08:17:48:

Once the lathe is bolted down, put a piece of, say, 25mm diameter bar by at least 180mm long in the lathe between centres. It must be between centres, not held in the chuck. Then by taking fine cuts along the length of the bar, you can measure it and determine if it is turning parallel within reasonable limits. If the test piece comes out parallel within limits (say, .001" or less) there is no need to adjust anything any further.

Err.. I think you have that the wrong way round. You need to turn work held in the chuck to test for bed twist.

Russell.

 

Hmm, no, I think I have it right way around. We are not checking for bed twist. We are checking for tailstock alignment.

Bed twist is best checked with a precision level.

Holding a long test piece in the chuck is mostly used to check for headstock mandrel alignment with the lathe axis. It can show bed twist too, but you don't know for sure that the error is not caused by headstock misalignment. Plus, long unsupported test bars in small lathes tend to flex and bend and chatter and carry on on the usupported far end so its hard to get an accurate cut and reading.

Turning a test piece between centres is often regarded as the best way to check for tailstock alignment. Unlike tests with dial indicators, it tests the lathe under working conditions with cutting forces applying pressure to the various parts.

But as with most things, there is more than one way to skin a cat I am sure.

 

 

Edited By Hopper on 30/06/2015 13:21:28

[HopperParticipant @hopper]

Posted by Eugene Molloy on 30/06/2015 09:19:26:

"When Whitworth was working on The Standard Inch, he devised his "millionth machine" to compare different standard bars.

It 's accuracy depended on the feel of a scraped disc passing between the scraped surfaces of the sample bar and that of a facing piece. Whitworth claimed a skilled operator could indeed detect a difference of one millionth of an inch between "standards".

Link to the free E-book description **LINK**

Eug

Edited By Eugene Molloy on 30/06/2015 09:24:57

That is a great book. Thanks for the link. Downloaded no problems. Funny, I was just thinking about Mr Whitworth creating order out of chaos this afternoon after watching "Mad Max Fury Road" with all its steampunk inspired machinery and mechanisms.

Millionth of an inch by feel, that's pretty good eh. I reckon I can feel a half a thou in a big end bearing on a motorbike engine but have a ways to go yet to get to Mr Whitworth's standard. Feel was something the old time tradesmen prided themselves on. One little dodge on old fella taught me as an apprentice toolmaker was when feeling for tiny ridges or imperfections on the surface of a stamping die, particularly around radiuses, use the middle finger of your left hand (if you are right handed). It has less callous on it than the fingers of the right hand, or than the index finger of the left hand and so gives a more sensitive feel. One of those things I'm sure they don't teach in college today.

[Author]

Posts