Thread: lathe alignment

Originally Posted by Michael G

Not necessarily. You are assuming that the surface you are running on is square to the spindle and that the cross slide is square to the bed. Usually this is not the case as manufacturing tolerances are arranged so that in use the lathe will face off, any "errors" accumulating to give a concave surface (if only very slight).

I'm with Phil on this one - because the lathe has been dropped, it is quite possible that the headstock has moved. It really depends on the force of the blow and the quality of the materials the lathe has been made from.

Michael

Guys, you need to be careful with the Headstock alignment. I do not know how the interface between headstock and lathe bed is made on this particular lathe. But it appears to be an Asian lathe. Many low cost Asian lathes do not have the headstock carefullty scraped to fit the bedways like old American lathes. Nor do they have the Headstock finely precision ground to fit the bedways like modern European lathes. Rather, the underside of the headstock is machined rather coarsely - the headstock is simply adjusted during lathe assembly by way of "torque shimming" the bolts that mount the headstock to the lathe bed. For example, tightening the right two bolts a bit firmer than the left two bolts will have the spindl center line pointing slightly upwards... etc. Sometimes during lathe assembling at the factory, there is not enough adjustment this way, and wthey do is simply insert some thin paper shims, and if the error is greater some metal shims. Of course this not the "proper" way to do it, but it works and it allows the new lathe to be sold at a prce affordable to the hobby user.

The torque shimming method leads to a lathe that (at the factory) perfectly meets and exceeds the Schlesinger standards. But it has several downsides:
- the headstock alignment can be lost in the case of a transport accident like dropping the case or the container it comes in, or a collision whilst transporting installing the lathe on site or in a showroom
- removing the headstock from the bed means the alignment is completely lost (there is often no guidance of the HS by the bed vee's). Even just slightly undoing the headstock hold down bolts, means the headstock alignment is lost.
- completely losing the headstock alignment, means that it will not be possible (or it may be extremely time consuming) to get the headstock height to match again the tailstock height. This because at the factory, they only have to adjust the HS by torque shimming to be parallel to the bed. They then select a tailstock (from a pallet full of tailstocks) to match whatever headstock height resulted from the HS torque shimming. For the owner trying to re-align the HS at home that is a nightmare, because additionally to align the HS parallel to the ways, he will aim at getting the center line to match the one and onlt tailstock that he has. And that makes the whole alignment much much harder.

What I want to say, before fiddling with the headstock of an Asian mlathe, you are well advised to make damn sure its really the headstock that is off, and not something else. The only way to align the HS is to begin with a perfectly level and untwisted lathe bed. That will require a precision level.

Originally Posted by casjon

I'd agree with that, with one big however: the machine has had a pretty hard life by the sound of it, all the crap under the gap, broken wheel, chipped carriage, missing gibs would attest to that. I was trying to avoid getting the OP jumping in at the deep end. I think he should start at the begining, sort the machine out first, even if it's just a simple clean and adjust gibs, then run the checks. No point in resetting the headstock, if there are other problems that should be resolved first. simple to complex always seems to work best.

Thats the plan.

Originally Posted by cba_melbourne

Guys, you need to be careful with the Headstock alignment. I do not know how the interface between headstock and lathe bed is made on this particular lathe. But it appears to be an Asian lathe. Many low cost Asian lathes do not have the headstock carefullty scraped to fit the bedways like old American lathes. Nor do they have the Headstock finely precision ground to fit the bedways like modern European lathes. Rather, the underside of the headstock is machined rather coarsely - the headstock is simply adjusted during lathe assembly by way of "torque shimming" the bolts that mount the headstock to the lathe bed. For example, tightening the right two bolts a bit firmer than the left two bolts will have the spindl center line pointing slightly upwards... etc. Sometimes during lathe assembling at the factory, there is not enough adjustment this way, and wthey do is simply insert some thin paper shims, and if the error is greater some metal shims. Of course this not the "proper" way to do it, but it works and it allows the new lathe to be sold at a prce affordable to the hobby user.

The torque shimming method leads to a lathe that (at the factory) perfectly meets and exceeds the Schlesinger standards. But it has several downsides:
- the headstock alignment can be lost in the case of a transport accident like dropping the case or the container it comes in, or a collision whilst transporting installing the lathe on site or in a showroom
- removing the headstock from the bed means the alignment is completely lost (there is often no guidance of the HS by the bed vee's). Even just slightly undoing the headstock hold down bolts, means the headstock alignment is lost.
- completely losing the headstock alignment, means that it will not be possible (or it may be extremely time consuming) to get the headstock height to match again the tailstock height. This because at the factory, they only have to adjust the HS by torque shimming to be parallel to the bed. They then select a tailstock (from a pallet full of tailstocks) to match whatever headstock height resulted from the HS torque shimming. For the owner trying to re-align the HS at home that is a nightmare, because additionally to align the HS parallel to the ways, he will aim at getting the center line to match the one and onlt tailstock that he has. And that makes the whole alignment much much harder.

What I want to say, before fiddling with the headstock of an Asian mlathe, you are well advised to make damn sure its really the headstock that is off, and not something else. The only way to align the HS is to begin with a perfectly level and untwisted lathe bed. That will require a precision level.

while im not saying i dont believe you, i do find this hard to believe, especial when they sell spare parts for such lathes. have you got any proof of this method?

I have a generic 12x36 Chinese lathe. Several years ago I removed the HS from the bed and while I didn't find any paper or shims, it was evident that the majority of the HS base was hollowed out with an angle grinder (or similar). The only points of contact were where the 4 bolts took up. I assume they did this so that they don't have to grind or scrape the HS base flat to stop it from rocking on the bed. When I replaced the HS on the bed, it did take a fair amount of frigging around to get it aligned in the vertical plane but I did manage it. Horizontal plane was easier as it has the typical side adjustment bolts near the motor mount. If I was really keen I would remove the HS (again) and grind/handscrape the base to a proper fit of the bed. But for what? It does the job as it is. Cheers, Simon

The Chinese make their hobby lathes in volume, making them affordable to the general hobbyist necessitates manufacturing to price rather than quality. so it would make sense to select matching head and tailstocks from a pile. The machines made decades ago were very, very expensive in their day, they were manufactured and sold in small numbers intended for industry rather than hobby use and therefore quality of finish and fit was foremost. Manufacturing lathes in small quantities doesn't provide the opportunity to select matching head and tailstocks from a great pile, rather they would be machined to exact tolerances for each individual machine.

I've removed/replaced a few headstocks and can attest to the woeful machining (hacking). Secondary fit machining (angle grinder usually) on headstocks is almost always very, very evident, not so on tailstocks. I've never seen any packing (hard or soft) though, packing is usually only found on very old, very worn, second hand machines.

You will also notice the quality of finish on Chinese lathes differs greatly from manufacturer to manufacturer, or onseller to onseller. Inspecting and testing cross and compound slide surfaces is quite often a good pointer to quality: some quite obviously have been machine scraped whilst others have only been machined, the difference can be felt in progressive tightness/looseness as they are wound in and out.

There is nothing wrong with the manufacturing/assembly practices utilized today, it is cost effective and cost effectiveness is what makes lathes affordable to the masses.

Some bag Chinese machines for their seeming lack of quality and finish, quite obviously, had the older machinery been made to the same price then the quality would have suffered similarly, that is a given in any manufacturing process. But from the other side of the argument, if Chinese hobby lathes were made to the same standards as the lathes of yore, you and I couldn't afford to buy them and we'd still be working with file and straight edge. So the question is: would you rather work with a file and straight edge or an affordable mass produced lathe, which may have some (none insurmountable) foibles?

This may be of use ..or maybe not http://www.mig-welding.co.uk/forum/t...e.48022/page-2 This is how lathes were sold years ago .......with a genuine report on alignment . As opposed to the photocopied report that Asian hobby machinery seems to come with these days Mike

Most Chinese lathes come with a manual and some come with an inspection report I‘m told, although that hasn’t been my experience.. My current lathe came with a manual which included a report at the back with actual measurements pencilled in beside the allowable specifications. I checked some measurements, once unpacked, and found everything I checked was as stated. I was more than happy with that, but must admit it wasn’t my expectation and certainly not my experience. When buying a first lathe, I don’t think anybody really cares too much if a report is provided, as long as everything is there, everything works as it should, and their first turn is successful, seasoned machinists obviously would differ in that respect. That aside, from then on it’s just a matter of marvelling at how your new toy can turn square objects round, and with the right attachments, round objects square. For some that shine may turn to shi(t)e, for others, like myself with four lathes under the belt, the shine just gets shinier! Unfortunately, I suffer badly from greener grass syndrome, despite having a newish lathe that more than exceeds my expectations, I now find myself lusting after a C8. What an expensive hobby this is!

Originally Posted by casjon

Most Chinese lathes come with a manual and some come with an inspection report I‘m told, although that hasn’t been my experience.. ..................................

Whilst inspection records come standard with nearly all industrial class lathes of any size and with most Asian lathes 13" swing and above, this is not so with the smaller hobbylathes. Fact is, the vast majority of small bench hobbylathes (11" swing and under) do not come and never came with inspection certificates. Not only the cheap Chinese ones. Even the well regarded Myford lathes, did to my knowledge not automatically come with an inspection certificate. Wabeco lathes do come with a test certificate, some larger EMCO lathes did come with test certificate, Southbend/Hercus/Boxford etc did, some larger Taiwan made lathes did too.

Hobbylathes as small as the Chinese BV23 (9" swing) have occasionally been reported to come with an inspection record (I have at least one exaple documented). A test certificate is an option that the importer can specify when placing an order with the Chinese factory. But it does always cost extra. And this whilst the majority of people buying a first hobbylathe do not understand why they should pay more for a lathe with certificate from dealer X, if delers Y and Z sell the "same" machine for less without the piece of paper. So for a dealer, doing the right thing may actually mean loosing business - because nearly all hobbyusers turn over every dollar several times before spending it. And faced with the choice of having an inspection record or having an extra chuck.... the chuck probably wins.

I believe that it would take most "first hobbylathe buyer" at least 1-2 years before he really misses the test certificate - and half of all hobbyusers will probably never bother. Whilst many an upgrading "second or third hobbylathe buyer" may already have gained enough experience to buy an industrial class lathe in good nick, or even consider restoring some old iron in not-so-good nick. And by the way, such pre-loved old iron lathes rarely come with the original inspection certificate - because documents like this along with the invoice would typically have been lost at most 20 years after the lathe was once bought new.

this may seem like a very dumb question, but when shimming the lathe feet, the shim doesn't extend further then the bolt hole or this will just start to shim the other side up? hope this make sense?

Originally Posted by brendanh

this may seem like a very dumb question, but when shimming the lathe feet, the shim doesn't extend further then the bolt hole or this will just start to shim the other side up? hope this make sense?

In the benchtop lathe category there are lathes that bolt down with 2 bolts (small lathes) and 4 bolts (larger lathes).

Smaller lathes, say 8" swing and below, often do not require any shimming at all, because the small and short bed does not twist enough to cause taper cutting. In this case only the headstock end is bolted down rigidly, the tailstock end is simply left loose.

Shimming is usually only done at the tailstock end. The Headstock end is simply bolted down.

On a lathe that bolts down with 4 bolts you are correct, you just shim right around the bolt. Either around the bolt behind or the bolt in front of the tailstock.

On a lathe that bolts down with 2 bolts, you have to place the shims either behind the single bolt, or in front of the single bolt, just under the edge of the lathe bed casting.

Much better than using actual shims, is to use jack nuts. Some better lathes come with four such jack bolts as standard. Some other offer these as optional retrofit extras. With cheaper lathes you may consider making your own - here an example how that may look: http://modelengines.info/lathes/IMG_2993-3.JPG

For shimming to work at all, a torsionally very rigid benchtop surface is needed. Ideally cast iron but that is only found on industrial cabinets. Or a heavy gauge steel cabinet, with reinforced top. A more than 50mm thick high density chipboard plate is torsionally rigid enough for a 9" swing lathe, probably not for anything larger. But a thin walled steel cabinet as often sold with low cost lathes is torsionally just not rigid enough. If you try to shim a lathe on such light gauge cabinet you just twist the cabinet such that it then stands on 3 feet and wobbles. With light gauge cabinets it is better to bolt the lathe rigidly onto the top surface, and instead shim the cabinet feet - in extreme cases you still may end up with a wobbling cabinet, and in this case the only way is to bolt the cabinet to the concrete floor.... but then you need be aware that thin concrete slabs as used in home garages are very much alive and moving with the seasons.... and yes it matters because the lathe will turn different taper depending on the seasons and soil humidity. At least that is what I found on my garage floor.

Ive got a sheet metal stand thats been bolted to the slap. slaps 100mm thick. the sheet metal stand seems to be rigid enough to be helping untwist the lathe a little but maybe not rigid enough to remove it all. ive thought of maybe trying to spread to the load and put a couple of steel plates under each foot think this would be worth it? Ive replaced the gap, but i don't think its in right as the readings im getting seem to be different once i start to move onto the gap. Ive got 4 collars machined on a 300mm piece to be able to tell.
a better stand is something im looking into, i would probably make one myself so i can have storage shelfs/draws but is going to be a sort of last resort until Ive exhausted all options. jacking screw defiantly is something i want, shims are just to put it nicely.

Originally Posted by brendanh

..........Ive replaced the gap, but i don't think its in right as the readings im getting seem to be different once i start to move onto the gap. .................

Absolute cleanliness is paramount, a grain of dust and the gap will not fit perfectly. That said, it depends a lot how well and heavy the lathe is made around the gap section. Do you have the owners manual of your lathe? I ask, because the user manual of some Chinese made gap bed lathes says clearly that, if you remove the gap once, there is no guarantee it will ever again fit perfectly. What this means to me is essentially, that the owner has the choice of having a) an accurate lathe without gap, or b) an accurate lathe with a permanent gap AND an inaccurate late with the gap reinserted. And the choice can only be made once in the life of the lathe.

To verify a gap alignment error, you could place a magnetic stand on the saddle, attach a DTI to the arm, and slide its finger over the gap - you should clearly see the magnitude of the error, and you may try if you can somehow minimize it depending how you fit the gap....


PS:
I choose this example of the Grizzly G9249 12x37 lathe, simply because they have the user manual online. On page 58 of this manual it states as follows:
theel

the Model g9249 comes equipped with a gap
section below the spindle that can be removed for
turning large diameter parts or when using a large
diameter faceplate.

The gap is installed, then ground, at the factory
during lathe assembly for precise fit and align-
ment. Factors during the remaining assembly
apply additional forces to the gap making the
replacement of the gap to the original position
very difficult. If you choose to remove the gap,
we do not recommend attempting to replace it.

The pdf manual can be found here: http://cdn0.grizzly.com/manuals/g9249_m.pdf
I believe that many if not all the China made gap bed lathes sold by Grizzly come with a similar warning.



I hope this helps understanding the problems of a gap in a lightweight low cost lathe. It just is not the same thing as in a heavy industrial gap bed lathe, where the gap alone may be as heavy as an entire hobbylathe.

Yeah i read in the grizzley manual about that, i dont really know what to do now. Leave it out or put in back on. Seems a bit stupid that you only get one shot at it.
I used an indicator to get the gap as best as i could but it always moved when bolts ahere tighnted and them tapper pins didnt seem to be holding it where i wanted. Will take alot of time to get it back right.

It may be worthwhile using the search function for lathe stands. Quite a few members have made their own with some novel approaches. I did a search a few days ago, Rod someone posted his on the forum, showing sliding shelf for coolant, old toolboxes filling in for storage, very neat. Found another with a novel leveling system. Unfortunately I can't remember the headings so haven't been able to find them again. I can feel another long night coming up.