My "Learning to use a Lathe" Journal

[Brendon M]

Hello again,

I thought I'd create a new thread to detail my ongoing fun and learning of the Sheraton 9" Lathe at the Connected Community Hackerspace in Melbourne, since the last thread "my first use of a lathe" was beginning to bug me with it's increasingly inaccurate title.

I have various projects on the go, but at the moment, the main two are

• Making a catridge refillable pen
• Benchtop Gyroscope (by Clickspring)
  

Tracking down the large diameter stock for the Gyroscope has been a little difficult, so I have been focusing on the pen.

After making the metal scriber (also by Clickspring), I decided to try and make a pen version. As an additional challenge, the pen needs a retraction mechanism.

I decided to base it off the twist retractable type, as can be seen in the bottom of this photo. You can see that the twistable barrel end is placed next to the second design revision.


The basic idea of my twist retraction mechanism is to use a threaded rod that has a pin that interlocks it with the pen itself so that it can't turn. Turning the outer barrel will cause the threaded rod to wind in or out, which in turn causes the ink cartridge to extend and retract... I hope that made sense.  :toilet_claw:

I attempted to make this part first, it houses the threaded rod, and the outer barrel fits over it.


I have drawn it up for the benefit of this post, otherwise I just worked from paper. Mind you, drawing this up in cad would have helped me realise just how small a part it would be.

Making this small part was not as easy as I thought it would be. I am on the second attempt, and it is still a failure^H^H^H^H^H^H^H"practice piece".

In the first attempt, I learned two things:

• 3-jaw chucks introduce error when rechucking, significant enough to notice concentricity issues
• Drilling out before using a thread die is a bad idea

You can see the effect of the second point - threading apparently subjects a part to a lot of stress, and I ended up accidently bending it.


After turning down the non-threaded side, I wanted to drill it out so that I would not introduce error by rechucking after threading. This ended up being a mistake. And in the end, the effect of unchucking, reversing the part and re-chucking introduced a noticable amount of error.

The obvious answer was that I needed to learn how to use a 4-jaw chuck, but initially I thought I could not do it because the 4-jaw at CCHS was unable to hold small pieces. There are a number of remedies I could have employed that did not occur to me until afterwards.

Que the second attempt. The idea was that I chuck the work piece just once, and I attempt to turn all outside diameters in one pass, to make sure the threaded and non-threaded sides were concentric. This then avoided introducing any error by rechucking.

Of course, as part of the lesson learned about threading before, I had to part off and rechuck in order to perform the threading. But how would I ensure concentricity of the drilled hole?

I spent an hour trying to drill out a larger piece of rod that would accept the part, and I would glue the part in -- basically a superglue collet that would make the 3-jaw chuck error irrelevant. This did not work because I did not have a 8.62mm drill, because I had apparently turned the outermost diameter of the part a bit less than 9mm :facepalm:

Out of curiosity, I checked to see if I could fit the part in the 4-jaw chuck. It just fit, and I decided then and there I would learn how to centre a piece on a 4-jaw. To my surprise, it was not as difficult as I thought. I would turn the part in the 4-jaw, and watch the dial indicator reach it's peak. I would then back off the nearest jaw that was opposite to the peak of ecentricity (I hope that made sense), and tighten the jaw in the direction of the ecentricity, and keep repeating this.

I managed to get the total indicated runout down to 0.03mm, or about 1.2 thousands of an inch, which I thought was good enough!

Unfortunately, after threading and drilling out, the part was still assigned to the "practice pieces" bin :facepalm: the inner and outer diameters were not concentric


It seems as though while machining the non-threaded end, it got bent. It becomes apparent in this photo:


I was holding the non-threaded end with a live centre, and I think that the pressure from the cuts has caused it to become bent?

Anyway, once again another massively long post, I hope you found this interesting. Thanks for reading :)

[10KPete]

This is great stuff you're doing. There is no better teacher than hands-on. It's so easy sometimes to forget the learning experiences of almost 60 years ago and look at what a 'beginner' is doing and chuckle at the ignorance. But just a seconds thought brings back our own learning and the chuckle turns into a laugh at our own trail of scrap!

Keep it up, and keep posting. Writing about what you've done is a great teacher in itself...

And thanks for keeping this old coot grounded.....

Pete

[crueby]

For the large diameter stock you need for the gyroscope, a cheap place to get it could be the Drop Zone section of the website at Yarde Metals. They sell offcuts of many metals from thier commercial sales, reasonable shipping too. Sizes available vary since it is offcuts, but I can usually find what I need. Not much thin diameter stuff.

[Chipswitheverything]

Thanks for an excellent write up of your learning experiences ,Brendon - anyone getting to grips with using a lathe will find much to think about in your accounts of what does actually happen when you try out various methods and ideas.  The component that you are having a go at making, with it's smallish size and thin walls, is not so very simple, and you have an element of added difficulty in using a lathe that is a sort of "maid of all work" rather than your own familiar machine.

cheers, Dave

[Roger B]

I'm glad your posting this    Hands on learning is the best way and unfortunately too many people won't post what went wrong, which is the most helpful part for others who are also learning  I always try and post the problems as well as the successes 

[AOG]

Been there done that. I had the same problems with the cheap Chinese three jaw that came with my lathe. I started useing my four jaw but I hated reclocking the part in every time I had to adjust the part in the chuck. Eventually I found the joys of the collet chuck. It makes life so much easier for small diameter parts. You might want to look and see if they have one. If they don't have one and you are stuck with the four jaw, I recommend makeing a tool post DI holder. It makes things much easier. See this thread:

http://www.modelenginemaker.com/index.php/topic,5001.msg95436.html#msg95436

Tony

[Gas_mantle]

High Brendon

I'm a beginner myself so take what I say with a pinch of salt, but to turn the part you mention, I'd be inclined to turn and thread one end then remove it and put a piece of scrap in the chuck. Drill and tap a matching thread in the lathe and providing you don't remove the scrap from the chuck you should have a true running thread to hold your workpiece. If you support the piece with a centre and take small cuts you may be able to turn the non threaded end to size and maintain the concentricity. It should then just need  drilling through.

I can't say I've tried it but I think that's how I'd go about it and it may be worth a go 

Peter

[Brendon M]

Thank you Pete, Dave and Roger for your encouragement

For the large diameter stock you need for the gyroscope, a cheap place to get it could be the Drop Zone section of the website at Yarde Metals. They sell offcuts of many metals from thier commercial sales, reasonable shipping too. Sizes available vary since it is offcuts, but I can usually find what I need. Not much thin diameter stuff.

Hello crueby, you have just reminded me to update my profile with my location** - Melbourne Australia. Sounds like a great place, I am still yet to find a convenient place like it in Melbourne.

**Update: I have added it to my profile, but it does not want to show up under my name for some reason.

Been there done that. I had the same problems with the cheap Chinese three jaw that came with my lathe. I started useing my four jaw but I hated reclocking the part in every time I had to adjust the part in the chuck. Eventually I found the joys of the collet chuck. It makes life so much easier for small diameter parts. You might want to look and see if they have one. If they don't have one and you are stuck with the four jaw, I recommend makeing a tool post DI holder. It makes things much easier. See this thread:

http://www.modelenginemaker.com/index.php/topic,5001.msg95436.html#msg95436

Tony

Thank you Tony. As we don't have collet chucks, I will check it out that link. I am actually thinking of buying a few accessories for the lathe at CCHS, and a collet chuck set would be on that list.

High Brendon

I'm a beginner myself so take what I say with a pinch of salt, but to turn the part you mention, I'd be inclined to turn and thread one end then remove it and put a piece of scrap in the chuck. Drill and tap a matching thread in the lathe and providing you don't remove the scrap from the chuck you should have a true running thread to hold your workpiece. If you support the piece with a centre and take small cuts you may be able to turn the non threaded end to size and maintain the concentricity. It should then just need  drilling through.

I can't say I've tried it but I think that's how I'd go about it and it may be worth a go 

Peter

Thanks Peter, I had thought of this but was worried if the thread (M7 thread) would be up to the task.

One more thing I have realised I need to account for is the grip marks left behind on the outer-most diameter, highlighted here:


This is caused by the part turning in the chuck when I perform the threading (maybe I am doing something wrong, but threading takes a lot of effort!) What I should be doing is taking that cut last to remove any marking.

I've gotten over my fear of the 4-jaw chuck, so my revised strategy is

• Chuck a 1/2inch rod
• Turn down non-threaded side to 6mm (or should that be 1/4 of an inch, so I don't fight the lathe's native measurement system?)
• Turn down outside diameter by 10 thou, make it concentric and also to give smooth surface for dial indicator.
  
• Part off
• Flip the part, rechuck and re-centre
• Turn down to 7mm (fun working with Imperial Lathe and Metric thread die/taps!)
• Do thread
• Drill out entire part to 5mm (most nerve wracking step!)
• chuck up a piece of scrap rod, drill out to accept 7mm thread (I need the practice for tapping a thread anyway)
• turn down outermost diameter to 9mm, to remove tool marks

I'm going to try step 9 and 10 on a mock piece of scrap first to see what will happen to the thread. If it does fail, then a "superglue arbor" is next on my list, it's just something I've never tried.

Once again, thank you all for reading

[Chipswitheverything]

Hi Brendon, thanks for the update, and your new method will probably work out, but the drilling through while holding the 6mm dia , you have correctly identified as a potential difficulty!  Also, there still isn't a lot to hang onto earlier while exerting a lot of torque with the die threading...

 It would be possible to make this component, holding the 1/2" bar stock in the four jaw ( for added torque resistance during the threading procedure ), without removing it from the chuck until the component was completed.

 I think that if I was doing it this way, I'd chuck the 1/2" bar with about 5 mm more material length out of the chuck than the finished item.  Then turn the thread OD, and get the thread die -ed on while the beefy full dia. is holding the bar nicely.  Then turn down to the 9 mm "boss" dia.  right the way down to near the chuck jaws, and get your nice finish on the section that will remain as 9 mm.
 Then, centre drill the thread end, and open out with your 5 mm drill ( maybe in a couple of stages, 3mm or so, and then the 5 ), but just take the drilling to a depth a mil or two past the threaded length for the time being, so the 9mm section is remaining solid.
 Now, the bit that might need a trial beforehand on a bit of scrap! , and a little bit of preparation.    I would grind up ( well, I've got one! ) a stubby parting off type of tool, from a square tool bit,  (say, 1/4" or 5/16" square tool bit, doesn't need to be massive...)   - the blade perhaps 2mm wide at most, and about 8 -9 mm long, so it has a good stiffness.  The corners of the working edge could be honed with a slip stone to give a small radius, as the idea will be, not to part off with it, but to use it as a stubby turning tool, that will cut in both directions....
 Such a tool will be capable of being fed in a few thou, perhaps a bit more,  at a time, and worked sideways, to bring the 9 mm dia section between chuck and "boss" down in stages to the 6 mm dia.  And as that area of the material hasn't been drilled yet, the bar is still quite strong. If the top slide, set parallel, is used for the traverse of the tool, then you can work to a zero on the dial to preserve the shoulder length dimension.
 Then !, finally complete the drilling through the component with the 5mm drill, gently!, withdraw the drill to clear the chippings fairly often.  The drill will have a nice start in the previously drilled hole ,  -  and part or saw the thing off the parent bar.
  In fairness, there are various approaches to this sort of machining problem, and some members will say "Oh, I'd never do it that way! ", - anyone with an excellent collet set available probably would not -  but it does get the brain working to throw some idea about...!   Cheers, Dave

[Brendon M]

Thank you Dave,

I actually tried a variation of your suggestion on "practice piece" #2, I even ground a round nose general purpose cutter, though based on your description I did not grind the end thin enough (on that note, I should ask in my other thread how to properly grind a round nose cutter, I can't find any info on it).

It worked, but I only cut enough so that I could get a right hand cutter in to finish the job.

In the end, I still wound up with the threaded and non-threaded sides being out of alignment, I noticed this when I chucked up piece #2 in the four jaw to test Peter's (Gas_Mantle) idea of creating a threaded arbor(?) to allow me to turn down the outside diameter to 9mm. It was there I noticed the non-threaded section was spinning eccentrically compared to the threaded side. How I managed to do this is a bit of a mystery to me at the moment.

By the way, the threaded arbor did work, once tightened it the part was able to be centred with 0.01mm total runout, and the thread did not self distruct under the cutting load.

[Brendon M]

Been there done that. I had the same problems with the cheap Chinese three jaw that came with my lathe. I started useing my four jaw but I hated reclocking the part in every time I had to adjust the part in the chuck. Eventually I found the joys of the collet chuck. It makes life so much easier for small diameter parts. You might want to look and see if they have one. If they don't have one and you are stuck with the four jaw, I recommend makeing a tool post DI holder. It makes things much easier. See this thread:

http://www.modelenginemaker.com/index.php/topic,5001.msg95436.html#msg95436

Tony

Hello Tony, I finally checked out your link, that is such a brilliant and simple idea, thank you

Also, just to clarify, my issues are more likely being caused by wear and tear, if the "Made in England" is anything to go by!



I haven't finished machining the part as of yet, but I felt I should comment on my technique of centering a 4-jaw: there are better and faster ways. See here and here for two similar approaches.

My technique, while it worked, relies a bit too much on guessing the right amount to loosen and tighten, and I could spend many minutes chasing a decent runout, which meant I spent more time mucking with the 4-jaw than machining, hence why I didn't get far on my machining. 

Anyway, what I did attempt to do was to true up a bit of rod stock. The unknown mild steel bar I bought from the hardware store comes factory bent and slightly eliptical. I wanted to start with accurate rod stock for ease of centering in the 4-jaw chuck.

What I would normally do is hold the other end with a tailstock while I do my machining, but I've learned that you're not supposed to hold the stock with a chuck when turning between centres; the most likely outcome is a tapered rod.

That left another technique, where you machine a bit, as close to the chuck as possible, move the piece out, re-center, cut again, re-center { repeat until happy }

Centering as close as I can... On a side note, this 4-jaw is also made in England.


One bit done


After a few repetitions...


And I'm done... finally.


So I'm definitely keen to try out those faster techniques at my next session!

[Chipswitheverything]

Hi Brendon, would have sent a note earlier but for forum issues....     
    Don't worry about using ( or not using, as you have tried to do) the support of a tailstock centre for turning longer pieces of material when held in a chuck.   It's a perfectly valid method of giving rigidity to any slender barstock item.  The only proviso would be that the tailstock does need to be accurately lined with the centre line of the lathe.
  It's not all that often that true "turning between centres" happens in the workshop, and a tailstock that is "out" would render that liable to give a taper in just the same way.  On the whole, between centres turning is used for times when a component has to be removed from the lathe and replaced with certain accuracy, or turned end for end a fair amount.   Some of this technique dates back years to the days when lathes were a bit more primitive, using a modern precision lathe with good collets would mostly make the between centres method a bit redundant.
 Most lathes have a tailstock that can be "set over" for taper turning, and that also allows the centering alignment to be checked, and tweaked back to correct if there is a discrepancy.  ( Say, if someone has done some taper turning, but not restored the tailstock to centre position again  with care )  The accuracy in the vertical axis does depend on the general wear of the lathe, not so much that can be done to sort that out.
  If you have the necessary material for an item longer in length , such as the component that you have just made, chucked so that there is enough extending from the chuck, then centre drill and bring up a centre in decent condition, there's no reason why you shouldn't turn the length of it without having to muck about with the tedious re-centering and gradually extending to finish the turning operation.  The sharpness of the tool itself will help here too, honing it to a really nice edge pays dividends - it will cut effectively without deflecting the material very much.  Using something like a free cutting leaded steel, and a coolant oil also makes the task easier.

Cheers, Dave

[PStechPaul]

(1) You need to put your location in "Personal Text" for it to appear. 

(2) One way to deal with small parts may be to use a drill chuck or a min-lathe chuck, possibly held in the four-jaw chuck. The smaller chuck may provide a better grip, and possibly better concentricity. And you can still dial the four-jaw in as needed.

(3) You may also be able to make a set of soft jaws that grip evenly around a delicate thin-walled piece.

(4) It may be possible to make a collet by boring a hole the size of the part, and then cut thin slits so that the lathe chuck can apply pressure evenly.

(5) You might be able to insert a piece of stiff steel, perhaps a dowel, in the bore, and then chase the outside threads with no danger of bending or distorting the piece.

You're doing a good job with these small pieces. Thanks for sharing your experiences - many of us are amateurs and can always learn more tricks and techniques. 

[Brendon M]

Hello again. My apologies in advance, this is going to be a long post. But first, I will answer some replies:

Hi Brendon, would have sent a note earlier but for forum issues....     
...
 Most lathes have a tailstock that can be "set over" for taper turning, and that also allows the centering alignment to be checked, and tweaked back to correct if there is a discrepancy.  ( Say, if someone has done some taper turning, but not restored the tailstock to centre position again  with care )  The accuracy in the vertical axis does depend on the general wear of the lathe, not so much that can be done to sort that out.
...
Cheers, Dave

On this lathe, the tailstock does not appear to be adjustable for taper turning. So for precision rods, I am probably stuck with the tedius method. An incentive perhaps for me to start with precision stock to begin with

That said, I was trying to do this with a 3-jaw chuck - perhaps with the 4-jaw I can probably get the rod running close to true as possible and I won't see the problems with taper that I was seeing with the 3-jaw.

(1) You need to put your location in "Personal Text" for it to appear. 

(2) One way to deal with small parts may be to use a drill chuck or a min-lathe chuck, possibly held in the four-jaw chuck. The smaller chuck may provide a better grip, and possibly better concentricity. And you can still dial the four-jaw in as needed.

(3) You may also be able to make a set of soft jaws that grip evenly around a delicate thin-walled piece.

(4) It may be possible to make a collet by boring a hole the size of the part, and then cut thin slits so that the lathe chuck can apply pressure evenly.

(5) You might be able to insert a piece of stiff steel, perhaps a dowel, in the bore, and then chase the outside threads with no danger of bending or distorting the piece.

You're doing a good job with these small pieces. Thanks for sharing your experiences - many of us are amateurs and can always learn more tricks and techniques. 

It would appear a moderator has updated my profile for me, thank you to whoever that was

I had thought about using a drill chuck (though I was lacking a suitable means of holding it in the 4-jaw), but I decided it was time to learn how to use a 4-jaw chuck.

My recent attempt at holding the workpiece was to drill out a piece of scrap rod, tap an internal thread, and use this to hold the workpiece for the final finishing cut for the outermost diameter. This seemed to work well enough, but I still managed to stuff it up. I will get to that soon I reckon I will be trying your suggestion #5 for the final cuts.

First bit of good news: The lathe at CCHS has received a significant upgrade!



No more shimming the tool up to the centerline. While we only have two toolbit holders, for me it was more important to be able mount a toolbit and quickly adjust to centerline. Having a second holder means I can swap between two different toolbits quickly, but in general I only need one.



Now of course, the QCTP being purchased online means that it did not fit without a custom part being made. The original toolpost holder had a half inch bolt; the new QCTP had a bore of 16.4mm (0.6457 inches), so a sleeve was fabricated.



I did not make it. Instead, a regular member (and experienced metalworker) by the name of Rob at CCHS offered to make the sleeve, provided I supply the dimensions. As an added bonus, I got to see an experienced metalworker in action.

One thing that really impressed me was that he could convert from metric to imperial on the fly. You may recall that the Sheraton lathe is an Australian made knockoff of the Southbend 9", so all the controls are naturally imperial measurement. Not a problem for Rob; he would take measurements in millimeters, mentally subtract the remaining material to remove, and turn the cross-slide dial by the required thousands of an inch. I on the other hand, am not great at mental arithmetic. My working memory is shocking, so I need a pen and paper to keep track of previous calculations.

Furthermore, I rely more on my measurement instruments. If I am turning to a specific diameter, I will first set the digital calipers to the required dimension, and then zero. The caliper then keeps track of how much material I need to remove. This idea was borrowed from MyfordBoy.

On the other hand, CNC is considered acceptable, so I don't feel too bad on my reliance on computing machines

I also got shown yet another method for centering a 4-jaw chuck. Rob would wind the cross-slide in until the toolbit touched the outside diameter of the workpiece, and make a note of position on the cross-slide dial. He would then wind it back out, turn the workpiece 180 degrees, and wind the cross-slide back in again, noting the difference between the two readings. He would adjust the 4-jaw and repeat the above procedure until the cross-slide dial reads the same for both.

Again, I'd need a piece of paper to record the previous cross-slide dial reading, so I think I will stick with the dial test indicator!

And now for the bad news: I managed to muck up the part, so yet again I consign this to "trial pieces" bin. But I did take some pictures, so that's good.

As per my last post, I went with this plan of attack:

• Chuck a 1/2inch rod
• Turn down non-threaded side to 6mm (or should that be 1/4 of an inch, so I don't fight the lathe's native measurement system?)
• Turn down outside diameter by 10 thou, make it concentric and also to give smooth surface for dial indicator.
• Part off
• Flip the part, rechuck and re-centre
• Turn down to 7mm (fun working with Imperial Lathe and Metric thread die/taps!)
• Do thread
• Drill out entire part to 5mm (most nerve wracking step!)
• chuck up a piece of scrap rod, drill out to accept 7mm thread (I need the practice for tapping a thread anyway)
• turn down outermost diameter to 9mm, to remove tool marks

First up I decided to do step 9, where I drilled out and tapped a M7x1 thread in a piece of scrap rod stock -- the only part that is reusable between failures^H^H^H^H^H^H^H^Htrial pieces.



I then chucked the 9mm rod I created I created earlier in the 4-jaw. Using the centering techniques from the videos I listed in my last post, I was quickly able to get within 0.05mm runout. I probably spent a bit too much time afterwards trying to get it down to 0.01mm, but anyway practice makes perfect.

I then turned down to 7mm for the thread. Here is the finished M7x1 thread. Cutting threads is becoming less scary over time.



I then chucked up the threaded mandrel(? according to this forum, I should be saying mandrel) in the 4-jaw, and screwed the workpiece in tight to finish outside diameter, and trued up the workpiece as best as I could using the 6mm non-threaded end as the reference.

It was at this point I realised something had gone wrong. After turning on the lathe, I could see that the 6mm non-threaded side was running true, but the rest of the part was wobbling about the centerline!

I decided to true the part up in the 4-jaw using the outermost diameter as the reference. What I found is that most of the part is concentric, but the very end of the 6mm non-threaded side has a distinct wobble!

I have now realised that Step 2 should come after step 8, according to advice given here on turning thin walled parts. It had not occurred to me that drilling will produce a radial pressure, and considering the resulting wall is only 0.5mm for the non-threaded side, no wonder it keeps bending.

I continued out and turned the outermost diameter to 9mm, and I thought I'd try remove 5 thou off the 6mm non-threaded end to try and correct the wobble.

You can see here that the surface finish leaves a lot to be desired:



I think the problem here is chatter. I don't know if you can see it, but the surfaces look slightly warped, caused by an uneven cut along the length. My guess is that cutting these surfaces after drilling out has reduced the regidity of the workpiece.

Referring back to the advice earlier about turning thin walled parts, I should consider making a plug to fill the bore of the part while I turn down the outside, in order to reduce vibration. In which case, it appears I need some kind of expanding mandrel or perhaps a "superglue" mandrel for the final steps.

Sorry for the long post, and thank you for reading!

[Chipswitheverything]

Hi Brendon, thanks for your well illustrated and entertaining post on the latest progress with the Sheraton lathe.  Don't worry about the length of post, nice to have an article to read over breakfast here in the UK  !
  Looking at the photo of the lathe in your post a while ago, and the link about the machines, I can see a small screw head showing at the side of the tailstock base casting.  There is probably one on the back of the base too, and these are used to push the upper part of the tailstock body a small amount sideways along a tongue and groove guide within  the castings ( once the tailstock is unlocked from the bedways ) in order to do the setting over for taper turning.  Not suggesting that you necessarily have a play with this, but if there should be an alignment discrepancy, that would be the means of tweaking the tailstock centring.  You can run a check on the centre accuracy by putting your dial indicator on a small mag base on the chuck body, and running it ( by hand !) gently round a centre in the tailstock barrel and seeing that the reading is just the same either side.

  You are experimenting with an assortment of turning techniques that will give a good repertoire for other components that "turn up" !   Looking back to my comments about machining this particular small threaded sleeve ( Nov 13th ), when I suggested a way of leaving the item on its parent bar throughout the sequence of operations, I'm still inclined to favour adopting that approach.
 In general, as can be seen in a lot of the illustrations of machining processes here and there on this forum, keeping the component for as long as feasible on its "stalk" as you might say, can be more helpful than separating it and then having to devise ways of hanging on to a small scrap that is getting a bit fragile to clamp and secure.
 The smaller the component, and the more delicate the sections or walls ( and what you are presently making does come into that category, with the drilling through ), the more helpful it can be to think of making it on the end of a parent chunk, and cutting it free at the latest point possible.  When turning, it makes the concentricity problems much easier to solve.
  Though it's not in the lathe, the two pictures of the crosshead for my beam engine, still on a piece of 1/2" bar when mostly machined,, give an idea of what I'm getting at...
Cheers, Dave