Some questions about lathe

[Mechanicboy]

Take a check on the lathe bed and you will find that there may be wear on the lathe bed that it gives a measurement error on the test bar. Be sure the lathe is not twisted.

 

[clockworkcheval]

The measurements to check the alignment of the centerline of your lathe can be complex and time-consuming as illustrated in the texts above. A quick way to check whether such measurements are required is to put aan thin metal plate between the centers in the headstock and the tailstock. The thinner the better. Any slight misalignment wil show up as deviation of the position of that plate from perpendicular from the centerline. As you can see from the pictures the alignment of my lathe seems to be OK.

 

[Mechanicboy]

The measurements to check the alignment of the centerline of your lathe can be complex and time-consuming as illustrated in the texts above. A quick way to check whether such measurements are required is to put aan thin metal plate between the centers in the headstock and the tailstock. The thinner the better. Any slight misalignment wil show up as deviation of the position of that plate from perpendicular from the centerline. As you can see from the pictures the alignment
of my lathe seems to be OK.

Although the plate between the two tips shows that it is in order. There is something else with the lathe bed itself that is most worn from about the middle of the lathe bed and further close to the head dock that it results in the dial gauge as shown in the explanation in the youtube movie.

 

[terryd]

what you want to do is to put a piece of metal between centers, turn it with a sharp tool, making several passes without changing the cutting depth, until there is no more cutting, then measure the diameter of the bar along its length. if it is uniform diameter (say within a tenth of a mm) then you are good. if it tapers uniformly, your tailstock is not centered with the headstock in one or more axis, if it has a irregular taper that generally indicates wear on the ways.

Or if there is a taper present the bed may be twisted and need adjustment with shims. There is a lot of information on the internet on how to rectify it. I first experience this when starting in a toolroom in '65. If taper evident when parallel turning first check is indeed tailstock offset, then if not that then bed twist.

I tend to not use the chuck when doing long turning jobs, I keep that for short work. I use the work mounted between centres using a catchplate and drive dog. Method is to centre drilll one end using chuck, fixed steady and tailstock. Then reverse work repeat centre drill at this end. remove chuck, mount catchplate and centre in spindle, a new centre (preferably a live centre) in tailstock mount drive dog on work and workpiece between centres (Fasten drive dog to drive spindle with wire or nylon zip tie). Work away to your hearts content.

TDX

 

[terryd]

Hi
I have been through the process of adjusting bearing pre-load on my Denford Viceroy lathe.
Take a look at this link to see what I did Headstock bearing adjustment

Hi Dazz,

I atach a small pdf, part of a larger one, from Boxford on replacing headstock bearings and setting bearing preload. Horace Denford as you probably know founded Boxford when he moved his business to Box Tree mills, it was he who introduced the A, B, C and CSB models based on the Southbend 5. He sold the business to Harrisons and started a new business (still in same premises) and as the Viceroy was aimed at the same educational market as the Boxford it is likely that there are similarities between the two.

Regards TDX

 

[pete]

Ok a properly heat treated, ground test bar made from the correct materials and no doubt thermally stabilized & lapped to size (for the very expensive one's) shouldn't show any warping changes in the future and be unquestionably correct to the guaranteed accuracy it's stated as having. However that's not the real world and mistakes or errors manage to get through the quality control of even the best company's in the world. I checked with Mitutoyo and even there high end steel gauge blocks aren't permanently stable. So with anything of high accuracy you first have to start with an already verified baseline and work out from there. I've got some pretty decent North American made MT test bars. The very first step is personally checking it's diameter along it's length. To .0001" or better if you and your micrometer can do so. The full length may be the exact same diameter, it still doesn't mean it's accurate to that level because that's only half the checks. Those diameter measurements can't prove it's even straight. For that you need to indicate that test bar while it's supported by a pair of V blocks and slowly rotated. Since nothing is ever "perfect" there will be some measurable deviation on even the best that can be produced if your indicator has enough resolution and repeatability. Any minor inaccuracy can still be worked with since the amount and where, is then known. If you don't personally check what you have your already lost because of the uncertainty of any test numbers your getting. I check my test bars first with the parallel length on the V blocks, indicate each end as well as the middle, and then spreading the V blocks apart so the small end of the MT is supported by and rotated on one V block. The change in height between the two ends makes no difference since your only checking the bars actual run out. Then I run one last check with the MT's large end resting on that V block and again indicate both ends. If it's not obvious yet, both ends and at least the middle should be indicated for each check. And as Perertha correctly pointed out, re-checking your test bar after some time is a worthwhile just in case since it takes only a few minutes.

There's been multiple methods and variations invented to check multiple areas on machine tools for there alignment. Some well meant but misinformed one's as well because many haven't taught themselves to properly visualize the task in all 3 dimensions or fully understand what there checking and why. Lucky for us someone back around 1930 literally wrote the book about basic machine tool alignment checks and how there measured and properly done. Run a simple Google search for the free online PDF of the book Testing Machine Tools written by a Dr. Georg Schlesinger. His concepts and methods are almost universally accepted and form the basis of machine tool certificates or when fully rebuilding them pretty much world wide even today. My own lathes certificate of accuracy was certainly based on that same information. A few modified and additional methods for today's multi axis CNC have been added by others, but the basics for manual machine tools are still as true as the day his first edition was printed. A simple check of that PDF will show that many don't seem to have heard of or know that the better and best lathes ever made are purposely misaligned at the factory for both the head and tail stock. That's for a couple of sound logical reasons. Those head and tail stocks are pointed both uphill and towards the operator by around .001" over 12" to help compensate for work piece weight and the forces involved while there cutting. No that less than .0001" per inch isn't much, but it's an important and necessary detail. Secondly that very slight misalignment forces the lathe to face concave and start to wear in towards facing flat instead of immediately wearing towards facing convex. That flat or concave condition is so two faced parts will fit face to face without any highly undesirable rocking. And fwiw, I also had to learn the hard way a few lathes ago that any new machine should be checked using Schlesinger's methods for any gross errors while it's still under warranty. Cheaper off shore machines can't and won't be nearly as accurate as his maximum allowable numbers, but they should be at least in the ball park of being correct.

 

[Mechanicboy]

Googled and found the book


The book Testing Machine Tools written by a Dr. Georg Schlesinger , See the size 57 about "Testing lathes".

 

[william_b_noble]

was looking to see if my copy of "the Starrett book" was 1st edition (it might be, it's dated 1915), and I ran across this Starret Book that might be useful to some, and it's on line and free.

 

[dazz]

Hi Dazz,

I atach a small pdf, part of a larger one, from Boxford on replacing headstock bearings and setting bearing preload. Horace Denford as you probably know founded Boxford when he moved his business to Box Tree mills, it was he who introduced the A, B, C and CSB models based on the Southbend 5. He sold the business to Harrisons and started a new business (still in same premises) and as the Viceroy was aimed at the same educational market as the Boxford it is likely that there are similarities between the two.

Regards TDX
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Hi
The Denford Viceroy is definitely better built than the Boxfords. Hardened chrome bed, more/better accessories, separate lead/feed shafts as standard etc etc.