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[How do I?] "map" The Errors On A Older Lathe?

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jjtgrinder

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#1
I am at the point that I want to "MAP OUT" all the wear so I can determine where the problems are. I feel like that is the best first step. Then I can determine how to correct them, and so forth.

I have been "slogging" thru the "Machine Tool Reconditioning" by Connolly and the articles that Micheal Ward wrote in the "Home Shop Machinist" magazine. I am at a point that making measurements would be informative for determining the next action.

I read that there may be a method that allows using lasers to make the measurements.

True or rubbish? Any ideas or help would be greatly appreciated.
 
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#2
When I look at a machine tool such as a lathe, there are three areas i look at.
1) wear on the ways
2) mechanical things like the apron, headstoock and such,
3) Electrical

Wear on the ways.
How worn are the bed ways? With a little experience, you can make a determination of the degree of wear. Is it not too bad? Is it worn to the extent that it shows ridges and obvious areas that are worn? Compare the worn areas with that is not worn. And this is something that can be done without a need of an straight edge. Straight edge can be used later for fine tuning how much wear there actually is.
Next move to the cross slide ways. Again what degree of wear does it have. Is the cross slide loose in the middle and tight on the ends?

Once these things have been done then you can work on how to fix these things. OR not to fix them. Do you scrape and re-fit slides? or do you send it out and have the bed re-ground? If you have a decent Bridgeport size mill, some of the repairs can be done right there in your own shop.

This is just a start. It goes on and on.

BTW- I just bought a 14 x 40" Rockwell lathe just like the one in your avatar.
 

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#3
As Connelly pointed out many times in his tome, Machine Tool Reconditioning, you need to look carefully at the guiding ways of machines for the least worn areas to find the original surface planes and then scrape "straight down."

You will need a decent straightedge as long as the ways are to map out the wear properly, and a scraped precision straightedge(s) to scrape them. For instance, after looking carefully at the ways, use the unworn ways along the headstock and the relatively unworn ways at the tailstock end to reach an estimate of the original surface plane in those sections alone. Then lay the straightedge on the ways and check the gap all along the bed. Typically you will find the most wear near the chuck and in the first couple feet from the chuck toward the tailstock. The straightedge and feeler gauges can give you a good idea of the wear that exists. When you go to recondition them, please read and understand Connelly carefully and well. Starting with the wrong parts first and using poor choices of which ways to do first will cause much extra work, perhaps enough to scrap the lathe before it is done. Understand his methods. It makes sense when you truly understand what you are trying to achieve and how it relates to successive parts of the machine. Scraping is slow work at best, and you need all the help you can get. I am sorry, I know nothing about using lasers and do not trust me using the concept because of it. It is not rocket science, they could do fine work in the mid to late 1800's with the tools they had then, why not today?

Tell us about the machine...
 

jjtgrinder

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#4
Thank you for the replies. I am still trying to finish reading the book by Connelly. I thought I would begin trying to identify all the problem areas while I'm still reading the book.
My lathe is also a Rockwell Delta 14 x 40. Most of the wear is in the carriage ways near the chuck. The lathe cuts a taper when you chuck a round bar and make a light cut. The taper is smallest near the chuck.


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chips&more

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#5
Maybe just live with it. Use the lathe as it is. Wear conditions can be foreseen and then planned around. Something broken or missing on the lathe, maybe not so and must be fixed. My lathe has a few tenth’s taper in it when turning round. I live with it. Most of the time it means nothing in my projects. If it does, then I know it’s coming and work it out. If this is your hobby lathe and not building stuff for NASA. Maybe just live with it…Good Luck, Dave
 

jjtgrinder

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#6
Understood, chips.


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#7
When you say "it gets smaller at the chuck end" How much are talking about?

Typically with a worn bed, the taper is usually big at the chuck end and small toward the tailstock.
 

jjtgrinder

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#8
When you say "it gets smaller at the chuck end" How much are talking about?

Typically with a worn bed, the taper is usually big at the chuck end and small toward the tailstock.
Ken,
I would have to make a cut and make some measurements to give you solid figures. Do not remember the differences. Like .002 in 4" if I recall.
 
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#9
Ken,
I would have to make a cut and make some measurements to give you solid figures. Do not remember the differences. Like .002 in 4" if I recall.
If you are only getting that much in 4", that is pretty darn good in my book. My best lathe is lucky to get that in 2" on a good day!
 

astjp2

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#10
if the ways on the bed of a Rockwell are worn, you can scrape in the carriage but the bed will need to be planed not scraped. Many of the Rockwell lathes have hardened ways and scraping is not practical for them. I have the 11 Rockwell, you can see pics of how I measured my ways by doing a search and you can see my king way tool, I also have been accumulating different indicators in the .0005 to the .0001 range. Someday I may actually have my lathe back together.
 

hermetic

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#11
It is easy to become obsessed with accuracy on older machines, but the truth is, unless you know what the dimensional accuracy of the machine was when it left the factory, you cannot know how far it has deviated from that point. In order to make any useful measurements on bed wear it is absolutely useless to start from the 3 jaw chuck which is very likely the most worn and inaccurate part of the machine. Even a brand new 3 jaw chuck of good quality will run out .003" to .004". If you really want to do an objective test, you need to start from the machine spindle, not a chuck. Remove the chuck and carefully clean both the headstock and tailstock tapers Get a test bar, and fit this between centres of known good accuracy (or new, with a certificate of tolerance), and fix a good DTI in the tool post. Move the compound slide until the V ways are fully hidden, then tighten the gyb screws to lock the top slide. Zero the DTI on the test bar and lock the cross slide or tighten the gybs. Run the DTI along the side axis of the test bar, then adjust the tailstock set over till you get the least deviation possible on the side axis. If you now run along the top axis you will get a reading of the fall between the headstock centre and the tailstock centre. Make a note of this. Move the DTI to the headstock end of the test bar, lock the carriage, and rotate the lathe slowly by hand, and note down the deviation Mark the high and low points with sharpie on the bar. Move the DTI to the tailstock end of the test bar, and repeat, turning by hand and note the reading. Now set the test bar so that the marked high and low points are on the top and bottom faces of the bar, so that the finger of the DTI runs along the null point of the front axis (face) of the bar. Wind slowly and gently, if you wind too hard the pressure on the gears will move the carriage slightly, remember that cutting force pushes the saddle onto the bed Vees. Note down the deviation. Move the carriage to the tailstock end of the bed, where the wear will be least and try to rock the carriage across the lathe using A LIGHT push pull motion. Remember there are no cutting forces present to push the carriage hard down on to the bed, and you are trying to detect front to rear movement on the carriage without forcing the carriage up the vee ways of the bed, note the deviation, and repeat at the headstock end, and in the centre. You now have some idea of the wear in the bed, but remember, the harder you push, the more deviation you will see, but what you are seeing is not necessarily wear, it is just the carriage moving because there is no cutting force present to hold it down onto the vee ways.

Now you have a simple choice, either spend time and money correcting it, or live with it. Personally, I live with it unless it begins to affect what I make, then I find the problem, and find a way to work around it. The only thing a super accurate lathe does is grant you bragging rights in the bar, I know many turners who turn out accurate professional work as employees using machinery that is far from new. Most accuracy comes from the operator knowing his machine, and making allowances for any wear present. I used to use a 3 jaw chuck which ran out about .015" if you put a bar in it and tightened it up. With some care and tapping, I could get the error down to about .006", but if the component I was making was being turned on all surfaces, finished and then parted off the bar, the fact that there was .006 difference in concentricity with the bar left in the chuck is completely irrelevant. This is why you should always start with a bar slightly larger than your finished dimensions and turn all to size, rather than start with a bar with the finished outside diameter. Even a brand new quality lathe is built to tolerances, and I know that my worn machines are still more accurate than I am! Remember if everything was turned to 0.0000 (were it possible to do this) as soon as the temperature changed, it would seize up!
 

Al 1

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#12
That was very well written Hermetic. I agree. Al
 

jjtgrinder

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#13
If you really want to do an objective test, you need to start from the machine spindle, not a chuck.
Hermetic, First and foremost, thank you for this very thorough and well written information.

As a supplemental to my understanding, if I chuck something (2 1/2" round stock)and turn it with a light cut, upon measurement, I will see the error in that portion of the ways that the saddle/carriage traverse. True? Understanding that there are some influences such as gib adjustment and so forth.

My main goal at this point is to fully understand all the dynamics of the current "state of affairs", thus I can be a better operator of the machine and consequently know how best to proceed. Proceed with
some corrective action or work with the machine as is.
 

jjtgrinder

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#14
Hermetic,

I would like to hear your ideas on the diameter of the test cut being smaller at the chuck end of the test cut bar.

Would the automatic feeding of the carriage being pulled tend to wear the ways ahead if the saddle? The leading wipers were not replaced and had imbedded cutting chips, and so forth. Cutting chips can be like small hardened material that scrapeand wear the cooresponding ways.
 

hermetic

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#15
Hi jjtgrinder,
What you need to do first is establish the runout on the chuck, by putting a dti onto a piece of ground round stock held in the chuck. The drawback with doing this is that the three jaw chucks are not repeatable, that is, if you take the bar out of the chuck and then replace it and test again, you will probably get a different set of readings, and the more worn and bell mouthed the chuck is, the more variation you will get. That is why I suggested to take the chuck off and work from the spindle. Really (in my above post) you should put a centre in the spindle, then check that with a tenths DTI mounted in a locked carriage , when you have confirmed that the centre is concentric with the spindle, fit the test bar, centre the tailstock, and then with a DTI in the SPINDLE run round the tailstock centre to see if that is concentric with the spindle! In other words, how far do you want to go? there will be minor inaccuracies in ALL of these readings, but you can learn to live with them. If of course you find that the centre is NOT concentric with the spindle you must stop the process, remove the centre and look for the reason it is not concentric, such as damage to the spindle bore taper, dirt or swarf etc. When this is removed/repaired and the centre is concentrically seated in the spindle, (remember there WILL be runout on the spindle, it will be small, but measurable, and can only really be measured on the internal taper of the spindle, or the outside of the chuck register if there is one, not easy!) You continue to the next stage, removing as much error as you can at each stage. If you are going to use a chuck, first strip it and clean it, and check for wear on the scroll (the spiral which operates the jaws) and check the fit of the scroll plate in the chuck body, because if there is more play (wear) than there should be, when you tighten the chuck, the scroll plate moves slightly sideways and the jaws tighten unevenly. You must also check the fit of the chuck on the spindle and that the chuck backplate is concentric with the spindle when fitted. Any damage to the register behind the thread is critical to the chuck being concentric with the machine, it is the register which centres the chuck, not the thread. Likewise if you have a chuck that fits to a taper fitting like the L0 type, that taper must be undamaged for the chuck BODY to be concentric with the spindle, this does not mean that the jaws will be concentric with the spindle for the reasons given above, this is why it is best to work from the spindle, you are removing several areas of possible inaccuracy that you could eliminate instantly by buying a new or better chuck. Three jaw chucks are workhorses, they are not ever accurate to close tolerances, and they are NOT repeatable. That's why the most accurate chuck you will ever own is a 4 jaw! (Or a collet!)
Phil
 

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#16
Hi Again, you posted while I was typing.............. we need to get the terminology clear here, most important. If you mean by "the diameter of the test cut being smaller at the chuck end of the test cut bar." You mean that the lathe removed more metal nearer the chuck, or to put it another way the diameter of the test piece is smaller nearer the chuck, and gets larger as you move away from the chuck. If this is the case this would more likely be a slight twist in the bed, which can be corrected, and would mean that if you stand at the headstock end of the lathe, looking down the length of the bed, the twist is clockwise, IE the vees get slightly further away from the centre as you move away from the headstock.. Embedded chips I don't like the sound of! Is there visible scoring on the Vees, if so as long as it doesn't cover the whole of the vee, the bed should not have dropped, and you can correct wear (to a certain small amount, by slightly twisting the bed in the opposite direction, but we are getting way ahead of ourselves here) can you post up some pics of the lathe, and some closeups of the bed, especially the areas you think are the most worn.
Phil
 

hermetic

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#17
if I chuck something (2 1/2" round stock)and turn it with a light cut, upon measurement, I will see the error in that portion of the ways that the saddle/carriage traverse. True? Understanding that there are some influences such as gib adjustment and so forth.

Yes, this is true...................to an extent, what you need to know is where the inaccuracy is, and the problem is that what you are seeing is cumulative errors, a bit here and a bit there, it depends on the type of lathe. Once you have taken a full cut from the outside of the bar, the bar will be concentric with the spindle (subject to any spindle error) but may not be (probably won't be) parallel. If the lathe is bolted to its original cabinet stand and on a fairly level floor there should be no bed twist, but if there is, you would correct this by shimming where the bed bolts to the cabinet stand. If the lathe is the type with separate legs at either end, it must be shimmed to the floor , which should be as level as possible, and then bolted down with the bolts just snugged against the shims, then you do a turning check and add or remove shims till you get as near perfect as possible, or you run out of patience and say "near enough"! What I am trying to say is that you cannot make sense of wear in the bed until you know that what you are seeing is wear, and not twist, or a combination of the two, and if you have the separate leg type of lathe, or a bench lathe bolted to a wooden bench, you MUST untwist the bed before you can make any other measurements, Thats why I have asked for some pics.
Phil
 
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#18
When I did a test cut on my 20" L & S lathe a while back, it did the same thing, taper smaller toward the chuck. Measured .0015" in 12". Bar diameter was at 3" OD. Material was ductile iron, something that was handy at the time. I made sure the bed was level with no twist at the time I made the test cuts. Tool push off, I doubt it! Using positive rake tooling, very stout setup, freshly rebuilt lathe, including a re-ground bed. I'm not a bit disappointed! In fact tickled to death that it cuts that close and good for a 60 year old lathe! If you follow Dr. Schlesinger's guide to "Testing Machine Tools" accuracy, he says .0008" in 12" allowable in either direction! Ouch! Do we really need that kind of accuracy in the lathes we play with?

Ken
 

hermetic

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#19
No Ken, we don't, that is good work, and a machine that is as accurate as it needs to be, in fact probably more so! Of course you could try a .0015" shim under the front tailstock end foot....................................here we go again!!
 

hermetic

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#20
I have two lathes, an early sixties Colchester Mk1 Student, and a Covmac. I have just had the workshop floor in what is going to be the new "machine shop" re concreted, and it is very flat and level, thanks mainly to the fact that I didn't do it! I got a pro in with his lads and a powerfloat. My Student is a straight bed model on an original steel cabinet, but the Covmac is on separate legs and so it will definitely need shimming and bolting down in order to get it to turn parallel.
 

hermetic

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#22
This lathe, but mine has a box pillar under the headstock with a door on it which gives access to the belt adjuster .
 

jjtgrinder

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#23
Hi Again, you posted while I was typing.............. we need to get the terminology clear here, most important. If you mean by "the diameter of the test cut being smaller at the chuck end of the test cut bar." You mean that the lathe removed more metal nearer the chuck, or to put it another way the diameter of the test piece is smaller nearer the chuck, and gets larger as you move away from the chuck. If this is the case this would more likely be a slight twist in the bed, which can be corrected, and would mean that if you stand at the headstock end of the lathe, looking down the length of the bed, the twist is clockwise, IE the vees get slightly further away from the centre as you move away from the headstock.. Embedded chips I don't like the sound of! Is there visible scoring on the Vees, if so as long as it doesn't cover the whole of the vee, the bed should not have dropped, and you can correct wear (to a certain small amount, by slightly twisting the bed in the opposite direction, but we are getting way ahead of ourselves here) can you post up some pics of the lathe, and some closeups of the bed, especially the areas you think are the most worn.
Phil
I will post some pictures tomorrow. I"ve been busy with family today. Just thought I would respond , you've been so kind to offer all this information. The vees are scored somewhat. The lathe did indeed remove more metal nearer the chuck. I am headed out to the shop to work on a side project, I will snap the photos for you. I have some of the saddle and ways posted in my album on the yahoo Rockwell Delta forum. Can you see those? If so I will add all photos there for future reference. My lathe is on a wood platform which is on a flat concrete floor. The lathe bed is bolted to sheet metal cabinets.

Thank You again.
 
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#24
No Ken, we don't, that is good work, and a machine that is as accurate as it needs to be, in fact probably more so! Of course you could try a .0015" shim under the front tailstock end foot....................................here we go again!!
Won't work on my lathe! It has a center leg in the equation. I could shim the center leg. I leveled it with a 199 level for twist only. I could have left a dip in the middle, I doubt it though. It's setting on a 3" slab at most, with fairly stable ground under the concrete. I sure if I had a lazer with readings down to six places, it would pick up me walking on the concrete! May even pick up into a tenth or two, walking across the concrete floor!

Anyways, getting way out of text here.
 

hermetic

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#25
A centre leg! never thought of that, now that complicates things no end................................I think i feel a headache coming on!
Phil
 

jjtgrinder

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#26
43c3b6e5fc9153bbebbbc04556bb846d.jpg


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jjtgrinder

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#27
Hermetic,
I could not create an album in this forum , got a server error. I posted some photos in the Yahoo Rockwell Delta Forum album under "John Wrights Rockwell 14". Can you see those?
 
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#29
John,

The wear you're showing in your pictures, is about the same wear I have in my 58 year old 13" Sheldon Sebastian lathe. Really not bad! Could be better. I just live with the wear. I do have intentions of rebuilding the lathe in the near future for the second time since I've had it. For me, there's a place in Dallas I can take the bed to and have it reground for a start. Just realized you are over in Mississippi. I don't know if there is anyone closer to you or not? If you want to have the bed reground, I can give you some direction on getting it done and shimming and scraping and fitting the saddle to the freshly ground bed.

edit: BTW, my Rockwell lathe may be in a little better shape than yours as for the bed. Now the rest of my lathe may not be.

Thanks for sharing.

Ken
 
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#30
Here's some pictures of the "mapping out" of the wear on my L & S bed before and during grinding. I made a "sled" that ran up an down the bed tracking on areas that are not worn by the saddle or any other equipment on the lathe to map out the wear on the bed, similar to what John has done.

I also used this sled to do the grinding on the bed too.

DSCN0588.JPG DSCN0589.JPG DSCN0638.JPG DSCN0640.JPG
 
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