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Thread: run out on Sheraton model A
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17th May 2011, 06:35 PM #1
run out on Sheraton model A
Hello
My old Sheraton AR has a runout issue when I fit a MT 3 ? sleeve into the main spindle .
It appears to be about 008" measured on the dial indicator with a MT2 dead centre fitted into the adapter . I am wanting to use a collet chuck eventually , and will this runout affect the accuracy of any work.
I checked the runout of the normal 3 and 4 jaw chucks screwed on the spindle end , and these are fine , no problem there. My MT3 taper in the spindle end may be stuffed up maybe ?
Mike in victoria
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17th May 2011, 08:19 PM #2Most Valued Member
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Have you checked the internal area of the MT to see if there is any damage or dags.
If there was something there you might be able to clean it up with emery,file stone or reamer.
If the Collet chuck was intened to be used to hold material of a finish size you would have trouble with that amount of runout,if on the other hand you were only holding material and turning the OD it wouldnt be much of a problem.
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17th May 2011, 09:22 PM #3Cba
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Mike,
Make sure all the taper surfaces are PERFECTLY clean, no dust or oil is allowed.
Any little dent or nick or scratch you should smooth out with a small handheld fine grade oilstone.
The sleeve you are using, is it from a reputable sorce? There are some very cheap sleeves around that have steps in the taper and other faults. If unsure, use some greasy "engineer's blue" (the one you use for scraping) to check if the inner and outer tapers really make contact. If you have no greasy blue, you may try with a marker. In doubt, buy a new sleeve from another source.
You mention a dead center. Usually the center you put in the headstock is a soft center. It is soft (as opposed to hardened) so you can true it up by turning everytime before using it. You are supposed to do this before turning anything between centers, that is supposed to come out accurate. Now you may be unknowingly be using such a soft center that was trued up before - maybe by the previous owner - and then it will obviously be totally out when you simply re-insert it at a random angular position.
If any of the tapers is in very bad condition (essentially past its useful life), an old trick is to rub it with some chalk (blackboard chalk) before fitting it together.
A stuffed spindle taper is no reason not to use collets. Many collet chucks are fitted to the spindle like a chuck, not by the taper. These have no through-spindle drawbar either, so you can fit thicker stock through the spindle too..
Chris
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17th May 2011, 10:26 PM #4Most Valued Member
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Chris can you elaborate on this soft centre that you inset into the spindle bore and then true up.
I have never come across one before.
The only (soft) centres that I have used are ones that I have made myself from round parallel bar held in a 3 or 4 jaw chuck.
The only spindle centres that I have used on numerous lathes have all been hardened.
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17th May 2011, 11:39 PM #5Cba
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Pipeclay,
no lathe spindle is pefectly accurate. Obviously a Hardinge or Schaublin spindle has less runout, but even these are made to tolerances and not perfect. Most good quality industrial lathes will allow for something like +/- 0.01mm runout in the internal spindle taper, and often it is twice as much.
To this you have to add the tolerance of a center. A good brand name center would be made to the same 0.01 to 0.02mm tolerance. Now if you put them togeteher, the errors will at random cancel out or add up. I have seen cheap centers that were almost 0.1mm off (not sure if from China or India, but in the $ 5 to 10 price range).
To make matters worse, the lathe may already be older and its spindle taper a little worn. The worst is actually if someone did put a not-so-clean chuck from a drill press into the spindle taper, and let it slip. Then the error can get REAL big.
Now, if you want to make a part as accurate as possible, that is when you consider making it between centers. Because by turning it between centers, you can correct for many of these small imperfections and errors that each lathe suffers from. For this purpose, the center that goes into the spindle is (or should be) always soft. You carefully clean the parts, tap the center into the spindle, set your topslide to the 60 degree angle, and at high rpm with a very sharp tool skim the point of the taper. Now, the point is running perfectly true. Anyway, as true as the spindle bearings will allow. Typically, even on a lathe with taper roller bearings (which never run as "round" as plain bearings do), runout shoud now be much better than 0.005mm. Even so on an old worn out spindle.
This "perfect" accuracy can of course only last for as long as the center remains in the spindle. If you remove it and later re-insert, it will most likely be totally off, You must true it up again by taking a skim cut.
Another (unrelated to above) reason to use soft centers is, that if a chip gets accidentally between the taper seats, the resulting dent will be in the softer (and very much cheaper to replace or repair) center. Not in the spindle taper, since better industrial lathe spindles are case hardened before being finish ground on journals and nose and inner taper.
Chris
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18th May 2011, 01:03 AM #6
Thanks
Interesting replies and very practical advice as well . Makes perfect sense when you listen to others who have the experience.
Mike
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18th May 2011, 08:33 AM #7Most Valued Member
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Chris as I said I have never come across these MT soft spindle centres and was curious as to where you purchase them.
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18th May 2011, 09:22 AM #8Cba
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The one I have came new with the Emco lathe 25 years ago, and I still use the same. So never had to buy one.
I think the large machinery tooling dealers should have them. I remember there are two kinds: either fully soft, or hardened with only the tapered tip left soft. I guess you have to pay the prices that these dealers ask.....
For home use you can also buy so called "morse taper arbor blanks". These ara available in many sizes wth tang or with a dawbar thread at the small end, and with a cylinder on the other end for you to machine. I just ordered and received five of them from Chronos in the UK (a supplier of tools for model engineers). Often ordering from the UK is cheaper than ordering in Australia. The saved GST goes towards the international postage. go here:
Engineering Supplies for model engineers | lathe and workshop equipment, Myford Boxford
and in the search window top right enter "arbor blank", you will be presented with 2 pages full of them. I found they sell sets of 5 for tyhe price that some folks here downunder want for one.
Chris
PS: maybe you have to ask explicitly for lathe spindle centers. Tailstock centers are of course always hard.
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18th May 2011, 12:59 PM #9Most Valued Member
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I have seen the Blank Arbors and was always under the impression that they were designed to allow you to machine the soft end for the purpose of fitting tooling to it which was not available off the shelf.
In all my experience I just have never heard of them being used in this manner or someone actually machining the point on a centre that is fixed in the lathe spindle.
Not to say it shouldnt or cant be done I just find it unusal.
What do you do with the remains of the MT after you have machined it beyond use?
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18th May 2011, 08:43 PM #10Diamond Member
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Soft Lathe Centres
Regarding Soft Lathe Live Centres a reply to Pipeclay & CBA Melbourne.
The Concept of using a Soft Lathe Centre, that is the Live Centre in the Headstock has been around for a long time.
I was taught this during a Toolmaking Course at Sydney Tech back in1959.
This method of trueing the live centre with the Compound Slide on the Lathe at 60 degrees ensures accuracy.& is a proven method.
By the way, thanks Pipeclay for the beaut set of transposing gears you made for me some weeks ago.This allows me to use my Imperial Hercus 260A Lathe to cut Metric Threads. The gears have been used & are great.Totally recommended.
Abratool
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18th May 2011, 10:16 PM #11Hercus 260
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Spindle Runout
FWIW the Bison 4MT centre (hard) when fitted in my 260 spindle shows zero runout on a Mitutoyo Dial Indicator ( 0.01mm marking)
Rotating it in the spindle makes no difference, the needle does not move.
I checked it many times.
So to measure any runout I need a much more expensive indicator!
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19th May 2011, 12:42 AM #12Turning useful pieces of steel into scrap metal.
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I too was taught ( back in the seventies) to always true a centre prior to turning between centres. HSS steel was the way to go with the truing tool, so the centres could not have been all that hard.
Turning useful pieces of steel into scrap metal.
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19th May 2011, 10:28 AM #13Cba
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Pipeclay, you only have to take a very fine skim cut to true a center, less than 0.05mm will do - that would be some 200 uses for 1cm length reduction. As I said, I am still using my very first center that I bought 25+ years ago, and it does not look too short to use yet.
I only do the trueing when I want to do a particularly accurate smallish diameter job.
As for the blank arbor idea, I only suggested this in case you have problems finding a soft center. It would take less than 5 minutes to turn a 60 degree tip onto a cheap blank arbor.
The soft center used to be explained in old machinery textbooks - but maybe not anymore in these days of computer controlled lathes. It is still mentioned here though:
Lathe center - Wikipedia, the free encyclopedia
Chris
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21st May 2011, 12:25 PM #14
Found problem
I found a score mark and a ridge about half way down the spindle end #3 taper bore . No wonder I was having problems . I will have to buy a 3 morse reamer and ream it out .
There was some discussion on the South Bend 9 forum as to the actual taper . Some are saying it isnt a #3 morse taper, but a taper South Bend used so only their adapter would fit . Is the Hercus/Sheraton definately a #3 morse taper in the spindle end ?
MIKE
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21st May 2011, 01:04 PM #15Most Valued Member
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Cant tell you if it definately is a 3 or not,only that a 3 will fit.
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