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Precision Tailstock Alignment

I think I've got half a good idea, but need help with the other half!

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mgj23/04/2011 08:59:33
1017 forum posts
14 photos
I wonder we need to go lowering headstocks.
 
I imagine there is a serviceable tailstock base, - its the bit above which is the poblem.
 
Were I going that route, I would ask the suppliers to get me a blank casting for the tailstock upper and machine. Or I'd go to someone like College Engineering Supplies and buy a chunk of cast iron the right size and machine that up, to fit existing quills and the like. It would involve a fair bit of miling, but none of it would be complicated. That might be a lot easier than trying to take a headstock off and cutting vee bedways and the like.
 
First stop for me would be to check to see if fitting a new quill would do the job and is feasible. Work out the new diameter , set the lathe bed exactly and precisely, bodge up a tailstock puller off the carriage to permit power feed, and bore the tailstock to the new dia off the lathe. Once the "tube" is bored, I'd fit the new quill and fittings, and bore/ream the MT in the quill, again finishing in situ.
 
It might not have the funny angles,(it would be dead true) but then nor does my Myford, and that seems to work well enough!
Scrim23/04/2011 09:27:19
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19 forum posts
On second thoughts, my bed fitting technique is only for taking off small amounts of metal so I wouldn't want to try lowering the headstock myself. Instead I think I'll end up doing a good job raising the tailstock with shims.
Gordon W23/04/2011 09:47:20
2011 forum posts
It seems to me to be a crazy idea to try to lower the headstock, which presumably is all OK. Apart from all the other problems you'll lose height over the bed. Making/ acquiring another tail-stock seems the easiest. Is it possible the machine has been dropped at some time, maybe on the long journey? Or am I missing the point?
Clive Hartland23/04/2011 11:56:31
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2929 forum posts
41 photos
It has just come to me, how do they bore out the quill shaft hole in the tailstock?
Is there some boreing tool that can travel and be driven from the headstock?
 
mgj's idea sounds good but possibly bore a few mm oversize and make a sleeve and fix in place and then bore that to take the existing quill shaft, later true up the taper from the headstock with an MT reamer.
This will bring it all up to the headstock height and also bring it in line.
 
I think that the idea that the tailstock has been switched at some time is more than feasable and no doubt there is someone else out there iether oblivious of a problem or who is also seeking an answer.
 
Clive
Les Jones 123/04/2011 12:19:13
2292 forum posts
159 photos
I too like mgj's idea. I think before doing this it should be confirmed that there is no dirt between the bed and headstock and that it is seated correctly. (Sorry to repeat this comment from a previous post but I think it is important.) I also think it would worth measuring the centre height of the headstock from the flat surface of the bed so that others could be asked to check theirs for comparison. (If it is not the standard height there would be no point in even considering buying a new tailstock as a possible solution.)
Les.
mgj23/04/2011 12:44:25
1017 forum posts
14 photos
Boring tool .
 
You need a pilot hole - I don't know how long this one has to be. If its short enough you could use jobbers drills.Or a set of blacksmiths drills - any cheap way of getting a near sized hole.
 
If its long, one is going to need a proper gun drill to make that first incision as it were. That will cost.
 
 
Next step is to get the hole to size - you just make up a big thick boring bar, or several if you are going up in steps. I did a TE piston rod guide with a 1.25" dia bar carrying a 1/4" bit inclined fwds at 45deg. I locked it in the 4 jaw since that gives a better grip than the 3 jaw. Best would be an MT and a drawbar I suppose.(and properly adjusted headstock bearings)
 
Bit has to be really really sharp and you just go backwards and fwds twice (I think) per size of cut to make sure all the spring gets taken out of the tool. Its not difficult, its just tedious.
 
The great thing about such holes is that they are always parallel (apart from the very first smidgen where the load is applied, and thats not going to affect us) If one has a sexy applier of the bit, then one can cut to size. Otherwise you get to a close size and make quill to fit. I'd finish size the quill with emery and oil to have a clearance of about .0005"
 
You do have a chicken and egg in that you need a quill to make a quill, and you have no accurate tailstock. So you have to make a plug for the Tstock bore to carry a centre, once you have a new aligned bore.
 
Or one finds a friend (if one has have any!(with machine tools) ), or you join the SMEE (plug for worthy cause ) if you live near London, and use their machinery.
 
----------------
Scrim - we have a problem.Several actually
 
You are talking about measuring with calipers. Calipers, even nice Mitutoyo ones are all well and good, but they only read to 1/2 a thou. They are nice quick and convenient. Accurate in the true sense of the word, they are not. We (Gray me and the others) are talking about measuring to 1/10 of a thou.
 
How  can you set up a lathe straight, and talk of bed adequate bed fitting, when it would appear that you cannot, with the equipment you have available, measure to within 100% of the limits required?
 
So that is one direction that you need to go in - because you cannot set your machine up to do the preliminary work with a pair of calipers.
 
The other is away from hand grinding which I think you mentioned. Perhaps we are talking of different hand grinding, in which case I apologise in advance.
 
At the moment you have merely a dodgy tailstock, and you could get round that temporarily using an offsettable boring head fitted with a centre, or shims. Start hand grinding and you will have a glossy bit of junk which you will never repair.
 
This has been a very intriguing post, - I have enjoyed it a lot - but my most earnest recomendation is that you take the time to get the machine back to the suppliers, and get them to sort it. You write the cheque of course, and it will possibly be quite a large one, but not though as large as the one you may have to write if some of your suggestions are adopted?
 
If genuinely you have the expertise to sort this problem, good luck to you, and all credit - but if you have that expertise, why  start this post? If you have doubts, then just throw money at the problem - its the quickest, cheapest and most painless way of making it go away.

 
 
 


Edited By mgj on 23/04/2011 12:45:39

Edited By mgj on 23/04/2011 13:13:47

Scrim23/04/2011 15:42:27
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19 forum posts
Thanks again for all the help. I feel confident I have all the issues in mind now and one way or another I'll get the problem solved.
 
The hand grinding technique I have in mind is described somewhere on the web for fitting a saddle to bed by using double sided taped strips of abrasive paper on the bed ways. Done carefully it can produce a very good fit, but it's a very manually intensive.
 
I mentioned the caliper just to illustrate that some parts of the lathe are accurate to 0.01mm whilst other parts can be out by 0.5mm.
 


mgj23/04/2011 16:11:26
1017 forum posts
14 photos
Well I did apologise in advance, but I hope you will allow me to suggest that there has been a lot of grabbing at fixes, without clearly identifying where the error lies.
 
May I ask a three questions?
 
1. What exactly is the error?
2. What is causing it.?
3 What steps have been taken to eliminate the effects of other factors which may influence that error?
 
For instance, its no good shimming anything(except under the feet of the lathe)if the bed isn't set straight. If as Les has suggested, there is a chunk of grot or a bit of paint under the headstock, you will always get an error. How do you identify Les suggestion without taking half the machine apart? I have heard nothing of the use of test bars or turning tests, yet you need these things to find these errors, never mind reassembling the machine after lapping/grinding bits off it. Do you have them?What tests did you do, and what were the results?
 

 
 
 

 
 
 
 

 

Donald Wittmann23/04/2011 18:14:01
40 forum posts
Scrim,
Before you go adding to, or taking off anything from the tailstock you must first ensure that the HEADSTOCK is set true and there is no twist in the bed. You should turn up a dumbell and held in the headstock and first get that to turn true [parallel] then you have eliminated any error in the head stock. and should only then move on to the tailstock.
it may even be a combination of errors involving the headstock and the tailstock hence the need to eliminate any [if any] error in the headstock . and if you use a clock then use a good one that measures in 2 or 3 microns it might sound overkill for a chink lathe but once you have found out where the error[s] lie then it will make your life a lot easier. in getting your lathe set up just right. How long it will stay like that is another question.
Good luck.
Donald.
mgj23/04/2011 19:25:56
1017 forum posts
14 photos
Absolutely.
Scrim26/04/2011 00:55:19
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19 forum posts
OK, I really do need to check the headstock fitting and everything else, but I've come to this problem being happy with the way the lathe cuts in general and just wanting to make the tailstock usable for now rather than take on sorting the whole lathe alignment out at the moment, but I do understand the points made about this.
After further thought this is what I intend to do for now, until I get around to the full fix. I'll finish the job I started, fitting the lower part of the tailstock to the bed. Then I'll find what shims are required between lower and upper tailstock and epoxy these in place such that the tailstock is at least a lot better than currently. Right now I need the tailstock to do some work. When time permits I do the full check of my lathe alignment, identify what need to be done and then consider how to do it in the light of all the great help offered here.
Thanks again. I hope the discussion has been as useful to others as to myself.
Regards,
Scrim
David Clark 126/04/2011 09:44:17
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3357 forum posts
112 photos
10 articles
Hi There
First, set up your lathe.
Check out this article
 
It shows how I set up my myford lathe.
The principle is the same for your lathe.
 
Then I would check the alignment of the headstock.
You can do this by facing a plate in the chuck.
Does the lathe turn flat or perhaps a thou dished?
Then and only then, you can shim the tailstock if necesary after clocking up the bore and ensuring the tailstock is on centre.
Clock it with the barrel fully retracted and then about 3 inches (75mm) out.
If it clocks the same horizontally and vertically, the bore is probably true.
All you need to do then is ensure it is correctly in line with the headstock and shim it up if necessary.
 
Do not lower or otherwise modify the headstock.
Modifying the headstock is rather stupid and a recipe for disaster.
regards David
 
 
Scrim27/04/2011 02:56:48
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19 forum posts
Thanks again.
Currently my lathe is sitting on a flimsy desk using the basic rubber feet it was supplied with! It's better than a hammock, but not much! I'll be moving to its final location in a month or two where I'll really concentrate on fully setting it up.
 
To answer an earlier question, my Super C3 headstock axis of rotation is located 90.45mm above the flat areas of the bed when measured just in front of the supplied 3-jaw chuck. I measured it by facing a short bar in the chuck and lightly scribing three fine lines across its face with a height gauge, turning the chuck 1/3 turn between scribes. By trial and error, cleaning off the last lines with fine abrasive, I got all three lines to cross at one point as viewed through a 10x loupe, and then recorded the height gauge reading. As a rough indication of accuracy, a second measurement a few days later when I mistakenly thought I'd lost the first one came out just 0.01mm lower.
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