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  1. #16
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    Michael, this is the rwason why I think a smaller 3mt tool would have more purpose than a 5mt even if there was a tradeoff in some accuracy. Thanks Techo. Yes a 2 collar test would be a good way to verify alignment. I did attempt some realignment using 2 collar method but having to tension up the headstock bolts each time to redo another test cut was painful. At least with a test bar they can remain somewhat loose for the entire process. A 2 collar could be used once they have been tensioned up.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  2. #17
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    Quote Originally Posted by Techo1 View Post
    Using a test bar is not necessarily the best method to align the headstock, Colchester recommend using the "Two Collar Method" with their adjustable headstock models, after removing any twist from the bed, of course.
    - The two collar method bases on the assumption that the headstok has been accurately scraped to the bed. To verify this assumption, a test bar is needed.

    - Colchesters are expensive lathes and it is safe to assume headstock to bed are accuratly scraped together and can repeatably be reassembled. But low cost lathes do rarely have the headstock scraped to the bed (else they could not be low cost). On these machines headstock alignment is done by torque shimming. Which is not repeatable neither in the horizontal nor in the vertical plane. Hence the need for a test bar. The two collar method cannot work in this instance, because the spindle center line can be tilted up and down quite a lot, before you would notice a diffence in two collar diameters. The two collar method is very sensitive in the horizontal plane, but not so in the vertical plane.

  3. #18
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    Quote Originally Posted by cba_melbourne View Post
    - The two collar method bases on the assumption that the headstok has been accurately scraped to the bed. To verify this assumption, a test bar is needed.

    - Colchesters are expensive lathes and it is safe to assume headstock to bed are accuratly scraped together and can repeatably be reassembled. But low cost lathes do rarely have the headstock scraped to the bed (else they could not be low cost). On these machines headstock alignment is done by torque shimming. Which is not repeatable neither in the horizontal nor in the vertical plane. Hence the need for a test bar. The two collar method cannot work in this instance, because the spindle center line can be tilted up and down quite a lot, before you would notice a diffence in two collar diameters. The two collar method is very sensitive in the horizontal plane, but not so in the vertical plane.
    I haven't posted here for a very long time, but couldn't let this mis-information go without comment as it perpetuates a myth that seems to feed itself.

    The above statement is completely false and Techo1 is quite correct in what he has stated. Vertical alignment can be confirmed by running an indicator along both the top and side of the collars once they're turned. If they mic the same size and clock the same both vertically and horizontally, the headstock is aligned with the axis of the bed. End of story, and no, a test bar is definitely not required.

    What you've done by turning collars is create your own "test bar" that will be as accurate as you're able to turn. Indeed you don't even need to turn collars, and they simply make the whole process faster as it can be quite laborious if you turn full length multiple times when aligning things. Personally I have never understood why amateur machinist buy test bars. As Michael has pointed out they are more useful for other purposes, and especially aligning a tailstock, however once again one can be made on the lathe itself and will be as accurate as you would ever need it. Furthermore, as that alignment is done between centres, it doesn't matter what taper you have, as you won't be using it.

    Test bars are used in professional applications as they make alignment much faster and don't require the lathe to be powered. That can be critical when rebuilding a lathe and scraping components in. However with a running lathe it is not required and I would consider them a complete waste of money for most people. Personally I would encourage anyone to instead spend the money on quality stock that you know the pedigree of so you can just go out and make "stuff" rather than wasting money on "gadgets" like test bars.

  4. #19
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    Simon,
    I am surprised no one has yet mentioned "Rollie's Dads Method" (use Google).

    The method assesses alignment of the headstock relative to the saddle traverse, both horizontally and vertically.
    It is as sensitive as the measuring equipment and the surface finish on the test bar and does not involve operating the lathe.

    The bar can be bent, non-parallel and mounted in any chuck, but the closer all aspects are to a perfect set-up the easier the number crunching will be.

    John

  5. #20
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    Well I had made the decision to buy a test bar and now you guys come up with some very good reasons why I don't need one. Pete F. (nice to hear from you, been too long) mentions wasting money, well I certainly don't have money to waste so perhaps I should heed the advice he and others have given me and try other methods. Michael, I know you mentioned making a test bar but I dismissed it siteing that I needed a TTA. I have since realised that I don't. The MT taper can "easily" been turned between centres. Of course I don't need to tell you that! I have never turned a taper B/T centres so it din't jump straight into my head. I have a piece of steel that may be made for such a project, it's from an old car axle. Perhaps I should live with the alignment for now and put that on my "to do" list?

    Hi John. I have heard of RDM. I don't think it's a recognised method of headstock alignment. I think it's more for when you know you HS is aligned (as it usually would be) and it's used to level a lathe in the absense of a precision level. I could be wrong, I know a few people here have mentioned it's not a suitable method for HS alignment. Such subjects tend to be robustly discussed when brought up, which is why I was trying to avoid HS alignment theory but it's pretty hard not to get into the theory and in any case I now know more on the subject than I did yesterday!

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  6. #21
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    Quote Originally Posted by simonl View Post
    Hi John. I have heard of RDM. I don't think it's a recognised method of headstock alignment.
    It's a kludge for worn lathes to get them to turn more or less parallel.

    I agree with Pete F - you don't need a test bar. Get a nice chunk of aluminium about 300mm long, 40mm dia and a really razor sharp tool. Cut & measure diameters next to the chuck & 150mm out from the chuck. Adjust until you get the same measurement or run out of patience.

    Recently did this with my Colchester Chipmaster which is *designed* to align the HS in this fashion - full instructions in the manual. I got the taper down to 0.0003" in 6" whatever that is in metric. and it took me maybe 30 minutes, probably half of that. Could have improved on the taper but I had work to do and that was close enough for getting a good sliding fit for a shaft inside a bearing carrier (more prop shaft work - thrust bearing assembly).

    PDW

  7. #22
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    Simon,
    you can just use the compound for cutting your taper rather than having to go through the process of offsetting the tailstock.

  8. #23
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    Quote Originally Posted by Pete F View Post
    ........... Vertical alignment can be confirmed by running an indicator along both the top and side of the collars once they're turned. If they mic the same size and clock the same both vertically and horizontally, the headstock is aligned with the axis of the bed. End of story, and no, a test bar is definitely not required.............
    Yes, you can first align the headstock in the horizontal plane until both spools have the same diameter, then align it vertically until the indicator clocks the same on top of the spools whilst ensuring the diameter of the spools remains the same. In practice this will work on a good quality lathe whith the headstock scraped to the bed, where errors are very small to begin with.



    On cheap lathes that use torque shimming to align the headstock, this method is simply not practicable. It would take several days to complete. The floating headstock has simply too many freedoms of movement:
    - it can move back to front
    - it can rotate around the vertical axis
    - it can rotate around the horizontal axis
    - it can move up and down

    That is four adjustments to take care of, with the help of only the four hold-down bolts being torqued differently, and maybe some shims. Each and every of these adjustments will affect ALL others. It has to be done recursively. That would require hundreds of spool test cuts if no test bar is available. I believe that you have never had the chance to align a headstock that requires torque shimming. Here the sequence of such alignment:

    1 - it can move back to front: you position the headstock, such that it lines up horizontally with the tailstock set to its center mark. There often are grub screws in the headstock that brace against the hold-down bolts to facilitate this.

    2 - it can rotate around the vertical axis: You slightly tighten the hold down bolts, and rotate the headstock until the test bar is parallal to the ways in the horizontal plane. Then re-check 1 which will have moved

    3 - it can rotate around the horizontal axis: You tighten or loose the two front and the two rear hold down bolts alternatively, until the test bar is parallel to the ways vertically. This may require shims as well. Then re-check 2 which will have moved. You do 2 and 3 alternatively, until the hold down bolts are reasonably tight, whilst the test bar must still be parallel in both axes. Of course, you need to re-check bed levelling between these steps, as a perfectly untwisted bed is prequisition to all above.

    This is how its done at the factory, and it can take half a day if you do it first time. At the factory they now select a tailsock from a pallet full of tailstocks, that matches the center height of the heastock. But you only have one tailstock, and that is very time consuming to adjust, particularly upwards. You now must adjust the headstock height.

    4 - it can move up and down: You can torque all four hold down bolts together to move the headstock up and down. You may have to add or remove shims, as without shims you can only move a few hundrests of a millimeter this way. Some lathes have paper shims between headstock and lathe bed to increase adjustmant ranges. After every adjustment, you have to correct 2 and 3 and 4 recursively. You have to do that many times over. Its a 4 to 8 hour job with a test bar, but it would require hundreds of spool test cuts and probably a week or more with the spool method. This step 4 can be an incredibly time consuming complication. If it was easy, there would be no need for factories to use matched tailstocks.


    I hope you now understand the difference between an expensive lathe and a cheap lathe. Frankly, I would rather start scraping the headstock and the tailstock to the bed, rather than to try to align the headstock of a cheap lathe by torque shimming if all I had was the spool method to verify alignments. It would be much quicker.

    Now you will ask why are there at all lathes that use torque shimming headstocks? It is because many of us simply cannot afford the price of a good lathe. To my knowledge, all cheap Chinese bench lathes are made like this. My Austrian Emco lathe is made like this too, albeit with much better finished (ground, not just machined) interface between headstock and bed. It still has to be torque shimmed into Sclhesinger specs, but its an easier job than on coarsely machined Chinese lathes.

    NEVER touch the headstock hold down bolts of a torque shimmed lathe, NEVER separate headstock from bed of a torque shimmed lathe, unless it is absolutely necessary. As doing so opens that can of worms described above.

  9. #24
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    Thank you Chris, I feel I have a good "understanding" of lathes, cheap or otherwise.

    The fore/aft alignment you mention makes zero difference to a lathe's accuracy, and a competent person should be able to align a headstock as you describe with only a few iterations. We are not discussing scraping anything, although the principles remain identical.

    A statement has been made that an alignment bar is required to align a headstock. That statement is false. Yes an alignment bar will make coarse alignment faster and more convenient, but it is not and I repeat, NOT a requirement to align any lathe. Cheap, expensive, or somewhere in between. They are the facts and that's the end of that. If somebody feels that convenience is what is desired that's great, and if they wish to spend their money on test bars who am I to say not to. However I personally think the time would be better spent on doing it the traditional way by turning, thus gaining a greater understanding of how lathes actually function and improving one's skills in the process. The money can be spent on materials and/or tools instead of something that gets used only seldom before being shoved to the back of a cupboard. While factory built lathes are definitely aligned with test bars in a factory, the final test in any quality lathe is to do test turning and confirm the lathe is turning within tolerance. Anyone is free to skip straight to this step, notwithstanding the fact that it requires the lathe to be powered. As we are all end users and not machine manufacturers, that shouldn't provide much imposition.

    A hint incidentally is to shrink and/or Loctite some collars of more easily turned material on to a pipe to make the whole thing less tedious and faster to make instead of turning down solid stock. Take a couple of thick disks of brass or aluminium and bore them to shrink onto the pipe. They then form the "collars" for the test, while the pipe is rigid and light. In case it's not obvious, each time this "test bar" is removed from the chuck it will need to be re-turned when returned to the chuck. If you really want to get fancy, plug the end of the pipe and centre drill the ends, the test bar can then be used between centres for tailstock alignment.

  10. #25
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    Don't be too dismissive of Rollie's Dad's Method but, the method is specifically not useable for detecting bed twist.

    Simon has stated that his lathe has a bolted attachment that allows sideways rotation of the headstock on the bed and that this is now suspect.
    Correction of this situation is exactly what RDM does best.

    I have read threads where the author described scraping in the head bolting surfaces of a Monarch lathe.
    This involved multiple test/remove headstock with RDM bar left in the spindle/scrape/refit cycles.
    There is an enormous body of forum discussion on this subject.
    Subjects like bent spindles, bar sag and mathematical analysis all add to the discussions.

    RDM is not the perfect tool for all requirements, but it does this one very well.

    Just try it Simon, you might be surprised.
    John.

  11. #26
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    Quote Originally Posted by electrosteam View Post
    Don't be too dismissive of Rollie's Dad's Method but, the method is specifically not useable for detecting bed twist.

    Simon has stated that his lathe has a bolted attachment that allows sideways rotation of the headstock on the bed and that this is now suspect.
    Correction of this situation is exactly what RDM does best.
    Huh???? If the lathe HS has lateral adjustment, you level the bed, measure the taper and adjust the HS to eliminate the taper. RDM has nothing at all to do with it.

    Quote Originally Posted by electrosteam View Post
    I have read threads where the author described scraping in the head bolting surfaces of a Monarch lathe.
    This involved multiple test/remove headstock with RDM bar left in the spindle/scrape/refit cycles.
    There is an enormous body of forum discussion on this subject.
    Yes, it has been thrashed to death ad nauseum on PM. RDM is a kludge. It's mainly used on lathes with beds like wet noodles (South Bends and Hercus come to mind). Try it on something rigid like a 10EE, a CVA or a Chipmaster and see how you get on.

    I recall abom tweaking the levelling screws on a big Monarch but it had bed wear and the HS is scraped to fit on the bed V ways. I have the same model lathe so I'm very familiar with it. Different animal altogether - moving the HS on one of those isn't a 30 minute job that's for sure.

    Quote Originally Posted by electrosteam View Post
    Subjects like bent spindles, bar sag and mathematical analysis all add to the discussions.

    RDM is not the perfect tool for all requirements, but it does this one very well.

    Just try it Simon, you might be surprised.
    John.
    DON'T try it, Simon, if you have an unworn level bed, do it the proper way. It might take longer but in the end you'll get a better result.

    As for torque shimming, the HS has already been *off* this lathe so any settings are already history. Therefore it's irrelevant. Forget about HS lateral alignment with the TS, that's why tailstocks have lateral adjustment. Check to see it's not pointing up/down and here a test bar would be useful then align to cut parallel.

    If the HS is out in a vertical plane it's time to break out the scraper anyway. Cheap manufacturers might shim at this point but there's no way I would.

    Must be a million threads on PM about this, I can't be bothered arguing over it any further.

    FWIW and totally unconnected, I was in Hare & Forbes the other day and the AL960B is still the cheapest/smallest lathe that has any decent quality.

    PDW

  12. #27
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    Quote Originally Posted by Pete F View Post
    ........... Yes an alignment bar will make coarse alignment faster and more convenient, but it is not and I repeat, NOT a requirement to align any lathe. Cheap, expensive, or somewhere in between...............
    You have never aligned a headstock that required the torque shimming method, have you? There is no point before you have made this experience yourself.

  13. #28
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    Quote Originally Posted by electrosteam View Post
    .......Don't be too dismissive of Rollie's Dad's Method but, the method is specifically not useable for detecting bed twist.......
    Actually, Rollies Dad proposed this method explicitely and only to untwist the bed, without needing to own a precision level and a test bar.

    An undisturbed and correct headstock alignment is prequisition for this method. Thus follows this method cannot be used to align the headstock without the bed being untwisted first. And that CANNOT be done without a precision level and a test bar.

    Over the years, many folks have forgotten what the RD method was originally intended for, and they make use of some techniques described in the RD method and taken out of context to do all sorts of magic things. It usually does not work in practice.

  14. #29
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    Quote Originally Posted by cba_melbourne View Post

    - Colchesters are expensive lathes and it is safe to assume headstock to bed are accuratly scraped together and can repeatably be reassembled.
    Well actually they are cheap lathes for UK made machines of the day (that is why training centres use them and not say DSG lathes) and they sit on flats so the headstock is adjustable..
    Gold, the colour of choice for the discerning person.

  15. #30
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    Quote Originally Posted by .RC. View Post
    Well actually they are cheap lathes for UK made machines of the day (that is why training centres use them and not say DSG lathes) and they sit on flats so the headstock is adjustable..
    True. The only really good lathe Colchester made was the Chipmaster and it has plenty of shortcomings - Kopp variator and short bearing area saddle being but 2. They do have quite massive bed castings and a rigid HS spindle in Gamet bearings though.

    OTOH it at least has a 3MT TS with locking tang slot, unlike the superior Monarch 10EE, which is a flimsy 2MT.....

    The Taiwanese made Dashin lathes were a better machine than the Colchester that they copied IMO. Funnily enough I was looking at a used one in H&F the other day.

    PDW

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