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618 Headstock Alignment

Discussion in 'ATLAS, CRAFTSMAN & AA' started by marchyman, Mar 21, 2017.

  1. marchyman

    marchyman United States Iron Registered Member

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    Background: My lathe is a Craftsman/Atlas 618 (sleeve bearings) probably made in the '40s. It had been sitting for 15 to 30 years before it was given to me as mostly a pile of dust and rust. I took it apart, cleaned it, removed the rust, slapped on some primer, and with the help of the 618 Yahoo group was able to replace most broken or missing parts. The result is a mostly running (if well worn) lathe.

    The issue is this. The headstock is lower than the tailstock. A center placed in the tailstock points above a center in the headstock. My choices are to mill the tailstock or shim the headstock. I've not the equipment or experience to hold the tailstock square and level for milling. With shims I can safely make mistakes.

    I want to measure the difference in heights to figure out what size shims I need. I was thinking of mounting some drill rod in the four jaw and adjusting until it runs true then measure the height with a test indicator in the tool post. Next I'd put the same drill rod in the tail stock. Measure again. Calculate the difference. That should be the thickness of the needed shim.

    Will that work? Is there an easier way?
     
  2. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    It seems strange that the headstock would be lower than the tailstock. There is no opportunity for wear of either the bed or the headstock. I would suspect that wear at some other point on the lathe ways is creating the misalignment. It may be that when you bring the tailstock up to check the center alignment, the back end of the tailstock is in an area of wear on the ways which would tilt the center upwards. You could check this by measuring the misalignment of the centers with the tailstock quill retracted and extended. If there is a tilt, you will see a difference.

    You can tilt the tailstock center downwards by placing a shim between the tailstock and the base at the rear of the tailstock.
     
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  3. marchyman

    marchyman United States Iron Registered Member

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    I measured the height of the quill extended and retracted. That's only 1 and a half inches. I used a bore gauge (because it's what I have) between the quill and a parallel across the ways and made measurements with the tail stock at different locations. My ways are worn so I expected differences. Surprisingly the tailstock was mostly parallel to the ways. Measurements were within 0.002" and it didn't make much difference if the quill was extended or not.

    I don't like the idea of shimming the rear of the tail stock since it is mostly parallel to the ways.

    But I don't know if my spindle is parallel. Hmmmm....
     
  4. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    As has wisely been stated in other threads, you need to identify the source of the misalignment before attempting any corrections. Corrections made in the wrong places will create other problems, oftentimes more serious. It isn't too likely that the lathe came from the factory with the headstock set lower than the tailstock but it is possible that the previous owner made some changes. At this point, nothing should be ruled out though.

    Dirt or a burr in the Morse taper sockets can throw the center off quite a bit. In the headstock, it would manifest itself as runout which can be checked by rotating the spindle. It is harder to detect in the tailstock though.

    You can evaluate wear in the ways with a straightedge and the assumption that the bed nearest the headstock and the far right end have experienced little wear. A known good straight edge and some feeler gauges should give you some information. I have a 6" Craftsman, albeit a decade or so newer than yours and there is a small strip running down the middle of each way where neither the carriage nor the tailstock travel which should be a fairly pristine surface.

    It is also possible that the bed is twisted.. The lathe has only two mounting points on either end but it has a fairly broad foot. If the lathe were mounted to a less than flat surface, tightening the mounting bolts could twist the bed. Improper shimming could also create a twist problem. If the bed hasn't been permanently sprung, loosening the mounting bolts should improve the situation.

    Wear in your spindle bushings could cause the spindle to droop. My lathe has bearings and is tight but bushings require some clearance to function properly. The clearance will increase with use. If the spindle is tight, then you need to check the spindle axis alignment. A two collar test or Rollie's Dad's method will tell you if the spindle axis is parallel to the ways.

    With the spindle running true to the ways, you would move on to the tailstock. There are a number of ways to check for tailstock alignment. Edge Technology (http://www.edgetechnologyproducts.com/lathe/) makes a tailstock alignment bar. An adaptation of Rollie's Dad's method will also do the job. Have you checked your tailstock for shims? It is possible that the tailstock was replaced with one from a different year which may have had different dimensions. There are others on this forum who are far more knowledgeable than I am regarding Craftsman lathes who could offer some insight into that.

    A few ideas. A systematic approach to diagnosing the problem should determine where the problem(s) lie. Good luck!
     
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  5. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    Another quick and easy way to check headstock/tailstock center alignment is to trap a piece of shim stock between the two centers. The shim stock will align in a plane perpendicular to a line between the two points. The shim should be fairly thin as the angle developed is the arcsin of the offset/shim thickness so a thin shim is more sensitive to offset. I used piece of utility knife blade which I ground to about .8" x 1.5". As I recall, the thickness is around .035"
     
  6. marchyman

    marchyman United States Iron Registered Member

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    My spindle bushings are new. Spindle axis alignment is unknown and needs to be checked. The Rollie's Dad method was unknown to me -- looks easy enough. Thanks for that pointer. Bed twist is a real possibility. I have almost zero space in the garage and the lathe is on top of a movable cart/table. I have to move the cart to use the lathe. It is not the most stable of work surfaces. I should see about trying to stiffen up the base before doing anything else.

    The MT2 taper in the spindle was badly chewed when I got the lathe. I lightly ground the taper such that I can get repeatable readings, but I still don't trust it. If use of a center is needed I re cut the center taper each time it is installed in the lathe. Or I cut a center held in the chuck.

    My vertical offset can easily be seen with the naked eye -- maybe .020". I need to get it a lot closer before using a shim between centers to check alignment.

    Thanks for your comments. I've plenty to do to address this issue and get the best results possible from the old lathe.
     
  7. David S

    David S Canada Active User H-M Supporter-Premium

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    The tail stock body is actually two parts. The lower part that travels in the ways and the upper part that can be adjusted to offset it for taper turning. Have you checked to make sure the two sections are seating securely?

    David
     
  8. marchyman

    marchyman United States Iron Registered Member

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    Yes, there is no discernible gap between the two sections. Given the large offset between headstock and tailstock it would be easy to see if a gap in the tailstock was the cause.

    And I just remembered this:

    [​IMG]

    I found that crack after removing the rust from the bed. It is at the headstock end of the lathe. It does not go all the way through the bed but it could contribute to misaligned spindle, e.g. the spindle might be pointing down enough to make me think there is a height error. I'll be checking if the spindle axis is parallel to the ways later this afternoon.
     
  9. David S

    David S Canada Active User H-M Supporter-Premium

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    Oh that does not look good at all.

    David
     
  10. Round in circles

    Round in circles United Kingdom Active User H-M Supporter-Premium

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    I checked the alignment of my headstock chuck & the tail stock chuck using two large sharp darning needles that I'd cut the eyes off .

    With every thing closed up , the trailstock ram inboard there was barely a discernable difference between the needle points , four inched back with the tailstock & fully extend the ram , a bit more showed , reduced to nothing when I gently applied the ram clamp a bit but not so tensioned as to lock the ram . .


    In truth when you think it through , it matters not much whether the center line is up or down a few thou , it is across the lathe bed that alignment that matters .
    That's why you should use the gibs on & the adjusting screw at the rear lower edge of the tailstock to set it true to the centre line or for an offset as the need arises .

    It took me a while for the penny to drop wrt alignment till I purchased an old second hand book of lathe practices . It showed how to make test bars & said why you needed them .
    So may I suggest that you look up turning a test bar between centers ?

    Make a 4 " one & then without doing any adjustments try & make a 14 " between centers . No doubt you'll be very surprised to find that on most lathes you can't do it with any great degree of accuracy . So to do the 14 " test bar between centers you'll have to sort out /check the alignment again .

    If you make up an accurate set of say a 4 , 8 ,12 & 14 inch long test bars ( treat them like delicate eggs & protect them in individual packages ) it is a matter of just a few minutes work to change the alignment for the different distances & to compensate for any wear between the bed surface inner edge faces . all you do is pop the centers back in the head stock & tail stock then use a rounded blunt tool or a roller bearing on an angled bar securely held in the tool post clamp to lightly touch the bar at both ends ..... adjusting as required at the tailstock adjuster .

    It may sound a total PIA but after a while when you get used to doing it with accuracy you'll speed up & start to get some precision in your turnings over varying lengths.

    Scrub all the above I've just seen the " Very Interesting crack " after I posted this .

    A pal had recently repaired a heavy casting off a big wood cutting cast iron bed bench saw for me that was broken in two at a point that was 3 inches long x 1/2 inch thick cast iron .It's holding a big 24 inch dia bench saw blade spindle to the saw bench .

    Perhaps someone with cast iron arc brazing knowledge for an autisinal ( SP?) weld can give you some better advice than me .

    For I'd say grind the faces clean of all paint , rust & crystallized broken cast iron . Then grind it out with a 2 mm thick disc into an equal Vee at the edges & cut right through the crack as far into the metal web as you dare .
    Set it to be level over blocks of steel , using heavy weights or big clamps to ensure the bed is flat & true . Then arc braze it from both sides of the cleaned out crack . Leaving a decent ridge of braze standing proud across & above the crack on both sides .
     
    Last edited: Mar 22, 2017
  11. marchyman

    marchyman United States Iron Registered Member

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    The spindle wasn't even close to being parallel with the ways. A close inspection shows cracks on both sides of the bed. The crack are in line with the chuck side of the headstock housing. Playing with shims under the lathe legs I got the vertical offset down from 0.023" over about 8 inches to about 0.09". That took about 3/16 worth of shims under the foot pretty much below the cracks. The horizontal offset was better, but is still off about .006" over 8 inches.

    I'm beginning to believe the only way to get the lathe where I want it to be is to replace the base and the cost of that makes it more likely that there will be a modern mini lathe in my future.

    Thanks for everyones ideas.
     
  12. francist

    francist Canada Active User H-M Supporter-Premium

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    Thats really unfortunate, looks like someone might have dropped it or something. Regardless, it's a real drag and I feel for you.

    -frank
     
  13. wa5cab

    wa5cab Downloads Moderator Staff Member H-M Supporter-Premium

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    marchyman,

    This has nothing to do with your alignment problem but although your lathe is a 6x18, it is not a 618. The 618 is the Atlas model number of the lathe with Timken spindle bearings. Yours is a 101.07301.

    WRT your problem, it's just my opinion that you are spinning your wheels attempting to shim the errors out. You need to replace that bed. I'll add that yours is the first one that I ever heard of that was cracked.
     
  14. yendor

    yendor Active User Active Member

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    As a thought.
    You pretty much never see beds come up on ebay as they are just too much to ship.

    But all the parts that you see on ebay came off a lathe and there was a bed attached to them at some point.

    If any of the parts sellers are local to you, you could try emailing the vendors.
    They typically sell of the beds for scrap, but if you could do a local pickup you might get a good one cheap.
     
  15. David S

    David S Canada Active User H-M Supporter-Premium

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    If this was my lathe here is what I would try first, all depending on whether I would be doing light turning or more heavy stuff.

    First make a good base for it. For my 618 I made a support out of multiple layers of MDF glued together to form a flat thick base.

    Next drill 3/8" holes in the feet close to the base so that a piece of all thread could be passed through the head stock foot, under the bed and through the tailstock foot.

    Next bolt the headstock end to the base. Now with nuts on the allthread, start drawing the feet together to see if you can close up the gap. Check alignment. If you can get it back in alignment bolt the tailstock feet down, lock the nuts on the all thread.

    If it doesn't work you aren't out much, and the lathe should have a good base anyway.

    David
     
  16. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    If you braze or weld the crack in the bed, you will most likely create warping issues which could destroy any alignment built into it. On the other hand, a crack like that could grow to the point where bed breaks in two.

    I think that I would bridge the break with a short length of angle iron mating to the side bottom of the bed, drilling and tapping holes into the casting. An L shaped piece, with a cross section something like this: Mend  Plate.JPG

    You may have to cut relief for the half nuts, depending on the location of the break and you should clean up the casting for a better fit. I would use flat head screws on the front surface for clearance for the apron but the back and bottom can be hex head or socket head screws. I would also bed the angle with epoxy to fill any irregularities and help to stabilize the mend.

    It is possible that you could correct some of your alignment problems by loading a stout bar between centers to straighten out the bend caused by the cracks. I would do so with caution, however as rather than closing the gap, you may further the crack. Perhaps a better idea would be to use two bar clamps to pull the lathe feet together.

    You won't be able to restore the lathe to pristine condition but you will be amazed at how much you can do with a less than perfect machine.
     
  17. David S

    David S Canada Active User H-M Supporter-Premium

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    I think if you consider my post and RJ's you may be able to still get a useful lathe. I was thinking of "sister" strips or "fish plates" over the crack along with JB weld once all is brought back to true.

    You can'/t make it any worse and I think you could make a huge improvement.

    Let us know what you decide.

    David
     
  18. wa5cab

    wa5cab Downloads Moderator Staff Member H-M Supporter-Premium

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    I'm afraid that I have to disagree with any attempts to weld a cracked lathe bed. The lathe already has too many issues with alignment. Any welding will most likely just add more. Given the number of Atlas parts that turn up on eBay, there are a lot of beds floating around. You just need to find one with good ways.
     

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