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  • Is my lathe broken?

    Hi folks,

    I picked up this Denford Viceroy lathe a few months ago and have just finished replacing the transmission with a belt drive and installing a VFD. I was planning on converting it to CNC (an ambitious undertaking, I know!).

    I don't know exactly what I'm looking at, but, I'm getting some odd behavior from the spindle. I've uploaded a video to YouTube showing my various tests.

    Firstly, the lathe has not yet been levelled, and is cutting a 0.06mm taper over 50mm, but, I don't know if either of these facts impacts on the problem shown in the video.

    The 'register' is indicating less than 0.01mm of runout, but the internal taper (and any center held in it) are running out massively, and the register on the chuck backplate that came with the lathe has massive run out, yet the face of it is running true.

    I've no idea what's going on here but I'm hoping I don't have a bent spindle.

    If I chuck up a straight part - like a chrome rod or a piece of drill rod - I get loads of runout, but, that might just be because the chuck is knackered, and I only have one that fits this lathe.

    I would really appreciate it if anybody who knows a thing or two could look at the video and let me know what to do/check next, as I'm beginning to worry I have a dead horse on my hands.

    If the internal taper on the spindle is simply rough/damaged causing the dead center to run off, then why is the register on the chuck backplate (shown at the end of the video) showing massive runout too?

    I'm tempted to order a new chuck backplate and a 4-jaw chuck and just see how close I can dial a part in, but, I don't want to spend any money until I know what I'm looking at.

    Spindle bearings are adjusted with a little preload here, and the spindle taper has been cleaned religiously.



    Cheers,
    Rich
    Last edited by loply; 10-09-2012, 05:02 PM.

  • #2
    How about reboreing the taper in the spindle?

    Richard

    Comment


    • #3
      I know the video is a bit long but if you watch it to the end you'll see that the chuck backplate is also running out, so I think the issue goes beyond the spindle taper.

      Comment


      • #4
        The outside of your spindle seems to be running true, as is the edge of the register, since your faceplate isn't running out, but the inside of the spindle seems out of kilter when measured directly or with a centre inserted.

        Could it be that the internal taper of the spindle has been damaged or incorrectly reamed out? I would get a known good male taper, blue it up and offer it to the spindle taper to see what kind of contact you're getting - that should give you an idea if the spindle taper is out of whack. It might be something as simple as a burr that needs flattening.

        Comment


        • #5
          Get yourself started on the right path by begging, borrowing or stealing a good Dial Test Indicator with an extra long probe.
          Clean the inside taper of the spindle then run your finger around inside and feel for burrs or rough spots. Indicate the inside taper and mark and record the high spots, then indicate the exposed bearing race that is turning in the video mark and record the high spots again.
          Report back.
          Has the spindle been removed at some point and reinstalled if so the bearing can be "cocked" or have the bearings been replaced?

          Comment


          • #6
            I don't like seeing the runout get worse as you get further from the bearing. That makes me think the spindle is bent, but hopefully there's a happier explanation.
            Any products mentioned in my posts have been endorsed by their manufacturer.

            Comment


            • #7
              Look at your bearing. It most likly in bearing not the spinlde. Look for any chips some lathes will get chip in the roller/ball

              Dave

              Comment


              • #8
                Are you supposed to beable to see inside the bearing like it shows near the end of the video? Seems like it should be sealed or covered. I now see where a cover must bolt on.
                Last edited by flylo; 10-09-2012, 06:52 PM.

                Comment


                • #9
                  Hi folks,

                  Just been out and had another look at things.

                  First off - one problem solved - it turns out the bore on the back of the chuck backplate is 3 thou oversized, which explains the large amount of chuck runout. I checked the spindle register and it is precisely 1.5000 inches but the backplate bore is 1.5003 so that can hit the bin. I could rebore and sleeve it I suppose...

                  Now that I seem to have solved that I can presumably get a chuck mounted properly, so I'm hopeful I simply need to run a reamer through the spindle taper. I need to get a new backplate to find out for sure though, I guess.

                  With regards to the bearings, the spindle has been out, but the front bearing remained in place on the spindle, and the rear one is pushed back in place by tightening the locking nuts that would preload the bearings, then slackening them off again. I'm confident that bit isn't the problem because neither bearing races were removed from the headstock, and you can exert great force to reset the rear bearing on the spindle by tightening the locking nuts.

                  I notice that the DTI on the taper doesn't swing constantly like it would with a bend, it stays static for 90 degrees at a time then shifts suddenly, as it the taper has been squared out a bit... Perhaps by having things bashed in it to remove dead centres or suchlike.

                  Comment


                  • #10
                    The name on the video is quite catchy, sounds like an Army training film!

                    Comment


                    • #11
                      Originally posted by MetalMunger View Post
                      Get yourself started on the right path by begging, borrowing or stealing a good Dial Test Indicator with an extra long probe.
                      Clean the inside taper of the spindle then run your finger around inside and feel for burrs or rough spots. Just a reminder directed at any new people on the board...never do this under power, always by turning the spindle by hand. Even if your finger is highly unlikely to get caught in the taper that is probably a #3 MT, it's a bad habit to get into, especially if you happen to do it with a #2 MT. Indicate the inside taper and mark and record the high spots, then indicate the exposed bearing race that is turning in the video mark and record the high spots again.
                      Report back.
                      Has the spindle been removed at some point and reinstalled if so the bearing can be "cocked" or have the bearings been replaced?
                      Originally posted by loply View Post
                      Hi folks,

                      Just been out and had another look at things.

                      First off - one problem solved - it turns out the bore on the back of the chuck backplate is 3 thou oversized, which explains the large amount of chuck runout. I checked the spindle register and it is precisely 1.5000 inches but the backplate bore is 1.5003 so that can hit the bin. I could rebore and sleeve it I suppose...

                      I don't think that affects it at all. The registers on my chuck backplates are all considerably oversized and they all thread on and register properly every time, unless there is a small bit of swarf in the threads. It appears that the 60 degree angle on the threads is all that is necessary to center the chuck properly. This has been discussed in the past also, btw.

                      Also in your video, I didn't notice you indicating the vertical flat where the bolt holes are located that is the surface the chuck body seats against. The large flat on the face of the backplate that you did show doesn't touch the chuck body, there's quite a gap there at least on mine there are.


                      Now that I seem to have solved that I can presumably get a chuck mounted properly, so I'm hopeful I simply need to run a reamer through the spindle taper. I need to get a new backplate to find out for sure though, I guess.

                      With regards to the bearings, the spindle has been out, but the front bearing remained in place on the spindle, and the rear one is pushed back in place by tightening the locking nuts that would preload the bearings, then slackening them off again. I'm confident that bit isn't the problem because neither bearing races were removed from the headstock, and you can exert great force to reset the rear bearing on the spindle by tightening the locking nuts.

                      It certainly appears that you can see the balls in the front bearing. That means there's a huge hole where swarf can enter the bearing. That's a most serious concern!

                      I notice that the DTI on the taper doesn't swing constantly like it would with a bend, it stays static for 90 degrees at a time then shifts suddenly, as it the taper has been squared out a bit... Perhaps by having things bashed in it to remove dead centres or suchlike.
                      Hope this helps.
                      Location: Saskatoon, Saskatchewan, Canada

                      Comment


                      • #12
                        Originally posted by loply View Post
                        I notice that the DTI on the taper doesn't swing constantly like it would with a bend, it stays static for 90 degrees at a time then shifts suddenly, as it the taper has been squared out a bit... Perhaps by having things bashed in it to remove dead centres or suchlike.
                        This is the type of indicator you need to properly measure your spindle:

                        Comment


                        • #13
                          Yes.....

                          The "register" is not intended to be a wringing fit, which is the only way it could possibly do any meaningful centering.... I have several chucks and not a one has a close fit there, some have 25 thou clearance, but they all repeat nicely, and chuck up work without more than normal runout.

                          In any case,,,,,

                          What I think I am seeing is....

                          1) essentially no radial runout on the unthreaded exterior of the spindle

                          2) essentially no runout on the FRONT FACE of the chuck backplate (axial movement) Incidentally that is NOT the chuck contact surface...... or should not be....

                          3) a significant runout of the accessible part of the spindle taper, and adapters etc put into it.

                          4) significant radial runout of the chuck backplate

                          5) a missing cover on the front of teh headstock.

                          6) all runout is fairly smooth and "sinusoidal", not really jerky or limited to one spot, although there is a suggestion that the indicaator is losing contact with the surface part of the time in some tests

                          OK.... #6 almost eliminates an issue of crud in the bearing... that would be jumpy and associated with one place, not fairly smooth.

                          I am going to say that #2 eliminates most bent spindle thoughts.... a bend should have made the backplate "wabble".

                          #4 is interesting, but COULD be a function of the backplate itself..... it isn't a for-sure property of the spindle. it does not seem to be the same AMOUNT as inside the spindle....so isn't necessarily related

                          #1 means the spindle itself, AND THE BEARING must be reasonably decent on the OD and as far as rotating smoothly around a fixed axis without wobbles.

                          #3 suggests that the rest of the spindle taper needs to be investigated with a lever arm type indicator similar to that illustrated.

                          I don't quite see how the taper can be bad and the exterior be good, unless the thing was made badly originally, or unless the taper was bored out to a different one, done badly. The suggestion of a 'flat spot" is interesting, although I think the effect was loss of contact and not a "geometric feature".... Not sure how the flat spot " could occur without more damage.
                          Last edited by J Tiers; 10-09-2012, 11:21 PM.
                          1601

                          Keep eye on ball.
                          Hashim Khan

                          Comment


                          • #14
                            I think what I'm seeing is the spindle being fairly true, but the threaded end being off-center and probably a bit out of round. Maybe it had a crash that didn't bend the spindle proper, just the threaded end. That would account for the runout in the taper and the anomaly in the eccentricity. Because the threads are responsible for centering the chuck, it leaves the chuck eccentric, but the register keeps most of the wobble out. That would explain why a faceplate could run fairly true.

                            You would be able to make a setup whereby you can true up the taper, using the crosslide, but you won't be able to improve the threads without re-cutting them. If you did that, you would be reducing the diameter of the threaded portion by roughly 10 thou by the time you had all of the thread flank area 'accuratized'. I'm guessing at this figure by the amount of runout you are showing- could be more, or could be less. Either way you might still have enough 'overlap' between the spindle threads and all the threaded adapters and back plates you have so that nothing is compromised by the re-cutting.

                            Of course you also have to consider how hard it would be to re-cut the threads. If they are hardened, your best option might be to grind them, but it's unlikely you'd have the setup to do that. If you started with a regular single-point threading operation and it failed because the cutter couldn't stand up to the job, you might be left with more damage than is already there. But I think with the right cutter and a rigid setup, you probably would be able to clean up those 'dented' threads.

                            So far I've been assuming that I'm right about only the last inch or so of the spindle being significantly out of whack. The test for this is to indicate further into the taper, and right into the small end if possible.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                            Comment


                            • #15
                              I'd like to see you check the axial runout of both the shoulders near the DTI at the start of the video. The chuck seats against one of those shoulders as you tighten it into place, and any runout there will affect the chuck.

                              I think the threaded part of the spindle is bent, and the flat inside the taper is on the side which is closer to the spindle axis.
                              Any products mentioned in my posts have been endorsed by their manufacturer.

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