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Back Plate Problem

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  • Back Plate Problem

    My SB Heavy 10 has a spindle mounting arragement and I was machining a back plate to fit a new chuck I bought. I screwed the back plate blank on the spindle and machine the new back plate to fit the new chuck.

    Now that I'm done, I can not loosen the back plate from the threaded spindle. I tried gentle torquing with the back gear engaged but that was not enough to break it loose. I'm very concerned about breaking a gear tooth/teeth if I keep the back gear engaged to lock the spindle and torque the back plate to loosen it.

    I've tried heat but it is still stuck. I didn't get it too hot as a I was afraid of affecting bearings and the tempering in the lathe head/spindle.

    Anyone have suggestions? Appreciate any help.

    Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

    Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

  • #2
    I hope it wasn't hot and a close fitting thread when you screwed it on the spindle.

    You may have to heat the area around the threaded area quickly and use a strap wrench as you heat it to get it off. Is there holes in the backplate you could put a bolt with nuts in to help knock it off?

    I think fast heat is your only hope without beating the heck out of it.
    It's only ink and paper


    • #3
      I agree with Carld.
      Was the back plate hot-to-the-touch when you screwed it on the spindle nose?
      If so, you may be in trouble. The plate may have shrunk .001-.002.
      Or the threads may have galled-up on ya.
      A Strap wrench with a long cheater bar may break it loose.
      Are there holes drilled & tapped in the back plate for your chuck mounting?
      You could put two bolts in these holes and use a bar to wrench the plate loose.


      • #4
        Here's a link to a thread on removing a stuck chuck over on PM, hopefully you won't have as much trouble as this.


        • #5
          Is it not more likely that the backplate became hot whilst being machined, whilst at the same time being tightened by the cutting forces.

          You're unlikely to get the backplate hot enough to cause the spindle any problems with tempering. I'd try boiling water to heat it up. It's a trick I use for washing down sheet metal after degreasing, it evaporates so fast there's no rust.

          Do you have an air or electric impact wrench? You could weld a bolt head to a length of bar and bolt it to the backplate (use the chuck mounting holes if you already have them). Dis-engage any gears, just hold the spindle by hand (use heavy gloves!), so no shock goes through the teeth.

          In extreme cases the backplate needs to be machined off the spindle nose. I've heard of one case where someone rigged up a very thin parting blade and relieved the pressure, but saved the backplate.
          Paul Compton


          • #6

            The back plate blank was screwed onto the lathe spindle when the temperature was about 40 to 45 deg. F. so the plate was not hot when put on. The plate did warm up when machining it but it was never too hot to touch. I was trying to remove the plate so holes could be drilled in it for mounting the chuck.

            My biggest concern is holding the spindle when untreading the back plate. As I said I do not want to use the back gear to lock the spindle. I will dissassemble the head to see if there is some way I can lock the spindle with a block of wood or look at using a large strap wrench on the pulley shives and a big pipe wrench on the back plate.

            Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

            Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.


            • #7
              Bob, you can grind a piece of wood on the end to about a 45 deg tip and use that to wedge in between the teeth as you strike or pull on the strap wrench.

              I would quickly heat the area around the threads to relieve the pressure and then strike the strap wrench. You have to do this fast because you don't want the heat to travel to the threads before you start striking the strap wrench. It helps to have two people doing this job, a heater and a beater.
              It's only ink and paper


              • #8
                Can you hold on to the bull gear with a tool or something (I see someone mentioned a wedge), so you don't put the pressure on the back gear locking pin?

                This picture shows how I managed to loosen the chuck on my Myford without any damage:

                (I think the chuck was never off the spindle before I got the lathe home)

                Edited because of fault with picture link

                Last edited by Thomas Staubo; 05-11-2010, 05:47 PM.

                Problems worthy of attack prove their worth by hitting back
                - Piet Hein


                • #9
                  Perhaps cooling the spindle will make it shrink enough to allow the backplate to release. It may take a combination of cooling the spindle and heating the backplate. You may be able to cool the spindle by shooting CO2 from a fire extinguisher through he spindle hole from the side opposite the spindle threads.

                  One other thought; one can weld a bead on a bearing stuck on a shaft to heat it up quickly without heating the shaft allowing it to slide off the shaft easily. The bearing is toast afterward but it works. The same method may work by welding a bead on the backplate a short distance from the spindle nose. It could be turned off later and not damage the accuracy of the finished product. Even if the backplate is cast iron it may work as weld strength isn't the object, you only need the rapid heating.

                  Fortunately I've never personally been faced with your problem so please understand I'm just tossing out ideas.



                  • #10
                    I'd capillary in some penetrating oil, to the threads and the register several times a day. Play a heat gun over the chuck and give whatever torque device you've set up (like Thomas Staubo's) some light raps after taking up all backlash. I think small shocks are better than mighty wallops, and a combination pull and rap is even better. Might take several days.

                    Could you drill a tooling hole in the mounted back plate for a bolt that would give you a place to lever and tap?

                    I had to do this soak/heat/slug thing to remove a stuck taper in my tailstock. Took a week, because I didn't want to offend my 'baby.'



                    • #11
                      In my opinion the back gears and spindle are always worth more than the stuck on face plate or chuck so every effort shoud be expended to protect them from damage.

                      I think the best way of freeing a stuck chuck or face plate is to fix a lever on the face plate (or chuck) something you can really bash with a lot of effort. The lever must be long enough to contact the lathe ways.

                      The technique is to ensure the splindle is absolutely free to rotate, no gears or belts engaged then place a protective block of wood on the rear lathe ways and bang the lever down hard on the block of wood, use all available effort if required and really, really bang it down until the face plate (or chuck) comes free.

                      Note, you are turning the spindle backwards until the lever contacts the block of wood at which time the faceplate/chucks stop suddenly and hopefully the momentum of the spindle assembly will loosen the thread.


                      • #12
                        Two things are really needed here.

                        Firstly to reduce the grip the backplate has on the spindle, which is going to mean heating the backplate whilst keeping the spindle cool.

                        Secondly, some means of providing rotary shocks to the spindle/backplate union to overcome the friction locking the two together.

                        When it comes to the latter, what better tool is there than an inpact wrench? The internal hammer action works with some form of face cams to produce entirely rotary shocks. As long as you don't bottom the socket on the nut you're driving then NO hammering force is transmitted axially along the shaft or bolt. I use mine all the time for getting the alternator rotor of Morini V twin motorcycles. The cambelt only has a 12,000mile or three year life and is behind the alternator. The rotor is mounted on a taper and many people struggle. I've read many reports of people winding the puller up as tight as they can and then hitting the end with a hammer.

                        NOT WITH MY CRANK BEARINGS!

                        I do what the main Morini specialist does in their workshop and use my air impact wrench on the puller bolt. The flywheel usually comes straight off without any fuss and without even using the top torque setting. I only need to hold the rotor firmly with one hand, no pin or strap wrenches needed. My air wrench is rated at 230 ft/lbs average torque and the peak is two to three times higher.

                        I'm know that most of the other methods sugested will work, but anything that wedges or clamps the spindle at least risks damaging it. Putting in offset loads with a bar risks bending the spindle, or damaging the bearings, particularly if they're rollers rather than plain.

                        Bolt or clamp a piece of plate or bar to the chuck backplate with a big nut welded to the middle and try an impact wrench. If that doesn't shake it loose, then I think you're going to be machining the plate off the spindle nose.

                        Having said all that, just how tight is the backplate?

                        Obviously it's too tight to unscrew by hand, you're going to have much less grip on it compared to a chuck. With stubborn chucks on the Boxford, I'd put the lathe in a low speed that still allowed me to turn the spindle by hand and use a leather strap wrench on the chuck. I'd hit the wrench handle with nothing more than the heel of my hand and the spindle could move to limit the loads through the transmission.
                        Paul Compton


                        • #13

                          By using several of the methods suggested here, I was able to break the back plate free this AM. By putting a large strap wrench on the stepped pulley and a BIG pipe wrench on the back plate and with several blows from my lead hammer on the end of the pipe wrench, the back plate broke free.

                          I will chaulk this up as a "learning experience." From now on, I will lubricate the threads on both the spindle and chuck's back plate BEFORE I assemble them.

                          Thanks to everyoine who respond and offered suggestions. It is really great to be able to obtain the wisdom of so many people.

                          Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

                          Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.


                          • #14
                            Originally posted by BigBoy1
                            From now on, I will lubricate the threads on both the spindle and chuck's back plate BEFORE I assemble them.
                            I don't know if it's correct or not, but I always use a thin film of antisieze on my spindle threads to prevent the backplate from getting locked on.


                            • #15
                              Don't use grease on your threaded back plate.

                              You do not want to use a normal grease in this application. You need a tool joint compound like is used in oil well /waterwell drill pipe. It is a anti gaul compound with copper and zink and is designed to not be slick like grease. Grease is going to get you back where you have been. Jet Lube is one of the better tool joint compounds. Permatex anti seize would probably work. If you have a waterwell driller around they will probably give you all you need. I can get you some but it is going to be a week or so.
                              Byron Boucher
                              Burnet, TX