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Lathe build: Part 1B, spindle housing

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  • Lathe build: Part 1B, spindle housing

    I would have posted this on the first thread if it hadn't morphed into the Hydra. I cannot believe the number of views.

    At any rate I have finished the housing for the spindle. To review some of the primary criteria for this lathe:

    CHEAP
    Big swing, 16" minimum
    Make from materials on hand if at all possible without compromising performance
    Use scrap and recycled materials as much as possible
    Form follows function


    Some secondary considerations:

    Weight to be kept down so that it can be moved in sub assemblies by two people without special rigging
    Explore the use of novel or unusual materials and geometries
    Automation/electrification of some functions
    Compatability with existing tooling and accessories
    Discussion of headstock bearings is substantially complete

    -----------------------------------------------------------



    The housing is made from portions of two old automotive generators, one from my Land Rover since I replaced it with an alternator years ago. To insure alignment and strength the spindle nose bearing housing is threaded onto the smaller central housing. The visible threads may appear to be partial depth because they are filled with aluminum antiseize compound. The nose bearing is a light press fit into the housing. The brush ventilation opening will serve nicely to mount a hall encoder sensor to monitor the spindle rpm.



    At the tail end is the drive pulley and a spindle extension. The spindle extension is drilled through with a half inch hole to permit the use of a tommy bar to assist in removing the threaded chucks.



    I intend to buy an 8" 4 jaw chuck sometime in the future. It will become the more or less permanent chuck on this machine.

    Here is something for some discussion: I am seriously thinking of using some composite construction the help keep the weight down. What I have in mind is to laminate jatoba wood with steel strap to make some structural members. Jatoba is one of the hardest of all woods and has excellent mechanical properties as well a very good damping properties. It is exceptionally dimensionally stable with a coefficient of expansion with temperature less than half that of steel. It takes threads well and is better worked with metal working tools than with wood working tools.

    Has anyone tried something like this?
    Free software for calculating bolt circles and similar: Click Here

  • #2
    I would suggest that something with more mass be employed in the headstock. The gen housing looks a tad lightweight for a headstock.

    I don't know what you intend to use the jabota wood for, if for the bed, wood construction was employed early on on metal lathes and soon replaced with cast iron.

    Lightweight subassemblies handleable by two men translates to something like 200# for me.
    Jim H.

    Comment


    • #3
      Jim,

      The spindle housing is to be mounted in a mounting frame for attachment to the headstock. It will be subtantially supported and restrained.

      I was thinking of using the jatoba/steel laminate as cross bracing in the bed since the bed will be of built up construction. 200# is at the upper end of what I consider movable. I only have one way into my basement and that is a full length flight of rather steep stairs. There is very limited possibility for any sort of rigging at the top of the stairs because of the orientation of the entrances vs the stairs. It is a poor design.

      I would like to thank you again for those threading dies you sent some time ago. They have been very useful for the threading portions of this project so far.
      Free software for calculating bolt circles and similar: Click Here

      Comment


      • #4
        The problem with using any kind of wood is not thermal expansion but rather dimensional changes due to changes in moisture content. I haven't seen any numbers for jatoba...It's not in the charts in my 1961 Dry Kiln Operator's Manual.

        But bear in mind that it won't take much of a change in moisture content of any wood to destroy the accuracy that you are building into this project.

        That said, I'm following this project closely, as I'm thinking of building a spinning lathe, and have already acquired some rather massive laminated mahogany beams to use for the bed and possibly the headstock.

        Comment


        • #5
          Jatoba is very stable with changes in moisture. If well sealed it will be even more stable. More important is that the humidity here hardly varies and even then it only varies from about 20% RH to the highest that I have ever seen at 55%. This is a very dry climate, officially a semi-arid zone. Average precip per year is 15 inches. Most of that falls as snow when the humidity is bone dry.
          Free software for calculating bolt circles and similar: Click Here

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          • #6
            Evan,

            Jatoba sounds expensive, so I guess you have some on hand?

            Even so, I'd think it more economical to ebay it and build the lathe structure out of steel for stiffness, and add some form of CSD (constrained layer damping), i.e., thin plywood adhered w/Liquid Nails for Subfloors (stays compliant).

            Comment


            • #7
              I have a nice plank of it that has had a good chance to dry to local conditions. I want to add some damping to the structure since it will be steel instead of cast iron. I can do plywood too. I have some nice baltic birch that will do for that. That does give me some ideas. I have about a half sheet of new 0.100" steel and about the same amount of 0.125 birch ply. A stack of maybe 5 layers of steel and 4 layers of ply would make a *VERY* strong and rigid structure and would weigh about 60% of what a solid steel plate would weigh.
              Free software for calculating bolt circles and similar: Click Here

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              • #8
                Would you glue that stack together?

                With what?
                Gene

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                • #9
                  I will use glue, probably contact cement after painting all layers. Then I would rivet it with tinner's rivets. Maybe then cut some lightening holes with the mill. I am seriously considering doing this. The lathe will have plenty of mass in the areas where it needs it. In other areas it needs rigidity more than it needs mass. The two are not synonymous.
                  Free software for calculating bolt circles and similar: Click Here

                  Comment


                  • #10
                    Originally posted by Evan
                    It is exceptionally dimensionally stable with a coefficient of expansion with temperature less than half that of steel. It takes threads well and is better worked with metal working tools than with wood working tools.
                    Evan,
                    Does this mean the strap will expand at twice the rate of the wood? If so, what adhesive would allow this shear without failure and still provide the strength you obviously need? I would think that at the very least, the pieces would not remain in the same planes.

                    Keep in mind that I live in Texas and we have WILD temp changes here.

                    Comment


                    • #11
                      It won't depend on the adhesive. I will use fasteners. The rate of change with temperature of steel isn't that large. It's less than brass, bronze, copper, aluminum and most other common metals. Jatoba is close to nil. The main thing is to always make the lamination system balanced so there isn't any possibility of making a giant bimetal thermostat strip. Those considerations apply to all machine tools and are especially important when different metals are used together.

                      Wood/metal laminated structures are used sometimes in aircraft. That's where I first ran into them. The floor panels on the Swiss Pilatus Heliporter utility aircraft are very thin aluminum with a core of balsa. They weigh almost nothing but can stand just about anything up to and including full fuel drums. Composite structures have much better strength to weight ratios than conventional single material structural elements. This is especially true of trusses and beams. Laminated carbon fiber is unbelievably strong for its weight with a really unusual degree of stiffness.

                      It would be really cool to build an ultra rigid lathe using only ultra light composite materials so that something the size of a SB9 could be picked up with one hand. Even more interesting is to implement active vibration cancellation so that chatter doesn't have a way to start.
                      Free software for calculating bolt circles and similar: Click Here

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                      • #12
                        I have always been under the impression that lots of mass in a machine tool was necessary for rigidity and vibration dampening. I don't understand how making a sandwich of wood and steel would achieve this.

                        Comment


                        • #13
                          Originally posted by Evan
                          Jatoba is one of the hardest of all woods and has excellent mechanical properties as well a very good damping properties. It is exceptionally dimensionally stable with a coefficient of expansion with temperature less than half that of steel.
                          The C.T.E. for wood is anisotropic, if this matters. According to http://74.125.95.132/search?q=cache:...lnk&cd=1&gl=us
                          The thermal expansion coefficient of
                          oven-dried wood parallel to the grain appears to be independent
                          of specific gravity and species. In tests of both hardwoods
                          and softwoods, the parallel-to-grain values have ranged from
                          about 0.000031 to 0.0000045 per K (0.0000017 to
                          0.0000025 per °F).

                          The thermal expansion coefficients across the grain (radial
                          and tangential) are proportional to wood specific gravity.
                          These coefficients range from about 5 to more than 10 times
                          greater than the parallel-to-grain coefficients and are of more
                          practical interest.

                          I expect you know this, just mentioning it in case you did not.
                          Allan Ostling

                          Phoenix, Arizona

                          Comment


                          • #14
                            That is cool, a lathe spindle cartridge. Wooden lathes were fairly common here in the states prior to the civil war. White oak was often used for the bed and head stock, and lignum vitae was used for bearings (still used in some industrial bearing applications). Now, most of these lathes were used to build artillery pieces, and were not the most stable in the world. Have you thought about using a cast iron engine block as the headstock? Something like an old four cylinder Volvo block is very rigid but can still be carried by one person. I just got a 2kw mitsubishi servo in tonight that is either going to go in a home rolled 4th axis or a dedicated cnc lathe, so I won't be too far behind you in building something.

                            Comment


                            • #15
                              Originally posted by Evan
                              It would be really cool to build an ultra rigid lathe using only ultra light composite materials so that something the size of a SB9 could be picked up with one hand. Even more interesting is to implement active vibration cancellation so that chatter doesn't have a way to start.
                              I follow this idea and 6-8 others come to mind at the same time.

                              I figure of active dampening on the ways, you'd need something akin to hydraulic tensioning which could be done with less mass if you could space and brace cross members. A single (or group of) 1" diameter piston(s) with a 1/2-1" stroke could be used to alter any resonance though the only trick would be to do it without changing the positions of the headstock, tailstock, and tool when it happens.

                              Bearing material for the ways shouldn't be too difficult either, but what happens when something does impact the bed? Blue and stone? Relaminate? Epoxy fill/resand/refinish? Could the saddle be made longer and have bearing parts ride under or into the headstock and around the tailstock? H-shaped vs square or rectangle when viewed from above?

                              Of course, you don't have to sacrifice mass to be lightweight and portable. A composite structure could be carried into position then mass added from a garden hose. Pop the drain plug(s) out while you pack tooling or remove the headstock. Any structural members that get filled could have baffles included for extra strength and be designed to limit any harmonic sloshing. A bucket of water grabber would gel everything, though flushing might take more work. In that case, some warm saline and a long plastic stir stick in a drill might really speed up any flushing efforts.

                              I'm sure this isn't the last related idea I'll have in the next 48 hours, but if you are building the composites yourself, you could include strain sensors to let the computer modify spindle and feed speeds on the fly. On the opposite side, you could load up a knurler when you are done for the day and let it sing you to sleep.

                              Now I'm going to be having strange dreams about an engineer core backpacking in a full CNC machine shop to somewhere insanely remote.

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