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Po' man's TP grinder, as it sits now...

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  • Po' man's TP grinder, as it sits now...

    It’s a long way from being finished but I decided to start a thread anyway as it might motivate me to keep at it ‘til it’s done.

    The Sherline spindle was picked up cheap on ebay a couple years back to make a 3rd axis CNC milling spindle for the ORAC but it just sat there in the box & the project never got any traction. I decided a lightweight, compact QCTP grinder would be easier to build and more useful.

    I sawed the excess aluminum bracket off of it & then milled a dovetail to fit my AXA toolpost. That process was made so much easier by the new DRO on the X-3! It fit onto the toolpost perfectly and the original motor bracket boltholes faced upwards in perfect position to mount the new homemade motor bracket.





    The motor choice slowed me down for a while but I finally decided to pick one via my usual calculating method called “SWACAG”. Scientific wild-a$$ cheap- a$$ guess. The LMS cheapo TPG lists a 150W motor so I figured around 200W would be about right for me. Originally I was enamored with the big brushless model motors but they’re a bit pricey when you figure in a controller. I ended up with a 150W (advertised) 24VDC scooter motor off ebay for $32.50 shipped. I took it apart & milled in some cooling holes in the endbells & mount bracket & machined up some pulleys

    .



    The first powered tests were very disappointing; it didn’t put out enough power to even start itself up in the higher speed pulley mode even wide open at 33.5V out of my homemade power supply. Hooked up an ammeter in series last night & quickly found it was only seeing 2.2 amps from the power supply. Bummer!

    Woke up this morning thinking about the oddball 36V KB speed controller’s plug-in horsepower resistor & when I took a look it was a only .1 ohm (1/8 hp) value. I have no idea what the correct value should be with this one since it came with a Peco add-on board that was designed to run on 36V. I changed it to a .025 ohm (1/2 hp) resistor and it immediately woke things up. The motor started up with authority and I could load it down with a rag to 6.5 amps. About 200W if my cipherin’ is right.

    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

  • #2
    The Sherline bearings must be pretty funky because it would start to wind up to full chat in the high speed pulley mode & suddenly bind up at around 7000 rpm, slow back down to 4000 and still show max amp draw. I’ll have to replace the bearings with better quality ones & re-set the preload a little looser before spinning it up to the planned >10K for my little 3/8” round stones to straighten up the taper on the cheapo ER16/R-8 collet chucks I bought. The lower speed setup runs fine & looks like it will manage the light cuts I have planned for the 4” dia’ 1/8” wide CBN wheel. Gotta make a 1 ¼” flanged arbor for it yet though.

    I also plan to make a guard/splash shield with a big coolant return pipe on the bottom to allow a stream of coolant to run on wheel & make its way out of the shield & back to a big reservoir. Hopefully it will reduce the spread of abrasive debris onto the lathe.





    I ran it wide open for about 20 min on the low speed pulley setup & took a few rpm/temp notes. Unloaded at 33.5V the motor ran 5250 rpm; with the belt on it ran 5050 rpm, spindle speed was 3860 rpm, safely below the CBN wheel's stated max speed of 4700. At the end of 20 minutes, the motor read 120 degrees, the spindle got up to 135 degrees, too hot for my taste.
    Milton

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

    Comment


    • #3
      Good post, ill be watching for the updated progress on this.

      Comment


      • #4
        Milton-
        I am very impressed with that you have so far.
        Super idea.

        --Doozer
        DZER

        Comment


        • #5
          Thank you sirs; makes my chest swell with pride!

          Let's hope the rest goes reasonably well. I just ordered some Nachi C3 rated bearings to replace the funky original ones. Actually it should work out pretty well since I need to turn an accurate arbor to mount the wheel. With the spindle out of its housing, I can dial it in the lathe & turn the arbor "in situ."

          Rummaged around & found foot-long piece of 1/4" wall 4 1/2" ID alum tubing. Should be able to slice off an inch or two to get a good start on the shield. I'm trying to make everything out of hefty aluminum stock to get as much heat-sinking as possible.
          Milton

          "Accuracy is the sum total of your compensating mistakes."

          "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

          Comment


          • #6
            That's better than my wooden clamp and Dremel tool. I did use really good plywood.

            Comment


            • #7
              Originally posted by CarlByrns View Post
              That's better than my wooden clamp and Dremel tool. I did use really good plywood.
              ...and a heckuva lot less work! I've done something like that as well but was looking to make something more powerful and rigid. We'll see how it actually works out.
              Milton

              "Accuracy is the sum total of your compensating mistakes."

              "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

              Comment


              • #8
                Really nice compact design .. I like it.

                Are you afraid that crap will get into the motor through the cooling holes you made ? Its a pretty messy
                operation.
                John Titor, when are you.

                Comment


                • #9
                  Originally posted by Mike Amick View Post
                  Really nice compact design .. I like it.

                  Are you afraid that crap will get into the motor through the cooling holes you made ? Its a pretty messy
                  operation.
                  Thanks Mike, I don't think it'll be a problem especially if my guard system comes out like I want. I envision it covering the entire wheel except for a small opening barely large enough for the wheel to contact the work. Hopefully it will contain all the grinding residue. I chose a CBN wheel to prevent having to deal with the aluminum oxide wheel dressing mess.
                  Milton

                  "Accuracy is the sum total of your compensating mistakes."

                  "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

                  Comment


                  • #10
                    Oh yea .. I forgot, you did mention a guard ... please post pics when you add that ..
                    And thanks for the heads up on the CBN wheel .. didn't know that.
                    John Titor, when are you.

                    Comment


                    • #11
                      Originally posted by Mike Amick View Post
                      Oh yea .. I forgot, you did mention a guard ... please post pics when you add that ..
                      And thanks for the heads up on the CBN wheel .. didn't know that.
                      Will do Mike. Tied up right now whittling an arbor for said CBN wheel out of a big rectangular chunk of 2024. Lots of slitting saw work & interrupted cuts but I've just about finished it other than the OD of the actual boss that the wheel ID fits on. Gonna wait 'til the new bearings get here to tear down the spindle & try to turn that to final size while fitted to the spindle shaft itself.

                      I'm real nervous about the runout of the Cheapo Chinese wheel because it's a major ordeal trying to dress CBN. I may regret making a perfectly true (well as close as I can make it) arbor. May need a little runout to mix n' match the wheel to.

                      Now that I think about it, maybe I should make a quick "mule" arbor to test the wheel before finishing up the real one. It never ends!
                      Milton

                      "Accuracy is the sum total of your compensating mistakes."

                      "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

                      Comment


                      • #12
                        You can chuck a piece of rod with about 6 inches or so sticking out from the jaws, then turn a snug-fitting portion on the outboard end for the wheel to slip over. When you run the spindle again there should be no vibration of the rod. If there is, you could turn down the portion slightly to fit a shim and thus experiment with wedging the wheel in place. You'd be running the wheel offset, and you would then find out where the shim should be to offset the wheel in the right direction to reduce vibration.

                        But now, looking at the wheel again- I'd be surprised if you had any vibration worth trying to reduce or eliminate. It would be nice if we as HSMers could have a simple but effective device that would at a minimum show a light or heavy side to within some degrees. Then you could drill divots on the heavy side or add weight to the light side. Years ago I did some crude balancing using a device I made up using a strobe tube. It relied on the mounting shaft vibrating in response to an off-balance, and an adjustable contact point to trigger the strobe. Pretty crude, but it did work- the heavy point was where the shaft vibrated in a direction to touch the contact.

                        You do have another option. Because that disc is thin you don't have to worry about a different offset from side to side, so it's only a simple balance problem. Take an ordinary washer and bore it to closely fit the same shaft that you mount the wheel on. Then drill a hole on one side to off-balance the washer. Assemble it to the arbor along with the wheel. Mark a series of numbers around the wheel so you can reference the position of the washer. Now it's trial and error- keep testing and rotating the washer one mark at a time until you find either a worst peak or a close null. If the minimum vibration is greater than it was before adding the washer, then you drilled the washer too far offset. I know this is crude and time-consuming, but it does work and will allow you to keep the arbor diameter a close fit for the wheel.

                        As far as the motor you're using, 150 watts isn't much power but it could be enough. For one of my TPGs I salvaged two satelite actuator motors to make one motor, then wound the lengthened armature myself. I epoxied it while having it slowly spinning in the lathe to distribute the epoxy into all the windings and around the core. Balancing was crudely done on knife edges to show the heavy side, and epoxy was added at the top (light side) until there didn't seem to be any preferred stopping place as I rolled the armature.

                        The original motors were rated at 1/6 hp, so with double the armature lamination stack and double the magnets, that would translate to 1/3 hp. The rewinding was done to raise the operating voltage by about 30% and thus allow the current draw to remain within reason. Because of the higher motor rpm, the output power would now be more like 1/2 hp, or 375 watts. In use I don't think I'm using any more than about 150 watts, but the excess capability allows the motor to remain fairly cool even if running for tens of minutes at a time. This is where I think you'll get bit- your motor is going to heat quite a bit if you're taking it near its power rating for any real length of time.

                        I'm not advocating that anyone should turn two motors into one- that's a lot of work and time spent. What I would suggest to anyone going the same route is to try to find a motor with a higher voltage rating. Minimizing the current draw does help to reduce motor heating, and the higher voltage motor would probably have a higher rated output as well- plus the fact that controllers will run them well.

                        For my machines with treadmill motors and converted motors, I have built power supplies that range from variac with bridge rectifiers to transformer based multi-tap secondaries with rectifiers and filters. This all becomes expensive unless you have access to surplus parts- plus with the exception of the variac they don't give smooth speed control, just several steps, and none are regulated. It all works well, but most people would be best advised to find a higher voltage motor like a treadmill motor, and use an available controller.
                        Last edited by darryl; 01-31-2016, 08:04 PM.
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

                        Comment


                        • #13
                          Originally posted by DICKEYBIRD View Post
                          ........ but I decided to start a thread anyway as it might motivate me to keep at it ‘til it’s done...................my usual calculating method called “SWACAG”. Scientific wild-a$$ cheap- a$$ guess.......... It never ends!
                          So, I guess I'm not the only one who works like this?

                          Great project and I'm glad you posted it.

                          Thanks!!!
                          Best wishes to ya’ll.

                          Sincerely,

                          Jim

                          "To invent you need a good imagination and a pile of junk" - Thomas Edison

                          "I've always wanted to get a job as a procrastinator but I keep putting off going out to find one so I guess I'll never realize my life's dream. Frustrating!" - Me

                          Location: Bustling N.E. Arizona

                          Comment


                          • #14
                            I made one awhile ago and posted it here. The motor I chose was a harbor freight 4-1/2 grinder for$9.99. Worked out great

                            Comment


                            • #15
                              Originally posted by darryl View Post
                              You can chuck a piece of rod with about 6 inches or so sticking out from the jaws, then turn a snug-fitting portion on the outboard end for the wheel to slip over. When you run the spindle again there should be no vibration of the rod. If there is, you could turn down the portion slightly to fit a shim and thus experiment with wedging the wheel in place. You'd be running the wheel offset, and you would then find out where the shim should be to offset the wheel in the right direction to reduce vibration.
                              Thanks Darryl, that might just work. I'm not worried so much about vibration, mostly about runout which would cause chattering & lousy finish. I ran out of energy for the day so a test arbor will have to wait. I'm still not 100% recovered from the stroke but I'm not complaining under the circumstances.
                              Milton

                              "Accuracy is the sum total of your compensating mistakes."

                              "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton

                              Comment

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