Announcement

Collapse
No announcement yet.

Turning bushings from flat stock - tips?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Turning bushings from flat stock - tips?

    I need to make a bushing out of some flat stock, and am wondering how to best do it. I know there must be some tricks, and that my inexperience has me over-complicated this.

    In my present case, the flat stock is .75" thick plastic, and the bushing will be .875" ID and 1.375" OD, and all of that .75" long. I also need a .125" x .125" lip on the OD.

    Those largish dimensions, and the plastic, make this example task a lot easier than it is in many cases.

    I often wonder the best way to do it, with the best possible outcome and the least time. It is something I will need to do again and again. Sometimes we only get one chance - like when a friend gives you a small piece of PTFE for a project. Maybe there are some simple fixtures that can be re-used for this again and again?

    Since it is plastic, I can draw an OD and rough it on the bandsaw. Or with a hole saw. Sometimes the stock available will be too small for the bandsaw and my fingers. Maybe hot glue it to a spoil board? Though perhaps not in the case of PTFE.

    Since this lathe does not have collets, I'm thinking I'll put the rough OD in the chuck, bore and turn the ID. Then... Hmm.. I'm not sure the jaws of this chuck can grab the ID. I could make a "quick" mandrel, with a shoulder, a set screw and washer to sandwich the bushing. Then I can turn the OD. Given the ample wall thickness, I could then face the ends by holding it in the chuck. But that wouldn't always be possible.

    A mandrel that could expand slightly, and not need to sandwich the bushing, seems like a nice thing to have.

    Or maybe grip the stock in the four jaw chuck (hate to switch), or screw it to a spoil board. Then turn the OD, cutting it out of the flat? The trick there is getting the OD diameter right, since it will lightly press into a bearing race, and I'd really like to do test fits with the bearing. I can't do that with this setup. The mandrel would allow trial fits.

    This is a task I can do, but not quickly, and not very gracefully.

    Aluminum or steel. Or smaller dimensions, make this all more challenging.

  • #2
    I'd use a stub mandrel. I've made lots of expanding mandrels and they are handy, but with plastic I'd be concerned abound dimensions. Depends on tolerances I suppose, but the expanding mandrel would to some extrent expand the ID past nominal.
    .

    Comment


    • #3
      Bit o discussion here http://www.practicalmachinist.com/vb...andrels-76861/ but some of the links are no longer, this may give you some ideas as to size http://www.dunhamtool.com/expanding_mandrel.html. from Frank Ford's site, http://www.frets.com/HomeShopTech/To...rtenchuck.html those "adapters" are for shortening screws but something very similar can be made for turning washers (making use of the screw attachment points of a 2 part lathe jaw).

      Not really a "how" but if you know you are going to have this as a repeat operation, albeit of different sizes, IMO its well worth the time to figure out a method you are happy with. Perhaps look towards a more production operation (turret lathe) to get ideas [I am not saying get a turret lathe, just import some of the ideas for holding but also when it really benefits to spend time with perhaps a better/quicker/more efficient set-up]

      Comment


      • #4
        I would find the center of the part on the flat stock, then drill and ream a 1/2" hole there. Then cut out on the bandsaw to rough oversize. Make up 2 stub arbors of brass, steel or alum. with a 1/2 diam. x 1/2" long part to fit in the hole on each side of the bushing and a 3/4" diam. x 1" long other side with a center drill in the middle. Put one arbor in the chuck, stick the part on it and put the other arbor in the part and support it with the live center in the center drill hole. When you wind up the tailstock and press the stock against the chuck the friction of the chuck will drive it. Then you can turn the OD with step. You can take out the mandrel for checking size as many times as you want. The ends will not need to be faced as the part is already to length and the hole is at right angles to the ends. Then you can chuck the finished OD and drill and bore the ID.

        Comment


        • #5
          This sounds like a good time to stock up on some Delrin rod. To get it done today I would saw a slug larger than I needed and mount that on a stub mandrel somewhat smaller than the needed ID. Machine the outside to the desired dimensions. Mount it on the OD and bore the ID to dimension. Plastic machines so easily you can rough something from oversized stock very quickly.
          Byron Boucher
          Burnet, TX

          Comment


          • #6
            If you need to do this repeatedly, why do you not start with 7/8 in rod? Why are you using flat stock? As mentioned, without knowing the tolerances, it is difficult to help. Bob.

            Comment


            • #7
              I make a lot of parts from solid pvc. The odd time I get in a mood to make some blanks, so I mount a hole saw in the mill and cut out several rounds of a few sizes. Later on I can reach into a drawer and pull one out to use for something. The stock I start with has been anywhere from 1/8 to 1-1/4 inches thick, and the blanks I usually start with a 1-1/8 hole saw, so those could be finished to 1 inch or anything smaller of course. The largest blanks I usually cut are 3 inches across.

              I have made up a few mounting bosses ( I guess you could call them faceplates) to which I mount a piece of mdf, usually 3/4 thick. I'll turn a recess into them to suit a size of blank, and make it a press-fit. Then when I need to bore a blank for some application, I mount the appropriate boss and press in a blank. Removing them is sometimes tricky, especially if I'm boring a fairly large center hole, but almost never is the recess made so deep that you can't still get a grip on the OD and work the piece out.

              Certainly, you can use a chuck to grip the blank, but many times the grip distorts the shape of the blank- then when released, the bored hole is no longer round. These mdf mounting jigs work pretty well to prevent that.

              At any rate, if your bored hole is large enough, you can expand chuck jaws to hold the part for OD turning, or you can turn part of the exposed OD in the first operation, then remount the part using that turned portion to turn the rest of it.

              If it's important to turn both the ID and the OD in one fixturing for concentricity, then I'll often add three equally spaced holes through the part so it can be screwed to the mdf. Sometimes I'll mount a part in a slight recess, then bore the central hole, then bolt the part in place through that hole and into the mdf, the turn the od- removing some of the mdf as well if required to machine the entire OD. At one point I made several mdf blanks just to have ready. I've pretty much used them all up now- I need to make more.

              Where there might be a hole pattern required in the final part, sometimes I drill those out near the beginning of the machining process, then use those to pass temporary holding screws through.

              One of my partially completed projects is a multi-jaw chuck which will have a jaw kit made for it. I would mount some jaw blanks, adjust their positions, then turn the ID to suit a workpiece. For a mostly round workpiece you can keep a better grip on it than you might be able to with an ordinary chuck. Plastic has a habit of squishing out of the jaws if you get overzealous with the cutter. I've also considered that nothing stops me from lining the inside of a set of specially turned jaws with sandpaper ( contact cemented on) to provide more of a grip on slippery plastics. Come to think of it, you could use a normal chuck and form some aluminum strips over the jaws, then glue some sandpaper to those to give you a better grip on slippery and/or squishy plastic without needing too high a clamping force. I haven't tried that, but it seems like it would work well. You can always form the strip over the top surfaces of the jaws so there's no tendency for the whole thing to slide inwards- or you could crush the jaws down onto a steel rod with the strips in place to 'seat' the strips a bit onto each jaw before you apply the sandpaper. That would help, maybe not by much, but help a little to keep the strips in place. You could number the strips later so each could be returned to the same jaw for future use.

              Just throwing a few ideas out there- hope I haven't put anyone to sleep-
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

              Comment


              • #8
                When you do jobs like this use stops on the bed for the carriage. Stops can be as simple as C-clamps holding a chunk of aluminum for the carriage to hit. This really speeds up the work and insures repeatable precision as well as accuracy. The carriage can be brought to the right against a stop, the tool advanced in the path of the work, the work fed to against the tool and chuck tightened, the work machined up to the left stop etc.
                Free software for calculating bolt circles and similar: Click Here

                Comment


                • #9
                  My fave workholding trick: the 5 minute expanding mandrel

                  Step 1: Turn stock OD to a thou below the ID you want to grip
                  Step 2: Drill and tap 1" or so hole in end of stock, along the length of the rod
                  Step 3: Use bandsaw in vertical mode (or hacksaw? Mill sliting saw? whatever) to cut a slit down the center of the rod, cutting through the bolt hole, PAST the end of the drilled hole.
                  Step 4: Put bolt in lathe, turn tip to a point.

                  Done. I have tried it without the point on the bolt tip, using just where the tap runs outta threads to 'expand' the mandrel and it worked but the screw would deform with in a few uses (Using a chinese soft #6 screw in a 1/4" expanding mandrel, in that case) and it would stop working, but with a point on the end of the bolt to wedge into the slit, it worked much better for a good 10 uses with little wear.
                  Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                  Comment


                  • #10
                    Like that idea and want to make myself a self like that. One thing I was wondering is "is there a way to keep it true in a 3 jaw chuck". I know the chuck isnt the best way to hold stuff, as it seems to go off true and change every time you remove and replace it in the chuck. I try to use the tail stock to set it, but it never comes back to the exact point it was. Getting to the point Im contemplating making another chuck plate to fit on the lathe and adding a collet holder to it, so once I true it, it stays that way. Figure I can start by making some mandrils with a cross slit and a small circular wedge for the screw.

                    Comment


                    • #11
                      What about using soft jaws after you have turned the outside on a mandrel. The mandrel could be made to be held in the soft jaws. The soft jaws could be made out aluminum and be nearly like a collet as in how much of the circumference of the material they are gripping. The soft jaws would have a recess in them so you could put your material in against the face of the soft jaws and you could make the depth so you could face the material if you wanted also. I think it wouild be plenty fast to get all your operations done.
                      How to become a millionaire: Start out with 10 million and take up machining as a hobby!

                      Comment


                      • #12
                        Thanks for the great ideas.

                        I am off to the shop, to turn a ptfe bushing for the new fixture. I can't wait to try turning a bushing on a mandrel.

                        Comment

                        Working...
                        X