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How do I cut a spiral?

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  • How do I cut a spiral?

    I've got a buddy that wants me to make him a pair of 12'plastic discs with matching spiral v-gooves in them (mirror image) that have a 1/4" offset per rev. It will be a reel for holding large photo film in a developer tank. This is too wide for my micro CNC and it is just a one off of course, so tried to do it manually on the BP. But cranking the rotary table for all I was worth while the table feed went as slow as it would go gave about a 1/2" groove offset. Made a coupler to socket a drill drive speed reducer to the rotary table and got the offset down to almost 1/4" but the feed speed on the outside of the spiral was so high (3"/sec) that the cut goes bad. This is too much swing for my little lathe so I'm all out of ideas and so am turning to you wonderful people for how to do this right short of buying an A-axis for the MAXNC.

  • #2
    I think you ruled out the obvious ones - but somehome, either mechanically or electronically, the linear and rotary axis must be connected. ie that already exists with the lathe mechanically or electronically for the cnc.

    the solution depends on how much trouble you want to go to - so my idea is to simplify that connection (instead of gears etc)

    what about a small steel cable (model airplain control line stuff) wrapped around a cylinder on the rotary table handle, the going to a homemade pully bolted on the corner of the table (used to change direction, like a bell crank) and from there to cylinder where the axis mill handle used to be. Rotating the table also rotates the linear axis screw??

    [This message has been edited by Mcgyver (edited 09-12-2005).]
    .

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    • #3
      First take the lead screw out of the mill table so it can move freely. Then a post in the center of the rotary table with a cable attached to it and anchored to the bench or wall. As you turn the rotary table the cable will pull the mill table, thus creating a spiral.

      And now we will hear from someone that really knows what they a talking about.

      ------------------
      Gene
      Gene

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      • #4
        Sounds like a place for the dividing head or rotary table, geared to the table feed. That way you can set up any feed per turn you want, so long as you have the gears for it.

        AFAIK that is the standard way to do it. Drive hooked into the fastest rotation, which would be the head/table, and the takeoff from that going to table drive.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #5
          All the film reels I've seen were made of wire welded to several U-shaped spokes, like this:
          http://www.calumetphoto.com/ctl?PAGE=Con troller&ac.ui.pn=cat.CatItemDetail&ac.item.itemNo= CP9076&ac.cat.CatTree.detail=y&type=PRDINDEX

          There are some made of plastic, but they are similar. That design allows the best flow of the processing solutions around the film. I don't see how you could have adequate flow with grooves cut into two discs of plastic, unless you're going to drill a gazillion holes, too.

          Roger



          [This message has been edited by winchman (edited 09-12-2005).]
          Any products mentioned in my posts have been endorsed by their manufacturer.

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          • #6
            The key words here are "I've got a buddy that wants"

            Thanks Winchman,

            ------------------
            Gene
            Gene

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            • #7
              <font face="Verdana, Arial" size="2">Originally posted by topct:
              The key words here are "I've got a buddy that wants"

              Thanks Winchman,

              </font>
              Is that like, Do me a favor and........


              ------------------
              The tame Wolf !

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              • #8
                I'm with Roger. All the film reels I have seen were either SS wire welded to spokes or molded plastic. I would think about the SS wire and a way to hold it in a spiral. A tack welder would be great, perhaps with special tips to conform to the wire.

                Or, make a mold with a flat plate and epoxy a wire spiral to it. Use it to make a rubber mold or use it, itself as a mold and pour some plastic molding compound. I think this would be easier than milling a spiral.

                One more thought. For film, it does not have to be a perfect geometric spiral (and there are several types). So what you could do is use the lathe to turn a series of uniformly spaced circular grooves on the face of a plate. Cut another plate with grooves where the lands are on the first and lands where the grooves are. Then cut the plates in half on a their diameters and DEBUR.

                Now reassemble one half from one plate with one from the other plate on a backing plate but offset them so that the lands match lands and the grooves match grooves. Use a good waterproof adheasive to join them. When you do the second pair, be sure to do the offset in the OTHER direction. This will make two spirals that wind in opposite directions.

                Paul A.
                Paul A.
                SE Texas

                Make it fit.
                You can't win and there IS a penalty for trying!

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                • #9
                  Yes to the circulation thing. I have done some darkroom work and can assure you that it will need lots of holes for the chemicals to circulate. Used up developer needs to be circulated away from the fiml and fresh developer needs to get to it on a continous basis. And for proper development, that process needs to be uniform at all places on the film - edges; center; inside, middle, and outside of the spiral. For a five or ten minute development we used to agitate every 20 or 30 seconds. More often for shorter periods.

                  The film holders I have seen for larger film (line 5x7 and 8x10) have held it flat, not in a spiral.

                  Paul A.
                  Paul A.
                  SE Texas

                  Make it fit.
                  You can't win and there IS a penalty for trying!

                  Comment


                  • #10
                    How about this?

                    Take a long piece of copper wire (maybe #8) and bend it into the spiral you need. Leave enough at each end to bend down for attaching leads from your welder or battery charger. You'll have to drill two holes in one of he discs for these ends to pass through.

                    Put a piece of particle board on blocks, and put the disc with the holes on top of it. Drill matching holes through the particle board. Put the spiral in place, and connect the leads to the ends poking through the holes. Put the other disc on top of the spiral, and weight it down evenly. Make sure everything is lined up like you want it.

                    Apply just enough current to get the wire hot enough to sink it slightly into the plastic discs. Now you've got each disc marked for where the spiral needs to be, but the grooves aren't deep enough yet.

                    Now remove the top disc, and put some spacers around the edges of the other one. You just want something to set the depth the wire can go into the disc. Put the partical board on top of the spiral, and weight it down as before. This time apply a bit more current, and let the weight press the spiral down until the spacers are holding the particle board.

                    Repeat the process for the other disc. You'll have the two discs with mirror image grooves of the same depth.

                    With a little luck that should give you something he can use. Winding the spiral will be the tough part, but putting some spacers between the wraps as you go should give you something pretty close on the spacing.

                    Roger

                    [This message has been edited by winchman (edited 09-12-2005).]
                    Any products mentioned in my posts have been endorsed by their manufacturer.

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                    • #11
                      Convince him to buy a digital camera.
                      Free software for calculating bolt circles and similar: Click Here

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                      • #12
                        <font face="Verdana, Arial" size="2">Originally posted by topct:
                        The key words here are "I've got a buddy that wants"

                        Thanks Winchman,

                        </font>

                        The only way to properly end that quote is...

                        ...to by me a case of beer."

                        Have fun,
                        Ed
                        Ed Pacenka

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                        • #13
                          The circulation shouldn't be a BIG problem, I'd just mill in some fairly wide radial grooves from the smooth side, deep enough to intersect the spiral.

                          The spiral can be pretty loose, the usual metal ones are...

                          The plastic ones I have from the B&W days are basically the spiral with intersecting grooves. If agitated, it should slosh well enough to work perfectly, if the grooves are wider than the spokes.

                          You DO want the grooves smooth and a very even spiral, so the film slides through easily. If it folds and scrapes against itself, you can lose emulsion.
                          1601

                          Keep eye on ball.
                          Hashim Khan

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                          • #14
                            1. He's a proffessional photog and passed the cost-is-no-object hurdle. He's got an automated machine from the 70's that you can't get parts for.

                            2. Has the little wire reel deals but needs to be able to do film 5" wide by 30 feet long.

                            3. Decided that holding this wide film by its edges in grooves might not be safe with irreplaceable negatives.

                            4. Came up with a way to make a reel consisting of a spiral pattern of rods that he'll have to slip into it while winding on the film (in the dark). Main consideration is to not let anything touch the elmusion during the process.

                            Thanks for the ideas
                            Greg C.

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                            • #15
                              5" wide.... that could be a problem with rubbing together.

                              I don't have any ideas for that.....
                              1601

                              Keep eye on ball.
                              Hashim Khan

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