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Thread: Need Help on Designing a Small Beveling Device

  1. #1

    Default Need Help Designing a Small Beveling Device

    Howdy, Folks. New member, referred over here by my good friends at Practical Machinist.

    I have a need to design a small shop device for my business. I make high-performance guitar picks. The model pictured below is one of our more popular sellers. Believe it or not, our picks start at $30 and go up to $50 (and soon, higher). I totally fell into this by accident, and now it has become a thriving business. I still make my living full-time as an English professor, but this will be my retirement gig.

    Here's my problem. I buy this material in sheets that are about 3.5 mms (.100") thick. We lie the sheet flat and cut the pick shape from above, with laser. Cuts beautifully. We then take this object to a grinder house, that grinds it down to a thickness between about .040-.060."

    I have to find a way to do the edges on these. The material is called casein plastic, and it hates everything -- heat, water, friction, humidity. It's just miserable. I've tried tumbling, but if tumbled too aggressively it warps from the heat; too slowly and it takes FOREVER (weeks).

    There are other solutions that will work down the road, but I am building this on sweat equity, not capital, and I refuse to dip into my retirement funds to do this. We have an excellent reputation and are growing every year.

    CNC is too expensive, and I don't need a huge, lumbering machine to do such a small job. I have a jobber who has done some centrifugal discs tumbling for me, and that works, but he is too far away and I have no control on lead times (the best shops are always the busiest).

    I'm very stubborn and I WILL solve this, but I'd love any thoughts you may have.

    I am working on a concept of two Dremels, side-by-side, with barrels about 1.50" in diameter, almost touching. However, 5000 rpm is probably too fast. In such a scenario, the sandpaper would need to be around 2500 grit. Oh, one piece of good news: You CAN use water for wet-n-dry sanding, as long you wipe the workpiece down right afterwards.

    Thoughts?

    Thank You!
    SCD
    Last edited by SoCal Dude; 07-04-2019 at 03:30 AM.

  2. #2
    Join Date
    Oct 2013
    Location
    Setubal, Portugal
    Posts
    625

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    If they're all the same size, you could have a 2 part polished aluminium mold and thermoform the edges by pressure.
    Helder Ferreira
    Setúbal, Portugal

  3. #3

    Default

    Helder, thanks. This particular material is really strange. It's called Casein plastic and is derived from milk, believe it or not. I buy it in sheets. It is as hard as stone, and I don't think what you're suggest would work. It needs to be sanded, with water. I'm doing it by hand now, but I'm trying to automate, to increase production.

    Thank You!

  4. #4
    Join Date
    Jun 2004
    Posts
    1,066

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    Quote Originally Posted by SoCal Dude View Post
    I am working on a concept of two Dremels, side-by-side, with barrels about 1.50" in diameter, almost touching. However, 5000 rpm is probably too fast. In such a scenario, the sandpaper would need to be around 2500 grit. Oh, one piece of good news: You CAN use water for wet-n-dry sanding, as long you wipe the workpiece down right afterwards.

    Thoughts?

    Thank You!
    SCD
    Make yourself a couple of pulley driven spindles based on ER11 chucks on 10mm or 12mm straight shanks.
    If you benefit from the Dunning-Kruger Effect you may not even know it ;-)

  5. #5
    Join Date
    Oct 2013
    Location
    USA MD 21030
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    5,478

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    I looked up casein, and apparently the plastic version you describe may actually be "Galalith", which is produced by treating casein with formaldehyde. It was most popular in the early 1900s, when other plastics were not available, but now is less common, except for some buttons, and perhaps the guitar picks you make.

    https://en.wikipedia.org/wiki/Galalith

    Per your description, it would appear that the edges should have a cross-sectional profile that is parabolic, although circular may be acceptable. Perhaps some sort of precision sandblasting might work. Otherwise, it may require some sort of CNC set-up, which could follow the contour of the piece with something like a Dremel with sanding discs or diamond burrs.

    I'm more knowledgeable about electronics, so hopefully you will get more help from others with appropriate experience. And, welcome to HSM

  6. #6
    Join Date
    Nov 2006
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    durban s africa
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    Welcome . Its so hard to say something and not sound stupid if you dont know the properties .So an open flame wouldnt work to break the edges. How would water cutting work instead of laser.?Would sand blasting or water jetting with aggregate not be selective enough to target the edges.Would a buffing wheel maybe do it

  7. #7
    Join Date
    Oct 2013
    Location
    USA MD 21030
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    5,478

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    It might be interesting to try making your own casein plastic, which can be molded into a shape like a guitar pick and then allowed to dry and become hard. I found some simple instructions:

    https://www.instructables.com/id/Bio...-Based-Plasti/

    https://www.instructables.com/id/Homemade-Plastic/

    It might be possible to use formaldehyde to make Galalith, but I didn't find any DIY information. However, here is some info on the material and the range of colors that can be made:

    http://blogs.getty.edu/iris/galalith...ge-of-plastic/




  8. #8
    Join Date
    Jun 2004
    Posts
    1,066

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    A micro-router table with a fence and a suitable edge rounding tool, in conjunction with a holder matching the part outline and a guide to allow accurate mounting of the part to align to the holder would do what you need.
    A suitable non-permanent means of retaining the part to the holder such as three dots of double sided tape, blu tack or similar would be required.
    You may need to build your own spindle, but that's a very easy and quick job if you have access to a lathe.
    If you benefit from the Dunning-Kruger Effect you may not even know it ;-)

  9. #9
    Join Date
    Jul 2007
    Location
    Earlville PA
    Posts
    366

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    Something like this with a fixture to hold the pick.

    https://www.google.com/aclk?sa=L&ai=...9aACCDc&adurl=

  10. #10
    Join Date
    May 2011
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    868

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    Take two razor blades and overlap them to form a "V" at the tip and bond them together on their surfaces with a good adhesive like epoxy or Gorilla glue. The "V" should be about .070" deep. Cover the rest of the cutting edges of the blades with several layers of tape for safety. Now drag the edge of the pick through the "V" and shave off the edges.

    The material of the pick is somewhat brittle and you should get the same effect as running a thin metal ruler (scale) along the edge of a piece of Pexiglass. This is the way I broke the edges of Pexiglass throughout my career.

    If this works with the material you are using then I think a machine can be made which utilizes the holes in the center of the pick to hold it and pass it through the blades on a sort of conveyor belt. The holding device can be preloaded with a mild amount of spring pressure. [EDIT]Obviously the device would have to pivot at some point to accommodate the radius and the other edges. It would just make a rotational movement at a second station along the path and reverse direction till all edges and radii are broken. [END EDIT]

    It think it would be a fun project and I think it is entirely doable in a home shop.
    Last edited by DATo; 07-04-2019 at 07:53 AM.

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