Results 1 to 17 of 17
  1. #1
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826

    Friday? Sunday? Monday? I don't know what day it is, but time for show and tell.

    I built a very rudimentary and (for now) single speed rotocasting machine.

    Outer:inner axis ratio is roughly 2.3:1

    Check it. (Sorry if the video is stupidly rotated in your browser.)

    Going to experiment with various silicone resins for use in bladder inflation molding some carbon fiber lugs.

    Reasons:

    1) I hate grinding carbon fiber.
    2) I don't much care for vacuum bagging.
    3) Using prepreg carbon with bamboo (I make bamboo frames...) isn't such a friendly combination due to *too much* water loss, high thermal expansion rate of bamboo.

    Problems with bladder inflation molding (so I'm told, I haven't succeeded yet) is the concept of damaging bladders in general, and getting bladders stuck in the inside of the layup if the bladder does not closely mimic the finished shape of the mold (minus a little bit of volume to account for layup thickness).

    I previously experimented with wax plugs and dipping them in thinned latex - oh my god, time consuming, and material consuming... what I got out vs what I put in really totally sucked.

    Learned about rotocasting and am going to give this a shot. I don't have any finished bladders yet, but I was just so excited to get this thingamajig moving that I had to post. I really like the concept because you get out what you put in, in terms of consumables, all very efficient. Mannequins and plastic alligators and other complex/hollow/discardable sh!t is made this way.

    Next up, find the resin that works the best, then get my mill working for making molds.
    Latitude: 44.93 N

  2. #2
    Nemophilist
    Reputation: TrailMaker's Avatar
    Join Date
    Sep 2007
    Posts
    1,687
    Ha;

    Stoopidly rotated, but the gist is still clear. Keep hackin my friend. Somehow I had it in my mind that it needed to turn really fast. Guess not...

    You forgot Saturday. That must explain the calendar issues.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  3. #3
    mtbr member
    Reputation:
    Join Date
    Dec 2012
    Posts
    50
    Weren't Spin wheels roto-molded?

  4. #4
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826
    Quote Originally Posted by TrailMaker View Post
    Somehow I had it in my mind that it needed to turn really fast. Guess not...
    Somehow I continue to omit an important detail :P

    The first resin I'm testing, one I *really* like in basic materials tests, I do not recall the specific weight, but visually seems somewhere between artificial maple syrup and molasses during pour. Polytek went out of their way to give me an initial rotocasting test video with the stuff, and their result was *almost* good. We mutually suggested that a small amount of resin was needed, and set at a ridiculously low RPM.

    Eager to see!
    Latitude: 44.93 N

  5. #5
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826
    The inside view is properly barf-worthy: Life inside a rotocasting machine - YouTube
    Latitude: 44.93 N

  6. #6
    Nemophilist
    Reputation: TrailMaker's Avatar
    Join Date
    Sep 2007
    Posts
    1,687
    You see...

    I was ignorant and thought it was massive rotational force that slung the excess resin out of the part, and/or compressed the fabric against the mold. Perhaps that is what is still what is happening, but with far less force necessary than I imagined? Or, perhaps it is intended to keep the distribution of resin more equal throughout the part by foiling the force of gravity?
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  7. #7
    Most Delicious
    Reputation: dr.welby's Avatar
    Join Date
    Jan 2004
    Posts
    989
    Quote Originally Posted by TrailMaker View Post
    You see...

    I was ignorant and thought it was massive rotational force that slung the excess resin out of the part, and/or compressed the fabric against the mold.
    He's rotomolding the rubbery bladder that's going to go inside a rigid mold and compresses the composite with air pressure. But I think you're right that the distribution is via gravity, not centrifugal force.

  8. #8
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826
    ^ Yep.

    Initial test result: mixed! I initially thought I used way too much resin based on slowly it distributed. The entire interior surface of a Gatorade bottle has a thin film, but it also has globs in some places. Sounds crazy but I think 2 RPM is ... too fast.
    Latitude: 44.93 N

  9. #9
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826
    I don't know if I stated the reason for going to this length: I talked to a nontrivial number of companies about having custom shaped bladders made. The basic concept is an economy of scale. If you want one, prepare to buy a hundred.
    Latitude: 44.93 N

  10. #10
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826
    (BTW, I didn't link the words "Gatorade Bottle"... this is completely off topic but I really hope MTBR removes these asinine auto-generated ad word link things. No one likes 'em.)
    Latitude: 44.93 N

  11. #11
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826
    First test with a 32 oz Gatorade bottle. Too thin in spots, too thick in others. But basic concept shows some promise.

    http://dillerdesign.com/random/bike/...119_182832.jpg
    http://dillerdesign.com/random/bike/...119_182845.jpg
    Latitude: 44.93 N

  12. #12
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826
    Hmm... I think I'm coming at this backwards.

    I have another silicone test going. I watched it for an hour. It has a lower viscosity, so the RPM seems okay, very quick coverage of all surfaces, within a couple of minutes.

    But, it's a thermoset. What I'm seeing is thin sheets of partially pooled resin that slough, like rain down a properly graded sidewalk, at almost the same speed compared to the big main glob. This suggests to me that the glob maintains a higher temperature. That's probably bad once it really starts to set.

    I probably need a thermoplastic. I know next to nothing about the specifics and have to start from square one here - but when things thin out, cooling will be faster for the hanging surfaces...

    I'd just need to find one that has a melt point I can justify that is higher than the cure temp of the actual epoxy resin I'd use in a carbon part.

    I suppose this part is more experimenting than show and tell. Time to go back into the cave.
    Latitude: 44.93 N

  13. #13
    mtbr member
    Reputation:
    Join Date
    May 2007
    Posts
    160
    In my head I'm picturing myself trying to evenly coat a large frying pan with a small amount of oil. The surface tension in this scenario makes the oil want to pool up when you tilt the pan, instead of flowing freely across the surface. And when it does flow it wants to flow straight across in a thin bead, not covering a very large area. The solution here is to reduce the surface tension, not the viscosity.

    No idea if this is applicable to your problem, or how one would reduce the surface tension of a fluid, but it makes me feel a bit like a proper engineer Probably not a bad thing if I intend to actually attempt this PhD I've applied for...

    Edit: BTW, it's really good to know that there are DIYers out there working with materials other than steel, as much as I love the stuff.

  14. #14
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826
    Joe - good food for thought.

    And thank you for the encouragement. I feel a bit like a prima donna in the sense that I have rejected a *bunch* of composites advice as it relates to bikes ("just use tow", "just use compression tape", "just use vacuum bagging, it's good enough"), and seemingly all the DIY advice on bladder molding is related to RC planes, where bladders operate in one, um, plane (coordinate wise).

    I like my bikes so far but each build I've thought "there must be a cleaner way". Not to mention repeatability, some of my friends who will be beta testers are big, mean riders, and the significant voids I found in a frame that I cut apart late last year discouraged me from continuing to use vac bags. Not to mention the amount of stuff that gets thrown away with vac bag use.
    Latitude: 44.93 N

  15. #15
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826
    Getting closer, the bottom got messed up because of a machine cog dismount. What I did differently was apply less silicone, but in multiple batches (just two). Noticeable improvement. This suggests there is an ideal silicone volume to surface area ratio.

    Demonstrating reversibility and tear strength: Rotocast test: Gatorade 20 oz bottle with Platsil 71-11 - YouTube
    Latitude: 44.93 N

  16. #16
    tiny rider
    Reputation: cartographer's Avatar
    Join Date
    Jun 2006
    Posts
    601
    This is a cool effort. Thanks for documenting it here.

    What will you use to design the positive(?) to create these molded bladders?

    Quote Originally Posted by Drew Diller View Post
    Demonstrating reversibility and tear strength: Rotocast test: Gatorade 20 oz bottle with Platsil 71-11 - YouTube
    I love the audio, by the way

  17. #17
    will rant for food
    Reputation:
    Join Date
    Jan 2010
    Posts
    2,826
    Quote Originally Posted by cartographer View Post
    This is a cool effort. Thanks for documenting it here.

    What will you use to design the positive(?) to create these molded bladders?

    I love the audio, by the way
    Documentation: It seems to be a thing missing from the web. It is really just a combination of existing ideas. I claim nothing truly unique here - nothing.

    Positives: The actual molds will be enclosed female molds of two to three parts. Third part will be used for the seat stay and chain stay yoke areas. Two is enough for head tube lug. Molds will be machined from blanks using a modified 3 axis desktop mill (Shapeoko) such that it is heavier duty and much larger in the XY plane than its default configuration. My first DIY jig, in fact, is going to be reused for the XY plane so I will have several square feet of flat cutting area and about four inches of depth cutting. EDIT: The rotary tool will be different, as well as the Z range supported on two rails instead of one. I'd like to be able cut aluminum with it if needed.

    Audio: you're the second person to say that! Other dude said it was like aliens eating I'm sorry that the only recorder I have right now is my cell phone
    Latitude: 44.93 N

Similar Threads

  1. Black Friday or Cyber Monday
    By Van G in forum General Discussion
    Replies: 3
    Last Post: 10-31-2013, 09:17 AM
  2. It's Friday.. my time to show
    By becik in forum Frame Building
    Replies: 17
    Last Post: 03-19-2012, 06:30 AM
  3. Friday - Monday show and tell.... tooling
    By RCP FAB in forum Frame Building
    Replies: 4
    Last Post: 03-07-2012, 06:52 AM
  4. Sunday or Monday Shuttles? Riggse?
    By butocabra in forum Arizona
    Replies: 33
    Last Post: 10-21-2011, 11:09 PM
  5. Show and tell monday
    By j-ro in forum Frame Building
    Replies: 17
    Last Post: 10-15-2011, 08:47 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •