Saturday, May 21, 2011

J.J. Cale/ After Midnight


  1. I admire your work.

    I think the beam structure of your cargo platform could be simplified (the "amphibious" addition to the platform was the best move you made, IMO). Here is a picture of what I recommend: [IMG][/IMG]

    My concern is for the large number of "transverse" ribs in your prototype.

    Another subject: May I recommend steam bending of raw wood for chain and seat stays? I'm getting ready to build a skin-on-frame canoe and steam bending is the way to get wood to do what we want. I understand you are committed to plywood, just a thought.

    Finally: I wondered you kept a metal seat tube on your frame. Then I thought any equivalently strong structure in plywood would be much bulkier and too flexible, so I think you made the right choice.

    Sorry, not from an exotic location. Just sleepy Summerville, SC. Best, Robert Peters

  2. Thank you for the input. FYI, your photo bucket link didn't work. I agree....there are rather too many ribs in our proof of concept. The next version will have half as many which will also allow hatches to internal storage. We considered steam bending and Jeff certainly has the skills and experience to do it, however, we as we are trying to avoid using large jigs to hold all the hard points in alignment it just seemed easier to use the inherent accuracy of the CNC routing to create 'stacked laminate' stays which interface with other elements in a more predictable way. I do agree that steaming would be a cool way to go and we may well play with that in a later interation.......

  3. Michael and Jeff, It is curious about the photo bucket link. I just tested it by copying it from between the [IMG] brackets and pasting into a new browser tab, worked fine (but my browser may be priveleged because I created the link?). Anyway...

    I recommend you eliminate the transverse ribs entirely. IMO, your primary concern is the bending cause by the front and rear wheels applying upward forces and your load and bicyclist applying downward forces, classic beam loading. As evidence, remember how much stiffer your platform got when the amphibious modifications were made? You tranformed your narrow-section beam into a much deeper and stiffer beam. So, I recommend only one _longitidunal_ rib down the center to help define the upside-down flattened pentagon profile and be one of three webs between the flanges of the top of the deck and the bottom of the hull. The two other webs would be your side walls. Holes in the deck for internal storage aren't too bad as long as you have reasonably tall side walls. The taller the side walls, the stiffer your beam, but then you run into practical reasons for not making the side walls too tall: gust load from side winds, etc.

    The CNC machine is an excellent tool, good plan to use it to maximum.

    An aside: are you planning on fenders and a complete chain cover? I such a lazy cuss, I hate cleaning stuff that can be covered!

    Best, Robert

  4. Michael and Jeff, back on the beam thing, again. Something else to watch is to maintain a relatively smooth change in beam stiffness from end to end. If you build a beam that is extremely stiff in the middle and one end, the weak end will proportionally respond to loads, to the detriment of the weak end of the beam. Probably the place to most watch this concern is near the attachment to the front fork.