suggestions for best glue for fixing waste block to wood blank

Discussion in 'Tutorials and Tips' started by victortmina, May 17, 2010.

  1. Barry Elder

    Barry Elder

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    You didn't mention what the weight was but it doesn't really matter. If you use a slow cure epoxy like they use on the heat shield tiles on the Space Shuttle, (it takes a week to cure) you shouldn't have a problem.
     
  2. Pope

    Pope

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    Turn a tenon

    I pretty much always turn a tenon on the external end of the intended bowl. On the really large and wet and heavy ones I may initially mount a faceplate on the intended center section, thus not having to worry about screwholes.
    I just don't trust glued on waste blocks. I ALWAYS use the tailstock for as much support as possible and keep the speed reasonable. I also use the Stubby 750.
    Good luck
     
  3. Robert Manning

    Robert Manning member

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    Hi Barry,


    I remember a few of those tiles coming off in the early part of the program.

    I would be very interested to hear you elaborate on the shuttle tile process. What is the substrate and how is it prepared? Is the epoxy thickened? How do they cure it? Who made the epoxy? What are the tiles composed of?
     
  4. Bill Boehme

    Bill Boehme Administrator Staff Member

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    That is not at all how the heat shield tiles are manufactured. I worked for the aerospace company that developed reinforced carbon-carbon over forty years ago as a heat resistant material for the earlier space programs.

    Basically, the fabrication of RCC begins with building up many layers of a rayon cloth that is graphitized and impregnated with phenolic resin and then cured in a vacuum autoclave. Next, it is pyrolized which converts the resin to carbon. The result is a very porous and lightweight material without a great deal of high temperature strength at this point. The porous carbon structure is impregnated with furfural alcohol in a vacuum chamber and then pyrolized which converts the furfural alcohol to carbon. This process is repeated at least three times until the desired carbon-carbon properties are achieved and all voids are filled. At this point the RCC material is very strong even at 3000° F.

    For increased wear and oxidation resistance, the exterior surface is converted to silicon carbide by packing it with a mixture of alumina, silicon and silicon carbide in a retort and heated to 3,200º F in an argon environment. The outer layers of the carbon-carbon are converted to silicon carbide which prevents oxidation. Further treatment with tetraethyl orthosilicate is necessary to deal with minute surface cracks in the silicon carbide. The final result is a material that durable from minus 250° F to about 3,000° F.

    The problem with the tiles came late in the program, not early, when NASA farmed out some of the RCC fabrication to lower bidders that had no experience in this process.
     
  5. Gretch Flo

    Gretch Flo

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    Space shuttle Loose tiles

    ''Out sourced" to China?????? Gretch
     
    Last edited by a moderator: May 23, 2010
  6. Dave Ogren

    Dave Ogren

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    Large Burl Bowl

    Is this burl balanced with a built in foot or something to rest the bowl on ??
    If not and you have to do a little turning on the bottom for a foot, why not use an 6" or larger face plate, turn a recess, chuck in the recess to hollow out the inside ?? I have turned hex shaped pieces that measure 26++" in diameter with an 6" face plate and a 2 5/8++" recess sucessfully, and I don't even have a tail stock.

    Ref. to the shuttle tiles, in a past life, I built the entrance chamber and doors for the vacuum heat treat furnace that the tiles were heattreated in.

    Good luck and Happy turning,

    Dave
     
  7. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I should have been more clear since there were various types of heat shield material. Our company built the RCC components that took the brunt of the heating -- the nose cap and the leading edges of the wings and parts of the fuselage where the wing leading edge fared into the body. The program was called the LESS (Leading Edge Space Shuttle) program. One of NASA's main responsibilities was creating acronyms for program names. :D

    There were also white colored "tiles" used on other parts of the shuttle that was a separate program from the LESS program to build the RCC components (the RCC componentxs are light gray color). I do not know what company built the while tiles, but they were the ones that started peeling off during the tragic accident several years ago.
     

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