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Straightening 1/4" rod?

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  • #16
    This is the lowest tech method I’ve used successfully. Use thin wood shims under the shaft on each side of the bend on a table or work bench near the edge. Bend up. Using a c clamp at the highest point of the rod, bend the rod till it touches the table. Release and measure. Gradually increase shim thickness and repeat until the shaft is straight in that section. If you start with too thick of a shim you will bend the shaft in the opposite direction so keep reducing the shim thickness until the shaft is straight. It won’t take long to zero in on success as this is a quantitive approach.

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    • #17
      I'm surprised at the reactions so far. Am I the only one sweating blood at the idea of a shaft that long with only three bearings spinning at that sort of RPM? Depending on what it's doing it would not take much to cause it to bend. And once it does I can't imagine the vibration that would occur.

      Chilliwack BC, Canada

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      • #18
        I have managed to straighten a few bits of thin material by rolling it between two blocks of wood.

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        • #19
          How about using a 1/4" diameter drill rod? I have one I bought from Enco years ago. It is a ground rod, very straight and it comes in 36" length. In addition it was very inexpensive, don't know how much they cost these days.
          We have to realize that rod of such geometry will bend significantly under its own weight if used horizontally. The bearing in the middle would help if it is concentric with the end bearings, otherwise it could make things worse. When we are talking about long 1/4" shaft being straight, we mean local possible bends. Such shaft can be straight only in vertical position where weight does not affect it.

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          • #20
            I am with several others... More bearings and a new shaft.
            Robin

            Happily working on my second million Gave up on the first

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            • #21
              Originally posted by BCRider View Post
              I'm surprised at the reactions so far. Am I the only one sweating blood at the idea of a shaft that long with only three bearings spinning at that sort of RPM? Depending on what it's doing it would not take much to cause it to bend. And once it does I can't imagine the vibration that would occur.
              Come on BC, try reading post #9.

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              • #22
                Originally posted by reggie_obe View Post
                McMaster Carr


                Inch—1566 Carbon Steel
                Lg. Lg. Tolerance Straightness
                Tolerance
                Surface Smoothness,
                microinch
                Edge Type Hardness
                Rating
                Hardness Heat Treatment Yield
                Strength, psi
                Surface Yield
                Strength, psi
                Each
                36" -0.03" to 0.03" 0.002" per ft. 8 Chamfered Very Hard Rockwell C60 Case Hardened 75,000 250,000 6061K61 $18.59
                Not in the budget, especially with the $10(+-) shipping.

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                • #23
                  Originally posted by old mart View Post
                  Is there any way you could add a couple of extra bearings, a 1/4" shaft supported at 18" spacing and at that speed is a poor design.
                  Originally posted by reggie_obe View Post

                  ........at 36" spacing and.......
                  What is the device? Very long high speed mixer or agitator?
                  18": there's a center bearing.

                  Maybe the next iteration could have more bearings. It would be hard to know how many, though.

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                  • #24
                    Originally posted by JHartley View Post
                    This is a technique that I have used often for small rods. Works well and should appeal to your cheap side.
                    This youtube is a decent explanation.
                    Youtube titled: Saxophone Repair Topic: Straightening a Rod
                    https://www.youtube.com/watch?v=RvPTAIAF5EQ
                    [snip]
                    That is neat!! I'm gonna' try it. I'll use the drill press & avoid having to work around my lathe's 24 inches between centers.

                    Thanks for link!

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                    • #25
                      Originally posted by I make chips View Post
                      Curious what it is as it buzzes to 10K.

                      If it's a weed eater, toss it and get a new one.
                      Short answer (I'll post a build later): it's a mini weed eater. The string is only 2" long, so the RPM has to be 8x that of my 16" trimmer, to get the same tip speed.

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                      • #26
                        Originally posted by rickyb View Post
                        This is the lowest tech method I’ve used successfully. Use thin wood shims under the shaft on each side of the bend on a table or work bench near the edge. Bend up. Using a c clamp at the highest point of the rod, bend the rod till it touches the table. Release and measure. Gradually increase shim thickness and repeat until the shaft is straight in that section. If you start with too thick of a shim you will bend the shaft in the opposite direction so keep reducing the shim thickness until the shaft is straight. It won’t take long to zero in on success as this is a quantitive approach.
                        I'll try this if the saxophone fixer's technique doesn't work. I used the press & got it much better, but still not as good as I'd like.

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                        • #27
                          Originally posted by mikey553 View Post
                          How about using a 1/4" diameter drill rod? I have one I bought from Enco years ago. It is a ground rod, very straight and it comes in 36" length. In addition it was very inexpensive, don't know how much they cost these days.
                          ...
                          The product cost of drill rod, even turned-ground-polished, is very reasonable. The shipping costs are not.

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                          • #28
                            Summary: the trimmer works exactly as I hoped it would, the vibration being annoying, but not causing dysfunction. I built it out of "stuff", as is my preference. Now that I know it works I may splurge on good rod, but I'm gonna' try to get it straight (enough) first.

                            Thanks for all the replies - good stuff.

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                            • #29
                              Use a dial indicaor, instead of a Stone Age 2x 4 ..
                              someone is going to have to explain why you cant straighten a 36 inch shaft in a 24 inch lathe.
                              if you are trying to straighten supporting only the ends, then yes it could be a problem.

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                              • #30
                                How about a redesign to have the motor much closer to the head?

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