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V rails not the same length.

Discussion in 'General Talk' started by anigeek65, May 11, 2016.

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  1. anigeek65

    anigeek65 Veteran
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    Anyone else have these kinds of issues? I would expect a small amount of different lengths bit wow.. I could rough cut better than this...
     

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  2. Jonathon Duerig

    Jonathon Duerig Veteran
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    I've sometimes had length differences like that. Usually when I order them in multiple batches. The ones from one batch might be a bit different than those in the other batch.

    FYI, If you want to trim them to exactly the same size, you can do so with a saw, a fixed stop, and a piece of scrap. Take the shortest one and place it next to the stop. Place the scrap between the shortest one and the blade. Clamp it and cut it. Then set aside the shortest one. For each of the other ones, put the trimmed scrap next to the stop and then the other piece next to the trimmed scrap. When you finish, all of them will be almost identical length.

    -D
     
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  3. Ronald van Arkel

    Staff Member Resident Builder Builder

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    Hello @anigeek65,

    V-Slot isn't cut to precise lengths, it's about +2 to 4mm. Also, ends are never straight. They are just rough cuts. This is done on purpose as some V-Slot might be damaged in transport and this gives a margin to cut V-Slot straight. C-Beam on the other hand is machined at the ends with 4 holes tapped M5, and due to the difficulty to cut them straight, we do the cut for the customers. But the last can be risky some times with for example the heavy (3162g / 6.96lbs ±5%) 1500mm C-Beam; they tend to bump in transport, well, at least when they are shipped to me.

    There are more tips on cutting V-Slot straight on the forum other than @Jonathon Duerig posted ;).

    -Ronald
     
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  4. anigeek65

    anigeek65 Veteran
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    I kind of guessed that after looking at my "c" beam parts. They were alot closer but I did have a bent one at the very end. Much like you said. I am not sure it got bent in shipping since I had 4 others packaged around it and they were just fine. I will just trim the long one since I have a table saw that cuts aluminum.

    Thanks...

    Alan
     
  5. Jonathon Duerig

    Jonathon Duerig Veteran
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    @Ronald van Arkel I'm always interested in trying to improve my techniques. The one I mentioned before seems to work out pretty good. But I am interest in your two phase cutting idea. What is the benefit of the second cut that 'shaves' a 0.5mm off? Is this to do with the tool you use, or is a more general thing? Is the 'shaving' cut from the other one in how you do it?

    I'm asking because I have a setup where I am using a cold cut saw or a horizontal bandsaw to cut specific angles/lengths on extrusion. It would be fairly easy for me to cut to length+0.5 and then do a second cut of length. But I would be using the same blade, the same speed, etc.

    What benefit could I expect from a second shave cut? Would it be more precise/repeatable because the blade is only cutting a bit off instead of cutting in half? Would the cut be squarer because there might be less blade deflection? Or would there be less chance of a burr? Or would the edge finish itself look better?

    My intuition has been that if I'm using the same blade and cutting in the same way, I won't see a benefit. That the benefit comes in from doing stuff like adding lubricant/oil like you suggest or using a more fine-toothed blade. But if this intuition is wrong, then I might start trying your two-cut suggestion.

    -D
     
  6. Ronald van Arkel

    Staff Member Resident Builder Builder

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    Hello @Jonathon Duerig,

    The machine I'm using is just a miter saw, I said miter box before but for me that's the same ;). It does spin the blade 3800rpm in free air. I only use one blade, 96t I think.

    This is what I do:

    Grease the blade or use some WD on the extrusion. I use as safety goggles and hearing protection. Gloves will reduce my "feel" and I don't see the need for it. Some use even a respirator o_O, well, i think this is only for people that have their mouth wide open when cutting :D. I shave one end of the V-Slot/C-beam without the need to clamp it down (Again, against the rules ;) ). When I shave 0.5mm or even 1mm you won't feel much feedback from the blade trying to push the extrusion to the left (presuming you are right handed). Then I turn the extrusion around and measure the length I need and mark it followed by a cut that is about 0.5 from the mark. Next I shave it precisely on the mark. I never clamp anything down, no need for it. Normally I cut that precise that you hardly can feel the difference with my finger tips when I put the parts on top of each other that should have the same lengths. Same lengths are needed for the Ox gantry as it uses two 20x60mm and one 20x40mm V-Slot that need to be cut as precise as possible. I know this doesn't work when you cut 50pcs of V-Slot ;), but for the CNC kits I sell it works well.

    I hope this makes sense... :confused:, just try it out. Less burr, less debris sticking to the cut extrusion.

    I've never tried cutting with a band saw or a table saw, but I'm sure a table saw would be best.

    -Ronald
     
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  7. Jonathon Duerig

    Jonathon Duerig Veteran
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    @Ronald van Arkel I can never get that precise with a measuring tape and marking. I can maybe get within a few mm that way. And even then, it takes me a lot of time and care. I think my technique of using a piece of scrap as a template works better to get precise cuts for me. Especially when I have a lot to cut.

    But I will definitely try out what you suggest with regard to a double cut. The finish looks mostly good, but reducing the chance of burrs might be a win for me.

    BTW, you need to clamp every time! Who has two thumbs because he always clamps his work? This guy! :)

    -D
     
  8. Barry Danks

    Barry Danks Veteran
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    I'm actually working on a design that has a linear digital readout :) stepper controlled using C beam but using a different metric rod :)
     

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