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Thread: Sanding Straight Edges

  1. #1
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    Sanding Straight Edges

    I've been doing a lot of bondoing for the past like week, and I keep on having to redo it because i can't get a strait edge so it doesn't look nice. I used a sanding block but everytime i treid making a strait edge it turns out crooked somehow, i drew lines to guide the sanding but it never seems to work. what do you do to sand strait edges? or is there a tool that I dont' know about?

  2. #2
    MySQL Error Scouse Monkey's Avatar
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    clamp a straight edge up against your work if you can made from metal or summit and sand using you block pushed onto this edge more then your work.

  3. #3
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    hey thats a great idea, never though of that, any more???

  4. #4
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    are you using long or short strokes? it won't completely prevent the problem but it will help lessen the wavyness of it...

    what scouse monkey said is a good idea....

    are you trying to stay with the lines in the dash or something? if you had a pic we might be able to better advise.....

    it could be that you have too much bondo on there, that is of course all depending on the situation though....
    Jan Bennett
    FS: VW MKIV Bezel for 8" Lilliput - 95% Finished

    Please post on the forums! Chances are, someone else has or will have the same questions as you!

  5. #5
    I've got no answer! Question's Avatar
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    Quote Originally Posted by Red GTi VR6
    are you using long or short strokes? it won't completely prevent the problem but it will help lessen the wavyness of it...
    You might want to clarify which one would lessen the wavyness..

  6. #6
    Constant Bitrate
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    Use a long block and very long strokes. Applying even pressure to the whole block, of course. With some practice you'll be able to cut a straight line out of anything. If you are doing this on a small object, make sure it is clamped down well and securely mounted. That will be the easiest way to cut a good line.
    And again, the key to making smooth bondo is to cut it as close to the right shape as you can BEFORE it dries. Use that cheese/wood grater, it's the best!

    D

  7. #7
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    some say long strokes some say short! which is it





    here's a picture, the edges does look kinda strait here (top and right side), but its a bit curvy imo and total perfection is very important to me, I've taken the advice of using a c clamp and sheet of metal i'll let u guys know how it goes!

    And I dont think it is possible to sand complete strait edges free hand no matter how skilled you are! (maybe after 1 yr of everyday practice?)

    this is my 3rd time reapplying bondo becuase the edges are not strait hope it works!

  8. #8
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    looks almost like you have too much bondo...

    also, Question...I didn't answer my own question because I wanted to know what his answer was...

    Long strokes works best, as big_cali_dave said as well....

    my advice: sand it down with something like 100 grit for a while (you will remove a LOT of material) then step up to 220. What are you sanding with now? Also, another method that a lot of body shops use and that I have found to be very helpful, when you put the bondo on let it kick for a few seconds but not completely. At this point take that 100 grit and start to go over it lightly, body shops use what they call a cheese grater as that's kinda what you are doing and what it looks like when it's being sanded off...

    the other thing is that it doesn't look like you used your spreader to spread/trim the edges while putting the bondo on, when you put it on there use your spreader to remove the bondo from the edge....don't really know how to describe it...maybe someone else knows what I am talking about and can explain it better.....

    it almost seems like you aren't removing enough material before you start putting another layer of bondo on too, you will remove most of the material before you put another layer on there....

    good luck!
    Jan Bennett
    FS: VW MKIV Bezel for 8" Lilliput - 95% Finished

    Please post on the forums! Chances are, someone else has or will have the same questions as you!

  9. #9
    Maximum Bitrate Altimat's Avatar
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    Pick up a slap of 3/8" or so balsa, and several sheets of self adhesive file paper strips. I use 80, 180. Cut a special block for every purpose from the balsa, and wrap it on 3 sides with the adhesive-backed file paper cut to size with a razor. When sanding up to corners, you then have an side with sandpaper on it and one without to suit your purpose.

    Always sand in a diagonal crosshatch 25-45 degree pattern across the surface so you don't creat gouges parallel to an edge. As soon as scratches are established in one direction, change to the other. This is the most efficient method as you are always cutting off the "mountainpeaks." Also sand like a human milling machine. Evenly cut down the entire surface you are sanding by establishing a pattern a cycling across the part over and over until your reach the level you want to establish, and all edges are perfectly feathered into the sandscratches you left underneath your filler application. If you still have low areas refill and repeat.

    For finish sanding use the full size wet/dry 3M sheets, but alway cut the sheet in half across the long dimension, then in thirds across the long dimension of each half, fold these 6 pieces into thirds and sand with those. Sandpaper folded 3 times works best. Use the same method described above. Sanding lightly by hand with good technique on an accurately established surface will not create waviness.

    I always knock down my finished filler work lightly with 400 before priming and by hand, and sand the primer with 400. I also lightly knock down the 400 scratches right before painting with 500, or sand the very last coat with 500.

    One other technique I use is to ignore radiuses until the flat surfaces are established true and flat. Leave them all sharp and at 90 degrees. This way you can insure that your work is straight. When thats done create your inside radiuses with a fingertip, and radius the outside corners to match the other factory radiuses around the dash.
    Fabricator

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