How to build from drawings missing angles and cut lengths?
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  1. #1
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    Default How to build from drawings missing angles and cut lengths?

    I’ve dealt with a lot of blueprints for construction. I even spent a year of high school doing pre-cad drafting. But I don’t have much experience dealing with metal fabrication/mechanical drawings, so I have some questions.

    I was looking at the free plans available online for the Hossfield #2 bender clone. I’m unsure on common practice when working with drawings that negate info such as bend angles and cut lengths.

    Is it standard that this type of info is negated from the plans? Am I supposed to print the plans full size and make my measurements or is it common to have to use trig to get the

    Basically I’m wanting to know common practice when building from drawings.

    If you’re unfamiliar with the plans, here’s the link:

    Bender Similar to the Hossfeld #2

    If you look at ‘Sheet 02 Main Frame Arms’ you’ll see that the piece is bent and the bend angle and cut lengths aren’t in the

    8167253a-6ab5-4c46-8086-012af745ca18.jpg

    Thanks.

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    If both arms are to be parallel to each other,your bend angles would be 45 degrees up and down. For placing the bend lines, I would call for clarification. Since it is not called out. one would assume the bend lines would be 1.625" from either hole. Usually repeating features or dimensions would be marked as "typ." which stands for typical. They would be the same throughout the plans. If you print to size and trace, make sure you know what scale the drawing is in, otherwise you are going to wind up with a part that is the wrong size. Just a guess, but i would think the measurements are on a flat part. To get total length just add up all the dimensions across the top. In this case it would be 28.125" total.

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    Quote Originally Posted by SofaNinja View Post

    I was looking at the free plans available online for the Hossfield #2 bender clone.
    "You get what you pay for".....

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    Had a quick gander at the plans, thanks for the link as I might need one if ..... happens.

    Looks to me as if all the un-dimensioned bends are pretty much in the wind. The exact angle and position doesn't matter so long as the holes in the parts each side of the bend are in the right place. Not uncommon practice with drawings for a hand made one-off. Idea seems to be that you adjust the bend angle to make the spacing of the two flats correct.

    That said I'd prefer to specify the position of one end of the bend so you only have one end to adjust to adjust the angle for. Depends on your tooling of course. This one looks intended for hammer and vice methods so adjust as you go will be a given. If they were my drawings I'd be calling out a pin and bar bending jig, and still no bend dimensions as the jig does it for you.

    Adjusting on the fly makes my ears hurt!

    Clive

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    There are .dxf files available for download from the site. Even though they only contain 2D drawings, at least they can be dimensioned. I brought the sheet you posted into Solidworks and checked the unlisted dimensions. Long leg is about 14 inches, short leg is about 9.5 inches. Angle is about 30 degrees. That being said, I think that if all your holes landed in flat sections and the step between the flats was 2 3/8 inches, you would be good. I'd probably take a look at the assembly and see if there are critical dimensions between holes on either side of the bends. If there are I would definitely drill those after bending.

    I am sure there are free .dxf viewers out there that would allow you to investigate other missing dimensions.

    Teryk

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    The exact angle isn't really important. The critical dimension is getting the spacing between the parts of the two arms correct while maintaining the dimension shown between the 29/32" hole and the rightmost bend. I estimated the angle shown on the drawing as 30* and then checked my Hossfeld #2 to confirm that the angle is actually 30*.

    Given that angle and the "rise" that can be computed from the dimensions given (half of the difference between 5-1/2" and 3/4"), you can compute the "run" using trigonometry. I calculate the rise as 2-3/8" which yields a run of 4.1"

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    Some people would probably just be satisfied they had a half assed drawing of the key dimensions to work too to knock of a internationally recognized design, if thats still too hard for yah, just go on ebay and buy a knock off.

    But IMHO and this is not a dig, you can not interpret that much info and make a working bender, i really question just WTF you think your going to be able to make with the bender??? Guess i get now why Andrex put the instructions on the back of the packs these days.

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    Redraw the part in CAD and then measure the results.

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    a bootleg drawing of a knockoff, what could possibly go wrong.
    that said, cut length is 29 1/4" using 1/2 inside bend radiuses. The drawing is not that bad, it should have angle call out, simple scaling gives you a 1/2 tan = 30 degrees, and you know the part only needs to match it's sister. More critical than angle is consistency; if you drill holes first (easier to drill flats) is the bends are the same on both parts, same top/bottom bend, and same start of bend. The hardest math is the layout of 3rd 21/32 hole, with uncheck maths is 9 1/8 from the second unfolded, assuming 1/2 inside radius bend.
    Drawings with bends do not call out cut lengths often, and be sketched when they do. different shapes have different neutral axis.

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    Quote Originally Posted by memphisjed View Post
    cut length is 29 1/4" using 1/2 inside bend radiuses.
    If I were building this, I would probably make a jig (out of steel) with the shape of the bent profile of the part and then use it as a form to hot bend the parts. Starting with a 30" piece one could locate the bends in their approximate positions and then drill the holes to get the overall spacing correct, trimming the ends to the proper length afterward.

    Drilling the pieces post-bending would not be difficult given that the two legs are parallel. Setting up on a milling machine would be pretty simple using jacks, etc.

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    Prob going to need a Hossfield #2 bender to make those parts.

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    Many angles just come out that way coming off from the important sizes. In a pinch you might draw the parts perhaps on a roll of craft paper to then use a protractor, and a yo yo to check sizes.

    Some times one can protractor the drawing, but all drawing can not be trusted for doing this.

    Often one view will leave something out and another view will show the need.

    I worked at a bridge shop where many part print left much off because the angles were not that important and would just come out right if the stated specs were made.

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    Quote Originally Posted by Scruffy887 View Post
    Prob going to need a Hossfield #2 bender to make those parts.
    Better yet, the Op should just e-mail to Hossfield for those missing dimensions.


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