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  1. #1
    Join Date
    Aug 2006
    Posts
    33

    Help Drawing up requirements

    Hi folks, I'm wondering if someone would be good enough to give me some guidance on how to draw up my requirements. I'm looking to have a sill guard made for my car, it isn't too complex but I need to figure out and specify the profile.

    Looking from outside the edge rolls around 90 degrees like a quarter circle, it then flattens and finally has a small lip on the other edge. It is uniform all the way along.

    So, what is the best way to measure and specify how I'd want this made? My tape measure isn't really going to be effective, how would you go about measuring this then drawing it up? (I'm not worried about the drawing, once I've figured out the dimensions).

    Any help would be appreciated.

    Chris.

  2. #2
    Join Date
    Dec 2005
    Posts
    3319
    When I was in engineering school, the first course that they taught was drafting. 2D in paper and pencil. The logic was that if you couldn't convey your thoughts in paper in 2D dimensions, you couldn't expect a machinist someplace else to make it.

    For this reason, the first objective was that "the drawing must speak for itself". THus, length width depth materials, section views, descriptive geometery, whatever had to be spec'd by the designer or else the drawing NEVER got to the shop floor. Even then, if the drawing was lame, or a view was unclear, you had the wrath of a shop supervisor on your A$$ to make sure the drawings were done properly the next time.

    Sadly, the 'assumption' of ANSI and goodness knows what other types of "standards" has dumbed down the quality level of a lot of drawings of late. Seems that CAD and speed have allowed un/poorly qualified "designers" to permeate the industry. Simply put, poor/bad drawgings make for poorly made/substandard quality parts.

    If you haven't taken a decent drafting course, perhaps you should. IF you have, you should be able to create a decently dimensionsed drawing that should survive a decent design review. Once you have a drawing that YOU think is makeable, give it to a machinist friend to see if he can make it without having to ask a bazillion questions.

    If you get an "I can make that " reply, the drawing is adequate. If the drawing gets a deer in the headlights look, you need a bit more and/or clearer definition on your drawing. IF you're drafting teacher says the drawing was adequate and the machinist still can't make it, listen to the machinist and find a better teacher.

    Sadly, there are a lot of college level "design" courses that are woefully inadequate in their educational process. Even though CAD is pervasive and has permeated the industry, there are STILL instances where a well done napkin sketch will suffice for the creatiion of a complex design. Besides, you won't always have access to a computer/CAD tube when out/at/in the shop.

    Simply put, "does your design/drawing speak for itself without you having to explain it in chapter and verse?"

    If you can answere YES to this question, the drawing is adequate. If not, you should know by now what to do about it.....

  3. #3
    Join Date
    Aug 2006
    Posts
    33
    Thanks NC but I think I may not have been clear, it isn't so much the drawing as the measuring that concerns me. I've attached a sketch of the profile of my door sill, I have the car but i don't really know how best to go about measuring the physical dimensions and profile of the sill I want this piece to match up to so that I can draw it (or have it drawn).

    I know the profile drawn in the attachment is pretty close but I'm not sure if it is close enough, the best way I have been able to judge this so far is to print it on paper, cut around it and hold it up to the car. The cutting and holding introduce margin for error, I'm just not sure if I should be concerned or not about that degree of detail.

    Thanks for the advice,

    Chris.
    Attached Thumbnails Attached Thumbnails sill profile.jpg  

  4. #4
    Join Date
    Dec 2005
    Posts
    3319
    I assume you drew the sketch by either:
    A) drawing it with a compass, straight edge and/or stencils or
    B) traced it from a section that you cut thru in true view/form.

    Either way, you should be able to "find" and/or measure the centers of the radii. Once you find the centers of the radii, you then reference them to either a gage surface or a flat surface that you can readily measure/"find" on the form.

    This is a classic/simple case of using tangents to circles/radii to find the edge of the OD. When you do that, you can then find the centers and then reference the intersection points of the circles to the flat surfaces that you also will/can reference off of.

    Not to be obnoxious but this is an elementary mechanical drawing problem that a first or second quarter drating student should be able to do for you if you yourself are "mechanically drawing challenged".

    As far as fabrication goes, I've seen decent sheet metal/tin men fabricators make more complicated shapes with worse drawings done on flimsy napkins providing they have a brake and/or roll former.

    The only thing you're lacking is dimensions and material thickness and specs. Accuracy of fabriction is something that you'll have to negotiate with your metal smith. Visual closeness will be quite affordable - exact match to the form to be copied can cost you a pretty penny. How accurate does it need to be??????

  5. #5
    Join Date
    Aug 2006
    Posts
    33
    I have the dimensions for the drawing but it is a sketch. My question really is this:

    Here is the door sill on my car, it is this shape, how would you go about measuring the physical profile of that door sill and creating a technical diagram of it such that I can have a piece made that matches it as closely as possible.

    I'm coming to the conclusion that sketching, printing cutting and holding a piece of paper up to see how well it fitsthen refine and repeat is the best approach.

    Thanks,

    Chris.

  6. #6
    Join Date
    Jan 2007
    Posts
    24
    make the curved edge on the left into a circle find the center, extend the surface that connects to the circle so you can measure strait up to that extended line. on the right side make an squared edge strait down measure from center of circle to this line.

    use this right edge along with the long horizontal line to take the rest of your measurements.

    you should be able to figure out the small angle on the right side after doing this

  7. #7
    Join Date
    Sep 2006
    Posts
    318
    DIY stores have whats called a profiler which is just like a load of steel spines which you place against whatever you need the profile.then you can create the drawing from the profile.A lot of tilers use it to work out complex shapes.Hope this helps
    Drakkn Custom Shop http://www.drakkncustomshop.co.uk

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