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    Default RFQ Turned Tube

    Looking for some quotes on a piece to be turned. The part is a steering stem for a motorcycle. It is fairly simple work but threading may pose a problem. This is what i have been running into locally. Shops that would even consider custom one-off pieces don't seem to have the experience/equipment/confidence to accurately reproduce the external threads.

    I really only need a single piece but would consider multiple copies if the price is not much more dependant than on material costs. Part to turned from aluminum (6061?) or some type of alloy steel. Still undetermined on this aspect. Price is a major deciding factor.

    The through hole in the piece has no specified diameter as its dimension need not be exact. For that matter the hole could technically not even be required. Bending stiffness will surely improve with it though. The "lofted" type feature in the middle of the shaft is also not specified as it need not be precise. Its only purpose is to neck down the shaft slightly to ease the installation of a lower bearing race.

    All dimensions are metric and i believe i have specified the thread callout correctly. The pitch is 1.0 and the outter diamter of the threads are shown on the drawing. Tolerance is 0.01mm.

    I have modeled the part in its entirety in solidworks, threads included, and can export a Solidworks part, parasolid, IGES, step, or STL file. Drawing can be seen in the link below.

    CR Stem Modified RFQ

    Thanks
    Matt

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  2. #2
    Monkeywrench Technician DareBee's Avatar
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    An overall tolerance of .01 will extremely elevate the price of the part.
    I would not dream of trying to make a thread to that tolerance.
    All your shoulders are shown as sharp and standard lathe tools have radii.
    Threads have to be made to "textbook" specs unless you are buying a nut somewhere that they could be fitted to (and fitting is still no good for .01 tolerance).

    I see what you are doing and can make that part no problem, but what you are spec'ing is unrealistic IMHO.

    www.integratedmechanical.ca


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    Hi Matt,
    no criticism meant but although you may have an industrial background (just reading between the lines here) when it comes to making parts like this, find someone who knows what they're talking about and with plenty of experience and then let them set the tolerences and material choice because they cross these same bridges every day of the week.
    As an example of this, check out Darebee's business and also what hobbies he has and you know straight away that he knows what he's talking about. That's just an example but you use who you wish.



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    Matt,

    With your probably unnecessary tight tolerances you are turning a $150
    part into a no bid or a 5 times higher price. Knowing what the part does I doubt
    any length needs to be tighter than +\- .1mm, diameters probably a little tighter, but nowhere near +\- .01mm unless pressing a bearing. Those thread
    major call outs? I have seen over engineered parts going on space shuttles,
    that had more open tolerances, just my opinion,........Bob



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    Gold Member acondit's Avatar
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    Matt,

    I am no expert, but I have measured a number of metric outside threads and often find the measurements to be considerably smaller than the designated diameter. I wouldn't be surprised to find that those two threads were originally called out as 24x1 and 26x1 threads.

    Alan



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    OK! I had a feeling i'd get burned but i think i'll go hide in a corner now! I would like to thank each of you for the insight into producing a part like this. I obviously have no experience in machine operation but do very much appreciate the tips for a more economical and realistic product.

    Quote Originally Posted by DareBee View Post
    Threads have to be made to "textbook" specs unless you are buying a nut somewhere that they could be fitted to (and fitting is still no good for .01 tolerance).
    Hence the reason i have had no luck with local "mom and pop" type shops. This thread is not standard. The motorcycle mentioned is a Honda and it seems that the threading and mounting hardware is a proprietary thing. Maybe it was designed to fit the bearings first and foremost?

    Thank you for the information about tolerances. (Refer to above) I'm here to learn.

    Quote Originally Posted by skippy View Post
    find someone who knows what they're talking about and with plenty of experience and then let them set the tolerences and material choice
    Was just shooting for completeness. Quotes don't seem to be taken too seriously when they lack any thought for material or machining specifications.

    Quote Originally Posted by Dualkit View Post
    Those thread
    major call outs? I have seen over engineered parts going on space shuttles,
    that had more open tolerances, just my opinion,........Bob
    Care to elaborate on the threads? Thanks for your opinion.

    Quote Originally Posted by acondit View Post
    Matt,

    I am no expert, but I have measured a number of metric outside threads and often find the measurements to be considerably smaller than the designated diameter. I wouldn't be surprised to find that those two threads were originally called out as 24x1 and 26x1 threads.

    Alan
    Thank you. You know i had wondered the same thing as the size did seem a bit odd. I wouldn't think they could be worn down as the corresponding bolts have been removed/assembled maybe 4 times.


    I have updated the drawing with the suggestions made. I really had no idea that an edge could not be achieved with standard lathe tooling. It always looked like a sharp corner to me. Also did away with that wierd loft in the middle. That was totally unnecessary and would likely rule out the use of a manual machine.

    Thanks again for the help. I hope to be PM'ing some of you for further discussion.

    CR Stem Modified R01 RFQ



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    If you want to get the part made at the best price, I suggest that you spec the threads as approximate and that the part is to be made to fit the mating parts that you will supply. If it is important, you can spec the class of fit.

    Otherwise, there is a good chance that you will either over spec the part, or it will be made according to spec and will not fit, or it will be over specified, will be made to spec, and will not fit.

    You should probably also say that the bidders may cancel their bids if inspection of the mating parts finds them to be unreasonable. (For example, what was assumed to be a straight thread is actually tapered.)


    Ken

    Kenneth Lerman
    55 Main Street
    Newtown, CT 06470


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    Matt,

    I think you got on people's bad side by calling this "fairly simple work" then
    making the part overly difficult. I had visions of a 22 year old fresh out of college
    engineer that thinks he knows everything. Anyway a thread "major" which you called out a +/-.01 tolerance to only controls thread height, and is not the most critical dimension if you want tighter threads, pitch diameter is most important and that would need to be measured with a pitch micrometer, optical
    comparator or thread wires. You need to measure the thread more accurately
    than you have done or find out what they are supposed to be, using calipers
    on the thread major and measuring the thread lead is not enough information



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    Quote Originally Posted by kawamatt2 View Post
    It is fairly simple work but threading may pose a problem.
    Quote Originally Posted by Dualkit View Post
    Matt,

    I think you got on people's bad side by calling this "fairly simple work" then
    making the part overly difficult. I had visions of a 22 year old fresh out of college
    engineer that thinks he knows everything.
    Did i get on your bad side?

    If you had nothing constructive to add why even waste your time here. Except of course to make assumptions.

    This is a Request for Quote. NOT a detailed specification sheet or build sheet. I realize that some of the initial requirements were improbable. Thats why i'm here. If i knew it all i would not waste any of the members time, nor would i accept any of the suggestions and criticisms of the members here. As the former is not true, I am open to any and all suggestions and opinions; short of those concerning my background or character. I would, and do, appreciate anything constructive you have to add to the design intent i am shooting for.

    With that said, i had no idea that measuring metric threads was so involved. I am not familiar with a pitch micrometer. You learn something new every day though right!

    Man, i did NOT wish this thread to take this turn.

    Thanks all for your suggestions and ideas.



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