need advice for machining programs- Mtbr.com
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  1. #1
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    need advice for machining programs

    Hi everybody,

    i decided to ride with my own stem so i made drawings with autocad for blue prints and solid works for 3d. Now i'd like to know what else i have to do if i want to ask to a professional to machine my part. I'm open to all the piece of advice.

    Thanks.

    Steph.

  2. #2
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    i think that should be enough. as long as you have all the needed dimensions and materials specified. not sure about heat treaments required or needed.

    you can use an add in for solid works called camworks and it can program the G codes for the CNC machine. i'm taking that class right now so i'm not too familiar with it yet

  3. #3
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    Hey, there is lots of info about machining in this thread that just popped up a few days ago.

    http://forums.mtbr.com/showthread.php?t=2781

    As far as the materials are concerned, you'll probably end up using 6061-T6 and it will already come heat treated. Unless you're welding to it, you won't need any further heat treatment. If you DO weld to it, then it will certainly need to to be heat treated.

    If you are making your own stem, make sure that you run at least some FEA on it: a stem failure is one of the worst things that i can think of failing and you don't want to loose all your teeth plus break a bunch of ribs because your stem failed.

    Anyway, good luck and make sure to show it off here when you're done!
    Noel Buckley
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    www.knollybikes.com

    Instead of PMs, please contact me here.

  4. #4
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    Quote Originally Posted by steph
    Hi everybody,

    i decided to ride with my own stem so i made drawings with autocad for blue prints and solid works for 3d. Now i'd like to know what else i have to do if i want to ask to a professional to machine my part. I'm open to all the piece of advice.

    Thanks.

    Steph.
    The machine shop will need a drawing with the tolerances and material of your stem. If you have a 3D model created in SolidWorks you can give the machine shop a STEP or IGES file of your part if they use a CAM program like MasterCAM to generate the tool paths. 6061-T6 aluminum would be a good material to make it out of. There is some stronger aluminum alloys out there but 6061-T6 is the most common. I would follow the other guy's post about doing FEA on it and if it is welded it needs to be stress relieved. Make sure you don't have any sharp corners in the areas that would have higher stress because sharp coners will create stress risers and cause your stem to fatigue crack.
    Erik,
    Balle Racing
    www.balleracing.com

  5. #5
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    Thanks for your piece of advice, my design has a lot of round corners, so on this side it should be fine. I should some fea too, but the software i have downloaded is not really convenient. I think that a good think to do is to machine in the direction paralel with the strength line and lot orthogonal with, i.e in the case of a stem, machine in the direction parallel to the length direction of the stem. Tell me if i'm right.

    My stem will be completely machined, no welds, i thought their would be to much stress remaining after welding event with a heat treatment, more over, after welding, you have to realign the part, so according to me, it's not really convenient.

    Once the part is done, i'll post some pictures here and the testing period too. Maybe i'll make a website, it should be awesome.

    Thx.

    Quote Originally Posted by BalleRacing
    The machine shop will need a drawing with the tolerances and material of your stem. If you have a 3D model created in SolidWorks you can give the machine shop a STEP or IGES file of your part if they use a CAM program like MasterCAM to generate the tool paths. 6061-T6 aluminum would be a good material to make it out of. There is some stronger aluminum alloys out there but 6061-T6 is the most common. I would follow the other guy's post about doing FEA on it and if it is welded it needs to be stress relieved. Make sure you don't have any sharp corners in the areas that would have higher stress because sharp coners will create stress risers and cause your stem to fatigue crack.
    Erik,
    Balle Racing
    www.balleracing.com

  6. #6
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    Quote Originally Posted by steph
    Thanks for your piece of advice, my design has a lot of round corners, so on this side it should be fine. I should some fea too, but the software i have downloaded is not really convenient. I think that a good think to do is to machine in the direction paralel with the strength line and lot orthogonal with, i.e in the case of a stem, machine in the direction parallel to the length direction of the stem. Tell me if i'm right.

    My stem will be completely machined, no welds, i thought their would be to much stress remaining after welding event with a heat treatment, more over, after welding, you have to realign the part, so according to me, it's not really convenient.

    Once the part is done, i'll post some pictures here and the testing period too. Maybe i'll make a website, it should be awesome.

    Thx.
    Yes machine from the side so the radius will be lengthwise because your highest loads will be from the top of the stem with a downward force ( like when you go off a jump and case it hard) You will also have twisting loads from steering and occasional side impacts from laying it over in a burm.
    Erik,
    Balle Racing
    www.balleracing.com

  7. #7
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    Quote Originally Posted by BalleRacing
    Yes machine from the side so the radius will be lengthwise because your highest loads will be from the top of the stem with a downward force ( like when you go off a jump and case it hard) You will also have twisting loads from steering and occasional side impacts from laying it over in a burm.
    Erik,
    Balle Racing
    www.balleracing.com
    Ok thanks for the advice, after machining, i tought that some polishing could attenuate the grooves made by the tools. But it is just to add some fine touch to the final product. Do you think polish makes a great difference.

    I have also a question about tolerance, what is the usual tolerance accepted for machined parts like stems. Particularly for the hole of the steer tube and the hole that will receive the riser bar. Is a tolerance of 0.1mm acceptable or do i have to make a narrower tolerance?

    About my stem, it is 50mm long, and a 0 rise.

    That's it, but i accept the piece of adivce of everybody who has expertise with machining.

    And again thanks to everyone who already answered to my post,it really helped me.

  8. #8
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    Just the drawings.

    Most shops will just need the drawings most likely in dxf. I would'nt try to generate your own code because their are so many things that can go wrong. As for a shop that could do it for you, we've done many custom stems in the past and would be happy to make yours. Just drop me an e-mail @ [email protected] also, if your concerned about the machined finish, we could use a large face mill that would leave a mirror finish.

  9. #9
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    Quote Originally Posted by machineshop
    Most shops will just need the drawings most likely in dxf. I would'nt try to generate your own code because their are so many things that can go wrong. As for a shop that could do it for you, we've done many custom stems in the past and would be happy to make yours. Just drop me an e-mail @ [email protected] also, if your concerned about the machined finish, we could use a large face mill that would leave a mirror finish.
    Thanks for the offer and the advice, but i live in europe, so i think it gona be difficult for both of us to meet each other. I'm supposed to come to the SEAOTTER Classic, so maybe we could meet there, and i'll show you my stem.

  10. #10
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    Quote Originally Posted by steph
    Ok thanks for the advice, after machining, i tought that some polishing could attenuate the grooves made by the tools. But it is just to add some fine touch to the final product. Do you think polish makes a great difference.

    I have also a question about tolerance, what is the usual tolerance accepted for machined parts like stems. Particularly for the hole of the steer tube and the hole that will receive the riser bar. Is a tolerance of 0.1mm acceptable or do i have to make a narrower tolerance?

    About my stem, it is 50mm long, and a 0 rise.

    That's it, but i accept the piece of adivce of everybody who has expertise with machining.

    And again thanks to everyone who already answered to my post,it really helped me.
    On the Tolerance of the stem it would be best to check the tolerance of the steer tube and the handlebar first, they are probably +0 - somthing so your tolerance would be like maybe +.002" (.05mm) -0. You may want to take the handlebar and your fork to the shop and have the machinist measure them and tell them to make it a slip fit.
    Erik,
    Balle Racing
    www.balleracing.com

  11. #11
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    Quote Originally Posted by BalleRacing
    On the Tolerance of the stem it would be best to check the tolerance of the steer tube and the handlebar first, they are probably +0 - somthing so your tolerance would be like maybe +.002" (.05mm) -0. You may want to take the handlebar and your fork to the shop and have the machinist measure them and tell them to make it a slip fit.
    Erik,
    Balle Racing
    www.balleracing.com
    i would think an interferance fit for the handlebars would be more appropriate. This way when tightened down, the contact area will be more uniform, whereas a clearance fit will force the material to deform un-uniformely (like a crimp) when the interface is tightened. Pinch bolts and split collars will allow for easy installation of the interferance fit which is based on the diameter once a clamping force is exerted.

  12. #12
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    Quote Originally Posted by zedro
    i would think an interferance fit for the handlebars would be more appropriate. This way when tightened down, the contact area will be more uniform, whereas a clearance fit will force the material to deform un-uniformely (like a crimp) when the interface is tightened. Pinch bolts and split collars will allow for easy installation of the interferance fit which is based on the diameter once a clamping force is exerted.
    Actually, i don't understand exactly what you mean, do you tell me that i have to take into account the deformation of the material under a clamping force?
    Could you explain me more in details the role of the split collars and pinch bolts. If you have time of course.
    Anyway, i keep that in mind when i go with my stuff to the machine shop.

    Thanks.

  13. #13
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    Quote Originally Posted by steph
    Actually, i don't understand exactly what you mean, do you tell me that i have to take into account the deformation of the material under a clamping force?
    Could you explain me more in details the role of the split collars and pinch bolts. If you have time of course.
    Anyway, i keep that in mind when i go with my stuff to the machine shop.

    Thanks.
    think of it this way, say you made the diameter of your steerer clamp a millimeter larger than the steerer. In order to get a clamping force, the clamp would have to deform and would no longer be circular, it would be oval (or other depending), so the contact area would not be uniform, and neither would the stresses. When you clamp things together, effectively you are trying to create an interference fit, the closest you can make your clamp diameter to this interference tolerance, the more uniform the contact area, strains and stresses will be. This is why heavy press fits (or cryo fits as fork makers like to call them) are superior to clamp type interfaces.

    fit specifications and tolerances is all about taking into account the deformation of the material; they directly dictate how the interface will perform and the ease of assembly.

    You always bring in a stem for them to accuratly measure, then work out a resonable tolerance with them.

  14. #14
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    Quote Originally Posted by zedro
    think of it this way, say you made the diameter of your steerer clamp a millimeter larger than the steerer. In order to get a clamping force, the clamp would have to deform and would no longer be circular, it would be oval (or other depending), so the contact area would not be uniform, and neither would the stresses. When you clamp things together, effectively you are trying to create an interference fit, the closest you can make your clamp diameter to this interference tolerance, the more uniform the contact area, strains and stresses will be. This is why heavy press fits (or cryo fits as fork makers like to call them) are superior to clamp type interfaces.

    fit specifications and tolerances is all about taking into account the deformation of the material; they directly dictate how the interface will perform and the ease of assembly.

    You always bring in a stem for them to accuratly measure, then work out a resonable tolerance with them.
    Ok now it's completely clear in my mind, thanks for this explanation.

    I think that now i have all the tools in my hands to make something interesting.

  15. #15
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    Zedro you have some good tips

    Quote Originally Posted by zedro
    think of it this way, say you made the diameter of your steerer clamp a millimeter larger than the steerer. In order to get a clamping force, the clamp would have to deform and would no longer be circular, it would be oval (or other depending), so the contact area would not be uniform, and neither would the stresses. When you clamp things together, effectively you are trying to create an interference fit, the closest you can make your clamp diameter to this interference tolerance, the more uniform the contact area, strains and stresses will be. This is why heavy press fits (or cryo fits as fork makers like to call them) are superior to clamp type interfaces.

    fit specifications and tolerances is all about taking into account the deformation of the material; they directly dictate how the interface will perform and the ease of assembly.

    You always bring in a stem for them to accuratly measure, then work out a resonable tolerance with them.
    Zedro you have some good tips on the handlebar fit. One more thing to have the shop do is make sure the handlebar clamp does not have sharp corners where the handlebar exits the clamp because the clamp could create stress risers in the handlebar. This has been a problem with motorcycle handlebars on motocross bikes, the stock handle bar clamps had sharp corners and would put a small indention into the handlebar creating a stress riser so the handlebar would fatigue and break. The fix was to file and sand the edges smooth.
    Erik,
    Balle Racing
    www.balleracing.com

  16. #16
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    Quote Originally Posted by BalleRacing
    Zedro you have some good tips on the handlebar fit. One more thing to have the shop do is make sure the handlebar clamp does not have sharp corners where the handlebar exits the clamp because the clamp could create stress risers in the handlebar. This has been a problem with motorcycle handlebars on motocross bikes, the stock handle bar clamps had sharp corners and would put a small indention into the handlebar creating a stress riser so the handlebar would fatigue and break. The fix was to file and sand the edges smooth.
    Erik,
    Balle Racing
    www.balleracing.com
    Actually, i integrated this in my design, i thought that a sand blasting could be interested to harden the alloy on its surface, but i don't have enough expertise to know if it's makes a big difference.

    Anyway, all the things you taught me here, helped me a lot to refine the design of my stem. I'm sure it will make gain a lot of time when i'll have to work with people at the workshop.
    Thanks to everybody again. I hope i could have a prototype before the end of the month, so stay tuned, i'll show it to you.

    C.U

  17. #17
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    Quote Originally Posted by steph
    Actually, i integrated this in my design, i thought that a sand blasting could be interested to harden the alloy on its surface, but i don't have enough expertise to know if it's makes a big difference.

    Anyway, all the things you taught me here, helped me a lot to refine the design of my stem. I'm sure it will make gain a lot of time when i'll have to work with people at the workshop.
    Thanks to everybody again. I hope i could have a prototype before the end of the month, so stay tuned, i'll show it to you.

    C.U
    its not sandblasting you want (thats just an abrasive treatment), you mean shot-peening, that work hardens the surface. In the case of a stem, i really dont believe its necessary; shot peening is more benificial on more critical high stress/high cycling geometries like tubing where it can prologue fatigue resistance. I wouldnt bother with the extra expense.

  18. #18
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    you should learn Geometric Dimensioning and Tolerance (GD&T), and use those techniques to apply tolerances to the drawing.
    G O N Z

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