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Thread: A-Arms construction

  1. #1

    Join Date
    Nov 2002
    Location
    Montréal, Québec, Canada
    Posts
    14
    I have a question about a pretty basic issue. I'm finalizing A-arm design (construction now, geometry is pratically done). We have used for some years Chassis Shop's tube adapters because we are limited in our machining time and prefer to use it for more critical parts.
    This situation has 2 inconvenients: first it limit the weight saving possibilities by imposing a unique thickness for a given tube outside diameter. Second we find it a little expensive.

    So I am curious to know if other teams, beside of completely machining their owns, have found a less expensive way of fixing rod-ends to their A-arms. I'm not considering the use of spherical bearings for the inboard mounts this year because I'm waiting to know if we can reach the level of precision needed in the construction of the frame...
    Last year some teams 'seem' to use modified nuts to fix rod-ends to the a-arms. Am I wrong? This option seems to be a little hazardous on the safety side, because it doesn't give a lot of surface in the inside of the tubing, near the weld, to give adequate mechanical resistance...

    Gabriel
    Ecole Polytechnique de Montréal FSAE

  2. #2

    Join Date
    Nov 2002
    Location
    Montréal, Québec, Canada
    Posts
    14
    I have a question about a pretty basic issue. I'm finalizing A-arm design (construction now, geometry is pratically done). We have used for some years Chassis Shop's tube adapters because we are limited in our machining time and prefer to use it for more critical parts.
    This situation has 2 inconvenients: first it limit the weight saving possibilities by imposing a unique thickness for a given tube outside diameter. Second we find it a little expensive.

    So I am curious to know if other teams, beside of completely machining their owns, have found a less expensive way of fixing rod-ends to their A-arms. I'm not considering the use of spherical bearings for the inboard mounts this year because I'm waiting to know if we can reach the level of precision needed in the construction of the frame...
    Last year some teams 'seem' to use modified nuts to fix rod-ends to the a-arms. Am I wrong? This option seems to be a little hazardous on the safety side, because it doesn't give a lot of surface in the inside of the tubing, near the weld, to give adequate mechanical resistance...

    Gabriel
    Ecole Polytechnique de Montréal FSAE
    Gabriel Denoury
    Ecole Polytechnique de Montréal FSAE
    www.fsae.polymtl.ca

  3. #3
    Hey bud, last year we made little 'plugs' that would insert into the end of our A-arm tubing. They probably took about 10 minutes each to make, we had 2 lathes going and got pretty efficient at it. Basically about a 3/8" section would fit inside the tube, with a 1/8" lip staying outside. They were then drilled and tapped for the rod ends, pressed into the tube, and TIG welded around the lip to tube.

    We had no problems with this, other than a bit too much weight. I suppose for things like tie rods you would want to put a hex (no, not a curse) on your 1/8" lip so that you could put a wrench on it and hold the tie rod still.

    We looked at the chassis shop option, but felt that cost was very prohibative. But if you don't have shop time I can see the need to buy them. Personally I'd find the time to make them though... The chassis shop ones seemed rather large if I remember correctly... multiply that by 40 units and the weight adds up fast.

    This year, we're trying something completely different... but not with rod ends

    -------------------------
    UVIC Formula SAE Team

    http://fsae.uvic.ca
    -------------------------
    UVIC Formula SAE Team
    http://members.shaw.ca/drax77/Formula%20UVic%20Sig.jpg
    http://uvic.fsae.ca

  4. #4
    <BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Hey bud, last year we made little 'plugs' that would insert into the end of our A-arm tubing. They probably took about 10 minutes each to make, we had 2 lathes going and got pretty efficient at it. Basically about a 3/8" section would fit inside the tube, with a 1/8" lip staying outside. They were then drilled and tapped for the rod ends, pressed into the tube, and TIG welded around the lip to tube. <HR></BLOCKQUOTE>

    That's basically what we used too. We had them batch-CNC-machined with a conical section at the end but you can very well do without that.

    Marc Jaxa-Rozen
    École Nationale d'Aérotechnique

  5. #5
    we go the same route, making our own inserts on a manual lathe. they take very little time to make. you could have your whole set made in about 3 hours with one person on one lathe, or less if you have more men/machines. very cost effective way to do it.

    www.formularpi.com
    Rensselaer Polytechnic Institute
    Formula SAE '00 - '04
    Team Leader '01 - '03
    www.formularpi.com

  6. #6
    We make them too, hell, they are a very simple part to make on a lathe. The only tools you need are a lathe, bit, drill, and tap. You probably have everything you need.

    It's a good freshman project to get them used to lathe work . Purchasing them is very expensive, we've never really considered it.

    -Charlie Ping
    Auburn University FSAE 1999-present
    -Charlie Ping

    Auburn FSAE Alum 00-04

  7. #7
    For all of our tie rods and toe links and pull/push rods, we use Chassis Shop tube inserts. Simple, and easy.

    For our A-arm however, we custom machine spherical housings which are then end prepped to the arms themselves. Sphericals are then press fit into the housings and retained using a snap ring. Simple, quick, light and easy to make. Looks REALLY clean too.

    Vinh

    University of Toronto Formula SAE Racing Team
    www.fsae.utoronto.ca
    Vinh Pham
    Toronto FSAE Alumni 01-04
    www.fsae.utoronto.ca
    2003 Formula Student Champs!

  8. #8
    Senior Member
    Join Date
    Sep 2002
    Location
    Birmingham, England
    Posts
    765
    We machine our own tube inserts for pull roads and steering arms.

    Wishbone wise, we machine a spherical bearing housing, weld it in and use Aurora HAB-4TG 1/4" bore staked sphericals. Aurora have actually just supplied us with the first ever batch of HAB-4TGs, never having done this bearing with a staking groove before.

    It's a very clean solution and avoids circlips.

    Ben
    Tyre Analysis Engineer - Caterham F1 Team
    Alumnus of University of Birmingham
    www.ubracing.co.uk and Formula Student Design Judge

  9. #9
    I often use standard lugnuts. Look into lugnuts designed for lawn equipment or a MG miget has 3/8 fine lugs

    see

    http://www.ncs-stl.com/racecar/MVC-011S.JPG

    http://www.ncs-stl.com/racecar/MVC-004S.JPG

    http://www.ncs-stl.com/racecar/MVC-010S.JPG

    Hope this helps

    Andy

  10. #10
    We also turn our own a-arm bungs on a manual lathe, it's easy and our freshman can crank them out in no time. It's a good project to put new people on since the tolerances are not all that tight. This year we'll be uaing spherical bearings for the outboard mounts, and flexures inboard

    Lehigh Formula SAE

    www.lehigh.edu/~insae/formula
    Lehigh Formula SAE 1999-2004

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