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Building trailing arms

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mu View Drop Down
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    Posted: Dec/06/2009 at 1:06am
This year I our team is looking at a semi trailing arm suspension.  One issue I was concerned with is the bearing keeper.

I originally though about boring the hole for the bearing out of a piece of round stock and then welding that to some tubing to make the arm.  What I'm concerned about is that the hole will warp when I go to weld it.

The other option would be to weld the keeper on first (without the hole) and then bore out the hole using the mill but I think this would be a pita, especially with our equipment.

The third option I could think of would to be to EDM the hole after welding.  This would require us to send it out.

Just wondering how other teams have done it and what their results were.
Andy

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shocker Racer Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2009 at 1:11am

we bore our's out of mild steel pipe. (The only part of the car thats mild steel) We start with some heavy walled pipe looking at something like 3/8".  By the time we get done the wall is somewhere around .125-.25".  Then we weld it in.  We didnt notice too much distortion, a tiny amount but it didnt seem to affect things.  If you are worried about it i would suggest a putting around 8 tacks evenly spaced around it before fully welding it.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2009 at 1:46am
Usually something that you want to keep a tight tolerance on you'll bore out undersized, weld in, then bore out to final size provided you can still get it in a machine.
-Chris Reedy
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2009 at 8:31am
I designed and made the exact same thing last year, two piece bearing carrier. I had a 4in OD pipe with a 1/8 wall thickness that we didnt touch. We machined the second piece of the carrier out of mild steel and welded it on the pipe. The design is such that its self aligning and jigging. The bearing fit was good before the welding and fit well the welding. Frankly, i didnt even bother with measuring warpage since the bearing still fit after words.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote johnfar109 Quote  Post ReplyReply Direct Link To This Post Posted: Dec/06/2009 at 10:58am
You can try the part in at final dimension but use a brass or copper heat sink to keep the part from getting to hot. I would suggest TIG and brake the weld up in to 6-8 segments alowing the part to cool in between each. I have done this king of thing on a few parts were i was trying to keep warpage down.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tebjunkie07 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/20/2010 at 3:19pm
We didn't weld a bearing carrier to the trailing arm, but we welded a sleeve over our spline couplers to connect two different size splines.... Our welder put down small beads at a time, let them cool, then put another pass down. The amount of distortion measured was about 10-20 thousandths change in diameter when put in a lathe and measured as we rotated the chuck by hand. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote neilan Quote  Post ReplyReply Direct Link To This Post Posted: Apr/21/2010 at 1:17am
Hands down the best way to do it is to leave the part a little over-sized and bore it to the final dimensions after its been welded. Our knuckle jig is designed so the centering post in the middle can be removed and the same jig used to weld it can be used in the mill hold it.
OSU lead fabricator? or something like that

-Bo
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Seb_BCS Quote  Post ReplyReply Direct Link To This Post Posted: Apr/21/2010 at 11:50am
We are running tubular semi-trailing arms with aluminum bearing keepers which were inserted in a DOM tubing cylinder that was previously machined on a lathe and TIG welded carefully. Even if we broke the weld in several beads and let it cool, we had at least .010" ovalization with 1/8" wall. We just sanded down the aluminum keepers on a lathe to fit them with a soft hammer, they are also bolted to prevent them from coming out.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GT Steve Quote  Post ReplyReply Direct Link To This Post Posted: Apr/22/2010 at 12:22pm

I personally haven't ever built trailing arms, but our front control arms had spherical bearings at the outboard end pressed into cups which were machined prior to welding.  Tubing was 0.065" / 0.083" and the bearing cups were about 1/8" wall.

We would use a steel slug in the bearing cup that was machined a little undersized of the actual bearing, and welded with that slug in place.  It served the dual purpose of preventing most of the distortion in the bearing cup and giving us a convinient place to bolt that end of the arm to the jig.
 
That being said, i'm sure there was some distortion.  As others have said, the best way is to weld then finish machine (thats how we do things up here in the boat yard), but i realized thats not possible for most baja teams, so carefully welding is the way to go.  Keep the heat at the absoloute minimum and you should be close enough.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote p.lewis Quote  Post ReplyReply Direct Link To This Post Posted: Apr/22/2010 at 12:38pm
One thing reccommended to us by one of the instrument machinists on campus was to grind a knife edge onto the end of a triangle file and scrape any warping from the bearing keeper by hand. Kind of like whittling wood. The file's hardened steel works on 4130, 1018, and 1010 steel just fine. I've done this at least half a dozen times. Scraping with a knife by hand takes off 10 thousandths of warpage just fine if you are patient and careful. I'd say it is easier than trying to rejig the work on a machine to make the finish cut after welding.
 
Also we weld with blank disks of steel in the bearing keepers that are nearly the same size as the bearings we intend to use. It helps with alignment jigging. Of course, if you want a particular kind of fit between your bearing and keepers, that'll take extra consideration.
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