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Cut vs. Rolled thread strengt differences

Discussion in 'The Garage' started by 1979jimmy350, Oct 16, 2006.

  1. 1979jimmy350

    1979jimmy350 1/2 ton status

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    I am starting to make a list of the parts needed for my crossover steering, I am going to use chevy DRE insted of heims becasue this is still a street truck. what i am wondering what will be stonger of these two options

    1) Use the allot threaded inserts the fit tight into the DOM and then are welded to the DOM tubing providing the threads for the DRE, the benfits that i see are greater thread strength becasue of the rolled threads and stronger material in the insert cons: the part is welded to the DOM and there might be less thread engment than threading the tube

    2) Get the taps and drill the ends of the DOM to the correct diameter and run the thread into the tube Pros: more thread depth, no welded parts in the steering system Cons: the threads are cut in the DOM which might not be as strong as the alloy inserts

    what do you guys think is better the inserts or the cut threads in the DOM?
     
  2. AussieK5

    AussieK5 1/2 ton status

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    Rolled threads are far superior to cut ones, cutting thread does no favours to the finished product. That said you can mitigate this downside by increasing the component size and reduce the possibility a stress riser from the cutting of the alloy will propagate into fractures.

    Depends on too much to give a finite answer on your application.
     
  3. greyhoundjc

    greyhoundjc 1/2 ton status

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    One other thing to consider is the cost of the taps and I couldn't find any local shops that had one. The 7/8 -18 left hand thread tap is pretty spendy, I think around $115.00 from www.tapcousa.com. I had a tie rod made by WFO and there price and service is pretty hard to beat. I went with the welded inserts for if I decide to go crossover/hi-steer then I just have the rod shortened and a new insert welded in for the hi-steer.
     
  4. 1979jimmy350

    1979jimmy350 1/2 ton status

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    the cost difference is not a big deal for me, if i have to buy the taps i don't care this is not a one time deal i plan on doing a few crossover setups and link suspensions eventually
     
  5. rdn2blazer

    rdn2blazer 1 ton status Premium Member

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    what is the thread length of the insert compared to the actual thread engagement of the part into the taped hole if you went that route?

    also what is the engagement length into the tube of the insert? I know everyone welds these around the diameter where the insert meets the end of the tube. this is actually a weak weld joint, or I should say its not the strongest way to weld an insert in.

    you only have a single plain of strength with that type of weld. a better type of weld joint IF there is sufficient engagement is to drill holes at atleast 3 different radial points stagared in length from the end on the tube, and plug weld the part into the tube. you get more then a single plain weld joint that way. you also have a joint that its strength is in a linear plain with the tube which is the strongest plain vs. at 90 degrees or perpendicular to the tube.

    in other words your joint has leverage against the force it is resisting against so its not just relying on its total strength to keep from breaking. a weld around the diameter esentually is the pivot point. if there is even a few thousands clearence for a slip fit of the insert into the tube it will want to flex back and forth until if fails. if its going to be welded around the dia. it should be a press fit so it wont pivot.

    a plug weld has base material and structure around the entire dia. of the plug weld to maintain its integrity. a weld at the end of a tube does not. the insert is a completely seperate piece that under load has no resistance from being pulled except for being held in place by the shear strength of the weld.

    a plug weld is effectively pinning a insert in place because of the penetration into the insert body.

    I would go inserts IF there is sufficient thread length and engagement length into the tubing for plug welding. if there not I would tap it deep. those threads wont pull out. you could allways sleeve the OD of the DOM tube and plug weld it into place for extra thickness over the threaded area if you worried about it breaking at the ends. sorry this got so long.
     
  6. ntsqd

    ntsqd 1/2 ton status

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    It is rare that female threads are rolled, so either method results in cut threads, be they done with a tap or single-pointed.

    As rdn pointed out, what is the thread length of the insert vs. how deep can you tap the tube? The sole set I've made so far I tapped the the tube clear to when the tap wrench bottomed out on the end of the tube (a tap of that size will have a reduced shank diameter). So figure three, possibly pushing 4 inches of threads for that method. Granted, the TRE's don't have that much thread, but at least all of their threads are engaged in the tube.

    If you tap the tube directly then you will have two fewer failure points in the steering, i.e. where the inserts are joined to the tube.

    If you tap the tube you will need a thicker tube wall to have the material to be able to tap it.

    Try http://e-taps.com/ for the taps. Last time I looked them up it was a considerable savings over other sources.
     
  7. marv_springer

    marv_springer 1/2 ton status

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    This is what I think too.... it's a wash...

    I've seen lotta links get used and have seen none of them pull the threads out. Even the ones I made from solid 6061 Alum. :ignore:

    Marv
     

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