straightening a threaded rod

[kco]

I bent the top link on my DK35 yesterday while mowing with my rotary mower. I took it with me today when I went to get the filters for my upcoming 50 hr service thinking the dealer might have the right hand threaded part that I had bent.

I was amazed how he straightened it on his press in about 1 minute. No heating, he just supported the non-threaded end and cylinder on two small metal blocks and used an small aluminum block over the threads where he pressed it. Did one operation with the press, eye-balled it, did one more press, and it was straight. Then he used a triangular file to touch up the one thread that was damaged.

My Kioti dealer is also a machine shop (Timberstar in Vernon) so they are used to doing that type of work. But it is really neat to see how easy it is for people who have the skills. It's no big deal to them. I imagine it is the same for spyderlk.

 

[SPYDERLK]

I bent the top link on my DK35 yesterday while mowing with my rotary mower. I took it with me today when I went to get the filters for my upcoming 50 hr service thinking the dealer might have the right hand threaded part that I had bent.

I was amazed how he straightened it on his press in about 1 minute. No heating, he just supported the non-threaded end and cylinder on two small metal blocks and used an small aluminum block over the threads where he pressed it. Did one operation with the press, eye-balled it, did one more press, and it was straight. Then he used a triangular file to touch up the one thread that was damaged.

:thumbsup: Yeah. Im guessing your bend was not severe? - lo straightening risk. Do you know what happened to make it bend? Im asking because if it bent from compressive force [buckling] it would be termed more a failure since this is a normal function called upon in use. If it bent from accidental side force I would call it damage. Id rather be fixing the accident, but upgrading the failure. See what I mean?

I will always use heat when straightening any non trivial threaded part that is bent enuf to impede a nut. The reason is notch strain. Virtually all bending movement takes place in the very small area at the bottoms of the threads - an extremely intense situation when you think about it. Heat eases the abuse by softening things up a bit. The harmless limit is around 600F. This is where shiny steel colors blue/purple. A straw-brown color precedes this, occuring around 400F. Any heat helps. The colder the metal the more difficult and abusive bending is. Threads/notches are just a worst case.
larry

 

[RoyJackson]

I wonder how the OP (ducks13) made out with his repair/replacement?

 

[kco]

:thumbsup: Yeah. Im guessing your bend was not severe? - lo straightening risk. Do you know what happened to make it bend? Im asking because if it bent from compressive force [buckling] it would be termed more a failure since this is a normal function called upon in use. If it bent from accidental side force I would call it damage. Id rather be fixing the accident, but upgrading the failure. See what I mean?

I will always use heat when straightening any non trivial threaded part that is bent enuf to impede a nut. The reason is notch strain. Virtually all bending movement takes place in the very small area at the bottoms of the threads - an extremely intense situation when you think about it. Heat eases the abuse by softening things up a bit. The harmless limit is around 600F. This is where shiny steel colors blue/purple. A straw-brown color precedes this, occuring around 400F. Any heat helps. The colder the metal the more difficult and abusive bending is. Threads/notches are just a worst case.
larry

I'm quite sure I bent it with compressive force, likely transitioning at the bottom of a sharp rise. That is, going from flat to rising or even straddling a concave section. It's a fairly tough 4' mower and does not move side to side. I mow some steep, winding, and rocky walking paths.

The link that came with the DK35 is longer and thinner than the one I previously used with my old L275 DT. I will leave one of my old heavier links on the rotary mower. I'll likely make a similar modification.

It is a quite tough (and ugly) International Machinery mower from China and has a plate that swivels at the top link attachment that has two arms attaching to the rear of the mower to provide some up/down play of the rear of the deck. But I guess not enough play for my use.

I saw on another thread where someone had replaced the two bars that support the rear of the mower with chains, thus allowing more movement when the rear wheel must move higher as in a concave situation.

I did some equally mindless, and more expensive, damage last year when mowing with my Kubota L275 and going over a rounded hump. The mower lowered enough that the driveshaft contacted the drawbar, severing the driveshaft guard. That won't happen on this Kioti--as long as I remember to remove the shackel that I normally have in the drawbar.

There was very little bend in the threaded part of the top link and it was barely noticeable by eye and a bit of damage on about 1/8" of one thread.

 

[Soundguy]

I would disassemble the part and use a piece of pipe over the threaded portion to straighten it. You can feel the yield point when it starts to move at constant force.
If you want to replace the allthread McMaster and Fastenal have the high grade stuff.

ditto that.. hard allthread is a nice thing to have in the shop when making things.

can order from fastenal too.


soundguy

 

[SPYDERLK]

I'm quite sure I bent it with compressive force, likely transitioning at the bottom of a sharp rise. That is, going from flat to rising or even straddling a concave section. It's a fairly tough 4' mower and does not move side to side. I mow some steep, winding, and rocky walking paths.

The link that came with the DK35 is longer and thinner than the one I previously used with my old L275 DT. I will leave one of my old heavier links on the rotary mower. I'll likely make a similar modification.

It is a quite tough (and ugly) International Machinery mower from China and has a plate that swivels at the top link attachment that has two arms attaching to the rear of the mower to provide some up/down play of the rear of the deck. But I guess not enough play for my use.
There was very little bend in the threaded part of the top link and it was barely noticeable by eye and a bit of damage on about 1/8" of one thread.

Compressive failure is heavy duty, and can surely happen as you describe. When I see damage to a thread tho I suspect a side thrust was present. Some lost motion swivels will not let the link swing thru. I have one on my flail like that. The threads are bumped at full swivel trying to bend the link a little. At that point the link goes into compression and the whole 3ph assembly rises. If its driven all the way to the top stop something definitely will give. Sometimes even before the stop with weaker links experiencing compression and sidethrust.
larry

 

[ducks13]

I decided what with various people talking of the ease of straightening this with press etc. that I would take to the only good machine shop in town that I've found. $92 later I have it fixed I believe. Not as clear on how he did it and stuff as I'd like, I had my sick 4 year old with me when I picked it up so I didn't have time to thoroughly understand and it isn't fixed quite like I'd hoped when I took it in but it seems like a good repair and the guy knows what he is doing. They mostly work on heavy engine, I found them after asking the Onan parts department who they used after being disappointed with two shop I'd used so far trying to get my B43 Onan cam bearings in right.

Anyway, he said the threads were bad in the casting, perhaps I screwed them up in my first strightening attempt, and that they were metric threads and he didn't have metric helicoils but it just so happened that 20 mm thread is 10 tps just like a .75" english thread. So he put in the .75" helicoil and turned down the shaft about 0.030 to get it down to .75 and then recut the thread. A lot more involved than I had hoped. I still don't know how he got it straight enough to get it apart but he said that there was still a little kink in it that turning it down got rid of. I'll put in on tomorrow and see how it work but all seems fine.

This machine shop is kind of surprising to me. When I came in there before they guy was making a part for a heavy truck automatic transmission. I as amazed that they could make a part cheaper than buying a new one. He probably spent 15-20 minutes on my cam bearing problem and didn't charge me anything so the $90 wasn't so bad.

 

[Soundguy]

wow.. i'd have welded a 2" coupler nut to the top after trimming, then ground for contour, then transplanted some hard ( gr5 ) allthread ( fastenal , mcmaster car.. ) to the rod, and been done with it for under 20$ and some rod and electricity... and not worried about a helicoil.

BTDT with this type of transplant repair.. never have regretted it or had one let go.

have had straightened threads break on me though, as was stated in a prev message..

good luck

soundguy

 

[RoyJackson]

This machine shop is kind of surprising to me. When I came in there before they guy was making a part for a heavy truck automatic transmission. I as amazed that they could make a part cheaper than buying a new one. He probably spent 15-20 minutes on my cam bearing problem and didn't charge me anything so the $90 wasn't so bad.

Glad to read it's squared away and I hope it holds up for you!

Good jobbing machine shops are usually pretty small (low overhead) and very flexible (hence the lower cost for that heavy truck tranny part). They can also be great for reverse-engineering.

 

[SPYDERLK]

I hope it works for you. Regardless of skill in application, a helicoil does not make an optimum working thread. Virtually continuous load changes and dirt are issues. It is a good fastener thread where you tighten it good and forget it.
larry