Adding Hydraulic Side Links

[SPYDERLK]

Quote: But 150,000 is better....by a lot!!
I any case, my point is that it wil be strong enough....agreed??? And the locktight is good along with the 3/8-16 cross bolt.

3RRL, I just threw that out based on a reasonable expectation of what a high grade thread of that size will hold before failing. I figured yould dropped a zero. I see now that you were talking about working load. The forces generated in working a load can be many times the weight of the load itself due situations where the load motion is stopped, started, or changed quickly -- a jerk. I think the 15K work load limit is pertaining to medium strength steel with a safety ratio of about 6 to allow for jerking. Your situation, with an open sided nut is pushing you more critical and begs for optimization within that inherent strength disadvantage. Two easy things; 1)use a green high strength loctite like #638, and 2) go to 3/8 x 24 NF Gr8 for the pinch bolt. The aim is to eliminate any possibility of relative motion. With these measures youve got an intimate metal to metal multi thread joint with all space filled with an incompressable material. The open, weak, side is relatively flexible but has been made more rigid by use of a bolt having a larger root. The tendency of the open side to open under load is better resisted. I would probably say good enuf and leave it at that, however I would pay close attention during assembly of the joint. The threads would be clean, loctite would fill the joint end to end, the threads would float together vs being biased by tightening the clevis against the cylinder before the pinch is done. Tighten pinch to bolt spec. Give the loctite a day of room temp cure, then a couple days in hot sun to fully cure - - it continues strengthening for awhile. Use it and dont worry about it, but keep your eye on it for any sign of relative movement, because thats the only way it would fail - - motion induced wear. With your mill you have the ability to set up for a larger pinch bolt moved inward by the change in radius. Such would further rigidize the weak side if it must be done. One further measure - when you have room, always leave 1-1/2 to 2 threads beyond the stressed portion of the joint. This portion is "leaned on" as the joint bears stress. The forces initially borne by the outside of the bolt must have a little distance to find their way gracefully to the core in order to take advantage of the bolts strength over its entire cross section.
I think you have a significant overbuild so dont worry. The easy measures are just good insurance!
Larry

 

[3RRL]

SPYDERLK,
Hmmmm....interesting observation.

 

[Brad_Blazer]

I also had to mill some more clearance onto the upper lift bars to allow enough pivot room for the larger hydraulic cylinders.

Nice project Rob. Did you do a strength calculation on those lift bars? Max bending stress is MY/I. M = Moment (torque) Y = max distance from neutral axis (half the height) I = 1/12 * width * height^3. So max stress is inversely proportional to height squared. I would say you have removed at least half of the strength in the area you cut. Just make sure stress does not approach the yield strength of the steel arm and think about those working load factors..


Brad

 

[3RRL]

Brad, I appreciate your concern as I had concerns with that myself. (but I did not do the calcs) Anyway, here's my thinking on that. Also, if I have failure, I'll attach the swivel ball below the arm to obtain the necessary clearance while keeping the original arm thickness....sort of like a "dog-leg" attachment. I was going to do that initially, but decided to try it this way first, instead.

The machined the clearance still leaves the arm almost 1.700" thick at the skinniest point. I felt it would more than likely be sufficient for 3pt use. My reasoning is the arm thickness where where the swivel ball is housed is only Ø2.370" and the ball and socket is Ø1.660" So at the thinnest section the arm surrounding the ball is only about .355" thick....IMO being the weakest link anyway.

In other words, I think the ball would tear out of the arm socket before the arm fails. Another reason I feel it's going to be ok is because I work with a lot of heavy injection molds 3,000 to 4,000 lbs that we regulary move and lift with 1" eye bolts and lift bars. I realize it's not exactly the same, but I think that arm being reduced to 1" X 1-3/4" should stand up to 3pt use on my tractor. Brad, I think you have the same tractor as me, so I'd be curious to see what you think about that.

Disclaimer:
It's obvious that there have been a few technical and engineering concerns and understandably so.
Some of the things I share with you guys may not be normal or commomplace techniques nor safe...so just to be clear, I am NOT advocating anyone to do this. They are for my own pleasure and I enjoy sharing them with you guys. If you guys feel that they are dangerous or maliscious and may end up causing harm to other TBN members, then I will stop posting my projects from now on.

Thanks,
Rob-

 

[Ductape]

Rob,
I'd say take the posts as friendly advice. I, for one, do not want you to stop your tractor modification posts. I'm sometimes a bit jealous, reading your threads..... but only because i wish i had the:
1) Time
2) Money
3) Skill
4) Equipment
to make similar modifications to my own tractor.

Keep the posts, and more importantly, pictures coming ! I feel that your legal disclaimer is a given for ALL tractor owners here who modify or build their their own implements and equipment. Without posts like yours, i wouldn't have much reason to hang around here

Scott

 

[JerryG]

Some of the things I share with you guys may not be normal or commomplace techniques nor safe...so just to be clear, I am NOT advocating anyone to do this. They are for my own pleasure and I enjoy sharing them with you guys. If you guys feel that they are dangerous or maliscious and may end up causing harm to other TBN members, then I will stop posting my projects from now on.
Thanks,
Rob-

Don't you quite posting your projects. Some people just get carried away with somethings and this has been one of them. Keep posting just like you have been.

 

[Brad_Blazer]

Hi Rob. First let me say there is nothing wrong with anyone posting what they are doing and while "anyone can sue anyone for anything" I think it is a little far fetched for you to assume liability for someone else's modifications.
In fact what better way to promote safety than for you to show your mods and let us armchair engineers pick on you?

I looked at my upper lift arms and they do not strike me as being way over designed. They are big at the splined pivot end and taper toward the ball end because they are cantilever elements and bending moment increases linearly from the ball end to the splined end. I did some thumbnail calculations based on your measurements and some of my assumptions. The rated lift load is 9.2 kN or 2068lb. It looks like the load on the end of the upper arms is about 2.5x half the rated load since the link hits the lower arms less than half way to the end. So I'll say each upper arm gets 2585 lb at the ball. There is no bending moment at the ball so if the area of the steel there is 0.53 in^2(inches squared) the stress is 2585/0.53 = 4800psi (no problem)
I used dimensions at your cut of 1.7" high, 1" wide, and 6"(I am guesing at this important dimension) from the ball.
2585lb x 6" = 15,510 in-lb of bending moment (M).
Moment of inertia (I) at the cut is 1/12 x 1" x 1.7"^3 = 0.409 in^4
Max bending stress MY/I = 15510 x (1.7/2) / 0.409 = 32,200psi
Combined stress (adding shear stress as a vector) will be only slightly higher so I think we are in the ball park.

Yield stress (where it will bend and not fully recover) for 1018 low carbon steel is about 50,000 psi. I am guessing the arms are a similar material.

That leaves a safety factor of less than 2 so if you put the max load on the hitch and bounce it you might bend an arm.

You might also do a calculation based on what your tilt cylinders will lift since they may be stronger than the 3-point lift.

You can restore some strength and maintain function by welding a bar to the top of the arm spanning that area. The 1x1 solid bar like I used on my tooth bar would probably work nice. I even have some left over but I'm betting you have some appropriate material in your stock.

Here's my disclaimer: While I am a registered PE in NC, I am now at home and my reference materials are not with me. This analysis is "ballpark" and based on several assumptions and as such should be used for theoretical understanding only. The calculations have not been independently checked for errors. I do not have expertise in designing for the dynamic working loads that may be encountered by tractor implements other than occasionly tearing up my own equipment.

 

[Brad_Blazer]

I did your 3" cylinder calcs. 16Mpa is about 2300psi. Pushing against the full 3" diameter area (7.1 sq in.) you will get about 16,000lb per cylinder. Pulling against the cylinder area minus the rod area (4.7 sq. in) it's about 11,000lb. So if you use those cylinders against a load, something will probably move or break before the relief kicks in.

Man I sound like a wet blanket! I can see the fine adjustment advantage of using the big slow cylinders. I am just saying you'll have to be carefull how you apply them. I am used to implements that tolerate full relief pressure.

You are fitting your tractor with a great set of features! I have to wonder what's next, a hydro pump upgrade?

I am currently working on an ATV style rack to attach to the rops where the pins go when folded.

Brad

 

[3RRL]

Thanks for the calcs Brad. I figured the big slow cylinders were going to exceed the strength of the 3pt system...even left unaltered...just a guess on my part though. I'm gonna have to wait several weeks before total assembly because of the family Labor day campout-get together. No tractor time with the grandkids up and their pesky parents (my kids). hahaha

Be sure to post some pictures of your ATV tractor rack. That will be a real handy addition for all of us. I can see lots of uses for that.
Rob-

 

[3RRL]

I went up to the property for Labor day and was having the kids and grandkids up for a giant camp out. It sure was a lot of fun to have most of them up there. I didn't think I'd have time to do any work on the tractor, but Loretta took Friday off so we left Thursday night, giving me a little time to work on the side links after all. I brought up many swivel connectors to be sure I could do the job.

Here's some fittings and stuff I brought up.