I have a Kubopta KX121 that had a WB thumb added to it, I am replacing pins and bushings and bushing the holes in the bucket. I can't get the replacement pin from the manufacturer so I have decided to make a replacement. I have 4140 annealed shaft that I can use and I have some 4130 that I can make the bushings from. Could someone make a material recommendation for the pin and bushing material for the bucket. Thanks, Steve
You can use 4140 for all the pins and bushes. You will need to have the pins induction hardened and the bushes heat treated. They are too soft as they are.
No problem heat treating the pins and the bushings, the bushings for the bucket will have about a 1/2" wall thickness and be 1 3/4" long I plan on welding them in place should I be concerned about tempering the bushing with the welding heat? Steve
If you weld heat treated 4140 it will soon break and it will temper it out. They just need to be pressed into a machined bore. Work on about a thou interference for every inch of diameter.
Ok, so i'm a mechanical engineer. I just have some heavy equipment as tools/toys on my property. Don't make the pins and bushings out of the exact same material. You'll end up with the 2 materials galling against each other. In general, materials interact poorly when mated with the same material. http://www.flowserveperformance.com/performhelp/_media/sizing_selection:valtek:08:table9.gif Ok, 4140 isn't on that list, but what you'll see is that most material (except some exotic ones) have a P (poor) in the box where the same materials intersect. An excellent wear combination would be heat treated 17-4 stainless steel (for the pin) and 440C steel for the bushing. Those are not the cheapest materials, but they would work very well together. Unfortunately, i'm not a materials engineer, and wear combinations is not my specialty, but i do know not to make 2 mating parts out of the same material. Try asking about good wear material combinations on an engineering forum, such as this one: http://www.engineersedge.com/engineering-forum/forumdisplay.php/13 . I can post an appropriately-worded question if you want
Like materials in terms of steel alloys live okay together as long as the heat treatment of the different parts is to different hardness specs in my opinion. Since pins have to flex in most applications, make the bushings 5 to 10 points harder on the C scale, should be fine. I don't have any letters after my name, no offense, just real world experience.
None taken. Real world experience will substitute for letters any day. Different heat treats will certainly help, but it's far from the best solution. A lot of times i get too caught up in trying to make things perfect, when good-enough works just fine.
I've not had to replace any bushings, but I have had a local machine shop make several back up pins and also the kubota quick coupler ears that I have welded to make custom attachments. The guys at the machine shop deal with properties of materials engineering everyday. Try picking their brain and see what you can get. That's my opinion, hope it helps.
The manufacture generally makes pins and bushes to 58 to 62 Rockwell. The pins are usually induction hardened 4140. Bearings are usually EN14 and carburised. For smaller machines I have often made bearings out of 4140 and hardened by quenching in oil. I recall one set on a small 8 ton digger still being tight after 7K hours.
Isn't there some sort of professional etiquette class for engineers? Like doctors and shrinks learn not to diagnose their friends, and lawyers learn to generally shut up. Mechanical engineers must have it tough though, that's such a broad field it's hard to know one's limits. I'm curious what the factors are with pins and bushings that lead to seeming to ignore this principle of like materials galling etc. Obviously there are lots of different manufacturers making very similar joints over the last couple centuries, so I'm gonna assume that they've tried some different things. "Perfect" might be considered roller bearings and keeping contaminants out of the joint That will work about as well as a roller bearing on the apron drive of a manure spreader, if it gets greased enough to keep the roller bearing working then steel on steel will work just fine.
I'm not quite sure where you think i broke the line of ettiquite. Just because i'm not an expert in the subject, doesn't mean i have zero knowledge about it. If i had zero knowledge about it, i wouldn't have posted anything. I told everybody my knowledge about the subject was limited, but i told everybody what i DO know about it. Excuse me for posting something that i thought people might find useful..... That's how internet forums work, don't they? People help out others by adding in their knowledge about a subject? Then there's always those who also like to start arguments. You lost me as to where you're going with your second paragraph. I would be extremely surprised if any equipment manufacturer out there is making the pins and bushings out of the same material, different heat treats or not. Will it work? probably? is it the best solution? no. Roller bearings would be a lousy idea. the dirt contamination would grind those to a pulp pretty quickly. the best solution i've seen (notice the qualifier "i've seen" there) is greasable spherical bearings. Large wear surface area, and they will automatically take up any misalignment in manufacturing or repair.
Every pin and bushing "I've seen" has been very hard steel on very hard steel. From this forum I've heard of bronze(ish?) bushings in some joints. I've never seen cast iron or aluminum alloys, like you see steel shafts riding on in gearboxes etc. So there's Mechanical Engineer Mike who says that RayF's opinion is not the best, who do you think I believe? I believe there are factors at play that Mike is not taking into consideration that are more important to the performance of the materials. Just my guess. Maybe etiquette is the wrong word, no offense intended. Definitely making fun of you a little. Maybe this is a better example: I think I know more about labor and delivery than my wife, having assisted in the births of hundreds of animals, but in the heat of the moment, I SOMETIMES know enough to keep my mouth shut. But seriously, doctors and lawyers are taught to avoid offering professional advice for lots of reasons, right? Are engineers not warned of the dangers of a little bit of knowledge being a dangerous thing. And remember, the members of this forum are far more "on the spectrum" than the general population...
Ok, this is going to be my last post on the subject, so i don't drag out this disagreement any further. On the subject of giving advice/experience, isn't that the whole point of internet forums? For people to share experience and advice? No, we don't have any kind of "don't share advice" class. Whether my advice is professional, or personal, is up for debate. If you don't like me sharing my advice, or think i don't know what i'm talking about, you don't have to use any of it. nobody does. Everybody should use what everybody else says online to form their own opinions anyway. We're all just a bunch of random internet people to each other. Any one of us could be just making **** up. I, for one, like hearing other people's experience / advice. I often learn something, and i share mine, so others can do the same. I don't believe every piece of advice in every post, neither should anybody. On the topic, i never said RayF was wrong, I never really made any comments towards Ray's post. I agree with him. He's done something to make them work together. From Ray's experience, it looks like carburizing, in combination with the hardness of whatever pin he was using, makes 2 parts of that specific material work well together. Perhaps you misinterpreted what i said, but i never said there was anything wrong with hard steel on hard steel. There are hundereds of different kinds of "steel", many of which work well together. (like the 4140 and EN14 that Ray mentioned) What's NORMALLY a bad idea is the exact same steel alloys together in an application where there's motion between them. Can they be made to work together? Yes, and apparently Ray has had success with this specific material in question, which he's shared the details of, and i thank him for sharing his experience. I found that very useful. My experience is that unless you know of a specific combination that works well together (which we now do, thanks to Ray) if you want the greatest likelyhood of success between moving parts, you should make them out of different steels, (or different materials). It's certainly not the only path to success, but it's the most likely. In the end, the OP is free to do whatever he wants, and follow, or ignore whatever opinions he wants. Thank you for your time reading this.
I think one example of two identical materials not working well with each other is the problem we had many years ago on a bucket leveler on a 560 Hough loader. This leveler was what we would call a slide trombone design. A tube with a solid bar that slid down inside of the tube. There was an air valve mounted to this assembly that activated the bucket leveler. As the original assembly was very worn and not working reliably we purchased new parts, tube section and rod section. New parts came in made from some type of stainless steel, looked real pretty. The tube section had a piece of steel flat stock welded to one side that the air valve mounted on. For some reason it did not look perfectly straight. Anyhow to make sure things were good I slid the rod down inside the tube. Sure enough about 3/4 of the way in it started to get tight. Now this was just being slid in nice and easy with hardly any push from one hand. Figured we had a problem so tried to remove the rod, don't recall but seems like it took a good long time with a slide hammer to finally get the two back apart. And both were galled up to the point to be totally junk. Lucky we had a good understanding dealer and they warranted the two parts. Next one came in without the slight warping from the flat stock welded on the one side and we grease the ..... out of them before assembling them.
I agree entirely. I'm sorry for being such a jerk.
For excavator bucket & stick pins , or pin of any kind I generally just stop at the machine shop & tell them to hack off a length of " cold rolled " such & such size . Seems to work fine . http://metalsupermarkets.com/blog/difference-between-hot-rolled-steel-and-cold-rolled-steel/
I am also a mechanical engineer, BSME, 1986 University of New Haven, plus graduate industrial engineering at Cincinnati, MSE, 1996, plus ABD PhD Industrial Engineering, also at Cincinnati. The Industrial engineering stuff is advanced research techniques in System Safety and doesn't really apply to this discussion. I grew up doing machine ship work...and in this case we have a partial rotation plain bearing, heavily greased. For the Bushing, I would use a high carbon steel, like a 1090 and most likely case harden, since we also want some toughness and ductility. The pin I would want to be softer, and use a lower carbon steel, like a 1050, but do a full heat treat, since it will have sufficient ductility at full hardness. I would want the pin to wear first. Galling is a type of corrosion from pieces that are fixed, and if they rotate with grease, galling is not really an issue. By using the same basic material, steel, galvanic corrosion is minimized. The key is GREASE to avoid metal on metal contact. And we also have to realize that when we order parts from a machine shop, they will use easily available materials, exotics are expensive, need special tooling and separate scrap handling. High and medium carbon steels are ideal for this task. No need to use high chromium stainless and certainly no need for nickel alloys. I make my living doing advanced analysis with system safety application to defense production facilities, my hobby is mechanics and restorations. I spend some time as a heavy mechanic between high school and engineering school and it has served me well. There is no ONE ideal material, and every selection is a trade off. At some point, some manufacturer is going to offer a carbon fiber boom and stick, to save weight and add stiffness and we are going to hate it, but love the extra length and stiffness. Flame away...
I might add a bit of clarification to my post. OEM bearings are not usually made of 4140. Its more expensive than a carbon steel. As I said they use similar to EN14. Its cheap and can be carburised to make an excellent bearing. The reason I sometimes use 4140 in bearings is that while more expensive I can harden it in my own workshop using a torch and a bucket of oil. Sounds crude but it works extremely well and it takes 10 minutes,not days to send it to a heat treating plant. The reason OEM pins are 4140 and sometimes 4340 or similar is that it induction hardens very well.Fast cheap and very good. It also has much better core strength than the carbon steels like K1045 or 1090. I've just learnt this as going along over 29 years of line boring and using a heat treatment and engineering shop doing my pins and bearings. I did a lot design modifications on large buckets and troublesome pins that continually broke in extreme conditions due to incorrect heat treatment,bad lube hole placement or just weak material. Apologies if I'm pumping up my own tyres but some may find the info helpful.
I would not allow any bushes to be welded or pressed in place, they should be heat/ shrink fit, ie, cool the bush heat the boom. Any time I have seen other methods used the bush soon breaks loose and the boom requires line boring to correct the failure adding to the cost of a job poorly done in the first place.
That's one that I hear about all the time. People (bosses) who think they can patch up a worn out bore in a boom by slipping in the bushing and run a bead around each end. Sure with some care it can be done and look pretty when finished. But looks only get you so far! A couple passes at the stock pile and the bushing cracks at the weld and now you are worse off that when you started.
if the bushings are tight in the bore from either pressing (high pressure) or shrink fit, it should make little difference since the loads on the bushing should be compressive. However, if you put a new standard sized bushing into a oversized eggshaped hole, and run a bead around the end to secure, now the full load is on the brittle bushing, with soft and hard zones from the welding!
I've used 4140 for my pins. I buy it pre hardened, annealed and its precision ground. 4130 should be fine for the bushings, but I would forget about welding them in. I would just shrink or fit press fit them. But on second thoughts if your talking about putting the bushings in the actual bucket ears then I spose you could weld them in if you couldn't machine to perfect tolerance for a good press fit, but not really ideal.
Hey Guys, Thanks for all the information. A little clarification on the machine, it is a Kubota KX121-2 mini excavator for playing in my yard and not used commercially, not that I don't want to do it right .... just that the machine will see limited use. I checked the hardness of the pins this morning and the OD of the 40 MM pin was Rc 55-56. The piece that I hole sawed out of the bucked was only Rc 20. 4140 doesn't heat treat up to Rc 55 any thoughts on what the pin might be made from? I plan to weld bushings into the holes in the bucket that I hole sawed out, based on how soft the bucket material is (RC 20) I don't think it matters too much what I use, any recommendations on what to use? I will research pre-hardened 4140 for the pin, but my initial search did not yield much 40 mm shaft, can anyone recommend sources? Thanks, Steve
http://www.metricmetal.com/products/round.htm http://www.ebushing.com/mssb.html
If you are wanting 55 You can get 4140 to 55 with a 400 deg. tempering.
http://www.mscdirect.com/browse/tn/...=12102054+4287984395&searchterm=4142+shafting Not the cheapest, but I usually get it from MSC because it's easy. Greyson
What you can do, is build up the hole on the existing ears with weld exept for the start of the hole. With about 3mm or 1/8th in you measures of original hole in the ear you can bore it out with a 40mm hole saw. The none welded section guides the holesaw through. If you do this, start the drill in the hole so you don't shatter the teeth, and drill a hole with the holesaw before hand so its not a brandnew holesaw when you use it and it should come out about 39.9mm and then you can just die grind the last bit. I don't think the bucket ears need to be that hard because the pins don't normally spin in the ears under load. If you have already drilled the holes big for the bushings then i would probably use the 4130 I think you said you had. I also don't think the pins need to be 55Rc The pre hardened and tempered stuff I get hear in Australia from my steel supplier is not that hard and they the majority of the precision ground stuff (often called ground centreless) they sell is for excavator pins. The recently bought 1m of 35mm for $60 so it wasn't expensive.
We produced pins and bushings made of steel 40Cr. American counterparts 5135, 5140, 5140H, 5140RN. Pin Round Steel. Bush of the forgings. Tempering. Pin turns softer and it wears out quickly. Clients are happy.
G'day Guys well we build Pins and bushes a hell of a lot of them and well 4140 for 90% of the applications we use but they are harden here is some photos of some pins and bushes we made for our PC1250 Buckets. the material was 4140.
So I read the begging of this post when it started, and wondered what the cost savings are going to be on a pin and bush project on a smaller machine like this. I do understand the challenge or fun of making things yourself, I also have a lath and milling machine and do enjoy making my own parts sometimes. What do the parts from manufacture or parts house cost for this? And what will your costs be? Is it even worth the fooling around to make them? I am not trying to be a butthead Just kind of curios. Will be interested to see how it turns out. cheers
It varies between machines. Some OEM is so cheap you could not make it for the price. Another manufacturer will want 10 times what it costs to make. A lot of the older Cat bearings on their loaders are very cheap. I remember below 10 bucks for loader frame bearings in the older 930's. You couldn't buy the steel for that.
If you read the first post, the OP stated that the pin was not available from the manufacturer, I believe it's an older machine. This is common, or long lead times even for current production machines. There are also many instances where special pins are needed to suit attachments such as a thumb or coupler and it's much easier to get it right doing it local rather than wait for some attachment manufacturer (which may have since gone out of business) to make you a replacement that you hope is correct when it arrives.
Opps I missed the not available part from the first post. ointhead Still s good thread to learn from.