Specifically on older bobcat skid steers, has anyone reinforced the loader arms to gain rigidity and strength? I've noticed that my machine being an F series has less welded structural reinforcements (between the arms and on the bobtach) than the later G series version. I'm thinking of designing some weld on elements(about 1/2" thick) and cutting them out using my plasma table. Any thoughts?
Have you bent or broke your arms ? Abusing to the point of bending, then reinforcing will cause failure some where else. Sometimes with catastrophic results.
Use some harder steel if you do it, not just mild steel...
1/2" is probably huge overkill.. something like 1/4" Domex or A656 would be better, lighter, more closely match the parent metal, etc. Be sure to preheat some and use a low hydrogen (7018) stick or welding wire to reduce porosity and cracking. :my2c
Unless you're having a problem there really is no need to reinforce the loader arms, they're pretty much designed structurally to lift what the capacity of the machine is, both hydraulic lift capacity and tipping capacity. There were some problem models, like the 873 had a penchant for breaking the boom, but most models perform as designed without many glitches. One thing the F Series was bad about was cracking the weld for the pin boss where the tilt cylinder attaches to the loader arms frame. As for the G Series, that's more of an apple to orange comparison, the F Series was a radius lift and the G Series is more of a vertical lift. Plus the G Series machines were typically a little greater in capacity than the F Series. But if it makes you feel better to reinforce the loader arms, feel free to do so, just keep in mind in doing so you may actually create a stress point on the arms that wasn't there before.
Seems to me that the plate used to sandwich the arms where the lift cylinders attach is about 1/2". and since that is what I would be welding to, then I thought it would be good to match it as close as possible. Yes I definitely plan to preheat, I usually aim at 500°F and test with my infrared gun . If I do it I'll probably use my mig. What metal did Bobcat originally use? The reason I started thinking about this is that I noticed some cracks around welds which attach the cross member to the arms. The cracks are right in the same place that got extra reinforcing material on the G series. The loader arms seem to be straight and in great shape other than the need for new bushings which I'm getting around to replacing. I've put less than 5 hours on this machine so far, just enough to test it out and figure out where it needs attention before putting it to real work . It's an 863 with just under 2,500 hours. Any advice on avoiding creating stress points on the arms from welding as willie59 cautioned? And as lantraxco suggested, I plan to use A656 or Domex with 7018 welding wire, and of course preheat.
If you already have cracks you need to fix those first. Try to take off the paint and make sure you find the ends of the cracks, then drill stop holes. next gouge out a v-notch making sure you just barely get all the way through. (too much of a gap and you will have trouble filling it in. Then weld the notch, starting your bead just outside the groove so you get good penetration and no cold spots. Grind any high spots and lay the gusset on top. Make sure to copy the bobcat design (thickness, shape, and start/stop points) as close as you can because you can be sure they tried a few ideas out. Otherwise like others said you will just make a new high stress area. What you want to do is have gradual changes in thickness. Going from 1/2 to 1" is too much, 3/4 to 1/2" is better. ISZ
500 deg's preheat is little high, 300 should be fine. Make sure you burn your MIG hot to get full penetration and fusion. I'd prefer 7018 if I had a choice.
Sorry but I have a sick feeling in my belly with this thread. No offence but, OP please find someone with some experience to give hands-on advice. I could be way off but you seem a bit green on this project. The comments on preheat and metal thickness just make me wonder. I'm glad that you are looking for advice. That is why there are forums like this. You are working on something that can crush a person. I've done many repairs like you're talking about and I'm sure you will successfully do many in the future but do the first one right. Experience is priceless. I may be all wet with my opinion. We're all glad to help. I'm sorry if I came to the wrong conclusion but I've seen too many bad/fatal repairs.
Another thing to remember is that for every pound of reinforcing plate and weld that you put on the lift arms, a pound comes off the load that the bucket will lift. So put 100 pounds of plate & weld on the loader arms and that's 100 pounds less the machine will lift before tipping. You'll be surprised how much "reinforcing" adds up if you actually get down to weighing it all. If it was me I'd look to properly gouging out the existing cracks and re-welding them as the designer originally intended. You might be surprised just how much difference there is between what the designer intended and what the fabricator on the shop floor (who's trying to make his bonus) actually did ....... Regarding preheat if the material is a standard structural steel with no heat treat (and I se no reason that it should be on something so simple as a skid steer) then 150-200 would probably be fine. All you need to do is to drive all the moisture out of it. It also might pay you to do some research into what materials the factory actually uses and try to match them wherever possible. It'll make welding so much easier.
I can't swear to it, but I seem to remember being told that the lift arms on the bobcats back in the eighties when I worked on them was some form of high strength steel. Nothing exotic because they were formed, but not A36 either. YMMV
Wow! thank you all for responding to my inquiry. I definitely understand the concept of how every little bit of weight adds up and decreases the lift capacity. Seems like the consensus is to remain with the original design and I agree. The 500°F preheat is what was recommended for welding spring seats to the new 6k lb axles I installed on my skid steer trailer. After a thousand miles they're still there. Is 300°F better? I avoid taking on projects before doing sufficient research and feeling confident in delivering a substantial improvement. attached are a few photos of the cracks and bobtaches. I'm about to remove the old bobtach(and replace all bushings/pins) because it has a terrible busted ear repair which is causing the bushing to rapidly wear out(hopefully not at the boss yet) . the replacement bobtach is a newer version with reinforced ears. I have not yet begun to prep for repair. but I did scrape some loose paint. Left side zoomed out Left side zoomed in Right side zoomed out Right side zoomed in
New vs old bobtach old bobtach, right and left(busted) side New bobtach Left side
If it were me I would try to de-rust those spots near the cracked joints. Blast, or consider using a rust removing solution (Menards sell some). I've taken some of the rust removing solution and applied it to a paper towel on a vertical surface, stick the wet towel to the area ....add a little more solution every once in a while over a couple hrs and the rust will be gone. Good, clean way to do it. Then protect the area with a self-etching primer after the repair. To the welding pros out there, if an owner WERE going to use a common off-the-shelf steel for reinforcement purposes (only), would you guys think cold-rolled be the better choice, due to it's higher 'yield' strength over hot rolled? Or neither?
Not a welding pro but yes, cold drawn is much better than hot rolled steel. There are several grades of cold drawn but typically 1018 is what you'll find locally. A36 hot rolled flat bar and 1018 cold drawn flat will usually be fairly close to the same spec for ultimate tensile strength (the point at which the metal fails completely), but A36 has a yield strength (the point at which the steel deforms and will not return to it's original shape) of 36,000 psi, the 1018 spec is around 54,000 psi. So, the cold drawn will take a lot more stress without deforming, basically has a bit more spring to it. As I mentioned earlier, I'm a fan of Domex, or A656 plate. Going upscale to the more esoteric alloys for bucket or grapple parts say, I favor T-1 or Weldox/Hardox or the like. Gotta pick what's right for the application.
I wonder what grade of steel the 'good' OEM buckets, say from Cat, Bobcat, Case, etc. are made from, anyone know? I see a lot of buckets and other skid attachments on Ebay and C/L which state they are made of A36 steel like this one: http://www.ebay.com/itm/72-BOBCAT-D...501817?hash=item3cc57f72f9:g:qTYAAOSw3xJVfzpF Makes me wonder....
To my mind making any bucket out of A36 which is the generic spec for structural hot rolled steel is just a waste of time and money, they're just gonna bend. YMMV