keep breaking pins in my grapple

grapple man · Oct 29, 2013

Hi All,
I run a tree and brush clearing business in central illinois. We run skidsteers T770s with shears and grapples. We currently have 2 ten tine wide gorilla grapples from sidney manufacturing. The company sends out these grapples with grade 8 bolts with a zerk in the end as cylinder pins. We keep breaking these. I have even went to just grade 8 bolts thinking it would be stronger without the grease galley. I am still breaking these. Wondering if anyone would have any idea of anything stronger.

thanks

Joe

oosik · Oct 29, 2013

Welcome to TBN. Sorry your first threads are regarding problems but I do have a couple ideas. Perhaps its better that the pins are breaking rather than something more important. And perhaps this is trying to tell you that the grapples are not heavy duty enough for the jobs you are doing. I would hesitate using heavier cylinder pins until I found the root cause of the problem. IMHO

grapple man · Oct 29, 2013

oosik said:
Welcome to TBN. Sorry your first threads are regarding problems but I do have a couple ideas. Perhaps its better that the pins are breaking rather than something more important. And perhaps this is trying to tell you that the grapples are not heavy duty enough for the jobs you are doing. I would hesitate using heavier cylinder pins until I found the root cause of the problem. IMHO

no worries on the having problems. I have been in business several years now its all part of it. There is no doubt I use my equipment to its fullest potential and then some. I buy heavy stuff for that reason. We have had smaller grapples from this company and did have near the issue. These new ones are considreably wider and picking up 5000 lbs of material and squeezing it hundreds of times a day is hard on stuff. I think the issue is cause when the grapple teeth do not contact the material all at the same time allowing the teeth to torque different angles such as on a curved log or logs. And yes I understand your logic of having the cheaper pin break rather than the cylinder.

I am thinking of trying grade 8 bolt blanks since i am sure the threading process does weaken the bolt.

kevin37b · Oct 29, 2013

Your analysis is correct . Some grapples have 2 jaws that tighten up independently , and the relief stalls before you break it . I have a hoe with a thumb on it and trees are the hardest thing on it . They tend to slip and tear shtt up .Try some hitch pins instead of the bolts . HTH .

Midniteoyl · Oct 29, 2013

Try the blank.. It will prolly still break, but should last longer. Threads tend to gall the bore too..

How much slop is there in the bore? Limiting the slop should help too.. even if you have to get a few blanks turned down.

grapple man · Oct 29, 2013

I have been considering the hitch pins and yes i have a little more slop than I am comfortable with. I think I will see about going up to 1 1/8 or getting some bigger bushings. Thanks for all the insight

aczlan · Oct 29, 2013

I might contact the manufacturer and ask if they have any suggestions.
A bolt will be weaker than a pin if the threads are in the load bearing area (the threads are weaker than the unthreaded area) so make sure your bolts are long enough that any shear lines are not in a threaded part of a bolt.

Aaron Z

MechE1 · Oct 29, 2013

Hi grapple man. My first post ever. I'm a mechanical engineer in CU. Give me a shout. Maybe I can help troubleshoot your issue. I deal with hydraulics, pins and linkages quiet frequently and run into this problem from time to time.

jmc · Oct 29, 2013

Without seeing your setup, I'm wondering if there is too much width clearance within the clevis joint. That makes the pin endure some bending as well as shear. Pure shear resistance for a 1 1/8 hardened pin is tremendously. And with two shear areas per clevis, well...

Definitely get the thread beyond the shear area. If the reduced area isn't bad enough, that sharp notch plays h*ll in cyclic loading.

ChristianHF · Oct 29, 2013

To add to Aczlan's suggestion, where specifically are the bolts breaking? In the threaded area or on the unthreaded section? If its the threaded portion, which I suspect it will be, possibly look for a roll threaded grade 8 fastener instead of a cut thread (which is by far the more common of the two). Rolled threads don't have nearly the problems with stress risers at the roots of the threads. Also consider asking a company like ARP | The Official Web Site for a solution. Their material exceeds grade 8 spec's and they use the roll threading process. ARP is the fastener to use in racing/automotive circles. Good luck!

Chris.