keep breaking pins in my grapple

[grapple man]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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.

 

[TomSeller]

If in doubt I would keep feeding them grade 8 bolts so something else does not break. Curious what the mfr will say. Is it the top or bottom pin that is breaking, or both? Nice grapple you have.

http://www.sidneyattachments.com/10tinewidegrapple.php

 

[grapple man]

wow, thank you for all the replies. I have been buying attactments from this company for 7 years now and I have talked with them several times about this and other issues. As what I have found to be the norm for me when I have an issue the response is always wow you are the first time we have had the problem. BLAH BLAH. Anyway yes the bolts are breaking typically right where the threads meet the shoulder. I have very little gap between clevis and knuckle on grapple. I will check with the company and also going to try the blanks as soon as i can get them

thanks again

 

[grapple man]

If in doubt I would keep feeding them grade 8 bolts so something else does not break. Curious what the mfr will say. Is it the top or bottom pin that is breaking, or both? Nice grapple you have.

10 Tine Wide Gorilla Grapple - attachments for skid steer loaders, small compact construction equipment - Sidney Manufacturing Co. LLC

ha i was just looking thru my thousands of photos to post a good pic of the grapple and couldn't hardly find one. Yes they are really nice grapples we have two of the ten tine wide and one 6 tine one. the top pin is the one that breaks most often which this pin would be subject to much more flex and torque. Anyone have any suggestions for the best way to take up some of the slop i have in my holes. i will post one of my you tube videos. one minute.

 

[TomSeller]

ha i was just looking thru my thousands of photos to post a good pic of the grapple and couldn't hardly find one. Yes they are really nice grapples we have two of the ten tine wide and one 6 tine one. the top pin is the one that breaks most often which this pin would be subject to much more flex and torque. Anyone have any suggestions for the best way to take up some of the slop i have in my holes. i will post one of my you tube videos. one minute.Video Link: http://youtu.be/WtniM8BXCxA

The forces have to be equal and opposite on the cylinder so as long as you have a grade 8 in the bottom you should protect the equipment. I wonder if a stronger and maybe smaller diameter pin would work in a test try, in case it is the twist or flex at that end that starts the break in the pin.

 

[Guesseral]

To get rid of slop like that I have welded the hole shut and re-drilled it, just how large is the pin I don't remember seeing a size. You can get 3pt hitch pins for cat 1, 2, 3 they get pretty large. Or you could always go to a machine shop have them mic it and make a pin for it, I am sure they can get something stronger than grade 8.

 

[MechE1]

Wow. Very interesting. I would never design a cylinder/clevis joint like this using a bolt, and I have designed hundreds up to and over 50 tons of force. You should change this out with a properly fitting pin. Although grade 8 bolts are strong, they are also brittle and are designed to have strength when torqued, but not with side loading. There should be pleanty of pins available via hydraulic suppliers that would work for your situation. You'll have to check clearances along with diameter. If you have trouble finding one let me know.

 

[jmc]

That slop shown in the video could add impact loading on top of everything else.

 

[TomSeller]

That slop shown in the video could add impact loading on top of everything else.

After seeing the video, that much slop is very abnormal. It seems the hole may be sized for a larger pin.

 

[SPYDERLK]

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.

Breaking pins often cause secondary damage that is difficult to fix. The absence of stress risers is what you need. You are not actually breaking the bolt or pin, but fatiguing a specific weaker area on it. Your breakage is undoubtedly originating at a stress riser. A bolt whose shank extends all the way thru the stress area would work. That might be cheaper than the bolt blanks which will undoubtedly work.
larry

 

[TomSeller]

What are the operators doing when the pins break? Holding loads on the bottom of the grapple does not take much force. Are they crunching concrete? Dragging with the lid?