|
In my opinion as a Mechanical Engineer, BAD IDEA!! My reason is as follows; The grade of a bolt is an indicator of it's strength, of course, BUT it also is an indicator of the HARDNESS of the bolt material. The harder the material is the harder/stronger the cutting edges need to be to keep from being deformed by the material being cut. Think of hardened hasps on locks, you don't cut them easily and I have seen them ruin the jaws of a good bolt cutter. Typically for a rotary mower (bushhog), the gear box input shaft and the PTO shaft collar have the shear bolt through them. Thus they are the “cutter” and are designed to have ONLY a (SOFT) grade 2 bolt used to transmit power between them. By using a harder bolt, you cause the edges of the holes in the shaft and collar to deform - or wallow out. As the holes wallow out they allow more and more “slop” between the two cutting edges. This looseness will allow the shaft and collar to shift back and forth creating an additional “banging” force above the simple torque load needed to turn the blades. Things break much easier when they are “hit” because you can generate much larger forces through impact. Thus you may be breaking shear bolts easier than if the holes were “clean and tight”. Yes the grade 2’s deform a little when they shear and you may need to drive them out, or at least hit them to get them started to come out. My experience has been the the pieces in the collar fly out and are lost immediately. Then with the collar off the shaft the piece in the shaft somehow is gone by the time I get back to the barn - even though I could not push it out at first. I should also add that using a grade 5 or 8 bolt will put much higher stresses on the teeth of the gears in the gear box. Kind of expensive things to break, which is why the shear bolt is used - it is cheap and easy to replace. YESSsss, the gear boxes are typically 40 or 80 HP rated, BUT there is a difference between HP, which is a force applied thru time and distance, and simple force which can get very large even with low HP driving it. That is what low gear is all about! Please use the right grade (#2) shear bolts, and be easier on your equipment - and safer, IMHO. Regards,
Larry
| 
