Rotary Cutter How do I ream out hardened steel?

[jrlogan]

I don't see what all of the fuss is about with eliminating the shear bolt. He has a slip clutch. I have a slip clutch on mine and as far as I know it never had shear bolt from the factory. If the clutch is adjusted properly I don't see an issue. Am I missing something? Do they usually come new with a "back-up" protection device?

Exactly. When I bought this from the dealer I told them I wanted a slip clutch, and this was my first bush hog purchase. I don't think they had a proper setup for a slip clutch, and they used what they had available to rig something together for me, and it's been a pain in my keester ever since. Had I known more about bush hogs at that point I would have declined to purchase. It should have had a splined shaft on it from the beginning. What's the point of having a slip clutch if I'm still replacing shear bolts all the time?? I'm not going to fool around with trying to make a 3/8 bolt work, believe me, I have already tried. I've ordered a 1/2" cobalt bit that I hope will drill my shaft out, and then I'm putting in a 1/2" grade 8 bolt. Hopefully, the last bolt I will ever put in...

[SPYDERLK]

Exactly. When I bought this from the dealer I told them I wanted a slip clutch, and this was my first bush hog purchase. I don't think they had a proper setup for a slip clutch, and they used what they had available to rig something together for me, and it's been a pain in my keester ever since. Had I known more about bush hogs at that point I would have declined to purchase. It should have had a splined shaft on it from the beginning. What's the point of having a slip clutch if I'm still replacing shear bolts all the time?? I'm not going to fool around with trying to make a 3/8 bolt work, believe me, I have already tried. I've ordered a 1/2" cobalt bit that I hope will drill my shaft out, and then I'm putting in a 1/2" grade 8 bolt. Hopefully, the last bolt I will ever put in...

The 1/2 cobalt wont drill it if its as hard as you described earlier. Carbide probably will, but as mentioned "fragile" in a non rigid setup. There are several carbide options; a twist drill, a die drill, a masonry drill, a carbide burr. Greatly different costs and risks of failure.
... A 1/2" masonry drill has a slightly oversized carbide tip that can be sharpened down to size and good edge to cut metal. Its cheap, but sharpening and finesse of use will still be critical.
... A twist drill is expensive and fragile,
... A die drill is more rugged. These come solid carbide or carbide tipped. Still expensive - still control problems to favor success.
... A 1/2" Rough Cut burr in ball profile could present the basis for everything you need for success. You would get one with the tip brazed to a 1/4" steel shank [common practice -alot cheaper]. You would bush the shank to 3/8" to fit the existing hole and then pull the bit thru the hole. This will give you the stable guide you need to coddle the carbide. For further "safety" you would use a batt electric hand drill with torque limit settings in the spindle. "Drilling" would be done in short pecks with continuous water spray to flush chips.

But, I think you may have a situation where the bolt is breaking from cumulative impact due to play in the joint - both the oversized hole in the collar and wear in the shaft and collar. Before I went to machining I would use Loctite #638 hi strength retaining compound to saturate the entire joint to stabilize it and see if that stopped your problem shearing. A small bottle is about $10 I think.
larry

[Soundguy]

man.. lots of engineering and rethinking going into reworking a shaft when a perp hole in the easier to drill yoke is gonne be the fastest answer.

[mikehaugen]

man.. lots of engineering and rethinking going into reworking a shaft when a perp hole in the easier to drill yoke is gonne be the fastest answer.

Hey, I am with you soundguy... I think it was a good idea.

I do however question the hardness of the metal. Why would the shaft be that hard? (no, I didn't mean it to sound that way) We have plenty of gearboxes at my work that do a lot more work than a tractor implement and I haven't come across one that wasn't able to be drilled with a HSS bit. A hardened input shaft just doesn't make sense to me, as it becomes more brittle. Unless the shaft is one piece with the internal gear, but I doubt that even, and if it was, would the entire piece be hardened vs. just induction hardening the gear end? Perhaps they were dull bits?

[SPYDERLK]

Hey, I am with you soundguy... I think it was a good idea.

I do however question the hardness of the metal. Why would the shaft be that hard? (no, I didn't mean it to sound that way) We have plenty of gearboxes at my work that do a lot more work than a tractor implement and I haven't come across one that wasn't able to be drilled with a HSS bit. A hardened input shaft just doesn't make sense to me, as it becomes more brittle. Unless the shaft is one piece with the internal gear, but I doubt that even, and if it was, would the entire piece be hardened vs. just induction hardening the gear end? Perhaps they were dull bits?

Can you think of any complications with that idea?

The hardened shaft and collar are a necessity with use of shear bolts. Otherwise they become damaged with every shearing. Theyre not going to be superhard - that would embrittle as you say, and they would be prone to chipping. I expect their hardness is well above Gr8 tho.
larry

[mikehaugen]

Can you think of any complications with that idea?

The hardened shaft and collar are a necessity with use of shear bolts. Otherwise they become damaged with every shearing. Theyre not going to be superhard - that would embrittle as you say, and they would be prone to chipping. I expect their hardness is well above Gr8 tho.
larry

I guess that makes sense, I was not considering the sheared pin consequences. I have never actually had to deal with shear pins (luckily). The PTO attachments I have have slip clutches. The gearboxes I was referring to are either keyed or have ring fetters.

[SPYDERLK]

I guess that makes sense, I was not considering the sheared pin consequences. I have never actually had to deal with shear pins (luckily). The PTO attachments I have have slip clutches. The gearboxes I was referring to are either keyed or have ring fetters.

Yes. Shearpins present special hassles as well as hi impulse load at shear. Nuisance shearing causes people to use stronger bolts. Use Gr8 and it will damage the shaft and collar some as it shears. Probably on the verge of cutter gearbox damage at that point.
...Perhaps you didnt notice, ... I was asking if you noted any of the complications in the idea of drilling the collar?
larry

[Soundguy]

i see it being easier then drilling the shaft.

[mikehaugen]

I guess it would be difficult to get a hole drilled perfectly through the center without putting it in a mill.

[orezok]

I guess it would be difficult to get a hole drilled perfectly through the center without putting it in a mill.

I would drill a hole through one side then slip it on the shaft using the shaft to center the second side by drilling through both. If you sincerely want to drill the hole in the shaft larger, I would use a bridge reamer. The long taper prevents binding and they will cut hard steel easily.