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  1. #1
    Bronze Member
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    Mahinda 7520

    Default How do I ream out hardened steel?

    Hey folks. I have a 5' bush hog with a shear bolt. The input shaft of the gear box only has a 3/8" hole, not 1/2" like every other one I've seen. I break this shear bolt fairly often, and I'm quite sick of it. Especially since I have a slip clutch as well, so the bolt really isn't necessary. Unfortunately it is not a splined input shaft. So I would like to ream this hole out so I can put in a grade 8 1/2" bolt and hopefully never break it again. Obviously I can't do this with a regular drill bit. What is the best way? Should I use abrasives and a die grinder? Carbide drill bit?

  2. #2
    Veteran Member
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    Branson 2400H

    Default Re: How do I ream out hardened steel?

    Carbide is brittle so unless you could get this shaft into a drill press I doubt you could keep from breaking the bit.

    Wouldn't it be easier to adjust the slip clutch so it slips?
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  3. #3
    Super Star Member k0ua's Avatar
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    Default Re: How do I ream out hardened steel?

    I would tend to agree, that you should be working on the slip clutch not the backup bolt.. You do know you have to adjust and test the slip clutch at least every season right? Lets say you do ream out the hole in the input shaft and put a nice grade 8 1/2 inch bolt in there and now you hit a stump. is that rusted slip clutch going to slip, or are you going to have a nice repair bill on your PTO components of the tractor.. Lets see if some other more experienced guys than I weigh in here, but these are my first thoughts.. I think you are headed down a dangerous road.

    James K0UA
    James KØUA

    Kioti DK35se hydrostat with 2 QA buckets, 48 inch. King Kutter Rotary Cutter. 750 lbs ballast box. Loaded tires, Construction Attachments SSQA Lightweight Pallet forks. EA 50 inch single lid "wicked" Grapple. Satisfied Everlast PA160 welder owner How to add a link to a post . Best way to search TBN


  4. #4
    Member
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    north bay ontario
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    john deere 4400

    Default Re: How do I ream out hardened steel?

    it you Walt apsalutly to drill go Wotherspoon ciment car éloges bit and shrapnel Wotherspoon silicone câblée Stoneham Luke a normal bit but i not récompense berceuse next you Blake thé gearbox shaft and then big problem. work on the clutch instead and put a good grade five bolt . make sure no play with the bolt and shaft.better is to get a key way machined......good luck

  5. #5
    Super Member Gary Fowler's Avatar
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    2009 Kubota RTV 900, 2009 Kubota B26 TLB & 2010 model LS P7010

    Default Re: How do I ream out hardened steel?

    If you are breaking a grade 8 3/8" bolt frequently, I don't think I would have an issue with drilling out the hole for a bit larger bolt especially since you have a slip clutch, but I think I would go up in steps to a 1/2" grade 5 rather than an 8 and see if that fixes your problem. I have to agree with you that a 3/8" shear bolt is not adequate for the new PTO switches that slam everything into gear without being able to feather it in with the clutch. You do need to loosen off the bolts on your slip clutch to make sure it will spin and is not rusted together, then retighten to where it only slips briefly when engaged or under super heavy load.
    As for drilling the hole, a normal HSS bit with titanium oxide coating should drill thru that shaft easily enough if you go slow and use a cooling fluid on the bit. If not, go with a cobalt bit but again the secret is to go slow and make sure the shaft doesn't try to rotate and bind the bit because it will snap easily if it does.
    2010 LS P-7010C 20F/20R gear tractor & FEL, 2009 Kubota B 26 TLB, RTV 900 Kubota,17 foot Lund boat with 70HP motor, 2012-20 ft 12k GVW trailer, 2011- 52" Craftsman ZTR mower, 3 weed whackers, pressure washer, leaf blowers, 7 foot bush hog, 8 foot landscape rake , 8 foot 3 PH disc, 2 row cultivator, 350 amp CC AC/DC welding machine and all the tools needed to keep them all repaired and running.

  6. #6
    Bronze Member
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    Mahinda 7520

    Default Re: How do I ream out hardened steel?

    Yeah, the slip clutch is fine. I think a big part of the problem is the drive shaft is made for a 1/2" bolt and the gear box input shaft 3/8, which means the bolt gets slammed repeatedly by the yoke of the driveshaft and breaks needlessly. For folks warning me about putting too big a bolt, most of the time these are put together with splined shafts, which I would gladly change to if I could easily. There is absolutely no need for a shear bolt in this setup.

    I can't drill this with a titanium or HSS drill bit, I've tried. Might as well try drilling a diamond.

  7. #7
    Veteran Member Mickey_Fx's Avatar
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    Default Re: How do I ream out hardened steel?

    See from your last post you have in fact determined the shaft is hardened. You will need something tougher than an HHS bit. I'd try either a cobalt or carbide bit. In addition since you are likely going to be do this sorta free hand is to use a drill bit with a pilot to help guide and keep the bit from wondering around. trying to do a decent job on a round rod/shaft is very difficult without something to hold the bit in place. A pilot will do that.
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  8. #8
    Veteran Member
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    Default Re: How do I ream out hardened steel?

    Like others have said on here. I'd work on your clutch, your shear bolt is to protect you equipment. Beef it up and something bigger breaks.

  9. #9
    Epic Contributor Soundguy's Avatar
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    Default Re: How do I ream out hardened steel?

    so.. you have a smooth input shaft mower with a 3/8 hole.

    and you have a slip clutch made for said smooth shaft.. but with a 1/2" hole?

    the movement of the 1/2 hole ont he 3/8 bolt is cutting it.

    i think I'd drill a 3/8 hole perp to the 1/2 hole so you can use it on either.. before I'd deface the mower gearbox imput shaft. slip clutch is cheaper and easier to rremove to setup to drill.

  10. #10
    Super Star Member k0ua's Avatar
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    Default Re: How do I ream out hardened steel?

    Quote Originally Posted by Soundguy View Post
    so.. you have a smooth input shaft mower with a 3/8 hole.

    and you have a slip clutch made for said smooth shaft.. but with a 1/2" hole?

    the movement of the 1/2 hole ont he 3/8 bolt is cutting it.

    i think I'd drill a 3/8 hole perp to the 1/2 hole so you can use it on either.. before I'd deface the mower gearbox imput shaft. slip clutch is cheaper and easier to rremove to setup to drill.
    Now that sounds like an idea to me, and you can get the coupling off and put it in a drill press where you can get things lined up and steady, and be a heck of a lot easier to drill. the only other thing I could think of was to try to get some thin bushing to go over the 3/8 bolt to fill the gap in the 1/2 inch hole in the coupling. But I like your idea better.

    James K0UA
    James KØUA

    Kioti DK35se hydrostat with 2 QA buckets, 48 inch. King Kutter Rotary Cutter. 750 lbs ballast box. Loaded tires, Construction Attachments SSQA Lightweight Pallet forks. EA 50 inch single lid "wicked" Grapple. Satisfied Everlast PA160 welder owner How to add a link to a post . Best way to search TBN


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