Trueing CBN stones for honing
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  1. #1
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    Default Trueing CBN stones for honing

    Sunnen suggested using lapping compound to true CBN stones. I have some medium grade 600 grit diamond lapping compound. Would that be a good choice for truing? Any tricks? I am used to truing standard Sunnen stones with oil. I have to hone 150 pcs of a 5/16 ID bushing 64 R/C. Never used CBN for honing, I have used it plenty for surface and cylindical grinding. I have a 280 and 600 grit CBN stone on the way . 75 pcs have .0003 martial to come out, 75 pcs have .0012 to remove, hence 1 stone to rough , 1 to finish. Have I got what I need?

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    Put some lapping compound on the inside of the Sunnen truing rings. Also what you can do is run those 75 pcs with the new CBN stones and hone it undersized. By the time you do those 75 pcs that CBN stone should be pretty darn even. Then true it again with the Sunnen truing ring and now run all pcs again.

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    You need 100 grit or courser silicon carbide git, diamond grit will glaze the stone. Make a slurry and hone with a truing sleeve with no oil. When the slurry starts to get dry put a few drops of oil on it to get back to a wet slurry.

    If you have a high spot rub it with an course abrasive stick. Don't make love to it use some serious pressure.

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    The diamond compound will work but it will dull the CBN grit more than SiC compound. The whole purpose of using the loose grit lapping compound is to dig/scoop out the proud CBN particles (sticking out past the perfect cylindrical surface you want) by eroding the binder around them that's holding them in. In the process the CBN particles that stay put will also be abraded somewhat, so ideally you want to use something that will cut the binder but not the CBN abrasive particles. SiC will do that. Diamond will cut both, albeit less of the CBN.

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    If the most stock removal you have is .0012" that 280 grit stone will be a tad rough. I'm thinking you may do everything with the 600 grit. I don't know which model machine you have but if everything is working correct I would use a cutting pressure in the 1.7 area and around 2000 - 2200 RPM. And don't forget Sunnen MB30 oil.
    I don't know what mandrel you have but you will need one that is heat treated. It will have a "H" at the end of the part number like a K10-308-AH or a BL10-308-AH. If you don't have a heat treated mandrel the mandrel will wear out in a handful of parts.

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    I have a MBB 1660 hone and a heat treated mandrel. I'll get some silicon carbide grit and give it a try.

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    Quote Originally Posted by RJT View Post
    I have a MBB 1660 hone and a heat treated mandrel. I'll get some silicon carbide grit and give it a try.
    That machine will do the job. Make sure you indicate the mandrel in to the part or it will shake very bad. If you have questions I'd be happly to help

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    Some good advice above... the 'truing sleeve' that is available is soft material and will weaken the bond on the CBN as described above. keep flipping the sleeve end for end. Same for your part, develop a decent 'stroke' and go with small increments of stock removal and flip the part.

    keep tabs on the bore size with PG700 gage and appropriate finger, you can check bore for 'bell' and 'barrel' conditions.

    If you 'know' of a high spot on the stone, the hand held diamond dresser can 'spot' dress the stone...

    I certainly miss Ron LaPorte, the Sunnen area rep for 'years', he was an expert and often rolled up his sleeves to assist. He's been retired some time now.

    Ahhh the smell of MB30 in the morning... LoL...

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    Quote Originally Posted by thall View Post
    Some good advice above... the 'truing sleeve' that is available is soft material and will weaken the bond on the CBN as described above. keep flipping the sleeve end for end. Same for your part, develop a decent 'stroke' and go with small increments of stock removal and flip the part.

    keep tabs on the bore size with PG700 gage and appropriate finger, you can check bore for 'bell' and 'barrel' conditions.

    If you 'know' of a high spot on the stone, the hand held diamond dresser can 'spot' dress the stone...

    I certainly miss Ron LaPorte, the Sunnen area rep for 'years', he was an expert and often rolled up his sleeves to assist. He's been retired some time now.

    Ahhh the smell of MB30 in the morning... LoL...
    Ron was one of the good guy

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    Follow up. I used the advice given and it worked out really well. Got some silicon carbide and made a paste, put some in a trueing sleeve and dressed the CBN, then honed with oil. Ended up just using the fine stones even on the bushings with .0012" material to remove. Spring pressure and RPM as suggested worked great. About 6 hours total even with some maintenance on the hone and we were done. Had to adjust size a few times, but using our Sunnen dial bore gages it was easy to keep track of. Thanks everyone,it made that job a no headache breeze. Ended up just using a piece of emery cloth to grip the bushing. The Sunnen "strap wrench" gripper kept ripping the emery cloth. Rubber gloves and emery cloth worked the best to grip the bushing.

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    I'm happy everything worked out. It sounds like you weren't using emery cloth Sunnen sells on the strap wrench. The stuff they sell is every heavy duty and won't tear.

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    We just used some emery cloth that we had in the shop, nothing special. Quicker just to wrap it by hand than use the strap wrench, and holding it by hand didn't tear the cloth. For a larger part, I could see using the strap wrench, but these were small bushings.


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