What method be to line ream (hone) 2 installed bushings that need 0.0007 to 0.0013"
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  1. #1
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    Default What method be to line ream (hone) 2 installed bushings that need 0.0007 to 0.0013"

    Four parts just arrived in shop and need to be line 'reamed' (incorrect process) to true up two bushings taht are separated by 3" from inner side to inner side, and 5" out side to outside.
    The existing diameter /s are Ø1.4955 to Ø1.4962" (and at 1 place I measured 1.4970" but it is slightly out of round by 0.0008")

    The desired diameter range is Ø1.49626 - 1.49682" The surface finish must be 32 or better (a 16 would be best)
    The perpendicularity from the main part to the line reamed bushings is exact. Meaning no tolerance to speak of.
    Also, these are the blade grips on an EC145.
    In the picture, look at the 4 large diameter holes on the cardinals, close to the outside diameter of the blade clamps.

    ec145-rotor-head.jpg

    20210921_144054.jpg

    I am 50/50 on this project. It may be worth the hassle, maybe not.
    I mean we DO make and work on flight critical components (always under a customer's PMA or an existing STC) but this is tight, and I don't have tons of confidence of doing it in my shop.

    First off:
    1) Flight critical.
    2) People can die if something goes wrong.

    3) There is a LOT of money on the table.

    I believe a reamer would only rub / burnish, and I would only have 1 shot at getting it correct. Not my favorite option.
    Boring in a CAT40 wouldn't be my favorite option either. Removing that small amount doesn't seem like it would work either.
    Roller burnishing?? The upfront tooling would be pricey, but may work well....

    Barrel lapping may work...
    Most of my local vendors are into gun drilling & honing.
    Would a quality lapping company be able to perform within the above stated parameters?
    (In this case I am thinking https://holespecialists.net/honing-services/ )

    Is there another method I should look to?

    Thanks,

    Doug.

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    I would vote for honing as long as you only care that the bores in spaced-apart bushings line up and don't care nearly so much about relative location and axial alignment among the holes as a group. Then again you said you have no tolerance available on perpendicularity. It seems like you are hosed on hitting size pretty much regardless, since you already found a place that's oversized, and you might be hosed on perpendicularity. If you are allowed to go oversize on the holes, you might have a fighting chance on hitting some bigger size with a tight tolerance. I would not attempt reaming (or single-point boring) - there's nothing to cut. I would not attempt roller burnishing - I don't see how that would fix hole alignment issues, much less allow tight enough size control. You'd also be work-hardening the surface, and I would not want to do that on a flight-critical part without lots of input from engineering. A jig grinder might do the job, but you'd have to be allowed to go oversize.

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    An automotive machine shop with a Sunnen Line Hone (for line honing engine blocks) should be able to hone that within tolerances for you.

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    Yep, line hone.

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    A line hone is not required and not actually available in this size. A standard P28 Sunnen mandrel with 2 stones would do the job if there was some decent amount of material to remove but in this case there is not and one bore is actually oversize in one place already and the others are too close to the required size.

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    tomorrow? It is oversize then it is worn out scrap

    Sent from my SM-G781V using Tapatalk

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    Quote Originally Posted by LexD View Post
    A line hone is not required and not actually available in this size. A standard P28 Sunnen mandrel with 2 stones would do the job if there was some decent amount of material to remove but in this case there is not and one bore is actually oversize in one place already and the others are too close to the required size.
    In good hands the Sunnen hone works to tenths every day. I'd take them to a shop with the powerstroke version and ask if they're comfortable guaranteeing to hit your numbers.

    jack vines

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    A helicopter main rotor hub

    Through mandrel with two sets of stones or one with long stones

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    I would agree with Mechanola. You don't want to mess around with hones on something like this.

    Grinding with a mandrel (or a precision internal grinder) is the reliable and consistent way to do this.

    You obviously need to have a precision internal grinding machine to do this really cost effectively. If you do not have such a machine, the setup to do this on a mandrel would probably be not worth the time. If you do not have an internal grinding machine, I would recommend contacting a shop that does aerospace machining, because all such shops have precision internal grinders.

    Also, note that there are shops that do nothing but grinding. So, for example, in Texas there is Western Grinding in Dallas that specializes in grinding jobs.

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    I wouldn’t like to be the person grinding these with little to nothing to remove, honing would be ideal if there was more material available in the bushes.
    A question for the OP - has someone already tried to get these to size and left them the way they are now?

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    Grinding would be a giant pain in the ass. Just trying to get everything set so that it would clean up with that little material to be removed would be a bitch. Honing is definitely the better approach IMO. Unless I'm mistaken, Mechanola was also suggesting honing, not grinding.

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    Quote Originally Posted by LexD View Post
    ...A question for the OP - has someone already tried to get these to size and left them the way they are now?
    I was wondering that myself. Having worked with some helicopter companies in the past (doing accessory stuff, not airframe parts) I;m
    curious about the source of these parts.. I would think that under normal circumstances they wouldn't have been allowed to leave the
    factory unless they were "perfect".

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    Remove those bushing, install new bushing, hone to size.

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    Quote Originally Posted by muckalee View Post
    Remove those bushing, install new bushing, hone to size.
    Just what I was wondering about a minute ago. What a hassle when you don’t have at least one specimen of the through bolts? The job is stinking something. Actually the bolts ought to be fit to the bushings or vice versa depending on how easy it is to remove a bushing. They can talk about surface roughness but the question should be: what’s the materials pairing? Are the bolts harder than the blade bushings? Tough they need to be in order to not break. I fear you have a darn complicated collocation of steels and the engineer has no clue of how the forces are distributed. The tolerance on the diameter is 0.00056" or 0,014224 mm. 1/2673 relative to the diameter, I mean the bolts must be very well cylindric to go in.

    Of course am I saying to hone. Internal grinding leads to deviations rather than brings the two orifices in line. Long stones are simpler only at first sight, they will wear unevenly. Two sets of honing bodies on one mandrel can be brought to action much longer across their length each for well distributed load. Although here you have little enough stock left according to your measurement. I’d like to watch a Eurocopter mechanic remove the bolts once . . .

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    I have seen these parts before and method choice is honing. The rule of thumb for honing tandem holes is a stone length AT LEAST twice the length of the center to center distance of the holes. In this case the distance from the center of one hole to the center of the other hole is 4" which means the stone length has to be at least 8". In Sunnen land it translates to a 3 stone P28 mandrel which will give a stone length of 9.843"

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    The Sunnen P28 type hones are effectively line hones - I agree, definitely the way to go here. The slight over sized area shouldn't be cut any larger by the hone as long as the bores are in line. This one could be trouble. If I were doing this, I'd warn the customer that this is iffy being that you have a bore that's already oversized in one place but I'd try it - but failure is on them, not me. If it fails can the bushings be changed? If so, I'd try it for sure.

    I would think that a couple tenths over tolerance in this application should not hurt the function of the part. On the other hand, if a blade cuts loose imagine the liability! I would definitely have them write something up specifying that they are okay with the finished dimension if they approve the finished product.

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    With a hone what ever problem you are trying to correct, out of round etc. You need too hone out at least twice that amount.

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    The part dimension described is amazingly close to hundreds of automotive spindles that use a solid kingpin. Sunnen has been making hone mandrels to do that job for 75 years or more. The p28 three stone mandrel quoted above is the Sunnen Industrial mandrel equivalent of the old kingpin hone mandrels. Regardless of the process, grind or hone, you have to have sufficient stock in the bushings to hit the finish size. I too would hone them.

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    RED FLAG! RED FLAG!

    gettyimages-515035696_sq-2360fde6d7a44d93c362691ace00152a4b5ce602-s800-c85.jpg

    Considering that these are paramount to the lives of the people who will be operating/carried by the helicopter I would treat them as if they are weaponized uranium and hard pass. There is A LOT of money on the table because the replacement cost is that high and most likely no one else would touch the parts. The correct process is align honing, in a manufacturing perspective grinding may be the original application but that implies a large scale operation with dedicated tooling and fixtures.

    This is not the same as making components from scratch based on a drawing set, this is modifying an already existing component, a big FAT red flag from the FAA.
    Send them back to the manufacturer and have the manufacturer do it. Even if there is a spec, and these hubs are outside of the spec, the FAA may not allow a modification.


    Here is one last idea: before you do the work, call your insurance carrier and ask them if they will cover this type of work. When they are done chuckling in the background you will have your answer.
    Attached Thumbnails Attached Thumbnails 7416a213633cd5e82b339d189bd72ce0.jpg  

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    The rotor blades rotate on axial bearings, not on the bolts for which the work is in question. Therefore the rather tight fit. Besides, each blade is arrested by a second smaller bolt in trailing direction. The forks and blades should form a rigid unit in two dimensions. Perpendicularity of the bushings and bolts to fork and blade is crucial. I should also say that too little material is left for the job. You cannot make things align and that’s what I meant with something stinking.

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