Sunnen honing 660 bronze; Anybody done it?
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    Default Sunnen honing 660 bronze; Anybody done it?

    Hi All:
    The title says it all.
    I'm making some 660 bronze bushings with super tight bore tolerances.
    Boring them is such a pain in the ass, and I am too lazy to put them up on the wire EDM.

    Have any of you had bushings made from 660 bronze, Sunnen honed?
    How much stock did you leave?
    Did they come out nicely?

    The bushings I'm making have a bore diameter of 0.5002 +/- 0.0001 and are 1.625" long.
    I have 20 to make.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    660 hones just fine. use an aluminum oxide stone. I think I would rough hone to about .0005 under and then go to a finer stone and sneak up on your size, and let the parts stabilize. I think I would try leaving .002/.001 for honing stock to start. make a little holder out of a loop of abrasive cloth clamped between two pieces of aluminum stock if you don't have the little Sunnen handle that does the same thing. Certainly hand heat is going to make your life miserable if you try to just hold them. The length should not be an issue, but be carefull with your overstroking to keep bellmouthing to a minimum.

    Just being nosey here- how do you plan on measuring these? Dan

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    + one on what Dan wrote....
    Cheers Ross

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    Quote Originally Posted by implmex View Post
    Hi All:
    The title says it all.
    I'm making some 660 bronze bushings with super tight bore tolerances.
    Boring them is such a pain in the ass, and I am too lazy to put them up on the wire EDM.

    Have any of you had bushings made from 660 bronze, Sunnen honed?
    How much stock did you leave?
    Did they come out nicely?

    The bushings I'm making have a bore diameter of 0.5002 +/- 0.0001 and are 1.625" long.
    I have 20 to make.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    Check here: https://www.sunnen.com/graphics/asse...45b2132df8.pdf

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    Should be straight forward on the hone. Bore to .002 rough, finish hone. I like to finish with a KL5 stone.

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    Exactly what Dan wrote. Really not a big deal. We do it here, often enough. From 0.090" up to 1.500", so far. One thing I will add is to let them sit for a little while after the roughing hone cycle, in effort to cool completely. THEN take your measurements. It should not be terrible for what you are doing, but it is a general rule that I have come to employ regardless, when dealing with finicky bores. Have fun.

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    Hi again All:
    First of all I want to thank all who responded; as always this has been super helpful.

    Next an update:
    Further to Dan's query about how I propose to measure these bores, well I got to thinking, so I phoned the customer and asked how HE intends to measure them.

    Dead silence on the other end of the phone, and then...."well, they have to fit over these 1/2" dowels we buy from McMaster and they can't have any slop"

    OK that changes everything.
    So now the tolerance is all over the map because nobody knows how big, how round and how straight McMaster dowels are, never mind what the tolerance band of the dowels is.

    Thank you very much Dan, for bringing this up...I might have walked myself right into a potential major nightmare if you hadn't asked this simple question, so I owe you one, bigtime!

    Now there is hopefully going to be a proper engineering evaluation of what the tolerance band should actually be as well as what the nominal target dimension should be.

    BTW, these bushings allow an alignment plate to slide up and down and the unit has to work at minus 100 degrees centigrade.
    I asked whether they've made allowances for the different coefficients of thermal expansion of bronze against 416 stainless...guess what...they haven't, but I think they will now.

    The second thing; I tried to find a honing shop here in Vancouver with a simple Google search.
    I can find lots of shops in the USA, but nobody locally; there doesn't appear to be a single shop with a Sunnen that's advertising this service in Vancouver.

    So I might just go FUKIT, and charge them what it takes to do these bores on the wire (once we actually find out how big they're supposed to be).

    The other option is to send them across the line, but they wanted these by this Friday...I'm still chuckling about that one.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Is this a regular customer? I see this turning out weird. Imagining 4 bushings in a plate with dowels measuring bang on .5 and forgetting the temp issue AND imagining you manage to hit size and parallelism and concentricity "perfectly" they need to really know what they're doing putting the holes in the plate. Are they press fit?

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    Quote Originally Posted by implmex View Post
    BTW, these bushings allow an alignment plate to slide up and down and the unit has to work at minus 100 degrees centigrade.
    I asked whether they've made allowances for the different coefficients of thermal expansion of bronze against 416 stainless...guess what...they haven't, but I think they will now.

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

    Ugh! I was thinking to myself when I read the original description that someone needed to shoot the designer (really, I was), but I didn't think it was that bad!

    If this current iteration doesn't work the way they want (and they damn well better not blame you for it), they should investigate using orthogonal posts with ceramic-balled (no lube) instrument bearings mounted on them to make a sorta linear bearing setup with the OD of the ball bearings riding on the posts.

    A third bearing on some sort of spring loaded swing mount retains the assembly together opposite the other bearings to capture the rod but allow come compliance for OOR/bends/deviations. Use something similar on the second post for rotation constraint.

    What sort of environment (besides cold) will this mechanism have to work in? Hopefully a non-condensing vacuum chamber of some sort...

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    Good morning All:
    The bushing threads onto a small sliding plate and the assembly runs up and down on a single post: it is the only sliding element but a second post constrains radial rotation using a slot, so the basic design is reasonable for its purpose.
    It goes into a cryogenic chamber and is part of a biopsy specimen management system.

    The design issue is only with the tolerances; they were unaware that commodity grade dowel pins are not geometrically very consistent for the kinds of clearances they thought they needed.
    So the problem was as much one of unfamiliarity with the specs of the parts they intend to use as anything else.

    Clearly they were also unaware of the large influence of temperature when trying to deal with close fits and dissimilar metals.
    Also, as it turns out, the temperature in the unit is actually -20 to -30 degrees celsius, but they thought to state -100, "just to be safe"

    At my suggestion, the solution they're now considering is that I supply a set of Deltronic pins and a single bushing with a wire cut bore so they can assemble them in the chamber and evaluate various clearance options quickly and cheaply in the conditions under which they will need to work.
    Revised specifications will follow.

    Since the acceptance criteria are pretty subjective: "no slop" , and "a nice silky sliding fit" I figured this was going to be the fastest cheapest and most certain way forward, rather than looking up coefficients of thermal expansion and guessing from there.

    They are considering it, and I should find out later today what the next steps are.
    They're also looking into having the pins lapped.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by implmex View Post
    Hi again All:
    First of all I want to thank all who responded; as always this has been super helpful.

    Next an update:
    Further to Dan's query about how I propose to measure these bores, well I got to thinking, so I phoned the customer and asked how HE intends to measure them.

    Dead silence on the other end of the phone, and then...."well, they have to fit over these 1/2" dowels we buy from McMaster and they can't have any slop"

    OK that changes everything.
    So now the tolerance is all over the map because nobody knows how big, how round and how straight McMaster dowels are, never mind what the tolerance band of the dowels is.

    Thank you very much Dan, for bringing this up...I might have walked myself right into a potential major nightmare if you hadn't asked this simple question, so I owe you one, bigtime!

    Now there is hopefully going to be a proper engineering evaluation of what the tolerance band should actually be as well as what the nominal target dimension should be.

    BTW, these bushings allow an alignment plate to slide up and down and the unit has to work at minus 100 degrees centigrade.
    I asked whether they've made allowances for the different coefficients of thermal expansion of bronze against 416 stainless...guess what...they haven't, but I think they will now.

    The second thing; I tried to find a honing shop here in Vancouver with a simple Google search.
    I can find lots of shops in the USA, but nobody locally; there doesn't appear to be a single shop with a Sunnen that's advertising this service in Vancouver.

    So I might just go FUKIT, and charge them what it takes to do these bores on the wire (once we actually find out how big they're supposed to be).

    The other option is to send them across the line, but they wanted these by this Friday...I'm still chuckling about that one.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    I love it!
    That is the reason I hate aerospace so much. "But this is just clearance for a screw (of which I am privy to the entire ass'y), so the true position is out by .0005, big deal." NOPE NOT TO PRINT!!

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    Marcus- most grinding shops have honing equipment, so try that.

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    I wouldn't worry about the McMaster-Carr dowel size. I you supply the parts the right size you have done your job. With the standard AG-300 gage that most people have with their Sunnen hone you can hit the number within a tenth. If you want, you can get 2 of the dowels from them and use the Sunnen setting fixture (it makes it easier to set the gage). Then can ask them how much clearance they want and give it to them.

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    Quote Originally Posted by implmex View Post
    Good morning All:
    The bushing threads onto a small sliding plate and the assembly runs up and down on a single post: it is the only sliding element but a second post constrains radial rotation using a slot, so the basic design is reasonable for its purpose.
    It goes into a cryogenic chamber and is part of a biopsy specimen management system.

    The design issue is only with the tolerances; they were unaware that commodity grade dowel pins are not geometrically very consistent for the kinds of clearances they thought they needed.
    So the problem was as much one of unfamiliarity with the specs of the parts they intend to use as anything else.

    Clearly they were also unaware of the large influence of temperature when trying to deal with close fits and dissimilar metals.
    Also, as it turns out, the temperature in the unit is actually -20 to -30 degrees celsius, but they thought to state -100, "just to be safe"

    At my suggestion, the solution they're now considering is that I supply a set of Deltronic pins and a single bushing with a wire cut bore so they can assemble them in the chamber and evaluate various clearance options quickly and cheaply in the conditions under which they will need to work.
    Revised specifications will follow.

    Since the acceptance criteria are pretty subjective: "no slop" , and "a nice silky sliding fit" I figured this was going to be the fastest cheapest and most certain way forward, rather than looking up coefficients of thermal expansion and guessing from there.

    They are considering it, and I should find out later today what the next steps are.
    They're also looking into having the pins lapped.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    I'm not sure I understand your thought/comment about "commodity grade" dowel pins. Aren't they all manufactured to +.0002/-0.0 specs? With the exception of .001 over/undersized you buy for some special purpose. Yes I know +/-.0001 is out of range for that, but I ass-u-m-ed all dowels were created equal??

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    Quote Originally Posted by Mike1974 View Post
    Yes I know +/-.0001 is out of range for that, but I ass-u-m-ed all dowels were created equal??

    Pfffft!!! < spits drink > Yeah, I made that mistake years ago, too.

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    Hi rickseeman:
    That would be a great idea if the McMaster dowels were round, straight and all the same size but they're not.
    In the past, I've gotten all kinds of variation from dowel pins right out of the box, so making the bore dead nuts is kind of pointless until that issue is resolved.

    Part of the problem is they want clearance in the low tenths; if the dowels are lobed, tapered and crooked by a tenth or two nothing will go together like they want, and it'll quickly become my problem if I let it.

    If I supply my parts to their spec and the assembly doesn't work, I can cry foul as much as I want; it's still going to be a problem that I don't want to have to deal with and might never get paid for.

    Sad reality, but it is what it is, so I'd rather find a way that will work for sure than make it just like the picture and get the nasty phone call when they can't put it together.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

    On edit: I see others got there before me while I was still typing

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    You want silicon carbide stones. Aluminum oxide is for steel

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    You'll go to this mammoth amount of trouble to make the things, and they'll end up reaming them with an adjustable hand reamer to 'make 'em go' anyways And they'll have .0005 to .001" clearance and they'll think they're perfect. A real close sliding fit like that doesn't work in the real (dirty) world where things slide back and forth.

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    Do you think you’re part of their design team? You’re the one who makes them bushes. Is the tolerance really 0.0002 inches? Any additional prescription such as on cylindricity, roundness, straightness? A nice silky sliding fit—
    the hens behind the barn go laughing.

    I know a guy who comes back to me invariably once a year. Last time he was to reinvent the tape recorder. When I told him that to turn the capstan won’t be precise enough he went silent. Now he wants me to move my workshop into a large kitchen he rents for cheap so that we could combine resources. It wouldn’t surprise me, if his next project were the manufacture of glass elements for a new sensational lens he’s thought out. Guess what, I could mill even aspheric surfaces, CNC equipment is cheap today.

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    Most automotive shops use a Sunnen hone to finish connecting rod wrist pin bushings to those tolerances daily.

    Consider having them give you a print with dimensions. Hit that and whatever happens downstream is theirs to solve.

    jack vines


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