cylinder lapping/honing on a lathe?
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    Default cylinder lapping/honing on a lathe?

    I need to lap/hone a small part (half inch square) that has a curved face with about an inch radius (the specifics shouldn't really matter for the question right?). It occurred to me that this could be done pretty effectively using the appropriately sized ID of a cylinder impregnated with the appropriate abrasive compound - I would build a tool that mounts to the ways that I could vertically adjust to hold the part against the ID rigidly enough to get a good result. What i'm wondering is if anyone here has done anything similar or know any pre-existing solutions (like a cylindrical hone or lap) that would work for this?? i'd be much obliged for any help.
    Last edited by Mr Science; 01-05-2020 at 07:14 PM.

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    Be good if you post a good drawing or photo of the part and note the surface you wish to hone to what size and tolerance. From what size to what size.

    Maybe if your lucky someone close may be able to do it as your stating how to do it and then asking how to do it...it appears you need a few clues.

    Bad spelling, really bad spelling makes it appear as if your a 12 year old.

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    It sounds like we are talking about a section of a round diameter. Like taking a cylinder and cutting it in half along the long axis. Yes this could work, you'd just make your own lap out of brass or copper. No need to make any sort of contraption to mount on the ways, just get a small steel bar and mount it in the toolpost and use that to apply pressure against the back side of your part while it's inside the lap. Ideally you'd leave that floating and not fastened so the part can self-align. Might need a small divot for the bar to grip such that the part can be moved to and fro a bit. Is this being lapped for size and geometry or only for finish?

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    hi - it looks like this - i'd really rather do it myself as a small challenge though if i can ... shouldn't be so hard really.

    https://www.reelanalogaudio.com/wp-c...d-overhaul.jpg


    is my spelling really so poor?

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    Quote Originally Posted by eKretz View Post
    It sounds like we are talking about a section of a round diameter. Like taking a cylinder and cutting it in half along the long axis. Yes this could work, you'd just make your own lap out of brass or copper. No need to make any sort of contraption to mount on the ways, just get a small steel bar and mount it in the toolpost and use that to apply pressure against the back side of your part while it's inside the lap. Ideally you'd leave that floating and not fastened so the part can self-align. Might need a small divot for the bar to grip such that the part can be moved to and fro a bit. Is this being lapped for size and geometry or only for finish?
    well for geometry - subtly anyway - i want to lap off a flat wear patch across the middle to return it to the same original geometry. it's a tape head in case you were wondering. There are services that do this for a lot of money but i have a number to do and I'd like to 'DIY' - who knows? maybe it will lead to something else ....

    yeah you're right - i should just make a mount for my tool post!

    so getting to the business at hand - yes my first thought was just boring out a section of pipe or solid alu bar to the correct ID - but I figured a lap would require some sort of specially prepared surface. I can use use whatever native metal it is but slathered (lightly) with lapping compound?

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    I suppose with the above scenario (using my own 'cylinder' with lapping compound, I would need to check wear on my improvised lap pretty frequently - as it would likely be getting lapped at least as much as my part (?)

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    Yes, you'd need to make several if you have a lot of parts to do. If the actual radius isn't critical it probably wouldn't be that big of a deal, just let the lap wear a bit. As the lap wears to a larger diameter, that will make it easier to get your flat spot out anyway, as that radius increases less material will be removed at the edges and more in the middle near the flat spot. Set a limit on the max bore size and change it out when it's reached.

    You could also make an effort to embed the grit in the lap with a bearing race that fits inside the bore. Before using the new lap, spin the lap with the lathe, apply compound and using a good level of pressure let the bearing roll over the grit to push it into the lap. That will help the lap last a little longer.

    If you got into production mode it would make more sense to have a custom grinding wheel made. I'm thinking something like a bushing but with diamond grit electro-nickel plated on the I.D.

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    Quote Originally Posted by Street View Post

    Maybe if your [you're] lucky someone close may be able to do it as your stating how to do it and then asking how to do it...it appears you need a few clues.

    Bad spelling, really bad spelling makes it appear as if your [you're] a 12 year old.
    I had to...

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    Quote Originally Posted by Mr Science View Post
    hi - it looks like this - i'd really rather do it myself as a small challenge though if i can ... shouldn't be so hard really.

    https://www.reelanalogaudio.com/wp-c...d-overhaul.jpg


    is my spelling really so poor?
    It's more the lack of proper capitalization that gives your text a bit of a "lazy" look, but I guess that's concomitant with Generation Text...

    On topic - for what you're doing, I'd look at using an abrasive film, essentially a fine grit deposited on a Mylar strip, long enough to be used just like a reel to reel tape recorder itself.

    So imagine a drag-clutched feed wheel, a pair of free rolling capstans set close together (with the gap between them being the lapping zone), and the powered take-up reel dragging the abrasive tape along. All mounted to a hard plastic or metal platen, as the tape moves you press the head against the tape in between the capstans, with the pressure conforming the strip against the head.

    With the right abrasive and linear feed rate, this should take about one or two seconds a head to clean and polish the face. It'll take you longer to switch out the heads than to polish them.

    Might even be possible to cannibalize an old VHS player to make the workings, as there should be variable speed capacity to slow rotation as the take-up reel fills.

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    As long as the geometry isn't important that's a good idea. I'm still not sure if that even matters or not...

    Would be really easy to make a "lapping" cassette tape you could just drop right into the player and fast forward and rewind to do the lapping. Additional bonus, no disassembly of the cassette player to do the work. Might even be able to sell a few of those...

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    Quote Originally Posted by eKretz View Post
    Would be really easy to make a "lapping" cassette tape you could just drop right into the player and fast forward and rewind to do the lapping. Additional bonus, no disassembly of the cassette player to do the work. Might even be able to sell a few of those...
    I think "back in the day" (gods, I feel old) there were cleaning cassettes in a variety of sizes. If the OP is dealing with loose tape heads then a cassette itself won't work as easily as an open structure.

    Might even be easier to just try to make a mini-belt sander by splicing a length of the Mylar tape to make a loop. You'd want to replace it after some use to prevent scratching of the head, but I bet you could get ~5 to 10 heads cleaned with one loop. Still would need the capstans and one roller spring loaded to get the deflection/conforming needed to wipe the whole head face. Cellophane tape should be enough to do the splicing.

    OP, if you want to give this a shot I have some fine polishing tape as I've described, if you want ~10 feet or so of it I could mail a piece to you for postage and a danish (the pastry, not the citizens).

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    IMHO This is a turning job not an abrasive job. In fact I wouldn't recommend any abrasives touch those soft surfaces, lest they become laps. After taking a look at what your doing, I suggest you make a fixture to hold the head at correct radius and sharp HSS cutter to turn the wear off as necessary.

    If it were me I would make the fixture with small shank that fits in my boring head and has a threaded end to fit in the part with jam nut. That would make it easy to dial radius in. Then chuck the boring head up in the lathe and turn the radii. clamp the next part, rinse repeat. Hope this helps.

    Best Regards,
    Bob

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    QT RJS[ [I suggest you make a fixture to hold the head at correct radius and sharp HSS cutter to turn the wear off as necessary.]

    I agree to Turning the part with it held on center or off center enough to make the desired arc in the correct place. looks like on center would do

    Simple box fixture held in a chuck would seem ok.

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    The head is not from a cassette deck, it's from a reel-to-reel deck.

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    Missed a comma .. capital two Is and a mist, spelit wong "cynindrical"
    No big deal but you can type a message on a word document, correct it, and then paste on the PM site.
    Could mention the intended machine, perhaps a lathe or a mill, and mention the part material.
    You might also mention if a one-up/few-up or a production part,

    Lap and hone are most often finishing operations for surface finish or making a close held/tolerance size.

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    Quote Originally Posted by rjs44032 View Post
    IMHO This is a turning job not an abrasive job. In fact I wouldn't recommend any abrasives touch those soft surfaces, lest they become laps. After taking a look at what your doing, I suggest you make a fixture to hold the head at correct radius and sharp HSS cutter to turn the wear off as necessary.

    If it were me I would make the fixture with small shank that fits in my boring head and has a threaded end to fit in the part with jam nut. That would make it easy to dial radius in. Then chuck the boring head up in the lathe and turn the radii. clamp the next part, rinse repeat. Hope this helps.

    Best Regards,
    Bob

    that was my very first thought on the subject - to spin it into a cutter of some kind - but since the only secure way to mount it is a single M3 screw hole at the bottom I thought it might not be rigid enough and that making a holder and driving it into a spinning (curved) surface might be better. the centrifugal force may well be an issue too ... i wasn't sure if it would damage the fragile coils inside or not. So - with both those issues ... that's why i went in this direction instead.

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    Quote Originally Posted by eKretz View Post
    As long as the geometry isn't important that's a good idea. I'm still not sure if that even matters or not...

    Would be really easy to make a "lapping" cassette tape you could just drop right into the player and fast forward and rewind to do the lapping. Additional bonus, no disassembly of the cassette player to do the work. Might even be able to sell a few of those...
    only has to be within a thou or so of the original ... so in terms of the kind of mission critical specs one sees in the machining world no - not sooo tight ... if it werent' important at all i suppose it could be done by hand but that's not the case

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    Quote Originally Posted by michiganbuck View Post
    Missed a comma .. capital two Is and a mist, spelit wong "cynindrical"
    No big deal but you can type a message on a word document, correct it, and then paste on the PM site.
    Could mention the intended machine, perhaps a lathe or a mill, and mention the part material.
    You might also mention if a one-up/few-up or a production part,

    Lap and hone are most often finishing operations for surface finish or making a close held/tolerance size.
    OOPSY! i made a typo. i don't really capitalize - more for 'philosophical' reasons that aren't really important here.

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    pedant |ˈpednt|
    noun
    a person who is excessively concerned with minor details and rules or with displaying academic learning.



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    well in my view there's lots of room in this world for varying personalities and styles of communication ... it just makes the world a richer place. certainly that exists whether you try to enforce it or not. there are even people for whom english is NOT their first language, believe it or not! you should see some of the utterances people like that throw out from time to time ... but we get by don't we?


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