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    Default Vector / vehicle for aluminum oxide abrasives for lapping machine - DIY ...

    Hi All,

    I have a hopefully "simple" question that I hope one of you may be able to help with ... (BTW I also hope this is the right sub-forum to post in).

    As it is I have recently built a lapping machine and now am looking for a suitable "abrasive media" - preferably "DIY" and environmentally friendly.

    To this end I have bought some ~400 grit aluminum oxide powder and have learned that I should dissolve this powder in water together with a suitable amount of a "vector / vehicle". I have also heard that some use WD-40 as this vector/vehicle but if possible I would prefer using e.g. a vegetable oil (or e.g. a bicycle oil like Pedro's Chainj, if appropriate) instead. Also, since I will be using the lapping machine in my utility room it is much preferred if the vector/vehicle is odorless ...

    The lapping machine includes an "abrasive media" container with stirrer so the abrasives will be continuously mixed.

    I will mainly be lapping copper, aluminum and plastic plates (Polyurethane modeling boards).

    Might one of you have experience with this - and some suggestions?

    Cheers and thanks for any insights

    Jesper M

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    The abrasive does not "dissolve". It is suspended in the vehicle, usually oil. I'm afraid that you have the wrong abrasive for your purpose. Aluminum oxide is quite hard and will embed in the soft metals you want to lap, turning your work pieces into laps. There are others here more experienced than me but I'd guess that you want a softer, more frangible abrasive like feldspar and probably a finer grit.

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    Hi tdmidget - & thanks for your feedback ...

    The abrasive does not "dissolve". It is suspended in the vehicle, usually oil.
    Well, not being a native English speaker sometimes the words may not be correct particularly in new subject areas where I am not familiar with the terminology. So thanks for clarifying - I will use "suspended" onwards ...

    What I am looking for is a suggestion for which "oil" (mixture) to use, preferably environmentally friendly and without odors as I will be using it inside my house.

    Aluminum oxide is quite hard and will embed in the soft metals you want to lap, turning your work pieces into laps. There are others here more experienced than me but I'd guess that you want a softer, more frangible abrasive like feldspar and probably a finer grit.
    Hmmm ... I actually chose the aluminum oxide because due to lapmaster-wolters' webpages it should be one of the less hard abrasives. However, I obviously don't want to turn my work pieces into laps - so might someone else have experience with this?

    Regarding availability of feldspar powder (preferably within the EU) I did a quick search on Google and it doesn't seem to be that easily found. Any chance you can suggest a vendor of such powder?

    Cheers & thanks again,

    Jesper

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    When lapping soft materials it is worth trying to charge (embed the grains into) the lapping plate with abrasive rather than trying to use use loose particles. This way the grains are anchored into the lap, and (when done properly) do not transfer over to the workpiece.

    It's a somewhat more laborious process, and takes some trial and error to get right, but it might work better for your needs.

    To learn more, search for terms like "charging a lapping plate".

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    If you are making your own slurry and thinking of mixing it with water you will need a suspending agent to stop the abrasive settling into a solid lump when the machine is not in use. If you mix oil with water you will be trying to make an emulsion which is not recommended.

    Either just mix the abrasive with water, and live with the settling, or we use a pre-mixed lapping media called Kemox that has suspending agents as part of the formulation. If you’re lapping copper and other soft materials I would use an 800 grit rather than 400 to get a better finish, we use a product called Kemox O-800S for this application.

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    @Milland & j_landers ... thanks you also for your feedbacks - very helpful

    search for terms like "charging a lapping plate".
    I did a google search for these words and found e.g. this youtube video: YouTube

    I suppose this is what you mean with charging the lapping plate, right? Lard oil or something similar should be accessible - could be a way of doing it - I will just consider ...

    Either just mix the abrasive with water, and live with the settling, or we use a pre-mixed lapping media called Kemox
    Hmmm ... just using water would indeed be a simple way to do it But it would also be preferred to not have to loosen the abrasive every time I need to use the machine ... I did a search on the Kemox products and if I am not mistaken the O-800S is kerosene based ...? This is not really feasible in my context since I will be using the machine in-house. I did notice though that Kemet also has some water based solutions e.g. the W-950. I reckon this could be an option as - according to the product sheet - it also gives a fine surface finish on softer materials.

    Makes me think - would there be a simple suspending agent that I can use together with water so as to eliminate the solid abrasive formation while not using the machine?

    BTW I just checked the aluminum oxide powder I have bought and comparing its "grittiness" with some sandpaper of a supposedly similar grit value I'd say that this powder is more like ~1000 grit (the seller didn't specify the actual grit value). At least it's quite different from - and finer - than the surface of a 400 grit sandpaper.

    Thanks again both of you,

    Jesper

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    Quote Originally Posted by j_landers View Post
    If you are making your own slurry and thinking of mixing it with water you will need a suspending agent to stop the abrasive settling into a solid lump when the machine is not in use. If you mix oil with water you will be trying to make an emulsion which is not recommended.

    Either just mix the abrasive with water, and live with the settling, or we use a pre-mixed lapping media called Kemox that has suspending agents as part of the formulation. If you’re lapping copper and other soft materials I would use an 800 grit rather than 400 to get a better finish, we use a product called Kemox O-800S for this application.
    A lap has to be softer than the part being lapped. Otherwise the part being lapped will become charged with the lapping compound and become the lap. This does not do anything for the practice of lapping an aluminum or copper part. This in my mind is not a proper practice.

    Roger

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    Loose abrasives on soft material will be a disaster. That said, I've used RV antifreeze as an additive and it works better than nothing. It's propylene glycol so it's pretty safe stuff. It does not work as well as the commercial water based products, but some of those (expensive) ones smell pretty strong. I can't use them at work because everybody complains.

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    Hi Roger & Conrad ... Thank you also for replying and suggesting

    @Roger: I get the first part of your post but this I don't really understand - can I ask you to clarify what you mean ... :

    This does not do anything for the practice of lapping an aluminum or copper part. This in my mind is not a proper practice.
    .. Should one not lap a copper or aluminum part or ... ? As it is I need to achieve a very flat surface (<10 um) on some relatively small copper frames (roughly circular 90 mm copper plates with a Ø68 mm hole in them) and similarly for polyurethane modeling boards. Would you suggest something else than lapping for this?

    @Conrad:

    Loose abrasives on soft material will be a disaster.
    Hmmm ... always surprises it seems ... However, as it is I have made the top rotating plate of the lapping machine replaceable so I could make an additional top plate with a fixed abrasive. Here there's some enthusiasm about fixed diamond abrasives (I realise they are not softer than copper/plastics):

    How To Page

    but maybe it will work if attached to the lapping surface and a fine grit? I have been thinking about this, yet - assuming it may be a solution - need to find a way to adhere the diamond powder to the lapping surface (an epoxy, or?) ...

    I would appreciate your suggestions as I am quite new to this ...

    And then a probably quite simple question: What does RV in RV antifreeze mean (an acronym for)? It would help if I am to find something like this here in Denmark - and a google search doesn't give an explanation for "RV" ...

    Have a good day

    Jesper

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    Quote Originally Posted by Jesper M View Post
    @Milland & j_landers ... thanks you also for your feedbacks - very helpful



    I did a google search for these words and found e.g. this youtube video: YouTube

    I suppose this is what you mean with charging the lapping plate, right? Lard oil or something similar should be accessible - could be a way of doing it - I will just consider ...

    Jesper
    That's sort of what I was talking about, but sometimes a hard steel roller (like a brayer but made to impress materials) is used to force the abrasive grains into a soft lapping plate, turning the plate into an abrasive disc. The video show an adhesive attachment (using the lard), which might work in your case - you could test for functionality.

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    Perhaps, a different solution could be using lapidary disks, with electroplated diamond or other abrasive of a specific grit. The challenge would be to find a "solvent" that carries away the soft particles. Otherwise the disks would gum-up in no time.

    Paolo

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    Quote Originally Posted by Jesper M View Post
    Hi Roger & Conrad ... Thank you also for replying and suggesting

    @Roger: I get the first part of your post but this I don't really understand - can I ask you to clarify what you mean ... :



    .. Should one not lap a copper or aluminum part or ... ? As it is I need to achieve a very flat surface (<10 um) on some relatively small copper frames (roughly circular 90 mm copper plates with a Ø68 mm hole in them) and similarly for polyurethane modeling boards. Would you suggest something else than lapping for this?

    @Conrad:



    Hmmm ... always surprises it seems ... However, as it is I have made the top rotating plate of the lapping machine replaceable so I could make an additional top plate with a fixed abrasive. Here there's some enthusiasm about fixed diamond abrasives (I realise they are not softer than copper/plastics):

    How To Page

    but maybe it will work if attached to the lapping surface and a fine grit? I have been thinking about this, yet - assuming it may be a solution - need to find a way to adhere the diamond powder to the lapping surface (an epoxy, or?) ...

    I would appreciate your suggestions as I am quite new to this ...

    And then a probably quite simple question: What does RV in RV antifreeze mean (an acronym for)? It would help if I am to find something like this here in Denmark - and a google search doesn't give an explanation for "RV" ...

    Have a good day

    Jesper
    To clarify my post: Lapping copper or aluminum work piece is not a good idea. I make laps out of brass. "The work piece has to be harder than the lap". Find another way. Making a lap or grinding using diamond. Press or hammer the diamond grit into the surface of the blank.
    Do not grind aluminum, the wheel will become loaded with aluminum. It can be sanded. RV antifreeze. RV is "Recreational Vehicle".

    Roger

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    @Milland, Paolo & Roger: Thanks again for your feedbacks and suggestions.

    I think one challenge in relation to this machine is that I prefer to make things "future-proof" (as well as I may, of course) - cost & environmental considerations - and therefore this lapping machine's lapping plate is 43 cm in diameter. This also means that it may lap quite big work pieces - but finding lapidary discs of this size I reckon is not that simple (and likely also not exactly cheap?).

    And then an idea: Given that the lap should be softer than the material lapped would it then make sense to e.g. use an acrylic or polypropylene lapping plate where the abrasives are either pressed into the acrylic/polypropylene or floated on top? And also - with this in mind - would it be feasible to use e.g. feldspar powder as suggested by tdmidget earlier on in the thread?

    I'm just trying to get a grip of how much softer the lapping plate ideally should be ...

    Cheers from Denmark,

    Jesper

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    A P.S.: Came to think of - would it likely work to press the abrasives into e.g. an epoxy (or maybe even a hydraulic wood glue) just as the curing process is about to end? That is the glue is still slightly flexible here - yet the abrasives will not be pressed so deep into the glue that it will "disappear" ... Anyone have experience with this?

    Cheers,

    Jesper

    ... well, I can see that the previous post - coming before this one - is yet to be moderated. So the sequence is a bit off ... but, well, so it is ...

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    It is common practice within industry to lap aluminium and copper using conventional abrasives like aluminium oxide and silicon carbide on cast iron lapping plates.

    These are non-impregnating abrasives that remove material by plucking out rather than cutting. In fact aluminium oxide slurries are used to remove diamond particles from resin based composite lapping plates because of the way they remove material without impregnating themselves. They will remove material from both the lapping plate and the components, but clearly they will remove material from the softer metal parts faster than they will remove material from the cast iron lapping plate.

    You should use a cast iron hand lap plate and an aluminium oxide based slurry for this application. If you’re making your own, you can buy suspending agents, but these will cost more than simple buying a pre-mixed slurry.

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    Hi j_landers ... thanks for your feedback - this is also what I've heard regarding the aluminum oxide & cast iron. So I think I will just consider the feedbacks you and others have given here and then decide how to progress ...

    Cheers,

    Jesper


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