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  1. #41
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    For the benefit of my education and those who land here in the future, heres a mesh to microns conversion chart.

    mesh-microns.jpg

    So far ive only found one place in the UK who supplies diamond abrasive powder Diamond Abrasive Products by Lapmaster International . Does anyone have any other contacts? (cheaper the better)

    Mark Rand
    I've got 50 carats each of 5-7micron and 1-2 micron diamond powder;
    According to bebop the guys are using 300 - 400 mesh, thats some 40 odd microns. Any particular reason you went for the finer stuff?

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    Looks like you trick yourself!

    ww.jpg
    This is a calibration/verification of a level with a nominal resolution of 0.01 mm/m
    Horizontal scale is in divisions of the level, vertical scale in arcseconds. The level was measured on two different dividing heads. That alone shows, in what reagions you are trying to work.

    The accuracy of a level is not God-given!

    If you buy a straight edge (what you call a SE is a camelback), you can calibrate it on your surface plate. You need gage blocks, a micrometer and a depth micrometer.
    Put the SE onto the surface plate, both ends sitting on known gage blocks. Calibrate your depth micrometer at one end of the SE. Move to some point (say the middle) of the SE and measure height difference. Flip the SE over, so the previous measuring face that was up is now facing the surface plate. Measure the gap between SE and surface plate with a gage block (height indicator would work too). Repeat for the other face. Now if you measure the height of the SE at that place, you know how much that surface is bowed.
    Repeat every mm.

    With this method, it doesn't matter how much off the surface plate or the SE is.


    Nick

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    If you want diamond, buy it on ebay from the india direction, the savings are huge and it works just fine for stuff like this. other option is to look at the diamond impregnated plastic velcro backed pads stone - concrete polishes use. There avalible from 3000 grit polish, to 50 grit take the corners of the bolder range. They work ace on concrete brick paviours (to be a kitchen work top). Equally well on some old granite tiles i tried them on. Gotta be used wet though!

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    Quote Originally Posted by Demon73 View Post
    Interesting. These guys use a guide coat to show the progress. Reminds me of my car bodywork days!
    calibration and resurfacing service of granite surface plates - Cleveland Ohio, Chicago Illinois Optiaml Calibration

    Edit:
    Actually. Taking another look at the pics. It looks as though they rub the plates dry, without water. The light parts are the places that are high!


    I wonder what caused that ring in the corner?

    Attachment 77984 Attachment 77985 Attachment 77986
    Yes lapping is done dry. That corner is something that I have seen on almost every surface plate Ive lapped ... its caused but people putting a piece abrasive paper on the corner of the plate then scrubbing there part back and forth and waring a hole in the plate. The problem with using sand paper on a surface plat is compounded by not cleaning the louse particles of abrasive from the back of the sandpaper before placing it on the surface plate. In effect your lapping the plate as you sand your part. The 300-400 mesh diamond compound cuts fast enough ... with out cutting to fast ;-)
    Cheers Don
    Last edited by bebop; 06-02-2013 at 09:54 AM. Reason: added verbage

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    I got my diamond grit from a chap in the Ukraine. EBay item number 321122204486 is the only size he's got on offer at the moment.

    The reason I have gone for the 1-2 and 5-7 micron diamond powder is than I'm interested in correcting a plate that's off be 1-2 thou. The 5-7 powder on a cast iron lap will remove a thou in about 3 minutes work on a smaller area. That's pretty bloody fast to my mind! Don't forget, 6 micron powder will make a 0.1 thou scratch if embedded 50% in the lap.

  7. #46
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    Quote Originally Posted by Nick Mueller View Post
    Looks like you trick yourself!

    ww.jpg
    This is a calibration/verification of a level with a nominal resolution of 0.01 mm/m
    Horizontal scale is in divisions of the level, vertical scale in arcseconds. The level was measured on two different dividing heads. That alone shows, in what reagions you are trying to work.

    The accuracy of a level is not God-given!

    If you buy a straight edge (what you call a SE is a camelback), you can calibrate it on your surface plate. You need gage blocks, a micrometer and a depth micrometer.
    Put the SE onto the surface plate, both ends sitting on known gage blocks. Calibrate your depth micrometer at one end of the SE. Move to some point (say the middle) of the SE and measure height difference. Flip the SE over, so the previous measuring face that was up is now facing the surface plate. Measure the gap between SE and surface plate with a gage block (height indicator would work too). Repeat for the other face. Now if you measure the height of the SE at that place, you know how much that surface is bowed.
    Repeat every mm.

    With this method, it doesn't matter how much off the surface plate or the SE is.


    Nick
    Thats a very interesting chart Nick, thanks. I can understand that the level wont be calibrated in absolute terms (although its not really something ive considered tbh),and any number using it as ive done would have to taken with a giant pinch of salt. The only counter ive got is that im not really interested in the actual number as so much as the repeatability of the level (which im happy with). Also im working in the same area of the vial, aiming to see a hairs width of daylight between the end of the bubble and the graduation line. If its not ill rub it till is. Im aiming at being as consistent and accurate as i can with what i have.

    Re your SE method. I dont fully understand it yet tbh, although i think ive come across a similar method here. http://www.practicalmachinist.com/vb...44/index2.html
    The general idea is that the errors cancel themselves so to say, a low wil turn too an equal and opposite high when the SE is turned through 180 degrees. 'flat' = error / 2. I think, kinda, sorta.

    Hope the cats well, feel like i almost know him after watching your scraping videos so many times.
    Cheers D

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    Quote Originally Posted by adama View Post
    If you want diamond, buy it on ebay from the india direction, the savings are huge and it works just fine for stuff like this. other option is to look at the diamond impregnated plastic velcro backed pads stone - concrete polishes use. There avalible from 3000 grit polish, to 50 grit take the corners of the bolder range. They work ace on concrete brick paviours (to be a kitchen work top). Equally well on some old granite tiles i tried them on. Gotta be used wet though!
    Cheers for the tips. I just searched ebay to find a guy in California! Diamond Powder Polishing,Lapidary. Seems cheap enough so i got 500 , 1000 (in case the 500 freaks me out!) and 5000. I think that should cover it.

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    The general idea is that the errors cancel themselves so to say,
    Right.

    To the vial:
    The problem is, that the reading isn't linear. It only works if you have exactly the same reading at every spot*). And you are already stressing your metrology quite a lot with the 0.05 mm/m resolution.

    *) OK, that is your aim.

    Cat is, well, sleeping all day. He'll have his 16th birthday this year.

    Nick

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    Quote Originally Posted by bebop View Post
    Yes lapping is done dry. That corner is something that I have seen on almost every surface plate Ive lapped ... its caused but people putting a piece abrasive paper on the corner of the plate then scrubbing there part back and forth and waring a hole in the plate. The problem with using sand paper on a surface plat is compounded by not cleaning the louse particles of abrasive from the back of the sandpaper before placing it on the surface plate. In effect your lapping the plate as you sand your part. The 300-400 mesh diamond compound cuts fast enough ... with out cutting to fast ;-)
    Cheers Don
    That makes sense, ive noticed abrasive on the paper side as you pull a sheet out the pack.

    Re the diamonds. I cant resist, i have to try it. I really like the idea of seeing where your cutting. You dont get that when doing it wet. Plus the wet and dry, at first it cuts, then it sorta cuts, then it sorta just polishes! Or at least it seems that way . I tried a small cheapy diamond lap on a vertical section round the back where it doesnt show. It certainly did CUT!

    Mark Rand
    The reason I have gone for the 1-2 and 5-7 micron diamond powder is than I'm interested in correcting a plate that's off be 1-2 thou. The 5-7 powder on a cast iron lap will remove a thou in about 3 minutes work on a smaller area. That's pretty bloody fast to my mind! Don't forget, 6 micron powder will make a 0.1 thou scratch if embedded 50% in the lap.
    Got you. Well you can see how i get on i guess. If i start turning my 4" plate into a 3" plate then you know youre right!

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    I wonder if one can bake bread with granite flour...

    Sounds like you've got a good selection on the way.

    Pity diamond isn't the same price when you buy it in one lump. The Mrs wasn't all that impressed when I showed her the 80 Carat self-assembly diamond kit I'd bought her.

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    Quote Originally Posted by Nick Mueller View Post
    Cat is, well, sleeping all day. He'll have his 16th birthday this year.
    About the same age as mine. Still remember him jumping over my shoulder and under the pedals as drove him home!! Time flys!

    Mark Rand
    I wonder if one can bake bread with granite flour...
    Ill send you some!..Let me know!!

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    Quote Originally Posted by Demon73 View Post
    Cheers for the tips. I just searched ebay to find a guy in California! Diamond Powder Polishing,Lapidary. Seems cheap enough so i got 500 , 1000 (in case the 500 freaks me out!) and 5000. I think that should cover it.
    IMHO the 500 grit will remove granite fairly quick at the dimensions your chaseing, jumping to 1000 is a fair leap too. 5000 is probably border line to fine for anything but optical finishing and i would rate it as a massive leap from 1000 grit finish.

    Am surprised about doing it dry though. Wet to flush away the waste makes a massive difference when diamond polishing to a finish. Just makes any dust so easy to clear - wipe up using the finer grits.

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    Quote Originally Posted by adama View Post
    IMHO the 500 grit will remove granite fairly quick at the dimensions your chaseing, jumping to 1000 is a fair leap too. 5000 is probably border line to fine for anything but optical finishing and i would rate it as a massive leap from 1000 grit finish.

    Am surprised about doing it dry though. Wet to flush away the waste makes a massive difference when diamond polishing to a finish. Just makes any dust so easy to clear - wipe up using the finer grits.
    The way i see it is according to bebop, 300-400 is what the guys who are doing this for a living are using, so it seems like a logical place to start. Tbh, i got the 5000 with honing scraper blades in mind.

    I know what you mean about the dry vs wet, i was surprised as you.However. In my past experience in car bodywork (some 15 years +), rubbing dry seems to almost half the scratch depth. Ie 400 dry kinda works out about the same as 800 wet. Also, you can clearly see where you are rubbing and how the cut is going rubbing dry. When rubbing wet you really need a guide coat (thin film of colour over the primer) to see your progress (the colour being left in the low areas until you sand deep enough to remove it). I dont know how much of this will translate to rubbing granite, but theres only only one way to find out.

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    How do you switch to the finer grit when the coarser grit is already impregnated into the cast surface plate?

    I have two cast iron lapping plates for general lapping use. Each for a specific grit compound, and the two never mix.

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    Ive several small cast plates. id keep them seperate too. Can i ask what kind of diamonds you use btw? Natural or synthetic?

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    Or if theres any diamond experts out there which one of these would be most suitable for the task? Everyone ive spoken too this am thinks rolling diamonds into a cast plate is nuts lol!
    INDUSTRIAL DIAMONDS | INVEDIA | LONDON

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    Look at a site called woodcentral.com . It is a woodworking site with a subforum called handtools. A gent named Bill Tindalll has done numerous posts on loose diamond honing to sharpen various cutters. He has done a lot of experimentation on creating charged diamond laps using cast iron as well as other substrates.
    Get to the hand tool forum and enter loose diamond sharpening in the search box.
    Should help figure how to best use the loose diamond paste.
    Joe

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    Look here, Diamond abrasive is not that expensive and a little goes a long way. Stone or cast is to diamond are like bar soap is to beack sand.

    micron diamond powder | eBay

    Figure 5 karats per gram and a little over 27 grams to the oz.

    Diamond is hard stuff and expensive per unit of weight. Clean up the lapping swarf with a brush and pan. Save the dust and segregate the diamond from the swarf by panning or some other means of differentiating.

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    Quote Originally Posted by Joe Rogers View Post
    Look at a site called woodcentral.com
    Thanks Joe. Some very interesting reading over there! Sounds silly now but i never thought of using the the paste to 'embed' diamonds!

    Forrest Addy
    Look here, Diamond abrasive is not that expensive and a little goes a long way. Stone or cast is to diamond are like bar soap is to beack sand.

    micron diamond powder | eBay

    Figure 5 karats per gram and a little over 27 grams to the oz.

    Diamond is hard stuff and expensive per unit of weight. Clean up the lapping swarf with a brush and pan. Save the dust and segregate the diamond from the swarf by panning or some other means of differentiating.
    Cheers Forrest. I have actually got some dry powder on order from the states atm, theres none on ebay UK. They do have the pastes though which i also ordered here diamond paste selection , dirt cheap, just to try. Paul at Invedia is very kindly sending me 10cts of natural 325 - 400 mesh dry, very helpful guy! So its all on its way.

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    Don't have much advice for flats, but a dead easy way of making a cylindrical diamond hone of any radius you wish is just turn that diameter to a fine finish in a bit of bar, i have used everything from copper to mild steel, then simply roll your chosen grit of diamond paste into it and hone away (do cover the lathe ways though! Because trust me, tool post grinders can't even hack diamond grit!) There's no real need for lose grit and you need about a small lentils worth of paste for a lap say 5/8" diameter and 2" long. A little goes a long long way! Being in a paste just makes it easy to apply. Its a great way of putting lovely radiuses in form tooling. I find about 10 micron about right, using wd40 as a lapping oil to wash the swarft away.

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