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Thread: Sandpaper and how long to use it.

  1. #1
    Join Date
    Jun 2008
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    Sandpaper and how long to use it.

    I read Toni's post on sandpaper belts and did not want to hijack the subject but Tim mentioned how long he used belts till they were smooth.

    This has prompted me to ask a question here that has bugged me ever since i got my hand on a piece of sandpaper errr well not quiet but almost.

    We learn at some point about going through the grits sizes when preparing an item for finshing.

    So how does one decide on when the paper is done.

    This subject has come up for me with the sharpening method using sandpaper.

    I find especially the water paper seems to propagate through the grit sizes on its own. So say you start with a piece that is 220, i find as it wears it changes to higher order grits, so much so that when taking the next leap up its almost like you start again.

    So what to do next time discard the piece cause it aint 220 anymore.

    Alternative is you sanding a wooden item and you have you various grits, when do you stop and move on and then do you keep the previous piece and assume its good for the same purpose next time round.

    I find i am either one extreme or the next. Either i dont give up on one piece till i have finished off the grit on it or i waste sandpaper cause i am too afraid to wreck the next item i finish by using old paper that i dont know where i am with.

    What it boils down to is i dont have a clue about how to use sandpaper properly such that i reach a happy medium.

    Any help out there for some practical remedy.
    cheers

  2. #2
    Join Date
    Oct 2006
    Location
    ozarks
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    4,993
    i find it`s kinda by feel rob

    for my r/o sanders i order cloth-backed PSA discs designed for metal removal 36-80 grit, then for the higher grits i use a good quality paper backed disc.

    the only way i can tell if they`re dull is by feel......how long a disc takes to remove "x" amount of a given species of wood.

    not much help eh?
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  3. #3
    Join Date
    Oct 2009
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    Bradford, Vermont
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    425
    Quote Originally Posted by Rob Keeble View Post
    I read Toni's post on sandpaper belts and did not want to hijack the subject but Tim mentioned how long he used belts till they were smooth.

    This has prompted me to ask a question here that has bugged me ever since i got my hand on a piece of sandpaper errr well not quiet but almost.

    We learn at some point about going through the grits sizes when preparing an item for finshing.

    So how does one decide on when the paper is done.

    This subject has come up for me with the sharpening method using sandpaper.

    I find especially the water paper seems to propagate through the grit sizes on its own. So say you start with a piece that is 220, i find as it wears it changes to higher order grits, so much so that when taking the next leap up its almost like you start again.

    So what to do next time discard the piece cause it aint 220 anymore.

    Alternative is you sanding a wooden item and you have you various grits, when do you stop and move on and then do you keep the previous piece and assume its good for the same purpose next time round.

    I find i am either one extreme or the next. Either i dont give up on one piece till i have finished off the grit on it or i waste sandpaper cause i am too afraid to wreck the next item i finish by using old paper that i dont know where i am with.

    What it boils down to is i dont have a clue about how to use sandpaper properly such that i reach a happy medium.

    Any help out there for some practical remedy.
    Technically... sandpaper doesn't change grits, although it seems like it does. What happens is the individual grains break off, leaving a flatter grain surface that apparently gives you a smoother finish. 220 will always be 220, but as it wears (the crystals shear off) it becomes DULL 220.

    Unless you're a pennysquasher like me, the PRACTICAL point at which sandpaper SHOULD be considered "worn out" is when you wipe it across a surface with very light finger pressure and it doesn't generate much dust any more - when there's a distinct difference between fresh (sharp) paper and the paper you're using.

    Now... when to change grits, stepping up. You'll be starting with a relatively coarse sandpaper. With it, you'll do all the basic "erasing" work, taking out tool marks & surface imperfections. Stop with that grit when they're gone, or when they're JUST BARELY less than gone. At that point you make your first step up - I like to step up by about 150%, so 80-grit steps to 120, and 220 steps to 320.

    Now with this next grit, your job is to erase all the scratch marks left behind by the coarse paper and replace them with finer scratch marks. So... sand with this grit until you can't see any remainder of those first coarse scratch marks any more - it helps if you sand in a different direction so the scratch marks remain distinct until they're gone. Now step up again.

    Keep repeating the process with progressively higher grits until the scratch marks you've just left aren't visible among the wood grains any more. With very coarse-grained woods like ash & oak, that may be around 220-grit. With very fine-grained woods like kingwood and pink ivory, you may need to go all the way up to 2000-grit (I do).

    When to discard paper? That's pretty personal... for high production, it's best to discard it when it becomes dull enough to slow down the sanding process - that's maybe 15 minutes of use. For low production on a budget (or just for tightwads), some folks choose not to discard it until it simply cannot do its job (of erasing lower-grit scratches) any more... or when it becomes clogged or ripped or contaminated (as with metal, which will mark up the wood).

    I might point out that garnet paper, which is the cheapest stuff you can buy, cuts VERY FAST because the garnet crystals are VERY SHARP, but wears out quickly. It's an excellent choice for sanding materials that may clog paper (cherry, for example, which is pretty bad about clogging the paper with resins). Aluminum oxide paper isn't as sharp, and the "dull point" isn't as distinct, but the more-rounded crystals are a lot tougher & last a lot longer. Silicon carbide papers will cut nearly anything - including glass and tungsten-carbide tool tips - but aren't as tough as aluminum oxide. Someday diamond will get so cheap they'll make abrasive papers with it...
    -- Tim --

  4. #4
    Join Date
    Jun 2008
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    Thanks Todd and Tim. I never thought about the type of crystals on the paper before. I have stayed away from Garnets because growing up its all my dad had in the shop and i got to see how quickly it wore out. It was pretty obvious at least to me when the paper became blank pretty quickly but i suspect on reflection that also had something to do with how old the stuff was.

    I have tended to use the 3X aluminum oxide variety and now you mention it you get to feel its sorta smoothness of grit even when new. I think thats a little of what puzzled me too. Once you use it a little it all sorta begins to feel the same.

    I also never though to try and sand in a different direction. That was always like painting across the grain taboo as far as i was concerned cause it introduced more scratches but if one gets to understand what you are trying to achieve well then its not a problem I guess.

    I have inflicted my scratches of my own (my bad) in the past by starting at too low a grit for the existing scratches.

    I appreciate the practical advice guys.
    cheers

  5. #5
    Join Date
    Dec 2006
    Location
    Central Illinois
    Posts
    936
    I was once told to "Use it like someone else bought it!"

    It is costlier, but like sharp tools, it makes the job get done faster.

    Bruce
    Bruce Shiverdecker - Retired Starving Artist ( No longer a Part timer at Woodcraft, Peoria, Il.)

    "The great thing about turning is that all you have to do is remove what's not needed and you have something beautiful. Nature does the hard part!"

  6. #6
    "Use it like someone else bought it"
    Is a good practice if you want effort free sanding. But for the rest of us who have to buy our own... Use it till it appears to be more work than progress. I was in my friend's business and watched several of the employees using sanders, It was surprising how differently they changed papers. I saw some who spent as much time changing as they spent actually sanding whilst others would use the same disc 3-4 times longer than the quick change artist. The quick change guy was often done far quicker than the grind it smooth guys. so which was a better job and more effecient? The fellow who took less time but spent a lot on discs, or the fellows who saved on discs but took longer to complete the task.

    With me personally... I usually loose the paper before it is worn out, either the DC sucks it up or it falls on the floor and under a bench, but when I clean up my shop I put paper pieces in a box for the next project, when it makes its way to the trash can, it is pretty much spent.

    In the school shops we had students to get new if they needed it (had to ask personally) but to use out of the recycle box as much as they needed. Each year or season we would empty the recycle box and start new, some were good new sheets and some were wadded up pieces of grit-less paper.

    My opinion, if you feel it needs changing, then do it.

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