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Thread: Sanding turnings to "exact" size.

  1. #1
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    Sanding turnings to "exact" size.

    I use the Vega duplicator and templates to get my instrument pegs to around one (1) mm over the final size. Then I sand from 80-320 grit to remove any cutter marks. I have a hard time controlling the diameter as wood is removed as I go through the grits. I am very experienced at doing one thing at the lathe, i.e. using the duplicator to make pegs. I am a very inexperienced wood turner.

    For example: My Bb clarinet pegs are 47 mm at the base. They often end up at 45.5 to 46 mm even if I set the template for 48.5 to 49 mm. There is plenty of wiggle room on these instrument stands. But when musicians order a double stand I want the pegs to look identical. Woodwind players, especially high double reed players use precision tools to make their reeds. They will spot variances of 1-2 mm. So do I!

    An ideas would be greatly appreciated.

    Thanks,
    Gordon
    Ask a woodworker to "make your bed" and he/she makes a bed.

  2. #2
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    Due to the nature of wood I find it difficult (or impossible) to sand to precision sizes. I have zero experience with a duplicator but can usually get the size I want by using calipers with a sharp parting tool to cut grooves a little large then finish cut with a skew where appropriate. After that, a good negative rake scraper can make incredibly smooth surfaces in good wood without the variability problems of sand paper. I've made pegs and replacement parts for spinning wheels with this method. Some of my smaller NRS for small things, straight and tapered:

    NRS_small_thompson.jpg

    However, I've had fairly good results with sandpaper glued to a flat board, usually plywood.

    sanding_blocks.jpg

    I make various sizes of these, small to get into tight places when necessary. I last used them to smooth a rolling pin but I didn't measure to 1/2 millimeter dimensions.

    Also, I've made a few wooden things that needed to be precise using my metal lathe or milling machine. With good wood (hard, fine-grained, like african blackwood, dogwood, hard maple, lignium vitae,
    mopani, etc) the results can be good. Use dry wood, of course.

    JKJ

    Quote Originally Posted by Gordon Stump View Post
    I use the Vega duplicator and templates to get my instrument pegs to around one (1) mm over the final size. Then I sand from 80-320 grit to remove any cutter marks. I have a hard time controlling the diameter as wood is removed as I go through the grits. I am very experienced at doing one thing at the lathe, i.e. using the duplicator to make pegs. I am a very inexperienced wood turner.

    For example: My Bb clarinet pegs are 47 mm at the base. They often end up at 45.5 to 46 mm even if I set the template for 48.5 to 49 mm. There is plenty of wiggle room on these instrument stands. But when musicians order a double stand I want the pegs to look identical. Woodwind players, especially high double reed players use precision tools to make their reeds. They will spot variances of 1-2 mm. So do I!

    An ideas would be greatly appreciated.

    Thanks,
    Gordon

  3. #3
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    Thanks John. I figured this was not so easy. My machinist friends tell me working with wood is harder than working with metal. I think what they mean is getting precise measurements on a material that changes size every day is damn near impossible. Press fit, friction fit is measured in thousands. I think that is 10,000th of an inch. Here in the Detroit area my neighbors make robots, million dollar testing machines and tooling for automotive parts. But if they want a stock on a $5000 shotgun cut for a recoil reducer they come to my shop!!!

    Cheers,

    Gordon
    Ask a woodworker to "make your bed" and he/she makes a bed.

  4. #4
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    is it necessary to start with 80? that sounds pretty coarse fro something thats been turned town.
    Last edited by Stan Calow; 10-15-2021 at 9:22 PM.
    Hobbyist

  5. #5
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    Let me just say that I have only done a little turning over the years. But many years ago I was turning some parts for Christmas presents that needed to be reasonably identical and accurately sized.

    I made a sanding fixture that worked pretty well. I'm sure I didn't invent it but not sure where I saw it. The fixture resembled one end of an open end wrench made out of wood, except it was wider than a wrench, close to 2 inches but it can be whatever is needed. The two "flats" of the wrench were also angled ever so slightly so they were closer at the back of the "wrench". The opening was sized so at the back it was exactly the desired final diameter of the turning. One leg of the "wrench" was partially lined with adhesive sandpaper. The sandpaper stopped a little more than 1 radius from the back of the "wrench". In use, the open part of the wrench is pressed against the spinning turning, riding on the leg with no sandpaper. The sandpaper will remove stock until the diameter gets small enough to slip by the sandpaper. At that point the wrench slips down all the way.

    I recall it took a little practice, but after a short while I was turning out pretty consistent parts.
    --Certainty is the refuge of a small mind--

  6. #6
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    Good idea. I tried starting with 100 and it was better. Maybe 120 will work once I get my new carbide cutter from Packard Woodworks.

    Thanks Stan
    Ask a woodworker to "make your bed" and he/she makes a bed.

  7. #7
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    That is ingenious. My pegs are tapered so that might not work. But the idea of sizing to a final size with a sandpaper jig has got me thinking. And that can be a dangerous thing!

    Thanks Paul.
    Ask a woodworker to "make your bed" and he/she makes a bed.

  8. #8
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    Would it be possible to replace the cutter in your duplicator with a negative rake scraper after you rough out with the normal cutter? That might get you closer to the final size without sanding with the courser grits.

  9. #9
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    Quote Originally Posted by Paul Williams View Post
    Would it be possible to replace the cutter in your duplicator with a negative rake scraper after you rough out with the normal cutter? That might get you closer to the final size without sanding with the courser grits.
    I think something along those lines is possible. I would do all of the same template oversize and change to a custom made scraper to the finish size. Thanks
    Ask a woodworker to "make your bed" and he/she makes a bed.

  10. #10
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    If you sand, your pieces will probably not end up round because of the differences in the grain. A skew is your friend for precise sizing. Use a go/no-go gauge (an open end wrench works well) to show a burnish mark on a slight taper on the last 1/8" or so of the piece, then turn the diameter down so that the burnish mark only just disappears and the piece is uniform in diameter. You can size tenons to a couple thousandths of an inch that way, and much higher accuracy is possible than with a metal lathe and scraping tool. On a nice turning wood like maple no (or very minimal, 400 grit) sanding should be required.

    Same principle applies to things other than tenons, use a parting tool to create key diameters every inch or more, depending on the size of the piece, just slightly bigger than the desired diameter, such that when you connect the flats and just turn away the tool mark you will end up at the right diameter. Sizing to a mm is quite easy this way, with care higher accuracy is possible. Having some obvious "features" like beads or V-groves along the length of the piece that the eye will use to align things helps.

    Also remember that what is important is that pieces look identical, not that they be identical. Suspending a model immediately above your work piece so you can easily see both at once makes it easy to make one look like the other, whether or not it really is. The farther apart they are the better this works-- old hand turned bedposts or table lege will have major elements always at the same distances along the piece, but diameters are all over the place when you measure, nevertheless they look the same. (Also old work is almost never round, having been turned from green or air dried wood. We have an 1800's bed where the 100 mm posts are out of round by a good 5-6 mm; you'd never notice it without measuring.)

    Sandpaper is your enemy when it comes to accuracy. Getting a finished surface off the skew will make your life much easier.

    Just about to launch into a couple hundred organ pipe stopper handles, they need an accurate tenon to glue into the stopper and handles that look alike across ranks of pipes. We'll see how I practice what I preach, I've never tried to do those kinds of numbers before!

  11. #11
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    Thanks Roger. My lack of basic turning fundamentals is the problem. Your excellent explanation exposes that. So I will attempt to stop using sandpaper as a turning tool and learn about skews and scrapers.

    Thanks again.
    Ask a woodworker to "make your bed" and he/she makes a bed.

  12. #12
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    In my opinion you should turn it closer to final dimension. I'd turn it to .5mm and then sand with a sanding file. I use one of these, https://www.ptreeusa.com/abrasive_ha...ding_tool.html
    If you do a lot of pegs, I'd use an old jointer blade and make a pencil sharpener style tapering jig to get to final dimension. Like this, https://www.stewmac.com/luthier-tool...SABEgKJVvD_BwE

  13. #13
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    Thanks to all the great responses and ideas from the turners. I took as much as I could from each post. I was in the middle of a run of Oboe pegs when I said screw this and stopped. The detail cutter on the duplicator is getting dull leaving flaky cutter marks. The coarse sandpaper I was using cut like butter on the walnut and left scratch marks to be sanded off with more sandpaper. Bad circular logic!

    Based on what I learned here I set the template oversize and then moved around to the front of the lathe (my duplicator is on the back) and used a skew with a planer cut to bring down to .5 mm over and remove the cutter marks. I then started with 150G and up to 320 to bring the pegs down to size.

    I am a little afraid of the skew so I ordered a carbide skew which is more like a scraper and has a 30 degree shaft. I am hoping to sand starting with higher grits. This is still a work in progress but no more melting down pegs in a cloud of dust!

    My father-on-law always said: "Green you're growing, ripe you're rotten.

    Thanks,

    Gordon
    Ask a woodworker to "make your bed" and he/she makes a bed.

  14. #14
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    If there is a local chapter of the Am. Assoc. of Woodturners nearby go to a meeting, many chapters have "mentors" who are happy to come to your shop or have you come to theirs to work with you in a free hands-on session on trying to solve this kind of problem. Most can show you several ways to do it. Seeing it done and then having someone who can put a hand on your tool while you're working and rotate it 10 degrees --going from a nasty to a perfect cut-- can be incredibly helpful. They will almost certainly help you with sharpening as well.

    There are 11 chapters in MI: https://www.woodturner.org/Woodturne...9-a722bab7417d

  15. #15
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    Quote Originally Posted by Gordon Stump View Post
    ÖI am a little afraid of the skew so I ordered a carbide skew which is more like a scraper and has a 30 degree shaft. I am hoping to sand starting with higher grits. Ö
    You are not alone - many turners seem to be afraid of the skew! This usually comes from having a bad experience while experimenting or from listening to other turners who never learned to use the skew.

    When I started turning several people told me to stay away from the evil skew, it will bite you, it will hurt you.

    I learned turning mostly from a few good books and guess what, I found these experts were all using the skew! I determined to learn to use it or die trying. By following their instructions and much experimentation the skew is one of my favorite tools. A catch is extremely rare, mostly when I accidentally bump the point into the wood due to carelessness. I keep a variety of skews on hand, from 1-1/4Ē done to less that 1/4Ē and in a variety of angles and profiles.

    I developed a method to teach the skew that so far has been 100% effective, When I start a new student, even one who has never touched a lathe before, the first tool in their hands is the skew chisel. With my approach the student is usually making nice planing cuts within 10 or 15 minutes before we move on to v groves, peeling cuts, etc. After the skew we move to the roughing gouge then the spindle gouge. I make sure the person gets plenty of practice on spindle turning before I introduce face/bowl turning.

    Iíve taught like this dozens of times and Iíve NEVER had a student get a catch. Several told me later the skew was their favorite tool! In addition to beginners, Iíve used the same method to teach experienced turners who were a little afraid of the skew or just never took the time to learn it.

    Too bad you donít live closer or you could stop in for a skew lesson! My fee is a good story or a good joke! Results guaranteed or your money back. Road trip?

    BTW, I havenít tried one but I canít imagine the value of a carbide skew except as a negative rake scraper, and even then, not a good one since it wouldnít be possible to create the burr needed. To be really useful, the skew has to be arm-hair-shaving sharp or clean cuts may not be possible. How can you maintain this level of sharpness with carbide, especially when it gets a little dull? I wish I had one to evaluate but I donít think Iíll buy one for that. I still think you can get the results you want, if not by learning to use the conventional skew, by using a properly ground NRS. Precision small-diameter tapered pins would be so easy with a small NRS ground straight across.

    PS, Iím typing this from an iPad and donít have access to all my photos but if you are interested I could post some photos of tapers Iíve done with the skew, small and long, mostly thin spindles - one of my favorite types of turning.

    JKJ

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