Sanding wood with widely different hardnesses

Discussion in 'Newbie' started by Hy Tran, Sep 8, 2016.

  1. Hy Tran

    Hy Tran

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    I've done a couple of projects with woods that have pronounced different hardnesses between the early wood and the late wood, and I'm getting ridges after sanding--with the lighter colored wood (generally the early wood) having valleys and the late wood having ridges.

    I'm power sanding after the final cut with a gouge and a couple of passes with a scraper to take away bumps. I'm not good enough with my fingers to feel what grit to start sanding with, so I generally start with a fairly rough grit (120, 150), unless I have tearout.

    Power sanding is with a 2 1/2" disk on medium-firm pad, and when I get to the 200's, I switch to a softer pad. I stop the lathe and do several hand-strokes (sandpaper disk in my hand) with the grain before switching to the next grit level.

    While my end product looks good, I can feel distinct ridges which were not there before sanding. This is especially pronounced in pine and fir, but no ridges in maple.

    Suggestions greatly appreciated...
     
  2. Steve Worcester

    Steve Worcester Admin Emeritus

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    The problem you describe is pretty common with softer woods like Mountain Ash, Sycamore, Silver Leaf Maple I have in Texas.

    You can start any any grit you like, understanding that you may need to backdown. But that isn't necessarily the problem. Make sure you are not running the sander in the opposite direction of the bowl, as for less aggressive sanding, go in the same direction. And I would try starting out with a higher grit, but softer pad. You may burn up a few soft pads until you get a more delicate technique, and it may take a little longer, but if you have to sand with lower grits, you will get better results
     
  3. Bill Boehme

    Bill Boehme Administrator Staff Member

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    Steve is the expert in sanding.

    Back when I was doing flat woodworking, I sometimes used fir for cabinets. It's a beautiful softwood. I used a 6" ROS with a medium firm pad. That seemed to work well. Unlike in woodturning, in flat woodworking the boards are fairly smooth after planing so I could start sanding with 220 usually. Also in flat woodworking there isn't the problem of dealing with all the different grain orientations that woodturners encounter.
     
    Last edited: Sep 9, 2016
  4. robo hippy

    robo hippy

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    Hmm, at first I thought you were having problems with wood that has punky areas in it. A broad firm pad will 'spread' the abrasive surface across a wider area, which might keep it from digging in so much on softer areas. With the woods you are having problems with, I don't know if you can keep that from happening. Redwood is another one that does this. This is more like antiquing, or weathering, kind of like sand blasting or hitting with a wire brush...

    robo hippy
     
  5. john lucas

    john lucas

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    The real trick is to simply cut the bowl clean enough that you can start sanding with finer grits. I also agree with the firm pad. I normally use a soft pad for all of my finishing but on occasion when I get a wood like your describing I have some discs I got at the automotive store that don't flex at all. A very light touch and with almost no pressure on the wood is needed when using these. I have also use a cabinet scraper on the outside of vessels. The wood should be moving very slow. I have used round cabinet scrapers on the inside but only with the lathe off.
     
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  6. Hy Tran

    Hy Tran

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    Probably one of the things I need to do is to take something like flat samples of a medium hardwood, and sand with various grits--to get a "feel" comparison for what grit level I need--then, save my samples, so I can always check what grit I feel I should start with.

    I generally feel that my outsides are better than my insides.

    Practice will likely help, yes.
     
  7. john lucas

    john lucas

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    I've been turning a long time and my outsides on bowls are almost always better than my insides. Not by much it's there. I wonder if I just get tired or lazy after turning the outside and push the cut too much on the inside.
     
  8. Fred Belknap

    Fred Belknap

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    John one reason is we can visualize the outside better.
     
  9. hockenbery

    hockenbery AAW Advisor Staff Member

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    I find this to be true on bowls for me.

    The outside I can cut with a pull cut which gives the cleanest cut I have learned to make with the Ellsworth gouge. It uses the sharpest part of the gouge 30-25 degree part of the wing and I can drop the handle to have the shear angle at 80 degrees if I want but usually go for 45-60 degrees. Then I can shear scrape to an even finer surface.

    Inside I mostly use the shear cut with the leading edge of the wing. The bevel angle here is in the 45 degrees range not as sharp. The shear angle is 60 degrees of so. I don't bother to use a scraper inside unless curly grain is leaving bent fibers in the bottom. So the surface is good but not a smooth as the outside.

    One oddity is most of my beginning bowl students over the years get much better surfaces inside their first few bowls than outside and they are using the bevel riding push cut. This may be due to:
    All the practice the got turning the outside, most being right handed, the curvature of the bowl tends to guide the cut and lock the bevel.

    Al
     
  10. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I'm glad to see that others are saying that they have trouble with the inside because that has been a major frustration for me. When I think that I have a nice curve on the inside I'll discover that it is a series of straight segments especially near the bottom.
     
  11. Zach LaPerriere

    Zach LaPerriere

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    It's definitely not just you, Bill! With much more recent experience as a newbie, I can say that interiors have driven me crazy!

    As for woods of different hardnesses, that's a good percentage of what I turn... After a fair bit of trial and experiment, the best I've come up with is to sand the interior with the lathe off, a hard backing pad, and fresh course paper on the parts I know will sand inconsistently or take extra sanding time. I especially concentrate on any tear out in the end grain. Lighter pressure seems to be best. Once I'm satisfied that I have a decent 120+ finish on the more difficult parts, I'll start power sanding. I also have had better switching to a medium-soft pad at a higher grit than normal. I try to powersand the bare bones minimum I need to at each grit, which is just an experience thing. Can't say I always get that right.
     
  12. odie

    odie

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    Yes!

    Hy......as you can see from the responses here, you are experiencing the same thing as EVERYONE else does. The interior of bowls are definitely the most difficult part of bowl making. A turner does need to develop a systematic way of doing interiors, and then continue to "evaluate, revise, and refine" that technique.

    One thing that makes this very challenging, is it's difficult to see just where your high and low spots are when the lathe is running. Although I've learned to "see" much better with experience, there is something turners can do to help know exactly where these high/low spots are......use a laser pointer mounted to an adjustable/flexible arm. This way, you can pinpoint the exact location of the area you want to identify while the lathe is turning.

    Generally, but not always.......the push cut can be used on the sides of the interior, while that can change to a pull cut, once you "turn the corner". This depends on how radical a curve the interior takes, and doesn't necessarily apply in all cases. The more aggressive the curve, the more this may apply.......

    Frequent use of calipers, plus I've evolved to rely on the Tompkins Gage'T Thickness Gauge for making sure the wall thickness is a constant throughout the sidewalls. This is a great tool, and I recommend it wholeheartedly.....
    https://www.woodturnerscatalog.com/p/87/3730/Tompkins-GageT-Thickness-Gauge

    ko
     

    Attached Files:

  13. hockenbery

    hockenbery AAW Advisor Staff Member

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    As you have said being able to use the pull cut inside very much depends on the shape of the bowl.
    Pull cut inside a bowl is limited to shallow bowls with near flat bottoms. Also need a lathe where the handle doesn't hit the ways.
    A pull cut cannot work on Hemispherical shaped bowls because the handle hits the Walls.

    The pull cut is an effective cut for platters and many platter turners use it a lot.
    Most bowl turners don't use it because it only works in shallow bowls.
    Cutting into endgrain on a flat surface requires very thin cuts.

    One of the tricks to getting a clean cut on the interior is cutting a continuos curve from rim to bottom center. With a continuous curve the cut is always across the fibers which are supported by fibers behind them.

    When the bottom is flat a cut will hit end grains head on. The cutting edge will slide under some end grains. Scraping a flat surface Is often more effective than cutting it since the scraping edge is perpendicular to the grain.
     
    Last edited: Sep 28, 2016
  14. odie

    odie

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    Hello Al.......

    Yes, I agree implicitly.....a platter shape, or elongated flat interior does ideally lend itself particularly well to the pull cut.....but, a bowl shape is not excluded from using the pull cut effectively. This is not to imply that it's useful universally......sometimes yes, sometimes no. This is specifically dependent on the shape of the grind for the gouge, and as stated before, the shape of the interior is a part of that equation. The standard grind sometimes does particularly well in this mode of negotiating the curved interior of a bowl in a pull cut mode, as well as being useful for platters for the same cut ......

    ko
     
  15. hockenbery

    hockenbery AAW Advisor Staff Member

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    The standard grind is incapable of doing a pull cut. So there must be some definition problems

    In the pull cut the handle leads and the cut is made in the direction of the handle by the wing of the gouge with the nose of the gouge trailing the cut. A standard grind is straight across so there is no way for any part of the cutting edge to contact the wood.

    A side ground gouge with a short wing can work
     
  16. odie

    odie

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    The standard grind I'm using is very similar in capability to the side ground gouge with a short wing.

    There are many possible shapes with the standard grind, or traditional grind, depending on the angle of the bevel. Perhaps we do have definitions that are not the same, but if we do not, it's nice to know that I can do the impossible! :D

    ko
     
  17. hockenbery

    hockenbery AAW Advisor Staff Member

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    Here are some diagrams.
    We need one for the 40-40 or 45-45

    image.jpeg image.jpeg image.jpeg image.jpeg
     
  18. Bill Boehme

    Bill Boehme Administrator Staff Member

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    I'll agree in principle that we typically think of a pull cut being made with the handle leading if we are using a gouge with a swept back grind. Sometimes I think that the written word can confuse more than it can communicate. Another reasonable person might define a pull cut as using their muscles to pull the tool towards them regardless of whether the handle is leading or trailing. The shape of the grind may influence how difficult or easy it is to make any particular cut.

    I'm still trying to sort out what might be a standard grind (or "traditional grind" is another term that I've heard bandied about) ... if such a thing actually exists. Right now, I'm leaning towards a standard grind being a scraper. Jerry Glaser's gouges milled from round bar stock had a rather wicked side grind. Del Stubbs used what we typically call "continental" gouges (sort of like a shallow SRG) with what he called a "ladyfinger" grind. The there is the "Irish" grind which is also swept back . I don't know how far back in time that shape goes. I believe that scraping tools predate any cutting tools by centuries if mot millennia so any of your cutting tools are all just Johnny-come-lately pretenders to the title of being the standard or traditional grind :D.
     
  19. hockenbery

    hockenbery AAW Advisor Staff Member

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    The pull cut can be made by pushing the tool away from you as long as the handle leads the cut and the nose of the gouge trails. I push the pull cut to cut from foot to rim of a NE when it is mounted in a Chuck because I need to see the surface to reposition the cut.

    I think of all the cuts in terms of how the cutting edge participating in the cut moves over the surface being cut. How we hold and move the tool is freedom of choice but the edge must move over the wood in a predetermined manner defined by that cut.

    :)
    First rule of English is that it doesn't always make sense and the second rule is that it was not necessarily created to communicate.

    Sort of why @Bill Boehme should write the AAW DICTIONARY of woodturning terms. :)
     
  20. odie

    odie

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    For clarification, a standard, or traditional grind gouge, is any shape of grind on a gouge that's produced by rotating the tool shaft along it's longitudinal axis while the butt rotates at a fixed point.....or, with the Wolverine, the "v arm". There are many shapes possible with this method.

    The side ground gouge is any shape of grind that is produced by swinging the butt of the tool around an arc. There are many shapes possible with this method, as well.

    These two terms can be applied universally, and the many possible grind shapes from each basic method can be divided into subsets from the root term. This is how it was described in the distant past, and from that point forward, there have been re-definitions according to an individual's perceptions. I understand this, and am using the terms as they were originally applied.

    ko
     

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