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Thread: Carving Float vs Rasp Surface Quality

  1. #1
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    Carving Float vs Rasp Surface Quality

    This is a follow-on from my previous thread about the toothing on Iwasaki carving floats. I remarked there that the surface left by the floats seemed "shinier" than that left by a good quality fine-toothed rasp (Liogier cut-14 modeler's rasp). The purpose of this thread is to try to understand what's going on at the wood surface to create that impression.

    I grabbed a random piece of offcut, which happened to be the edge of a piece of plainsawn birch, hence a quartersawn surface. I first worked the surface with the Liogier rasp, sawed off a ~3/16" thick section (kerf included), and then worked the resulting surface with an "extreme fine" Iwasaki carving float before sectioning again. I wiped each surface to remove loose debris, but did not otherwise work them. In each case I worked the tool close to the grain direction but not exactly along the grain.

    Here are 3.6 x 2.4 mm sections of each, imaged at ~1.3 microns/pixel. I used one grazing light source from above (perpendicular to grain/tool directions) to accentuate surface profile differences. These would both look a lot smoother under "head-on" lighting. The camera is looking straight down on the wood, such that it doesn't really see specular reflections or shininess in general. The left image is the rasp, and the right image is the float:

    birch_liogier_14.jpgbirch_iwasaki_xfine.jpg

    I think that the pictures speak for themselves. The results with the Iwasaki are smoother, with most discontinuities arising from the wood's pores rather than the tool itself. It's not as good as a plane can achieve, but it's very good for a freehand shaping tool. I worked the Iwasaki in basically the same direction as the rasp (slightly up and to the left), and I don't see much going on along that axis. The Liogier rasps's teeth do cut very cleanly as evidenced by the minimal tearing to the wood fibers, but the fact that they form a non-planar surface can't be hidden.

    For a sense of scale, the large pore just left and above center of the Iwasaki image is about 6 mils (0.006") wide. The tracks from the rasp are maybe double that.

    I think the rasp very much has its place and strengths (the Iwasaki is a lot harder to manage for complex forms IMO) but so does the float.

    Geekish details: Canon 1Dx II and MP-E 65, 5X magnification, cropped down to half size. Canon MT-24EX flash, one head active, grazing from above. RRS TP-243 tripod, Arca-Swiss d4 head, RRS B150 dual-axis focusing rails.
    Last edited by Patrick Chase; 09-24-2017 at 8:07 PM.

  2. #2
    We've been using the flat and half-round Iwasaki rasps in med, fine, and XF for the last couple years - mostly for profiling necks and other heavy stock removal where the smoother, flatter surface left by that rasp makes layout of the center line and cross-section stations a little easier. For shaping, most students seem to prefer the Auriou 9"/10 grain or Corradi rasps due to the sensitivity the Iwasakis show to grain orientation...there is a 'catchiness' to use that is not present with the other rasps, but reminds me of my platemaking floats.

  3. #3
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    Quote Originally Posted by Todd Stock View Post
    We've been using the flat and half-round Iwasaki rasps in med, fine, and XF for the last couple years - mostly for profiling necks and other heavy stock removal where the smoother, flatter surface left by that rasp makes layout of the center line and cross-section stations a little easier. For shaping, most students seem to prefer the Auriou 9"/10 grain or Corradi rasps due to the sensitivity the Iwasakis show to grain orientation...there is a 'catchiness' to use that is not present with the other rasps, but reminds me of my platemaking floats.
    I know I've droned on about this in multiple threads, but the fact that we're even mentioning Aurious and Corradis in the same sentence is a testament to how far machine-cut rasps have come. Those Corradis are really good, to the point where I think that the lower-quality hand cut ones like the Dragons and Ajax-Blundells no longer make all that much sense.
    Last edited by Patrick Chase; 09-24-2017 at 11:33 PM.

  4. #4
    Hand cut rasps have been too expensive for me for the few handles I have made in Beech and Apple. I have some Iwasaki "floats" and they have been very usefull for this job. I do as much work as possible with coarser tools like chisel, gouge, cheap harware store rasp. Then refining the surface and bringing it up to final shape with the Iwasaki rasp. For the final surface preparation I have used sandpaper on my first handle making work, but have reverted to scraping on the later examples. I wouldn't say the the finish of any of these rasps is good enough for final preparation.

    For me, these Iwasaki's are great. A lot cheaper then the Liogiers/Auriou's. And they perform very well. Like mentioned they can be grabby, and they certainly have a prefered cutting direction. Something you learn quickly enough.

  5. #5
    We've been running the Corradis alongside the Aurious for the last batch of students (3 builders in long term tutorial of 250-300 hours each). Experience with hand tools varies from none (had a "...here, honey - let me do that for you..." parent) to prior instrument building experience. The tyros seem to prefer the Corradis due to the smoothness of cut and the lack of handedness when working the treble side of the neck, while the more experienced student prefers the hand-stitched tool for the more aggressive cut. My latest Auriou has a few wonky teeth that will wear and even out over time, versus the Corradis (10" cab'maker rasp in 10 grain and 8" 10 grain half round) that felt broken in after just a few minutes of use.

    The Iwasaki def rewards disciplined technique and punishes casual use in the medium and fine grades. The EF cuts more like a traditional rasp than the coarser grades, but still have that ability to generate a little pause/tiny catch in the stroke when the user is not paying close attention. Even the half-round shows this characteristic, although the tool is capable of getting down to the lines in the heel area very quickly and with less cleanup with a file than just about any other tool in the shop besides the drawknife.

  6. #6
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    Interesting test, but it just reinforces the gut feel that I would have (wouldn't everyone?) that a rasp is not intended to create smooth finished surfaces. I would never expect a finished surface from a rasp, regardless of who makes them, hand stitched or machine cut.

  7. #7
    I agree, Pat - none of these tools are ever going to generate a satisfyingly smooth finished surface. The issue for me is more about degree of smoothness, and how much additional work/stock removal is needed to get to a finished surface.

  8. #8
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    Quote Originally Posted by Pat Barry View Post
    Interesting test, but it just reinforces the gut feel that I would have (wouldn't everyone?) that a rasp is not intended to create smooth finished surfaces. I would never expect a finished surface from a rasp, regardless of who makes them, hand stitched or machine cut.
    In this specific test the surface off the Iwasaki is actually pretty smooth, on par with some planed surfaces. Again those images are at 1.3 microns per pixel (3.6 mm x 2.4 mm total) with raking light from above to accentuate defects. While neither are what I would consider "finish quality" the Iwasaki result is better in some respects than you could get from, say, 220# sand paper. Maybe I'll throw in an example of that.

    In general you're right, though. The results from both tools would require more work, particularly when you look at what happens in less "friendly" grain orientations.

    In any case this was mostly a reply to a comment in the other thread, which asserted that fine-tooth rasps like the cut-14 Liogier leave as fine a surface as the carving float.
    Last edited by Patrick Chase; 09-25-2017 at 12:08 PM.

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