Hmm, me edit while you post Carlton
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| Fractures in wood from Rotory Tools? http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=7503 |
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| Author: | johno [ Thu Jul 13, 2006 2:08 pm ] |
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Has anybody heard about the phenomenon of top (or back) plates being fractured by rotary cutting tools? I am talking about things like the Rotary Safety Planer that lots of guys use to thin their tops. I have seen where tearout occurs along a grain line with a router, so it makes sense to me that a rotary cutter spinning 90 degrees to the grain lines could separate, fracture or weaken these plates when they thin a top. I heard this mentioned last summer at the ASIA symposium and I have considered using a tool to like this to get me down to dimension a little faster than an abrasive cut, but I keep hearing those voices saying words like fracture, crack or failure. |
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| Author: | Kim [ Thu Jul 13, 2006 2:55 pm ] |
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Heard lots of good about the Wagner, never once heard of any fractures occurring along the grain or otherwise. Guess it could happen, but it would not be a common thing surely. Edit: Johno, I would think a fracture would only be caused by a blunt cutter, or a tool that has been set up to hog too much in a single pass. Steady, steady wins the day me thinks especially when you are working high figure. Cheers Kim |
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| Author: | Serge Poirier [ Thu Jul 13, 2006 3:10 pm ] |
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Probably depends on the piece of wood itself, the Wagner planer has been around for quite a while now, we would have heard of a whole lot more similar stories unless people wouldn't want to admit that their tool was responsible for a failure like you mention. |
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| Author: | CarltonM [ Thu Jul 13, 2006 3:25 pm ] |
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Now, John, I've never used one, so this is only conjecture. It seems, since the planer moves in a circle, and (IIRC) the blade edges are slanted, and not parallel to the radius of that circle, the cut is never at a 90 degree angle to the grain. If that is the case, then any tearing is probably caused by dull or improperly set-up blades. Contrary opinions? |
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| Author: | Kim [ Thu Jul 13, 2006 3:29 pm ] |
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Hmm, me edit while you post Carlton
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| Author: | Colin S [ Thu Jul 13, 2006 8:13 pm ] |
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I've used and still use the Wagner for thinning tops, back etc and have never experience any negative effects. Providing that you keep it sharp and keep the stock moving. The thin cuts that we tend to take, almost just kiss the wood and even with high figure stuff just seems to need the ROS run over it afterwards. Never had any fractures. AS with any tool it's all in the set up. Any errors are probably due to operator interference. Colin |
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| Author: | Don Williams [ Thu Jul 13, 2006 8:59 pm ] |
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So John, you gonna hook that up to the spindle? |
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| Author: | Michael McBroom [ Fri Jul 14, 2006 2:59 am ] |
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I've used the Wagner also. The only caveat I can think of regarding its use for thinning tonewood is it tends to make the wood chatter, which might lead to the splits you were hearing about. Folks who use a Wagner a lot usually rig up some sort of system of rollers or such to hold the wood snugglyy against the table as its being passed under the cutter. I was up at Brian Burns' place, using his, and he had built a set of rollers to use with his Wagner for this reason. Best, Michael |
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| Author: | Scott Thompson [ Fri Jul 14, 2006 3:48 am ] |
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I use the Wagner to rough thickness and have never had a problem with fractures. I use a hold down and a fence so don't experience the chatter. |
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| Author: | johno [ Fri Jul 14, 2006 4:26 am ] |
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[QUOTE=johno] Has anybody heard about the phenomenon of top (or back) plates being fractured by rotary cutting tools? [/QUOTE] So nobody has answered the question ... Has anybody heard of this ... maybe I dreamed it. I think I remember the word "microfractures" in this dream so it may not be something you would see. |
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| Author: | LuthierSupplier [ Fri Jul 14, 2006 8:47 am ] |
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John, I've used the Safety Planer also on my own guitars, and also at the school with Robbie, and we have never experienced this phenomenon of wood being fractured. Nor have I heard of this phenonmenon. I think you may have associated this with something else by accident. Tracy |
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| Author: | Kim [ Fri Jul 14, 2006 9:48 am ] |
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[QUOTE=johno] [QUOTE=johno] Has anybody heard about the phenomenon of top (or back) plates being fractured by rotary cutting tools? [/QUOTE] So nobody has answered the question ... Has anybody heard of this ... maybe I dreamed it. I think I remember the word "microfractures" in this dream so it may not be something you would see. [/QUOTE] No, never heard of it...ya dream'in
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| Author: | Scott Thompson [ Fri Jul 14, 2006 9:48 am ] |
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[QUOTE=johno] [QUOTE=johno] Has anybody heard about the phenomenon of top (or back) plates being fractured by rotary cutting tools? [/QUOTE] So nobody has answered the question ... Has anybody heard of this ... maybe I dreamed it. I think I remember the word "microfractures" in this dream so it may not be something you would see. [/QUOTE] Sorry John, I interpreted your question as "Do I need to be concerned with this happening?" which from the testimony of the posters here, you don't. |
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| Author: | johno [ Fri Jul 14, 2006 11:12 am ] |
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Scott, No need to apologize, I appreciate the all the feedback but I also want to hear from the people who may have heard of this “microfracturing.” Could it be happening at a level that may not be visible to the eye and even if it is, maybe it doesn’t mean anything. I am not saying to you guys that use the wagner, “Don’t use it,” I just wanted some feedback on this as I have reached for the wagner a bunch of times, but my sander albeit kind of slow, still works just fine. |
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| Author: | Shawn [ Fri Jul 14, 2006 12:12 pm ] |
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If you are concerned with it but like its approach to thinning material you can use the sanding disk tool of similar design that was first built by John Gilbert. The operation is identical to that of the Wagner with the difference being that the "cutting" replaced by an abrasive sanding action from a plexi sanding disk mounted on a 1/2" steel shaft that is mounted into a drill press. LMII sells a version of it (John Gilbert's original disk was a disk made from 1/2" aluminum bar stock. It is just over 4 1/2 inches in diameter so a 5" adhesive backed disk does a good job (4 1/2 will work also). |
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| Author: | Alan Carruth [ Sat Jul 15, 2006 10:29 am ] |
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Sorry to be so long getting in on this. Several posters have addressed the subject of immediate fractures. As mentioned, these can be caused by: 1] too deep a cut: I try to keep it to no more than 1/3 the thickness of the stock, or 2mm, whichever is less, 2] too wide a cut, which does cause the cutter to be sweeping across the grain at a right angle. In particular, make the first pass shallow; say around 1/8" in from the edge, so that the stock is backed up, or run against a fence, and, 3] setup issues. These could be; a dull tool, or cutters that are set at different heights. I'll note that I got one Wagner planer that had warped cutters, and the bottoms of the pockets weren't flat, so they could not be set securely. An hour or so of lapping the cutters and scraping the pockets sweetened that one right up. This does not seem to be the issue you're really interested in, though: microfractures are ellusive by nature. I don't have hold down rollers, and have not missed them for the most part. I do find there is some surface tearout, particularly on figured wood, and conceivably that could extend deeply enough to do damage if you violate The Rules above. Obviously, for example, it's possible to tear apart a piece of curly maple or ebony veneer if you take too heavy a cut or whatever. In general I find that leaving .2mm extra thickness to scrape off later is sufficient, or maybe just a little more on highly figured wood. But, again, that's all about visible damage. I'm not sure how to address the question about hidden damage without doing some science of a fairly time-consuming sort. You'd have to thin out some pieces of wood using both a sander and a DPP, glue them to frames, and run a lot of moisture cycles or other kinds of stress, and see which has the higher failure rate. I've used Wagner planers for thirty years, and don't beleive I've had abnormally high rates of cracking, say, at least since I got my humidity under control. But, of course, that's just anecdotal evidence: what's a 'normal' rate for this sort of failure, and what about the folks who are so disgusted with all the cracks that they just don't speak up? Without anything to compare my experience to I can't say. It does suggest that the effect is 'small', if it exists, and that you would need a fairly large sample in any real test to see it. Only you can decide whether your level of doubt warrents that much effort to ausuage. Is it likely to be any greater than the effect of, say cutting logs with a chain saw or ripping stock with a tapble saw? In that regard, there is one place that might have some answers: the Forest Products Lab. There is still a lot of wood being used in aircraft structures, and more was used sixty years ago. They did studies on things like sanding vs planing glue joints, for example, and if ripping with a circular saw could conceivably damage wood structure enough to threaten the integrity of an aircraft, you can hope they'd be on it. Other than that.... |
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| Author: | Don Williams [ Sat Jul 15, 2006 10:38 am ] |
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John, I believe Taylor guitars has some kind of rotary planer which they use to process boards for tonewood. It sounds like a much larger/more refined version of a planer. I've never heard of microfractures from rotary tools either. Anything can happen when you use a dull tool on wood, but a sharp rotary tool will shear the wood pretty much like a plane blade. Of course as someone with a machining background, you know that the geometry of the cutting tool will have a great impact on the quality of that cut as well... |
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| Author: | Don A [ Sat Jul 15, 2006 11:48 am ] |
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[QUOTE=Shawn] John Gilbert's original disk was a disk made from 1/2" aluminum bar stock. It is just over 4 1/2 inches in diameter so a 5" adhesive backed disk does a good job (4 1/2 will work also).[/QUOTE] Just so folks know, you can buy the aluminum disks directly from John Gilbert. I picked up a couple from him in the last year, and it was a pleasure dealing with him. They are not listed on his web site so you need to contact him about purchasing them. We had a thread on this a while ago, so try a search in the forum archives. The can be used for much much more than just thickness sanding (eg. add leather to the top and you can keep that chisel stropped in short order). |
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| Author: | Colin S [ Sat Jul 15, 2006 8:23 pm ] |
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[QUOTE=Don A] [QUOTE=Shawn] John Gilbert's original disk was a disk made from 1/2" aluminum bar stock. It is just over 4 1/2 inches in diameter so a 5" adhesive backed disk does a good job (4 1/2 will work also).[/QUOTE] Just so folks know, you can buy the aluminum disks directly from John Gilbert. I picked up a couple from him in the last year, and it was a pleasure dealing with him. They are not listed on his web site so you need to contact him about purchasing them. We had a thread on this a while ago, so try a search in the forum archives. The can be used for much much more than just thickness sanding (eg. add leather to the top and you can keep that chisel stropped in short order). [/QUOTE] Or just make your own in ten minutes. 
Colin |
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