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| Scraper Blade for Purfling and Binding Channels (Pics) http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=15976 |
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| Author: | WaddyThomson [ Mon Feb 18, 2008 11:06 pm ] |
| Post subject: | Scraper Blade for Purfling and Binding Channels (Pics) |
I was so impressed with how well it worked, I thought I would show the blade I made that scrapes channels instead of cutting with a knife edge. This is my understanding of the type of blade Romanillos uses for hand cutting these channels, from what I was told by Shawn. Here is the blade, made from a Jig Saw blade with the teeth ground off. All edges are ground and honed flat, with the sloped surface honed last, leaving a bit of a burr to act like a turned edge on a scraper. This blade allows you to get very clean lines in hard to work wood. Here are pictures of the blade from several angles. It cuts with the flat edge going forward. It is easy to start with the tool sloped in the direction of the cut a little, and get a shallow start to the cut, then come back over with a deeper, more vertical stroke. I used several strokes to get all the way through, but it cuts fast and clean. Attachment: P1000619 (Large).JPG Attachment: P1000621 (Large).JPG Attachment: P1000624 (Large).JPG For how it worked, Here are some close-up shots of my binding ledge. It has not been altered from the original cutting, except at the tail, where I caught the edge with a chisel, and cut off nearly an extra mm by accident. Attachment: P1000628 (Large).JPG I glued in a piece from the off cut of that side, at that end, and was able to re cut the groove with the cutter, and with only minor clean-up at the narrow end, got a pretty good repair. You can see where the repair was at the end where the end projects into the tail strip cut-out. It went all the way left edge of the picture. In the second shot, you can see where it stops because it is a little lighter on the top edge than the rest of the side is on the top edge. Attachment: P1000629 (Large).JPG Attachment: P1000631 (Large).JPG Suffice it to say that I like the way this blade works, and would recommend a blade like it over a knife edge for cutting side channels where grain variations may cause a knife edge blade to veer with the grain. Just thought some of you might be interested. |
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| Author: | KenH [ Mon Feb 18, 2008 11:26 pm ] |
| Post subject: | Re: Scraper Blade for Purfling and Binding Channels (Pics) |
Neat tool Waddy! I bought a German Made brass tool a while back that is very similar to this. It came with 2 blades and was meant to be used to cut the purfling channels on violins. I have used it a coupld of times and I like how easily it cuts the wood. With a blade like yours in it, I could see where it would remove alot of wood in a hurry. Thanks Man!! |
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| Author: | Chansen [ Tue Feb 19, 2008 1:29 am ] |
| Post subject: | Re: Scraper Blade for Purfling and Binding Channels (Pics) |
That is great Waddy! This is exactly the tool I was looking to find in my earlier post. With the scraper blade, I think it will be especially useful for me. Thanks for taking the time to show this! Christian |
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| Author: | douglas ingram [ Tue Feb 19, 2008 9:37 am ] |
| Post subject: | Re: Scraper Blade for Purfling and Binding Channels (Pics) |
I'm trying to get a handle on how this thing works. Is it used to cut the entire binding and purfling channel just by scraping? Is it use in conjunction with any other tools? Or is it a clean-up tool? Are chisels used? or just at the heel/neck area? Looks like a useful tool. |
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| Author: | WaddyThomson [ Tue Feb 19, 2008 10:24 am ] |
| Post subject: | Re: Scraper Blade for Purfling and Binding Channels (Pics) |
Doug, it is used to cut the initial channel. Then the waste above it is removed with a chisel, to the same depth of the cut from the scraper blade. One of the advantages is that it will cut to the full depth in hardwoods. It is difficult to do that with an knife edge. They get bogged down the deeper they get. This clears it's own channel. It also gives a little space, so you are not having to watch your chisel at the bottom of the cut as much. Although, you still have to be careful - see my error above. |
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| Author: | letseatpaste [ Tue Feb 19, 2008 12:35 pm ] |
| Post subject: | Re: Scraper Blade for Purfling and Binding Channels (Pics) |
This looks like a great tool, thanks for sharing. I'm still a little confused as to the process of how the channel is actually cut. So you use this tool to cut the side of the channel and set the depth, and then use a chisel to cut the bottom of the channel? What would stop you from turning this tool on it's side to define the bottom of the channel? That was the main point of frustration for me when I was using a regular gramil and chisel. The chisel kept diving into the grain of the side when I was cutting the bottom of the channel, even though I had used the gramil to define it at the edge. |
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| Author: | WaddyThomson [ Tue Feb 19, 2008 1:21 pm ] |
| Post subject: | Re: Scraper Blade for Purfling and Binding Channels (Pics) |
Let's see, how to explain this. The height of the cut is the height of the binding - or the distance the outside of the blade is from the stop than rides against the top or back. The depth of cut, is how far through the side you want to cut, i.e., 1mm deep, 2mm, deep, 2.2mm deep, etc. The blade accomplishes the height (distance from top/back to outside edge of blade) of the cut cleanly, and does not require much clean-up with the chisel... However, it only makes a 1+mm groove, so you have to remove the waste above the groove with the chisel. But your shelf is already established. That is, as far as the binding goes. For cutting the purfling shelf, I used an edge blade, like a knife, sharpened only on one side. It looks like a knife edge. Here: Attachment: P1000048.JPG Fits in the tool like this, and gives a clean outside edge. Attachment: P1000069.JPG This gives you a clean line and a depth to cut to, maybe 1.3mm or something like that. When Chiseling, you can tell when you are at the right depth, because the wood will separate cleanly along the cut edge until you get too deep, then it will start to cling to the side of the cut edge instead of separating. Don't go deeper, unless your blade slipped up during the cutting, which it will do some. Just try to stay level. Cut you purfling ledge, then remove the waste above the binding cut in the side. That establishes your two levels - one for purfling, one for binding. |
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| Author: | Ricardo [ Tue Feb 19, 2008 9:21 pm ] |
| Post subject: | Re: Scraper Blade for Purfling and Binding Channels (Pics) |
How do you hold the blade in the jig and adjust its depth? |
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| Author: | WaddyThomson [ Tue Feb 19, 2008 10:33 pm ] |
| Post subject: | Re: Scraper Blade for Purfling and Binding Channels (Pics) |
Go to my Circle/Purfling Cutter Tutorial, and look at how it fits together. The blade is held in place by a wedge arrangement, and the width of cut is controlled by a set screw. It is easier to see in the tutorial. |
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