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Thicknessing edges after rough arching...


Nick Allen
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Hey dudes and dudettes,

 

I have finished rough arching the back to fiddle #1, and now I'm at the stage where I need to properly thickness the edges of the plate. Currently, I'm using a narrow sweep gouge and a graduation punch to do it. After I make the little holes almost disappear, I go in with a bastard file and clean things up. This seems like the ideal scenario, but I can't seem to get the gouge close to the line and make a nice hard edge, which will leave me some leeway for the actual final arching. I used to use a safe-t-plane on a drill press for this job, which took the time from about an hour down to one minute or so. But alas I do not have one of those...

 

So, will anyone be willing to share how they do this particular process? I thought that it would be easy, but is quickly becoming quite tedious...

 

Any help would be greatly appreciated!

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If you have a drill press a series of holes with a very small bit drilled to a depth almost the finished thickness might help.  I like to use a drill press and small bit so I can take a mechanical pencil and mark the bottom of the hole.  That gives me a good visual to work toward.  If you have already rough arched you may be able to work down your edge with finger planes, then clean up with a file or sand paper stick. 

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I start with a deep cut from my cutting gauge to set the thickness and then highlight the line with a sharp pencil . A marking gauge works just as well.

This gives me a very definite starting point. Then I use a flat gouge . I pick up the scratch with the edge with each stroke . I find that if I work methodically, not trying to take too much with each cut, the work goes quickly. I run a thumbplane around after the gouge, just to knock off any bumps. There's no need for this to be a machined surface.

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I see this phase of the process as a part of the sculpture of the arching, setting it with a cutter does not save much time when viewed in this light.

I do it more or less like Conor, you can see it in my videos dedicated to roughing back and top plates, you can find them listed here :

 

http://davidesora.altervista.org/videos/belly-back/

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One way is to use something along the lines of a single-blade purfling groove cutter, but repositioned to index from from the back of the plate and cut into the side, rather than the conventional orientation. In other words, it would be like using a marking gauge to mark the edge height, but substituting a cutter for whatever marking device was in the tool.

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I already marked the side to a thickness of 5mm. I'm talking about the measurement on the top, from the edges inward. Basically where the channel comes back up with the arching and meets the edge in terms of topographical height.

That's what I'm talking about too. ;)

Unless I'm totally misunderstanding what you are talking about..

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Why not use a small laminate router with a 1/4" flat bit?   Simple to set it up at fixed depth of 5 mm.   Then if you need to lower the edge then you can use a sheet of cardboard as a shim or sheets of paper as a shim.   But you must have a relatively flat plate with very little warp.

post-24376-0-24730800-1454087417_thumb.jpg

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That's a swell idea. Maybe soon I'll make a jig for that. I do have a spare router motor lying around these days. Plus I love making my own jigs. The only thing worth noting about the machining method is the fact that the button and the corners are different thicknesses, so gouge work is required regardless of the method I guess.

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Do it like Conor and Davide, and if you must use power tools keep your digits clear. 

I also do it like Conor, and recently bought a nice mini multi function brass marking gauge with 
a circle thing that makes a great line to work to. That's really all you need, line to work to. 
If you spend a long time with machines getting everything 'just right', the end product
is very likely to look too manufactured, to some people. 

Use your time well, no point rushing. 

 

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I've done one set of plates.  So my solution to this particular puzzle might be considered as one of the ways you don't want to do it, but it worked well for me. 

 

After marking how far into the plate I wanted my 5 mm edge, I planed a block of wood 5 mm thick.  Then I took an inside gouge and registered it to the block so that it rested level at 5 mm high.  I then went all the way around the plate cutting to the line for how far into the plate I wanted to go.  Then I repeated the process with a flat chisel to knock off the high spots left by the gouge.  Then I smoothed out the transition from the 5 mm  shelf to the arch with a gouge.  It was fairly fast and easy. 

 

Again, not a pro, so maybe I just wasted some space on the thread.

 

-Jim 

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Again, not a pro, so maybe I just wasted some space on the thread.

 

-Jim 

Nope, I think it's a nice way of doing it, making a shelf the right height to carve off of.

I've also seen it done the other way around, clamping the cutting tool to the bench with the right-thickness shim between the tool and the bench, and pushing the plate into the cutting tool.

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Be careful of using a rotary tool for this job in a drill press. Drill presses aren't designed to have side load on their spindle bearings and over time using them like this will kill the bearings and possibly the drill press. This is why vertical mills are so much more expensive than drill presses, because they are built to handle side load.

M

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 On a related note, is the edge "shelf" set 10mm in, and the C bout section 7mm? These are the numbers that I recall, but am not sure aboot.

Those are the numbers that are commonly given, but are not that critical. I flatten about 10 mm all around, but I purfle after closing and trimming the overhang, so the flat narrows some. As long as you have enough for purfling (but not too much), you can finish later. It can be wider everywhere except the C bouts.

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 The only thing worth noting about the machining method is the fact that the button and the corners are different thicknesses, so gouge work is required regardless of the method I guess.

Maybe you have finished already but use the marking gauge to mark your edge heights and freehand pencil the lines to the corners and button.  I used a real sharp 1/2" chisel and went to the line and finished with a good scraper.  10-7-10 sounds alright, I think I started with 9-7-9 but after gouging purfling and recurve etc. a few mm's shouldn't matter.  I couldn't resist not rigging up an electric router for the purfling channel - that means I went flat all the way across from edge on in.  {homemade purfling for more working height}.  

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Sorry. I responded off topic.    After I rough the arching, I work the channel to a good thickness.  I use my punch for that.

 

But to control the actual edge, I just use a sharpened dogleg compass.

 

 

 

Punch:

post-30802-0-49097800-1454117859_thumb.jpg

 

 

 

I'll take some pics of one of my dogleg compasses and post.  I know others here use similar tools.   The dogleg is a super fast simple and reliable way to mark small distances and thicknesses.   And, as evidence seems to suggest the old makes did, it works by scribing a guide mark into the wood.

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Yes.  Any sort of marking gauge can do the job, and will track with your plate --no surprises from lifting up and suddenly cutting the edge too thin.

 

My dogleg compass:

post-30802-0-27191700-1454121063_thumb.jpg

 

 

 

 

These work best if you round the end of the shortened leg before sharpening.  That way it will scribe smoothly over the grain without snagging.    

 

Also, start with a very stiff and solid compass, with a good screw adjuster.

 

 

 

This is a basic and rather primitive kind of tool.  But if you start using one, it will become one of your favorites.

 

 

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I use pretty much the same method as Conor, Ben and David. I start by using a slitting gauge to mark the rough thickness all around about 1 mm thicker than the final edge specs then rough arch the plate keeping to the final shape and proportion. Then I remark the final thicknesses and run all the way around with a knife beveling the edge down to the marked line before carving the final arch. I run around the edge with a small flat thumb plane to finish the edge thickness and use a small curved bottom thumb plane to presink the  channel  before purfling and scraping the plate.

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I often see people making the edge 'platform' dead flat and and even before they carve the arching. We learned to do it this way in school.

 

I see no good reason to do it this way. I find that the hard edge distracts my eye, and as Davide says, this is where the shaping of the arching starts. Why spend all that time forming a platform that you don't really want, and that you'll be cutting away anyway?

 

I cut from the scribe line straight in and let each stroke flow up and over the arch, and a flat area at the edge looks after itself. After I've closed the box and purfled it, then I scoop out, either right to the edge or sometimes a little short of it, and it's the smoothness of this cut that determines how tidy the edge will be. The important thing for me here is the shape and sharpness of the gouge  use to sink the edge. Any little bumps will be taken care of at this point. When I round the edges over, I can decide where exactly my high point will be. 

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