Violin Forum/Message Board

Dave Chandler · Posted: Sat May 15, 2010 8:46 pm Post subject: A question about arch templates

HELP, I'm stumped.

I've been working on reproducing a violin shown at http://www.luthierslibrary.com made by Andrea Guarnarius, and have been stumped on their representation of the arches. As they describe the process, they give arch heights at 4cm increments along the back, to include the thickness of the edge. This is good, because I made my long arch using my graduating caliper. The width of the instrument at these 4cm intervals are said (by luthierlibrary) to be measured by flexible tape over the arch.

Their arches however, are shown as cycloid arches drawn by computer using the height (which includes the thickness of the edge) and the width used is that same "over the arch" measurement.

It would seem to me, and here's where I'm looking for some guidance.... you would want the lowest points of your cycloid arch to reach the bottom of the channel, and width to be actual width not measured over the arch, but straight line across.

SO...for the sake of using the cycloid generator program to form your arches, wouldn't you reduce the height by the difference between the edge thickness and the depth of the channel? i.e. if they say the arch height is 18mm, but your edge thickness is 3.5mm and channel is 1mm deep, then you would use 15.5mm for actual arch height from bottom of channel to highest point of the arch. Does that make sense?

So where do you want your arch drawing to stop? At the bottom of the channel, or the edge? That seems it would influence the arch a bit too. So if you figure the channel to be 10mm wide (for instance) and the bottom most point to be at 5mm in from the edge, would you then reduce the width for the calcuation by 10mm and let it stop in the bottom of the channel?

I'm at a dead stop till I figure this out, but in a day or so unless someone gives me something that makes more sense,....may go with my hunches, height from bottom of channel, width from bottom of channel.
_________________
Dave in the Blue Ridge
Southern Violin Association

"Success is the ability to go from one failure to the next with no loss of enthusiasm" Winston Churchill

"I took the road less travelled, and now I don't know where I am." Marco Polo

rs · Posted: Sat May 15, 2010 10:30 pm Post subject:

Hi, Dave.

I believe the way intended is to measure from the arch to the channel, not the edge. The reason, I believe, is that the bead can vary from instrument to instrument, but this rise from the bead or edge will not as greatly impact the measurement as arch rise from the channel. This is because the arch does not truly begin until it starts its rise from the channel, not the edge.

Hence, an aggressive channel would greatly impact the rise, or arching, and thus impact the sound of the instrument.

On the other hand, a "bold" edge would greatly impact your measurements if it was viewed as the start of the arching, even though this boldness would only be cosmetic, not structural.

That is just the way I calculate it.

All the best.
_________________
Randall Shenefelt

DonLeister · Posted: Sat May 15, 2010 10:51 pm Post subject:

I see what you mean by where to place the low point of the cycloid. For me it has taken some violins to see what works. Even using the same arch templates, you can move them laterally and change the arch significantly.
I try to keep from getting too scoopy, although with cc's it is hard to eyeball how scoopy to make it, they always look too scoopy, if that makes any sense. It's a fine line. . I could never eyeball a cycloid arch I think.
So are you generating your own cc's or going with the ones that Luthier's Library offers?
Their cc's are going to be their interpretation of what fits the laser photos of the arches, ya think? So it seems it would be a case by case study of each instrument and it's archings. It gets complicated quickly.

Dave Chandler · Posted: Sun May 16, 2010 4:19 pm Post subject: Arching questions

Thanks to both of you. I'll be using my own dimensions as mentioned in my initial post. It has stumped me in the past when the arch templates didn't seem to match up with the long arch.
_________________
Dave in the Blue Ridge
Southern Violin Association

"Success is the ability to go from one failure to the next with no loss of enthusiasm" Winston Churchill

"I took the road less travelled, and now I don't know where I am." Marco Polo

DonLeister · Posted: Sun May 16, 2010 9:12 pm Post subject:

You remember that the instruments distort over time so the height of the arch is relative to either the ends or the sides of the plate, right? so if the plane of the plate is going in a potato chip fashion then the arches are about impossible to copy exactly.

Dave Chandler · Posted: Mon May 17, 2010 4:33 pm Post subject: Arching questions

Good point! So I will try and determine what the maker started with, what his intentions were, not what it has distorted to over the years. I have to have a starting point, and lacking any other information, work with what I have been given...modified by common sense, and, I would add, "knowledge" -- (but then I'd be talking about someone else).
_________________
Dave in the Blue Ridge
Southern Violin Association

"Success is the ability to go from one failure to the next with no loss of enthusiasm" Winston Churchill

"I took the road less travelled, and now I don't know where I am." Marco Polo