# Laying Out Large Radius Curves



## craigwbryant (Jan 14, 2013)

Working on a trestle table that I started back around Christmas time (life/work got in the way, had to move for the Army and bounced around a few things at work, finally getting time to work again). The project has a few large radius curves that are meant to give a gentle appearance to some of the components. For example the legs of the table are roughly 23" tall and they have a curve in them that goes from 8" at its widest points down to 6" in the middle, so you'd "curve" in about 1" over 23" on either side. Up to this point in my woodworking life I've always been able to handle curves with a draftsman's compass or finding some sort of circular object that gets me to "close enough", but obviously neither of those ideas are going to work here. Does anyone have any suggestions on ways to layout these curves?

Thanks in advance for the help.


----------



## DaninVan (Jan 1, 2012)

Hey, Craig; If it were me I'd start with a paper pattern, go to a hardboard template, then move on to the real wood object.
Boatbuilders use a flexible device to allow the designer to fair the curve into other components while meeting certain criteria along the way.
Lee Valley carries a couple of suitable devices...
Flexible Curves - Lee Valley Tools
Blending Curves - Lee Valley Tools
There are probably others online. Check under 'Draughting Tools ' or as you guys say 'Drafting..."


----------



## kp91 (Sep 10, 2004)

You can make a bow. Find a thin piece of bendable material (hardwood, formica, etc.) and put a notch in each end. Connect a string between the two notches. Flex the bow by tightening the string. Lay out the start and middle points of your curve and adjust the bow to match as best as you can.

simple jig:





Fancier


----------



## DaninVan (Jan 1, 2012)

Either or any of the above, but do it onto a template first so that all corresponding pieces match (tablelegs for example...and or mirrored images)


----------



## Cherryville Chuck (Sep 28, 2010)

For drawing large curves I use a set of trammel points on a yardstick. Lee Valley sells the trammel points.


----------



## Stick486 (Jan 4, 2013)

*Maybe...*

this will help...


----------



## DaninVan (Jan 1, 2012)

There's maybe an assumption here that in fact the curve needed is a segment of a circle rather than a segment of a parabola or ellipse.


----------



## Stick486 (Jan 4, 2013)

sweeps???


----------



## Stick486 (Jan 4, 2013)

something like this???


----------



## Stick486 (Jan 4, 2013)

cheat...
use a flex ruler and set the shape by eye....


----------



## craigwbryant (Jan 14, 2013)

Stick486 said:


> cheat...
> use a flex ruler and set the shape by eye....


This is probably what will happen. I am going to stop by Home Depot or Lowe's after work today and grab some of the flexible PVC stuff shown in the first YouTube video and use it to lay out the arc. I figure as long as the arc touches the apex and the two end points its good.

Use that to make a template out of either hardboard. Trace the template on to the project pieces to hog out the large waste parts, then use some double sided tape to mount that template to the project pieces and its off to the router table to get a clean final cut.


----------



## kp91 (Sep 10, 2004)

When you are using you flexible piece on your template, it helps to dive a few nails in the stock to hold the piece. Have one at the apex on the inside of the curve, and one at each end on the outside of the curve. Just offset the nail the thickness of the strip you are using so it keeps it lined up with your desired line.


----------



## rwl7532 (Sep 8, 2011)

Beam compass
Beam Compass


----------



## Cherryville Chuck (Sep 28, 2010)

Stick486 said:


> cheat...
> use a flex ruler and set the shape by eye....


Very true. It doesn't have to be right, it just has to look right. In some cases that can make a world of difference in difficulty.


----------



## tomp913 (Mar 7, 2014)

kp91 said:


> When you are using you flexible piece on your template, it helps to dive a few nails in the stock to hold the piece. Have one at the apex on the inside of the curve, and one at each end on the outside of the curve. Just offset the nail the thickness of the strip you are using so it keeps it lined up with your desired line.


You can also cut a notch at either end of your flexible strip and use a piece of string to set the curve. Tie off the ends of the string and you don't have to fight holding the curve and hitting the points at the same time - you can just drive the nails at the required points, hold the strip with one hand and trace the curve with the other


----------



## DaninVan (Jan 1, 2012)

On a large area (flat) naval architects and boat builders use weights to 'anchor' (no pun intended) the flex curve
http://www.westlawn.edu/news/EdsonSplineWgtsWEB_files/image006.jpg

Incidentally, I just found this link...
Alvin 40" Tru-Flex II Flexible Adjustable Drawing Curve Ruler

and this one...
https://www.google.com/search?q=fle...oTCPDAsMaBwMgCFQf2YwodvyALhA&biw=1920&bih=864


----------



## tomp913 (Mar 7, 2014)

DaninVan said:


> On a large area (flat) naval architects and boat builders use weights to 'anchor' (no pun intended) the flex curve
> http://www.westlawn.edu/news/EdsonSplineWgtsWEB_files/image006.jpg
> 
> Incidentally, I just found this link...
> ...


I have one of these http://www.amazon.com/Acu-Arc-Crafts-Drawing-Accessories-Adjustable/dp/B000HESS0I which is probably better for this application as it's stiffer (parallel interlocking strips that "slide" relative to the adjacent one. although you still need weights to hold the shape while you trace the edge. I worked at a company that built dredges for a while and the drafters over there in the hull section had the long flexible kind with the weights Making Spline Weights aka A Pod of Whales All of this in the days before AutoCAD of course.


----------



## tbahorski (Nov 11, 2014)

Try this site https://atelierdubricoleur.wordpress.com/ The site is in French and English. He has a lot of ideas for jigs and tools. In the tools and jigs section are ideas for a large compass as well as the bows suggested by others.


----------



## graycat (Oct 14, 2013)

https://en.wikipedia.org/wiki/Beam_compass


----------



## tomp913 (Mar 7, 2014)

I used the trammel set shown to construct a perpendicular to the edge on the piece of plywood while making a fixture to set a right-angle on a saw guide. The trammel bar is 1/4" x 1" aluminum, pretty stiff within limits but it does get a little flexible as it gets longer.

If you're try to draw an arc with a specific radius, work backwards using Stick's formula to get the height for a given length, lay out the points on a piece of plywood, drive nails in as mentioned and set the arc with the flexible strip and a piece of string.


----------



## craigwbryant (Jan 14, 2013)

So, know its been awhile, but work (boo) and the arrival of a new baby (yay) got in the way over the past few months. My dad came to visit over the holidays and after messing around with a few things we actually were able to build a jig that let us cut one template, that we then used to cut the actual project pieces. In retrospect I wish we had taken pictures of the jig before I took it apart (what's the line about hindsight being 20/20), but in basic concept we had a piece of red oak, about an inch and a half wide and 3/16 or so thick. Obviouly this bent so we used it to trace out the curve onto a piece of 1x6 pine, then used blocks to and screws to hold it in place, this gave the bearing on the flush trim bit something to ride against. Then it was just a matter of cutting the template, then putting the tempate onto the project piece and cutting that. Attached is a picture of the stretcher for the table paired into the two side supports. For a first time cutting curves, I'm pretty happy with it! We also made a template for the curves that will be cut into the two side supports but I haven't quite yet gotten around to cutting those.


----------



## Stick486 (Jan 4, 2013)

so far so good...


----------



## craigwbryant (Jan 14, 2013)

Fortunately the weather was mild today so I was able to spend some time in the shop (which is really a garage, but shhh...I'm not telling the wife, if she found out she might try to park a car in there). Was able to get some more curves cut and got the piece mocked up. The feet and battens have curves too that will be cut next weekend, once a new, longer, flush trim bit arrives. This piece isn't perfect, there are certainly some "lessons learned" that have been incorporated in, but so far I'm really happy with how its turning out and where its going.




















Sent from my XT1080 using Tapatalk


----------



## Stick486 (Jan 4, 2013)

craigwbryant said:


> Fortunately the weather was mild today so I was able to spend some time in the shop (which is really a garage, but shhh...I'm not telling the wife, if she found out she might try to park a car in there). Was able to get some more curves cut and got the piece mocked up. The feet and battens have curves too that will be cut next weekend, once a new, longer, flush trim bit arrives. This piece isn't perfect, there are certainly some "lessons learned" that have been incorporated in, but so far I'm really happy with how its turning out and where its going.
> View attachment 181681
> View attachment 181689
> View attachment 181697
> ...


your secret is safe w/ us...
looking good...


----------



## Gaffboat (Mar 11, 2012)

craigwbryant said:


> ... I was able to spend some time in the shop (which is really a garage, but shhh...I'm not telling the wife, if she found out she might try to park a car in there).


Wait! You mean that room with the big wide overhead door that I use for my shop is supposed to be for cars? 30+ years my cars have been sitting outside. Hmmm. Ya' learn something new every day. Let's see, move the cars in and the shop out. Nope. Not going to happen. :no:


----------



## Stick486 (Jan 4, 2013)

Gaffboat said:


> Wait! *You mean that room with the big wide overhead door that I use for my shop is supposed to be for cars? *30+ years my cars have been sitting outside. Hmmm. Ya' learn something new every day. Let's see, move the cars in and the shop out. Nope. Not going to happen. :no:


can you keep that secret to yourself???


----------



## craigwbryant (Jan 14, 2013)

Got more work done today (weather, work, wife, and kids all cooperated to let me work in the shop). All curves are cut now, which feels like an insanely huge accomplishment for something so trivial. The interior curves in the feet were the toughest, but looking at the piece mocked up they really make all the difference as the little bit of light coming through them lightens the whole thing a bit. Definitely liking how it's taking shape. This week's task is to order the wood for the top. Going with quartersawn lumber for the top, found a great supplier here in the area, so order should go in on Tuesday and be able to pick up Saturday. The end is coming nigh!














Sent from my XT1080 using Tapatalk


----------



## Cherryville Chuck (Sep 28, 2010)

Craig there are lots of woodworkers who think the curve has to be perfect and symmetrical and go to great lengths to get that (literally at times with great long pendulums for marking or routering). You recognized that it only has to look perfect, it doesn't actually have to be perfect and there is a lot of time and effort between the two. Yours looks perfect whether it is or not and that's all it needs to be. That's a fine effort so far and I'm looking forward to the finished item.


----------



## Shop guy (Nov 22, 2012)

Looks very nice. Don't forget pictures of the finished table.


----------



## craigwbryant (Jan 14, 2013)

Cherryville Chuck said:


> Craig there are lots of woodworkers who think the curve has to be perfect and symmetrical and go to great lengths to get that (literally at times with great long pendulums for marking or routering). You recognized that it only has to look perfect, it doesn't actually have to be perfect and there is a lot of time and effort between the two. Yours looks perfect whether it is or not and that's all it needs to be. That's a fine effort so far and I'm looking forward to the finished item.


Thanks for the kind words. Lots of first in this project for me, so getting really stoked about it. Will definitely post more progress photos as things move forward with assembling the top!


----------



## craigwbryant (Jan 14, 2013)

Shop guy said:


> Looks very nice. Don't forget pictures of the finished table.


Thanks, I definitely will get them up!


----------



## DesertRatTom (Jul 3, 2012)

I really like that design. The curve design works against the straight parts in a really great way. I can visualize it and it looks great. What kind of finish do you have in mind?


----------



## craigwbryant (Jan 14, 2013)

DesertRatTom said:


> I really like that design. The curve design works against the straight parts in a really great way. I can visualize it and it looks great. What kind of finish do you have in mind?


I havent really gotten that far. It's solid red oak. I actualy think the natural color of the wood suits it very well. Maybe it's just me, and I'm sure I may change my mind when I get the top built and on it, but the whole thing has this "light" feeling to it that I don't want to ruin with a dark stain. I don't have any real fancy finishing equipment (no spray guns or anything) or no real experience with finishing much beyond brush/wipe-on polys. Do you have any recommendations?


----------



## DesertRatTom (Jul 3, 2012)

Not that experienced with finishing, which is why I asked. I once did a dresser of birch with rubbed in linseed oil that I polished really well that kept the lightness, today I'd probably add several light layers of lacquer and a final layer of highly polished paste wax. I'd probably plane the top and do a final pass with a scraper, which will make a glassy surface you can't get with sanding. Don't like a sanded surface very much, and scrapers give a final illusion of great depth.

I have several Wood River V3 planes including a #6 that I love using. The longer planes give you a flat surface that is glossy because they slice clean through the wood cells instead of raising fibers as Sanding does. Takes careful setup and then some learning time to use a plane, but the result always surprises me and I do love the sound they make.


----------



## craigwbryant (Jan 14, 2013)

Got the top assembled, cut the mortises and tenons for the breadboard ends, drilled holes in the BB and marked holes for drawbore pegs last night. Tonight's task is to drive the pegs...


----------



## Stick486 (Jan 4, 2013)

awwww man that is looking so good..


----------



## Cherryville Chuck (Sep 28, 2010)

That looks great Craig. Remember to cut slots for the pegs on the tenon so that the top can expand and contract without cracking.


----------

