Scalloping out a seat

[NastySpill]

How is that tractor seat shape formed in seats and rocking chairs. I've looked for a wide bullnose plunge router bit but can't see anything. Is this hows its done? I was thinking of using said bit to route the edge where it curves up to the seat surface, then just run the router all over to mill out the area's through the middle to create a flat bottom. Clean up with a sander.
I'd like to make a set of stools, so a repeatable template with a router was on my mind. Is there an easier way?

[Wood Borer]

A professional chair maker I know uses an arbortech.

He has the pattern of the seat on a piece of ply to trace the outline and then drills holes to the required depth. He does them in about 3 minutes with the arbortech and then sands them to shape using a sanding pad on an angle grinder.

The shapes are near enough identical on all the chairs.

To do them by hand, you can use a scorp or a curved spokeshave. Sharp tools is the key.

I haven't done them myself but watching the chairmaker was quite impressive.

[LineLefty]

He has the pattern..........on a piece of ply to trace the outline and then drills holes to the required depth.

I've seen a luthier do the same thing to a piece of rock maple for a curved top electric guitar. That is, a pattern, like contour rings on a map with each line indicating a certain depth for holes to be drilled. Tedious to say the least.

On the other hand, the thought of sharpening a scorp to the level required is a pretty scary one. Chain mail gloves methinks.

[IanW]

Nastyspill - there are at least 5 ways I know of doing it, but my favourite for speed and accuracy for a one-off or small set is the little double-radiused scrub-plane I made for the job. The radius of the blade (cutting edge) is a bit tighter than the radius of the sole, so it sticks out from the sole in the same way a regular scrub blade does.
I cut out the seat shape, draw the plan of the scoop-out on the blank, and go at it with the plane. You go cross-grain as much as possible, which removes a lot of wood with little effort. I've made quite a few, now, and it takes me about 20 minutes to get a seat ready for final sanding.
You can be a purist and clean up after the scrub with a scorp and rounded scraper, or do the bulk of it in 2 minutes with a soft, coarse, sanding pad on the angle-grinder (firm touch, and keep it moving, or you'll have some nasty gouge-marks).
The seats look best (and are more comfy) when you scoop them out nice and deep. On the first few I did, I was much too timid, and it looked pretty pathetic.
Haven't got any digital images of adult-sized chairs handy, but here are a couple of high chairs, and the plane wot scooped them.
Cheers,

[AlexS]

I use a similar method to IanW, except that I use a convex spokeshave, sharpened the same way as his plane, to remove most of the waste. Then clean up using a curved scraper. You can actually remove quite a bit of waste with a scraper by working across the grain, then tidy up working with the grain. I've never tried using a scorp, but thought I might try it next time I do a chair.

[IanW]

Alex - I bought a scorp years and years ago, after reading that it was THE chairmakers seat-gouging tool. It's a beast of a thing to sharpen, with its wincey wee mouth, and I never did master it. Once I saw how much wood my little plane can remove in a few minutes, I never persevered with it, and it has languished for years in the back of a very dark drawer! In fact I got it out tonight after reading this thread, and it is easily the dullest tool in my cabinet - no wonder it doesn't work very well!

I'm planning a garage sale of quite a few tools like that, when I get time to sort out my mess. This is prompted by an enforced down-size in sheds. Didja ever hear of anyone DOWN-sizing in sheds??? A very sad affair, but someday I hope to be able to move into something more luxurious.... :(

(And have the time to enjoy it! :) )
Cheers,

[NewLou]

Gidday NastySpill:)

Heres how Masterwoodworker David Marks goes about this kind of Job:

http://www.diynetwork.com/diy/ww_chairs_stools_benches/article/0,2049,DIY_14439_2417962,00.html

...........Hope this helps


Regards Lou

[AlexS]

Thanks for the advice Ian, maybe I won't rush into it.

[NastySpill]

Thanks for all the info. Looks largely like a manual job. Not sure if I have the skills to do this one - only one way to find out! Getstuckinuit!
I had heard that those sculpting blades for grinders pull themselves into the wood and go bezerka carving out a lot more than you had wanted.
NewLou - I like that approach on the link you showed. I might try and make a template to route the profile of the edges. I want a very delicate shape thats a little complex. And as the stools are otherwise very basic, the seat sculpt will stand right out. I'll post a procedure if I think I've come up with something novel.
As I said I want repeatability.

[Scally]

Nastyspill, I was introduced to the Arbotec a couple of years ago while doing a woodcarving weekend with carver John Van Der Kolk and woodworker Neil Scobie.

They are scary looking beasts and can certainly remove a lot of wood quickly.
It only takes a couple of minutes to get over being scared.

Attached is a pic of a stool carved with the arbotec.
The seat is cut to shape on the band saw and a bearing guided router used to round over the top 3 sides.
A template was used to outline the front profile and the edges of the area tobe scolloped.

The large arbotec disc removes timber quickly if held verticle but much slower if you move it over the job like a disc sander.
The little arbotec disc removes wood slower and can be used for tighter curves.
There are sanding disc that will do more finer shaping and get rid of most of the cutting disc marks. They do a great job.

When the seat looks good and is comfortable to sit on, it is time to get out the ROS.

I agree with the other comments that you should carve a deeper shape than you think. We never drilled holes to set the depth but checked the depth of cut and evenness of cut with a ruler every now and then.

It is a lot of fun using the arbotec and you can get things into shape very quickly.

I have seen trays carved with a router and a dishing bit so I can't see why you couldn't do the same thing for a seat althought you might be limited with the depth of cut.

[IanW]

One thing I forgot to mention was the choice of seat material. For the traditional type of 'Windsor' chairs, the Poms used Elm for seats, a moderately hard wood (but not in the same class as Jarrah, etc.) while the Yanks used softwoods such as White Pine (very similar properties to Hoop) and compensated for the softer material by increasing thickness. This allows a really deep seat to be carved, which to my eye looks much snazzier.
I've experimented with various locally-obtained woods, and my favourite, when I can get it in the right sort of sizes, is from that weed, Jacarandah. Because it's technically a hardwood, it doesn't have quite the same problems with fibre crushing that sofwoods have, and holds up in use quite well. It's moderately soft and easy to carve, and very stable.
And the grain is very reminiscent of Elm - stained up appropriately, you'd be hard-pressed to spot the difference without a bit of whittling...
As the above posts attest, there are a lot of ways of carving seats, but the general process is much the same - rough out by the best method you have, then refine, ditto. :)
Avagooday

[NastySpill]

Ok, let me attach a pic of the profile I'd like to replicate. The issue I see is with the centre ridge - its fairly sharp and delicate looking. Also the wood I have in mind for this project is scrap plantation structural hardwood from my brothers renovation. There are a few lengths at ~ 35mm x 110mm. Anyone care to comment on that choice. I've never really done anything with it other than use it for legs?

[IanW]

Nastyspill,
OK, I'll toss in a couple of cents' worth.
First off - the seat profile you've shown doesn't look all that deep, so 35mm thick stock should be plenty deep enough. The ridge up the middle shouldn't present any special problems - draw the saddle on the top of your seat blank and go at it. Also draw the profile of the leg 'dents' on the front, of course, to guide you. Otherwise just do the scalloping by eye, and get the repeats as close as possible. Even if there are small discrepencies when you put them side by side, not even another woodie is likely to spot it when they're set out at the bar. Especially if they're sitting on them! :D
The pronounced rounding over on the underside edge should be very straightforward - I'd go drawknife (or a chisel, if you don't have access to a drawknife), rasp, spokeshave, scraper or sandpaper. If all you had was a good rasp, that would do 99% of it, then clean up with paper.

What do you mean by 'plantation hardwood'? Plantations here or somewhere else? Young fast-grown Ash would be not too tough, but a seat made of Spotted gum might be pretty heavy gnawing - I'd probably be investing in an Arbortech wheel if I was tackling something really hard like that. I've only used one a couple of times, but it seemed to be semi-controllable, and sure wastes wood in a hurry!
Oh yeah, - nearly forgot - make sure you use a non-creep glue like hide glue or epoxy or melamine to glue the seat blanks up. This is one area where PVA glues are definitely out of their league!
Good luck,

[NastySpill]

Thanks IanW. I guess its a case of "easier than it looks / or sounds" I have a friend how can lend me an arbortech wheel. Looks like fun actually.
I have some glue called 956 or 659 or something like that. Sets up in 20 mins, any excess (Nasty Spills) squeezed out foams when you clamp it up, so its just a case of scraping off excess. And glues anything to anything, and is generally stonger that the material you are glueing together - I've been told. Should do the trick. I'll also throw in some biscuits.
By plantation hardwood I mean it isnt (I hope) old growth antique stuff. Its called F7 I think and it used as a lintel above window frames and doors in housing framework. So I assume its from a plantation..?

Thanks everybody for the tips. Time to stop postulating and put tool to wood.

[IanW]

Spiller,
(gotta shorten your pen name, but 'Nasty' is a bit rough when I hardly know you!). :D
Sounds like you're talking about polyurethane glue. I have no experience with the stuf at all, but reading this and other BBs I get the impression that some folk think it's the bees' knees, while others think it's more like their faeces. I tried looking up its properties, and it looks like it would qualify as a non-creep glue as long as the glue-line is very tight and allows no foaming (between the pieces, that is). Someone else out there may be able to advise on this one.... ( :confused: )

ALL glues can be said to be stronger than the wood they are joining, but that statement is often only true if the joint is 'perfect'. i.e. the thickness of the glue itself approaches zero. Most glues fall off significantly in the strength department at the slightest thickening of the glueline (and it looks like polyurethane is a champion for this fault). A good sidegrain to sidegrain joint made with any glue, if stressed to the point of failure, should do so with at least 80% wood failure. PVAs can meet that, but not if they are warm, or the glueline gets a few thou thick.

There'll be a few out there that won't agree with this, but it's a fact that biscuits and splines in a side to side joint are only for alignment, they add nothing to strength, and in fact may decrease the strength of a properly-made joint.

I'm harping on this one a lot, I suppose, because I've made a lot of chairs over the last 20-odd years, for most of which I had to glue up pieces to get wide enough seat boards. Early on, I used PVA, because I didn't know better. Even a few early failures failed to impact on my dull little brain untill I started to delve into the more theoretical aspects of w'working, and read about glues in general. Of course I soon found that others had figured this out long ago. Since I switched to glues like epoxy, resorcinol and hide glue, in this kind of application, there've been no more splintered bums. ;)

Yep, go at it, Spills - the best way to find out what works is to do it. Even if the first seat doesn't win a prize at the local show, the next one will get closer!
Cheers,