Author Topic: Carving therm feet  (Read 10015 times)

steveb

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Carving therm feet
« on: January 10, 2007, 01:48:29 PM »
The famous card table by John and Thomas Seymour, seen for example on page 340 of Robert Mussey’s book, contains “therm” feet that are carved from the solid leg. I am not certain how to carve those therms in a way that is as symmetrical and perfect as theirs. I assume that I have to build some type of jig that guides the chisels. Can anyone suggest a reference on how to make those therms, or give me some guidance on how to make and use the jig?

Wiley Horne

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Re: Carving therm feet
« Reply #1 on: January 17, 2007, 05:04:47 PM »
Steve,

I'm a newbie, but your request has been up a long time without answer.  So I'll relate my experience, which consists of having done 1 practice project with therm feet and other Federal details.  I was trying to learn stringing, inlay, therm feet, cockbeading.  If it is practical for you, sign up for a course with Rob Millard or Garrett Hack, or someone else who brings background and experience to the project.  With that caveat, here goes....There is a link below to my practice project.  I did it all with handtools, but you might make good use of a band saw, table saw, and/or router.

When I got started, it seemed to me that shaping the profile would be the most critical part of the therm foot.  But as I got into it, I realized that the actual shaping is not what is most difficult.  What was most critical was the definition of the arrises and reference lines which terminate the curves--if you get those right, the actual shaping will follow naturally.

I strongly suggest making 5 (at least) leg blanks, so you can use one as pure practice, and can discover all the keys and pitfalls for yourself.  As soon as you have your leg blanks finished, you begin the definition of the foot by sawing the upper limit of the shoulders--this is where your taper will terminate.  Sawing these shoulders is scary, because all errors are doubled.  So these are precision cuts.  I used a hand saw, but you might want to use the miter gauge of a table saw.  For example, if the leg is 1-5/8" square, and you want the leg to taper to 7/8" square right above the therm foot, then you want to make a 3/8" depth cut girdling the four leg faces, to define the top of the foot--you're going to taper to this point.  Suggest making that cut a hair less than 3/8" to allow for final detailing of the leg after you complete the tapering.  You can take a little more off, but you can't put a little more back on.

Now saw the tapers in whatever way that suits you, and clean them up.  At this point, you have to decide whether you want to string and inlay the legs next (I'm looking at p. 340, Mussey), or whether to make the therm foot next.  To make the foot, the next thing I suggest is to use a handsaw, table saw, or router to cut the step between the upper bead and main body of the foot.  Cutting that step will define the lines terminating the upper curved surfaces.  If, instead, you immediately start carving or rasping, the whole thing will soon be swimming in front of your eyes, because you're trying to cut your reference lines as you go.  Once you cut the step, then the upper lines of the foot are defined, and it's a matter of rasping and filing and 320g paper to form the upper surfaces.  I found that an Auriou 14-grain rasp (it's quite fine) was very useful for this part, followed by 2-cut and 4-cut files (European grading, e.g., Grobet).  I think you will be able to form the curves by eye, but as an aid you could make a template right off your drawings, and use the template to check your progress as you go.  By the way, if you don't want to invest in expensive rasps, you can do the same thing with PSA sandpaper on the right sized sticks.  Also, I suggest masking off the bottom of the legs right above the therm foot, to save them from stray tool marks or sandpaper marks.

I found the lower surfaces as tricky as the upper ones, especially the increasing curve into the bulb of the foot.  Lay the curves out, and I suggest using a coping saw or coarse rasp to rough away most of the waste.  When you start getting in range, shift to spokeshaves--what the shaves do for you is maintain smooth curves and neat edges for the lower foot, because these edges need to curve up smoothly and meet the edges of the bulb very precisely.  The shaves give you enough control to do this.  The shaves I found most useful were the LN small bronze shaves.  The curved one has about the correct radius for the fastest part of the curve, and the straight shave is useful for the lower foot.  The shave may leave a slightly rough surface right under the bulb, because you're shaving end grain in there.  Detail these lower surfaces with 14-grain rasp and files and 320g as before.

Well, as I said, I'm a newbie myself, but hopefully some of the above will help you focus your own thinking.  Take a class if it is at all practical, and get the benefit of expert advise.  That way, you will also get the best advice on the precise sizing of the legs and details of the foot--this is very difficult to scale from pictures.

Wiley

P. S.  Having a tough time posting a photo here.  My practice project can be seen here:

http://www.traditionaltools.us/cms/index.php?name=coppermine&file=thumbnails&album=35

steveb

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Re: Carving therm feet
« Reply #2 on: January 17, 2007, 10:58:41 PM »
Thank you very much for your very detailed advice, which I plan to follow. I have some experience with inlaying, etc, but not much with the use of spokeshaves and rasps. I will give it a try, starting with six legs.

Steve Bodner

chamfer

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Re: Carving therm feet
« Reply #3 on: January 19, 2007, 01:21:01 AM »
Greetings,

Since Wiley has provided such a substantial answer to Steve's question, I hope people won't mind if I steer this thread toward a more historic note.

When I first ran across the word "therm" associated with furnituremaking, I was left scrambling to gain some idea of its meaning. In the process, I ran across some information which astonished me. Everyone else may already be familiar with it, but I think it worth passing along to those who may not be. I find it interesting in its own right, but also because it may shed some light on an historic intersection of technology and design.

First, though, a couple of brief definitions. The earliest usage of therm seems to be associated with upwardly/outwardly tapering  rectangular pedestals to display statues - namely busts. At some point, but certainly by the latter part of the eighteenth century, therm also became associated with similarly tapering rectangular legs and feet of furniture.

As evidenced by the thermed feet shown by Wiley, these thermed legs and feet (most commonly used in classical revival furniture, such as Adams and Hepplewhite) were not necessarily just simple tapers. This is further demonstrated by the examples of thermed legs and feet from a 1792 cabinetmakers' price list - which I'm going to attempt to attach an image of. Unfortunately not a high quality image, but I hope the content makes it worthwhile.

In any event, what really caught my attention was the following quote from Penderel-Brodhurst and Layton's _A Glossary of English Furniture of the Historic Periods_, c. 1925:

  "THERMING. - A process in use towards the end of
the eighteenth century ..., by which the legs of chairs
and tables were thermed or tapered, by means of a
lathe provided with a cylinder about six feet in
diameter, on which the legs were placed and turned
down one side at a time. ... "

I've looked into this a little bit, but haven't been able to lay my hands on a couple of critical resources. However, in studying some small illustrations, it appears that a large number of leg blanks were squared up and fastened around the circumference of the large cylinder so that the details could be "turned" on the exposed surface of the leg blanks. Each leg blank would then be repositioned to present a new surface, and the process repeated until all four surfaces were shaped. While the resulting surfaces would be arcs rather than straight, the large diameter of the lathe cylinder would produce such slight curvature that they would pass, visually, for straight.

In addition to being quite interesting in its own right, I began to realize that this was an intriguing confluence of  technology and design. I've come to suspect that the "mass production" technology of therming lathes may have played a role in the popularizing of thermed legs/feet used in classical revival furniture styles.

I'd be interested in other people's thoughts on this topic.

Don McConnell
Eureka Springs, AR

pampine

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Re: Carving therm feet
« Reply #4 on: January 19, 2007, 10:51:16 PM »
Wow, Steve, thanks for asking this question. Wiley, your table is still incredible. Don, who knew that therm feet would get us to 6' diameter lathes and the like? That's such a sensible way to make matching legs, several sets worth. What kind of lathe would handle this type load?

Pam

Wiley Horne

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Re: Carving therm feet
« Reply #5 on: January 20, 2007, 10:48:36 AM »
My Goodness, what an astounding piece of information!  Big lathes that turn these complicated legs?!   Great post, Don. 

As an aside, I have read several places where machines came in early in America, whereas in England hand work remained the norm for much longer.  Don's post is making me wonder about this stereotype--sounds like the English machine tool industry was quite advanced quite early.

Hey Steve, never mind that rasp+shave business.  What you need is a big lathe, yada yada.

Thank you, Pam.

Wiley 

chamfer

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Re: Carving therm feet
« Reply #6 on: January 20, 2007, 02:32:41 PM »
Pam, regarding your question about the type of lathe which would be used for therming legs, I wish I had an appropriate illustration. Unfortunately, I don't, and it's been a while since I last saw one. So, I will have to go by memory - always a shaky proposition.

In any event, as I recall one of the illustrations, the cylinder was built around a stout shaft, and each end of the shaft rested on a brick pillar of the appropriate height. In other words, the brick pillars effectively served as "pillow blocks." The method of fixing the leg blanks to the cylinder was not illustrated in any detail, but I assume any clamping fixtures would have been adjustable to different lengths. From there, my memory gets even hazier, but I think there was some kind of line shaft arrangement for motivating the cylinder. Probably water driven early on, possibly steam driven later. I don't recall any details of tooling, such as tool rests, lathe tools, etc. The overall impression was fairly industrial in feeling, though.

It is my understanding that at least one edition of Bergeron's treatise on turning discussed (and possibly illustrated) therming lathes. Additionally, a couple of early 20th century German publications apparently discussed them. Unfortunately, I've not been able to get hold of any of these publictions, though I have made quite a bit of effort. In any event, these references and the British one I previously mentioned, give some indication of an awareness of this technology in France, Germany, and the U.K. I've yet to see any indication of such an awareness in the U.S.

There remains some question as to how common this technology was. The presence of rates to be paid journeyman for therming legs in the price lists of the 1790's indicates that some (many?) legs were thermed "by hand." Alternatively, the fact that they seem to have been paid extra for this job may indicate that thermed legs were more typically supplied to the journeymen. I think this merits further research.

Wiley, I agree that this may be a case where the U.K. adopted machine technology earlier than in the U.S. Maybe British firms were supplying thermed legs to U.S. cabinetmakers? I still think the stereotype that machines were more quickly and commonly adopted in the U.S. is largely true - primarily because of a relative lack of skilled labor in a rapidly growing and expanding economy.

Now for a brief return to the question of technique. I've never done thermed legs or feet, so bring this up purely speculatively. In thinking more about the therming lathes, I've begun to wonder if there would be any advantage in affixing the four (or six) legs together to work two (opposing) surfaces of all the legs at the same time? Seems there might be some advantage in working across a broader surface, though I'm sure this would largely depend on the pattern. Also, I'm thinking that floats might be used to some advantage in this process. (disclaimer: Though I mention floats because I honestly feel they might be useful, I do have a commercial interest in their sales.)

Glad to see this has sparked some interest.

Don McConnell
Eureka Springs, AR

pampine

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Re: Carving therm feet
« Reply #7 on: January 20, 2007, 09:46:04 PM »
Don, with 18.84' circumference, I'd say there's room for multiple sets of legs to be thermed/turned at once. Unless there's some reason, perhaps a maximum weight, for more sparsely populating the lathe.

In mucking about, I found a couple or three huge lathes that probably could handle this job, even though they're pattern makers' lathes:

1) http://www.owwm.com/PhotoIndex/detail.asp?id=2944
2) http://www.owwm.com/PhotoIndex/detail.asp?id=585

Thanks,
Pam

Wiley Horne

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Re: Carving therm feet
« Reply #8 on: January 20, 2007, 10:21:18 PM »
Don,

I'm going to start a separate thread in Hand Tools on general woodworking uses of plane floats.  I'm fascinated by the tools that C&W offers, but have never even had one in my hands.

Wiley

msiemsen

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Re: Carving therm feet
« Reply #9 on: January 21, 2007, 10:48:45 AM »
Interesting Stuff,
I believe that I could do this on my lathe with only a 20” swing. If my calculations are correct the height of the arc on the face of an 1½” wide leg would be less than 1/32 of an inch. It would be possible turn 20 legs at 1 time on a 20” swing. Draw it out full size and see!
It would probably be easier to make 4 legs using the bandsaw, spokeshave, gouges and rasps than to build the drum to turn 4 legs.
Mike

 Here is my research on the word therm.

From Wikipedia:
therming - mounting a carrier between centers, and then mounting the small workpiece(s) to the carrier, so that the axis of the headstock/tail-stock does not pass through any of the workpieces, and each workpiece gets cut only on one face. As noted in Wood-turning Methods by Mike Darlow, the etymology of the term "therming" comes via a corruption of the name of the Greek god Hermes, who was often represented as a statue set atop a plinth with a construction characteristic of thermed work.


From Word Detective:
Dear Word Detective: To "therm" a spindle, or a set of spindles simultaneously, requires an offset jig in the lathe. This is called "therming" a spindle. What is the etymology of the word "therm"? -- Arthur L. Duell.
The sort of "therm" you're asking about is not, I was surprised to learn, related to the Greek "thermos," meaning "hot," the root which gave us "thermometer," "thermostat," "hypothermia," "thermal underwear" and "Thermos" brand vacuum bottles.
A "therm" in furniture design is a square or rectangular leg that tapers toward the bottom, also called a "taper" or "spade" leg. The earliest appearance of "therm" in print found so far was in the early 18th century, but the history of the word (as well as the design principle) harks back at least to Ancient Rome.
The truly odd thing about "therm" is that it appears to be a mistake, a misspelling of the word "term." In this case "term" is a shortening of the name of the Roman god Terminus, deity of boundaries and landmarks ("terminus" is also the Latin word for "limit or boundary"). Statues of Terminus apparently traditionally consisted of a bust (just ol' Termy's head and shoulders) set atop a tapering pillar, so that the god would appear to spring up from the base of the pedestal. The word "terminus" or simply "term" came to be applied to the style of the tapering pedestal itself, and eventually even the lowliest table or chair could have "term" legs. Just how the word came to be spelled "therm" is a mystery, but it may have been through a mistaken association, much later on, with another deity, the Greek god Hermes.
Mike Siemsen
Green Lake Clock Company
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msiemsen

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Re: Carving therm feet
« Reply #10 on: January 23, 2007, 06:08:21 PM »
Here is a drawing of a bust of Terminus, I can see the connection here also to where the feet came from.  A 6' diameter drum could easily hold 75 legs 1 1/2 inch thick. So who is going to try it?
Mike
Mike Siemsen
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pampine

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Re: Carving therm feet
« Reply #11 on: January 23, 2007, 09:45:27 PM »
I've only got a little (36" long) cobbled-together-by-hand lathe that's packed up for the new workshop build, but I could see trying to turn 5 or 6 legs with a stronger motor. Or maybe this will convince me to build a big pole or treadle lathe. Maybe this summer?

Pam