Bannister back chair – preliminaries II
Many older bannister back chairs have straight rear posts. Ugh! You probably won’t want to sit for long in one of these. An appropriate description of the experience would be discomforting. So we’ve opted to replicate one of the types that incorporates a slouch angle in the rear post.
The long excepted method of creating this type of rear post is by cutting a blank that includes the angle, counter-weighting the blank, turning the upper portion of the post, then sawing away the waste to reveal the final shape. Some chair makers create rather sophisticated counter-weighted fixtures when making multiple posts as this allows for the best yield in stock. One of the drawbacks of these fixtures is that they increase the overall length between centers. The bulk of these posts are between 45″-50″, which is, already, a “stretch” for most lathes.
Curmudgeons are notorious for not, necessarily, believing everything they read. So we decided we’d do a little testing before we jumped right into the “good wood.” Who knows, we might find a short cut, maybe something like the fabled “Northwest Passage.”
So we cut our blank and counter-weight:
We mounted the blank without the counter-weight. Our test lathe is an extended Powermatic 35-20, plenty of weight, plenty of power. Our thinking was that, as in turning off-set legs, we might be able to turn the “out of balance” piece at a slower speed. The effective diameter we’re working with is about 16″, so an rpm range of 350 to 550 would seem to be a reasonable starting point. In short order, we realized that we were fighting deflection as well as an out of balance problem. So much for that “short cut.” The counter-weight was mounted.
A word of caution here. Having been on the receiving end of “things coming apart” on the lathe, please insure that any counter-weights are securely fastened. For this trial, we simply screwed the weight into the waste stock. However, the weight could be “rubbed on” with glue, fastened with banding or in any of a number of other ways. My guess is that we’ll screw mount and throw a couple of wraps of “hundred mile per hour” tape on it, just for peace of mind.
Needless to say, the mounting of the single counter-weight greatly improved stability. After some discussion, we agreed that by mounting two additional weights at 90°, right and left of the existing weight, the balance might be further improved. We may give this a try, “just for fun”, as we’re not working to any particular deadline.
It should be noted here, that on most of the rear posts (on original chairs) there is a cylindrical section immediately above the lower, angled section of the post. When I first noticed this feature, I wondered if some of these original posts might have been mortise and tenoned together (thinking that this would greatly simplify the task of turning). So I conferred with my friend, Jack Plane, www.pegsandtails.wordpress.com and he assured me that only late 19th and 20th century replicas (of the “less expensive” variety) were ever constructed in that fashion. The “real McCoys” were turned in one piece. It’s clear that the cylindrical sections on the original posts was a roller path for some type of “steady rest” device. Such a device will shorten the effective length and greatly reduce deflection.
More to follow.
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