Replies

1. 
   woodpeckerhead | Jan 27, 2005 08:32am | #1

   Well, Stewart, you have an interesting question there.  How does one make the buttprint in a chair seat.  Yes, indeed.  Well, I mean, there does seem to be something, let us say, intentional about those nice symmetrical indentations that you so aptly call "buttprints."Instead of getting right into tool-talk, let's savor this a bit.  We need to understand the fundamentals.  First of all, you may not be aware that buttprinting is not a one-size-fits-all proposition.  Buttprints are not unlike fingerprints.  Or snowflakes.  Well, here's my point: It doesn't matter if you have identical twins, God made every butt unique.  You may have read about the case where two medical students were accused of making photocopies of their butts on a hospital Xerox machine.  They denied it of course, but the prosecutor brought in an expert on butts.  The expert took actual photographs of the students "in the buff" so to speak, and he matched them up, point by point, pimple by pimple, with the black-and-white copies found in Xerox machine.  Here's the rule: 13 or more points of identification means there can be no reasonable doubt.  That's 13 on both cheeks combined.  Well, I digress.

   You know Stewart, this butt question has been raised by woodworkers for many generations.  Back in medieval times, they didn't actually make buttprints in chair seats.  They figured after a few hundred years of use, a chair will wear down to the desired shape.  In this age of instant gratification, where you can just log onto the old worldwide webster and ask any silly question that comes to mind, hain't nobody gonna wait 300 years for a seat to get comfortable.  So this brings us back to how it's done in modern times.

   If you're willing to take any old reasonable facsimile of a typical butt shape, you can buy a bunch of tools.  You can get a couple of scorps, a travisher, an adze, a set of scrapers, an angle grinder, a random orbit sander, and a CNC guided router.  But there's a secret method used by all the great chairmakers in history, when a custom chair is needed.  You can go all the way back from Maloof to Eames to Chippendale, and you'll see this same technique.  First lock the door for some privacy.  Get a spray can of adhesive 77 and spray the back of your butt thoroughly.  You'll need about 6 to 10 sheets (depending) of 40 grit sandpaper cut to fit your butt.  Apply these one sheets at a time until your butt and upper back legs are covered.  Allow the adhesive to dry completely then trim the excess paper.  You will then have a form for sanding the seat hollows, the "butt print" as you call it, and from there on it's really just a matter of twisting at the hip for a few hours until the seat is perfect.  It's great exercise too, and you can do it at work, in your car, or my gosh just about anywhere you can imagine.  Some of your clients may object at first, but they usually relent when you explain that all the English royalty do it this way. 

   If you experience some sensitivity at first that's to be expected.  If you or your client encounters unexpected bleeding on the workproduct, check to be sure the grit on the paper is face "out," toward the seat.  By the way, a little blood on mahogany or black walnut won't be a problem, but if you're working with soft curly maple or aspen, check the grit orientation before you start.

   Stewart, now you know more than most folks who visit this website about the finer points of seatmaking, or derrierrerie as the French call it.  Glad I could impart this rarefied bit of woodcraft information to the next generation of chair "artisani," as it were.  Please don't be bashful if you have other questions.  After all, there was a time when even I knew less about woodworking than the robotic arm at Sauder!  And that time was called preschool.

1. 
   georgek | Jan 28, 2005 12:19am | #7

   This was my best lunchbreak yet! Almost chocked on my sandwich!LOL

2. 
   AlbionWood | Jan 28, 2005 08:53am | #9

   Now that's funny, I don't care who ya are. A gin-u-wine expository masterpiece, yessir. Taunton should run it in the magazine.Now I gotta think up some more questions for you to answer!Wish I made them kinda chairs, I'd like to be known as a derriereriste.
   "Everything should be made as simple as possible, but no simpler."  A. Einstein

   http://www.albionworks.net

2. 
   UncleDunc | Jan 27, 2005 10:49am | #2

   >> ... the butt imprint,(for want of a better term) ...

   I rather like the German word, Sitzmark.

   If you have access to a Windsor chair, you could take some measurements. Mike Dunbar's book on making Windsor chairs has some guidelines, I would think. Your local library may have it, or other books on chair making.

1. 
   StewartL | Jan 27, 2005 02:19pm | #3

   Thanks,

   I will try to get a look at a windsor chair book.

1. 
   tms | Jan 28, 2005 07:31pm | #11

   This type of seat is found elsewere in the world as well. Think about tractor seats.In fact, Thos. Moser makes a number of barstools, and office stools with what he calls carved "tractor seats". You should look at his catalog. He also has published a book of his "Measured Shop Drawings". Good stuff.Tom

3. 
   BillLindau | Jan 27, 2005 04:01pm | #4

   Stewart, I too have studied butts and how to best accommodate them with a seat. The easiest way I have found to get the right "depression" is to sit in pile of sand. If you can arrange the pile in a shallow box and place it at roughly the height of a chair seat, you get the most accurate impression. It works best to sit down lightly and wiggle ever so lightly. Making the concavity large enough to fit the "biggest butt" doesn't take away from the comfort of those who are not as well endowed. The template that I use looks like a tulip. You want the front of the chair to receive the bottoms of the thighs as well, even when they are spread apart a bit. Let me know if you want more description or even a picture of a chair in progress. Bill Lindau

4. 
   douglas2cats | Jan 27, 2005 04:08pm | #5

   Stewart -

   I'm not positive, but I'm pretty sure "Woodshop Jigs & Fixtures" by Sandor Nagyszalanczy shows a jig for cutting out curves like you need. That might be the way to go if you need to do a bunch of chairs. If you just need a couple and don't want to do a full blown jig, I remember seeing a magazine article years ago (dont remember which mag or issue) that used a router and did something like the following to rough out the seat curves. After this I think they just switched to a RO sander or grinder to smooth things out.

   I mentally filed this away thinking I might have a use for it, but so far haven't had a chance to try it. To the best of my memory, it went something like this:

   1-Determine the radius curve you want on the buttprint.

   2-Cut 2 hardwood guiderails for your router. They need to be 2 times the height you need to let you cut the radius arc in them plus enough extra to leave you some solid wood at the bottom of the inside curve pc. Make sure they're the same length, and mark the midpoint of the length onto the rails on all 4 sides.

   3-Lay out the guiderails for holes to attach either directly to your router base or to a 1/4" ply sled with a hole in the middle for the router bit.

   4-Mark the arc on the guiderails and cut them on the bandsaw, staying exactly on the line.

   5-Sand the curved faces smooth on all 4 pcs

   6-Attach the outside curved parts to your router or sled. Lay the inside curved pcs onto your seatblank, lining up the mid-length lines with the center of where your buttprint needs to be and spaced to match with the spacing of the rails on the router.

   7-Attach screws through some scrap rails into the ends of the bottom curved rails to lock in the spacing, then clamp this whole affair to your seatblank at the middle (back to front) of the buttprint.

   8-Set the router onto the seat/rail setup so that the center of the router bit is at the midpoint line and zero the router bit to the seat surface. Then from there, set the bit to project beyond that by the depth you want at the center of the buttprint.

   9-Dont start your router until you slide it to the side and the bit clears the seatblank. Then power up and slowly slide the router through the curve.

   10-Unclamp, then reposition the seat-mounted section for the next cut, then clamp and repeat. As you work outward from the middle of the buttprint and get closer to the edges, start backing off the depth of the router bit so that you get some front to back curve as well.

    

   I love the smell of sawdust in the morning.

5. 
   JeffHeath | Jan 27, 2005 10:15pm | #6

   stewart

   Lots of good advice here, and I would like to add, if someone already hasn't, that if I were you, I'd make another seat out of something cheap like poplar, and experiment on it, instead of your finished seat blank.  When I design a new chair, I always make it first out of cheaper stock that I have lots of, which in my case is poplar.  Once you get it right, and have actually sat in it attached to the chair, you know you've got it right, and can duplicate your work on the final blank.

   Jeff

1. 
   StewartL | Jan 28, 2005 04:18am | #8

   Good tip! My philosophy is experimenting on the good wood and living on the edge. Actually I will take your advice and use some poplar. I was able to order the Michael Dunbar book through my local library.

   Much appreciation.

6. 
   WillGeorge | Jan 28, 2005 03:37pm | #10

   I am at a loss for making the butt imprint..

   I think it was solved by the woodworker that came up with upholstered chairs?