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Round Tenion on Square Spindle

kywood50's picture

Question, building new open stairs for our home, design includes square spindles that support the hand rail going through the outer edges of the treads.  Treads are  1 and 5/8 inch thick white oak and so far no luck making one inch square hole for spindles to go through the tread and entend below. Currently trying one inch round hole and corner chisel to make the square hole.  One inch morticing chisel did not work, could not push through the oak.

If this does not work then thinking of using 3/4 inch round hole in tread, cutting the square spindle into two pieces and making round tenion on the ends to fit into round hole in treads.  The spindles are 1 inch square white oak. Also would need the round tenion to end in a flat surface so the the spindle will fit flush witht the tread giving the appearnce the the square spindle goes through the tread ( the other part of the spindle would be attached to the bottom of tread). Is their a tool to make round tenions that I need from the square spindle?

Other suggestions on making square one inch hole?

Good news is that six posts were replaced yesterday as part the stair project.  This is a post and beam house ( I think it is a Lindal Ceder Home from 1970's), removed six white ceder posts and replaced them w/ 3 1/2 X 4 inch black walnut.


joinerswork's picture

(post #99488, reply #1 of 6)


Many old staircases have the balusters dovetailed or mortised into the end of the treads, with the joint cut from the end, and covered with a return molding matching the nosing on the front edge of the tread.

If this isn't an option, you may want to look at using a 3/4" or 1" heavy duty plug cutter to work the self dowel on the end of the baluster.  You will need to tilt the table of your drill press to vertical, and clamp a fence to align the baluster in the proper position.  I've done this to work 2" long, 1" dia round tenons on the end of the front legs for a set of Philadelphia Queen Anne chairs. Nip the shoulders square on the table saw.

Alternatively, you can chuck the balusters in a lathe, and turn the tenons.


Ray Pine

BG's picture

(post #99488, reply #2 of 6)


Interestingly, on The Woodworking Channel the router guys made round tennons on the end of tapered legs for what they called the 'Swiss Chair'.  They had a simple jig with a 1" plug screwed into the top of the spindle....and then just ran the router bit around the stock while the wheel in the bit rode on plug.

Ragnar17's picture

(post #99488, reply #3 of 6)

... square spindles that support the hand rail going through the outer edges of the treads.  Treads are  1 and 5/8 inch thick white oak and so far no luck making one inch square hole for spindles to go through the tread and entend below...

I'm having a hard time understanding why you would want the bannister to actually pass *through* the tread.  Am I understanding this correctly?  If the bannister passes through the tread, what supports the bannister?  Is it face nailed or pegged to the stair stringer?

If you want to give the *appearance* of the bannister passing through the tread, you could always attach a fake "tail" to the underside of the tread.  This would greatly simplify your installation problems.

As the previous post mentioned, traditional open string stairs often featured bannisters with a dovetailed end that slid laterally into the end of the tread.  This joint was covered by a "return" to the tread that was installed subsequently, thus eliminating the exposed end grain of the tread.

This approach would allow you to keep the bannister in one piece, but it would likely require lots of modification to your existing treads.

Lataxe's picture

(post #99488, reply #4 of 6)


There are a few standalone tools about that will cut round tenons on the end of square stock (have a look at the Lee Valley site for 3 variations of "tenon cutter" at various prices).

However, none of them make a right angle shoulder between the tenon and the square stock.  Luckily there is a tool that will make such a (very accurate) round tenon on square stock, the only drawback being you need a lathe to use it.

The tool is a 3/8 inch parting chisel mounted in a hood-shaped caliper that allows you to set an exact gap between the cutting edge of the parting tool and the caliper nose.  After roughing the end of the square stock to approximately round (but oversize) you use this tool to finish the tenon to the exact diameter you've set on it.  This also leaves a right angle transition between the round tenon and the square stock.

I was taught the use of this tool by Mike Abbot, on a greenwood chair making course.  The tool is used to make round tenons to 1/10 of a millimetre accuracy on the rungs of such chairs.  If you have a lathe, you can use the tool to make a very accurate tenon in about 2 minutes per tenon.

Robert Sorby makes the best version of this caliper tool.  See the Lee Valley site again (item 85B62.01 - Sizing Tool). You can probably buy it from many other Sorby resellers in the US.


Edited 5/18/2006 6:25 pm ET by Lataxe

kywood50's picture

(post #99488, reply #5 of 6)

Thanks for all the great help, I will post some pics soon.

thanks again,

mufti's picture

(post #99488, reply #6 of 6)

               Hope this is not too late and that you have a router.

     Take some 3/4 in MDF or similar about 12ins square. In the centre drill a hole to just allow a spindle to push through. Do that and clamp the spindle in your bench vice so just under half the tread thickness pokes through and the MDF  sits flat on the bench top.

     Put a straight cutter in your router and sit it over the spindle so the bottom of the cutter just touches the centre of one side of the spindle. Without moving anything fasten the router base to the MDF.

     You should now be able to rout the tenon by slowly rotating the MDF as you lower the cutter. I would set the depth stop to avoid accidents. Good luck!