From the side and underneath.   This test handle originally had a 1/2" notch under the handle to clear the fingers, but that wasn't enough, so I increased it to 3/4".

Here I'm marking the 3/4" notch in the edge of the brace.   The cross brace is 10" long so the center is 5" and assuming about the same curvature in the notch as in the hand hole, I would curve the ends of the notch.   I allowed 3-3/4" for the length of the oval hole and notch.

Marked the ends of the notch and the cut along the bottom (pic shows brace upside down).  

Here I'm using a socket to draw the curve at the end of the notch.   I find sockets are great for drawing curves like rounding off corners etc.  
Another way to do this is to clamp two pieces together and drill 1" holes in the center line at each end of the notch, then saw between outside edges of the holes.   Seems like I did that somewhere.

Notch drawn.   Now just jigsaw it out.

Here I've marked the two spots on a stool top for the 1" holes.   I'll drill two 1" holes then jigsaw out the remaining center.

All holes drilled and notches cut.  

Close up of a stool top with it's hole cut out.  

Notches cut out in braces.  

I used a roundoff bit and the router table to round the edges of the holes and notches.   The stool tops showing the edges of the oval holes rounded, ready to sand.  

Stack of cross braces with notch edges rounded, ready to sand.  

I am going to use biscuits to hold these together, here you can see all the edge slots are cut.  

All parts for one stool, layed out the way I marked the biscuit mortises and cutting the slots (mortises).   I found a horizontal center line through the oval hole, then marked a parallel line 3/8" above it, even across the aligned end pieces.   The 3/8" is the distance from the edge to the cut on my Dewalt biscuit cutter when on a flat surface.   Then I marked the position of each biscuit with a little tick mark.   I aligned the brace with the stool top and copied the tick marks, same for each end of the stool.   Here is a little more detail about cutting slots in flat surfaces.

I am going to engrave the name of each of the 5 small children in the family in his or her stool.   I wanted to engrave each child's name twice on each top so no matter which way it faced, the child could read their name, hence two setups for each name/top.   Here I am trying to set up the templates, the problem is each name requires a different setup to hold the template, it's supporting blocks, and the piece being engraved.   Each name has different number of letters (Zachary to Ian), each letter is proportional spaced (different widths), and I want the names to be centered in the top, so each name is a different setup.   Note the template is not attached to it's support blocks, the support blocks aren't clamped to the table, and the workpiece isn't clamped down either, lots of work to do, and redo for each of the small children.   The template is fixed length so I use extra letters as spaces (on left).  

The Kluge I came up with to engrave the stool tops, so far I have been really disappointed in the SignPro.   The 1x4 across the top is attached to a fixed board on the right holding the right end of the SignPro, a slider on the left holds the left end of the SignPro and allows replacing letters when moved to the left.   Two clamps hold the Kluge down, two more (foreground) hold the work piece (stool top).

The left end of the Kluge, allows the left end of the SignPro to be slid back separately from the rest of the SignPro, so letters can be changed without unscrewing the entire SignPro.   The slider unit consists of a 1x4 with slot, glued to a board that holds the end of the SignPro.

Here it is open for changing letters, note the rubber band, it needs something to hold it together so the letters don't fall out when the end isn't on.  

A little bit clearer pic of the slider.   You can see the 1/4-20 knob that secures the slider to the Kluge, also note a 1/4" guide pin (dowel) that keeps the slider aligned.  

One of the stools glued and clamped.   For pics of exactly how the biscuits are glued go to: Biscuit Gluing.

One of the assembled stools, with edges rounded, ready to sand.  

A shot underneath showing the crossbrace with handle slot.  

Stools sanded.  

Henry's after sanding, ready to fill in the engraving with paint.  

Right here a catastrophe occurred, when I filled the engraved names with paint, it wicked into the wood and looked absolutely horrible.   I wasn't going to have these children looking at and learning to read their own names smeared all over the place so I cut up all the stools for kindling and started over.   Sanding wouldn't take this out, it went deep into the wood all the way to the bottom of the engraving and below.
When I told my son John about it, he suggested I use woodburning (pyrographic techniques) to fill in the names, so I'm gonna give it a try.  
BTW: When I painted Ivy's bed, I filled in the engraving after a coat of paint, the wood was sealed so I didn't have a problem with wicking.   I also think oil in this paint is the culprit here, even though this paint is water based (its indoor/outdoor), it has some oil in it.  

I cut out new tops, engraved them, then did the woodburning.   Heres the second build of tops with the names routed then woodburned.   Note, I haven't cut out the oval handle hole, I did the least work I could until I saw how the new engraving/woodburning technique worked.  

Close up of Ian and Ivy's stool tops.   After I saw out the handle hole, and assemble the stools, sanding will get rid of the engraving alignment marks.

The router table set up to round the corners.  

Close up of the 3/8" rounding bit.  

I did the sawing, engraving, woodburning, marking, and mortise cutting, I had done on the first batch to get to this point.   Here is one of the second batch of stools layed out, ready to glue.   All the cutout work and engraving was already pictured in the previous batch of stools.

A close look at the center brace alignment marks.   The center brace is laying on top of the stool top (bottom view).   Again, note the brace alignment mark, its 3/8" from the actual center line.

Look at the biscuit mortises on one end.   There are 8 nbr 20 biscuits in each stool, it should be very strong.

Glue on a mortise ready for the biscuit to be tapped in.   Note a layer of glue on each side of the biscuit mortise.   You can see a center mark and the brace alignment mark.

Glue on the biscuit ready to clamp on the center brace.   The glue must be about the same on both sides of the biscuit.

Three of the stools, with engraved names burned, glued up and ready to round the edges then sand.   The next pic shows the stools after edge rounding and sanding.

The stools, edges rounded and fine sanded.   Look at preceeding pic to see how they looked before rounding and sanding.

All lined up on our hearth.   You can see the reflection of the firescreen in the top of Ivy's stool, they are all like that.

Beside Grandmaw's spindle table, bought in 1911, second hand.  

Ivy's paint is still not quite dry deep in the letters.  

But Noah's is.  

You can see here, close up, how the burned engraving worked.  

Look at lettering on 3 stools.  

Closer look at Henry's name.  

Ivy sitting on her stool.  

And its handy to just play with!  

The original stool.   Since this one is painted, I probably screwed it together (with glue) then spackeled the holes, sanded it, then painted the whole thing.   I built it years ago, so I'm not sure.

From the bottom, a very simple design, but works and it has lasted well.  

It lives in the small alcove next to the fridge.