Rushton rib pockets

[JClearwater]

Work on my Indian Girl continues as time permits. I looked at a piece of the broken inwale to see if I could figure out how Rushton made the rib pockets. See the attached photos. It appears that they used a Forstner drill bit (or some variation of it) to cut out most of the pocket and then used a chisel to remove the web left between the two holes. My Forstner bits have an indexing point in the center which is not evident on this inwale so maybe the bit used was somewhat different. It's interesting none the less.

There is a discussion about how Morris made their pockets here.
http://forums.wcha.org/index.php?threads/morris-rib-pocket-question.16476/

Jim

 

[Ed Moses]

Jim,

Looking closely at your pics, it appears to me as though the indexing point of a forstner type bit may have been cut out in the saw blade kerf when the double wide inwale piece was halved to make the pair of inwales with rib top pockets. This is technique that we believe Morris employed to make his pocketed inwales.

Ed

 

[Howie]

I'm pretty sure this is how Morris made the rib pockets. Not sure about Rushton...

It's much easier to bore any hole when the bit's 'center indexing point' is biting into the wood - otherwise either the tool or the wood would tend to drift. So it seems to me that the 2 rails started out as a single piece of wood wide enough in width to produce the two rails. I bet they bored the rib pocket holes down along the center of this wood. When they cut the wood down the center they had 2 rails with identically spaced rib pockets. The hole produced by the bit's center indexing point was lost as it was cut away by the width of the saw blade, and the width of the bored slot was a bit less than half the bit's diameter.

If I'm remembering correctly Morris ribs taper to just under 1" in width and under 1/2" thick - exactly the shape needed if the Forstner bit used was 1" diameter.

 

[JClearwater]

Ed, Howie,
I measured the diameter of the marks left by the drill bit at 3/4". The center indexing point should still be visible if the bit had one. Regardless of how they did it originally I will likely do it the same way Dave McDaniels showed it being done in the above attached link. I'm not going to try to make both inwales at the same time and rip them after, especially after I replaced half of all the ribs. The rib locations and their width may not be exactly in the same place as the originals regardless of how careful I am. The original ribs varied in width quite a bit where they joined the inwale - I presume because the pocket wasn't in the exact correct place so the rib was trimmed to fit.
Jim

 

[Dan Miller]

I have a set of period Forstner bits - you can see in the photo that the center point is minimal. One of the points of the Forstner bit is that you can overlap the holes. It is the outer rim, not the center point that guides the bit.

As can be seen in the overlapping holes I drilled into pine with the 3/4" bit, evidence of the center point is nearly non-existent.

 

[JClearwater]

Kudos to Dan. I guess I wasn't too far off with my original post. It just goes to show that when we try to figure out how people built things 120 years ago we should include in our thinking what tools were available at the time. Thank you to everyone for your thoughts and input. It was a good discussion.

Jim