Broken Norris Adjuster

[rxh]

I am looking at the possibility of repairing an adjuster belonging to a Norris A1 plane. The shaft has sheared off inside the swivel. To do the repair it looks a new threaded end would need to be grafted onto the shaft (as well as extracting the broken bit from the swivel). This will only be possible if the correct tap and die can be found. Does anyone know what sizes of threads Norris used? I have not yet examined the adjuster but from the photos sent to me I estimate that the larger thread is 1/4" x 40 TPI RH (which is no problem). The smaller thread is LH and might be about 50 TPI or 0.5 mm pitch.

 

[Trevanion]

I think these are notorious for breaking, especially if you try adjusting it when the blade is clamped.

You might have trouble finding a tap or die that’s 40tpi (if it is 40tpi that is) they were probably machine cut.

If I remember correctly spare ones can be had for a fair sum.

 

[Rhyolith]

I would have thought they would have die cut those. Doing threads that small with a lathe cutter would be challenging to say the least. So your main obstacle to repairing that is finding some appropriate dies.

 

[Steve Elliott]

I examined a Norris adjuster from the 1930s a number of years ago. The threads on the main shaft were 32 tpi right-handed and those on the smaller shaft 40 tpi left-handed. Over the years the design of the adjusters changed so yours might be different. The only other adjuster I've studied was the original 1913 model which had 35 tpi for the main shaft.

 

[rxh]

Thanks for the replies. I have now had the opportunity to examine the adjuster and measure the threads:
- on the shaft: 5/16" x 32 TPI RH
- on the traveller: 7/32" x 40 TPI LH
Dies are available for the RH thread or I could cut it using the lathe. Finding LH taps of that size is the remaining problem. I have Googled without success. Any ideas or leads would be very welcome.

 

[Rhyolith]

I’d get the die for the one you can regardless, it will be useful even if you decide to lathe it. The other you’ll have to do on the lathe.

 

[rxh]

I’d get the die for the one you can regardless, it will be useful even if you decide to lathe it. The other you’ll have to do on the lathe.

Well, I repaired it. I got a 5/16" x 32 TPI die for the outer thread but I needed to make taps to cut the 7/32" x 40 TPI LH inner thread. I cut the end off the shaft and made a 1 BA threaded hole in it to accept the new part. After screwing the parts together I drilled though and inserted a pin to stop them coming apart.

 

[MusicMan]

Nice work

 

[custard]

I thought that one was a goner, but that's an amazing deathbed resuscitation job!

=D>

 

[rxh]

Thanks for your replies Ryolith, MusicMan and Custard. I intend to take the adjuster to Richard Arnold’s charity open day on 8th June and meet the plane’s owner so that we can reunite it with the plane and try it out. Incidentally, this annual event is a great day out and I thoroughly recommend it.

I have added a post to the Metalwork section about how I made the 7/32” x 40 TPI left handed tap: “Making a tap for an unusual thread”.