Well my post this week will not be as long as last week's nor will it have as many items done. Never got in the shop until Saturday. At least we have a nice day here sunshine and just above freezing. Hopefully later this week it is supposed to go higher with 4-5C temp and possible rain. This will go along way to getting rid of some of that lousy white stuff around here. With the snow on my roof the solar panels are not making me any money this past month.
Meanwhile in the shop this morning we turned the blank around so we could machine the other end of the "shake adjusting nut". Last week I machined the pocket that would hold the bearing in it. This week I would machine the end that goes onto the large sprocket that mounts on the headstock spindle. This has a threaded connection between the two such that when you unscrew it, it pushes against the thrust bearing which secures the entire headstock assembly inside the headstock casting. For those who may not know what I'm talking about (Sis) here is a picture.

The above drawing from the 1919 brochure should help. This is a cross section of the headstock, the "shake adjusting nut" is the item with red ink on it. The "large sprocket assembly" mentioned above has the blue line in it and the "thrust bearing" has the green line in it. Since the sprocket assembly is secured to the headstock shaft which runs through the centre of the headstock, when you unscrew the shake adjusting nut it will push up against the thrust washer which in turn pushes up against the headstock casting. This then removes any horizontal slop out of the headstock assembly. Actually a pretty simple system when you think about it. You do not need a lot of torque on this assembly just enough to snug the bearing up securely.
So we flipped the blank around set it up in the 4 jaw chuck and carefully dialled it in such that we had less than 1thou runout on the previously machined surface. Unfortunately the picture showing this was way out of focus. Once it was dialled in we carefully machined out the inner dimension to allow the headstock shaft to come through the nut. We then machined out the pocket where the thread would go. Once that was done we machined two slightly deeper pockets one at the front of the nut and one 1inch into the pocket which would be depressions on either end of the thread to allow easier threading. Once this was done we machined the outside to the correct dimension to allow the sprocket assembly to slide over top. We checked this out with the sprocket assembly before starting the threading operation.
Here are two pictures first one showing the old nut, the second one showing the new nut ready for threading along with the old one sitting beside it on the lathe.

Carefully using thread gauges I determined that the thread was 24tpi. Set the lathe up to cut this thread and then carefully went at it. Threaded this by 5thous increments. Once we got to 25thous depth checked the piece with the sprocket assembly. It would start but that was all so went in again at 2.5thous increments and after two more passes got the assembly to thread on. I was quite happy as it seemed to thread on really nicely. However once I went to unthread the assembly it went 5-6 turns and then started binding up. I was frustrated in that after a few attempts to unthread it it would not come off. We persisted and slowly using a pin wrench managed to unthread the assembly. So went back in and carefully cleaned out the threads again with the threading bar and took three spring cuts to entirely clean out the thread. This time it spun on and off quite easily but with no slop on the thread. So I think a job well done. Here are two pictures. The first one is when I initially spun the sprocket on and the second one is once the threads were cleaned out some more. This time the entire assembly is out of the lathe.

The only thing left to do is decide whether to place knurls back on the nut like my two originals had, which gave you the gripping surface to tighten the nut. Or would insert either grooves or pin holes to use the adjustable pin or slot wrenches. A couple of the other owners with lathes newer than mine have the slots in the nut however I noticed on one of these machines these slots were quite badly damaged. I think boring 3holes in the nut at 120degreees almost through the flange area might be cleaner and less susceptible to damage down the road. I will have to think about this. I'll decide by the end of the week and then either bore it, slot it or knurl it. The only issue against the hole is I would need to buy the pin wrench required for the diameter of the nut since I don't have one at this time.
So that was all we did this week however I'm glad it's done. I'll most likely have to make at least one more for the #39 lathe somewhere down the road as it's nut is also damaged. However I'll probably wait awhile as I would like to see how this one lasts and works. I'm a little concerned that I might have used the wrong material. I used 12L14 round stock for this based on ease of machinability and the quality of the metal. Its tensile and shear strength looked good and the usage of this material was stated as being good for this type of application. Well the material machines beautifully however I noticed that just securing it in the 4 jaw chuck left little marks on the metal where the chuck jaws dug in. There was no real concern about this marking because it was easily cleaned off however it did leave me with a little concern about the strength of the material. However as mentioned before there is no real torque or pressure on this nut so it should still work as required. I might though look at getting a piece of Durabar for the next nut.
Now we need to look at working on assembling the headstock. The only issue I would like to resolve first is the damaged teeth on the back gear and one on the large sprocket. Decisions, decisions. I Most likely just drill, tap and pin into the large sprocket and then fill it with braze material before grinding it back down to the right profile and there's a good chance I'll do the same with the other broken teeth. One thing I'm waiting on is some special welding rod that can be used with my Tig welder that should take the place of brazing. Once I recieve this will trial some repairs on damaged gears and see how this material works.

Well until next week enjoy the weather and the Olympics especially when Canada gets the gold medal in Hockey :=):=)

Harold