Repairing A Broken Crossfeed Screw

I mentioned a few months ago that, when I was reconditioning my shop equipment after my house fire, the dolly under my Hercus (Australian SB9) lathe gave way and the lathe fell forward, bending the X-axis and crossfeed cranks and breaking the end off the crossfeed screw.

I finally have the shop far enough along that I felt it was time to at least start on repairing the lathe. I managed to straighten the X-axis crank well enough some time ago. It took a lot of brute strength and ignorance to take the crossfeed apart. Several parts had been bent to various degrees and were binding as the shaft was turned. The sundry components are seen here, including the end of the shaft that had been broken off.


After straightening the shaft in two areas, and the screw-in shaft bearing, I milled a slot across the end of the shaft with a Woodruff key cutter about 1/3 as wide as the shaft diameter. I milled a matching tenon in a piece of 1/2" CRS. A slip fit seemed like a good idea to allow room for silver solder to wick in.


After applying flux to the parts, I cut three short pieces of silver solder and placed them on the horizontal surfaces of the joint and heated the whole area with the oxy-acetylene torch, starting with the larger diameter piece, until the solder was thoroughly melted. I then allowed it to cool naturally.


The shaft was then mounted in my 5C collet chuck and centre drilled with a very small drill. After remounting it, using the bearing centre in the tailstock, I turned the added piece to match the original shaft end.


Next, the end section was turned down to a smaller diameter to fit into the crank. Then the tip was turned down to allow threading to #12 - 24, using the die-holder guided by the tailstock.


The whole arrangement fit together quite well. The only operation still required is to cut a 1/16" wide Woodruff key slot in the part where the crank body fits. That will require making a cutter, since I don't have one that small and they are dismally expensive. I guess that means I have to get the heat treating oven wired up and learn how to use it.

since you are only making one woodruff key slot, you could make a tiny "Fly Cutter" using a old carbide circular saw blade tooth tack welded to a shaft and ground to the correct thickness and diameter.

Darn nice repair. Good job.

Very nice work - great save!

Nice Work Hawkeye!!!
i too, have one of the little Hercus 9" lathes.
i love that lil' lathe
they are a beautifully crafted, improved SB9 clones.
if i could only get a 13x40 Hercus....

Thanks, gents. John, I was trying to think of a way to do just that today. The biggest problem is that the cutter has a radius of only 3/16". I might have a trashed saw blade with a narrow kerf out in the van. A tooth set into a 1/4" shaft might just do the trick.

I found the blade. The teeth are the perfect size. I think I'll give it a try tomorrow. Thanks for the suggestion.

Well done!

John suggested using a carbide tooth from a saw blade to make a one-tooth cutter, since I only needed it for one cut. I remembered that I had a trashed blade with a narrow kerf in the van. Turns out that it was exactly the right size - 1/16" wide. I cut a tooth off the blade, leaving plenty of metal on it for ease of handling.


Another chunk of 1/2" CRS made up the shaft of the cutter. I tapered it down to just under 1/4" diameter and cut a slot half-way through on the vertical bandsaw. A bit of fiddling made the slot wide enough to take the 'body' of the tooth. The carbide tooth itself was too wide to fit into the slot far enough to give me the 3/16"radius I needed, so a 1/16" endmill was used to cut a pocket for that. Thin tools make me nervous, but it worked easily.


The next task was to silver-solder the tooth into the shaft. The over-sized tooth body made it a lot easier. I didn't want the heat required to braze the cutter. That might have caused the carbide tooth to come loose from the body metal.


After that, the excess metal was cut and ground away, leaving a strong tooth with good clearance.


After carefully aligning (eyeballing) the centre line of the shaft, I fed the cutter into the steel. It cut like a comment from your ex. After the shaft of the cutter touched the body of the crossfeed screw, I measured the length of the slot and compared it to the one on the piece that had broken off. Perfect match. Here's the tiny Woodruff key in the new slot. For reference, the largest diameter seen here on the shaft is 3/8".


After cleaning up the tool marks (read vice-grip jaws - I did mention brute strength and ignorance) on the bearing body, I put it all back together. It all runs smoothly.


It's a long trip from feeling sick after the lathe toppled off the dolly and I saw the damage that was done. I feel a whole lot better now.

Think the lathe saw school time. Plenty of crash marks.

Looks like she's been around the block a time or two. If she makes chips and is half way accurate that is all you need. Getting there is the fun.