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+--- Thread: Repairing a Broken Crossfeed Screw (/thread-2980.html)
Repairing a Broken Crossfeed Screw - Hawkeye - 11-27-2015
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.
[attachment=12312]
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.
[attachment=12313]
After applying flux to the parts, I cut three short pieces of silver solder to the horizontal surfaces of the joint and heated the whole area, starting with the larger diameter piece, until the solder was thoroughly melted. I then allowed it to cool naturally.
[attachment=12314]
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.
[attachment=12315]
[attachment=12316]
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.
[attachment=12317]
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.
[attachment=12318]
RE: Repairing a Broken Crossfeed Screw - dallen - 11-28-2015
nice repair, glad that you were able to fix it without a lot of hassles
RE: Repairing a Broken Crossfeed Screw - DaveH - 11-28-2015
Nice job Mike
Always a good feeling when things turn out right
DaveH
RE: Repairing a Broken Crossfeed Screw - Hawkeye - 11-29-2015
Thanks, guys. I spent some time today working out the connections between the control module and the oven on the heat treating unit I picked up during the summer. It gets pretty hot, but the analog gauge doesn't want to go above 300. An infared thermometer went over its upper limit.
I pulled the digital thermocouple and display out of the oven I had been building before the fire and found that the untrained personel at the 'restoration' company had cut the cable about 4" from the screw terminals. I managed to repair it, so maybe I can get some better readings next time I try it. It will be interesting making the tiny Woodruff cutter I'll need to finish the shaft.
RE: Repairing a Broken Crossfeed Screw - Hawkeye - 11-29-2015
A guy on another forum 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.
[attachment=12340]
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 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.
[attachment=12341]
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.
[attachment=12342]
After that, the excess metal was cut and ground away, leaving a strong tooth with good clearance.
[attachment=12343]
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".
[attachment=12344]
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.
[attachment=12345]
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.
RE: Repairing a Broken Crossfeed Screw - Mayhem - 11-30-2015
Nice fix Mike