- Joined
- Apr 9, 2012
- Messages
- 45
My LeBlond lathe needs a replacement cross slide screw and nut. Nut was made of "grey iron" or cast iron, very worn and broken. The screw seems to have "disappeared", along with several other items that were removed and put in a box (some 0ne must have dumped the box and the contents). Making a replacement screw is easy since threaded rod (even Acme LH threads) are available and reasonably priced. The nut is another story (special shape, looks similar to SB). Closest I could find was $80, not including shipping to Hawaii (which, if you've tried it, is horrendous since some won't use USPS even for small items).
My course of action was to cut the internal threads, but that special tap is also very expensive. Decided to take a section of the all thread and make a tap.
This is what I learned: First, cutting acme threads (5/8 x 10) using a tap is very difficult. I drilled a 1/2" hole in a piece of delrin for the minor diameter. Then the tap went in for the threads. The tap was very tapered with 3 flutes. Someone had a post about such a tap (someplace where I can't find it again) so I just followed the concept. After getting about 1/4 the depth on the taper, turning the tap became very difficult. It was difficult enough to cause me to stop and try starting the threads with an internal threading tool (regular 60 degree since I don't have the 30 degree acme shaped cutter). It seemed reasonable that once the threads are cut with the 60 degree, the rest would be easy. This is not true. There is still enough material left to be removed that turning the tap was still too difficult.
The second thing I learned with that Delrin is, indeed, a tough material. I had reservations about using it as a nut for the cross slide, so this was just a practice piece. Trying to cut the threads has convinced me that it's plenty strong for the nut.
The third thing was a reminder that just because it can be done, doesn't mean it should be done. Yes, with persistence, I will be able to get the threads cut with the tap. My decision is that if I am to continue along this line, I will grind a proper cutter for the boring bar and use that instead of a tap. I'll probably give that a try since I enjoy playing around with this stuff, but I have a feeling I'll end up buying a couple of the correct size/type of nuts and just braze/solder them together for the part. I'll be able to adjust the backlash to practically zero using that approach too.
If this was a project that had time constraints, I'd be very frustrated at this point. Since it's not, it's been enjoyable and a nice learning experience.
I hope this saves others the potential for frustration if confronted with a similar situation/need.
My course of action was to cut the internal threads, but that special tap is also very expensive. Decided to take a section of the all thread and make a tap.
This is what I learned: First, cutting acme threads (5/8 x 10) using a tap is very difficult. I drilled a 1/2" hole in a piece of delrin for the minor diameter. Then the tap went in for the threads. The tap was very tapered with 3 flutes. Someone had a post about such a tap (someplace where I can't find it again) so I just followed the concept. After getting about 1/4 the depth on the taper, turning the tap became very difficult. It was difficult enough to cause me to stop and try starting the threads with an internal threading tool (regular 60 degree since I don't have the 30 degree acme shaped cutter). It seemed reasonable that once the threads are cut with the 60 degree, the rest would be easy. This is not true. There is still enough material left to be removed that turning the tap was still too difficult.
The second thing I learned with that Delrin is, indeed, a tough material. I had reservations about using it as a nut for the cross slide, so this was just a practice piece. Trying to cut the threads has convinced me that it's plenty strong for the nut.
The third thing was a reminder that just because it can be done, doesn't mean it should be done. Yes, with persistence, I will be able to get the threads cut with the tap. My decision is that if I am to continue along this line, I will grind a proper cutter for the boring bar and use that instead of a tap. I'll probably give that a try since I enjoy playing around with this stuff, but I have a feeling I'll end up buying a couple of the correct size/type of nuts and just braze/solder them together for the part. I'll be able to adjust the backlash to practically zero using that approach too.
If this was a project that had time constraints, I'd be very frustrated at this point. Since it's not, it's been enjoyable and a nice learning experience.
I hope this saves others the potential for frustration if confronted with a similar situation/need.
