Repairing Cross Slide Screw, Need Suggestions

[ltlvt]

Posting a link to your Moglice thread because it’s an ambitious undertaking. https://www.hobby-machinist.com/threads/anyone-here-actually-used-moglice-on-a-lathe-saddle.108654/

One of these day I’ll further investigate where the wear really is in my lathe and how difficult it might be to fix it. I usually only machine 1”-3” areas on a part and since the Victor has a spindle bore of 1-1/2”. I can usually work close to the chuck. Since I rarely work on the entire length of a piece the wear isn’t a big concern.

Here is the link to my ongoing saddle repair

Seeking knowledge at the well of Wisdom

Those are sure weird! That straight section next to the V way really complicates things! Is your cutter long enough for the full width, or are you going to have to trig your way down? You may need to grind the end flat. The surface speed will go to zero on the point. Sent from my SM-S911U using...

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[gard]

Its good that adjusting the gib helped with the problem, I think I will go check mine. Wear of the saddle can make the problem worse and wear on the bed can make it impossible to get a good fit at all locations along the bed.

The thing that causes this is the location of the cutting point relative to the center of the carriage. To illustrate, consider standing on a table to change a lightbulb. The table top extends outside the footprint of the legs. The most stable place to stand on the table is near the center. If you stand on the very edge of the table, outside the footprint of the legs, the opposite side of the table may lift off the floor. Probably making a great viral video. Anyway the tendency of the opposite legs to lift up depends on your weight vs the weight of the table and how far you are outside the footprint of the legs. The 4 legs are analogous to the 4 corners of the carriage (actually the saddle), your weight is analogous to the downward force caused by the cutting tool. Tightening the Gib or carriage clamp is like bolting the table to the floor, effective but unnecessary if you stay in the center.

To continue the analogy further as ltlvt has found, wear on the saddle corners can make it a lot worse. The bottom of the saddle tends to become curved so now it is sort of like standing on a rocking chair to change a light bulb. You need to be standing very near the center. You can measure this by placing a magnetic base on the bed and indicate a corner of the saddle. Then press down on each corner and look for movement. You have to press hard enough to overcome the weight of the saddle. Repeat the measurement at each corner.

Getting the cutting tool closer to the center of the carriage can be a little tricky and I think harder with QCTP than than with the antique lantern post but give it a try.

 

[ltlvt]

Its good that adjusting the gib helped with the problem, I think I will go check mine. Wear of the saddle can make the problem worse and wear on the bed can make it impossible to get a good fit at all locations along the bed.

The thing that causes this is the location of the cutting point relative to the center of the carriage. To illustrate, consider standing on a table to change a lightbulb. The table top extends outside the footprint of the legs. The most stable place to stand on the table is near the center. If you stand on the very edge of the table, outside the footprint of the legs, the opposite side of the table may lift off the floor. Probably making a great viral video. Anyway the tendency of the opposite legs to lift up depends on your weight vs the weight of the table and how far you are outside the footprint of the legs. The 4 legs are analogous to the 4 corners of the carriage (actually the saddle), your weight is analogous to the downward force caused by the cutting tool. Tightening the Gib or carriage clamp is like bolting the table to the floor, effective but unnecessary if you stay in the center.

To continue the analogy further as ltlvt has found, wear on the saddle corners can make it a lot worse. The bottom of the saddle tends to become curved so now it is sort of like standing on a rocking chair to change a light bulb. You need to be standing very near the center. You can measure this by placing a magnetic base on the bed and indicate a corner of the saddle. Then press down on each corner and look for movement. You have to press hard enough to overcome the weight of the saddle. Repeat the measurement at each corner.

Getting the cutting tool closer to the center of the carriage can be a little tricky and I think harder with QCTP than than with the antique lantern post but give it a try.

Excellent explanation. I've said it a million times "Anyone can make chips" What separates the heard is understanding how the chip is made and setting up the machine accordingly. My machining journey started with a dull drill bit. I wanted to know the correct way to resharpen a drill bit. I said Correct Way. Once I understood how a drill bit actually works then I could begin the process of sharpening it the correct way. That drill bit led me to the never-ending pleasure of restoring machine tools to near original operating conditions. I think the actual mental and physical labor of this hobby has a very positive effect on my spirit. Sounds crazy doesn't it but just think about it. Something inside of us drives the evolution of industry.

 

[David2011]

What really confused me initially was that I thought the front left of the saddle was dipping and while that was correct, it was a symptom and not the problem itself. It took me a while to understand that the worn gibs at the rear of the saddle were permitting the right rear corner to lift.

I've never liked to extend the cutting tool beyond the end of the compound nut when possible in the future and especially when making heavy cuts I'll try to keep the cutting tool closer to the center of the saddle. This exercise had definitely given me a lesson in how cutting forces affect the lathe. A better machine than I've had preciously has let me extend my wings a little more and push the cutting tools harder. If I had stayed with .020"-.030" I might have not seen the movement. I certainly know why I broke both ends of two carbide cutofff inserts when I didn't think I was doing anything wrong now. Actually, a YouTube video on why cutoff inserts break started this entire investigation and repair.

Initially I thought the problem was coming the worn cross slide gib and while it was adjusted all the way in. it was not significantly contributing to the problem. Glad it's shimmed to the beginning end of its range though. That's one less variable to contend with.