Results 41 to 46 of 46
01-31-2017, 12:32 PM #41
Hi - I recently rebuilt a 10K lathe and had to shim several places to obtain a good alignment. I don't have a motor on it yet, so I can't provide evidence of success, but i will relate my method and you may find it helpful.
When I initially installed the apron, I noticed excessive slop in the lead screw and rack engagement. The previous owner had given me the lathe in parts and dis-assembly, but noted to me that he had paid to have the bed ground true. My guess is this lowered the effective mounting location of the apron on the ways. I ended up shimming the rack down about .062 to engage the rack properly. I would not want to shim the apron, as this will affect the cross feed gear alignment.
Next issue: Is the lead screw straight and does it align properly with the apron and the end support? First, I removed the apron from the lathe and reattached the gearbox and end support. Then I measured with a dial caliper the distance from the bottom of the bed to the lead screw. I referenced the bottom of the thread with the thin side of the caliper and tried to make sure the flat of the caliper was flush with the bottom of the bed. A bit awkward, but I made it work. I measured the extreme left next to the gearbox and the extreme right near the end support, to determine the existing lead screw mounting height (without apron influence), and to note any differences. Turns out my end support was about .015 higher than the gear box. I shimmed the end support down to correct this and was able to measure an even lead screw height (within .001 to .003) every 4 inches or so along the entire length.
Then I removed the lead screw assembly and put the apron on and bolted it tight to the saddle. I put a piece of (3/4" rod I think) in the apron worm gear hole so I could estimate the height to the top of the apron worm gear hole. I measured this along several places on the bed to be certain it was consistent. I reviewed my measurements, considered my lead screw data was to the bottom of the thread, and determined my target height was about 1.610". I had to shim my gearbox and end support down another .045 to make this happen.
The end result is my apron moves evenly along the bed with no stress on the lead screw and it is even with the bed. With the caliper in place near the gearbox, measuring the distance from the lead screw to the bed, I can move the apron to the extreme left and the caliper is steady. I am not pushing or lifting the leadscrew. I repeated this for the far end and in the middle. In my mind, this indicates the lead screw is straight and the apron is aligned.
Best of luck with your project!
03-11-2017, 02:38 PM #42
To the OP. Any progress?
03-13-2017, 10:20 AM #43
Sorry for the delay, I've been dealing with some medical issues and haven't been able to spend as much time in the garage as I would have liked. Actually scheduled for surgery in 2 weeks to repair 3 discs in my lower back.
Here is where I ended up though....like many things, I don't believe my issue was caused by 1 single problem. I for sure had misalignment between the lead screw and the apron. I measured that alignment with a dial indicator that had a flat on the end rather than the smaller round point. Putting the indicator base on the bed, setting the indicator against the lead screw and measuring deflection both vertically and horizontally in multiple places along the lead screw, while moving the carriage from one end to the other. To fix this, I shimmed the gearbox and the bracket at the tail stock end. This helped my issue considerably, but there was still some evidence of the pattern in the part.
I also removed the lead screw from the machine and set it in 2 V blocks on my bench to measure for any bend. I found out that I had about 10 thou of bend in the lead screw. With the lead screw still on the V blocks I found the high spot in the middle and just used pressure from my hand to flex it down. It took a few attempts but I managed to get it down to around 2 thou of straight. My biggest concern was if it would stay or if it would eventually flex back. I figured I would go ahead and install it and check for any progress on the cut, and noticed what I would consider a slight improvement. I have not taken it back off to check it again.
As it sits today, the finish is about 75% better than it was before. The pattern is still there, but it's good enough that I'm not too bothered by it right now. I figure if I have a rare occasion that I need a better surface finish and don't want to spend the time with some emery paper and scotch bright, I can use the half-nuts. I know it's not best practice, but I don't think it would be happening too often.
Appreciate everyone's help on the issue!
03-13-2017, 02:55 PM #44
Sorry to hear you're not well. Apols for buggin' you.
I pinged here because I have the exact same issue. Some of the comments here have been very educational - like the 24tpi vs 4.45tpi thing.
I have a few higher priority things to fix on the old 10L but this will get to the top of the list soonish (maybe).
John's descriptions above of checking his leadscrew and height looks an excellent process. I'll be doing that.
I hope all goes well your procedure.
03-13-2017, 03:02 PM #45
When bending a shaft like the lead screw, you have to over bend the shaft and then turn it over and partially force it back to the original bend. Reason is when you over bend and get the part straight, there are trapped stresses that when released will want to bend it back to the original condition.
Over bend and then a stress relief rebend until the part is straight.
03-13-2017, 06:22 PM #46