I dislike adding another, "My equipment broke, help me fix it, please", type of thread to this place, especially because talking about something which I broke isn't very rewarding at a place where we tend to enjoy bragging about things we were able to succeed at making work. However, I've found myself in that wonderful position where it is beyond my exhausted Google or YouTube searching ability to find the knowledge needed to tackle my current problem as if I knew how to tackle it. Thus, here I end up--hope you don't mind. 
Ok, here's what's going on. I have a 10" diameter horizontal/vertical rotary table which has a 90:1 drive hand-crank wheel. It's mounted on my BP mill bed. I bought the table new almost 2 years ago. As my mill axes are power driven and used this way to partially eliminate sore muscles but mainly to provide good looking surface finishes, upon putting some time on this 90:1 drive rotary table, I was immediately considering power driving it solely to eliminate the sore muscles.
Right about the time my arm was killing me one day from cranking it 4000 times (does that sound right?), I grabbed the cordless DeWalt drill, grabbed a piece of threaded rod which I ground 3 flats on one end, threaded the rod into the center of the table crank wheel with nuts to prevent spinning, chucked the threaded rod into the drill, and within minutes I was actually starting to enjoy using the rotary table for once under battery power instead of arm power. My productivity went up about ten-fold this way on the table. Using it this way for some months I had no problems. Then one day recently, while I was milling a pocket the drill sped up and the part stopped moving as the crank wheel went into a free spin. I figured that the drive pinion shaft had probably walked itself out of mesh in the worm, so I loosened up the table drive engagement mesh lock screw to cam it back into mesh. It seemed pretty tight, but I grabbed the cam collar with a rag and a set of channel locks to make sure it was firmly engaged to the ring gear. I tighten the engagement screw back up, go to drive the table, it barely moves and the drive axle goes right back into a free-spin. Hmm. Ok, time-to-problem-solve mode begins.
This shouldn't surprise anyone, the rotary table is made by Shars in China; imagine that something not made in the USA would have a problem so soon. Here is the page link which shows the exact rotary table at Shars' website: 10'' Horizontal and Vertical Rotary Table - Rotary Machining Tables - Workholding - Products
What follows is about as much as I can gather about my own issue here at this point, which isn't a great deal without opening the thing up and having a peek inside--I haven't opened the table up because for starters I generally would like to believe that if I need to I will be able to reassemble what I have just taken apart in the same condition, and I don't know if these are wet sump units with oil in them that's going to drain out or etc. Secondly, I usually want to have an assembly drawing when digging into unfamiliar territory, for obvious reasons. I haven't been able to find an assembly drawing for this type of table, otherwise I might have a head start on this.
1. Rotary table worked for a combined total of maybe around 2 hours driving input shaft under cordless drill power.
2. Mesh engagement is lost at the ~270° table location, going into a freewheel no matter how tight the engagement cam is turned towards mesh side.
3. By hand cranking, position opposite of drive-loss side (~90° table location) gets considerably tighter in mesh and hard to crank for a range of degrees. This detail leads me to the first clue that the ring gear has walked itself towards this side.
4. I don't know how relevant this is to such designs, but when the mesh engagement screw stop is loosened to cam in or out of mesh, the input shaft has about 1/32" of inward or outward slop by pushing or pulling on the crank wheel. It would seem to me that this play would be shimmed out on the internal side of the input shaft against the bearing, because input torque between worm gears will want to either push or pull on the input shaft and the screw stop will be fighting not only rotational movement of the cam, but gear deflection-generated load inward/outward on the input shaft. Shimming would seem to assist the mesh stop screw from battling 1 of 2 directional forces during mesh. Someone who knows the gears better than me might chime in as to whether or not this slop should be there or not for proper mesh.
Final Notes:
* I just got to thinking, and I don't know if I have improperly called the gear system a "worm" drive, or if it's just considered a "ring and pinion" instead. Please correct me on what to call it.
** My main hope from posting this thread is that someone might be able to link to a drawing of the internals of such a rotary table similar to mine, and clarify if I will need any kind of oil to replace upon opening the unit (I assume it's probably a dry sump with some grease that I may want to improve while having it apart).
*** Will I need any special tools to likely fix the problem (gear puller)?
Thank you, and your help is much appreciated.
Ok, here's what's going on. I have a 10" diameter horizontal/vertical rotary table which has a 90:1 drive hand-crank wheel. It's mounted on my BP mill bed. I bought the table new almost 2 years ago. As my mill axes are power driven and used this way to partially eliminate sore muscles but mainly to provide good looking surface finishes, upon putting some time on this 90:1 drive rotary table, I was immediately considering power driving it solely to eliminate the sore muscles.
Right about the time my arm was killing me one day from cranking it 4000 times (does that sound right?), I grabbed the cordless DeWalt drill, grabbed a piece of threaded rod which I ground 3 flats on one end, threaded the rod into the center of the table crank wheel with nuts to prevent spinning, chucked the threaded rod into the drill, and within minutes I was actually starting to enjoy using the rotary table for once under battery power instead of arm power. My productivity went up about ten-fold this way on the table. Using it this way for some months I had no problems. Then one day recently, while I was milling a pocket the drill sped up and the part stopped moving as the crank wheel went into a free spin. I figured that the drive pinion shaft had probably walked itself out of mesh in the worm, so I loosened up the table drive engagement mesh lock screw to cam it back into mesh. It seemed pretty tight, but I grabbed the cam collar with a rag and a set of channel locks to make sure it was firmly engaged to the ring gear. I tighten the engagement screw back up, go to drive the table, it barely moves and the drive axle goes right back into a free-spin. Hmm. Ok, time-to-problem-solve mode begins.
This shouldn't surprise anyone, the rotary table is made by Shars in China; imagine that something not made in the USA would have a problem so soon. Here is the page link which shows the exact rotary table at Shars' website: 10'' Horizontal and Vertical Rotary Table - Rotary Machining Tables - Workholding - Products
What follows is about as much as I can gather about my own issue here at this point, which isn't a great deal without opening the thing up and having a peek inside--I haven't opened the table up because for starters I generally would like to believe that if I need to I will be able to reassemble what I have just taken apart in the same condition, and I don't know if these are wet sump units with oil in them that's going to drain out or etc. Secondly, I usually want to have an assembly drawing when digging into unfamiliar territory, for obvious reasons. I haven't been able to find an assembly drawing for this type of table, otherwise I might have a head start on this.
1. Rotary table worked for a combined total of maybe around 2 hours driving input shaft under cordless drill power.
2. Mesh engagement is lost at the ~270° table location, going into a freewheel no matter how tight the engagement cam is turned towards mesh side.
3. By hand cranking, position opposite of drive-loss side (~90° table location) gets considerably tighter in mesh and hard to crank for a range of degrees. This detail leads me to the first clue that the ring gear has walked itself towards this side.
4. I don't know how relevant this is to such designs, but when the mesh engagement screw stop is loosened to cam in or out of mesh, the input shaft has about 1/32" of inward or outward slop by pushing or pulling on the crank wheel. It would seem to me that this play would be shimmed out on the internal side of the input shaft against the bearing, because input torque between worm gears will want to either push or pull on the input shaft and the screw stop will be fighting not only rotational movement of the cam, but gear deflection-generated load inward/outward on the input shaft. Shimming would seem to assist the mesh stop screw from battling 1 of 2 directional forces during mesh. Someone who knows the gears better than me might chime in as to whether or not this slop should be there or not for proper mesh.
Final Notes:
* I just got to thinking, and I don't know if I have improperly called the gear system a "worm" drive, or if it's just considered a "ring and pinion" instead. Please correct me on what to call it.
** My main hope from posting this thread is that someone might be able to link to a drawing of the internals of such a rotary table similar to mine, and clarify if I will need any kind of oil to replace upon opening the unit (I assume it's probably a dry sump with some grease that I may want to improve while having it apart).
*** Will I need any special tools to likely fix the problem (gear puller)?
Thank you, and your help is much appreciated.
