Rotary Table Fix

[cfellows]

I wanted to share this info with the group as it might help someone who has a similar problem.

I bought this 6" rotary table a number of years ago. I bought it new and it was Chinese made so I got it for a good price. A few weeks after I got it, I was going to put it to use and discovered the table had a tight spot on one side and was loose on the other. It felt like the worm gear wasn't concentric with the spindle. I had disassembled the unit and a cursory examination looked like the worm gear and table were part of the same casting.

I decided there wasn't much I could do about so I put it back together. I have a smaller rotary table so didn't use this 6" model very often. Today, I decided to have another look at it and took it apart. A more careful inspection revealed that the worm gear casting was separate from the table, attached with 4 socket head cap screws.

I mounted the table on my lathe in the 4 jaw chuck and centered it on the spindle in the center. Turning on the lathe at slow speed revealed that the worm gear was not concentric and it wobbled slightly. Removing the worm gear casting revealed a depression in the table that the worm gear was supposed to seat in. However, it was .020" too small and slightly off center and the bottom of the worm gear casting was slightly bevelled which allowed the casting to cock slightly when tightened down. Since the worm gear casting had hole in the center that was designed to fit over and center on the spindle, I enlarged the depression with a boring bar so the worm gear casting would fully seat when tightened down. I rechecked it for concentricity and, Bingo, the worm gear now runs dead true.

I'm hoping when I get it back together tomorrow, my problem will be solved!

Chuck

 

[rodw]

Don't you hate that sort of thing? I fitted a 4 jaw to my old lathe and was really disappointed to see air between the chuck and my backing plate. I assumed i had stuffed something up. After I remade the backing plate, I realised the problem was one of the pins that hold the jaws in was sitting proud of the rear surface of the chuck so the chuck could not seat properly. So I replaced the chuck which i had bought new and it was all good. Shame about the wasted shop time though!

It was good you could isolate the fault and rectify it.

 

[Herbiev]

I suppose it's worth it in the end. You now have a precision rt at Chinese prices😊

 

[cfellows]

I suppose it's worth it in the end. You now have a precision rt at Chinese prices😊

Yeah, it's hard to justify buying the high priced stuff when you're not using it to earn a living. I have more time than money and there's a lot of satisfaction in making something work better.

Chuck

 

[gabby]

Hi there Chuck, I have to agree with you "more time than money" and I got one of those Chinese RT's like you I pulled it down as it didn't seem to be 100% and found the nut that holds the worm "in sitchu", had been tapped on a very off centered angle with a thread that I still haven't found a replacement nut for, it is close to metric M10 so I think I will force a nut onto it and leave it at that. (it's not like I have to remove the nut every day).
Cheers
Gabby

 

[rodw]

Hi there Chuck, I have to agree with you "more time than money" and I got one of those Chinese RT's like you I pulled it down as it didn't seem to be 100% and found the nut that holds the worm "in sitchu", had been tapped on a very off centered angle with a thread that I still haven't found a replacement nut for, it is close to metric M10 so I think I will force a nut onto it and leave it at that. (it's not like I have to remove the nut every day).
Cheers
Gabby

Maybe try an auto parts place. In Aus they usually have a stand with small packets of both metric and Imperial nuts and bolts with some sample threads to size your nut or bolt on. Maybe it is a M10 fine thread or 3/8". I'd be surprised if it was not a standard thread.

 

[gabby]

thanx RodW, I will try that.
cheers

 

[Mike N]

I wanted to share this info with the group as it might help someone who has a similar problem.

I bought this 6" rotary table a number of years ago. I bought it new and it was Chinese made so I got it for a good price. A few weeks after I got it, I was going to put it to use and discovered the table had a tight spot on one side and was loose on the other. It felt like the worm gear wasn't concentric with the spindle. I had disassembled the unit and a cursory examination looked like the worm gear and table were part of the same casting.

I decided there wasn't much I could do about so I put it back together. I have a smaller rotary table so didn't use this 6" model very often. Today, I decided to have another look at it and took it apart. A more careful inspection revealed that the worm gear casting was separate from the table, attached with 4 socket head cap screws.

I mounted the table on my lathe in the 4 jaw chuck and centered it on the spindle in the center. Turning on the lathe at slow speed revealed that the worm gear was not concentric and it wobbled slightly. Removing the worm gear casting revealed a depression in the table that the worm gear was supposed to seat in. However, it was .020" too small and slightly off center and the bottom of the worm gear casting was slightly bevelled which allowed the casting to cock slightly when tightened down. Since the worm gear casting had hole in the center that was designed to fit over and center on the spindle, I enlarged the depression with a boring bar so the worm gear casting would fully seat when tightened down. I rechecked it for concentricity and, Bingo, the worm gear now runs dead true.

I'm hoping when I get it back together tomorrow, my problem will be solved!

Chuck

I have one just like this with the same problem (tight & loose spots) I will tear it apart again & see if i can fix mine like you did, Thanks!

 

[cfellows]

Mike, if you need more detail on what I did, let me know, happy to help.

Chuck

 

[crankshafter]

Mike, if you need more detail on what I did, let me know, happy to help.

Chuck

Hi Chuck.

Me allso have the same issue with my RT. If you can give more detailed how you fix yours, it would have been great.

Have a nice day

CS

 

[cfellows]

Here's more detail on my rotary table fix (perhaps more than you wanted ).

You don't need to remove the crank or worm assembly. To remove the table, turn the table upside down. First loosen the socket head cap screw on the round nut, then remove the threaded nut (The slot head screw in the middle is something I added on mine to hold a #2 morse taper sleeve in place).

Next, turn the table upright and remove the rotary table clamps on each side.

Turn the table on its side and slide the table out of the housing. Turning the crank on the worm assembly may help with this. Then lay the table top down on the workbench.

Next, remove the 4 outer socket head cap screws which secure the gear to the table. You can then separate the gear from the table. You will probably need to use some gentle persuasion. I held the whole assembly up by grasping the gear casting and smacking the center spindle a few times with a rubber hammer. I know this warning is not needed, BUT: Clearly, you do not want to use a metal hammer and damage the threads on the sindle. You could thread the round nut back onto the spinde and hit that, but again, be careful not to damage the nut or any threads. Here's what it looks like apart...

On mine, I centered the gear casting in my 4-jaw chuck and made a very light pass across the bottom of the casting to be sure it was flat and square to the casting. Mine wasn't and I removed a few thou. It wouldn't hurt, while you have this mounted in the 4-jaw, to indicate the center hole and be sure it is concentric with the OD of the gear casting. If, by chance, it's not, you have different problem than I had.

Here was the big offender. The ID of the depression in which the spindle sits was not big enough, so I had to enlarge it about .020" so the gear casting would sit flat in the bottom of the depression.

Theoretically, if the center hole on your gear casting is concentric with the OD, and it fits snugly over the spindle flange, you can open up the OD on the table depression as much as you want. However, I only opened up mine enough so the gear casting would seat inside it.

Chuck

 

[ShopShoe]

Cfellows,

You got me thinking when you did this a few weeks back. I was just putting up with a tight spot on my 6 inch RT last time I used it. I just assumed that I got what I paid for and that if the accuracy was checking out OK I could live with other problems.

My table was Eastern European rather than Chinese, and the construction was slightly different.

I took off the table, with the gear and hub attached and then mounted it using the T-slots to attach it to my faceplate. Attached to the lathe, I indicated and centered it as one would with a four jaw chuck. I cross checked all of the machined areas while rotating the assembly by hand, then went on to find some un-machined areas that needed cleaning up.

On reassembly, I found the washer and tension-nut assembly also needed cleanup, with the washer needing special help as it was out-of-round and rubbing against a part of the casting.

It's much better now, but I may revisit this again as I was cautious and cut just a little since it is so hard to put metal back.

Thank you for reminding us to revisit the condition and improvement of such basic items.

--ShopShoe

 

[cfellows]

Glad you found the information useful, Shopshoe. On mine, the offending ID (which was too small) wasn't used as a datum for centering the gear on the table, so I was able to remove as much as I wanted. I didn't take any more than I needed to, but I did make sure the gear would seat properly when I reassembled it.

Chuck