Tight Worm on Rotary Table

D

Damn Yankee

H-M Supporter - Diamond Member
H-M Lifetime Diamond Member
Joined
Nov 30, 2022
Messages
105
Hi Folks,

As you can see, I am a Newb on this forum and in machine tools as a dedicated hobby. I recently purchased a milling machine and virtually every accessory I could think of (back to that later). As this is a learning experience, some accessories were cheap Asian tools that could be replaced with experience. I purchased a Vevor 8" Rotary Table - a doppelganger (by sight) of a Vertex. I paid $185 for it, including shipping, so no harm no foul. It arrived quickly via FedEx with every corner of the box mushed, but not badly. Upon removing the table, it was clear the worst mushed corner was where the worm hand wheel was and it was evident it had the most shock as the Styrofoam was discolored under the wheel and cracked adjacent to it, along the table's length.

I removed it and wiped it clean of the shipping lube. It really looked quite nice - until I tried to turn the handle. It turns but takes everything one has to do so. In the release position, the table turns freely. I contacted Vevor, and after a couple email and photo exchanges they refunded my full purchase price; I kept the boat anchor. This morning, I took it apart. I could not get the eccentric containing the worm out of the casting. The worm would not slide in the eccentric and the inner thrust bearing prevented removal from the casting. I ultimately used a dead-blow on the worm to remove it in two parts,

Though the two bearing surfaces of the worm mic-out the same, the most inner (closest to the worm) thrust bearing race will take a puller to remove it without distorting it for I can only coax it down so far with a pry bar. That is a head scratch as the rest of the bearing slipped right off. There is no visible damage to the hand wheel nor any part of the table assy.

Back to "all the accessories I bought", the one thing I did not buy were V-blocks, so I cannot confirm the worm is bent. So, what do I do? Can I hone a tad off the ID of the eccentric on one side (or both), knowing I may end up with more lash and perhaps a tight spot on the table? This thing is so close - it moves, just not freely.

All thoughts are welcome except beating me with a stick for buying Chinese crap. I am already stinging.

Thanks,
John
 
I would stone / wire brush / deburr every single working surface and then reassemble. The fact that it is a Vevor screams for a tear-down and cleanup. . . that just being part of buying Chinesium. It could be something as simple as the corners on the worm not getting chamfered, and then running into the bottom corner on the gear.
 
Thanks, Shotgun. The problem is not aat all the worm/wheel interface - it is the worm/eccentric housing fit. I can take the now disassembled worm and insert it one way or the other through the eccentric until the second bearing surface contacts the eccentric. Then, it would take that dead-blow to get it in, but no easy turning... my guess the worm is bent a bit.

Thanks,
J
 
Do you have a lathe that you can mount it in and then indicate it at several points along the length?
 
Hey Shotgun,

No lathe -I need to get beyond the mill first :(. I used a collet to mount the worm in the mill and used a dial indicator mounted on the bed. The collet doesn't like the non-round end of the worm too much so it is hard to get concentric, but not impossible and repeatable. By turning the quill by hand and moving the worm for least runout, it appears that .004" is the magic number.

Thanks,
J
 
Forgive if you are aware of this but RT's have an adjustable stop for the worm to control the amount of backlash in the dial. It works by changing the clearance of the worm teeth. On my Enco RT, the ring containing the stop pin can be rotated to adjust backlash. I leave mine for a full lock at the stop and when turning the worm, I back it off ever so slightly but how you adjust it is a matter of personal preference.

I obtained my 12" RT used from a foundry and it had a bent crank. The symptom was it would bind at a particular spot in the rotation. It is highly unlikely that your worm shaft is bent inside the outer bearing. I was able to straighten mine with a close fitting piece of pipe and some judicious bending.
 
@RJSakowski , thank you.
I just got a 12" Bridgeport rotary table. These have a lockable knob opposite the crank that slides left and right to move the worm in and out. The "lock" is a tab sort of thing that also has some left/right travel using slots for the hold down screws. I had been thinking it was just to make the fitting easier. . . but a 1/4" slot for a #8 screw? On a Bridgeport!? I can now see that it is used for backlash adjustment.
 
Thanks for all the replies, Folks!

The eccentric had to tome out first then the worm - they won't come out as an assembly. I'm not sure all RTs are like that, but I don't think so. In any event, I think I had several problems:
  1. As Shotgun suggested, it need a bit of deburring and cleanup.
  2. The bore of the eccentric had raised rings running the length of the casting - not like a screw thread, just evenly spaced raised ridges.
  3. The worm may be bent a couple thou.
My solution was to debur and clean. In my crappy setup, I could get a maximum of .004 runout of the worm at the furthest bearing end. It may have been less but that was the best I could do with what I had. Anyway, I took a 2-finger brake cylinder hone to both journal areas for an hour or so until the worm fit and turned by hand.

Fresh lube and greased, and reassembled, if the worm is bent, I don't feel it every half turn. I have about .25 seconds of backlash between the worm and wheel. I don't know if that is reasonable, but I can live with it. If it had't been jazzed-up it would have been $185 plus the cleanup anyway. This cost me nothing but the cleanup and some of your time. Thank you!

Oh, quick story and it is a bummer. For reasons of having too many balls in the air, I did my work on a piece of particle board on the dining room table. I had a bag of red shop rags and used them generously. The wife tossed a red rag (so I thought) on the table and I used it, thinking, "it sure is folded nicely...". Turned out to be a Christmas something-or-other for the table. I don't think I ever saw her so mad. I got the RT working but am in the doghouse and am looking for at least one lump of coal on Xmas to match the lump I got today.

John
 
They really should take the wheels off for shipping but maybe too much trouble for the factory
 
You must log in or register to reply here.
Back
Top