Help To Straighten A Worm.

savarin

savarin

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The worm for the azimuth drive on my scope is not straight. Its not out by much but it is sufficient to bind up tight in one position if adjusted on the inside of the bend.
As I dont have any "V" blocks and a press I wondered if the following would work.
(no pics as I havnt dismantled it yet)
The worm and shaft is one piece with a 1" length of shaft at each end of the worm.
If I hold one shaft in the chuck, the other end/shaft in a hole in the centre of a rod thats held in the drill chuck in the tailstock then mount my nudge bearing in the tool post and apply pressure to the centre of the worm whilst its rotating until (hopefully) it straightens.
Any chance it will work???????
 
If it is possible to adjust the axial position of the worm to the worm wheel while in place on the scope, you may be able to use grinding paste and lap it to fit, starting with some extra clearance and then moving the worm gradually toward the worm wheel while it wears in. Keep the clearance loose enough so the lapping mainly occurs on just the high side.
 
Trying to striating it while it is turning won't work. What diameter is the worm? You can either put it between centers or make a couple of small V blokes to find the high spot. If it isn't to large in diameter you may be able to use the quill of your mill or drill press to bend it. You will need to bend it past strait for spring back.
 
Tsk Tsk Sav......no vee blocks? Shame on ya! Time to make some if nothing else. You can use your arbor press, hydraulic press, or if this thing is small and not too hard, even your bp quill to press the high side down and keep spinning it with an indicator to check your progress. You didn't say the diameter, so can't advise you how much force it will take. You really should map out the bend. I used to work in a repair shop where we did a LOT of straightening, and I did quite a bit in my own for watercraft shafting a few years ago. Not really sure how those shafts get bent, but lots of them did. Seldom was the bend in the middle, so you have to find the real peak of the bend and support the shaft or whatever equal distance from that point to do a proper straightening.

Short of that, get one end and the worm itself running true in the lathe and turn the offending end down for a sleeve. Like I said though, you really need to know where it is bent.
 
Thanks Tony, For some reason I just assumed (always a bad move) it was bent in the middle.
If swmbo allows some shop time I will dismantle it and find the bend.
 
Maybe I'm not visualizing this right. But are you sure that it is the worm gear? What about the other gear that is meshing with the worm. It might have a piece of grit or something on the gear that is causing the problem.
 
brino said:
I remembered this from "Advanced Machine Work" by Robert H. Smith:
lathe_straighten.jpg

I have never tried it and considered it lathe abuse.....but I guess if the shaft is thin enough, and it was someone else's lathe...then I might have a go!
-brino

View attachment 121642
Click to expand...

While I've not seen that, I have seen (even participated in) some amazing feats of bending, twisting, cajoling of machines to get them back into tolerance.
 
I straighten shafts all the time while turning in the lathe. In fact, my son and I just did a propeller shaft for his RC helicopter last night. As you said, "bumping" with a bearing mounted on the tool post... I prefer using two bearing surfaces to keep the work more captive. Thinner things can have a nasty tendency to climb over the tool.

As mentioned above, you do need to know where your bend is. Rolling on a smooth surface, or turning in a chuck may be sufficient to see. V blocks and DI for finer determination.

The flaw in your idea of holding both ends and bumping the middle is that neither end can be held firmly and will want to change axial alignment as it rotates. If the bend is in the middle, than it is the middle that needs to be held just exiting the chuck jaws and one end bumped.

The "abuse" (as Brino mentioned) is dependent on the side force on the tool post, like knurling, it can be significant for short stout shafts and mostly affects the cross feed screws. Additionally, and more annoying for me, is the likelihood of belling the chuck jaws. In those instances I'll wrap the work with some brass shim stock before tightening in the chuck.
As you may already, you'll need to bump the work BEYOND it's point of elasticity to get the bend to resolve. Repeated bumps, adding a few thousands push each time usually gets you there, OR the part snaps!

I suspect the bend will be toward one end where the threads end. Hopefully, not where there's a through hole for a pin. It will almost surely snap if that's the case.
 
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