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View Full Version : I broke my rotary table (worm gear) - what to do/build with the remains?



aribert
12-16-2014, 01:59 PM
Greetings all:

I sheared many teeth off of my 6 inch rotary table last night. I think the original damage occured previously when I thought my part was slipping in the jaws of the chuck mounted on the rotab. I am modifying some wheel centers to make them match some deep drop rims (to increase the OD of my wheels by 1 inch and keep the stock hubcaps). I needed to turn the OD to about 12.3 inches and my 5914 Clausing swings a hair over 12 inches. Part on right is before modification: http://i290.photobucket.com/albums/ll272/aribert/Falcon/IMAG1104_zpsda189409.jpg (http://s290.photobucket.com/user/aribert/media/Falcon/IMAG1104_zpsda189409.jpg.html) ITs a bit hard to see in the image on the LH part but the mounting flange is 1/4 inch thick (after I have also removed stock on the inside of the part).

I did not want to grind a 3/4 x 1/4 inch groove into the bed (tailstock way) on the lathe so I mounted the wheel center onto the rotab and used the B'port to rought machine - I do the last few light passes on a 20inch lathe at work. I try to do as little as possible on that machine - the part rings, queals and is generally non discrete when I machine the final clean up passes (and the fab shop is not in my building so I am a bit out of place to begin with). I have just as much noise when using the mill but with the doors closed no one will hear the noise.

It would appear that the Chinese rotab was not able to take the abuse of the cutter loading on its teeth - since I needed to be able rotate and mill at the same time to approximate a lathe I was unable to use the table locks.

So, what could I make out of the rotab with the worn off teeth?

Rosco-P
12-16-2014, 02:17 PM
Probably the same worm and gear in a Phase II rotab. Why not contact them for parts?

A.K. Boomer
12-16-2014, 02:53 PM
I think it could be a great base for a merry go round just cement the base and then bolt up your MGR right to the table slots and off you go no worm gear needed...

PStechPaul
12-16-2014, 04:42 PM
At first I thought the pictures were of the rotary table after disassembly! :rolleyes:

It would help if you posted a picture of the ro-tab. It might not be too difficult to make a new gear or repurpose one from something else.

oldtiffie
12-16-2014, 06:33 PM
If you really need one soon or now then search for a good used one - it will save a lot of time, money and heart-ache.

You have well and truly found what you did wrong to cause this matter and so you are not likely to repeat it.

Ironwoodsmith
12-16-2014, 11:16 PM
I would have taken a 4" cut-off grinder to that first. Perfect application for a hand tool.

Arcane
12-17-2014, 12:07 AM
It would take quite a load to shear several teeth off. My RT has a provision to disengage the worm from the ring gear; are you sure your's isn't similar and disengaged on it's own from vibration?

aribert
12-17-2014, 08:18 AM
Thanks for the responses. Unfortunately from time to time I have need to do exactly what I think caused this rotab to fail - not locking the table when milling. I really liked the 6 inch size - with a 3 jaw attached I could easily lift it. I can't handle a 10 inch or larger and my workshop is too cramped for the luxury of a cart (especially a lifting cart) where I would only need to slide the rotab off a cart and onto the mill. I have thought about some overhead lift but I am some what limited by an 8' ceiling (I have a hole in the ceiling drywall to be able to R&R the drawbar)

The worm (ring )gear is machined into the table http://i290.photobucket.com/albums/ll272/aribert/metalworking/IMAG1126_zpsbd3aab0d.jpg I did some quick surfing for worm gears yesterday - hoping that I might find a catalog gear that I could fit. One thing that I noticed is that all the worms pictured had their mounting axis shaft on both sides of the worm. That was not the ase on my rotab. The worm was cantilevered on its shaft and therefore could potentially deflect and reduce the ammount of tooth engagement making it easier to shear a tooth or two (or dozen in a row)

Arthur.Marks
12-17-2014, 10:02 AM
That's a pretty standard design, though, IME. The rear nut on that central shaft holds the worm and wheel in line with each other. It also is adjusted to provide just enouth clearance with the tabletop to slide on the casting body without seizing. I assume you are aware of these facts already.

Under heavy milling--yes, rotating the table while milling--I've had the nut lose adjustment before. That's no good as the table likes to jump around or seize up from misalignment or both. I've also had the eccentric, rotatable worm engagement shaft snap a pin that set engagement position. Then it rotated into the wheel for goodness knows what reason! :confused: Common sense and basic logic says it would disengage. Nope. I am often blessed by such folly :(

All this said, nothing ever took a tooth off my wheel. Yours looks like a whole lower section of teeth cracked off horrendously. Bummer. I would think a replacement would have a hard time finding a good way to mount?

Sorry to not be more of a help. I really just wanted to assure you that a rotary table absolutely is meant to be useable for milling during rotation. There is nothing wrong with your expecting it to do so.

Rosco-P
12-17-2014, 10:08 AM
I really liked the 6 inch size - with a 3 jaw attached I could easily lift it. I can't handle a 10 inch or larger and my workshop is too cramped for the luxury of a cart (especially a lifting cart) where I would only need to slide the rotab off a cart and onto the mill.

No room for a shelf at table height alongside the column, behind the table? Then you could slide an 8 or 10" RT off the shelf after bring the milling table to the same height.

Jim2
12-17-2014, 10:48 AM
I didn't see any teeth sheared off. Your pic was pretty small though, so maybe I'm just not seeing it? The fact is your worm-wheel looks just like the one on my 8" rotab. I'm wondering if Arcane hasn't diagnosed your problem--the worm vibrated loose during the cut and became dis-engaged from the worm-wheel?

Jim

Arthur.Marks
12-17-2014, 12:33 PM
Jim, I agree, it is a little difficult to tell from the picture. I think I'm seeing the bottom half of the wheel teeth completely gone starting from about the middle of the table in the pic. going left. I feel a little obnoxious mentioning it at all, but was this table operated with a sufficient oil volume in the reservoir? Looks pretty dry to me in the image, but that isn't necessarily an indicator of conditions when in use and assembled. These rotary tables weep oil by design. They also run into loads of problems without sufficient lubrication.

aribert
12-17-2014, 01:44 PM
Authur M:
There was a grease film on the teeth - disclosure (figuratively hanging my head in shame) - I **never** oiled the rotab. I noticed the spring loaded oil port when I dismantled the rotab.

Jim2:
On the damaged teeth the upper (as in nearest to the tip of the tooth) half of the teeth are worn/sheared off. The base of all the teeth remain.

I suspect that as someone posted earlier that the adjustment of worm to worm gear may have loosened - there was a lot of vibration / chatter from the roughing endmill as I was turning to size the built up weld on the OD of the wheel center. I had taken a 12 inch dia part, built up about 1/4 inch thickness of weld on the 4 flanges of the wheel center and then rough machined it to a 12.37 dia

PStechPaul
12-17-2014, 04:18 PM
It looks like the gear does not have a convex tooth shape that would provide more contact area and less stress on the teeth. Also, I think the worm should be centered on the gear, whereas in your case it seems to be offset, causing the failure along the edge. To repair it, it might be possible to re-align the worm on the remaining unbroken teeth. Otherwise, you'd probably need to put the part in a lathe and remove the teeth, and then get (or make) a ring with a bore that is an interference fit, then heat it and have it shrink onto the table.

It might be possible to make a ring from a rack with the same tooth count, and then attach it to the outside of the table. The gear cutter for high tooth counts is the same as for a rack, so the shape might be close enough to work.

oldtiffie
12-17-2014, 06:08 PM
Were you climb-milling with the roughing cutter?

aribert
12-17-2014, 07:47 PM
oldtiffie:
Only climb milling was when the table skipped on a tooth or two. When this first started I thought that the wheel hub mounted in the chuck of the rotab was slipping.
PStechPaul:
originally I was thinking along the lines of buying a replacement worm gear and making it fit the table but a quick internet search did not yield many catalog options (just a lot of web pages for custom cut gears). I suppose I should clean the teeth on the table - my parts washer is covered in stuff and I figured if I did not readily find a replacment gear and I did not have any other repurpose use for the major parts there was no reason to clean the parts. I never considered reassembling with the damaged ring and trying to correct or improve the gear match / alignment. I'll have a quick look at it tomorrow evening when I expect to stop at my workshop on the way home from work.

My main focus of this posting was to see if there were any suggestions for re-purposing the rotab carcass (aside from making a merry-go-round as earlier posted).

I started looking on eBay for a used commercial grade rotab and am considering making a 1.25 or 1.5 inch dia arbor with Weldon flats to fit into an endmill holder and to the mount the vehicle hub so that I can mount (and rotate) the wheel center in the mill while holding the cutter in the mill vise. I'm not too excited about this option - it just seems like a big part to be swinging on a mill spindle.

oldtiffie
12-17-2014, 11:11 PM
I shuddered when I read the OP's last paragraph in the previous post.

I do hope that he is not - deliberately or otherwise - setting himself up for a "Distinction" or "Merit" award in the "Darwin Awards".

My guess is that trying to mark it with the "mark it with a file" test and see how hard - or not - the part he proposes to machine is - or is not - "machine-able".

If it were machine-able I think I's mount it on the lathe face-plate (slowest speed) and "trepan" the waste off - use a good TC insert - and have some spares of it too.

Otherwise - if it were me and if the cost justified it, I'd have it "water-jetted" as it will neither deform the part nor leave "hard spots" nor upset the material structure.

Baz
12-18-2014, 04:43 PM
As far as completing the current machining I suggest reassembly without worm and attaching a long lever to table with the part so you can manually rotate it against the cut, in a number of stages.
For the longer term repurpose of the table consider some simpler ratchet or index system - see the taylor hobson rotary table for engraving which has interchangeable indexing plates.