Rotary Table Failure

My 6" rotary table was made by Yuasa, not one of the cheap clones and the worm gear wheel was damaged while doing a rotary cut.

A replacement worm wheel was ordered from Yuasa in America for $195.

The rotary table performed as new after the new wheel was replaced but has broken again while doing a rotary cut with an 8mm dia cutter on a 75mm radius using light cuts to reduce the load. Care was taken to ensure that the worm and wheel were fully engaged.

I have been advised by the technical department at Yuasa, USA that:-

"this unit is not able to make curved cuts it cannot make curved or circular cuts it must be locked down completely".

Many of the cheaper clone brands are made with a similar construction and therefore should also be completely locked down and only used when stationary.

Paul.

'Gobsmacked' is the only expression that immediately comes to mind!

Am I missing something about RTs? Something that I don't know? (Well, there's a lot that I don't know, but...)

Roger

Edited By Roger Head on 10/08/2016 01:28:46

Paul,

I had never heard that a Rotary Table couldn't make a curved or circular cut. I often do that on mine, and so far without trouble. It is some time since I checked the worm gear on mine, but the worm gear looked fine then. After looking at your RT it makes me wonder what kind of material it made from.

Thor

Climb milling or conventional? I might just understand the failure, if the former.

Doesn't look like a very wide contact area for those wheel teeth (only a small diameter worm?). It strikes me that perhaps the worm is fully hardened and rough, while the wheel is in a softened state?

Not a lot of point for a rotary table if it must always be locked down - might just as well use a simple dividing plate?

One of their PDFs does seem to show two versions, one being described for use when making circular cuts.

.

Paul,

That's very useful advice to share ...

Thank you; and sorry to see you learned the hard way.

I suppose it's rather like the Micrometer maker telling you not to use it as an an adjustable spanner ... But much less intuitive.

For comparison ['though it's not a commonly used design] I think the arrangement on my BCA is worth a look ... This machine is only intended for light work, but the 8" Rotary Table has its 180 teeth cut on the periphery: This results in a much stronger tooth-form, which is more suited to milling.

MichaelG.

.

Note: the pictures of the early Boley and Leinen machine illustrate the design nicely:

http://www.lathes.co.uk/bca/index.html **LINK**

Don't care what they say that's just pure bad design.

OK you expect this from Chinese and Indian tables built to a price but a helical gear in cast iron making point contact is crap.

At one time if you paid your money you could get RT's with bronze wheels of an enveloping design, designed to take the load.

If this is what Yuasa is now turning out you are better just buying Chinese or Indian and saving your money. There is no difference in design.

When I used to to the shows with ARC demonstrating the CNC we used to run for 5 whole days with one machine on 4th axis work all that time.

Usually 8mm cutters in steel

If that was an inexpensive far-eastern RT there would surely be a chorus of 'unfit for purpose'.

My RT has a gear 1/4" thick in brass and it didn't have any problems cutting a curved slot at a similar radius. I rarely bother locking it.

Is there enough 'meat' to make your own gear on a steel sleeve to replace the old one.

Neil

Unfit for purpose.

Hang the bastard

Distant selling regulations.

Contact trading standards

Sell your yours shares in the company.

Edited By John Stevenson on 10/08/2016 08:47:38

Out of curiosity I just had a look inside my Soba one, seems exactly the same with a CI wheel except mine have pristine teeth and that has done work on the rims of 9" flywheels.

Maybe they should stick with making batteries?

You could try contacting YUASA Japan along the lines "you are surprised that a "Premier and respected Japanese Company" etc. The Japanese are very touchy about loss of face and will jump through hoops to prove how good they are.

Had a serious problem with Kawasaki UK spares sometime ago, a simple note to the parent company produced induced cooperation and everything I wanted from the UK operation!!

Comparing the pictures Jason's and the OP, the OP photograph shows serious lack of lubricant with much CI wear particles and bent teeth on the wormwheel. Just a trace of grease on the extremities of some teeth (lower right).

Did OP remove the surplus grease before the photograph? The teeth appear to be seriously overloaded and bent.

Posted by Neil 10/08/2016 08:44:07

Is there enough 'meat' to make your own gear on a steel sleeve to replace the old one.

Neil

Photo in album "rotary table" shows a new bronze sleeve fitted to the old gear blank and hobbed the same 1 module ,new worm milled using the acme thread milling unit that you published in MEW 241 to 243.

John

RT table has some wraparound on the wormwheel of course.

I notice that the pdf shows 2 worm ratio's. 90:1 and 120:1. You don't mention the size of the table  or wheel. All of these have an effect on the strength of the teeth. So it could be a case that they shouldn't offer these ratio's at some sizes because the teeth will be too thin and only ok for positioning and clamping before machining.

It looks like it uses gashed teeth unlike Jason's that may have been cut to suite the dia of the worm. On the other hand there have been several diy designs that use gashed teeth. Initially 40 or 60T depending on size but people want more as it must be better so in one case I think that has been increased.

Somehow I would guess you have the 120T one. Maybe you should ask if the 90T parts will fit. Frankly I can't see why people want more than 60T.

The size of the wheel matters as well. For instance my little 4 1/2" table uses a 60T 31/4 dia worm wheel. Westbury probably didn't want anyone to break it.

John

-

Edited By Ajohnw on 10/08/2016 10:46:18

OP said it was a 6" table.

A picture makes for a 1000 words - probably didn't read it all. I do suspect it's a 120 and would wonder about a 90 at that size but bigger numbers just have to be better don't they.

Looks like the last source of worms and wheels may have gone. I just looked on CES's site. No signs of them. They were better than the ones supplied for the versatile dividing head in some ways. Aimed at an 8" table casting kit that they stopped some time ago and the worm came with the shaft machined. Decent sized gashed wheels as well.

John

-

Edited By Ajohnw on 10/08/2016 11:29:02

.

John,

For convenient reference ^^^ I have quoted the first few words of Paul's opening post, plus the extra thousand.

MichaelG. 

Edited By Michael Gilligan on 10/08/2016 11:37:51

I wonder if the teeth are as deep as they should be because they look rather shallow cut compared to jasons, the typical radial relief to the center seems to be absent too, it should be able to handle this kind of wear and still work.

What shocks me the most is just how much has been scraped off. The cutting must have been really hard going to dig into the table that much. Is this machined grey cast? I wonder if it should be steel.

I have an american made small RT and a big chinese one, the american one is very well made and you can tell by how smooth the rotation is, the other is a little rough around places and wheel can be rather stiff at times, having said that it still works and perfectly operable if you can forgive the blemishes. 

Michael W

Edited By Michael Walters on 10/08/2016 12:01:00

I'd still like to know if it's a 120T, Strong guess that it is.

On the other Michael's post I have looked at a number of heads and tables at the shows and don't like the degree of backlash they show as supplied. It suggests that the makers don't have much confidence in the precision of what they turn out. Seems to apply to some pretty expensive ones as well.

So far me little one has done what I have needed. Also have another with stops and long handle to turn it with. I was offered it years ago and had it for if. A lot of work involved in engraving degrees and adding the adjustable stops but the rest is easy and no gears to break.

 Just add that if I do want a larger table I might make one with a long handle to turn and fixed locations via say 60 holes and a pin.

John

-

Edited By Ajohnw on 10/08/2016 12:21:05