Another rotary table question

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WARNING.

Ensure that the worm screw is adjusted so that it is fully engaged with the worm gear when you are the rotary table.

The engaging ring (the one with the small lever) has a tendency to undo when taking heavy cuts. The vibration caused by the flutes on the milling cutter will undo the ring and the worm will only be engaged with the tips of the teeth on the worm gear. The gear is only made from cheap steel and the teeth can break (see photo). The clamp screw (screw with small tee handle) which is supposed to lock the engaging ring does not always work.

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+1 Never a truer word written.

That gradual backing-off of the engagement lever increases the effective backlash of the system. If you are climb milling taking light cuts you may not notice it, but if your cut terminates at a feature which presents a slightly greater area to the periphery of the cutter, you can get a fairly violent 'dig in' . With a big cutter this can cause significant loads that can shift your workpiece even if it is clamped really well.

He's also correct about that little thumbscrew clamp.

Roger

Roger,

Backing off of the engagement lever not only increases the backlash but increases the stress on the teeth because the load is only taken on the tip of the tooth.

I was conventional milling with the rotary table to try and eliminate backlash and was actually applying pressure by hand to keep the worm gear in mesh when the breakage happened. I did not notice that the worm engagement was coming loose.

Problem was that I was using a 6" rotary table to machine a 250mm dia x 16mm thick piece of boiler plate (460 MPa) which is not easy to machine. The Rotary table was not one of the cheap Asian clones but a good one, made in Japan. To replace it I bought one of the cheap clones but was not as good as the original. Since then I have replaced the worm gear ($150) on the original.

Paul.

Roger,

Backing off of the engagement lever not only increases the backlash but increases the stress on the teeth because the load is only taken on the tip of the tooth.

I was conventional milling with the rotary table to try and eliminate backlash and was actually applying pressure by hand to keep the worm gear in mesh when the breakage happened. I did not notice that the worm engagement was coming loose.

Problem was that I was using a 6" rotary table to machine a 250mm dia x 16mm thick piece of boiler plate (460 MPa) which is not easy to machine. The Rotary table was not one of the cheap Asian clones but a good one, made in Japan. To replace it I bought one of the cheap clones but was not as good as the original. Since then I have replaced the worm gear ($150) on the original.

Paul.

Hi Paul, i did notice the metal looks to have the consistancy of hard cheese, and its good to see an illustration of how damage can occur.

What it be better to fit some sort of locking pin into where the clamp screw goes , as this would prevent the shaft moving even if the locking collar vibrates loose????

Haven`t had time to try this rotary table yet as been busy restoring a much larger mill.

But thought i would give it a try on my mini mill.

How do you cut a 14teeth pinion gear without dividing plates?? The table is 72:1 ratio so 5 degrees per revolution.

I stress that ive never used one before. I have a arbor and the right cutter size(14dp 14 1/2 PA No.7) .

The photos show what i want to do , its the pinion gear for the apron handwheel. I have two worn ones and on this apron the hole for some reason is almost  3mm larger than it should be and someone bushed the pinion shaft with brass. The hole should be 15mm or thereabouts and is now 17.3mm .I cant believe the hole had worn so much in something that is only turned slowly even under powerfeed. The pinion gear on the left of the top picture is how thick it should be,

Thanks

Edited By mark smith 20 on 29/10/2016 12:32:30

Edited By mark smith 20 on 29/10/2016 12:34:00

I came up with this but how do i do it??

Edited By mark smith 20 on 29/10/2016 12:43:57

If you go over to the Homemodelenginemachinist.com forum, someone just today posted a thread on Using the Rotary Table that includes a pretty handy downloadable 25 page PDF instruction manual on how to do it.

Here **LINK**

Basically you will have to use the graduated collar on the handwheel to advance the RT by 25.whateveritwas degrees at a time. Maybe not as accurate as indexing plates but good enough for a rack feed gear I reckon.

Edited By Hopper on 29/10/2016 13:01:26

.

Use this, and make a temporary dividing plate [seven holes or notches should do nicely]

http://www.cgtk.co.uk/metalwork/reference/divider

MichaelG.

I probably should have mentioned:

With a 72:1 ratio, and a seven hole plate; you then want five full turns plus one division, per tooth.

MichaelG.

HI Hopper and Michael both good information which i`ll have to read carefully .

Michael im unsure how to attach a dividing plate to this table as its not one of the one from Warco that you could buy a dividing set.

Ive just made a blank which fits nicely in the apron casting ,and don`t want to mess it up.

I have fixed a er32 collet chuck to the table  but dont have a tailstock ,which may be a problem ,as it will have to be cut with the table on its small end and the cutter fixed vertically in the mini mill on a arbor.

Edited By mark smith 20 on 29/10/2016 14:44:23

Edited By mark smith 20 on 29/10/2016 14:48:09

Wrap a bit of paper around the base of the handle and mark it so it's one full turn. Take it off and divide it into seven sections as accurately as you can.

Number the lines 0-6. take cut one line up with 0, cut two five turns + 1, cut three five turns + 2 and so on.

You should find this is easily accurate enough for your needs.

Neil

Thanks Neil, i have alot to think about now.

Discovered i couldnt quite mounted the table securely and havent any clamps suitable ,so set it up in the vice like picture , will this work or too unstable . I tested the cutter on some aluminium and it worked fine ,full depth with little vibration.

Problem now is im finding it hard to see the dials due to the position of the set up. It will have to wait till tomorrow now.

Edited By mark smith 20 on 29/10/2016 16:58:02

I dont want to rain on your parade but the rigidity of the whole setup is suspect.

For a start, since you have a milling machine you could make whatever is needed to mount the RT direct to the bed. Another issue is that the cutter is a long way from its bearings, Also the job itself has more overhang than ideal.

The table bearing in RTs are generally pretty basic and some appear to rely mostly on gravity to keep the one main load bearing surface in contact.

Regardless of the size of the mill, the less you have to raise the head of the milling machine the better, yours is only a small machine and it has the extra flexibility introduced by the column tilt feature.

Ian P

Ian, no problem at all, it looked less than ideal to me , so i may make some clamps ,i have another bigger mill but don`t have much tooling as yet for it or actually finished setting it up. .

+1

Get rid of the vice and minimise overhang. Also, if possible provide tailstock support, even if it's only a block with a rod in it that has a 60º taper on the end.

Andrew

Edited By Andrew Johnston on 29/10/2016 21:13:46

You could do what I did to my home made RT - I screwed a 10mm thick plate with two fixing slots to one side of it. A bit of care meant that it's accurate enough to sue one edge of the plate with a square for setting up.

Neil

Well thanks for all the advice i managed to get it cut using the set up i had above but moved the blank into the collet chuck further . I worked ok as far as my limited experience goes with no vibration of the set up.

The shaft and gear work fine and a big improvement on how it was. Because of the thicker shaft the order of asembly has to be slightly different as the shaft hits the large gear next to it when your putting it in otherwise!

I now have to cut a very thin groove for a wire circlip thing on near the end of the gear . This holds on the floating larger double gear next it. Whats the best way of doing this a fine slitting saw?

Thanks

Edited By mark smith 20 on 30/10/2016 15:17:49

Got the clip spring thingy done using a 0.6mm slitting saw and the rotary table.

works fine!

Edited By mark smith 20 on 30/10/2016 15:56:03

Mark,

I don't want to pee in your soup, either, but those tooth profiles on the pinion don't look right to me.  Too much material taken out at the root. Compare them to the tooth form on the larger gear and the gear cutter, for that matter. I guess it will work as long as it doesn't have to take too much torque.

John

Edited By John Hinkley on 30/10/2016 16:06:05

John , you may be right i don`t know ,as i said its my first attempt. Remember the other gear is worn as well.

Do you mean ive cut slightly too deep?

Its bound to work better than what they were they were worn to sharp points.

The cutter match the other gear tooth profiles exactly , so not sure how it can be radically different .