Author Topic: Making a Rotary Table  (Read 29440 times)

Online NormanV

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Making a Rotary Table
« on: September 04, 2014, 01:48:41 PM »
 I have started on my Rotary Table. Here is the worm and wheel that I shall be using. It is a single start worm and the wheel has 30 teeth. This will give me 12 degrees for each turn of the worm.

Online NormanV

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Re: Making a Rotary Table
« Reply #1 on: September 04, 2014, 01:50:19 PM »
Here are the drawings showing the main details of what I plan to do. The main body is 160 x x150 x 50mm.

Online NormanV

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Re: Making a Rotary Table
« Reply #2 on: September 04, 2014, 01:52:42 PM »
I will be making the main body of the table as aluminium castings. These are the patterns. Although the main body of the table will end up open topped I made the pattern with a thin plywood top to make the moulding easier.

Online NormanV

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Re: Making a Rotary Table
« Reply #3 on: September 04, 2014, 02:05:10 PM »
I've had two days of problems trying to produce the two simple castings. On my first attempt the flask opened and the molten metal leaked out all over the ground. The main casting was ruined but the flat top plate was OK.
This is the second time that this has happened with this flask, I am guessing that it is too light, it will become firewood.
I started to remelt the faulty casting casting and ran out of gas! I haven't got any transport at the moment so am unable to go to get any more so I decided to use charcoal.
I started today with the charcoal and could just not get enough heat, if I had the air blast too high I was showering the surrounding area with cinders and on a low setting the charcoal was burning too slowly. It was rubbishy charcoal, tiny pieces and lots of dust. After 3 hours the metal melted and I was able to pour the casting. It did not turn out perfectly but it is usable. The metal cooled and did not fill the top where I had used the thin ply. I had expected this and planned to cut it away anyway. There are also two quite large shrink cavities in the top but they are of no consequence as I have left quite a large machining allowance.

Offline vtsteam

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Re: Making a Rotary Table
« Reply #4 on: September 04, 2014, 07:54:21 PM »
You're forging ahead Norman! :thumbup: :thumbup: :clap:

I like your pattens with very heavy sections. Nice and solid.

3 hours to melt!!! That's painful. Must be very different to the charcoal briquettes we get here. Generally takes about 20-30 minutes from a cold furnace to melt 5 pounds of aluminum.

If I use the charcoal I make from wood (real charcoal) it does shower if the blast is too high, as you say, and it burns up faster, being less much dense. But the furnace temp can go much hotter than the commercial BBQ briquettes will take it. It will actually melt a steel rebar, and certainly melt bronze or brass. The downside is you have to add it a few times during an aluminum melt. Briquettes will usually complete an aluminum melt without any additional fuel top-up  for me. They are really different fuels.

Anyway, I'm glad you finally got your parts cast -- that was a Herculean effort in a 3 hour melt -- and a second one, as well. Great work!  :clap: :clap: :beer:
I love it when a Plan B comes together!
Steve
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Online NormanV

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Re: Making a Rotary Table
« Reply #5 on: September 05, 2014, 02:37:25 PM »
Thanks Steve, I won't be going back to charcoal unless there is no other choice.
I've started machining the main casting, I did the top and bottom surfaces with the casting held in the 4 jaw chuck in the lathe, I was delighted with the finish that I achieved. There were no bubbles or inclusions in the metal.
I've also done two of the sides on my milling machine, I was a little nervous of holding such a tall casting in the vice but I needn't have worried, it held very securely. Tomorrow I will do the other two sides.

Offline vtsteam

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Re: Making a Rotary Table
« Reply #6 on: September 05, 2014, 03:43:46 PM »
Nice having a mill to do that with!  :thumbup:  :beer:
I love it when a Plan B comes together!
Steve
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Offline mattinker

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Re: Making a Rotary Table
« Reply #7 on: September 05, 2014, 03:53:54 PM »
Thanks NormanV,

I'm enjoying this!

Regards, Matthew

Offline philf

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Re: Making a Rotary Table
« Reply #8 on: September 05, 2014, 04:01:59 PM »
Norman,

Super work.  :thumbup:

What's next after you finish the rotary table?

 :beer:

Phil.
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Location: Marple, Cheshire

Offline PekkaNF

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Re: Making a Rotary Table
« Reply #9 on: September 05, 2014, 04:18:05 PM »
Am I missing something here, I would imagine that you need a tail for this, or a second bearing, or is the table surface also a bearing surface to the rotab table? I'm not trying to be a pain, just curious.

Pekka

Online NormanV

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Re: Making a Rotary Table
« Reply #10 on: September 05, 2014, 04:55:12 PM »
Pekka, you may well be right, I do not mind the criticism. I had planned for the table to sit on the top plate and to be clamped to it. This would be fine for indexing but not for cutting curved parts. I could add a bridge piece with a bearing below the worm wheel, this would brace it. Any comments or ideas are welcome, I am no expert.

Offline Arbalist

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Re: Making a Rotary Table
« Reply #11 on: September 05, 2014, 06:17:04 PM »
That's a nice chunky looking casting Norman, looking forward to seeing how you progress!

Offline PekkaNF

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Re: Making a Rotary Table
« Reply #12 on: September 06, 2014, 03:32:19 AM »
I have normal #6 size rotab and it's fine with drilling and even light milling, but it is not happy when I  feed work against the mill, if it is even close to circumfrence of the rotab table. It looks like that the table is lifting or moving sideways.

If you only use the table for indexing, you may consider dimenssioning parts such way, that the bearing keeps everything in close contact and then you use clamps or dogs to pull the top (rotab table) into the body. If you can imobolize them for a cut, I believe it all would be fine for drilling and such.

The problem with bearings is that they are all designed to very spesific purposes and need some getting used to. Here you have short bearing distance and you need some rigidy in all directions. It would be simple if major forces would work only one or two directions.

Professional rotabs have very elaborate bearing arragements, simplest form is something like this on top:
http://www.wd-bearing.com/en/WD-YRT-Rotary-Table-Bearings/WD-YRT-Rotary-Table-Bearings.htm#.VAq2hmMsHOg

We hoppyist find it very difficuts to machine parts to make use of this kind of stuff and must hope that robot joint falls on front yard from e-bay or just make it the way it has been made in last 100 years - plain bearings:
http://www.deansphotographica.com/machining/projects/mill/rotary/50.jpg

The bottom bearing (surface) just pulls it all together. This does not look very different from yours:
http://www.deansphotographica.com/machining/projects/mill/rotary/rotary3.html

Maybe you'll find it useful.

Pekka
* fixed mass of typos, I wonder if anybody made any use of this. I got new mini laptop and keyboard is very different from the old one. Aso, I'm blind as a bat and this display is small. I allready got time on optometris. I need separate glasses for driving, work, reading and soon for a computer display. What next? A guide dog or white cane?
« Last Edit: September 06, 2014, 04:07:19 PM by PekkaNF »

Online NormanV

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Re: Making a Rotary Table
« Reply #13 on: September 06, 2014, 11:03:15 AM »
Thank you Pekka for your detailed comments, the Taig design is similar to what I intend to do including clamping the table to the body whilst making a cut. This of course does not enable me to make a cut whilst rotating the table. This is something that I had not given enough thought to as it is a facility that would be useful. There may be enough space under the worm wheel to fit a bearing that would give the support needed, but I do have a piece of equipment that may contain a ring bearing that would support the table. I'll only know this if I can work out how to dismantle it!
Today I machined the remaining sides of the body casting and faced off the top plate. I am really pleased with these two castings as they have no bubbles or inclusions where it matters. I am confused at the talk of the need to degass the molten metal, I do nothing other than skim the top of the melt before I do the pour. Forty years ago I did some aluminium casting at evening school and that metal was degassed but still had bubbles in it.
The milling machine does throw the swarf around all over the place, I had to spend a lot of time vacuuming it all up as I found it quite irritating crunching underfoot.

Online NormanV

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Re: Making a Rotary Table
« Reply #14 on: September 06, 2014, 11:06:46 AM »
By the way, does anybody have any suggestions as to the cause of the rings on the top plate? The feed was done by hand but the rings are equally spaced.

Offline vtsteam

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Re: Making a Rotary Table
« Reply #15 on: September 06, 2014, 09:36:33 PM »
Norman, I'm with you on not de-gassing (or fluxing) aluminum melts. I never have, but the aluminum stock I used was clean and always from castings rather than mixed extrusion scrap. I poured relatively cool, unless very thin castings were required, there was minimal dross, and the charcoal protected the top of the melt. It poured nicely, and it looks like yours does, too.

I don't think the circles are perfectly evenly spaced so I'll take a guess at what they are -- pickup of a small aluminum welded chip on the lathe tool tip, and it gradually wearing off, then picking up a new one.


I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Making a Rotary Table
« Reply #16 on: September 07, 2014, 04:26:28 AM »
Norman, consider a thin sheet of Teflon as a bearing if space is tight. The large surface area gives loads of load capacity, and as it will always be a slowish rotation there is no issue with speed and heat.
Andrew Mawson
East Sussex

Online NormanV

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Re: Making a Rotary Table
« Reply #17 on: September 07, 2014, 06:02:56 AM »
Teflon would certainly be less bulky than a bearing. I managed to dismantle the piece of equipment that I have with the ring bearing. Here is a photo, the balls run on hardened steel. Would this be Ok to take the cutting forces? The balls are approximately 4mm dia. Rather than try to clamp the table down onto the top of the body I could use a split cotter on the spindle. Any comments?

Offline awemawson

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Re: Making a Rotary Table
« Reply #18 on: September 07, 2014, 07:26:11 AM »
Does the Admiralty know that you have that gun mounting  :lol:
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Making a Rotary Table
« Reply #19 on: September 07, 2014, 09:51:36 AM »
I think it was just a really serious Lazy Susan  :lol:
I love it when a Plan B comes together!
Steve
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Offline BillTodd

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Re: Making a Rotary Table
« Reply #20 on: September 07, 2014, 10:37:00 AM »
With a slow moving thing like a rotary table, a plain bearing will give the better damping, making less prone to ringing.

Bill
Bill

Online NormanV

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Re: Making a Rotary Table
« Reply #21 on: September 07, 2014, 01:07:55 PM »
Bearing (!) in mind Andrew's and Bill's comments here is my revised design. I like the idea of using Teflon as a bearing surface and have exchanged the bearing with a bush, ideally this would be bronze but as I don't have any I will use steel. This should not cause problems when making a cut and hopefully I will be able to rotate the table to produce curved surfaces.

Offline PekkaNF

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Re: Making a Rotary Table
« Reply #22 on: September 07, 2014, 02:18:33 PM »
Is that from gunsight or "target finder"? I like that a lot.

I don't like PTFE that much. I have used it a little on fly reel bearing/brake, but it was not that easy to glue. Also it needs certain surface quality, too coarse is no good, but neither is too smooth. It is also very soft and has tendency to extrude when loaded. Therefore you need a LOT of area. You might get away on top, because you have a lot of surface area there, but I don't like the look of bottom bearing on teflon. I would use metal (or composite) plain bearing. Easy on lubricant, you don't want it on teflon. The good thing is that if teflon sucks, you can go on POM and after that you can go reinfoced composites, and by them you know a thing or two on syntethic bearings.

As you see I'm big on rolling bearings, but plain bearings are great on loads which would brinnel ballbearings in no time.

My 2 erocents,
Pekka

Online NormanV

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Re: Making a Rotary Table
« Reply #23 on: September 07, 2014, 02:38:01 PM »
I have no idea what the original use of the bearing was, I removed it from a piece of specially made equipment whose use I do not know.

Offline mattinker

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Re: Making a Rotary Table
« Reply #24 on: September 07, 2014, 03:12:17 PM »
You could use mild steel as a thrust washer against Al, Al steel are a good bearing combination. Example, steel camshaft running in Al cylinder heads. For the speed that your dividing head is going to turn, oil lubricated Al steel would be  good.

I liked the idea of a split cotter to lock the turntable.

Regards, Matthew.