# How do you Accurate Mill a Full Circle?



## oskar (Aug 31, 2018)

I want to cut 2 circles in 3/8” aluminum one 8” OD and the other 10” OD

Reading on various threads I gather a rotary table will be the only solution but my question is I don’t see how a rotary table will work unless this table is motorized?

Otherwise I will have to manually turn the table against a speeding end mill which I don’t think it’s safe to do

I don’t have a rotary table yet so I wonder how it works

Nicolas


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## shooter123456 (Aug 31, 2018)

Rotary tables can be used to cut manually. That is what they are for.  You can cut conventionally if backlash is an issue with the rotary table.

The rotary table will likely have a worm gear which will translate the rotation in the lever to rotation on the table.  They are set up to be able to handle cutting forces.  They aren't meant only for positioning. 

Depending on accuracy required, time you are willing to invest, and travels of the mill, you can create a chart of points around the outside and drill them, then use sandpaper to clean up the edges.  If you have a lathe, with sufficient clearance, that is also an option.


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## Technical Ted (Aug 31, 2018)

The turn tables I'm familiar with have a way to very finely adjust the worm to eliminate most, if not all, of the backlash. 

Yep, crank it by hand.

Ted


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## Mitch Alsup (Aug 31, 2018)

That is what rotary tables are built to do.

Although for 10" and 12" I would use the backplate on my lathe.....


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## BaronJ (Aug 31, 2018)

Hi Guys,

Yes I would agree !  Trepanning the discs on the lathe would be the way to go.  I can just manage 9" inches on my Myford using an 8" inch faceplate.
A well ground tool and plenty of WD40 or Kerosene.  Milling would be awkward and time consuming, plus you would have to arrange some method of workholding.

Actually I've just turned a couple of brass discs 2"inches in diameter by 2mm thick, trepanned out of a sheet 10" square using a drill press.


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## oskar (Aug 31, 2018)

Didn't know about Trepanning which may be a solution (after some practice). Also didn't know about the worm gear on the RT, must be expensive


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## BaronJ (Sep 1, 2018)

Hi Oskar,

Trepanning is a very very old technique for cutting round holes and plates.  Dating from around 6000 BC.


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## P. Waller (Sep 1, 2018)

BaronJ said:


> Hi Oskar,
> 
> Trepanning is a very very old technique for cutting round holes and plates.  Dating from around 6000 BC.


Used for making holes in skulls for medical treatment.

In the case of the OP's question buying a rough cut blank from a material supplier and finishing it on a lathe or mill is the most cost effective.
This is a 35" diameter aluminum disk cut with a bandsaw from plate by the metal supplier. This is a lathe faceplate fixture, I drill mounting holes for the part and faceplate mounting first.



Mount it to the lathe and turn it in place then clamp the part to it and do the work. None of this is fast, if the major concern is time when using a manual rotary table then Buck up and buy a powered rotary axis or a 2 axis mill that will interpolate the sizes at the accuracy required.


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## oskar (Sep 1, 2018)

Hey Walker, the size of your shop and equipment are amazing!

I’m retired which means I have tons of time and Trepaning looks like it’s for me but not for a 35” piece, my mini lathe is half that size LOL

Anyway a rotary table might be a good tool to have and I found a place close to my home which they have a reasonably priced one with tilt table for CAD$ 189.00 shipping included. It’s the 5th item on this page

https://www.busybeetools.com/search.php?search_query=rotary

Can you give me your opinion?

Perhaps in the States there are better ones but since I’m in Canada it has to be from Canada to avoid shipping cost, duties and taxes.

Nicolas


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## P. Waller (Sep 1, 2018)

Manual rotary tables should be easy to find used, most job shops stopped using them 30 or more years ago, I suspect that many of them are entirely to large and heavy for hobby machines however.

For general hobby use a vertical/horizontal tool with a tail stock would be far more versatile.


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## Bob Korves (Sep 1, 2018)

A rotary table (or a lathe compound, or other machine slides) feed can be operated quite smoothly and predictably using this relatively simple technique:




Starts at 6:15, money shot starts at 18:00
A drill with variable speed and an adjustable stop for the trigger is needed, along with a fabricated adapter to fit the handle.  The end mill can be ramped down into the work as the rotary table rotates, and also ramped out at the end, leaving a nice smooth cut.  This technique can be used with many machine tools to make an axis feed smoothly, a poor man's power feed and stepper motor.


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## stupoty (Sep 1, 2018)

oskar said:


> I want to cut 2 circles in 3/8” aluminum one 8” OD and the other 10” OD
> 
> Reading on various threads I gather a rotary table will be the only solution but my question is I don’t see how a rotary table will work unless this table is motorized?
> 
> ...




yeah hand crank for curved slot milling or as you say for cutting a circle.  As has been mentioned the worm gear makes it very light work , only risk is backlash if you change direction mid cut.

Depending on the accuracy required you could use a router and a circle jig.

Stu


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## P. Waller (Sep 1, 2018)

oskar said:


> Hey Walker, the size of your shop and equipment are amazing!
> Nicolas



Start by drilling and tapping a hole in the OD for a lifting eye.
This is a drill press (-:
Ugly, smelly and LOUD. A very unpleasant machine in every way.


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## Meta Key (Sep 1, 2018)

P. Waller said:


> Manual rotary tables should be easy to find used, most job shops stopped using them 30 or more years ago, I suspect that many of them are entirely to large and heavy for hobby machines however.
> 
> For general hobby use a vertical/horizontal tool with a tail stock would be far more versatile.



Yup.  Exactly.

One thing to consider is size.  I sometimes feel cramped on my 9" Troyke rotary table. Clamping stuff to the table takes room!  I'd be hard pressed to clamp much onto a 4" rotary.  But, if the stuff you're working on is small (yeah, I know, a relative term) then it might do the job..

OTOH, I have a 6" indexing head (Ellis) with a four jaw chuck on it -- love that thing!  

I think the used market for these things has dried up a little.  I don't see as many being advertised for sale as I did 20 years ago.  But, if you aren't in a huge hurry you might start asking around, watching the auctions, etc. etc. You might turn up a bargain on a 6" horizontal / vertical..

MetaKey


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## oskar (Sep 1, 2018)

Nice video and technique Bob, thanks

Walter that monster machine is a drill press? Never though they come in that size


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## P. Waller (Sep 1, 2018)

Radial drill as seen here but about 60 years older.
https://www.toolbarn.com/jet-320038...Yssw04_pcrid_90615788774_pkw_PLA_pmt_b_pdv_c_

Until about 6 years ago we had a machine that was designed for exactly what you want to do, a 36" Bullard horizontal turret lathe, these machines will trepan 10" circles all day and night.
Also a big ugly unpleasant machine but will do the work.
https://i.ebayimg.com/images/g/sWEAAOSwax5Yq0JH/s-l640.jpg


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## BaronJ (Sep 1, 2018)

Hi Oskar, Guys,

If you are going to buy a rotary table, don't waste your money on one with a tilt facility.  You will loose that all important rigidity.  There are better and safer ways of milling at an angle.


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## brino (Sep 1, 2018)

P. Waller said:


> . A very unpleasant machine in every way.



Unpleasant to pay for and unpleasant to move I would agree with.
However I would love to own and operate 
one.
-brino


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## P. Waller (Sep 1, 2018)

brino said:


> Unpleasant to pay for and unpleasant to move I would agree with.
> However I would love to own and operate
> one.
> -brino


If you ever have to use such a machine you will quickly change your mind (-:

I use this 40's-50's Warner and Swasey #5 turret lathe for drilling holes for boring operations finished in other lathes.
It is also big, ugly and smelly yet nearly silent when operating so go figure.
It will drill 3" holes through 8" of stainless without a spot or pilot drill all day long, a very powerful machine. 20" chuck and 5" through the spindle, turn it on and go and do something else until it is done drilling. 

It will however explode a 2 1/2" High Speed Steel twist drill but you are better off not being there when that happens, it will not stop.


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## oskar (Sep 1, 2018)

BaronJ said:


> Hi Oskar, Guys,
> If you are going to buy a rotary table, don't waste your money on one with a tilt facility.  You will loose that all important rigidity.  There are better and safer ways of milling at an angle.



Thanks for mention it but I thought about it and before I buy I will see the unit and check all details

Nicolas


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## T Bredehoft (Sep 2, 2018)

Bullard VTL's. The shop I worked in had a number of them, the largest had a 6 foot table, buried so the table was flush with the floor. They were installing a new CNC model when I retired. I ran a couple of them on occasion, not production, though.


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## jdedmon91 (Sep 2, 2018)

Bob Korves said:


> A rotary table (or a lathe compound, or other machine slides) feed can be operated quite smoothly and predictably using this relatively simple technique:
> 
> 
> 
> ...



I made on similar for my Grizzly. Thought I had a picture or video of it but can not locate it.


Sent from my iPad using Tapatalk


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## pineyfolks (Sep 2, 2018)

For an interesting trepanning tool forward to 15 minutes into the video.


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## MrWhoopee (Sep 3, 2018)

Meta Key said:


> One thing to consider is size.  I sometimes feel cramped on my 9" Troyke rotary table. Clamping stuff to the table takes room!  I'd be hard pressed to clamp much onto a 4" rotary.  But, if the stuff you're working on is small (yeah, I know, a relative term) then it might do the job..
> MetaKey



+1
For just milling the OD, you might get away with a threaded center stud as a clamp. In most situations, you need to put clamps around the OD of the part and, for that, the table must be significantly larger than the part.  To clamp a 10 in. diameter securely, you would need a 14 in. RT. Don't buy one of those baby RTs, it will only serve to frustrate you.


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## BaronJ (Sep 3, 2018)

Hi Guys,

Depending upon size and sometimes material I just use an adhesive between the work and faceplate.


This is a piece of 3 mm thick brass plate that is about to be made into a 65 mm round disc.


Almost completed !  Just needs facing off to remove the slight bow in the plate.  As it happens the chuck is also 65 mm diameter.  But since the chuck is sacrificial it doesn't matter if it gets damaged.


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## oskar (Sep 3, 2018)

MrWhoopee said:


> +1
> For just milling the OD, you might get away with a threaded center stud as a clamp. In most situations, you need to put clamps around the OD of the part and, for that, the table must be significantly larger than the part.  To clamp a 10 in. diameter securely, you would need a 14 in. RT. Don't buy one of those baby RTs, it will only serve to frustrate you.



Very good point which I never thought about it. Thanks

Nicolas


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## BaronJ (Sep 3, 2018)

Hi Guys,

But why ?  You would probably need a hoist of some description to lift a 14" RT up on to your mill, assuming that your mill would even be big enough to support it.

If you wanted to cut a disc, and your mill could swing a 7 inch radius, a six inch rotary table with a flat plate mounted on it, that you could glue your work to, as illustrated above could easily machine a 14" diameter disc in almost any material you wanted to use.

The method of workholding that I've shown, called a "Wax Chuck" has been in use for well over a couple of centuries. It is still in use today.


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## oskar (Sep 3, 2018)

That's another option to think, I was thinking to go with a 4" RT but I'm sure it is kind too small so perhaps a 6" RT might be the best. Anything over that for my hobby use will be an overkill. In any case have lots of time before I buy one, will happen around X-Mas hoping it will come as a "gift"


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## Bob Korves (Sep 4, 2018)

MrWhoopee said:


> +1
> For just milling the OD, you might get away with a threaded center stud as a clamp. In most situations, you need to put clamps around the OD of the part and, for that, the table must be significantly larger than the part.  To clamp a 10 in. diameter securely, you would need a 14 in. RT. Don't buy one of those baby RTs, it will only serve to frustrate you.


A smaller rotary table can be made to act larger by putting an oversize tooling plate on it.  That makes mounting parts a lot easier, just drill holes in it where they are needed.  Rigidity will not be improved, however, bigger rotary tables help that.  On my Millrite mill with 8x32" table, I find an 8" rotary table the Goldilocks solution.


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## BaronJ (Sep 4, 2018)

Hi Bob,

Yes I agree.  It bothers me when chaps who should know better drop hundredweights of tool holding on to a machine that obviously isn't designed to support it.  A 6" RT is right size for my Optimum BF20LB.  And as you say, a tooling plate solves a lot of issues.  Lack of rigidity was the reason I said that Oskar should avoid a tiltable RT.


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## oskar (Sep 4, 2018)

No tilt table for me and 6" sound good. Thanks BaronJ


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## P. Waller (Sep 4, 2018)

A little CNC treachery, Friday afternoon I parted the heads off of a bunch of 1/4-20 SHC screws, you may ask why do such a thing at all, the answer is That Is What The Customer Wanted.
Leave the set up in place and turn the lathe off until today. I do not trust these machines after being turned off.
Run the tool to where X axis Diameter 0.000 should be and about 1/16 from where Z axis +.500 should be.
As seen here, this is the actual 0, +.5 position



This is where the machine thought 0, .5 was this morning.



You may notice that the machine now thinks that the center of the spindle is now 27" on the back side and Z 0.50 is now 63" on the left side of the chuck. Do not trust the beasties after turning them off. The good thing is that these types of machines will not execute a canned cycle that is well outside of its travel parameters, it may do so if manually coded however, do not try this.

I did not notice until just now that the displayed soft stops also have absurd numbers with minus dimensions, go figure.


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