Rotary Table vs Dividing Head ?

[blanik]

Greetings,

I'm looking to buy either a Rotary Table or a Dividing Head for use on my Sieg SX2.7 Mini-mill.

I'm an instrument maker/Instrument Fitter by trade, and after a break from the trade of around thirty years, I'm now starting to get back into the work as a hobby. My current uses for a Dividing Head or Rotary Table include; instrument and clock gear cutting (previously done via a dividing attachment on the old lathe), radius cutting, etc. Future uses could be anything, as I have no idea where by hobby will take me during my retirement.

I notice that Rotary Tables are now being supplied with optional Dividing Plates & Sectors, and Tail Stocks. At first glance, that suggests that a modern Rotary Table (purchased with the dividing accessories), can do the same job as a traditional Dividing Head. Is this right ?

The 100mm Dividing Head that I'm looking at is the Vertex BS-0. That's the tilting version - I'd prefer the non-tilting version of the Vertex Dividing Head, but the local dealer doesn't currently stock it.

The 100mm Rotary Table that I'm considering is the Vertex HV-4, with the Dividing Accessories and Tail Stock.

Dimensions wise, the 100mm Rotary Table with Dividing Accessories, takes up a lot less space on the mill table than the 100mm Vertex Dividing Head. So, that's one possible plus for the Rotary Table.

Price wise, they're similarly priced.

So, the big question ....... Are these two tools, the Dividing Head, and the Rotary Table with Dividing Accessories, interchangeable ? Or, are there some jobs that one of those tools can do, that the other tool can not do ?

Looking forward to hearing your advice.

Regards,

Blanik

 

[kvom]

For gear cutting the dividing head option is a big advantage, as otherwise you'd need to potentially turn the work manually to precise settings on the degree scale.

 

[Dalee]

Hi,

With the add on dividing plates and parts, a rotary table can cut gears nearly as well as a dividing head. (I've found the RoTabs to be a bit flexy under heavy load). But a dividing head won't do arcs.

The biggest problem with either is the size. I never have a large enough RoTab, and the dividing head small enough. A horizontal/vertical RoTab is pretty large compared to a similar dividing head. This can cause problems on occasional setups. Nor do you get to a tilting option with a RoTab.

Which is right for you? Darned if I know. You need to figure out if you want to cut more gears or make more arcs. Can you live with an oversized index setup creating a headache sometime? Or do you need a more compact setup.

Me, I have a 6"(152.5mm) Vertex RoTab and no plates - yet. I'm more interested in making things like spoked flywheels at this point. But gears are on the horizon.

Dale

 

[bazmak]

Ideally you want the RT with the index plates.As others have said its what you want to use it for.I had never used one before and didn't want to spend a lot of money for limited use at my age.If you look at my threads under Bazmak
I made a simple manual rotary table and have just finished a simple indexing
head.Rough and ready but already I have lots of use and I enjoyed making them.If you are younger and confident they will be put to good use then purchase a decent one,the largest that will fit your mill

 

[Cogsy]

But a dividing head won't do arcs.

I've heard this before but I do arcs with my dividing head all the time. Why is it that people think it's not possible? (I'm not trying to argue, I'm honestly curious what the thinking is behind this)

 

[Wizard69]

Since you lean strongly towards gears and the like I'd go with a dividing heads. Sizing one for a small machine is a chore as most of the commercial units assume a larger machine. You might want to consider making one following any number of plans available out there.

 

[blanik]

I've heard this before but I do arcs with my dividing head all the time. Why is it that people think it's not possible? (I'm not trying to argue, I'm honestly curious what the thinking is behind this)

I've got to ask the same question. Why can't a dividing head do arcs ? Or,is this idea one of those urban myths that keep getting repeated ?

Blanik

 

[kiwi2]

Hi Blanik,
I've got both a Vertex BS-0 dividing head and an HV - 4 rotary table which I use on my SX 2.7 mill.
I bought the BS-0 more than 20 years ago. It was really expensive back then (about NZ$1,000 I think).
It swivels so you can set it up so the face is horizontal but by the time you add a chuck it's getting quite high and you sometimes run out of room for the tooling.
I bought the HV-4 a year or so ago as it was more convenient to use in the horizontal position and it was relatively cheap (about $300).
I have used it in the vertical position to cut a 107 tooth gear which isn't covered by any of the dividing head wheels I've got. I set up an excel spreadsheet with the angle required for each tooth which isn't as easy as it sounds as the rotary table is calibrated in degrees/minutes/seconds rather than decimal degrees so it took a bit of figuring out how to do it.
Anyway, I cut the gear all right (crossing out each angle on the spreadsheet as each tooth was cut) but you really need to be concentrating using this method.
The HV-4 is awkward to clamp in the vertical position as it has no clamping recesses low down so you need to clamp it on the top.
I had a few problems with it when I first got it which were covered in an earlier post.
http://www.homemodelenginemachinist.com/showthread.php?t=24264
One problem I had with the BS-0 is that the tapered hole isn't a #2 Morse taper but a Brown and Sharp taper which meant I couldn't find any collets for it. In the end I made a 1/2" collet out of brass which I found to be really useful. I don't know if that is the case with the modern versions.
I hope this info is useful.
Regards,
Alan

 

[goldstar31]

One problem I had with the BS-0 is that the tapered hole isn't a #2 Morse taper but a Brown and Sharp taper which meant I couldn't find any collets for it. In the end I made a 1/2" collet out of brass which I found to be really useful. I don't know if that is the case with the modern versions.
I hope this info is useful.
Regards,
Alan

Mine is No2 MT and threaded for the Myford tooling ie chucks, face plates collets etc

I was deliberate and ignored accessing the internet with whoever felt the need to become a 'novelist' or worse.

Where I got to was ignoring the somewhat anti Myford lobby and to realise what I was going to get. So I got a new 3 jaw chuck, a faceplate which was undrilled as well as a tail piece.
So I had three sets of collets. A set which I made to Sparey's old designs, the Myford imperial ones and a set of cheaper ER25's and holder. Not everyone's ideal kit, you may assume.

So it all goes on my little Warco mill drill as a conventional gear cutter using the 20DP, the 14 DP and the 16DP stuff as well as 24 and - a lot, which I might remember sometime

So I've got a Mark 1 Clarkson which made my Quorn redundant- if I had the wit to move the BSO onto it. So, apart from the Clarkies normal abilities, I can do milling cutter ends using the Myford collets- which are dead to size for Imperial cutters. With the reasonable but not perfect ER25's, I can do four facet drill grinding. Obviously, having to make a lot of my own tooling, the Myford chucks and impedimenta will go on the Clarkie and the mill drill.

Of course, having a undrilled faceplate, it should be possible to modify a chuck to go on it to do epicyclical and eccentric turning and grinding. I've found where the forgotten books are hidden in Newcastle!

After all the Clarkson was ALL of £100 and that included an electro mechanical chuck.

Not everyone's ideal but amusing

Norman

 

[SmithDoor]

It is more of what you plan to machine
A Dividing Head great for gears and drilling holes
A Rotary Table great for milling radius and angle cuts
Both can do the others job
My self after few years I purchase both note: I kept both on smaller side as found out large not fun to put on the mill table

Dave

 

[Dalee]

I've got to ask the same question. Why can't a dividing head do arcs ? Or,is this idea one of those urban myths that keep getting repeated ?

Blanik

Hi,

While you can mill an arc with a dividing head, you can't do it nearly as accurately as can be done on RoTab. For many things accuracy might not matter too much. But when you need an arc that is 34deg 25min, the Rotab is the weapon of choice for the manual machinist. As a side note, some dividing heads with threaded spindles for mounting a chuck can be a bit risky to try and mill arcs with.

When you need to divide a circle into 73 equal parts, a dividing is the tool to use.

In the end, this is why Rotabs and dividing heads are two separate, (if a bit obsolete these days), tools. Back in the day, this is why many shops had both.

Dalee

 

[Cogsy]

Thanks for that - I've never used a rotary table, only a dividing head so I had no idea. Cheers.

 

[Wizard69]

Hi,

While you can mill an arc with a dividing head, you can't do it nearly as accurately as can be done on RoTab. For many things accuracy might not matter too much. But when you need an arc that is 34deg 25min, the Rotab is the weapon of choice for the manual machinist. As a side note, some dividing heads with threaded spindles for mounting a chuck can be a bit risky to try and mill arcs with.

I want to add here that threaded spindles in general are something to be avoided if you are building up a shop from nothing. As pointed out the threat of a chuck unscrewing is pretty significant and forces you to select the direction of machining. I went with a 9x20 which has a screwed on chuck and kinda regret not choosing something different. In my estimation even the bolted on chucks of the 7xXX series are a better solution. This especially if you want to get as much versatility as possible out of a machine.

When you need to divide a circle into 73 equal parts, a dividing is the tool to use.

In the end, this is why Rotabs and dividing heads are two separate, (if a bit obsolete these days), tools. Back in the day, this is why many shops had both.

Dalee

The obsolete nature of the tools actually makes them a bit cheaper. Used or new prices are very affordable these days. However in some cases I really think people should consider CNC upgrades as the cost has become reasonable and is offset if you avoid a rotary table buy. A 3 axis CNC won't replace the need for a dividing head in some cases though.

I know people out there avoid CNC preferring to turn the cranks, which is fine, but for somebody building up a shop from ground zero CNC should be looked at simply due to potential cost savings. It is kinda strange to say that actually as CNC was once cost prohibitive, now it is more of a balancing act.

 

[Nick Hulme]

I want to add here that threaded spindles in general are something to be avoided if you are building up a shop from nothing.

This is because no one has access to the common sense or complex indexing and drilling technology required to add 3 evenly spaced grub screws to lock screw-on chucks to the register, oh, hang on :hDe:

 

[Nick Hulme]

While you can mill an arc with a dividing head, you can't do it nearly as accurately as can be done on RoTab.

Your previous answer to this direct question amounted to "Because it can't" and gave no logical or technical explanation making it look like you're passing on questionable information which you don't understand and cannot explain.
So why can't a dividing head be used to mill an accurate arc?

 

[lohring]

I only have a dividing head with a screw on chuck. I use it all the time to machine accurate arcs. It's easiest to machine an arc that's concentric with another round area that can be held in the chuck. However, I made a fixture to machine the arcs for a model outboard lower unit like the one below. There's a channel between the two aluminum halves, matching the outside curve, that contains a flexible shaft that drives the propeller. That type of arc would have been easier with a rotary table, but it's still possible with a dividing head using fixtures.

Lohring Miller

 

[KB3RLJ]

What about the spin indexers I see offered on eBay? They are sold less than $100. It takes collets that I don't have but can get. What kinds of things can you do with one of these?

 

[Wizard69]

What about the spin indexers I see offered on eBay? They are sold less than $100. It takes collets that I don't have but can get. What kinds of things can you do with one of these?

The quality of the cheap ones vary considerably. That is to be expected when they are made to a price point.

The biggest problem is that spin indexers aren't really designed to be a replacement for a dividing head. A dividing head can position something to very fine precision, almost infinite where as a spin indexer does either 24 positions or provides for one degree increments. Not every indexer on the market supports one degree increments, so checking capabilities is important. Some guys have taken these cheapies and have converted them to full dividing heads so it might be a good base for a DIY project.

Most of the spin indexers you will find in the USA take 5C collets! Before you buy an indexer and a set of collets you should really consider if these large collets fit into your shop needs. Due to the limited grip range you need to buy a rather large set of collets to cover the entire range 5C is capable of. ER collets might make more sense in a small shop trying to hold down costs.

 

[Wizard69]

This is because no one has access to the common sense or complex indexing and drilling technology required to add 3 evenly spaced grub screws to lock screw-on chucks to the register, oh, hang on :hDe:

Who would do such a thing. A spindle be it on a lathe, indexer or something else, is generally something you want to keep pristine. Damaging a spindle and the chuck register is just not something I'm prepared to do.

 

[goldstar31]

I want to add here that threaded spindles in general are something to be avoided if you are building up a shop from nothing. As pointed out the threat of a chuck unscrewing is pretty significant and forces you to select the direction of machining. I went with a 9x20 which has a screwed on chuck and kinda regret not choosing something different. In my estimation even the bolted on chucks of the 7xXX series are a better solution. This especially if you want to get as much versatility as possible out of a machine.

I am mystified! Years ago, I had a 918/920 which had a threaded spindle and was sold as an Axminster 9180. I converted it to accept Myford accessories.

One of the modifications which was general to both sorts of spindle was to add a set of tumbler gears- so that the lathe would actually reverse its leadscrew. So the British imports -unless modified, by adding Module1 gears and a fair amount knowhow- not unscrew in use.

As far as screwed spindles- proper and able to reverse the leadscrew, almost ALL the model makers lathes had them. Some with register and some without.

Presently, I have three lathes with screwed spindles together with accessories bought and made to fit. I can move the accessories about on and off my other machines.

I suspect that my tooling- with screwed spindles is rather more extensive than most. I have three different sets of collets, 4 self centring 3 jaw chucks, a sc 4 jaw and 2 independents and have added a Vertex DH, two RT's with a detachable threaded nose, a Quorn, a GHT small versatile DH and so on. Oh, and a gizmo for the spiral column in a Quorn.

Frankly, hundreds and indeed many thousands of model engineers have endured threaded spindles.

Would you like a date of sorts? The Tsar of Russia had a lathe with a threaded spindle- before someone shot him in 1917.

There you have it:hDe:

Norman