Rotary Table vs Dividing Head ?

[Nick Hulme]

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.

I ground a small groove in middle of the parallel section behind the thread of my Myford's spindle to facilitate the use of locking grub screws to prevent chucks unscrewing when machining with the spindle running in reverse.

Keeping something which doesn't do the required job in pristine condition and/or not carrying out a performance enhancing modification no sense from an Engineer's point of view ;-)

- Nick

 

[bazmak]

I have had many Myfords with no problems with running machine in reverse
Just because the machine has reverse why would you want to run it in reverse
I never found any reason to.The leadscrew can be reversed with the tumbler gears for screwcutting.A feature I really miss with the my Sieg SC4

 

[Dalee]

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?

Hi,

Sorry I did not have enough time to write everything out the first time. I will try to do better next time. I hope this attempt will be more satisfactory.

How much accuracy are you talking about? Cutting to a scribed line? A handful of degrees? Minutes? Seconds?

A dividing head has fixed indexes per the number of holes in a plate. You don't get to accurately locate between holes. And there is a physical limit to the number holes and spacing of holes one can achieve on a plate. But this limitation is fine for dividing a circle up into even parts. It allows for fast, accurate, and highly repeatable indexes.

A rotary table is run off of vernier scales. Degrees on the table base, minutes on the crank handle, and seconds on a, for want of a better term at the moment, "fixed" scale on the table base. This is a better set up to make very accurate arcs. It gives a very fine resolution to each degree, minute, and second. With no limitations placed on it by a physical index. But because it doesn't have the hard index, it can be quite the bear to create highly repeatable divisions.

So, again as I said before, this why back in the day most shops had both dividing heads and rotary tables. The type of work each excels at doesn't translate well back and forth. If it did, you wouldn't have needed both. And if you need very accurate arcs, (minutes and seconds accurate), you should really be using a rotary table. Want to make gears? Use a dividing head.

Dale

 

[Blogwitch]

Just to get things into my perspective.

I use Myford nose chucks on my RT and have never had one come loose when machining in the fwds/bwds mode, but I also ensure I don't use gorilla tactics when removing metal, it is better to use double the number of cuts than fewer heavy ones, plus you get far superior finishes. There are no time limits in this game, the job isn't going to run away at the first opportunity, so unless you are one of the impatient ones who can't wait to get the job done, take your time and do a decent job of it. It WILL save you time in the long run as you have less machining marks to get rid of.

I am lucky in that I use a Division Master on my RT, so that all those working outs with the vernier scales are not required any more, they are got rid of, taking the RT into the 21st century. I do use my Div head, but mainly for angle machining and drilling, and that soon will be converted to NC using the same controller, allowing me to carry out everything an RT can do plus all the angled machining as well.

Getting back to the original first post.

I would suggest rather than go with the BSO, which I would think is a little large for your machine, see if you can obtain the Vertex 4" tilting RT. I can't recall if that one can be fitted with division plates, but if it can, that would allow you to have the versatility of both an RT and Div head that would be suited more to your size of machine. Or even fit an RT with div plates to a sine table or tilting table to do the same sort of thing.

There are many ways to skin a feline.

John

 

[Mark Rand]

My rotary table and my dividing head both have 60 tooth gears. There is absolutely no reason why a dividing head cannot have a handle and vernier dial or a rotary table have division plates and sectors.

 

[Nick Hulme]

I have had many Myfords with no problems with running machine in reverse
Just because the machine has reverse why would you want to run it in reverse
I never found any reason to.The leadscrew can be reversed with the tumbler gears for screwcutting.A feature I really miss with the my Sieg SC4

I use reverse to cut right hand threads moving away from the head stock, when you're using carbide inserts in blind holes at the correct cutting speed it makes for a less stressful life ;-)

I also use a rear QCTP which allows a tool orientated for one job in the front QCTP to be used for another in the rear, with the lathe reversed,

- Nick

 

[Nick Hulme]

How much accuracy are you talking about? Cutting to a scribed line? A handful of degrees? Minutes? Seconds?

Got you,
with the standard plates my head has a theoretical resolution of 11 minutes, and given that it's easy enough to accurately enough judge a mid point between 2 holes you could manage 5 minutes and 60 seconds ;-)

- Nick

 

[goldstar31]

given that it's easy enough to accurately enough judge a mid point between 2 holes you could manage 5 minutes and 60 seconds ;-)

- Nick

Obviously a minute amount?

 

[bazmak]

Hi Nick,i have never cut a LH internal thread in a blind hole.For this, for me rare occation ,I could add an extra idler gear to my lathe to reverse the leadscrew or tumbler gears
I have often used a rear toolpost with an inverted tool and machine running forward.My SC4 has reverse and the only time I have used it is to test run the
model shaper I made
The point I am making is that a screw on chuck is not to mind a disadvantage
Regards barry

 

[Wizard69]

Obviously a minute amount?

Gold star has a golden moment. A little bit of humor is exactly what I needed after a 12 hour day at work.

 

[goldstar31]

Gold star has a golden moment. A little bit of humor is exactly what I needed after a 12 hour day at work.

12 hours day? Apt for the Equinox:hDe:

Regards

Norman