Dividing head connected to x-axis feed on Bridgeport

[WoodBee2]

I don't have much experience with this so please excuse my lack of knowledge and use of the proper words. Some time ago I bought a dividing head which had a extra coupling that I did not understand. I did some research and found out it is meant to mount a gear, which could be driven by a gear-train attached to the x-feed of a mill.
Recently I picked up a set of gears with mounting-accessories which I thought might be for such a dividing head and could be made to fit on mine. Am I correct? (see pictures)
Could anyone enlighten me on the use of such a contraption, other than milling spirals? Also, could this be usefull on a Bridgeport? (I also have the "angle head for the bp if that would be needed)
Any links to information about this is greatly appreciated.

These are the teeth counts on the different gears:
24(*2), 25, 26, 28(*2), 30, 32, 40, 44, 48, 56, 56 with stub, 64, 72, 80, 86, 88, 100, 127.

Thanks very much,
Peter348783348784348785

[azzrock]

Hi mate I don't think it is usefull for cutting helical gears ect on the bridge port, because the feed is not directly related to the cutter spindle. Ie the is two different motors. One for the feed one for the cutting head.
aaron

[pipeclay]

Cutter RPM and feed rate do not have to be connected.

Not sure if I have ever seen a mill which has the RPM and feed rate connected.

You may have trouble with a Bridgeport as all the ones I have ever seen or used have variable feed rates.

Idealy when using the universal dividing head you need to be able to select a specific feed rate and adjust the gear train to the dividing head with the change gears to achieve the desired feed rate for the work being held in the dividing head.

You may be able to work out the different feed rates given by the variable feed and mark positions around the dial but I think the accuracy in this method may be a little bit of hit and miss.

[Michael G]

For a helical gear you need to be able to link the rotary motion to the linear motion, so you would be good for that.
The other thing you can do is differential indexing, so making up gears with 127 teeth for example.

There are a limited number of things that you can do with a universal dividing head but having said that, there are some things that are difficult to do any other way (at least manually).
this is probably the last couple of major things that I did -
http://www.woodworkforums.com/showthread.php?t=190169&p=1825502#post1825502
http://www.woodworkforums.com/showthread.php?t=121056&p=1852386#post1852386

Michael

[janvanruth]

hobbing gears is one application for it

[bollie7]

You may have trouble with a Bridgeport as all the ones I have ever seen or used have variable feed rates.

I dont understand why this would be an issue. In this setup the DH is linked by the gear train to the table leadscrew. The gear train is what sets the ratio between the rotation of the DH spindle in relation to the distance traveled by the table. Doesn't matter what speed the table leadscrew turns at. The DH spindle will still turn at the correct ratio.
It might have a influence on cutting speed but that wouldn't be any different to an other common set up on a BP.
Am I missing something?

bollie7

[Hunch]

One of the toolmaking apprentices who won the end of year prize to work at the "UK" factory a few decades ago mentioned they weren't much in demand as far as he could tell, as that sort of machining was already not really the preserve of manual milling anymore.

Been a while since I've seen his documentation, I think there was an arbor support to use with the 90 degree head too, which was part of the kit.

[PDW]

I don't have much experience with this so please excuse my lack of knowledge and use of the proper words. Some time ago I bought a dividing head which had a extra coupling that I did not understand. I did some research and found out it is meant to mount a gear, which could be driven by a gear-train attached to the x-feed of a mill.
Recently I picked up a set of gears with mounting-accessories which I thought might be for such a dividing head and could be made to fit on mine. Am I correct? (see pictures)
Could anyone enlighten me on the use of such a contraption, other than milling spirals? Also, could this be usefull on a Bridgeport? (I also have the "angle head for the bp if that would be needed)
Any links to information about this is greatly appreciated.

These are the teeth counts on the different gears:
24(*2), 25, 26, 28(*2), 30, 32, 40, 44, 48, 56, 56 with stub, 64, 72, 80, 86, 88, 100, 127.

Thanks very much,
Peter348783348784348785

Cutting helical gears can be done on a B/port but it's a bit of a PITA.

The gear quadrant needs to be attached to the X axis leadscrew in some fashion - this may be a bit of a challenge to fabricate. Not impossible though.

Second issue is the B/port table can't be swivelled to get the cutter aligned with the angle of the cut. To deal with this you need to use a stub arbor in the vertical head and tilt the head to the proper angle, cutting the tooth spaces on the horizontal centre line of the work piece rather than the vertical centre line as done on a horizontal mill.

So as I say, it can be done but it's a PITA. In one of my reference books there's an example of setting up an indexing head using sprockets & chain on a B/port to mill long lead multiple start threads - what you want to do is sort of similar.

PDW

[WoodBee2]

Aaron and pipeclay, thanks for your replies. As far as I understand things I tend to agree with Michael, there is just the cutterspeed related to the feed and the feed related to the rotation of the dividing head. And the former is not critical in absolute numbers. So I believe this will not be a problem.
Peter

[WoodBee2]

Michael, thanks for your input. I didn't think of differential indexing, thanks for the idea! I googled it and have some idea now how it works. Now I need to check out if I can figure out how this could be set up on my dividing head.
I did check out the other threads you linked to. Nice work!
Peter

[WoodBee2]

hobbing gears is one application for it
Jan, thanks for the replie. Could you explain how that is done?
Peter

[WoodBee2]

Bollie7 thanks for your replie. As mentioned in an earlier post, as far as I understand things I think you are right.
Peter

[WoodBee2]

PDW, I understand what you mean. Attaching the gear quadrant to the x-feed should be possible although not straightforward. It would help to see an example though. Any chance you can scan the part of the book you mention?
As for the angle of the cutter: I see what you mean. I hadn't thought of the solution you described. I though it would have to be done with the 90° head (swivel the cutter instead of the table compared to a horizontal miller). What would be the advantages/disadvantages of both methods?
Thanks for your input,
Peter

[bollie7]

I didn't think of differential indexing, t
Peter
When I did my apprenticeship in the mid 1970's, being how I am pretty much a dunce when it comes to complicated maths, I was never able to get the calcs for differential indexing to work out properly. When the 3rd year TAFE final exam was coming up (none of this stupic competency crap back then) I was packing it that there would be a question on differential indexing in it. Luckily for me there wasn't.
Funnily enough, I have never had to use it since either. Thats probably because I was always more of a fitter than a machinist.

Where I did the first 2 years of my apprenticeship they had a big Cincinatti clone universal mill (made under licence by either BHP or the Newcastle State Dockyard during WWII) in the apprentice training centre. Even after 30 years back then, and who knows how many apprentices learning on it, it was still a nice machine to use. Had power feed and speed changing on it as well. Quick traverse on all 3 axes without having to have the spindle turning. I loved using that thing.
Anyway it also had a big Cincinatti dividing head. I can't remember the correct name for it but as well as the common 40:1 ratio on the main plate, it also had another smaller dia plate on top of the main plate with its own lever with a 100:1 ratio. It was 100 turns of the small handle for one turn of the main handle. You could do some fancy indexing using that if you could do the calcs (which were far too complicated for me) Plus it could be set up for differential indexing.
bollie7

[Michael G]

As for the angle of the cutter: I see what you mean. What would be the advantages/disadvantages of both methods?


Peter, if you are cutting a straight spur gear the head will be vertical but if you are trying to cut a bevel gear then the plane of the cutter must match the angle of the helix. On a horizontal mill that is usually done by swiveling the table but for a vertical machine you need to swing the head over, like this -

348973

If you don't, the form of the tooth will be incorrect.

Found a banjo picture - sort of (both pics from http://transistor-man.com/miters-jeep.html)
348972

Michael

[WoodBee2]

Michael,
Thanks for the pictures, that helps a lot. I understand what you mean concerning the helix angle, and yours likely is the more practical solution.
The solution I cunjured up was to put the 90° head on the quill, and than rotate this head to the helix angle and mill on top of the blank like on a horizontal mill (clear as mud?). Since there are no angle graduations on the 90° head setting the helix angle might be a challenge though.
Peter

[PDW]

Michael,
Thanks for the pictures, that helps a lot. I understand what you mean concerning the helix angle, and yours likely is the more practical solution.
The solution I cunjured up was to put the 90° head on the quill, and than rotate this head to the helix angle and mill on top of the blank like on a horizontal mill (clear as mud?). Since there are no angle graduations on the 90° head setting the helix angle might be a challenge though.
Peter

That should work - I'd use a sine bar or similar (basic trig and a dial indicator) to set the angle.

You have to 'nod' the head unless you're using the Y axis and cutting only short distances the other way.

Busy ATM - no time to find the photos I'm afraid....

PDW