Dividing head

[Richard1]

Hi guys,
been away from the workshop for 6 months due to a family crisis but this forum when I have had access to a computer has contributed greatly to my sanity. Thank you one and all.

Now my problem. I have a very nice spiralling dividing head (make unknown) set up on the Bridgeport and it works fine but the banjo and change gears to drive it from the lead screw are missing. I could make these but to further complicate matters the part I need to make is hexagonal, tapered with a 14 degree included angle and spiralled at 1 turn in 3 inches so I need to tilt the dividing head upwards by 7 degrees which would I presume make a gear drive off the leadscrew difficult. I am wondering if it would be possible to mount a stepper motor on the dividing head with some sort of pick up on the leadscrew and a simple??? controller to set the ratios between the screw and the dividing head.

If this is possible can someone tell me or show me how and if not possible any other ideas on how to do it?

Regards
Richard.

 

[Tin Falcon]

Richard I am new to cnc and sometimes feel like I am climbing the step learning curve.
From the reading I have done what you propose should be doable. thread milling can be done on the mill bases on a speed senser on the spindle and cnc thread cutting can be done on the mill with a spindle sensor on the lathe head.
Another option would be to cnc your lead screw and rotary table and then coodinate there movementst or possibley slave them together
It is my understanding this can be done but do not feel qualified to give all the detail you need. .
Tin

 

[gbritnell]

I think I would look into making or purchasing the appropriate gear train to drive the head to get the required spiral. As far as tilting the head up, do you mean actually 'tilt' the whole head'? Most dividing heads that I am familiar with can be unclamped and rotated on their own axis.
gbritnell

 

[Richard1]

The head will rotate on its axis and has a very accurate scale for doing this but this throws the gear train out of line. Not at home right now so can't upload images of what I am talking about. Raising the chuck 7 degrees would swing the gear train in 7 degrees towards the end of the table and make the gears drive only partly meshed which would work for this job but would get progressively worse for jobs with a greater tilt until it would eventually be impossible due to clearance problems with an angle of more than 20 or 30 degrees. On a friends computer may take a couple of weeks to upload images of what I am talking about.

Richard.

 

[gbritnell]

I am used to an old Brown and Sharp dividing head where the gear train drove the worm gear on the head. It didn't matter what angle the head was at because the spindle was driven by the worm. The differential gearing was connected to the handwheel on the table and this in turn drove the worm. The angle of the head was irrelevant.
gbritnell

 

[Richard1]

That would be sensible but this one doesn't seem to work that way, or maybe I am just going mad. Will have to drag it out and have a serious look when I get home. Seems to me that the gear drives through a 1:1 ratio driving the worm. Such that the input shaft is parallel with the output shaft and tilts with it when the head is inclined. Do you by chance have a list of the standard gears for the Brown and Sharp so I know what ones to buy or make. I assume the Brown and Sharp is a 40:1 the same as mine.
Richard.

 

[gbritnell]

I don't know all the gears that come in the standard set. Maybe someone who has them can help out. I found a good video of a dividing head with the differential gearing on it. They are cutting a helical gear with it. This shows how the gear train is separated from the main body of the dividing head, allowing it to be tilted if necessary. I can't imagine anything else. I can't believe that the gearing would have to be tilted so that the gears were partly out of mesh but I've probably seen stranger things.
gbritnell

[ame]http://www.youtube.com/watch?v=vyg0Emz4Vx4[/ame]

 

[John S]

40 : 1 head and based on a leadscrew of 1/4" pitch you need a 56 on the leadscrew driving a 28 with a 40 then to a 24 on the dividing head.

The 28 and 40 have to be doubled up on the same stud. You may have to put idlers in to space these out and get the correct rotation but the idlers can be any number of teeth as then don't affect to overall ratio.

Full set of gears is 24, 24, 28, 32, 40, 48, 56, 64, 72, 86 and 100.

My head is the same as Gbritnell's, no mater where it's tipped the input shaft stays level.

John S.

 

[putputman]

The part that really got me was the fact that he was climb cutting. It seems that with all that gearing, in the indexing head and machine table, there is a lot of backlash available that could screw up the tolerance on that gear.

 

[Richard1]

Thank you to all of you for your help. Seems I have a weird head but that is OK. Thanks for the list of standard gears John I will make them up, will be good practice with gear cutting and if I make them the same as Myford they may one day be useful there too, assuming the input shaft to the head is small enough to allow the gears to be bored out to fit, if not I will think of something else.
All this complexity is to make 12 brass spikes about 2 inches long and 14mm diameter. It has a round section about half an inch long turned to some decorative profile and then a twisted hexagonal spike running from half an inch down to nothing with a length of 1.5 inches. The whole thing to be highly polished, gold plated and put on top of a coffee pot. It is one of those weird jobs that came to me because someone (who didn't want the job) said he makes models he can make it for you. Expense is not an issue in this job as the customer is asking insane money for the finished item.

Richard.