A small dividing head

[steamer]

You"re going to be a very very busy man!

Coming along nicely...

[RReid]

Thanks Steamer! Busy is OK, helps ward off brain stagnation.

Using the DH in rotary table mode worked out pretty well to finish off those old truck mirror clamps.


With that out of the way I've gotten back to finishing the rest of the components needed to use it in the intended dividing head mode. That starts with getting the division plate I made earlier mounted. I turned off most off the boss for the existing 3/4-16 mounting hub, and bored it to 3/4” ID, removing the threads in the process. I then tapped in a brass plug. It's a nasty old thing, with an offset hole through it.  Doesn't matter though, it's only temporary and I could work around the hole.


I center drilled it, the took to whole shebang, still in the chuck, over to the mill to drill a ¼ hole using an end mill. Since the hole I want and the hole already there overlapped a bit, a drill bit wouldn't have run true, but an end mill will. I can now slip the division plate over the worm shaft where the crank arm also attaches. With the worm shaft and the division plate concentric, I tap drilled through the plate and into the side plate of the frame for 3 6-32 screws. Then the holes in the frame get tapped and the plate gets clearance drilled. Got two of the three done today, one left for tomorrow.


Last step will be to knock the brass plug out. Then move on to making a nicer crank arm with a sprung stop pin, etc.

[RReid]

To finish off the DH, I made a brass stop pin and set it up with a spring cut down from a ball point pen for engagement, and a 5-40 threaded shank with finger nut so I can retract and lock it for “cranking”. Since I've only made the one hole circle at this point, I didn't worry about making the pin adjustable for radius. Ditto for making a pair of sector arms, those these can be pretty easily added as the need or desire arises.



So at this point I consider this small dividing head to be “finished”. Here are few pictures of some of the set-up options it offers.

Horizontal, with 4J chuck. The chuck jaws are reversed and set for a 3” diameter, and there is still plenty of clearance over the table.


Horizontal, between centers with standard Taig tailstock. The dovetail plate is the same one Taig uses to mount the headstock on the milling machines.


Vertical, using the lathe's milling attachment.


Vertical, using a bit of extruded aluminum angle.


Mounted to the lathe cross slide.


Overall I have to say I'm pleased with the compactness and versatility of this design. It remains to be seen what shortcomings show up as I get to using it more!

[Kim]

That is really nice, Ron!

And you've got a lot of good 'use modes' covered with that design.

Well done!
Kim

[crueby]

Sector arms? What are they/what do they do?
 

[steamer]

Yes   Make ye some sector arms!....Saves a lot of counting and head scratching in use.

Dave

[steamer]

This is part two of his lecture on dividing heads...but he gets into the sector arms explaination, and how to use them   


Look at part 1 too...

<a href="https://www.youtube.com/watch?v=kFjSHtyhOmg" target="_blank">http://www.youtube.com/watch?v=kFjSHtyhOmg</a>

Dave

[steamer]

Also ...consider a spindle lock.    With a spindle lock, you avoid the work vibrating due to the back lash of the gearing...it makes for a very rigid setup, and better accuracy.

Dave

[RReid]

Sector arms? What are they/what do they do?

Sector arms are an aid to keeping track of the " turns plus holes" on the division wheel. They consist of two arms that can rotate independently on the worm crank axis, be locked to rotate as a pair, or be locked in place.

In use, one arm would be set at the "starting hole", which is also the hole you must return to to get one full revolution of the crank. The other arm is set at whatever number of holes beyond the starting hole is required for the job in play, let's say as an example 5 holes beyond. They are then locked together as a pair, so they can later be rotated together without loosing their angular separation.

The first cut is made with the pin in the starting hole, then the crank is rotated the required number of full turns (marked by the 1st arm, plus the 5 holes (marked by the 2nd arm), the pin is inserted there, and the second cut is made. Next, the arms are rotated together to bring the 1st arm to the current pin position, and the cutting process is repeated.

This image of a Brown & Sharp version should help.

[crueby]

Thanks for the explanations guys! Great videos too!

[steamer]

Sector arms? What are they/what do they do?

Sector arms are an aid to keeping track of the " turns plus holes" on the division wheel. They consist of two arms that can rotate independently on the worm crank axis, be locked to rotate as a pair, or be locked in place.

In use, one arm would be set at the "starting hole", which is also the hole you must return to to get one full revolution of the crank. The other arm is set at whatever number of holes beyond the starting hole is required for the job in play, let's say as an example 5 holes beyond. They are then locked together as a pair, so they can later be rotated together without loosing their angular separation.

The first cut is made with the pin in the starting hole, then the crank is rotated the required number of full turns (marked by the 1st arm, plus the 5 holes (marked by the 2nd arm), the pin is inserted there, and the second cut is made. Next, the arms are rotated together to bring the 1st arm to the current pin position, and the cutting process is repeated.

This image of a Brown & Sharp version should help.

 

[RReid]

Also ...consider a spindle lock.

Thanks for the input and the videos, Dave!

I do have a spindle lock, consisting of a nut at the back end of the spindle that can be tightened against the bushing. That is effective, but I can see where it may prove awkward if it requires two wrenches and two hands to tighten it without rotating the spindle. If that's the case I'll install a more traditional clamp style brake. That was the original intention anyway, so there is room for it.

[steamer]

Also ...consider a spindle lock.

Thanks for the input and the videos, Dave!

I do have a spindle lock, consisting of a nut at the back end of the spindle that can be tightened against the bushing. That is effective, but I can see where it may prove awkward if it requires two wrenches and two hands to tighten it without rotating the spindle. If that's the case I'll install a more traditional clamp style brake. That was the original intention anyway, so there is room for it.

 

[RReid]

One of the motivations for building this dividing head was a desire to learn to cut my own gears for future projects. Since my next engine project will likely be the Upshure Farm Engine, the future is now. That engine requires two 48 pitch gears, one with 30 teeth, the other with 60.

I've looked at the cost of involute gear cutters, read up on the Stevenson Button Method of making the same, methods for making hob-like cutters, etc. But as a trial attempt at gear cutting, I decided to go with my usual KISS approach, and see how well non-involute gears would work. To that end I reground a 60 degree threading tool to 40 degrees, making a simple, straight sided 20 deg Pressure Angle, single point cutter. I also made a flycutter style holder for it.

Armed with those, I turned up a pair of brass blanks to make the 30 tooth gear, and set it up on the mill, along with the dividing head and the tailstock for support, and starting wailing away.
.



I made two gears so, partly for practice, partly so I could see how well they mesh. They don't look as refined as good commercial gears, but they do seem to mesh fine and work smoothly enough at “finger rotation speed” on the sophisticated test fixture.




Those are the first gears I've ever made. After cleaning up, I came in and treated myself to a beer.

[crueby]

First set of gears came out great, and no pile of rejects in the bin - definitely worth the celebration!

For slow moving gears, the simple shape used in early clocks is not too hard to grind cutters for. Did that style on a wall clock 15 years ago, its still keeping great time.

Pretty soon you'll be cutting bevel gears, then helicals (I have not tried those yet myself! )