San Francisco Trolley Car Style Worm (Globoid worm) Drawn as a Solid

[David_M]

I saw where Edge Precision posted a Youtube video about a rolling element and worm positioner.
He used an alternative method to program the worm after finding some difficulty creating a solid model.

I tried to see if I could do it in Rhino.

How does your Program work for modeling a solid for something like this?

 

[john.k]

Looks very like the worm in a Gemmer steering box.

 

[moonlight machine]

I saw where Edge Precision posted a Youtube video about a rolling element and worm positioner.
He used an alternative method to program the worm after finding some difficulty creating a solid model.

I tried to see if I could do it in Rhino.

How does your Program work for modeling a solid for something like this?

So it can be drawn, how do you make it!

 

[Milland]

So it can be drawn, how do you make it!

With your everyday home shop CNC gear grinder, of course!

 

[EmanuelGoldstein]

So it can be drawn, how do you make it!

It's easier to make than to draw ... these are generically called double-enveloping worms the trade name was Cone Drive after the guy who invented them.

The wormgear is semi-conventional, they are made by tangential feeding a hob through the edge of the blank.

The worm is a little unusual, imagine a hobber except the blank goes where the hob would normally be. Now put a shaper cutter on the worktable that's the diameter of your target wormgear, except the teeth are thin. Feed the blank down onto the cutter, now you have teeth on the worm except they are fat. Then the cutter is moved forward a ways then aft a ways to get correct tooth thickness, then back to the middle for clearance. Now raise the work up off the cutter and remove from the spindle.

Michigan Tool was a big promoter of this type of gearset, it's quite nice and low-backlash and high capacity but expensive and runs hot because of all the intimate contact and rubbing, oooh They made automatic machines to cut these.

 

[john.k]

I dont see any relevance .........anyhoo,the straight sided worm groove is for the pre war Marles Weller steering box,the angled sides are for the WW2 Ransome and Marles box,that was also made by Gemmer ......a roller on the sector shaft runs in the groove,and they were maybe the best steering box of their era...........if you want a really hard to make worm ,try the one in the Ross steering box .

 

[EmanuelGoldstein]

With your everyday home shop CNC gear grinder, of course!

Nice video, the cubitron ii stuff is way more then ten years old though, but more to the point on this subject is, can't do double-enveloping on a threaded-wheel machine. It'd make a hell of a demo for a Hofler tho, if they could do it.

 

[memphisjed]

how to draw is easy, how to make- outside the scope...
Draw it like it is used.
Take a gear
extrude it around a circle with a twist of 1 tooth angle. This equates to 1 revolution of the worm- but we are revolving gear instead of worm.

Take the worm stock and subtract gear...

 

[john.k]

Cant be too difficult ...the originals were made in 1920s .........Incidentally ,what was the last car to have a rear axle hourglass worm drive ?.........Dropped in 1952 for a standard David Brown worm drive ,due to the 'lack of skilled men able to adjust the meshing of the gears satisfactorily'