is this enough info to make a worm gear segment today? 5

[Tmoose]

presumably this was enough info to make a worm gear from the 1930 until the 1980s.
please see attached image.

A new supplier wants to know what the pressure angle is, and is confused about what we want when we say "the single thread RH helix angle of 4 degrees 46 minutes"

We are trying to locate the print for the worm.

thanks

Dan T

 

[Occupant]

The pressure angle is generally, as far as I know, 20 degrees.

 

[3DDave]

Send the supplier example parts if you can.

The helix may be what sets the diameter of the mating worm, but I that's at the pitch diameter of the worm. If you advance 1/8 inch per turn, what diameter does the worm have to be if it is unrolled for the angle to be 4 deg, 46 minutes. I think this means a PD of .477, but that seems small for a .75 face width gear. Later it may occur to me what mistake I've made.

 

[gearcutter]

That drawing doesn't show a worm gear to me.
It's a helical gear with helix angle of 4deg 46' RH that mates with a worm shaft.

Having said that; the drawing doesn't have enough manufacturing data even if it is from the 1930s.

You'll need to give the vendor the pressure angle, specify if the pitch shown is axial or normal, the tangential span measurement or required chordal tooth thickness (make sure that you include backlash), the mounting distance and the mounting angle.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[gearcutter]

Here's an example of a RH helix helical gear meshing with a worm shaft.

Worm & Helical Gear 02 by ronvol, on Flickr

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[mfgenggear]

gear cutter star for you my friend.

gear cutter is absolutely correct. have a reputably gear mfg reverse engineer an existing part. & worm.
to get started needed info is # of teeth, normal DP, Normal PA, major dia, minor Dia,
helix angle, which hand, Measurement over wires for a helical gear. actual center distance for a worm gear & master worm. required back lash. the last vendor knew all of this.
go back to that vendor and ask for all the pertinent info.

Mfgenggear

 

[BrianE22]

Many years ago (1950's and older), a 14.5 degree pressure angle was fairly standard for single and double thread worms. Now it's not as automatic. That might be why that info was left off your original print.

 

[mfgenggear]

In today's world nothing can be led to chance. all data has to be straight forward. clear, & precise. no guessing. or there will be troubles you do not need.

Mfgenggear

 

[3DDave]

Those are not troubles - they are learning opportunities.

 

[tbuelna]

I would also agree with gearcutter's comments. From the drawing provided it appears the intent is for an 8DP, 56T, RH helical spur gear sector having a helix angle of 4.767deg. The PD and OD dimensions given for the blank are for a standard 8DP/56T involute gear, but as a minimum you would also need to define pressure angle and normal CTT at the PD. This combination of cylindrical worm and helical spur gear is a bit unusual, so if a certain level of precision is required at the mesh contact you should also provide specific details of the tolerances/modifications needed for the gear teeth.

The best thing to do would be to spend a day updating your gear drawing to add as much information as is needed to fully define the finished gear product you want the vendor to deliver. Spending a small amount of time to provide better engineering documentation to your vendor will result in better quality parts, fewer scrap parts, and a much better working relationship with your vendor.

Good luck to you.
Terry

 

[Tmoose]

We found the worm drawing. Among the recommended dwg changes will be reference to the mating part (parts ?))

Boston Gear catalog item, at least in the 40s/50s

thanks again to all

Dan T

 

[Occupant]

That makes more sense. Based on that, the worm gear is just a straight sided gear with a 14.5 degree PA and the worm by necessity - due to the pitch on the worm gear - has a helix angle of 4.7666 degrees.

 

[BrianE22]

...the worm gear is just a straight sided gear...

The worm is straight sided. The gear would not be straight sided (at least with hobbing or generating the teeth).

 

[Occupant]

You didn't read the drawings.

 

[gearcutter]

I think that BrianE22 means that the gear isn't throated in the same way that an actual worm gear is and I think that Occupant means that the teeth are not straight sided like the teeth of an involute rack.

So as to avoid confusion; one of the first rules in engineering is to try and get the terminology correct. The gear shown on that drawing is not a worm gear, it simply happens to mate with a worm shaft....that doesn't make it a worm gear. All it is is a shallow angle helical gear.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[spigor]

The problem with this setup is that the contact between the worm and the helical gear in a given moment is a single point. Is the gear made of bronze?

 

[gearcutter]

Drawing says: MATERIAL-CAST IRON.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[gearcutter]

Here's what your finished profile will look like as per the specs of the drawings.
The diameters shown are non standard. The gear drawing shows the diameter of a spur gear when in fact it is a helical gear.
The correct mounting distance should be 108.31 (4.264") which is a little over 4.250" so I'd double check the actual mounting distance and calculate the gear data from that.


8dp 14.5pa Z = 1-56b by ronvol, on Flickr


8dp 14.5pa Z = 1-56a by ronvol, on Flickr

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181

 

[Occupant]

gearcutter:
"I think that BrianE22 means that the gear isn't throated in the same way that an actual worm gear is and I think that Occupant means that the teeth are not straight sided like the teeth of an involute rack".

No, that's not what I mean. I mean exactly the opposite namely that he gear is not helical. What is helical is the worm. From the gear drawing: "mesh with worm of 8DP, single thread, right hand, helical angle - 4deg. 46min. And that's exactly what the helical angle turns out to be - given the pitch and pitch dia. of the worm.

 

[gearcutter]

Well I guess that might be possible but if that were true, then the mounting angle would not be 90 degrees. This is why I suggested in my first post that the mounting angle be shown on the drawing.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181