ZN worm profiles question 2

[RichardWattMatrix]

Hello,

As described in my other thread ZK worm parameters, I am working with an existing software application that generates dressing programs for different types of threads and worms and I am currently working on fixing a reported issue with ZN type worms in the application.

So far, I have been able to produce a NC program for a Siemens 840Dsl CNC machine from calculated profiles, but whenever we grind a part on the machine, the profile has always been wrong, i.e., the flanks are more curved than we think they should be.

I have the data for 2 ZN worm parts provided by our customer who reported the issue and I have posted some of the details below for the first one:

[ul]
[li]Worm Type: ZN[/li]
[li]Number of teeth: 2[/li]
[li]Single lead[/li]
[li]Right handed[/li]
[li]Pitch circle diameter: 12.42 mm[/li]
[li]Tip diameter: 17 mm[/li]
[li]Root diameter: 6.97 mm[/li]
[li]Helix angle: 20.14 degrees[/li]
[li]Flank angle: 14.5 degrees (for both LH and RH)[/li]
[li]Lead: 14.311 mm[/li]
[li]Normal plane angle: 20.14 degrees[/li]
[li]Tip fillet radius: 0.5 mm[/li]
[li]Root fillet radius: 0.5 mm[/li]
[li]Measuring wire diameter: 4.7455 mm[/li]
[li]Size over the wires: 19.77 mm[/li]
[/ul]

We also have a setting that controls the number of points that are generated on the flanks, and this value is set to 50 in this case.

One thing I will point out is that we have a "Normal plane angle" parameter which we always set to the helix angle.

I also have copies of log files created by the software for the worm profiles on the normal and axial planes and I will attach them later as I cannot seem to do this from the office.

Edited to add normal (ZN_SingleLead_NormalPoints.Dat) file, which has the format of (I'll post the axial one in the next post):

[ol 1]
[li]No. - this is the point number[/li]
[li]Width(mm) - this is the profile width (X coordinate) for each point[/li]
[li]Radius(mm) - this is the profile radius (Y/Z coordinate) for each point[/li]
[li]Normal(deg) - this the angle from the X axis to the outward normal vector from this point[/li]
[li]Attribute - this is a point label identifying where the point is on the profile[/li]
[/ol]

I was wondering if someone could kindly help me generate the worm profiles (ideally both the normal and axial plane ones) and compare them against the attached result files please?

If there is any other information you need, please let me know.

Best regards,

Richard

 

[mfgenggear]

spigor

I am reviewing the AGMA 6022-C93, Annex A, "I don't have the latest", formulas for worm thread profiles, Z1 & Zk
and see if I can write a spread sheet.

 

[spigor]

mfgenggear,
I had no mentors, only books, but they are not in English. But look at the formula 5.70 or 5.73 below. The helix angle on the reference diameter is called the lead angle. If the reference diameter is used, you calculate the lead angle, but you can use any other diameter on the worm to find what the helix angle on that diameter is:

 

[spigor]

...we would swivel to the lead or helix angle. and the helical gears lead would be correct. now I trying wrap my head why on worms. why it would be different.

Here the grinding wheel is also swiveled to the lead angle, so it's not different.

 

[mfgenggear]

Spigor

I found this interesting based on the AGMA 6022 Anex A
for general approximation of the change in profile, I made a spread sheet
check my math cause I am rusty.
the larger the grinding wheel diameter on a ZK worm less error. (5) inch diameter vs a (10) inch diameter makes a difference.
soon as I get free time, I will work on the formulas you provided.
edit I found this old paper from National Broach and Machine , Back to Basics, Once I brush up on my gear geometry.
I will instead take this approach. see attached.

 

[BrianE22]

Mfgengear -

Does AGMA 6022 Anex A actually give the equations? I tried to derive it but it's a bit too much trig for me.

 

[mfgenggear]

Mfgengear -

Does AGMA 6022 Anex A actually give the equations? I tried to derive it but it's a bit too much trig for me.

Brian my uploads are failing for some reason, could be operator error.
here is my spread sheet, and gear basics that explains layout for x & y format for the involute.
try again.

https://files.engineering.com/getfi...e1-48f3-aa5e-5ec9bb91e12d&file=geardesign.pdf

https://files.engineering.com/getfi...29-aede-9ae73823ca58&file=WormGearProfile.pdf

 

[mfgenggear]

Brian
the AGMA annex A is an approximation but it details how much error there is in the profile if not large enough diameter milling cutter or grinding wheel.
if the right size grinding wheel is used. then the error is much less.
the other attachment is old school but it's tough to find the equations for profile layout, I never had the time in the past as I relied on the tool manufactures to provide the correct geometry on the tools. but better late than never. I like using spread sheets to remove the tedious recalculation by hand with a calculator. ugg.
and once errors are remove is more accurate from mistakes. lol but my math is getting rusty.

 

[RichardWattMatrix]

Hello everyone,

I have been off last Thursday and Friday as I work on a revised shift pattern due to the pandemic, so I will need to go through the posts I have missed.

Thank you all for your contributions, they are much appreciated.

The good news is that we think we're almost there now - the ZN profile when measured with our Wenzel gear checker machine (which measures it as a ZN in the normal plane) is almost perfectly straight. My colleagues who have been helping me with the actual test part grinding are going to try adjusting some parameters (including the helix angle) to correct it.

I'll let you know how that goes as well.

Many thanks,
Richard

 

[spigor]

...it seems that the ZN worm should have slightly convex flanks on the axial profile, but we're seeing much quite curved flanks.

The calculations also show that the axial profile is convex .005 mm.

 

[mfgenggear]

Richard

how is the project

 

[RichardWattMatrix]

We've obtained another drawing from one of our other offices for a ZN part with an OD of 80 mm and will be trying to grind one of these soon although we need to order some material and make some test parts first, which will be done over the next 2-3 weeks.