Gearing Crash Course 3

[AuWing]

The person who did our gearing quit. Now I have to solve what should be a simple problem, but I am stuck.

First I am working off a drawing from 1956.

What I know.
Gear: 3DP, 107 Teeth, 35.66" P.D., L.H. Helical, 20deg Involute- Full Depth
Pinion: 3DP, 19 Teeth, 6.33"P.D., R.H. Helical, 20deg Involute-Full Depth

This is all the info on the drawing. Seems there is missing info, job security.

Question I was asked, Are these Transverse or Normal?
I was told there is a difference in the cutters.
Can anyone help?

 

[gearcutter]

The drawing information is suggesting that it is transvers pitch.
Pitch diameter for 3DP (normal) @ 20deg helix angle would be around 37.95".

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

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

 

[Occupant]

The only question I have is: who says it is a 20deg. helix angle? Normally I would assume 20deg. to be the pressure angle.

 

[AuWing]

I thought the 20deg was the pressure angle. And was assuming it was a 15deg helix angle.
Am I wrong in my thinking?

 

[Occupant]

Not necessarely, but if you have the CD for the pair, you could easily confirm this by calculating CD=(Z1+Z2)/(2*DP*cos(HelixAngle)

 

[AuWing]

The center distance is (Gear PD 35.6667"+ Pinion PD 6.3334")/2 or 21.000"
Hate to sound stupid, what do Z1 and Z2 stand for?

 

[Occupant]

Z1=307, Z2=19. But I got lost somewhere. The tool to cut the gears is used in the normal plane and defined, in your case, by DP=3.0. So how can you get to a PD of 35.6667 in the transverse plane - which in part determines the center distance of the set? In other words for a regular spur gear that would be correct, bur how does the helix angle enter into this?

 

[AuWing]

Occupant, I assume Z= Number of Teeth. And the 307 number is just a mistype.
The center distance is a set distance from the gearbox drawing. Which in part lead me to my answer.
First I want to say Thank You.
Using the information you gave me, some old DOS program and Inventor 14, I think I found the answer to my question.
The question I originally asked was; Are these Transverse or Normal?
The question I should have asked was; Are these gears cut with a Transverse Hob or a Normal Hob?
Transverse is not just another way of measuring a gear it can be cut that way. At least that is what I was told by others. Back to my original post that is why I stated "I was told there is a difference in the cutters."
If I set the DP @ 3 in the transverse direction in the old DOS program, I get the PD of 35.6667" which allows me to hold the correct center distance.
If I set the DP @ 3 in the normal direction I get the results Occupant stated.
Using Inventor 14 it only allows me to supply known information in the (Normal Measurement Direction)(That I can figure out). So when entering the 3DP as normal
it gives me information that does not match other known info on the drawing.
When I use 3.1058DP as the normal (Which equals 3DP in the Transverse)All the information now matches the other known information.
Therefore I think these gears need cut with a Transverse Hob.

Thank You Again

 

[Occupant]

Yes, I agree and in your case you'll have to cut the gears with a cutter in the normal plane with a DP=3.1058 and a helix of 15deg. as you stated.

 

[PeteDB]

I believe the DP is referring to the transverse DP. 107/3= 35.666. If it were NDP then you would need the helix angle to calculate the pitch diameter.

 

[Occupant]

Ok, my mistake was that I was thinking of milling the gears and I forgot that you can easily hob them with a standard rack with DP=3.0.

 

[mfgenggear]

Auwing

I am late in the game here. but FYI
I process plan gears for a living.
In the USA 99.9% the data block is given in Normal Plane
The data should be # of teeth , Normal Diametral Pitch, Normal Pressure Angle. Helix Angle, The hand direction RH or LH
Measurement over wires (2) wire or (1) wire over centerline. the normal circular max & min tooth thickness. Major diameter, The root Diameter, the Start of the Involute or TIF(Total Involute Form, Lead Tolerance, Involute Tolerance, The lead will certify the Helix is Correct, The Involute will specify the gear was manufactured to the correct Pitch & pressure angle(correct geometry)
if required the AGMA or equivalent gear quality class. or independent attributes. Index, tooth to tooth, Total Composite error. Pitch Diameter runout.

If the depth of the gear is standard then a standard hob can be used. the tool will be tilted to the correct angle to cut the correct helix angle & lead.
if this gear attribute requires close gear tolerance or requires heating after cutting by through harden or case hardening then it will have to be pre grind hobbed or shaped. then ground after heat treat.

It is then up to the gear manufacture to cut the correct gear attributes. The data is calculated from Normal to transverse by the manufacturer.

To my opinion You need to state on the drawing the correct normal & transverse attributes.
This just for your Information only.
I Am sure I left something out & other will be quick to jump in.

Take Care

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[Tmoose]

Any chance an original gear or 2 might be obtained somehow?

By "did our gearing" do you mean designed and drew, procured, or manufactured? The folks that made the last batch successfully might be able to help.

 

[AuWing]

mfgenggear

The company I work for is the manufacturer (now) the original OEM is out of business. We will machine the parts complete less the gear teeth. We send it out to have the teeth cut. The company that cuts the teeth asked the question, Are these gears cut with a Transverse Hob or a Normal Hob? .
Please read my original post and my 4th post again.
Also we do not have the gear box, our customer is limping along with it. And even if we had the gear box its self it would not be much help, as the pictures our customer sent to us shows there is not much left to the teeth.

So I will pose the same question to you. Are these gears cut with a Transverse Hob or a Normal Hob?

And the only info I have is listed above.

Tmoose

"Any chance an original gear or 2 might be obtained somehow?" No these parts are custom.


"By "did our gearing" do you mean designed and drew, procured, or manufactured?" We are a machine shop, our basic jobs are repair "which includes making new parts " for existing equipment. "by "did our gearing" I meant He came from a gear shop and he could backward engineer gearing from existing parts worn out or not. He could figure out gearing from existing drawings with missing info. And he could figure out gearing for new equipment, as long as it was in the realm of his degree from the School of Hard Knocks - 30 years of experience.

"The folks that made the last batch successfully might be able to help." The original OEM out of business.

 

[mfgenggear]

AuWing

all our Helical gears are cut with a standard hob with the correct D+F. that it will cut the correct depth. what the question should be is the part data in Transverse or Normal. I can use either to calculate the correct hob data required to machine the part. You said on you post you needed a crash course on gears. well in the USA data is in the Normal not Transverse. of course that said if the engineer decides to give the Transverse data the print should say so.

as soon as a part is cut it will be scrap unless the correct clear concise information is given to the gear manufacture.
you say you are manufacturing the part. That tells me a lot. since you don't have clue to what is going on.
The gear manufacture should always make the part complete. especially if it requires critique handling of the process planning.

HTH

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[Occupant]

As I have said before, I think originally the gears were hobbed with a rack of 3.0 DP in the trasverse plane because that's how the transverse P.D. calculates out based on the given CD. If you are looking in the normal plane you would need a cutter with a PD. of 3.1058 to arrive at your 15deg. helix.

 

[AuWing]

mfgenggear

Soooooooooooo; You can not answer the question? Nor could you answer your own question.

You are correct I am not a gear person. And judging by your answer you are not much of a people person.

If you would read everything I posted, You would see that I did not pose the original question. I am just trying to solve a problem.

If you really want to help, use the information from above and help.

If you are here to kick someone or put them down to prove you are smarter than they are, Well, I cave.

Now; let someone who wants to help, Help.

 

[AuWing]

Occupant,
Your previous info was very helpful.

And A big Thank You.

 

[mfgenggear]

AuWing

sorry to come across as you said. that was not my intention. on first post I explained what should be on you print that is all.
secondly Gear cutter answered your question as along with Occupant. My post was to guide you as what information needed to be on your print.
so be it. my information was to alert you to what is necessary on a print.
I calculate this stuff all the time so don't tell I could not the question. the question was already answered.

so I am done with you
Good luck.

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[mfgenggear]

Ok now that I am calmed down I will try to explain it again

The gear data can be in Normal or Transverse. it does not matter.

a normal diametral pitch gear hobber can cut eighter in transverse or normal, if the engineer or the hobbing setup guy knows how to
adjust the the machine to cut the correct geometry. it does not have to be a transverse hob.
what is important that a correct depth or whole depth is used to cut the correct depth (Minor Diameter) or root diameter.
& to cut the correct M.O.W or CTT.
if the mfg wants to use a transverse hob then most likely it will require to be designed for that part.
if the helical gear teeth of the part are not standard or special recessed gear is required a hob needs to be designed to that specific part.

all the mfg needs to know if the data is Normal or transverse. then he can adjust accordingly.& a standard Normal Diametral Pitch Hob can be used if
the head of the tool that locates the hob is tilted to compensate for helix angle that needs to be cut.

OK I have never needed to use transverse hobs but it does not mean it can not be used. it just cheaper for me to use my Normal Diametral Pitch hobs in stock
in the last 35 years I have never needed to use a transverse hob. thats not the case for gear shaping helical gears. thats another story.

it is more complex than knowing the P.D. of the cutter. since it is based on a rack. Because it is a helical I would need the part data & the hob data.
to verify that your hob will cut the correct geometry.


Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.