[How-To] Gear diameter question

[DavidR8]

I need to cut a 16 DP, 14.5 PA, 40 tooth gear in the semi-near future.
My calculations indicate they gear will have an OD of 2.625".
I have a nice piece of 4140HT but it's only 2.5" and will be a tad smaller than that after the OD is cleaned up.
That's roughly 1/8" smaller that the calculated diameter.
Can I get away with this or should I spring for a length of 2.75" or 3"?

 

[MyLilMule]

The teeth won't have the correct profile if you use a piece of material of the wrong diameter.

 

[DavidR8]

I realize the full tooth profile won't be cut, just wondering how significant the 1/16" will be to the gear performance.

 

[savarin]

Why not build the dia up with weld to 2.8" and turn it to the correct size then there will be no problem with the missing 1/16".
I have done this to various parts I didnt have sufficient size for the job with no problems, the weld turned down fine..
check post 10 here

The Giant Binocular

Its time to re-visit the binocular. This is roughly what I want. I started these over 5 years ago but got side tracked building recumbent bicycles. Now I've almost finished the refractor I've started back on these. This is being built entirely from scratch including grinding and polishing the...

www.hobby-machinist.com

and here

Plinth For Qctp On 9 X 20 Lathe

In my never ceasing search for more rigidity in my lathe I decided to make a plinth for the qctp. In its normal configuration I can often see the complete top slide assembly flex slightly. (I think I punish my lathe a bit) After seeing Bill G's plinth I felt it was time to go. I forgot to take...

www.hobby-machinist.com

Although I havnt done it for a gear blank

 

[DavidR8]

Why not build the dia up with weld to 2.8" and turn it to the correct size then there will be no problem with the missing 1/16".
I have done this to various parts I didnt have sufficient size for the job with no problems, the weld turned down fine..
check post 10 here

The Giant Binocular

Its time to re-visit the binocular. This is roughly what I want. I started these over 5 years ago but got side tracked building recumbent bicycles. Now I've almost finished the refractor I've started back on these. This is being built entirely from scratch including grinding and polishing the...

www.hobby-machinist.com

and here

Plinth For Qctp On 9 X 20 Lathe

In my never ceasing search for more rigidity in my lathe I decided to make a plinth for the qctp. In its normal configuration I can often see the complete top slide assembly flex slightly. (I think I punish my lathe a bit) After seeing Bill G's plinth I felt it was time to go. I forgot to take...

www.hobby-machinist.com

Although I havnt done it for a gear blank

Thanks, I love this idea!

 

[MrWhoopee]

Being 4140, turning should be no problem, but you will probably want to anneal the welds with a torch before trying to cut the gear teeth.

 

[DavidR8]

Being 4140, turning should be no problem, but you will probably want to anneal the welds with a torch before trying to cut the gear teeth.

Thanks, I have had mixed luck machining weld material. Good to know the reason.

 

[benmychree]

All it would take trying to machine weld material on 4140 would be one little hard spot to ruin your gear cutter, I'd go with the new stick of material. Depending on what this gear is doing, alloy steel may be overkill.

 

[DavidR8]

All it would take trying to machine weld material on 4140 would be one little hard spot to ruin your gear cutter, I'd go with the new stick of material. Depending on what this gear is doing, alloy steel may be overkill.

It's just a change gear.
I mention the 4130HT because I have 12" of in in 2.5" diameter. I'm sure hot rolled 1018 would be just fine for this low-stress application.

 

[Asm109]

The pitch diameter of a 40 tooth 16 dp gear is 2.5 inches. So you would be missing the entire top of half of the gear.
Making gears of any kind is no place for half arsing things. I would 3d print the gear before I faffed about with welding the OD.