Help finding a replacement gear

[Chucketn]

I need to help an acquaintance find a replacement gear for her fathers lift chair. She describes the gear as plastic, 2 5/16” diameter, 3/8” thick, and 55 teeth. The bore is ¾”. I have tried Stock Drive Products with no help.
She can buy an entire drive assembly replacement for the chair but the cost is prohibitive.
Is there an easy way to enter these specs to find a gear, or am I missing an important descriptor like diametric pitch? Any help in finding a replacement would be greatly appreciated.
Other than the description above, I do have a couple of pictures of the broken gear.

Chuck in E. TN

 

[Chucketn]

Here is what I have for pictures. Thanks all for your help.

Chuck in E. TN

 

[bvd1940]

What is the brand name and age of chair??
If I had to make the replacement I would use the existing gear as an indexer, put new blank an old gear on common shaft and grind HSS to shape to match old gear tooth and use a pawl on old gear to hold lashup in sink. Cut on mill or lathe. Just my 2 cents worth. This is one way but you could single point cut it also which is easier and quicker, [video=youtube;8UBxNPbg0ls] http://www.youtube.com/watch?v=8UBxNPbg0ls [/video]
Bill in SE Idaho

 

[Highpower]

It looks like (55) 4 missing teeth to me as well Chuck... :thinking:

 

[Chucketn]

She's supposed to bring me the gear and the assembly it goes on for me to measure and confirm dimentions. I'd make the gear if I had stock to make it from. Guess I could fire up a bucket of charcoal and cast a blank.

Chuck in E. TN

 

[Highpower]

Hi,

Well I measure the gap, then measure a corresponding “gap” where there are teeth.


I think there are 4 teeth missing. I’m also betting Willie and I have done it the same way.


DaveH

You would have won that bet too Dave! :thumbzup:

I measured between the two teeth on each side of the missing section with a pair of dividers. Transfer that over to a "good" section, and count how many teeth are between the divider legs. That, and my "Mark 1" eyeball said it just looked like more than 3 teeth missing. But notice that I decided to go with the dividers first. :whistle:

Of course I could be wrong too. Meh.

 

[george wilson]

There are 4 teeth missing. However,I would NOT replace that gear with ANOTHER weak PLASTIC gear. Boston gear may have a suitable replacement,or,as suggested,make a metal one at LEAST out of brass. Preferably steel.

Carefully grind a fly cutter that matches the teeth. On this job,reasonably close will be good enough,UNLESS it runs against another plastic gear.

 

[Chucketn]

The owner will bring the actual broken gear and the assembly to me tomorrow. I will carefully measure the gear. I had already decided to recommend replacing with a metal one instead of plastic.
Seems the origional chair was designed for the lift mechanism drive to be replaceable, but costly.
I don't know if I have the tools or the skill to make a replacement, but would be willing to try.
I'm hoping it is a "standard" off the shelf replacement except for maybe the bore of the gear.
That I know I can handle.

Chuck in E. TN

 

[Highpower]

It occurred to me that I have a 55 tooth change gear for my mini-lathe, so I just went down and measured it for giggles. :thinking:
Close - but not close enough....


Little Machine Shop

 

[george wilson]

Good thought,Dalee. Especially in this sue happy society.