Help finding gear supplier 1

[ENG101]

I need to replace an odd gear and am having trouble finding a gear supplier. The pinion is a 6 pitch 7 tooth gear on the ouput shaft of a 60:1 reducer. I have tried a few suppliers, but no luck, so any suggestions would be appreciated.

Thanks.

 

[Philrock]

It is fairly unusual to have so few teeth on a gear. One or more of the following will be present:

high pressure angle
large profile shift
undercut

Can you provide more specifications?

Are you looking for a stock / catalog gear or a custom made gear?

 

[ENG101]

This is an old and odd set up. This runs the power pivot on a 10K lb set of davits. A 1/2hp motor runs through a 60:1 reducer with a 6 pitch 7 tooth output pinion. The pinion turns a 58 tooth spur gear coupled to a 9 tooth 3/4 pitch chain sprocket that drives a 58 tooth chain sprocket on the bottom of the davit.

I am not sure but I think this puts the system at about 3200:1. Anyway, I have to replace the 6 pitch 7 tooth output pinion and the mating 58 tooth spur gear. I had thought about going to a pinion with more teeth, but I don't think that I have the ability to go larger on the mating gear. I am hoping that there is a solution other than a custom gear.

 

[Philrock]

From your description, I seriously doubt you'll be able to get a drop-in replacement without having a custom gear made.

Depending on speed and power levels, you might be able to get away with finer pitch gears, thereby having more teeth.

Another possibility is to increase the pinion size and decrease the gear size. This will change the ratio, of course, resulting in faster final output speed.

If you can't live with the speed change, perhaps you could change the ratio in a later stage to make up for the change in the 58:7 stage.

If you can post the center distance and pinion speed, I'll run a quick check on finer pitches. An accurate center distance measurement will be needed.

 

[ENG101]

Thanks for the help Philrock. It may take a few days to get back to you with the details. The one thing that can't change much is the final RPM. When your swinging a 26' cabin cruiser onto land, it slow, steady, and easy. The davits pivot at about 1/2 RPM, and sometimes that seems fast.

 

[diskullman]

Who is the manufacturer of the gear box? Always best & least expensive to replace with the OEM's part, if available.

Russell Giuliano

 

[dimjim]

I agree with Philrock that the pinion would have to be a modified tooth form for all of the reasons that he mentions. Maybe only the pinion has a modified form.
Can you provide the O.D. and root dimensions and dimensions over pins for this pinion. A 6 pitch 7 tooth
pinion is unusual.

It might be helpful too to know the center distance
and dimensions of the gear. It too might be modified.
You did not mention any particualar hardness of the
pinion and/or gear. The pinion should not be that hard
to replicate as a 6 pitch is not that uncommon.

 

[diskullman]

Boston Gear has 6 pitch pinon available in 6 tooth & 8 tooth. 7 tooth is not available. Perhaps you can use one of these, change your center distance slightly, and make up for any ration change in the sprocket portion of the drive.

Russell Giuliano

 

[ENG101]

Diskullman,

I think the answer is the BG 6 tooth pinion. Before ordering, I want to make sure that this is a 6 pitch gear. The mating gear to the oddball 7 tooth is a 58 tooth gear with an OD of 9.75" and an ID of 9.125", and what appears to be about .125" clearance.

I have the ability to adjust the distance between centers, so that changing from 7 teeth to 6 teeth should not be a problem. Also, since this is turning a davit, there is no "correct" speed; so the roughly 15% reduction in output speed should not be a problem.

Can you let me know what the BG part number is for the 6 tooth pinion?

Thanks

 

[diskullman]

Part number is NJR6 Item code 09824. You can download the specs at

http://bostongear.com/literature/lit_sections.asp?idLit=8

look for "Stem Pinions"

Russell Giuliano

 

[Philrock]

Be sure to check that the pressure angle of the new pinion matches that of the old pinion.

 

[dimjim]

I would be surprised to see 14.5 degree
pressure angles used for such a small
pinion and in a davit application.
I would expect possibly a stub form
20 pressure angle used for this application.
From your od and id dimensions it gives a
whole depth of 1.875/DP indicating a stub
form or a shortened addendum. I would also
go with 8 teeth instead of 6 for a replacement
for 7 tooth pinion. The od of the gear indicates
a profile shift for the gear and I would expect
a profile shift on the pinion.

 

[diskullman]

You could go with the 8 tooth pinion, and also buy the 66 tooth matching spur gear. The cost of both combined will be less than the cost of 1 custom-made gear, and the 8/66 combination will be extremely close to the 7/58 ratio. These other guys are engineers. I am a scrounger, my specialty is interchanging components, and finding the cheap way out, by knowing the STANDARD offerings of many manufacturers

Russell Giuliano

 

[ENG101]

Thanks for all of your help. Trying to replace this odd pinion is turning into quite the endeavor. Tell me what you think about this. Currently the pinion drives a 58 tooth change gear, (a 58 tooth spur gear to 9 tooth #60 roller chain sprocket that turns the davit). I am thinking about making the entire system a chain drive system. I need to maintian a ratio of about 8.5:1 with a distance between centers of about 5.5".

What do you think about roller chain instead of the spur gear? I was thinking about a #25 or #35 so that I can fit sprockets into roughly the same center distance and maintain a ratio of 8.5:1 or higher. I might have to go to a double chain for strength, but I have room for that.

Thanks.

 

[dimjim]

Where are the bearings in this application?
Is the Gear bolted to a bearing?
No mention of hardness of pinion or ring
gear has been mentioned. If a chain was
acceptable, I wonder why the disign used
a gear instead. Both pinion and gear are
special designs and any good gear/pinion
manufacturer could make them for you.
Why do both need to be replaced?

 

[dimjim]

Is it possible to recut the geared ring
i.e. sink a cutter deeper to clean up
the profile? You would still need to order
the pinion. I assume most of the wear
was on the pinion. You could then go to
an 8 tooth stubbed pinion to make up the
difference in center distance change caused
by recutting the ring gear.

 

[diskullman]

Befor I went crazy cutting custom gears, I would check out replacing the original motor & gear reducer with a gearmotor with a 500:1 ratio, and scrapping the open gear portion of the drive. You may end up with a more compact, effecient drive than what is currently in place, and avoid the expense of custom cut gears.

Russell Giuliano