What is your favorite method for attaching gears to shafts?

[archiver]

Posted by bill whitley at 04/30/2001 3:51 PM EST


Student on team #70, Auto City Bandits, from Powers Catholic High School and Kettering University.



What is the preferred method out there? In the past we have usually pinned the gears. I don't particularly like that because if (more like when) you have problems, it becomes more difficult to work on. We've tried set screws, with little success.

Bill

[archiver]

Posted by Joe Johnson at 04/30/2001 4:48 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: What is your favorite method for attaching gears to shafts?
Posted by bill whitley on 04/30/2001 3:51 PM EST:



I have been scared to death of anything but a welded joint in the past.

This year, we used a double-d with a tight press fit in a few of our gearboxes with great success.

I still feel better with a bead of weld for the higher torque shaft/gear interfaces but at least in some situations I can sleep knowing a well designed double-d with a tight press has been executed.

One final thing, we have also had good success with a bolt on design where flanges are welded to the shafts and then gears or sprockets are bolted to the flange. As long as we have done our homework on picking the right number of bolts to use and provided that we used the shaft itself to center the gear on the shaft (rather than using the bolt pattern to hold the center to center alignment -- not a great idea) we have had a fair amount of success. One nice thing this does for you is that you can change gear ratios without having to change the entire shaft.

Just some random thoughts on gear to shaft interfaces.

Joe J.

[archiver]

Posted by Michael Ciavaglia at 05/01/2001 7:40 AM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Interior Systems.


In Reply to: double-d with tight press fit
Posted by Joe Johnson on 04/30/2001 4:48 PM EST:



Joe mentioned using a shaft with a flange welded to it with the sprocket or gear screwed to it. Another advantage is that the flange and sprocket can be dissimilar metals (i.e. steel and aluminum). We made aluminum sprockets for weight savings but NEEDED a steel shaft to support the loads.

We did have some difficulties at first. One word to the wise, get the bolt pattern out far enough so the load on the bolts is minimized and there is enough room to tighten the bolts, should they ever come loose .

Mike C... iavaglia

P.S. If it were easy everyone would do it.


: One final thing, we have also had good success with a bolt on design where flanges are welded to the shafts and then gears or sprockets are bolted to the flange. As long as we have done our homework on picking the right number of bolts to use and provided that we used the shaft itself to center the gear on the shaft (rather than using the bolt pattern to hold the center to center alignment -- not a great idea) we have had a fair amount of success. One nice thing this does for you is that you can change gear ratios without having to change the entire shaft.

[archiver]

Posted by ChrisH at 04/30/2001 5:20 PM EST


Engineer on team #330, Beach 'Bots, from Hope Chapel Academy and NASA JPL, J & F Machine, Raytheon, et al.


In Reply to: What is your favorite method for attaching gears to shafts?
Posted by bill whitley on 04/30/2001 3:51 PM EST:



Bill,

It's very hard to beat a "double D" shaft. While you don't necessarily need a press fit, you do have to have some retention method. If you don't know what a double D is look at the end of a van door motor output shaft. The problem is that you either need to use a milling machine, EDM or a broach for the hole, depending on the exact shape. Our machine shop had a custom broach made for the van door shaft end a couple of years ago.

It's not too hard to make a square shaft out of a round one, but a square hole is harder. If you can make a square hole (see above methods), a square hole on a square shaft will work fairly well.

We like to use flanged fittings on shafts like Dr Joe said too. This is a very good approach if you're not quite sure on the gear ratio. Changes are quick and relatively painless if you have the gears ready.

Key ways and keys of various sorts also work well if designed properly. However they can be difficult to add to a motor in the field, so be sure to have spares with keyways pre-installed. If you want to check these out look for a good mechanical design book. "Machine Design" by Shigley has a pretty extensive discussion on keys and keyways.

BTW I regard "pins" as a four letter word in this context. They're almost as bad as set screws and we all know what set screws do.

Chris Husmann, PE
Team 330 the Beach'Bots

[archiver]

Posted by Jason Iannuzzi at 05/01/2001 10:13 AM EST


Engineer on team #11, Marauders, from Mt. Olive HS. and BASF, Rame Hart, CCM.


In Reply to: I agree with Dr Joe, but there are other ways
Posted by ChrisH on 04/30/2001 5:20 PM EST:



I think Woody needs to revise his famous kickoff statement regarding fastening methods.

When it comes to drive trains, "Pins AND set screws suck!" is a more fitting warning.

For the past two years, we have had the most success with welding everything in place. It's a rather permanent solution, but it's quick, it's easy, and it holds up very well. I'd say it's the best option for teams with fewer resources.

[archiver]

Posted by Gui Cavalcanti at 04/30/2001 9:35 PM EST


Student on team #422, Mech Tech, from Governor's School (GSGIS) and Verizon.


In Reply to: What is your favorite method for attaching gears to shafts?
Posted by bill whitley on 04/30/2001 3:51 PM EST:



I'm in no position to speak for my team, me being the programmer and all, but I now officially hate set screws. We have a reaaaaally simple 1:4 gear ratio drive train that propels us at a leisurely pace on treads... and we used set screws on the sprockets that were on the drive shafts. ::uncontrollable shivers::

We literally snapped 3 plastic sprockets (right down the set screw line, no less) on our shafts before reverting to steel sprockets that were PINNED. No problems as of yet...

Maybe this was off-topic with sprockets and everything, but still.

-Gui Cavalcanti
Team 422, Mech Techs

[archiver]

Posted by Patrick Dingle at 05/01/2001 7:56 PM EST


College Student on team #639, Red B^2, from Ithaca High School and Cornell University.


In Reply to: ... the horror... HORROR.... AHHHHH
Posted by Gui Cavalcanti on 04/30/2001 9:35 PM EST:



Steel set screws holding a plastic sprocket to a shaft is a bad idea. if you really are convinced you want to use plastic, you need to find a way to distribute the driving force all the way around the plastic sprocket -- not in one spot. One method you might want to try is using about a 1/8 diameter pin, and machining a 1/8 diameter hole tangent to edge of the shaft. Then you machine a hole through the plastic sprocket such that it lines up with this dent in the shaft. In other words, this is a pin that goes all the way through the sproket and shaft such that it hits the shaft at a tangent. The center of the pin should be exactly tangent to the shaft. You can do this twice on the same sprocket, two parallel tangents on opposite sides of shaft. Unlike the set screw, this will distribute the forces two four spots on the sprocket, instead of one. Additionally they will be compression forces which are generally stronger than set screws.

Patrick

: I'm in no position to speak for my team, me being the programmer and all, but I now officially hate set screws. We have a reaaaaally simple 1:4 gear ratio drive train that propels us at a leisurely pace on treads... and we used set screws on the sprockets that were on the drive shafts. ::uncontrollable shivers::

: We literally snapped 3 plastic sprockets (right down the set screw line, no less) on our shafts before reverting to steel sprockets that were PINNED. No problems as of yet...

: Maybe this was off-topic with sprockets and everything, but still.

: -Gui Cavalcanti
: Team 422, Mech Techs

[archiver]

Posted by Andrew Rudolph at 04/30/2001 10:01 PM EST


Student on team #168, Charger-Lightning Robotics, from North Miami Beach/Michael Krop Senior High School and NASA Kennedy Space Center/Cordis/HPE Automation.


In Reply to: What is your favorite method for attaching gears to shafts?
Posted by bill whitley on 04/30/2001 3:51 PM EST:



SET SCREWS!!!! !QUE HORROR! We did the set screw things on a little practice bot we made and brought to KSC with us and we broke the screws a milion times. For the drive train we had the double d and for our arm we use weld with hardened steel pins (I forgot what they are called) but they are almost impossible to pull out and we never had one break even in last years gave where we lifited the bot up with the arm (often with others pulling down) not to mention won arm wrestling with one of the schools biggest football players

Andrew

[archiver]

Posted by Matt Leese at 05/01/2001 2:19 PM EST


College Student on team #73, Tigerbolt, from Edison Technical HS and Alstom & Fiber Technologies & RIT.


In Reply to: Re: What is your favorite method for attaching gears to shafts?
Posted by Andrew Rudolph on 04/30/2001 10:01 PM EST:



For awhile our drive sprocket (the one coming off a shaft attached to the drill motor) was only attached by two set screws (albeit to flats in the shaft) and we never had any problems with it. I believe we did end up pinning and key waying it in the end (don't ask me, I'm not that much of a mechanical guy). Set screws, if used properly, are just fine. Use them properly and you'll be fine. Just like anything, using it improperly is bad.

Matt

[archiver]

Posted by Lloyd Burns at 05/03/2001 9:57 AM EST


Engineer on team #188, Woburn Robotics, from Woburn Collegiate and TorDistSchoolBrd, ScotiaBank. OntPwrGen, Enbridge.


In Reply to: Re: What is your favorite method for attaching gears to shafts?
Posted by Matt Leese on 05/01/2001 2:19 PM EST:



. Set screws inhale at a volume proportional to torque*, Matt. :-)

*and to the critical nature of their function (Murphy).

[archiver]

Posted by Ken Patton at 04/30/2001 10:58 PM EST


Engineer on team #65, The Huskie Brigade, from Pontiac Northern High School and GM Powertrain.


In Reply to: What is your favorite method for attaching gears to shafts?
Posted by bill whitley on 04/30/2001 3:51 PM EST:



For tight packaging, we use wire EDM'd square holes. For areas where packaging is not a problem, we use flange mounts.

Ken

[archiver]

Posted by Chris Hibner at 05/01/2001 8:41 AM EST


Coach on team #308, Walled Lake Monster, from Walled Lake Schools and TRW Automotive Electronics.


In Reply to: What is your favorite method for attaching gears to shafts?
Posted by bill whitley on 04/30/2001 3:51 PM EST:



We have three ways:

1) double-D with a set screw to keep it from coming off (the set screw doesn't carry any torque load, it just keeps the gear from sliding off of the shaft.

2) Welding (we rarely use this).

3) Key-way with key stock. This has become our preferred method over the past two years. We've never had a failure, it's easy to implement, and easy to fix and replace. (as a note, just like the double-D, we use a set-screw to keep the gear from sliding off the shaft)

[archiver]

Posted by Lloyd Burns at 05/03/2001 10:15 AM EST


Engineer on team #188, Woburn Robotics, from Woburn Collegiate and TorDistSchoolBrd, ScotiaBank. OntPwrGen, Enbridge.


In Reply to: What is your favorite method for attaching gears to shafts?
Posted by bill whitley on 04/30/2001 3:51 PM EST:



With the splines cut to involute shapes for better meshing,... but watch for the stress rise as you turn it down to go through mounting holes and bearings :-).

We used taper pins (pop) before keying became available. With a small machine shop, using a 1/8" end-mill, or a proper key-seat-cutter to make slot in the shaft, and a broached hole in the gear are ok for many applications we've had.

The main thing is - do not design gearing solely on a drafting program - gee it fits, so it must be goin' ta work ! Instead, figure out the load, and make sure the shaft and the gear will take the load, using the anticipated fixing method. It could even turn out that a set screw or loctite will work. Doing the math is the thing that the engineers do in private so you'll think they work magic !

[archiver]

Posted by Matt Berube at 05/03/2001 11:29 AM EST


Engineer on team #49, Delphi Knights, from Buena Vista High School and Delphi Automotive.


In Reply to: What is your favorite method for attaching gears to shafts?
Posted by bill whitley on 04/30/2001 3:51 PM EST:



One thing that worked well for us this year was a dutchman screw or a grub screw.

This is for situations where you are putting a gear or some other hub onto the end of a shaft.

You drill a hole on the interface of the shaft and the hub along the axis of the shaft, then tap this hole and put a set screw in it. For this connection to fail you will need to shear the entire screw lengthwise of split the hub.

Advantages of this connection are that it is strong,, easy and doesn't require a machine shop.

The dis-advantages are that it is very dificult to disassemble and re-assemble (don't plan on doing it) and that it will only work at the end of the shaft.

Hope that helps someone.
Matt B.
T49