Aluminum Shifting Dogs?

[sanddrag]

For everyone who has built dog shifter gearboxes in the past, do you think 6061 Aluminum shifting dogs would work? The shifting dog is 1" OD, engages the gears .130" has a 1/2" hex, 1/2" through bore, and is in the last stage of the gearbox where it is geared down approximately 15:1 from the input of two small CIM motors. Please let me know if you think aluminum will work. Please don't respond with "I don't see why not but I have never built one before." I'm looking for a definative answer and a reason to back it up. I need to know before 9:30 AM PST today (saturday). Thanks so much.

PS. The hex shaft itself will be steel, if it makes any difference.

[Travis Covington]

6061 is a little scary. If you said you wanted to use 7075 or 2024 I might say you'd be okay (maybe!).. but there is a significant strength loss going from say a 1018 mild steel to 6061 aluminum.

How many dogs do you need? Are you having difficulties machining the steel dogs? Or is it some other reason?

If it is an emergency, I might be able to scrounge up some dogs for you to use (you'd need 4, correct?)

Let me know.

Bottomline, 6061 sounds scary.... I could do the math real quick, but the advantages of steel are numerous, much more than its strength alone.

[sanddrag]

We were going to see if we could machine the hex, and the machinist would be happier (and could use smaller tools) if they were made from aluminum, but since a knowledgable person (Travis) is concerned, we'll just do steel. I just wanted to know if we could get away with aluminum, but I share your concern for things like wear on the hex and on the edges of the dog "fingers." If we take shallow cuts and slow feeds, we should be able to do the hex in steel. We'll just have to buy the machinist lunch.

[Travis Covington]

We actually have a 1/2" hex broach at the high school if you'd like to borrow it (but no arbor press to use it with!!). Otherwise, we still haven' broached our dogs (or 100+ other parts) yet, so we would easily be able to do a handful of dogs at the same time for you guys. We would probably do everything tuesday or wednesday of next week.

Again, let me know.

What ever happened with those gears?

[Andy Brockway]

The biggest problem with aluminum will be longevity. Shifting on the fly will reduce this and the interaction during the mesh will also hurt. Lube with grease and bring spares. The issue I see is that the edges will round and/or burr causing problems during shifting. They should be fine for driving the gear once engaged.

sorry for the delay in answering, did not go on-line til this morning, something about building a robot

[Andy Baker]

Originally Posted by Andy Brockway

The biggest problem with aluminum will be longevity. Shifting on the fly will reduce this and the interaction during the mesh will also hurt. Lube with grease and bring spares. The issue I see is that the edges will round and/or burr causing problems during shifting. They should be fine for driving the gear once engaged.

I have no experience with aluminum dogs, but I would stay away. As Andy mentioned above, the edges are likely to round. Once this begins to happen, you may see another problem occuring: the dog may be forced out of its mating gear. Dog gear interaction needs to be parrallel with the turing shaft. Any lead in our rounding acts like a cam, forcing the dogs apart while under a radial load.

Andy B.

[sanddrag]

I borrowed Travis's broach and we're doing them out of steel. But thanks for the comments everyone.