Securing gears on shafts

[vivek16]

eclips would probably be a good solution. I haven't used them before. I still don't think I have enough clearance for the locking collars.

What do you think about gorilla glue? It is a gearbox so there should be no side load on the gears. Wouldn't a few dabs of gorilla glue work?

thanks, Vivek

[Joe G.]

For most purposes, a decent Epoxy will hold better than gorilla glue. In either case, if you choose to do so, make sure all parts are completely grease-free before application.

you could also use a small roll pin, if you have the machining capabilities to do so (which you probably do, if you are custom making a gearbox) as the Tough box did this year.


How much clearance do you have?

If there is not enough clearance between the gears for shaft collars, but more than 1/16 of an inch, small spacers (cut from tube stock, or from the IGUS bag) have worked well for us in the past, with either shaft collars where there is more clearance, or the gearbox walls to hold all the parts together.

[vivek16]

By clearance I mean a gear from another shaft in the gearbox comes too close to the hex shaft which would need a collar/spacer. Sorry if that doesn't make sense. It makes sense to me but I have the gearbox memorized.

After talking to Chris lyddiatt from 1114, I've decided to go with roll pins. Although, more ideas would be appreciated if teams have found any creative ways to secure gears.

thanks, Vivek

[Joe G.]

Oh, I thought you meant that two gears on the same shaft needed to be very close together.

Roll pins should work fine.

[thatmorman]

set collars work very nice, but they are heavy. one solution that is a little more cheap is zip ties. it doesn't necessarily look nice, and its not the most affective, but it works in most situations...

[Dick Linn]

Snap rings would be good. You could also just use tubular spacer sleeves or thrust washers, depending on your setup. (One year the kit of parts contained a right-angle gearbox and required sleeves to locate the pinion over the larger helical gear.)

[,4lex S.]

I don't know if it has been mentioned already (possibly by a different name) but I have often seen circlips function well to keep things on shafts in place. Nylon spacers also work alright (assuming they don't grind on anything). If you have the space, a custom shaft can often be designed to have a high spot that secures the side of one or two gears too. I like circlips though because they are easily removable and take up little space on a shaft.

[vivek16]

How do you machine the groove needed for a circlip(snap ring, e-clip, etc)? Do you need a special lathe bit or will a triangular insert dealie suffice?

thanks, Vivek

[Aren_Hill]

Special bit is a requirement sad to say

[dlavery]

You don't need to resort to expensive insert systems for a basic operation like this. Grinding a cutting tool to cut a retaining ring groove is a fundamental lathe skill that you will want to practice. Based on the size of the retaining ring you are using, determine the groove width and depth. These standard dimensions can be found in Machinery's Handbook (if you don't have a copy, get one; it is possibly the most useful reference manual you will get in a long time). For certain size shafts, you can also look up the dimensions here.

Once you know the groove width, use a bench grinder to grind a piece of HSS tooling to the width of the groove. You basically want to grind the HSS to the shape of a parting (cut-off) tool, but shorter (there is a nice tutorial showing how to grind a parting tool here). The length of the cutting portion of the tool does not need to be significantly longer than the maximum depth of the groove. Grind in a 7-10 degree rake to the top of the tool, and appropriate relief angles to the sides and face (so only the tip of the tool actually cuts and contacts the sides of the groove). Mount the tool bit in a holder, and you are good to go.

Unlike carbide inserts, HSS tool blanks go for about a dollar each if you are a careful shopper.

-dave


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[=Martin=Taylor=]

I'd like to try these some time. They can securely lock a gear/sprocket/whatever to a shaft. preventing both slippage and side to side movement.

The best part? No machining or accuracy required the trantorques will expand to fill over-sized holes.

[AdamHeard]

He has already told us that a clearance issue exists (like in the AM toughboxes). The larger gear of gear cluster A (arbitrary name) is too close to the shaft of the large gear of gear cluster B for any spacer or collar to be added (The small gear of cluster B is on the same shaft as A). Please correct me if I am wrong, but this is what I am imagining.

A roll pin like in the AM gearbox is the least labor intensive solution I can imagine that doesn't have the possibility to move. I have used the press on retaining clips like Travis suggested, but they have the possibility of drifting (You could still use them, just be prepared to verify the alignment often). Snap rings would also work very well, have a lower profile than roll pins, and look better. They do require machining that is a tad more difficult, but still is a pretty simple machining operation.

[DonRotolo]

Originally Posted by dlavery

Grinding a cutting tool to cut a retaining ring groove is a fundamental lathe skill that you will want to practice.

This is a point worth repeating. Just because you can buy pre-made lathe tools doesn't mean you cannot make your own. In fact, there are times when making your own provides a far superior result. Making your own lathe tools is not at all difficult, as long as you follow some basic rules, and having that skill will serve you very well throughout your life.

Pre-made tools are best used when you need something that will last a long time, such as for a production run or an operation you'll repeat many times (like cutting screw threads). For short sample runs - and in FIRST, is there anything else? - unless you happen to have the right tool, grind your own.

FIRST is here to help you learn these skills. Go at it!

Over the years I have forgotten the details of most tools, but I DO know where to look them up, and that's just as good. I have a good tool grinding attachment for my grinding wheel, allowing for decent precision, and with just a little understanding of the principles, you can eyeball something if necessary. Pre-made tools in my shop are limited to 3 carbide jobbies and a parting tool.

Remember, you can use an e-clip even in a square shaft* - it's the groove that needs to be round, not the outside of the shaft. (*not recommended, but possible anyway)

Don

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[M. Mellott]

Our team is a big fan of E-clips (OK, me personally). Work great for as thick as the are. However, if you just need to space out two gears in a gearbox, Delrin spacers would be better--no need to cut into the shaft.

[IKE]

Originally Posted by dlavery

You don't need to resort to expensive..
-dave
.

You just dispelled my NASA stereotype that your post would have started with:
Install the piece of billet into the 7 axis CNC....

Like Dave and others have said, learning to make your own tools is a great experience.