I was wondering if there were any ways to secure gears on shafts. I don’t mean along the axis of rotation (that is easily solved by hex/keyway broaching gears or carefully welding). How would I keep a gear from sliding along a hex shaft if it was already broached to the correct size?
I have thought of tack welding, roll pins, spacers, and set screws in the place of roll pins.
I ruled out tack welding because it would be nice to be able to reuse the gears in a case of emergency, and I don’t have the clearance in some parts for spacers.
I am probably going to resort to using set screws but I was wondering how some other teams secured their gears on shafts.
Get gears with hubs. Drill a hole in the hub, tap it, and setscrew the gear to the shaft. It’s probably a good idea to locktite the setscrew, just to be sure
We use McMaster.com, go to their site and type in “aluminum collar”. Click on About aluminum collar and there you go, the best method, we used 20 aluminum collars this year on our robot for multiple purposes.
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.
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.
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…
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.)
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.
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?
You can grind a toolbit, or buy a thinbit style toolholder, and then a 0.030 grooving insert.
They’re not cheap. I had to go buy some from our local distributor during build this year, since we needed them ASAP and couldn’t wait to purchase them online. Each insert was about $12.
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.
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.
the trantorques will expand to fill over-sized holes.*