We are trying to connect the new gear for the chalupa motor to a 1/4" shaft. We drilled through the gear but cant tap it so our idea is shot. How is your team attaching the gear to the shaft?
Why attach the cluster to a shaft ? Just let it turn on a shaft that is fixed.
we have some gears that are just riding on the shaft, hence just freespinning on it. while on the other hand we have gears that are attached to the shaft, moving the shaft as it spins.
we pin our gears to those shafts. to do so, you would need to drill a hole the size of the pin. the pins can be purchased from small parts. they’re called spring pins, compression pins, etc.
hope this helps.
I imagine the only reason you want to attach the shaft onto that gear is so that the shaft is turning something else… For drive train or rollers for ball mechanism.
Well anyway, one way to attach the shaft into that gear is using keyways and a square stock. Just mill a slot on the surface of the shaft, about 1/8" wide and 1/16" deep , and then cut a similar slot in the bore of the gear using a broaching tool… And fit a 1/8" by 1/8" steel piece into the hole.
Keyway is one of the most effective way to attach gear/sprocket onto a shaft, if you have your bore drilled out in the gear already. Since there’s not much room on the gear itself to do modification, such as drilling in pin holes tangent to the shaft, or drill and tap through and screw in a socket head screw.
If you don’t want to mess with the shape of the bore in the gear, then go ahead and do a keyway. If you don’t have access to mills, then you can probably order keywayed shaft from places like McMaster Carr. You can probably buy a small set of broaching tools pretty cheap.
Keep replying if you want more options. I am sure other people have other ways to do it… Such as a transtorque, although I am not sure there’s enough room for one with that gear and shaft combination.
If you don’t have a broach tool, you can pin the gear to the shaft. However, you should use a bigger shaft than 1/4.
Here’s a simple way to pin a shaft using a drill, a tap, and a set screw (contrary to what Woody said, set screws can be useful as pins – I just wouldn’t use them as set screws):
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Put the gear onto the shaft in the location that you want it to be (you might want to hold it still with some clips or something).
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Drill through the gear hub and through the shaft being sure that the drill hole goes into the shaft symmetrically (ie through the center line).
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Leaving the gear on the shaft, tap the hole to the thread of a 1/8" diameter set screw (I can’t remember what the thread is off hand. Be sure in step 2 to select the proper drill for your set screw diameter and thread). You’ll want to leave the gear on the shaft when you tap so the threads go seamlessly from the gear to the shaft.
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Turn in your set screw so that half of it is in the shaft, and half of it is in the gear. You might want to use a little Loctite to keep the screw from coming out.
That is a pretty simple way to do it. You can hold quite a bit of torque with a pin this way. You can calculate the shear stress in the pin very easily and use a material table to determine if you’ll fail or not.
I would not pin the final stagegs of your drive train, but the torque at the output of the Chiaphua motor can be easily handled by a pin.
-Chris
One word…NITROGEN !!
Chris we tried the method of trying a set screw, but the gear wont take a tap. Its just too strong. I am interested in this keyway broach thing. I just have never seen it done. If anyone could describe it a little more that would be very helpful.
Thanks
Justin
Be glad that your set screw didn’t work. As its been said on this board many times before, set screws inhale audibly. Go with a keyed shaft, its what our team loves and they are also very strong. Other guys on the board can give ya better directions on how to do it than I can.
~Tom Fairchild~
*Originally posted by Tom Fairchild *
**Be glad that your set screw didn’t work. As its been said on this board many times before, set screws inhale audibly. Go with a keyed shaft, its what our team loves and they are also very strong. Other guys on the board can give ya better directions on how to do it than I can.~Tom Fairchild~ **
Tom:
Read my post before making negative comments.
I didn’t suggest using a set screw as a set screw. I suggested a way to turn a setscrew into to pin. The method that I described works very well if you don’t have the tools to do a keyway.
If anyone remembers our double jointed arm from two years ago, each arm had a double sproket reduction and we attached all of the sprockets using the setscrew pinning method I described. We never had a problem and we had to carry up to 150 ft-lb of torque in the “shoulder” joint.
Just a point to note: just because it uses a setscrew as one of the parts, doesn’t mean it is being used as a “traditional” set screw. The implementation is more important than the parts list.
-Chris
The gear in question was too hard to bore on a lathe (20"x6ft), so broaching is probably not going to be easy. Wire EDM made a nice hole for the shaft, and a great keyway too.
Quoting a wise engineer who used to post on this forum…
"I once considered what I am about to tell you somewhat of a trade secret. Considering that there may be others out there that have used this technique and because I feel bad hearing that so many people are having problems with keying hubs to shafts, I will tell you the best way to “key” a shaft to a hub that does not require a keyway:
It is called a “dutchman” key. You simply drill a hole through the shaft off-center such that it is tangent at the inner interface of the shaft and hub. Then press a dowel pin in the hole.
So why is this so much more reliable than just drilling a hole through the center? Because it is almost impossible to shear the pin. The failure mode is to compress the metal to the point that is has a little freeplay, but it will not break and will not come loose. The hub will crack from the pressure before you will get the pin to disintegrate. But that requires more force than you could possibly produce unless you use a shaft hub that is really small.
BTW, we only use this method on motor shafts or really tight spaces because we have better methods when we can just machine our own shafts. I won’t tell you this one right now - just come see our bot at our pits and I will explain."
-Raul
I am sure we all miss him a little bit now and then 