I'm sure I'm doing some wrong and in my sleep deprived state I can't figure it out. I've got a mill motor and a spider coupler to attach it to my mill. The coupler is 12mm to 12.7mm. Both the motor and the mill shaft fit snugly and the coupler is then tightened, but I still get some slippage. It doesn't surprise me really, the motor shaft is fairly greasy. Anyone care to correct a fool?
Well that’s a bit shit Int it. Get you out of trouble just put a nail or other suitably sized piece of metal down the shaft so the notch and the slot in the coupler line up. I put an unused pop rivet in the sacrificial link months ago as a temporary fix. Still there.
Post by Lyrebird_Cycles on Feb 12, 2019 19:20:50 GMT 10
OK, you've got a friction fit coupler on a keyed shaft, they're not designed to work together.
The friction fit coupler has limited torque transmission by design; they are intended for low torque applications. You can increase it by increasing the roughness of the mating surfaces: a few swipes with a file along the inside edge of the coupler (in the axial direction) will help a bit. IMO a torque limit is a good idea on a mill, prevents damage when a stone jams the rollers.
The keyed shaft will allow you to fit a much higher torque coupling: change to a jawed coupling with a set screw and put the set screw into the keyway. RS sell a range of jawed coupling at reasonable prices. BTW a spider is the insert that goes into a jawed coupling so yours is not a spider coupling in normal terminology.
The highest torque transmission will be if you match the keyed shaft to a keyed coupling but that involves a lot of faffing around.
Like I said the nail or suitability sized metal will form the key.
Yes, but I hate half arsed solutions. Do the job properly or not at all.
Sure but to get you out of trouble sometimes you need a fix that doesn’t entail ordering new parts. A work around if you will. When time and schedule aren’t the issue you can fix it properly. Or not depending on your disposition.
Here's my set up. Apparently I lined the grub screw up with the keyway, and got good enough engagement that I haven't had any issues with slippage.
Where are you getting the slippage, on the mill side or the motor? One thought I had, if the couplers were on the wrong way around, and you managed to get the 12mm on the 12.7 shaft, you would have a hard time tightening the 12.7mm side on a 12mm shaft. I remember mine being a snug fit for both sides, and I didn't have to overly tighten either side.
RE: LC's comments, I took a leaf from his comments on other motion dynamics builds and have used a small screw on the far side of the motor as the connection between the motor and the drive shaft. The drive shaft is thin wall aluminium from bunnings. The idea is that either the shaft or screw would let go if a jam occurred. This is a physical protection on top of the electronic protection as I ordered the jam sensing model that should automatically cut out if an overload occurs.
Edit: Forgot to mention, definitely clean any grease off the shafts and coupler. As LC said, it's all friction here so grease is going to cause issues.
Also, looking at your image again, it looks like you have a keyed shaft on the motor side, is that correct? Just clarifying that my motion dynamics motor had no shaft, and I used a straight length of tube sourced separately.
If you are using the mill master mini mill that we got from the bulk buy, it should have come with a key to go in the key way. If you have a key on both sides, you could potentially line these up and use the key along with the coupler to hold it in place. But as LC said, this physically locks your shafts together so it'd be good to have a fuse in the system somewhere to let go if a jam occurs.
Thanks all, it sounds like I grabbed the wrong coupler as it isn't keyed. That being said, I removed the grease and gave it a rub with a file, shaft grip is much better now.
Too much lubricant can be a bad thing.
While the the shaft is keyed, it doesn't mean it won't work without the key. Keyed couplers are harder to find, at least they were for me. The bearing places I talked to here in Toowoomba don't stock any, they take off the shelf couplers and mill them out for you to suit the key you have, which of course sends prices north at a rapid rate.
If you take any flat bit of metal that will fit in the two keyways you have, and file it down so that it doesn't sit proud of the shaft, you can still use the coupler you have to make it work. Or file the shafts as suggested above, or even wrap them in some sort of tape to increase the diameter and the friction.
Why is everyone calling it a coupler? It's really bothering me. It's a coupling, or more specifically a hub (the element goes in between the hubs to form a coupling). Whew that feels better.
The problem you have there MTB is that your coupling is designed for straight shafts as LC said. With a keyway there is less surface area on the shaft and hence less area for contact/friction. Also, you shouldn't put ANY lubricant for that type of coupling as it should just slide on the shaft. It's got me why you lubricated it anyway, you know lubricant makes things slippery right?
While I'm up here on the soap box, check out shrink disc couplings. These are friction couplings but do handle high torque. They don't require any keys or interference fit and can be tightened by a socket and torque wrench. Phenomenal gripping power simply by squashing the sleeve on the shaft, quire remarkable really.
Wondering if this is my issue - my milling speed went to absolute shit the last two batches and drove me nuts. Took me about 30 mins to mill 10kg. Thought it was gap related. Adjusted the gap about 4x each batch.
One half of the coupling needs to be for a 12mm shaft, the other half for a 1/2" shaft. What are the IDs of the coupling you bought? Is it a friction-fit like MTBs fitting on a keyed shaft?
If I were you I'd buy a 12mm keyed coupling and drill one half out to 1/2". All you need is a vice, drill, and 1/2" drill bit. You might have to file out the keyway with a small file, which is no big deal for coupligns of this size and power.
Edit: yes you can get 12mm taperlocks (1108) but they're quite large compared to the shaft: see here. You could then buy coupling halves to suit: see here.
The OD of the coupling will be 85mm with an overall length of 60mm. Ends up being a pretty bulky setup but will 100% get the job done. If you want to go down this route I could direct you to exact parts for a complete coupling assembly for your application.
Last Edit: Jun 25, 2020 21:40:36 GMT 10 by Wiggers
Any bearing / industrial transmission company will sort you out
That means talking to people
Any off the shelf online suppliers?
I'll fess up here and admit I ordered one off eBay that's similar as the one MTB has in the photo earlier. Doh!
It grips the motor fine but free wheels on the mill shaft.
It's a standard part and should be available easily without too much talking. I got a high quality one from a proper industrial supplier and it only cost $30 or so. Wasn't quite off the shelf but it was next business day in Toowoomba. Should be on the shelf in cap cities. Not sure where you are.
Do everything in your power to check it first. I discovered mine would turn fine until a load (I.E. grain) was added. Thankfully I learned of this when I was trying to record a video to send to my mate to show off my new mill.
Would have been bloody embarrassing if I had found out on brew day with all the boys there!
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