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View Full Version : Adding a second keyway in a hub ?



Dave P.
10-02-2012, 10:36 PM
I'm making a new drive hub for customer that's been a on-going issue.
It's 2in. long 1.5in bore and 2.75in od....has a 5/16 keyway full length
of hub. Eventually the keyways get worn out in the hubs, shaft has been
fine so far. I do a pm type service and change out the key every 3-4 months.
This time had to machine a new hub and had the thought of adding a second
keyway to the hub. If/when it wears just rotate the shaft into the new position.
That's easy to do but the access to change a hub takes about about 4-5 hours
of miserable work.
They are "married" to this design.....it's not getting replaced anytime soon.
I might be able to talk them into a split hub with some pinch bolts next time.
They pay well....I try to keep them happy.
Thanks
Dave

Doozer
10-02-2012, 10:54 PM
http://www.ringfeder.com/en/america/products/RINGFEDER/?g=382

Ringfeder.
No keys needed.

--Doozer

J. R. Williams
10-02-2012, 11:40 PM
Replace the hub with a 'taper lock' style and move on to a new project.

CCWKen
10-02-2012, 11:57 PM
It's wearing because it's getting loose. +1 for using a taper lock style hub.

Dave P.
10-03-2012, 12:28 AM
A taper locking hub would be good, but......the "open" end of the hub is tight to a weldment on the driven shaft.
Other end has a 1/2 in thick flat plate welded on that connects to a rubber coupler/damper with three 1/2in. dia.
bolts.
Not sure how short of hub is avail. in this dia....have to look.
For now they are stuck with this layout, without major redesign and $$$ spent I don't see it happening for a while.
I might be able to incorporate the Ringfer idea into the plate end of the hub, but not this time.
Going to download the specs on them and have a look.
As a "patch" any issues with the extra keyway, I'm not thinking of any as long as it gets a very slight radius
at the edges that contact the shaft.
Thanks
Dave

Jaakko Fagerlund
10-03-2012, 12:41 AM
That shaft size should have 7/16 inch key.

Dave P.
10-03-2012, 12:49 AM
Maybe it should but it's got a 5/16 in it and it's not coming out without them tearing a lot of "stuff" apart.
I didn't build or design the stupid thing and the people who did have sorta vanished.
It's a auger to move debris at a landfill's recycling center, passes stuff from one level to another.
Was built with no consideration for service.
Dave

becksmachine
10-03-2012, 01:45 AM
Two "solutions" come to mind, both of which are minefields with their own problems.

A tapered, gib head key will lock a hub on a shaft very effectively, but is usually limited to installation on the end of a shaft, which may or may not be the case here. In addition, locking a hub on a shaft this way is not the most reliable method to guarantee ease of dis-assembly, it also requires the ability to cut a corresponding tapered keyway in the hub. If dis-assembly is not required if the key/keyway does not fail, this may be a good fix.

Alternatively, locking keys can be made by drilling and reaming the key itself to receive a tapered pin. A 5/16" key would be rather small for this method, and is usually limited to end of shaft applications also.

Dis-assembly can be a little easier as drilling out the tapered pin "usually" allows simple extraction of the key.

Pick your poison. ;)

Dave

LKeithR
10-03-2012, 04:00 AM
I've been doing this kind of work for a long time and I've come to the conclusion that some customers simply can't be helped. You can make all the suggestions about upgrading a setup to make it more durable but in the end, if they won't listen (for whatever reason), you have two choices: Walk away; or just keep taking their money. If you've explained how to "fix" their problem and they haven't listened then you conscience is clear...

John Stevenson
10-03-2012, 05:16 AM
I've been doing this kind of work for a long time and I've come to the conclusion that some customers simply can't be helped. You can make all the suggestions about upgrading a setup to make it more durable but in the end, if they won't listen (for whatever reason), you have two choices: Walk away; or just keep taking their money. If you've explained how to "fix" their problem and they haven't listened then you conscience is clear...

Never has a truer word been written.

Local company to me has some very tall narrow cranes that pick items off floor to ceiling shelves, semi automatic.
The cranes have two double flanged wheels that run on a track and one support wheel right in the ceiling.
One of these lower wheels is driven by a 55mm [ 2 1/4" ] stub shaft from a geared motor which drives via a key.

The wheel is secured to the shaft by one of those sunken Ringfeder couplings that Doozer linked to. What happens is that the shaft spins in the coupling and the wheel and shaft is toast.
Shaft is no problem to do but getting a wheel out is major problem and a new wheel is mega expensive, you need a new wheel as it shags the bore up. Wheel is hardened as well.

Suggested to their engineer they needed a taper lock fitted with another key and that would cure the problems.
No, not on, usual not invented here mentality and keep doing to new wheels.

New engineer takes over, explain the problem to him and yes go for it do one crane.

All we get now are wheel changes because of worn flanges but the have found they can reverse the wheel to get a bit of extra life as they always wear one flange more than the other.

Really nice working with this new guy, the old guy cost the company tens of thousands of pounds by not doing his job correctly.

I hate those ringfeder couplings, many hollow shaft gearboxes use these to secure the stub shafts, in fact done one this week and one last week where the hollow shaft had to be sleeved because the stub shaft had started spinning.

mike4
10-03-2012, 07:52 AM
As Sir john has said , there are many customers around who dont like to change the design of a machine or attachment to either improve reliability or make servicing less of a pain in the proverbial.

I come up against similar situations in both electronics and mechanical areas.

I am often told that if it could be done a different way then the designers would have done it already.

Michael

John Stevenson
10-03-2012, 08:01 AM
Busy at moment but if I get chance later tonight I'll post a brilliant example.
Might not be until tomorrow as got to go out collecting, doing a Flylo tonight, round trip.
Bought ten flat screen monitors on a buy it now for 50, that's 5 each, all supposedly tested and working.
Then spotted an auction for eleven flat screen monitors about 20 miles away from the first. Banged a bid in at the last minute and I was the only bid.

Got all eleven monitors for 10, ninety one pence each.

Eat your heart out Flylo, sir John is back !!:)

Doozer
10-03-2012, 09:33 AM
Interesting Sir John to hear some Ringfeders slipping. Every application that I have
seen them used, they worked very well. Can you speculate as to why they failed?
Perhaps not properly torqued? Or the coupling was lubricated, causing to to slip?
Many times human error can mess up a well designed component.
Shaft or bore not to size? Interested in your feedback.
--Doozer

mike4
10-05-2012, 04:57 AM
NOT a gloat without pictures!!!!!
But you suck , thats monitors at less than a power cord each.

Michael