Seating a Keyway

Agreed.

Can't imagine why they would want that. Makes no sense to me if there's nowhere for the keys to go.

I've seen this done with fan blades on keyed shafts with hex screws thru the hub and seating on the key, mainly I think to keep the hub from travelling on the shaft...and there are key types that are secured by a screw at either end, with an additional tapped hole in the middle of the key for removal....I don't know the application where this would be required, but I would guess that it was added after experiencing problems with key movement....

Feather keys...

We used to use two set screws to secure slotted, keyed sleeves on pump shafts coupled to motors.

Mostly for ease of replacement.

If the key is captured, why screw it?

It makes no sense to me in this application. I have also seen set screws applied etc... but in this case I am going to try to convince the customer to reconsider their design request.

Thanks for your insights and replies.

The additional production costs are minimal and the reasoning could be an assemby issue

Most keys are for break away when loads are to great for the intended motor loads, if the OL protection device fails. Securing them in the motor shaft is a very bad idea.

In my experience of keys with retention screws the screw was brass (leaded bronze).

Here is one example, but, this is used to prevent the rigid coupling slipping. another place where i have seen the actual keys screwed into the keyway itself were on the occasional large propeller shaft and on some large pump shafts.

The top coupling is exactly what we used to use. We manufactured the entire pump assembly and mated them to 1-5 HP 3 phase motors.

It was not unusual for these pumps to pump acids and other chemicals for days/weeks at a time. There might be 50 of these pumps in a single line. Down time was kept to a minimum.

Well they are the most simple of the rigid couplings.......no flash machining operations required, ease of maintenance, etc............just as long as alignment is OK, there are usually no real problems.

Thanks for your comments everyone, but you we got way off point. This is not a cup point set screw issue or a coupling application and it has nothing to do with nuclear turbines.

This is simply a very BAD idea. If I put 3/8-16 FHSCS in those keyways...I guarantee you that if the key breaks, it will break at the sides of the hole where the screw is.

I have seen many twisted keys over the years, I don't mind, I just think "thanks for hanging in there keyway and key, that is what you are designed to do...almost fail...but not quite".

But if I compromise its total elasticity and affect its total yield strength by incorporating unnecessary stress concentration factors I am not allowing the keyway to do what it is intended to do ....

I still think this is a bad idea in this application, thanks again for your input.

I have to say that the previous 'good answers' are not really justified at all for this application. When I initially asked my boss "Why would they do that?" He replied "because they have no idea about how to manufacture what they are trying to build". Don't worry about it guys, I don't think I will be putting those screws in the keyways. But I will let you all know how it works out when I get back to work tomorrow. Thanks.

I just reviewed the last good answer above about offset loading....come on man, the shaft is over 200" long, do you think a cup point set screw is a good solution to do what you are talking about, or maybe should we use two of them?

Please refer to my original post and try to stay on topic, thanks.

And that goes also for the non captured keyways, I thought I provided enough information for this application question and now I see Good answers for suggesting using cup point set screws to counteract offset loading on a 5" diameter 201" long shaft.

I am going to watch football and let you all know how it goes tomorrow. Thanks

Gee, maybe I should use the Good Answer above and use a cup point set screw. I wonder which one I should thread? The bottom of the keyway? With a clearance hole in the key? HMM that don't seem to do much good... how about threading the key and bottoming against the keyway seat...shucks that just lifts the key out of the keyway....HMM maybe I should use two of them?? Please refer to OP.

Football must have been boring you more than the unwanted "help" you were getting here.

The forum is composed of a very diverse group of interested people with very diverse experience and education.

I am surprised that you have such a reaction to the members who took the time to respond to you.

It is your responsibility to separate the wheat from the chaff.

I saw no frivolous answers, no flaming and no outright dumb responses. The responders are obviously unable to provide the desired answer, but it isn't for lack of.wanting to help you.

Replying strictly to the OP,(Don't want to wander off topic), the answers to the only

questions posed :

Question#1 Nowhere.

Question#2 Yes,I have seen this before.

Do you have another question?

You come to this forum asking for help---free help,I might add, and instead of being

appreciative of the efforts of others,which required thought and effort,you try to

disparage the advice given.

If you wish to do that,I am sure you can find plenty of arguments at home with your

chosen significant other.

IF I were going to insult you,(which I am not going to do), I would say that you are

an idiot,that has led a very sheltered life as a mechanic,or mechanic's helper,

having never seen such a common practice before, and lacking understanding of the

valid engineering reasons for it.

I would also say the you are not an engineer,nor even a competent mechanic or

machinist,but a wanna-be but never will be either.

I would also say:

You wish for someone to support your invalid theory,and it pisses you off when they

do not give you the reward you seek,and now you, and you alone must defend an

indefensible position.

But I am not going to say all of that.

Instead,I wish you all of the good fortune to which you are entitled,

I for one,will not waste my time trying to help you in the future.

Good luck.

That would have been an excellent reply, it is a pity you didn't tell him what you you really thought...........perhaps you should tell him???

It is very hard to tell someone who knows everything, anything. You could probably tell him anything, but, you couldn't tell him much.

Why ask the question, when he already had, in his tiny mind, a preconceived answer??

I have seen keys bolted to taper shafts on machine tooling where there is a quickchange application, but to do this on a 5"x200" shaft that will be assembled pretty much forever does not make sense unless there is going to be some serious RPM (yes I know most people put the 's on the end of rpm but it is a pet peeve of mine) on this shaft that could unseat the key (keys are square keyways are not) causing possible shear load failure.

Just a thought.

This is not a tapered keyway, this has no use for cup point set screws. This is simply a customer asking to seat a keyway in captured keyways. This shaft has five machined keyways machined in. One on each end are only captured on one end and open ended where it will meet a stop of some sort on the bearing.

The three intermediate keyways are captured on both ends and cannot move.

The one keyway in center has two c'sink thru holes to secure two 3/8-16 FHSCS to secure the key to keyway. The long key left and right of the center key only have one 3/8-16 FHSCS securing it on one end only, close the center key.

This is a dumb design request.

I reviewed at least 300 manufacturing prints today, 100 of which need revisions. Including this shaft print of which we speak. They called out the keyway depth from the top of the shaft instead of from the bottom of the shaft to the bottom of the keyway.

I appreciate everyone's comments. Thanks for your good intent. No update today on the shaft print but I will let you know when I hear back from the customer.

The 300+ prints are for one product, part of $2.5M project of which I am only responsible for about $200K. This is small potatoes, but little things add up and the weakest link is the weakest part and if I put holes in those keys, I am going to weaken them and not let them do what they are designed to do from times long ago.

And the keys are in the main head drive shaft of the whole unit.

As I said, I will let you know what the customer determines after reviewing my revision requests.

Thanks.

Thanks Wrench:

The rpm is around 12. I left that out of the OP.

Hey HiTek: you were pretty rough on me there. Please tell me how two backed up cup point set screws apply in this application.

I have used two backed up set screws in various applications with a lock nut to boost.

Your comments have no use to the OP. Please try to pay attention to the printed words.

I know they are black and white and pretty boring, but taken in whole, they can provide a word picture where, if you think about it...everything you have said in this post is useless. Except of course your criticism of me, that may be useful to some.

Don't respond RedTek, you said you were done helping me, ... good, you have provided no help whatsoever....

...

The only reason I could see this being applied would be for an assembly issue, either in the shop or the field. If for some reason the key were subjected to unsupported gravity acceleration. Like if you had to stack things on a shaft when the keyway is in a six 0 clock position.

I know this does not apply in this application.

Even then, I would use some other mode of key restraint in the keyway without compromising the structural integrity of the key.

Such as:

Anti-seize compound

High Viscosity grease

Crazy glue [hey it works for a while, that's all you need is a while, 'til it's assembled]

Or rubber bands and hose clamps that can be removed once the keyway is captured.

There are many ways not to cause problems for you down the road.

Dilligaf?

Well you should, you will like this...

It is time for me to eat some HUMBLE pie.

I was wrong.

It turns out there is a good reason for the design request... go figure.

The shaft has about 30 'floating sprockets' engaged in the keyways, the sprockets positively engage with the 'carcass' side of a 'belt' of types I won't disclose.

Since the belt has to 'float' for tracking purposes, the sprockets have to float with the belt and those 3/8-16 FHSCS keep the keyways secured to the shaft so they do not interfere with the 'floating' of the sprockets and thus the 'floating' of the belt.

Well thanks for all your comments, I was wrong, I am sorry if I offended anyone in my replies.

And the reason there is only one screw on the outboard keys is because there is room there for a shaft collar which probably a preferred way to secure a key to a key seat vs. compromising the key.

Bottom line is the keys are going to be seated to the keyway seats.

Thanks.

Hah! They cancelled the design request on their own. Cool, no screws in the keys.

The assembler will make adjustment for the over sight

Keys are normally a snug fit in the keyway to retain them. If the key is loose, a setscrew with a conical point or dog point is used, not a flathead screw. Drill and tap the shaft radially just above the key and machine a corresponding spotface or drill point hole to accept the setscrew point.

One way to avoid having to tap a long hole is to countersink the hole but leave enough material for tapping a 1.5 X D threaded hole for the screw.

A 5" diameter shaft can easily accept a 1/4" setscrew. I

I'd recommend using a setscrew with a nylok insert so it won't back out.