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Creating a Hub for a D-shaft

Creating a Hub for a D-shaft

(OP)
Hi all,

At first it seemed like an easy thing to do, but not so sure now ponder.

I need to assemble a Hub on a D-shaft of 15mm Dia., the Hub already has a hole of 10mm Dia. so it needs to be enlarged and create the "shelf".
.
Can this be done without creating large radius (anything over R1 mm) at the seem between the hole and the "shelf"?

RE: Creating a Hub for a D-shaft

What is a D shaft and what is a shelf?

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

RE: Creating a Hub for a D-shaft

Broaching? EDM (wire or sinker)?

Aidan McAllister
Metallurgical Engineer

RE: Creating a Hub for a D-shaft

...file, whittling knife, chemical etching, waterjet, laser, ...

RE: Creating a Hub for a D-shaft

Wire EDM

RE: Creating a Hub for a D-shaft

I was surprised when Google did not pull up dozens of hits for D drive, D bore, or something.
Are the torque requirement so great a set screw and a sprocket with a 15 mm D bore would not work?
Or, must the sprocket slide?

At some point I'd consider afixing a plate or bar to the side of the sprocket to D-ify the bore.

5 down 5 to go.

RE: Creating a Hub for a D-shaft

(OP)

Quote (Artisi)

What is a D shaft and what is a shelf?
Sorry for the terminology, not a native speaker.
by "shelf" i meant the flat feature in the bore.

Quote (Tmoose)

Are the torque requirement so great a set screw and a sprocket with a 15 mm D bore would not work?
Or, must the sprocket slide?
The torque is the issue.

If the hub is 23mm thick, what is the most cost effective method from what you've suggested?
The wire EDM sounds like the best option for its accuracy but looks expensive.

RE: Creating a Hub for a D-shaft

How many hubs need machined? Just one?
What equipment is at your disposal?
What material is the hub made of? Steel? How hard?

A file has been mentioned, as have some very sophisticated techniques. They are vastly different, but each could actually be the perfect tool, depending on the circumstances.

Quote (Tmoose)

At some point I'd consider afixing a plate or bar to the side of the sprocket to D-ify the bore.

Deify the bore! All hail Bore!

RE: Creating a Hub for a D-shaft

If it's technically acceptable and easier/possible with your current equipment, could you go full diameter bore on the hub, add a keyway and rectangular key, almost like a half key? The inner face of the key then goes against the flat of the shaft. If you permanently install the key into the hub (press fit and/or tack weld) then you're as intended fit/form/function.

Does it need to be "done right" or do you just need it to work?

RE: Creating a Hub for a D-shaft

(OP)

Quote (Nescius)

How many hubs need machined? Just one?
What equipment is at your disposal?
What material is the hub made of? Steel? How hard?
I need to machine 30 hubs.
I'm outsourcing the job.
The hub is Hardened steel (waiting for a reply from the hub supplier for a more accurate description).

Quote (1gibson)

If it's technically acceptable and easier/possible with your current equipment, could you go full diameter bore on the hub, add a keyway and rectangular key, almost like a half key? The inner face of the key then goes against the flat of the shaft. If you permanently install the key into the hub (press fit and/or tack weld) then you're as intended fit/form/function.

Does it need to be "done right" or do you just need it to work?
I need it done right, with very specific and tight tolerances. neutral

RE: Creating a Hub for a D-shaft

2
Hardened steel, tight tolerances, sharp internal corners, weird shapes...all easily done with EDM.




RE: Creating a Hub for a D-shaft

Bores with keys are most often made by boring a round pilot hole and then broaching to the final shape. This requires a special broaching tool for each shape. These are readily available for standard shapes. Hardening would be done after broaching. I am trying to recall ever seeing a hardened hub.

RE: Creating a Hub for a D-shaft

Wire EDM, but it will be pricey. Since you have 30, maybe someone will give you a good price though.

When it comes to couplings we are always here to help.
WWW.PSCCOUPLINGS.COM

RE: Creating a Hub for a D-shaft

If you're outsourcing the job, why are you asking about process?

Draw what you need and allow your suppliers to quote. You don't care how the hole gets made, just what the final shape is.

RE: Creating a Hub for a D-shaft

(OP)

Quote (jgKRI)

If you're outsourcing the job, why are you asking about process?
I have to consider the manufacturing cost.
If it'll be to pricey to make i'll have to come up with a different solusion, which will effect other components in the system where the hub will be installed.

RE: Creating a Hub for a D-shaft

Helepolis,

It is going to be expensive, mainly because that feature is usually cast into the hub and it isn't a precise fit. But in order to cut it you have to either have space to get a tool in (which you don't) or EDM it.

When it comes to couplings we are always here to help.
WWW.PSCCOUPLINGS.COM

RE: Creating a Hub for a D-shaft

(OP)
CouplingGuru,

Im not very familiar with wire EDM, only from the media and a few parts tha I played with which some of the had a closed feature cut out from the middle without any apparent guide slots or holes. At list I didn't notice any.

RE: Creating a Hub for a D-shaft

We have to create a D bore for a spool used on a capstan drive. It's not very large - for an 8mm shaft, but our machine shop uses wire EDM to create it.

Kyle

RE: Creating a Hub for a D-shaft

Quote (Helepolis)

I have to consider the manufacturing cost.

I understand that you care about cost- but the quickest way to determine how much a parts costs is not to ask questions of forums about design details... the quickest method is to create a drawing detailing what you need, and send that drawing to suppliers for quoting.

RE: Creating a Hub for a D-shaft

The problem with the "D" hole is the corner of the "D" so you would need a very small diameter tool to get that almost sharp transition from curve to flat. That is where a Wire EDM is very good because the tool diameter is essentially the diameter of the wire which is like 0.015" approx. So you can get radii of 0.008". How does EDM work? they run a wire through your existing hole and the electrify the wire making it into a hot slicer basically. Kind of like how the cut blocks of cheese with a wire. except your are cutting metal. It is super accurate, and very versatile, but it is very slow and hard to automate. So it is fairly pricey, for instance drilling a hole 1" hole 2" deep may cost you $3, EDM the same hole and it is probably $50. That isn't including set up.

When it comes to couplings we are always here to help.
WWW.PSCCOUPLINGS.COM

RE: Creating a Hub for a D-shaft

"The torque is the issue."

How much torque are you transmitting thru a compromised 15 mm shaft?

Is an outboard bearing planned? The chain tension as a result the torque is trying hard to bend a cantilevered shaft, and if the D shaft in on a purchased part like a motor, the loading on the adjacent bearing may exceed what the motor manufacturer had in mind.

Any hub connection that is not clamped hard enough to resist micromotions due to torque variation and one direction radial loads is destined to experience progressive fretting wear, like the outside of this bearing race -
http://www.skf.com/binary/31-5621/ls401_48_tcm_12-...

or this keyed shaft connection-
http://photos.motoiq.com/photos/685053521_4wehK-M....

RE: Creating a Hub for a D-shaft

Hi Helepolis

it is common to broach large quantity's with a "D" hole. and it is precision hole.
bear in mind core hardness can not be more than 43 HRc. approximately.
if core hardness is 50 HRc or higher the options to broached before heat treat with a core harness of 33-43 HRc.
then do a final heat treat.
but must importantly it has to be a very stable material with very little distortion.

wire cut is an option but only for small production lots because of cost. plus there is always the issue with recast
on the surface. but if the means override the cost it is a very practical method.

a key way or splined hole would require the same procedures, but it is common.
if the material (for an example) is 4340M or 300M is has very little distortion when it is vacuum heat treated and gas quench ( high bar )

the problem is the precision required at assembly. and if alignment is required. then the cost is justified.
might also consider a press fit between details. easy to grind the O.D. easy to hone or ID grind the bore in the hub.

Best

RE: Creating a Hub for a D-shaft

Almost always gear, sprocket, pulley manufactures have the option to add a custom bore.

Send you requirement to whoever you are buying the sprocket from and ask "How much?"

RE: Creating a Hub for a D-shaft

The tolerances shown in your OP sketch (.0004" to .0007") are pretty tight, but a good wire EDM machine can hold them. For 30 pieces, wire EDM is likely your best option. The only things you need to consider are making sure the sprocket is accurately positioned when you begin the wire EDM cut, and watching for any deformation of the bore D profile shape after the wire cut is completed in your hardened sprocket material.

RE: Creating a Hub for a D-shaft

(OP)
Thank you everybody!
As usual, plenty of useful info.

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