Metric Keys - Are they commonly available?

[abeschneider]

Can anyone comment as to the suitability of specifying metric (as opposed to inch) keyways and setscrews, vis-a-vis the availability of power transmission components such as couplings, hubs, sprockets, etc?

I would like to stay completely metric in machine design if possible, but it seems like many mfrs just carry inch-based components.

Is it common to specify inch keys on metric shafts, or would it be better to stick with the ISO metric specs for the keys?

Thanks.

 

[R1100S]

I've seen english keys on metric parts. I also see quite a few NPT pipe threads and UNC threads on metric parts, the english threads are for machine shop handling. However, any supply house (McMaster, Fastenal, MSC, etc.) carries metric keys. If you're going with a metric shaft diameter, I'd use a metric key.

To complicate your question. I've found power transmission components are much easier to spec in english sizes, so you may want to use english shaft diameters and keys.

 

[eromlignod]

I'm not sure I understand your question. You have to specify a key for whatever the keyseat is in the purchased part (if it has one).

If you're fabricating both the shaft and the hub, then you can make the key anything you want. The key itself is simply chopped off of a bar of key stock, which is commonly available in English or metric. It generally comes in either medium- or high-carbon steel (like 1045) or stainless, and in "standard", "oversized", or "undersized".

...and please tell me you're not wasting time rounding the ends of your keys.

Don
Kansas City

 

[abeschneider]

I'm designing the machine from scratch, so I have the option of choosing metric or english. My question is along the lines of R1100S's reply; it seems the availability of PT components in English std is better than in metric...

 

[drawoh]

abeschneider,

Where do you live, and where is your design going to be used?

Try searching the local hardware stores for metric hex keys. If you can find them, it is safe to use metric. If you cannot find English keys, you had better use metric.

I bought my personal set of metrix hex keys at a Canadian Tire store. Metric is a safe choice here in Canada.

I believe that (almost?) all bicycles nowdays use metric cap screws.

JHG

 

[abeschneider]

Drawoh,
sorry to be vague; when I said "keys" I meant the term as in "key and setscrew", not a hex driver...

Thanks though...

 

[PeterCharles]

Of course, if you reside east of the Atlantic then metric keys are no problem what so ever.

 

[handleman]

If you're looking to stay completely metric in your machine design, check out Misumi. Their catalog is aimed specifically at design of factory automation equipment. Quick delivery and highly customizable/specifiable components, all metric. They have plenty of keys, shafts, pulleys, sprockets, etc. as long as you aren't looking for very large or very small components.

 

[Philrock]

Unless you have a compelling reason to do otherwise, use metric shaft keys and setscrews for metric dimensioned shafts, and inch shaft keys and setscrews for inch dimensioned shafts.

Metric shaft keys and setscrews are readily available in the U.S.

Standard dimensions for keys relative to shaft size are in Machinery's Handbook for both inch and metric sizes. Typically, key width is nominally 1/4 of shaft diameter, rounded to the nearest standard key size.

Specify key depth based on compressive stresses on the sides of the key, key material strength, shaft material strength, bore material strength, and an appropriate safety factor.

 

[abeschneider]

thanks for all the good information.

handleman - I checked out Misumi but it looks like their products are a little small for my application.

My torque is about 320 N*m, or about 3000 in*lbf. Any other recommended supplier who carries metric PT equipment (ie: flexible couplers...)