5mm Broach

[olf20]

I need to broach a key way in a small hub. Just one key way.
Looking at 5mm broaches and about the cheapest is $35.00.
I'm not a tight axx, but one key way and it will set on the shelf
for probably the rest of my life. O well!
ofl20 / Bob

[mikey553]

You can make a keyway on a lathe or mill with a boring bar which can take inserts. I am talking about square HSS insert, which you grind to your keyway width. Then make multiple passes about .001" at a time until you reach the full depth. The process is entirely manual and all power comes from you. It takes time, but you can get a decent keyway without a broach you don't have.

[reggie_obe]

Is the 5mm keyway in a part you are making for a customer?
If not, is there any reason you can't make the keyway 0.25 inches in both the hub and shaft?
What size keyway broaches do you have?

[olf20]

I just have a small set of inch broaches. Making a new hub for a axle with a key
already in it.
The total length of the internal key way is about 2".
Kind of long for the homemade version, or is it??
olf20 / Bob

[deltaenterprizes]

Make the hub keyway .25” and then make the a key 5mm on one side and.25” on the other!

[sarge41]

Delta beat me to it. Step keys are not uncommon. Its a good way to make a repair on worn keyways.
Sarge41

[JRouche]

Delta beat me to it. Step keys are not uncommon. Its a good way to make a repair on worn keyways.
Sarge41

Sounds like a nice work around. How does the step key work? Do you have a separate bushing for it? Sounds like a way to do off common cuts.

Why not just do the 5mm cut? Is it cost? I get it.

Can you sacrifice a broach to modify?

To me it seems like we broach to a certain dimension for fitment. I want a nice tight key way.. JR

[Paul Alciatore]

If your hub is large enough for a bit extra depth of the keyway, why not mill it?



An end mill that is greater than half the needed 5mm can cut a notch with three motions. And the end mill doesn't even need to be metric. Here is a suggested method using a 1/8" end mill (3.175mm). But almost any size smaller than 5mm would work. And the rounded corners will act as stress relief features so the result may actually be stronger than a keyway with sharp, 90 degree corners.

As I say on the drawing it may be necessary to take it in several steps, depending on the material and size of your hub and the end mill used.

[plunger]

What about a dutch keyway if the project is for yourself and functionality over aesthetics and correctness is not important.

[Richard P Wilson]

I'd hate to do a 2" long keyway with an 1/8" dia end mill.

[JRouche]

If your hub is large enough for a bit extra depth of the keyway, why not mill it?

As I say on the drawing it may be necessary to take it in several steps, depending on the material and size of your hub and the end mill used.

Very informative and educational. Its a keeper for me, the drawing and story. Thanks, JR

I do in fact like your drawing, top of the line.

[Paul Alciatore]

I would hate to do a 2" long keyway with a broach too. I guess I missed that detail. That's a bitch.

I would consider safety glasses a total must. And perhaps a vest too.

I'd hate to do a 2" long keyway with an 1/8" dia end mill.

[Richard P Wilson]

I'd make the hub, fit a steel slug into the bore, then drill through with a 5mm drill centred on the joint between the slug and the hub. This takes most of the metal out of the keyway, so I could finish off with the boring bar that Mikey mentioned in post 2. If you do it that way, its worth mentioning that its best to cut on the outward stroke, less chance of digging in.

[BCRider]

I've used Mikey's lathe method a few times for slots and other shapes. Even "broached" a hex into a hole with a special cutter that I made which has 120° V between the two cutting edges. It sounds slow and painful but in reality it goes pretty quickly and easily.

Cutting on the push is great if the bore diameter of your 2" long hole is big enough to permit a stiff enough bar. If not then I'd go with the idea of cutting on the pull stroke.

Such a bar is not that hard to make if a couple of shortcuts are considered. For example I feel like the option shown here would be easy and quick to make. In fact I think I'll do it this way for making up a couple of slotting bars in two sides to suit my shaper. Click on the pic for a bigger view.

[reggie_obe]

I would hate to do a 2" long keyway with a broach too. I guess I missed that detail. That's a bitch.

I would consider safety glasses a total must. And perhaps a vest too.

Sounds like you have some experience in the area of broaching.
Did the broach give any warning before breaking or shattering?