Broaching

Hi, I would like to make some keyways in 3 sizes of bores. 1/2" 5/8" and 3/4" for the traction engine I am building.

The drawings say 5/32 keyway broach for the 1/2" bore and 3/16" keyway broach for the 5/8" & 3/4" bores. My first question is, to save money can I use 3/16" on all 3 bores. There is only a small difference between the two sizes. And who sells the broaches and collars for these sizes.

Thanks

Garry

Edited By Garry Coles on 05/08/2018 13:24:06

Hi Garry,

RDG has both 5/32" and 3/16" keyway broaches.

Thor

I bought one of those in 3mm to connect a pulley I was making to the motor shaft.

Being a complete broach beginner, I soon hit a snag...

The spec said it could do a slot 30mm long, but the support collar and shim were considerably shorter than that.

Due to the terrible forces involved, overhanging the support seemed like a terrible idea. So I stopped.

Am I wrong?

No better to make a full length bush, I have quite a collection that I have made for flywheels. The length generally refers to the amount of shank above the last tooth so they will clear a 30mm thickness. ARC do extensions to push then further though I have not used the as a bit of flat bar seems to work for me.

They seem a bit on the large size. I'd use 1/8" on the 1/2" and 5/8" shafts, and possibly 3/16" on the 3/4" shaft. But I suspect 1/8" will be fine for that too. To some extent it depends on the application.

Andrew

You could use the 3/16" one on the smaller sizes but leave out the shim which will give a similar depth of keyway to what the smaller size would have produced. It will depend a bit on how much metal there is around the keyways as to whether the bigger groove will weaken the part but TEs are usually quite hefty.

I got my 3/16" one from Steelmans

The other option is to just buy the small one and do the big one by planing on the lathe , did these 3/16" ones that way before I had the broach

Thanks for that info, I think I will now make up my own sleeves to go in the bores.
Thanks
Garry

I, too am in favor of using the same broach for all shaft sizes. I agree with cutting a shallower keyway for the 1/2" size.

Jason: "Planing on the lathe" ??

Nige, Imagine a holder like this but with the tool ground square across like a parting tool on it's side.

Mounted in the toolpost like this

Then using the carrage handwheel move it through the hole in the part, slowly moving the cross slide towards you putting on cuts of 1 to 2 thou and you get a groove or keyway

Thanks Jason, got it 😊👍

Has anyone come across a reference chart for making broach bushes ? It would be nice to be able to look up the dimensions of the slot required for each size broach and not have to fiddle around measuring the broach everytime i need to make a bush , this would also give you the thickness of the shim ( if needed ) . I think i remember seeing on by minuteman but it was for imperial sized broaches , i also use metric .