• Scam Alert. Members are reminded to NOT send money to buy anything. Don't buy things remote and have it shipped - go get it yourself, pay in person, and take your equipment with you. Scammers have burned people on this forum. Urgency, secrecy, excuses, selling for friend, newish members, FUD, are RED FLAGS. A video conference call is not adequate assurance. Face to face interactions are required. Please report suspicions to the forum admins. Stay Safe - anyone can get scammed.

Single point keyway broach

C

Crosche

Super User
After cutting my first internal keyway in a blind hole and breaking several homemade broaching tools I knew that there had to be a better way. This looks like the better way and I am considering making some of these before my next broaching project.

 
Just a guess but I think its a combination of repeated cycling (in their case CNC driven), teeny DOC in-feeds per stroke and a very rigid system. Most carbides are less tolerant to intermittent cutting so if your setup is manually driven & not as tight (radially) you might have to take that into account. But if you can find an insert with suitable edge geometry/orientation & cheap, then having it replaceable like that certainly makes sense.

I've seen some pics of old school broaching bars in what looks like a glorified boring bar with HSS bits, lever operated stroking mechanism where (hobbyists) did it in the lathe. Some very satisfactory results in cast iron & mild steel. But the trick seems to be biggest bar you can accommodate for rigidity & take your time (small in-feed). I've only done this once myself & it wasn't pretty. My spindle cant be locked so I left it in a low gear. I traversed the carriage with every pass so it wasn't a clean stroke like with a dedicated mechanism. If I had more to do I think I'd build something.

Thinking about this some more, there is no reason you couldn't use HSS in lay down mode similar to the insert. When it sticks out like a boring bar it lacks support & now you have to secure it in ideally a square hole & set screw business, whereas lay-down you could mill a slot. Seems to me more rigid against stroking forces.
 
An interesting thing that I found during my broaching experience was that when I turned the cutting tool upside down and used a pull instead of a push that there was less deflection and the chips that were produced were cleared from the cut rather than stacking up at the end of the keyway channel. Were I not cutting a keyway in a blind hole I am sure that chip clearing wouldn't have been an issue.
 
Another thing that will help stop breaking cutters if you are cutting on the downstroke... You drill a hole a little larger than your keyway, right where the keyway is. this allows the chip to spearate cleanly rather than becoming 'hanging chaff' and piling onto the next one, etc.

-- great vid, BTW!
 
Dabbler said:
Another thing that will help stop breaking cutters if you are cutting on the downstroke... You drill a hole a little larger than your keyway, right where the keyway is. this allows the chip to spearate cleanly rather than becoming 'hanging chaff' and piling onto the next one, etc.

-- great vid, BTW!
Click to expand...
Hey John,

I did as you advised, but the problem was that the hole that I drilled for the keyway didn't extend to the bottom of the sleeve and therefore the chips didn't break off, they just clung to the side wall.
 
ah. That is why the hole has to be larger than the slot you are cutting. Then the chips separate. Here's a pic:

keyway hole.PNG
 
Did you fabricate the motor mount and table etc? That looks like top notch work.
 
Last edited:
Croshe
- did your WJ place have a minimum job cost? (for example specific parts were $60 but $75 to do any job). That's what I'm finding but maybe that varies by shop.
- is that belt sander work in progress I see in the background?
 
PeterT said:
Croshe
- did your WJ place have a minimum job cost? (for example specific parts were $60 but $75 to do any job). That's what I'm finding but maybe that varies by shop.
- is that belt sander work in progress I see in the background?
Click to expand...

Hi Peter,

There were 3 frames cut in total and yes, that is a 2" x 72" belt grinder in the background; however it's fully operational.
 
You must log in or register to reply here.
Back
Top