# Single point keyway broach



## Crosche (Apr 17, 2020)

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.


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## PeterT (Apr 17, 2020)

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.


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## Crosche (Apr 17, 2020)

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.


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## Dabbler (Apr 17, 2020)

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!


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## Crosche (Apr 17, 2020)

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!


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.


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## Dabbler (Apr 17, 2020)

ah.  That is why the hole has to be larger than the slot you are cutting.  Then the chips separate.  Here's a pic:


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## Crosche (Apr 17, 2020)

Dabbler said:


> ah.  That is why the hole has to be larger than the slot you are cutting.  Then the chips separate.  Here's a pic:
> 
> View attachment 8687



Got it. That makes sense.


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## Crosche (Apr 19, 2020)

Here is the end result of my project; hopefully the adapter is balanced.


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## YYCHM (Apr 19, 2020)

Did you fabricate the motor mount and table etc?  That looks like top notch work.


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## Crosche (Apr 19, 2020)

YYCHobbyMachinist said:


> Did you fabricate the motor mount and table etc?  That looks like top notch work.



The pieces were water jet cut and I assembled & welded them. The 9" sanding disk plate was purchased.


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## YYCHM (Apr 19, 2020)

Crosche said:


> The pieces were water jet cut and I assembled & welded them. The 9" sanding disk plate was purchased.



What did the water jet cutting cost?


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## Crosche (Apr 19, 2020)

YYCHobbyMachinist said:


> What did the water jet cutting cost?



It's been awhile, but as I  recall the cost was $60 per frame.


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## PeterT (Apr 20, 2020)

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?


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## Crosche (Apr 20, 2020)

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?



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.


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## Janger (Apr 20, 2020)

Nice sander. Are you putting variable speed on it?


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## Crosche (Apr 20, 2020)

Janger said:


> Nice sander. Are you putting variable speed on it?



Yes, I have a VFD already attached to my belt sander. I am going to install a 3 way switch to share the output of the VFD with the two sanders.


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