# Cutting Pulley Keyways - Without a Broach



## Earl (Jan 20, 2021)

I had occasion last week to make an aluminum pulley for a project I was doing.  The pulley was easy.  The keyway was not.  I am not interested in paying a couple hundred bucks for a broach set that I will only use once or twice in my lifetime.(plus the arbor press that I don;t have)  I had read an article about chucking up the pulley in the lathe chuck, making a cutting tool (like for a shaper) and running the carriage back an forth to cut the pulley.  It sounded good.  Very quickly reality set in and I came to the conclusion that whomever had written the article I read about this concept was either lying about it or I entirely missed how he was doing it.  I spent about 3 hours messing around with it.  I ground cutter to go into a boring bar.  After about 500 (at least is seemed like 500) passes back and forth with the cutter,  I had a keyway about 25 thou deep.  Perhaps the broach set is priced the way they are for a reason.    Has anyone done this type of keyway cutting?  Can anyone tell me how they cut keyways without a broach?


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## DavidR8 (Jan 20, 2021)

Earl said:


> I had occasion last week to make an aluminum pulley for a project I was doing. The pulley was easy. The keyway was not. I am not interested in paying a couple hundred bucks for a broach set that I will only use once or twice in my lifetime.(plus the arbor press that I don;t have) I had read an article about chucking up the pulley in the lathe chuck, making a cutting tool (like for a shaper) and running the carriage back an forth to cut the pulley. It sounded good. Very quickly reality set in and I came to the conclusion that whomever had written the article I read about this concept was either lying about it or I entirely missed how he was doing it. I spent about 3 hours messing around with it. I ground cutter to go into a boring bar. After about 500 (at least is seemed like 500) passes back and forth with the cutter, I had a keyway about 25 thou deep. Perhaps the broach set is priced the way they are for a reason. Has anyone done this type of keyway cutting? Can anyone tell me how they cut keyways without a broach?



I have done exactly what you did with the exception being that I used a HSS cutoff tool for the broach. 
It took ages and was complicated by the fact that it was a blind hole so the swarf had no where to go. 
Took me ages. 
I became a believer in a broach set after that. But I still don’t own a set.


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## Earl (Jan 20, 2021)

DavidR8 said:


> I have done exactly what you did with the exception being that I used a HSS cutoff tool for the broach.
> It took ages and was complicated by the fact that it was a blind hole so the swarf had no where to go.
> Took me ages.
> I became a believer in a broach set after that. But I still don’t own a set.


Thank you very much for your response.  I thought that it was me.   At the rate that I was removing metal (aluminum) it would have taken a couple of days to get that keyway done.   I ended up with a set screw and a dimple on the shaft to keep the pulley from slipping.  I think that if I ever have the need to do another pulley,  I will spring for the broach or just buy the pulley.


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## DavidR8 (Jan 20, 2021)

About a year ago I was bidding on a full set of Minute Man broaches. I ducked out when it hit $300. 
Now how much is my time worth. Hmmm


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## 682bear (Jan 20, 2021)

I bought broaches in the sizes I need from Shars... they are around $30 each... the bushings are $5 to $10 each, or you can make your own from aluminum. I have used them without a press by tapping the broach through with a brass hammer... don't hit it hard, just tap, tap, tap... you will be able to tell how hard you need to tap on it. 

This will cut your keyway in 5 minutes, for less than $40 plus shipping.

-Beat


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## ahazi (Jan 20, 2021)

Earl said:


> I had occasion last week to make an aluminum pulley for a project I was doing.  The pulley was easy.  The keyway was not.  I am not interested in paying a couple hundred bucks for a broach set that I will only use once or twice in my lifetime.(plus the arbor press that I don;t have)  I had read an article about chucking up the pulley in the lathe chuck, making a cutting tool (like for a shaper) and running the carriage back an forth to cut the pulley.  It sounded good.  Very quickly reality set in and I came to the conclusion that whomever had written the article I read about this concept was either lying about it or I entirely missed how he was doing it.  I spent about 3 hours messing around with it.  I ground cutter to go into a boring bar.  After about 500 (at least is seemed like 500) passes back and forth with the cutter,  I had a keyway about 25 thou deep.  Perhaps the broach set is priced the way they are for a reason.    Has anyone done this type of keyway cutting?  Can anyone tell me how they cut keyways without a broach?


Earl,

I made a lathe tool to broach bushings on an R8 Stub Milling Arbor like the one below:




The tool is similar to your description. The cutting edge is a small HSS square inserted in a 440C SS holder as you can see in the following video and pictures. I never did any broaching before and I did not want to buy a set before getting some idea and feel for broaching. The results were very good as can be seen by the nice chips generated.





*Increase the volume* to hear the nice positive cutting action




Starting the process



Some progress



Almost final depth



Nice fit!



Broaching tool and mounting in BXA holder. Nice size curling chips on the bottom

I hope this helps.
Ariel


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## Technical Ted (Jan 20, 2021)

I have dragged keyways in steel with success before. I use boring bars with a cutter ground to do cuts on the pull stroke, not push stroke. In fact, it was one of my first jobs when I first started working in the machine shop. That job was a blind keyway so a hole was drilled at the start position so the tool could be fed out to take the next cut. That's why it couldn't be broached (blind hole).

I don't know how ridged your lathe/setup is, but seems like it shouldn't have been too big on an issue to cut a keyway in aluminum. Maybe it was the way your tool was ground??? I like putting a roll on the top so the chip curls up on the way out... And plenty of good cutting oil in steel. 

Ted


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## Technical Ted (Jan 20, 2021)

Also, a lot of guys cut internal keys by dragging on their vertical mills...

Ted


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## Lo-Fi (Jan 20, 2021)

I've cut involute splines on my lathe using a boring bar and the compound turned parallel to the bed. The trick for me was to remove the leadscrew from the compound and rig up a lever from the back of the saddle running past the back of the compound and out to where I could tuck it under my arm. Feeding a thou at a time using the cross slide actuating the compound by moving myself side to side worked very well and it turned out to be a surprisingly easy operation. It works like a mini shaper or keyseater.


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## tech610 (Jan 20, 2021)

Technical Ted said:


> Also, a lot of guys cut internal keys by dragging on their vertical mills...
> 
> Ted


Good idea, maybe a drill press will work too.


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## savarin (Jan 20, 2021)

I've cut keyways in aluminium with a sharp honed HSS tool bit it worked ok, mounting in the tool post, setting the pulley so the cut is at 90'.
By sliding the saddle up and down the bed and moving the cross slide towards me it slowly cut the slot.
Its not fast but a couple of thou at a time and it got there.
I made the tool bit approx half the width of the slot I needed so it was easier but had to cut it twice to get the  width.
A broach would be way quicker but how much use would it get.


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## nnam (Jan 20, 2021)

How about these two ideas.  One is very basic, cut with a scroll saw using a modified/appropriate blade, then dress it up with a file.

Another is using a round rod. Drill and tap at the end to keep the cutting bit secured. Near the end of the rod, on the cylinder surface, drill a hole across the diameter through the center, then make a cutting bit from a same size drill bit's mounting end. The initial bit would have reliefs made to help cutting. The 2nd bit would be made without the end relief to have a flat final surface. The rod has the same diameter as that of the hole where the keyway is cut.
If the rod is big enough, tap a set screw at the other side of the bit holder hole to adjust the depth of cut.

I plan to make one using the second idea. What do you think? It appears to be very simple. I used the same idea for making scribe tool.


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## yendor (Jan 20, 2021)

I have seen a guy who used his MILL  to do this. He set up the pulley flat in a vise and used a small diameter 1/8" End Mill to cut a Round Bottom Keyway then moved over to the lathe and used the method you described to finish it up square.


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## macardoso (Jan 20, 2021)

I have purchased one off broaches for a reasonable amount of money. Like you said, you will rarely use the set. I do not own an arbor press, but you can use your lathe carriage to push the broach through. Can't be a huge broach, but I've done a 5mm keyway in aluminum on my 12x36 lathe and 1/8" in steel no problem (both 1" or more deep). put the part in the chuck (preferably backed against a shoulder or backing plate and push the broach in using the flat side of your toolpost. Just don't go nuts on the force you exert.


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## Earl (Jan 20, 2021)

macardoso said:


> I have purchased one off broaches for a reasonable amount of money. Like you said, you will rarely use the set. I do not own an arbor press, but you can use your lathe carriage to push the broach through. Can't be a huge broach, but I've done a 5mm keyway in aluminum on my 12x36 lathe and 1/8" in steel no problem (both 1" or more deep). put the part in the chuck (preferably backed against a shoulder or backing plate and push the broach in using the flat side of your toolpost. Just don't go nuts on the force you exert.





This is the cutter that I used.  It is 1/2 inch boring bar with a 3/16 HSS tool bit.   Too much flex in the bar even with minimal stickout from the tool holder.  The pulley was for a 5/8 shaft so I could not use a larger bar.   I started with a much shallower cut.  (about 2 -3 thou)  I even tried using the opposite side of the bar and pulling it thru the pulley.  I used wd40, tapmatic, and every other cutting oil that I had.  Broches are cheap!!!


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## SLK001 (Jan 20, 2021)

What you did should have worked - and rather quickly.  My only observation is that your tool might have too aggressive of an angle at the front and was therefore digging in - especially in aluminum.  If it was digging in, then the depth of the tool would have to be continually adjusted (deepened) because the boring bar was being pulled down onto your part (dragging).


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## Earl (Jan 20, 2021)

SLK001 said:


> What you did should have worked - and rather quickly.  My only observation is that your tool might have too aggressive of an angle at the front and was therefore digging in - especially in aluminum.  If it was digging in, then the depth of the tool would have to be continually adjusted (deepened) because the boring bar was being pulled down onto your part (dragging).


I re-ground that bit of hss 3 times during the experiment. (I have to call it that because it didn;t work for me) In the beginning there was almost no rake.  I kept increasing it until it is what you see in the pic.


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## Suzuki4evr (Jan 20, 2021)

Lo-Fi said:


> Feeding a thou at a time using the cross slide actuating the compound by moving myself side to side worked very well and it turned out to be a surprisingly easy operation


And by the sound of it, good exercise.


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## Lo-Fi (Jan 20, 2021)

It wasn't as bad as a thought it would be driving it mandraulic! I did work out that almost zero back clearance was key to stopping it digging in while maintaining a positive cutting rake. I also ran it through with a half width tool before going for the full profile which helped immensely.


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## Jim F (Jan 20, 2021)

Earl said:


> View attachment 351857
> 
> This is the cutter that I used.  It is 1/2 inch boring bar with a 3/16 HSS tool bit.   Too much flex in the bar even with minimal stickout from the tool holder.  The pulley was for a 5/8 shaft so I could not use a larger bar.   I started with a much shallower cut.  (about 2 -3 thou)  I even tried using the opposite side of the bar and pulling it thru the pulley.  I used wd40, tapmatic, and every other cutting oil that I had.  Broches are cheap!!!


The grind on that will cause it to dig in the deeper it goes.
It should be square at the front, with a relief on the side facing the work.


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## rwm (Jan 20, 2021)

I just did this. I used a shop made boring bar type tool with a shop ground HSS bit. Here are pics:


I use a zero rake with about a 7deg clearance angle on the end. The side clearance was guestimated and was probably only a few deg. Set screw in the end holds the cutter.







I just went back and forth with the carriage advancing the cross slide as needed. The whole operation took about 5 minutes once I was set up. You should give this another try with a different cutting geometry.
I could see a blind hole not being quite so easy but still possible. A blind hole will be even harder with a broach however! ; )
Robert


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## kb58 (Jan 20, 2021)

I've made keyways simply by milling them. While they end up with a radiused top (or bottom), it doesn't matter since the key can't go there anyway. I've had zero problems with them.


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## C-Bag (Jan 20, 2021)

I know you don’t want to hear this but an arbor press turned out to be a totally handy thing for me for pressing in and out bushings and bearings,(much easier and better than the old vise method) and shafts, straightening all kinds of things, like gibs and of course broaching. I bought a basic set from Shars also and have been making my own guides. Also buying broaches as needed off eBay.


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## ericc (Jan 20, 2021)

It should not be that bad in aluminum.  Use the sharpie trick on your tool to make sure that it isn't rubbing anywhere.  What is bad is to cut a key way in steel using this method.  I've done it, though.  Make a consumable "top hat" that plugs the hole and drill a hole right on the edge between the plug and the hole.  This will get a lot of the metal out.  Then, the boring tool doesn't have to eat too much.  By the way, the "top hat" can be used again if you don't lose it!


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## Earl (Jan 20, 2021)

I really do appreciate all of the comments and suggestions.  My lathe is a Grizzly g0709, plenty rigid for this kind of work.  I have no desire to cut another one unless sheer boredom sets in and I cant find anything else to do!  I have lots of respect for you guys that make this process work for them.  It just didn;t work for me.  I tried several grinds starting with almost no relief at all  and ending up with what was in the picture.  I believe the the real issue with my tool was the amount that it flexed.  The pulley is 2 3/4 deep.  A shorter pulley may have yielded better results.   The project is complete, not as I planned but it is workable.   Thank you all.


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## rwm (Jan 20, 2021)

I am glad you got it done. Your lathe should handle this no problem. I have in the past cut a keyway 3" long with a 1/2" bar.


I think there may be some confusion about rake angle and relief angle? Relief angle is almost unimportant in this application as long as it is slightly positive. Rake angle is critical and should be near zero. The last pic you showed had a very high rake angle. I just post this for any one else who might want to try this. Also for your next pulley!
Robert


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## hman (Jan 20, 2021)

I used a Grizzly G4000 lathe to cut a blind keyway in an aluminum arbor.  I'd cross drilled into the bore where I wanted the keyway to end, to allow the shavings to break off at the end of the cut.  See post #711 at








						Potd - Project Of The Day- What Did You Do In Your Shop Today?
					

For several years I’ve made very frequent use of a Delta 1”x30” belt/5” disk sander.  Never had much success with the disk part, so I turned an aluminum arbor/adapter and mounted a 6"x1”x1” Scotch-brite wheel in its place.  This wheel is absolutely the cat’s meow for deburring, polishing, and...




					www.hobby-machinist.com


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## Bi11Hudson (Jan 20, 2021)

Before purchasing a broach set, and a shaper, and other _questionable_ methods, I cut keyways with a hacksaw. Stacking several blades made short work of the pulleys. I cleaned it up, after a fashion, with a three square file. I have tried the method you describe with a lathe. If the cut won't fit the machine, it's a null idea. The pulley I was making did fit. But it took longer than my patience lasted, whereupon I reverted to the hacksaw and file. I still don't have metric broaches, so use a smaller broach and open it up with a file. The broach set cost a lot, way too much, but has saved a lot of time over the years. The hacksaw I still have around, the pins have been drilled out for stacking. But nothing in my shop gets thrown out.

.


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## rwm (Jan 20, 2021)

I have given some thought to making a broach. Shouldn't be too hard.
Famous last words....
R


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## WobblyHand (Jan 21, 2021)

I used a parting blade as a cutter, and cut a blind key way in a cast iron handwheel.  It was difficult and tedious, but it did work.  I mounted the blade horizontally rather than vertically and used the carriage to cut the slot.  The build up of swarf in the key way was a challenge.  I solved part of the challenge by slightly shaping the key.  Also cut a keyway in 12L14 the same way.  Both were blind so to speak.  I took small cuts.  The HSS parting tool had no problem cutting if one took small bites.  If you got greedy, it would dig.


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