View Full Version : Cutting Internal Slot

11-01-2002, 09:05 AM
Newbie question. I need to cut a new internal slot on a pulley and haven't a clue how to do so. Any reference would be greatly appreciated, or some step by step instructions. Thanks for your help. Ron in Central New York

Herb W
11-01-2002, 10:00 AM
There are a number of ways to cut an internal keyway. A fine big old vertical slotter would be just the thing for the job, but you don't likely have access to one of those!

Could also be done on a shaper. If you don't have one of those, it can be done on a lathe.

Another option (and probably the easiest) is to cut it with a broach.

Let us know what you have (or have access to) for machinery and maybe the dimensions of the pulley and we'll be able to give you more specific advice.


[This message has been edited by Herb W (edited 11-01-2002).]

Uncle Dunc
11-01-2002, 11:09 AM
This question got a pretty thorough airing several months ago, with quite a few suggestions for people without the right tool for the job. Try searching in the archives.

Al Messer
11-01-2002, 11:27 AM
Try cutting a groove with a round rat tail file that is smaller that the dimensions of the key. When you get it to the proper depth, square off the sides with a Warding File or a small triangular file that you have ground the teeth off one side to make it "safe".

11-01-2002, 12:43 PM
...or remove the initial bulk of the metal with an end mill slightly smaller than the final slot width you want, then do the filing to square up the corners and bring to final width.
It helps a lot to have the correct file(s), by the way. Worth the investment.

11-01-2002, 02:50 PM
& now for the easy way - turn a plug of the same material as the pulley to a light push fit in the hole, now drill a hole slightly less than key width in diameter on the joint line. Remove plug, the resulting 'half moon' is very easy to file square. http://bbs.homeshopmachinist.net//cool.gif

[This message has been edited by Tel (edited 11-01-2002).]

11-01-2002, 03:30 PM
Tel, that's brilliant. Falls in the category of .."why didn't I think of that!"

11-01-2002, 03:36 PM
BY GOLLY TEL!!!!!! thats neat!. I have cut slots free hand with a small home made chisel. But youres is a good idea, don't even have to turn a plug, use an old bolt and drill. or piece of shafting. maybe heat a piece of key stock to critical temp, cool slow, make a cutting shape, reheat, quench and temper and drive it through. Takes longer to wirite it than to do it (maybe i exaggerate a little). Damn sure faster than writing it and correcting my speeling http://bbs.homeshopmachinist.net//smile.gif

(EDIT COMMENT- lynn said it fast while i was composing!!- look at the times)

[This message has been edited by docsteve66 (edited 11-01-2002).]

11-01-2002, 06:58 PM
Why not just place your pulley on the shaft and drill into it to make a round key instead of a square one? Believe it or not, the round keyway is stronger than the square one, as are all radius features. Drill, ream if you want, tap in properly sized round stock, you're done.

11-01-2002, 10:50 PM
You sure are a smart bunch of folks!

11-01-2002, 11:51 PM
what's a broach

Herb W
11-02-2002, 12:45 AM
You know what they say about a picture! http://www.dumont.com/

11-02-2002, 02:58 AM
Even after removing the round keys on my Southbend lathe handles I still never thought of using a round keyway on my power transfer projects...I guess just because most of the shafts/pulley/gears I want to mate to already have a square keyway so I boxed myself into that thinking. Why are square keyways so prevalent?

11-02-2002, 05:01 AM
.. for one thing, the square key offers a good seat for a grub screw.

As far as the little winkle of drilling the hole goes - it also does the trick on new work - mark the centre of your hole, scribe the circumference & then a pop mark on that is where you drill a slightly - key size hole before boring your shaft hole. Just one o' them things I thought everybody did.

[This message has been edited by Tel (edited 11-02-2002).]

11-02-2002, 09:45 AM
Tel, You hit on a touchy point there. I think we all do some clever things, never mention them cause we either figure every one else must have known the trick long before 'we learned the trick OR we figure its is so simple that others would think they were being insulted by being told.

I have learned a lot here. Thanks to the newbies who have the self confidnece to to ask and the experieinced folks who adress the kids and INFORM old codgers such as I.

So to both the ignorant and educated, THANKS A LOT!!!!! and merry Christmas, little Tim.

11-03-2002, 12:03 AM
As far as the little winkle of drilling the hole goes - it also does the trick on new work - mark the centre of your hole, scribe the circumference & then a pop mark on that is where you drill a slightly - key size hole before boring your shaft hole. Just one o' them things I thought everybody did.

This sounds suspicously like the conversation my Lawyer had with his proctologist when he was getting his "asteroids" trimmed.

"So Doc, you are going to make me the consumate lawyer?" What do you mean? "You are going to make me the perfect A--hole!"

Another "Kodak moment"... http://bbs.homeshopmachinist.net//biggrin.gif

[This message has been edited by Thrud (edited 11-03-2002).]

11-03-2002, 02:00 AM
Right Dave, you must be feelin' better. http://bbs.homeshopmachinist.net//smile.gif

What have you got when you've got 12 lawyers buried up to the neck in sand??

kap pullen
11-03-2002, 09:12 AM
Another way to cut a real keyway is grind a parting tool, set it in line with the lathe centerline, and use the lathe like a shaper.
traverse the carriage back and forth while feeding the cross slide into the job a couple thou per cut.
may have to lock the spindle with a band clamp some how.

11-03-2002, 10:42 AM
The round key method is well known in the UK as "French Key".......I don't know why

Cheers.... John

11-03-2002, 10:49 AM
If you don't need any lateral movement of the pully and it is at the end of the shaft.
Then drill it on the interface of the shaft and pully (the round key as many have proposed) then tap it. This gives you a round keyway, a threaded fastener to keep the pully in position and you can use a long grade 8 setscrew for the key. If you want use an brass screw instead and you have a shear pin for safety. If the brass is too much make an aluminum bolt for the shear pin.

11-03-2002, 02:53 PM
...I thought it was called a Scotch key John, & I dunno why either.

11-03-2002, 06:31 PM
round key with taper of 1/16" ft. is known as Nordberg key, from 1940 referance, only round keyways I've actually seen had no taper, but have seen a lot of taper pins threaded on large end for easy removal.

11-03-2002, 09:02 PM
Tel - I think you don't have quite enough sand!

11-03-2002, 09:03 PM
Tel - I think you don't have quite enough sand!

11-03-2002, 09:19 PM

I would have to say a ***** cat that WAS very constipated! http://bbs.homeshopmachinist.net//biggrin.gif (that has got to hurt, eh?)

11-03-2002, 09:46 PM
Sprocket got it - 'not enough sand'

11-04-2002, 08:04 PM
I have heard the threaded pin called a "dutch pin"

11-04-2002, 08:05 PM
I have heard the threaded pin called a "dutch pin"

I heard it as "what do you call a bus load of lawyers going off a cliff?

11-04-2002, 10:02 PM
One thing you need to be careful about when drilling holes on the edge of shafts and hubs is if they are different materials. Your drill will tend to wonder towards the softer side.

11-04-2002, 10:55 PM
just finished pounding in a TIGHT bushing in son's wallowed out riding mower idler pulley , when the most talented practical mechanic ever born walked in & said " better pin it" ..i said , it is going nowhere ...he repeated "better pin it...drill a hole @ joint & drive a # 16 nail in ".. o.k. ..........that was 10 yrs ago ...idler is still functioning , Renick Hardcastle isnt .Lord , i miss him!.....he called it a "poor boy key"........he had survived the depression in rural ky, & could do more with less than anyone i have known..repose in pacem.......
best wishes

11-05-2002, 01:22 AM
An improvement?

Why did greenpeace save the lawyers thrown overboard from the ship they were harrassing?

They figured the Atlantic ocean didn't need even more toxic waste on the bottom.

11-05-2002, 09:09 AM
Answer to bus/lawyer question. A good start with much more to do.

I don't know what this has to do with keyways and such. We should be ashamed of ourselves picking on the legal profession--way to easy a target.

Back on task-- It is mentioned to be carefull when drilling a hole at the interface between shaft and pully/gear. The best tool is start with a center drill and then use a screw machine bit. The set-up needs to be fairly rigid if using disimmilar metals. If you need a bit more grunt drill, tap and insert first pin and then do a second pin.

11-05-2002, 09:36 AM
I agree Stepside. We shouldn't berate lawyers. They have feelings too. After all, it's only that 97 percent of them that give the rest such a bad name.

11-05-2002, 03:02 PM
Lynnl: it is impossible to berate or insult a lawyer. Vocabulary of average man is too limited to undersand the words (at least mine is). Best we can do is to try to describe them accurately in simple terms. Examples abound- used about a average criminal the words would be deemed "fighting words" and your ass would be in trouble.
Every notice that politicians and lawyers seldom are angered or embarrased by what you and I would think of as an unpardonable insult?

11-05-2002, 03:23 PM
You're absolutely right Steve. As long as they can keep feeding at the public trough they're happier'n pigs in sh.., er slop. Only thing they can't stand is to be ignored.

Herb Helbig
11-05-2002, 05:28 PM
Let's hear it from all you lawyer/machinists out there!


Al Messer
11-05-2002, 08:49 PM