View Full Version : Another Newbe Question

12-18-2002, 05:26 PM
Being a lurker for some time I though you all would be the kindest in answering a (stupid) question from someone who is new at this.
Serveral of the engine drawings I have considered call for keyways to be machined into hubs. I understand the concept of a broch (sp) but I have no idea how to use one. Do I need a broch machine? can this be done on my lathe? This is one of those operations that (it looks like) everyone takes for granted, however, I have not got a clue. Thanks for all your help.


Al Messer
12-18-2002, 06:17 PM

I would suggest that since you have never broached a keyway that you go by the local doughnut shop, buy a couple of dozen assorted and stop by a local machine shop about coffee break time and explain to the shop foreman what you are doing and that you'd appreciate it if he could show you how it is done. Chances are, he'll be flattered and be glad of a chance to show his knowledge to a novice.

Now, if that is not possible, I am told it can be done on a lathe by racking a special ground tool mounted in the toolpost back and forth with the hand wheel. I cannot say from experience. Good luck!!

12-18-2002, 06:27 PM
Thanks for the idea, I'll try that. In thinking about it, it seems there should be a way to move the broach back and forth through the hub and cut the keyway by mounting it in the cross slide. The part I'm stuck on is the depth of cut. How to control the up and down.


12-18-2002, 06:55 PM
Another device which is quite handy in such a situation is referred to as a file. Use a narrow one, and fit to the key. Should take about 10 minutes max.
There are several texts available for the machinist in training. Cruise eBay or your library for a couple, and read anything you can find on the subject. After a bit, you will be answering questions here.

12-18-2002, 07:26 PM
I find when I am in the states, that Cuban cigar helps a lot for getting information at a machine shop, the next best thing is donuts.

As to your problem, if you want to do it yourself, make some kind of jig that hold the piece and get a good file.


12-18-2002, 08:21 PM
I've never done it, but this is my understanding...

You can buy a key way broach and a bushing for it. The bushing has a slot in it to align the broach. You buy the bushing to fit the bore of the hole you want to broach. You insert the bushing into the bore, then press the broach through to create the keyway. I believe it's done in one pass.

see the following page at MSC which shows the broaches and bushings:

You need Acrobat Reader to see it.

Al Messer
12-18-2002, 08:52 PM

If you want to do it in the lathe, mount the workpiece in the chuck, lock the Bull gear to immobilize it. Mount the 'specially ground tool in the tool post just like you would to bore out a hole. Rack the tool back and forth with the carriage wheel on the apron. Feed the tool into the work with the cross feed about a half thou. at a time. The depth of the keyway will depend upon the width of the key, they are usually one half the width of the key, plus a bit. Have lots of cutting oil and patience handy as you'll need lots of both. Good luck!!

charlie coghill
12-18-2002, 10:44 PM
There are three ways to do this. One is the file works if the key way is not too big will still work on larger keyways but will require a lot of work. Another way is using the lathe. A shapper would also work like the lathe tool, back and forth. The tool bit will be ground with the reliefs simmular to the a normal tool bit except the end will be left flat and the width of the key. In setting up the tool the tool is put in a boring bar as if you were going to bore a hole. The flat of the tool will be aginst the side of the hole,the center of the tool on the center line of the hole you are broching. Use the carriage hand wheel to move the carriage and tool back and forth each time advancing the tool a .001 or so each time. Do this a few times and then do not advance it,just move the carrage back and forth. This will take care of the spring of the boring bar. You do this untill, as has been stated, you have reached 1/2 the key thickness.

The other way is to use a broch. You buy one the size of the key you will be using. You will need a bushing to fit the hole,also the busing will need to fit the broch, a "B" broch, a "c" broch ect.
The broch is pushed through the hole with a press, after the first pass there is a shim that is put in the bushing grove between the broch and the bushing and the second pass is made if the key way is not deep enough yet use the second shim along with the first shim and make the third pass. Use cutting oil and when you think you have enough on the broch use some more oil. Do not press the broch back wards as that will dull the broch.
The broch is made with some taper so that when it is being pressed through the first teeth will take a cut the next tooth will take a little more and ect.
Hope this helps you and kind of makes since.
Don't feel bad as I broched a key way for a fellow the other day who is in his 70's and had never seen it done either.
Machinery's handbook probably may give more information.

12-19-2002, 12:36 AM

Some of the HSM and MW articles of past dealt with this - try a search on the front of the board for "Keyways".

The method they used was using a special tool to plane the keyway in the hub as described by others above.

BTW, welcome, and don't be shy - ask away, speak your mind!


[This message has been edited by Thrud (edited 12-19-2002).]

12-19-2002, 01:12 AM
Hi Tadd -

I've done this all three ways mentioned above
and seen a couple more done.

The broach is the fastest, but you have to buy the tool, bushing and shim (the broach
gets pressed through twice, second time w/
the shim). Plus you need a press...

The file is hard to do cleanly, but if you
take a old file that still has reasonable
edges and grind one of the flats smooth, you'll have a lot easier time not "wallering out" the sides. You may also find files w/ a edge safed to be useful once the depth is correct.

The lathe works like a charm, but takes
patience. Note that if you have a taper
attachment, the lathe method lets you put
a key on an internal taper, a job difficult
to do using anything else.

Another way is one of those little broaching
heads on a Bridgeport, which really just
emulates the "cool" way to do this -
a shaper!

- Bart

Paul Alciatore
12-19-2002, 01:21 AM
I also have never done any broaching although I have read enough to have heard about the bushing and press idea. The use of shims is a new idea to me but it sounds very logical. Do the broaches or bushings come with shims?

Charlie says the broach is pushed through with a "press". I assume that the work would lay on or be clamped to the press's table and the bushing is in it's bore, but how is the broach held? Is it simply held upright by the bushing/bore combination or is some holder fashioned to hold it in the press's ram? I'm sure large forecs are involved so it sounds like the broach could be easily broken if it were to slip sideways.

Also, isn't there a way to use round stock for keys instead of square? It seems that I've read that a round pin laying in a pair of matching semi circular grooves in the shaft and hub is stronger than a square one. The corners of the square grooves allow stresses to concentrate there in the same manner as an inside corner without a filet. A round cross section eliminates those inside corners.

12-19-2002, 07:40 AM
I've cut keyways by making an approrpriate cutting tool out of drill rod, hardening it, putting it in the milling machine, and using the quill handle to move the tool down through the work that is clamped to the table (with a spacer under it). Put on the amount of cut by moving the table over. Basically the same idea as with the lathe, but the quill motion is faster than racking the lathe carriage back and forth. I think you can get more force behind the tool, too.

[This message has been edited by SGW (edited 12-19-2002).]

C. Tate
12-19-2002, 08:33 AM
You are in luck my friend. We are running 500 pump impellars right now and all have a .125 keyway broached in them. I will email a picture of the process and brief discription.

C. Tate

12-19-2002, 08:33 AM
This is similar to the lathe method that Al Messer suggested to use only it is done on the mill. I had to use this set up when cutting keyways in steering wheel centers that had a tapered hole. Since this is probably a straight hole you won't need a mill that has a tilting head. You need only to lock down your piece to the table squared to the spindle and so the bottom of the hole clears the table. You than place a boring bar with a cutter the size and shape of your keyway in the spindle and which is just long enough to past completely through the hole. Like the lathe set up place your mill in back gear or the lowest speed to prevent the spindle from turning. Now using the X & Y feeds position the cutter so you are taking a ever cut from top to bottom and in the center of the hole when advance the cutter through the hole via the spindle handle. You then advance the table a couple .001's after each cut until you reach the depth needed.

12-19-2002, 08:43 AM
Sorry, SGW didn't mean to copy cat your idea, I started writing this and didn't go back to see if anyone had posted before I finished. I quess we both "been there done that". Bob

[This message has been edited by Allmetal (edited 12-19-2002).]

12-19-2002, 09:10 AM
Some ideas on broaching a keyway.
1)When using a broach it is under compression, therefore the setup needs to be "square" to each other. That is the bushing, press table, the press ram and any adapters holding the broach must be either in plane or 90 degrees out of plane. The smaller sized broaches are quite easy to break.
2) The number of shims needed depends on the keyway depth. The shims do come with the set.
3) Lots of "cutting" oil is a good thing.
4) Put something like a rag or crumpled newspaper under the press to catch the broach if it drops as it clears the part. Grabbing it can cause keyways in your hands.
5) wear safety glasses in case the broach shatters.

Most manufacturing/mass production broaches are "pull" broaches. Then the broach is in tension and wants to stay straight. I was watching a broaching machine the other day that used a broach with a Christmas tree cross-section and was 30 feet long. Tons of oil and a slow steady speed.

12-19-2002, 02:52 PM
I have broched many ways before. I have used the industrial pull broaches, which would be great for this application, but a bit more costly thn you might prefer. I have a broach set for my arbor press, but most people do not have these.

For the home shop machinist, a file works.

However, I read above about the racking of a special ground tool in a lathe on the cross slide and using the carriage. I have done this for manual and CNC applications, and it works like a charm. Grind a lathe bit like a groove tool, only rake the front surface. I have done this many times. Fast, easy, and customized.

I have also done woodruffs on CNC machines with a broaching method.

If you wish more info, I can post it.

Best suggestion for the HSM is to end mill the basic depth, and file the corners in.

12-19-2002, 03:19 PM
In one of the Rudy Kouhoupt books, he describes a tool made up from (as I recall..been awhile since I read it) a power jigsaw blade for cutting small keyways on the lathe. He first makes a holder to match the bore then mounts the jigsaw blade in that and with multiple manual feeds with the carriage gradually deepens the keyway.

12-19-2002, 03:20 PM
In one of the Rudy Kouhoupt books, he describes a tool made up from (as I recall..been awhile since I read it) a power jigsaw blade for cutting small keyways on the lathe. He first makes a holder to match the bore then mounts the jigsaw blade in that and with multiple manual feeds with the carriage gradually deepens the keyway.

12-19-2002, 04:43 PM
Thanks guys, this is more than enough info to get me started on broaching a keyway. Thanks for all the help, this board is GREAT!!!

Al Messer
12-19-2002, 06:39 PM

One this noe of the others on the list have mentioned is the fact that broaches are relatively expensive. Example: Traver's Tool lists a 3/16" broach (the size I needed) for $23.31 for a TTC brand, $41.50 for a Hassay Savage, and $41.40 for a duMont, shims are included, but not bushings. A bushing I needed was $6.60. A Dake single leverage arbor press is listed for $240.00 for a 1 ton model.

Doughnuts is cheaper!!

Al Messer
12-19-2002, 06:41 PM
Can Santy Claus bring me some new fingers?

"One thing none of the others..."