View Full Version : Long Keyway

02-16-2006, 11:35 AM
I have 12 pieces of 4340 material. They are four inches long. The bore is one inch diameter. Would a broach successfully go through four inches of material without binding or would it gall and get stuck. Firstly its gonna be a borrowed broach secondly three sixteenth key size. I dont wish to damage my friends broach. I have a shaper but its down for repairs i cant adjust the stroke lengh on my 14 inch elliot anymore something insides wonky. Thanx

02-16-2006, 11:42 AM
Perhaps, with alot of oil and a full length collet.

The tame Wolf !

02-16-2006, 12:11 PM
I think it's time to fix the shaper Mike.

02-16-2006, 12:49 PM
I think it will be okay, if you make a full length bushing as iowolf suggested. Make the bushing slot extra deep so you can take multiple passes when broaching. Shim the broach out a little at a time, as it will porbably be cutting almost it's full length.

02-16-2006, 12:58 PM
Like was mentioned, use the shims to take small cuts, maybe a thou or so at a time. Also make sure that the force on the broach is straight, any sideways pressure at all and that's when trouble happens.

Another option might be to do them on a lathe (spindle locked) and use the carriage to feed a single point tool through. (Similar idea to using the shaper, except you get to supply the horsepower.


02-16-2006, 01:05 PM
If you can, rough out with a shaper, because of the small bore and length of bore plus it's 4340 material, the key way will be shallow in the middle from bar springing away from the work. But if you can rough out the key way in a shaper then use your buddys broach to clean out the high spots in the key way, if you only have a standard bushing, you will need to broach from both ends.

Trying to cut this key way with just the broach won't work because there isn't enough room in the gullets of the broach for the long chips. They do make broachs with every second tooth removed to give more room for the chip.

Two other options maybe available, take your material to a shop that has a industrial key way cutting machine (Mitts & Merrel Key seater), these are single tooth broaching machines made for long bores, or the machine shop may have one of these


National's model #2 will mill a 5" long key way in 10 min.(spec's from their manual)


02-16-2006, 01:13 PM
I know this is the home shop machinist but a friend with a wire edm would make accurate work of it and one could be cut in probably 5 to 10 minutes. No grunt work involved either.

Herm Williams
02-16-2006, 01:34 PM
Another idea would be to rough cut the keyway with a bandsaw then finish cut with the broach. Another way would be to use a special ground boreing bar in the lathe to cut the keyway. Its slow but it works. Sinker edm or tap disintegrator with a square electrode will work.

02-16-2006, 02:48 PM
You'd probably be better off with a shaper. A broach is going to require a lot of force, since every tooth cuts over the full length simultaneously. Take the shear strength of the material and the width of a tooth. Then multiply by the number of teeth to get the force required to cut, and add a factor for friction.

Leigh W3NLB

02-16-2006, 05:39 PM
Don't have any idea how much these cost;

02-16-2006, 05:44 PM
Harry, do you read ANY previous posts?

The tame Wolf !

02-16-2006, 06:51 PM
Prices for a National key seater mill model #2 complete was in 1998 $655.00ea.

I have paid as little as $2.50 ea at a local auction and up to $104.99 ea.on eBay,on average though $20.00 to $35.00 ea. on eBay.

I have 14 key seating millers that will key seat bores from 5/8"dia. to 2-1/4"dia. 23 offset bushings (allows you to cut keys in different size bores with the same miller) and 25 to 30 spare cutters and various spare parts.

I have even cut square splines in a hub for my backhoe.

To use the millers take a 3 jaw chuck with a flat back, place work in 3 jaw chuck. Place 3 jaw chuck on drill press table, hold miller drive spindle in drill press chuck, attach anti-rotation bar to miller. Energize drill press, feed drown, letting miller into work bore, continue to desired depth of key way,(these millers will cut key ways in blind holes too). Raise miller, remove work from chuck, remove burrs,your done.


[This message has been edited by vmil3 (edited 02-16-2006).]

02-16-2006, 08:21 PM
Don't even attempt the broach it will bust.The small series of broaches are only rated for 1-1/4" length max and the next series up will only do 2" max.

Your best bet would be the shaper or the old boring tool in the lathe carrage trick.

There is one other alternative.I have milled through the wall of the sleeve and welded in a section of keyway in the milled slot.You end up with a permanant key in the bore,but it's easier than cutting a long keyway.

[This message has been edited by wierdscience (edited 02-16-2006).]

02-16-2006, 09:03 PM
Completely missed that part of vmil3's first post, but there's nothing like redundancy.
Had a couple of those key cutters years ago, never used them, finally gave them away.

02-17-2006, 08:14 AM
I have cut a 4" keyway in steel using a broach BUT I made two full length bushings, a full length shim and did it in four passes very carefully with lots or cutting oil. Also, I did it in low carbon/easy to machine steel. I am not sure about 4340. If you only wanted one keyway I would suggest you give it a try but 12 - - not sure you should risk it with a borrowed broach.

This type of job is why I bought an Atlas shaper.


02-17-2006, 03:31 PM
I think edm is the way ill go. Thanx