Milling 3 flats 120° apart on a shaft

[macrls]

I’m a newbie and just finished my first major milling job. Can some of you experts suggest better ways of doing it?
I wanted to mill 3 flats on the end of a long 1/4” dia. drill extender. (To keep it from slipping in my hand drill chuck). But I have no rotary table or any way or measuring the 120° rotation of the shaft accurately. I figured it wasn’t terribly critical and a few degrees off wouldn’t keep the shaft from locking in a 3 jaw drill chuck. I clamped the shaft in my vise, fastened a miniature 6” woodworking clamp to the shaft with the handle pointing up and vertical (parallel to a door frame). For the second and third flats I “eyeballed” the angle of the 6” clamp relative to the door frame with a protractor.
Is there a more accurate way to do this?

 

[GK1918]

Do you have an sample or a known 3 flat drill or something for an example. OR you can scribe the
degrees on a washer and fit the washer on the shaft. OR paint or blue the shaft and use a metal
small level (on level) slightly tilted and rake the level -leaving a scratch mark. Old school way but will
get you there pretty close. The washer works best with a piece of tape on the vise with a witness
mark then mill a flat turn piece to the next mark on the washer and so on. And It doesnt have to be
a steel washer stiff cardboard glued to shaft will do the same. Back in the day I did quite a few
tractor PTO splines with a simple degree wheel glued on a shaft with a welding rod for a pointer.

 

[Beazld]

Drill out a hex nut to fit over the shaft. Use it to index the angles. Make it a snug fit. Machine one flat, rotate the shaft machine repeat.

 

[tarmo120]

Drill out a hex nut to fit over the shaft. Use it to index the angles. Make it a snug fit. Machine one flat, rotate the shaft machine repeat.

This would be probably not the easiest of methods but I would think, one of the most accurate for your project.
Or at least as accurate, as the hex nut is.:whistle:

 

[mekanix48]

Hi

If you have a lathe,machine a 1/4" dia. hole in the end of a piece of 3/8" / 1/2" hex' bar, insert your extension rod & braze or weld the two together this will keep your two pieces in line axially (with only minimal heat warping), plus you will have a choice of 6 flats to place in your drill chuck ).

Cheers
George

 

[eightball]

I have milled 120 degree flats by placing work in a 3 jaw chuck, using a precision level on all three jaws and scribing a line on work piece.then clamping in milling machine vice ,using an edge finder or dti, finding centerline of work. Using a center in spindle. I have rotated work to centerline in vice. While not the most accurate method it is remarkably close. I have also rotated flat on work to a nut below it in vice. For accuracy a dividing head is the way to go, but there are several ways to get close

 

[Corm]

You could also use a hex 5C collet block. Perhaps a bit of an investment up front, but less than a dividing head would be. I have a collection of 5C collets, and I bought a collet block set last summer. They're available from lots of places as a kit with a 4 sided and a 6 sided block, enabling you to mill 2,3,4,or 6 flats on a shaft. Very handy.

Corm

 

[arvidj]

Food for thought ...

Tighten a C clamp on the end of the rod so it can swing 360 degrees ... as in 'not get caught on the mill table'. Tighten the rod in the vise ... some type of v-jaws in the vice are assumed but not critical ... so the threaded part of the C clamp is eyeball level. Mill one flat.

Put something like this on the threaded part of the CD clamp, zero it out, the rotate the rod until it reads 120 degrees, plus or minus. Mill second flat. Turn the rod the other direction until it reads -120 degrees more or less. Mill the third flat.

You might say "but I spent 30 bucks on the device" but I think you might be able to find a lot of uses for it around the shop. I know that I have.

Arvid

 

[Ed T]

Second vote for the collet block. I use them often for similar tasks. Probably not super accurate, but way better than adequate for a hand held drill extension. Another way would be to make the extension out of hex stock or buy a 1/4" hex drill extension for a buck or two.

 

[TrevW]

Hi saw this and I know that you have completed the Job but I had a thought on how to do this without 'fancy' tools and set-ups.
My thought is to get a couple of nuts and drill through to suit the rod then drill and tap the nuts for a grub screw. Slide the modified nuts onto the rod near to the end to be milled, tighten one grub screw, place the assembly on a flat surface and position the second modified nut and tighten its grub screw.
Now you can place the assembly on the Mill Table and clamp down onto the nuts. You can now mill the first flat - make a note of the down feed dial (or zero). To make the other flats just release the nuts and rotate the assembly as desired and mill the other flats to the same settings.
To aid accuracy you can fit a couple of 'stops' (fences) on the table to make the re-alignment quick and accurate.
If you want to make a hexagonal shape then the depth of cut = 0.0667 * dia of rod which is 0.01652 for 1/4" rod.