making a hex head

[timeone]

Need some advice on making a hex head

Ive got a round bar and need to cut a hex head ( eg make a bolt head )

ive got a milling machine and rotary table with a small chuck mounted,
as i understand first i find centre
the diameter of the bar is 14mm so im not sure what size hex i can cut.
so whats the next step

[mklotz]

The largest hex you can make is 12.124 mm AF.  I would make it 12 mm implying a 1 mm DOC.

[Jasonb]

Mount the R/T vertically on the mill table, put work in chuck and then rotate until table reads zero. Touch down with the rotating milling cutter and note the setting remove 1mm of material. Rotate table to 60deg and repeat, Rotate to 120,180,240 & 300. You should have a 12mm hex. You may want to remove a bit less and then check the AF distance then go round again with a finishing cut of half the difference.

If its a bolt then turn the threaded part in the lateh first as its easier working on the end of a long round bar than trying to do it holding a small length of hex

J

[timeone]

perfect thanks guys ive just done a test and worked perfectly.
can i do the same when making a nut
my idea was to drill and tap a round bar first then put in the rotary table to do the hex then back in the lathe to part them off does this sound ok.

Another question when holding bolts in a chuck how do you protect the thread from getting damaged

[Troutsqueezer]

Screw the bolt into a nut and chuck that.

[PekkaNF]

Another question when holding bolts in a chuck how do you protect the thread from getting damaged

Most of the nuts are way off. Sometimes you'll find some stand-offs that are used on hydraulic valves and such, they tend to be true.

I'll chuck oversize to nut round rod, drill, tap, skim outside and face and part off. Now the thread and face is true. Then I'll stighten the bolt/nut/whatever AND use counter nut to tighten the whole cacadoodle up.

Never trust only one screwed joint when turning or milling. How I have learned this? Guess Also, camber the "secondary" side of the jig, then you know which is better side, you probably will need again.

Pekka
*typozz!

[Jasonb]

Another question when holding bolts in a chuck how do you protect the thread from getting damaged

As Pekka says make a small holder from round or hex stock. I have a whole load accumilated over time, Mostly made from brass hex with a female thread on one end and a male on the other comes in very handy when making things like steam fittings. Have the part you grip in the chuck about an inch long and it will be true enough to the lateh axis, trying to use just a nut will be hard to align true.

J

[No1_sonuk]

Another question when holding bolts in a chuck how do you protect the thread from getting damaged

This depends on whether or not the unthreaded part has some form of drive.
If it's a bolt (or you're making it into a bolt), you'd be best off making a long holder for it.  When you're done, you can unscrew it using the head for drive.  This method may lock the bolt into the holder because of the cutting action tightening the bolt.  It almost certainly will in a lathe.

If there's nothing to grip to unscrew it (like a particular part I make) you can use 2 nuts locked together.
This is so that you can grip the threaded part away from the end of the thread, meaning you can remove the nuts easily once they're unlocked.
A more accurate variant would be to make a holder shorter than the thread, and larger diameter than a nut, and lock a nut on the end.

[timeone]

Thanks guys
Today your answers got me thinking so ive made up several alloy threaded adapters to try im even thinking about running a slit saw down them so as i hold them in the chuck they get tightened.