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Tips for turning hexagonal stock on a lathe?

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Aaron_W

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#1
I'm getting started on a small steam engine kit, and it involves some turning operations on hexagonal brass stock.

Obviously this will involve interrupted cuts so cuts need to be light until round is reached. Just wondering if there was any other advice.


The kit assumes a mill is not available, but as one is, for the pieces with a mostly round section and just a small hexagonal area it seems like it might make more sense for me to start with larger diameter round stock (easier to turn), and use a collet block to create the small hex section.


Looking in the Machinery's Handbook it appears a hexagon can be made from the same diameter of round stock (so 1/2" round stock can be used to make a 1/2" hex), is that correct or would it be advised to go up in size a pinch?
 

Dave Paine

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#2
I think with brass you should not have a problem using hex or round stock.

I do not have brass hex stock so I would have to mill using collet block as you mention.

If you can accurately centre the work you could use 1/2in round stock. If you are not able to get the work exactly centred, the hex will be slightly undersized which may or may not be an issue.
 

derf

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#3
To make 1/2" hex from round stock, the round stock needs to be .577".
The formula: E(hex size) divided by .866 =D(diameter of round stock)
 

benmychree

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#4
Depending on what sort of lathe you have, you should be able to go from hex to round in one cut on brass. Yes, as above, if not precisely centered, the corners would not clean up, and would not look good, best to go a size over the desired hex size.
 

kd4gij

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#5
Brass or any hex stock is no problem to turn. The as the old saying goes the bark is much worse then the bite. I turned a brass nut that was 3" across the flats today with a sharp brazed carbide tool with a chip breaker ground in. no chipping. But the sound does get a lot of attention in the shop
 

Aaron_W

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#6
Ok, so nothing special then. Small lathe so I'll start slow and adjust as I go.

To make 1/2" hex from round stock, the round stock needs to be .577".
The formula: E(hex size) divided by .866 =D(diameter of round stock)
Thank you, I looked in the handbook and it looked like the diameter was measured the same way both round and hex. There is a lot of math in that section as well though that makes my eyes twirl. o_O
 

jbolt

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#7
Hex stock is sized across the flats not the points.
 

Bob Korves

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#8
If you make a hex out of round stock, with zero losses, the dimension from point to point of the hex will be the same as the diameter of the round stock it is made from. However, point to point is not how hex stock is measured, it is from flat to flat, and that is a smaller measurement. If you need to understand the math, contact me, Aaron.
 

projectnut

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#9
Cutting brass hex stock isn't going to be a problem, especially if you use HSS tooling. I have cut hundreds of pieces of 304 and 316 stainless, 6061 aluminum and 4140 steel to make various connecting rods, specialty nuts, and other assorted hardware. Some have been bored and threaded internally, while others have had a section turned to size and threaded externally. I have used either a Sheldon MW-56-P or Seneca Falls Star #20 lathe. Neither had a problem with any of the materials.
 
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#10
Very few metals on a lathe with the right tooling can not be turned fairly easy. Brass and aluminum are very easy on a lathe. If you were cutting hardened stock or titanium there you may or will find trouble. Don't worry about things till they show up. It's a hobby don't make complications to lose sleep over have fun learn cut and enjoy , mistakes mean your learning . Just keep learning.
 

epanzella

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#11
It's faster to make hex round than the reverse. Just stick the hex in a 3 jaw and turn away! To start with round and make it hex, you have to do the math, set up precisely 6 times, then turn the round part anyway as it will be bigger than the hex part if you don't.
 

TTD

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#12
I agree with @epanzella - throw your hex in the 3-jaw & go to town.

I also was a little leery my first time about the interrupted cuts on my little lathe, but as it turned out I was worried about nothing at all. Granted, I was only turning down 1” 6061 aluminum hex, but it was a piece of cake. I was being conservative seeing as it was my first try, but I think I started with .010” cuts until it was round, then .025” cuts after that.

A while back I needed to make an .850” o/d bolt knob & of course, didn’t have any 7/8” or 1” round bar left, but did have 6’ of 1” hex. Not the most efficient or cost effective way of going about it to be sure, but I got the job done nonetheless.

Pic of the leftover piece:
m_Hex into round 005.jpg
 
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Aaron_W

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#13
I wasn't too worried about it, but never hurts to ask. Thanks for the help.

Also I see what I did on the Hex measurement. Brain disconnected from the eyes. The diagram shows corner to corner, but then goes on to show that distance is greater than flat to flat....
 
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