# Hex from Round



## Tuscan8 (Dec 7, 2012)

Hi 
I am just starting Elmers number 11 engine and it calls for a 1 1/2" piece of Hex. How would you all go about machining it from round bar ? I ask because I can't find stock at the right size and have an off cut of ally available. I have a combination machine so a few suggestions would be gratefully received.

Many thanks 

Steve


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## dman (Dec 7, 2012)

you'll need to start with something like 1-3/4 round bar as a minimum if the hex is 1-1/2 across the flats. you can do the trig, i'm too lazy but 1-3/4 is close. once you find a round bar you like then you'll be able to figure out how deep to cut the flats quite easily. 

as far as tecnique, well depends on what accessories you have. you can always tilt the head 30deg on your mill. but you can also use a sine plate, or an indexing head or a rotary table if you are really careful. or a collet block with 6 sides. how long is the hex you need? what tools do you have to work with?


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## Tuscan8 (Dec 7, 2012)

No much as I am just restarting my model building. I can tilt the mill head. I will have to find a way of accurately setting the head as the mill mounted readout is a bit less than accurate. A rotary table is on the Christmas list and I am now going to google a sine plate


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## MachineTom (Dec 7, 2012)

Here are some ways to do a hex from round. Take the work and turn down  an end that will fit in a 5C collet say 1", (assuming you have some collets) using an indexing head? or a six sided collet holder grasp the work and index each 60° or every flat, mill as needed.

Or turn the end to some size mill a flat on it, then mill the first flat for the 1 1/2 hex, Take an angle block (chinese type are fine) take the 60° one and place it on the small flat, using a machinist square, turn the work so the angle block is aligned with the machinist square, now mill the second flat and the small end as well, repeat. 

These will each yield the similar results, the indexing head will likely be the most accurate.

Do not make the mistake of cutting to lenght the stock before milling it, You will make yourself cuss that action every time.


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## d-m (Dec 7, 2012)

If you have nothing to work with use a big nut thread a end of the round locktight it in the nut, the longer the stock the lighter the cuts will need to be.
Dave


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## dman (Dec 8, 2012)

d-m said:


> If you have nothing to work with use a big nut thread a end of the round locktight it in the nut, the longer the stock the lighter the cuts will need to be.
> Dave



genius answer! probably the best bet if you don't have accessories. 

the sine bar/plate or toolmakers knee is most accurate due to not having backlash but its not the best for doing multiple divisions. just happens that 6 divisions is easy to do without an indexing head. sine bars need to be shimmed up to an angle with gage blocks or pins. you use trigonometry to find the shim needed if you are doing an angle measurement hence "sine"... I sometimes make round pins in the lathe to use since its faster and easier to get a high level of precision and I don't own gage blocks. generally speaking the indexing head is the tool to make any number of even divisions on a circle.

both good tools to learn to use.


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## Cogsy (Dec 8, 2012)

I machined my first hex just yesterday, using my dividing head (and some math). Worked better than I had hoped, nearly perfect in fact, and was a lot easier than I'd thought.


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## gus (Dec 8, 2012)

Cogsy said:


> I machined my first hex just yesterday, using my dividing head (and some math). Worked better than I had hoped, nearly perfect in fact, and was a lot easier than I'd thought.



Have yet to hex a round bar using my DIY Rotary Table. You will the first to sse the fotos.

Gus


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## Tuscan8 (Dec 8, 2012)

Thanks all. Hex nut method is the way I am going to try due to lack of kit at the moment. I'll let you know how I get on


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## romartin (Dec 9, 2012)

Hi Tuscan8.
Have you seen [thread]18274[/thread] which I posted a few months ago? It describes a tool which can be used for making pretty good hex sections from round sections. I use it frequently; as a matter of fact I used it today to make a 3mm high hex section with 7mm across the flats at one end on each of four 12mm high brass studs with an M5 threaded hole down the center. 

Here are a couple of useful constants for finding the diameter across the vertices (V) from the diameter across the flats (F) and vice versa for hex sections. They are linked by the equation F = V cos (30°) so:

F = 0.866 V
V = 1.155 F


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## ELM6061 (Dec 9, 2012)

romartin said:


> Hi Tuscan8.
> Have you seen [thread]18274[/thread] which I posted a few months ago? It describes a tool which can be used for making pretty good hex sections from round sections. I use it frequently; as a matter of fact I used it today to make a 3mm high hex section with 7mm across the flats at one end on each of four 12mm high brass studs with an M5 threaded hole down the center.
> 
> Here are a couple of useful constants for finding the diameter across the vertices (V) from the diameter across the flats (F) and vice versa for hex sections. They are linked by the equation F = V cos (30°) so:
> ...


G'day Ian, love your little file guide tool but, I do have a couple of questions if you do not mind.

I am a little confused as to how you accurately hold your tool in the cross-slide tool holder, so it will not turn on the round while being subjected to filing pressure.

Do you have a slotted hole clamp, made from square bar, which is then held sucure in the tool holder?

Would it be better to actually have a square or hex bar, rather than the round, so you have flat surfaces for the tool holder to clamp too?

Regards
Eddie


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## Tin Falcon (Dec 9, 2012)

To find size of round stock needed to machine a hexagon, D = 1.1547 x distance across the flats.
Army TC 9-524 appendix C formulas
http://www.mwdropbox.com/tutorials/ARMY-TC-9-524/appc.pdf
Tin


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## Cogsy (Dec 9, 2012)

Tin Falcon said:


> To find size of round stock needed to machine a hexagon, D = 1.1547 x distance across the flats.
> Army TC 9-524 appendix C formulas
> http://www.mwdropbox.com/tutorials/ARMY-TC-9-524/appc.pdf
> Tin


 

Thanks for that Tin. I had no idea so just grabbed a bar 1.5 x the flat distance and hacked away at that. Would have been a lot quicker with your calc


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## dman (Dec 10, 2012)

this is off topic but tin I just noticed the air force maintenance coin for you avatar. were you a Metals Tech? of did you pickup machining elsewhere?

anyway to the op. the formula for a hex comes from the sine of 60 deg or cos 30 deg or their reciprocals depending on which way you do the conversion from hex to round(secant cosec if I remember my highschool math). you can overlay a 30,60,90 right triangle over a hex with the hypotenuse running from the an upper to a lower opposite corner of the hex to see it illustrated. just so you know where these numbers come from. trig can be really useful in understanding other geometry.


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## Tin Falcon (Dec 10, 2012)

Dman yes metals tech and aircraft structural repair .
Cogs I probably should have dug that up sooner . 
But I do my best to make people aware of basic reference material. i cant answer ALL the question all the time LOL
Tin


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## deverett (Dec 10, 2012)

A couple of other ways that have not been considered:

Can you index the bull wheel (if it can be divided by 3).  Or do you have a change wheel that can be mounted on the spindle end (away from the chuck) ?  It is quite easy to make up a detent to engage with the gear teeth.

Another simple technique is to make a pin about 1/2" diameter that when placed on the lathe bed, supports the jaws of the 3 jaw chuck horizontally in turn.  Do three sides with the pin on the front shear, then do the other three sides with the pin on the rear shear.

Dave
The Emerald Isle


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## romartin (Dec 10, 2012)

ELM6061 said:


> G'day Ian, love your little file guide tool but, I do have a couple of questions if you do not mind.
> 
> I am a little confused as to how you accurately hold your tool in the cross-slide tool holder, so it will not turn on the round while being subjected to filing pressure.
> 
> ...


 
Hello Eddie.

You are right when you say that the tool must be held firmly in the tool holder. I can only say that I've used it many times and have never had a problem with the tool moving while filing was in progress. My feeling is that that a turning tool taking a bigish cut on an irregular chunk of steel is subjected to rather greater forces that hand filing will produce.

However the tool doesn't have to be held accurately - it needs to be square (ie the rollers must be parallel to the lathe's axis) but the angle with respect to the horizontal of the file when pressed against both rollers is not critical because the fine adjustment of the distance from the lathe axis to the business face of the file is done by moving the cross slide. This works of course provided that this angle is not zero, ie that the file is NOT horizontal. The reason the holding bar is round is to allow you to set this tilt of the rollers at any convenient angle. You will find that the convenient angle depends on the size of the hex section you are making.

I hope this is clear; if not please dont hesitate to ask agsin.


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## d-m (Dec 10, 2012)

Another simple technique is to make a pin about 1/2" diameter that when placed on the lathe bed, supports the jaws of the 3 jaw chuck horizontally in turn. Do three sides with the pin on the front shear, then do the other three sides with the pin on the rear shear.

Dave
The Emerald Isle
Now that is clever !!!! way to go Dave 
Dave


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## rao_zeeshan (Dec 25, 2013)

how i can post a question ?


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