# How do I machine an internal Hex?



## RVJimD (Sep 14, 2017)

Hi Guys,

I would like to try and make some new rims for my 1/18 scale RC truck.  The first problem I see is how to machine the internal hex.  The hex/hole is blind which from my limited experience makes this more difficult.

Here is a short video showing the stock nylon wheel.  My plan would be to make a new wheel from aluminum.






Thanks for you input.


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## DAT510 (Sep 14, 2017)

Rotary Broach is one way.






Here's a previous H-M thread.  http://www.hobby-machinist.com/threads/shop-made-rotary-broach-down-and-dirty.48805/

You can also buy kits or pre-made rotary broaches.


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## Dave Paine (Sep 14, 2017)

Consider making a hole for a 6 sided socket to be epoxied in place then machined as needed.


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## ddickey (Sep 14, 2017)

You'd have to buy or make your own rotary broach.


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## Wreck™Wreck (Sep 14, 2017)

A rotary broach is an option if the quantity of parts is sufficient, if not mill it, this approach works well if you are not constrained by corner dimensions.

I suspect that there are few hobbyists that own a machine that has the power to push a rotary broach to good effect.


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## cascao (Sep 14, 2017)

Make the wheel with a bigger round role and press a allen head bolt into it. (Maybe it need to be done with set screws since it hex is deeper)
Or
Make the wheel with a round role and press a allen wrench segment thought it broaching the hex.( since aluminium isnt that strong)


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## Superburban (Sep 14, 2017)

A dremel, small file, and an exacto knife?

A drill press, or careful with a hand drill, you could drill out the corners, then drill/ file/chisel out the center.

Search out some premade inserts?












Its a matter of inventorying your skills, time, patience, and tools.


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## ddickey (Sep 14, 2017)

Convert the spindle the a square head. That would be much easier to mill.


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## dave2176 (Sep 14, 2017)

Consider a 6 point socket from Snap-on. The points are rounded out so the load on the bolt is placed a few degrees from the point. Superburban's photo illustrates this beautifully.


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## mmcmdl (Sep 14, 2017)

Rough an undersized hole with a FB endmill , find the coordinates of the corners and send the smallest end mill do finish depth and then simply mill in an indexer . Your corners will be undercut for the sharp corners on the male hub .


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## RandyM (Sep 15, 2017)

Here is a place that has Hex Hole Bushings.

Machine Tool Sleeves


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## Reeltor (Sep 15, 2017)

Randy, thanks for the link to the tool sleeve supplier


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## francist (Sep 15, 2017)

I remember quite some time ago Tom Lipton put up a video where he made some small broachess from HSS tool bits. Used his mill to press the broach through aluminum -- worked pretty good. The broach itself wasn't a typical stepped affair with lots of teeth, but just a single cutting end that had a slightly concave grind to it.

7mm hex isn't that big -- at least I have no problem deforming holes that size all to rat poo when I least want it -- wonder if a 7mm Allen wrench could be pressed (ha ha) into service as a broach? I'm assuming the use will be to make a few wheels, not dozens and dozens.

Just a thought.

-frank

Edit: ah, forgot about the blind hole aspect. Might not work so good.


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## kd4gij (Sep 15, 2017)

For your project 7mm sockets or cheep nut driver bits.


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## RandyM (Sep 15, 2017)

Maybe you can make it in two pieces and weld it together after the shaping.


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## Metal (Sep 15, 2017)

Question: is rotary broaching really tough on your spindle bearings? (If I were to do it on my bridgeport?)


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## chips&more (Sep 15, 2017)

Of course CNC can do it. What about on a pantograph machine?


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## Wreck™Wreck (Sep 15, 2017)

Superburban said:


> A dremel, small file, and an exacto knife?
> 
> A drill press, or careful with a hand drill, you could drill out the corners, then drill/ file/chisel out the center.
> 
> ...



Milling works well as long as the corner relief is acceptable which is not always the case, some engineers require a minimum corner radius, a blind hole with a flat bottom and minimum corner radius would require a sinker EDM to produce in metals.
In plastics injection molding will produce such forms.
 If doing it for fun just relieve the corners and have at it unless you often send yourself "Non Compliance" letters (-:


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## RVJimD (Sep 15, 2017)

Lots of good ideas thanks guys!  Someone pointed out that depending on how many or few I might make could have a big part of deciding how to do this.  I'm thinking about all the suggestions.  Jim


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