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Hexagon holes

How do you make a hexagonal hole?

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James Veitch07/02/2010 01:46:39
16 forum posts
This one has me stumped.
I need to make some hexagonal holes in the center of small gears and wheels.
How do I accomplish that to an acceptable degree of accuracy?
I would like to be able to make holes of various sizes, mostly fairly small.
The only thing I can think of now is to drill a round hole and brutally gnaw out the hexagon "by guess and by golly".  The results are pretty crude.
Suggestions please.
Thanks in advance, Jim V.
JasonB07/02/2010 07:56:38
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You could make a broach to finish the hole once its been roughed out as you describe, assuming its a through hole. You can buy hex broaches but at over £100 for the smallers sizes you would need to be making a lot of holes.
 
Depending what you call small and the depth of cut it could be done with a rotary table and small milling cutter, then just file out the corners
 
Or build yourself an EDM machine
 
JAson
Jens Eirik Skogstad07/02/2010 08:28:29
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Or go for this rotary broaching as here: http://www.rotarybroaching.net/support.htm 
mgj07/02/2010 09:38:22
1008 forum posts
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Or you go to Hemingway and make their slotter.
 
You'd need a dividing head connected to the lathe mandrel, which is just a bracketing job, if you already have the DH.
 
I have knocked out a load of square internal holes like that, and a hex is no different, other than the setting on the dividing head.
David Clark 107/02/2010 09:57:19
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3357 forum posts
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Hi there
Could you use the end of an Allen key as a broach?
Needs to be good quality but would probably work in brass.
regards David
 
Eric Cox07/02/2010 10:09:10
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As David suggests, drill with Dia. = AF size. Heat up the gear and either use an Allen Key or a nut. Grind the end of the Allen Key flat so you end up with sharp corners and reduce the length of the Allen Key to give a workable length.
Steve Garnett07/02/2010 11:22:54
837 forum posts
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Posted by JasonB on 07/02/2010 07:56:38
Or build yourself an EDM machine

Did you see the SMEE one at the model engineer exhibition? That was producing small hex holes in stanley knife blades in about 30 seconds - very neat little machine, as I've observed before.

TomK07/02/2010 21:23:07
76 forum posts
20 photos
There is an article in MEW 157 on making a rotary broach holder. Or a wobble broach as the writer calls it.
chris stephens07/02/2010 21:50:49
1045 forum posts
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Hi Steve,
Mike and Alan, from SMEE , have a wonderfully simple hand controlled EDM. I believe they plan to have it on the SMEE stand at Brighton this coming weekend., well worth a look.
chriStephens 
Steve Garnett07/02/2010 22:28:16
837 forum posts
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Posted by chris stephens on 07/02/2010 21:50:49:
Hi Steve,
Mike and Alan, from SMEE , have a wonderfully simple hand controlled EDM.

 That was the one they 'built' during their lecture session, wasn't it? That was good, but it was the rather more developed one that I was really impressed with. It was great to talk to them about it as well - really informative.

Ramon Wilson07/02/2010 22:33:42
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778 forum posts
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James,
If I may elaborate on one of the above helpful sggestions.
 
You state small holes in small gears/wheels. Assuming these are 4-5mm or under then depending on material and the power available to push it through, this can be done, as said, using a hex key of suitable size. However it is difficult to achieve a 'full', flat sided, hex. The fit on the points however will be a good fit on the key.
 
The hole size needs to be a few thou greater than the 'across flats' dimension. Open the hole at the top to the 'across corners' dimension just enough to position the key. You do have to sacrifice a key here - preferably make a holder by drilling a blind hole into a small length of mild steel a few thou smaller than the A/C dimension and, asuming you are doing this in the lathe, using the tailstock chuck, broach the key in to the holder until it stops.
Putting this holder in the tailstock drill chuck , you can now, if you are happy this will not stress the lathe, use this to broach the hole using the small recess in the workpiece to align it.  A small holder to grip in the chuck to centralise the workpiece if neccessary can also help but the closed jaws may suffice. (you can also use the drill  press but you need to ensure the tool is perpendicular to the workpiece or rather the hole is axial to the  broach). As previously mentioned grind the hex key off nice and square but preferably don't debur and use a good cutting fluid to get the best result.
 
As said it all comes down to material and size depending on size a fair bit of force is required relative to the small amount to be removed so be careful not to over stress things.
 
Hope this helps - Ramon
Circlip09/02/2010 15:40:51
1198 forum posts
As a "Mod" to Ramons suggestion, if you grind the end of the Allen key to form a "Dowel" type spigot, the diameter being the A/F size of the Hex., By forming a downward pointing Hook on the "Teeth" of the hex you can drill a pilot diameter in the blank and Broach the slot. Works with squares and whatever other shape you want.
 
  If you don't need concentricity, by "Cusp" grinding the end of the shape, the same can be achieved, - look in the sockets of some of the "Cheaper" socket head screws.
 
   Regards  Ian.
Ian S C10/02/2010 00:32:57
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7468 forum posts
230 photos
Circlip,Ithought of putting apilot on the hex bar,bu then the thought of were are the chips going to go,you'v got to clear the chips ahead of the broach.The idea sounds good as it would centralise the broach. Ian S C
James Veitch10/02/2010 02:01:26
16 forum posts
Thank you all for your fine suggestions. I appreciate them very much.
Yours, Jim V.

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