Hi again plunger:
You wrote:
Marcus remember I am a plumber so dont fully understand the available technology out there. So if I say something silly please forgive me. Could this whole setup be made by wirecutting. Can wirecutting do such small profiles . I understand wirecutting can make the female broach but how would it make the male broach. ?I will need to make a male,female extension and being a blind hole the broach will be limited in its stroke.
If I made a male part in copper or graphite and gave it too a company that does spark eroding could they burn a broach into a piece of hardened steel which would then become the female broach.?Can wire eroding cut the male broach and if it can be pinned to a holding tool would that work. ?
Not having the ability to CAD draw and having the ability to measure the angles and profiles accurately its hard to know exactly what the angles and profile is.
I made broach out of silver steel by making an indexing plate on the back of my emco v13 lathe using a 100 tooth gear and using a racking tool I made by converting my top slide . It worked but I would like to get it more user friendly .Its difficult to harden metal with fine detail using an oxy set in a home shop environment.
If I can get this made by EDM does it mean I can eliminate the hardening process or does EDM also struggle with tool steel in its hardened state.
I can get this hardened by a professional company.
Thanks for your assistance .
So to answer some of your questions:
Yes wirecutting can make extremely small things and this broach (both male and female) is well within its capabilities.
The only thing is that the wire has a certain diameter, 0.25mm is the most common size and this will leave a radius on every internal corner.
It will be a bit bigger than 0.125 mm.
Although it's an academic question for your circumstances (wire work is very expensive...you'll spend at least ten times what you would do to have it shaped on a gear shaper), the male broach is made by wire cutting most of the way around the profile on a slight taper, leaving a tab so it can be skim cut to precise dimensions (VERY precise dimensions...within microns), then it is chopped free of the stock with the wire, a holder is wire cut precisely so the almost finished punch can be dropped into it and then the tab is trimmed to blend perfectly into the rest of the contour.
Last a slightly smaller broach holder is wire cut on the same taper and the tapered broach is dropped in with Loctite to hold it so the business end is sticking out.
It can be cross pinned or a setscrew can be run in so it's held in tightly against the withdrawing force when it is being pulled back out of a broached hole.
A female form is much simpler to make...a start hole through your block is all you need and you just keep running around the profile until it is the size and surface finish you need.
Reverse burning on a sinker EDM involves wire cutting a copper or graphite female shape then dropping it over a punch blank to burn the male punch.
Below is a picture of a punch made this way.
Again, it's kind of an academic dissertation; no way can you justify all the expense of doing it this way, and you've expressed a desire to roll your own rather than taking it to an outside source to have it made.
BTW, yes these processes work just fine on hardened steel...EDM doesn't even notice the steel is hard.
With regard to what you CAN do at home in a decently equipped shop...you've found a way to make a decent male broach on your lathe, so a thing to consider changing is the steel you make it from.
The ones I recommended above (A-2 or D-2) are "air hardening" steels often used to make punch dies.
Both need to be professionally hardened to get properly hard and properly tough, but they will produce a tougher, longer lasting punch and because they both quench in air, the details will be better preserved and there will be much less distortion.
However, silver steel (W-1) properly handled will also produce a perfectly acceptable punch for broaching brass.
You need to do better than cooking it with the torch till it's kinda red and then tossing it in a bucket of water or motor oil.
The best way forward is to have it professionally hardened.
The next best way is to buy a little temperature controlled kiln and some foil wrap to shield it from excessive oxidation when it's heated.
The third best way, and the one most appropriate for you if you want to do it yourself with what you have is to put your broach into a short section of close fitting iron pipe with end caps. cook the whole works with the torch until a magnet won't stick to the pipe anymore, heat soak it for a bit at that temperature, and then quench the whole works in a super fast quench like brine.
You MUST have a close fit between the pipe and the punch...silver steel needs a fast quench to harden properly so you want heat transfer through the pipe and an air gap slows the quench down.
You can also pack the pipe with spent (cooked) cast iron chips to help with the heat transfer.
You can also try to fake it with A-2 this way...A-2 is air hardening so you just need to get it hot enough for long enough and then you can just let it cool in still air.
It won't be as good as the steel is capable of but it will still be pretty good.
Another way forward with the quench is to use an old blacksmith's trick for making edged tools and that is to heat to the critical temperature, then quench only the business end, descale it quickly while the shank is still hot and watch the tempering colours run until correct then quench again, descale again , watch the colours again and then do a final full quench in warm oil.
This gives you a graded hardness and toughness from the business end into the shank...perfect for your needs.
To make a female broach; the traditional way of course is to make a male first, harden it, and then force it through a soft female blank with a hole in it, then harden the female.
Depending on the size and number of the teeth it may take a huge amount of force...more than you can generate in a typical home shop and more than a silver steel punch can take.
If you don't have a press and don't want to risk pulverizing your beautiful, just made punch, the traditional way is to drill a hole in your blank, bore it to minor diameter then rig a single point shaper tool and shape it tooth by tooth just like you did for the male.
It's laborious, it's a pain in the ass, but you only have to do it once, it takes only gear you already have (plus a little creativity), and it works.
So that's it in a nutshell...have a look at the reverse burned punch picture below just for fun, and go to town with what you have.
Cheers
Marcus
www.implant-mechanix.com
www.vancouverwireedm.com