Spare Parts #13 - Making A Square Broach
Added 2016-03-10 01:04:41 +0000 UTCIt's not necessarily a common event, but when you need to make a square hole, it can be difficult to get a precise result.
One of the best methods to achieve a professional cut, is to use a custom made broach.
Free Plans:
http://www.clickspringprojects.com/uploads/3/8/2/2/38221101/small_square_broach_brass_only.pdf
Cheers,
Chris.
Comments
thanx for the response Chris, i didn't even consider distortion from differential hardening but it would definitely show up in a part like this, good to know how well the heating tray works, looking forward to your next vid, cheers
Jerry Vella
2016-03-15 20:14:42 +0000 UTCHey Jerry, I wondered the same thing about whether it would quench fast enough, but it came out glass hard from the tray, so no need to take it out any sooner. The whole mass cools down fast enough that it doesn't seem to matter. It wouldn't form scale if you were to take it out just before the quench though, so you could do that if you wanted to without consequence, and that might be required if the part was much larger. This broach is so thin that it quenches very easily. It also occurred to me that it might introduce distortion because of the heat differential on the inside surface, but it seems to be fine. Same result with the recent hands, so I'll continue to use it. Cheers mate :)
Clickspring
2016-03-15 08:45:25 +0000 UTCHey chris, great video as always, was just curious if if would be better to remove the piece from the heating tray just before quenching it to cool it down faster and improve the hardness, would it still build up some black scale if it was exposed for just a second? or are you getting it sufficiently hard with it still in the tray?
Jerry Vella
2016-03-15 08:11:57 +0000 UTCCheers Al!
Clickspring
2016-03-10 23:33:42 +0000 UTCNice video! I have no idea what I'd need to put a square hole in, but there must be something .... thanks
Al McKague
2016-03-10 23:23:16 +0000 UTCHey Paul, I agree with you its a far more effective way to do this than the wire - its now on the to do list! The current one would probably be a bit wasteful of boric acid and gas for something small like a screw, but I think maybe a set of trays from 1/5th size, 1/2 and then the current one would be a good idea. Another video?
Clickspring
2016-03-10 22:52:45 +0000 UTCThank you PJ! I started with an offcut of 3/16" ground flat stock, milled it to shape as you suggest, and then lapped it to the final surface finish and dimension. Have a great day mate :)
Clickspring
2016-03-10 22:46:39 +0000 UTCGreat camera work Chris! Better all the time! Did you start with 5-6mm RB and mill it to dimension or 4-6mm sq stock and mill it to get the 3.4mm square first? Pretty odd size, can't wait to see what it is. Thanks Much! ~PJ
PJ
2016-03-10 16:54:28 +0000 UTCAwesome. A surprise new video. As always, great work and a real joy to watch. Looking back to the beginning would that heat treat tray have been a good idea for the screws and other things you have done compared to the wire method. The tray seems a lot easier and reliable. The only problem now is when this and the previous video pop up on the subscription feed making me think even more new video's are released. Really looking forward to the next clock video.
Paul Busby
2016-03-10 14:19:23 +0000 UTCHey Ken, yes it will need to be hardened. Even though brass is quite soft to machine, when under compression like this it will quickly distort the annealed tool steel, and dull the cutting edge. Even when hardened and tempered, a carbon steel cutter still has a finite life before sharpening is required, even if its used exclusively in nice soft brass. Cheers mate, Chris.
Clickspring
2016-03-10 02:41:08 +0000 UTCGreat tip, Chris! I'm curious if the hardening would be necessary if you were only going to use the tool to make one or two broaches in brass.
Ken Condal
2016-03-10 02:14:27 +0000 UTCCheers Dan!
Clickspring
2016-03-10 02:01:46 +0000 UTCHey John, yes tempered to a medium straw just after the heat treat.
Clickspring
2016-03-10 01:54:27 +0000 UTCHey Paul, yes absolutely. Especially when you consider that often the holes are non standard dimensions to suit a particular need. I wouldn't like my chances of finding a 3.4mm square broach at an affordable price! Cheers paul :)
Clickspring
2016-03-10 01:53:56 +0000 UTCVery cool Chris. Thanks for posting!
Dan Cowsill
2016-03-10 01:53:10 +0000 UTCHey David, in this case I just did my usual thing of using a gentle heat while resting the part on some ceramic wool, a thin cross section part like this tempers very quickly. But it certainly wouldn't hurt to use the tray. Cheers, Chris.
Clickspring
2016-03-10 01:50:59 +0000 UTCAre you using your bluing tray to temper? Would be a great way to get a nice even temper.
David Rysdam
2016-03-10 01:39:42 +0000 UTCQuality broaches can be crazy expensive. But they are often made from pretty high grade steel. If you are just doing stuff with brass and maybe mild-steel, even taking the cost of labor into account, this sort of thing might still end up saving you money!
Paul Grodt
2016-03-10 01:23:40 +0000 UTCThat's really useful and well explained. Did you temper the broach after your hardened it?
John Creasey
2016-03-10 01:18:10 +0000 UTCYou'll be seeing excuses for square holes everywhere... :)
Clickspring
2016-03-10 01:14:09 +0000 UTCNot sure when I'll next need to make a square hole in brass, but I might have to make one of these just because...
Tom Colson
2016-03-10 01:13:14 +0000 UTC
