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Help Req ref Wobble Broach

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Alan Girvan29/06/2017 19:53:36
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I recently came across an article in issue 157 about making a wobble broaching holder by Jock Miller. Has anyone on the forum made this? I did make Michael Cox's rotary broaching tool and this done a great job but I now need something more industrial so that I can purchase commercial broaches. Jocks plan shows the broach holder 8mm, do you think it could be drilled half inch as this seems to be the common size for commercial broaches also the steel he recommends is Aisi 4340 or 4140, the steel supplier I use suggest it is now en 24T. Any help would be appreciated. If it was not possible to drill the tool holder to half inch do you think Harold Hall's advanced grinding rest would let me grind the cutters. From HSS I made one of these but never used it.

JasonB29/06/2017 20:01:28
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Looks like it would be a bit weak with a 1/2" hole in it as the spigot on the back is only 15mm and the grub screw would also not have much depth of thread..

If you are going to build the Jock Miller one then why not make it all 50% larger

Alan Girvan01/07/2017 20:11:07
39 forum posts
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JasonB thanks. I will have a go at trying to grind the cutters, As I said I made the Harald Hall advanced tool and cutter grinding rest but never linked it up to a grinder. My question is does anyone think this would do? Also the steel Jock recommends is Aisi 4340 or 4140 is this the same as en 24 T. Any help appreciated.

JasonB01/07/2017 20:19:36
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4340 is basically EN24T and 4140 is EN19T

This gives american to current UK and This gives current UK to EN

Edited By JasonB on 01/07/2017 20:21:18

Alan Girvan04/07/2017 19:20:20
39 forum posts
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Thanks very much Jason.

Sorry for the delay, not very good on the computer so always have to wait for someone to assist.

Mark Rand04/07/2017 23:48:07
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Note:- the T in the EN24T specification refers to the hardness it's been heat- treated to. Other specifications are available if you are buying enough...

There's a table here.

The T specification gives a steel hard enough to be used for many things as is, at about 30HRC, but EN24 can easily go up to 52HRC if you need it.

The alloys hardened to the T specification machine a bit more nicely than the annealed product, although dark brown to blue chips often result. The annealed versions can tear a bit.

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