Yes, good stuff, Charlie! Good bit. Small hole, then a bigger one. Slow.
And oil. Works great and was not strenuous.
73, Kim - WG8S
> On 07/29/2020 2:04 PM Charlie@thegallos.com <charlie@thegallos.com> wrote:
>
>
> Thanks, I meant to send it to the list, oops
>
> —
> Charlie
> 73 de KG2V
> Http://www.thegallos.com
>
>
> > On Jul 29, 2020, at 2:58 PM, Grant Saviers <grants2@pacbell.net> wrote:
> >
> > Charlie sent this off list to me, great advice.
> >
> > Grant KZ1W
> >
> >
> > -------- Forwarded Message --------
> > Subject: Re: [TowerTalk] Mast slippage
> > Date: Wed, 29 Jul 2020 11:43:48 -0400
> > From: Charles Gallo <charlie@thegallos.com>
> > To: Grant Saviers <grants2@pacbell.net>
> >
> > Geez,
> > How big a hole are you planning on drilling in that poor mast that you need
> > a rotabroach?
> >
> > Let's face we are probably talking somewhere in the 3/8-1/2 inch size range
> > (I could not find a manual to see the size of the hole in the clamp)
> > 4130 is tough, but it isn't THAT bad (I drill a lot of 4140 pre hard)
> >
> > Get a good 135 deg split point cobalt drill. something like
> > https://www.travers.com/nachi-cobalt-jobbers-length-twist-drill/p/01-021-332/
> > don't want to spend that much, try
> > https://www.travers.com/ttc-surface-treated-jobbers-length-twist-drill/p/01-001-232/
> > or
> > https://www.travers.com/triumph-hss-jobbers-length-twist-drill/p/01-331-032/
> >
> > 4130 is .30% carbon, which puts it on the border between mild and alloy
> > steel You probably want to keep it < 70sfm - which, for a 1/2" bit means
> > 535rpm. Let's be conservative, and keep it down to 400rpm or so
> >
> > Use a coolant (cutting oil, not lubricating oil), and just go drill it. Use
> > a simple jig to start things because pipe is round.
> >
> > If you aren't getting a good chip, because you can't apply enough pressure,
> > SLOW DOWN
> >
> > You can also pre-drill with a smaller bit (why I recommended a split point,
> > less need to pre-drill, and a 135 deg has shorter cutting edges than a 118,
> > so less pressure needed )
> >
> > Charlie
> >
> >
> >> On 2020-07-29 10:41, Grant Saviers wrote:
> >> Ron,
> >> I shouldn't generalize, as it is possible to mag drill on a tower as
> >> you are doing. But rigging my 60# mag drill on a tower with a custom
> >> fixture and using Rota-Broach drills is not in most ham skills and
> >> toolboxes. Maybe the fact my mags get heavier every year is another
> >> factor ;) .
> >> Grant KZ1W
> >
> > --
> > 73 de KG2V
> > Charles Gallo
> > http://www.thegallos.com
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
>
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