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
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