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Re: [TowerTalk] Drill bits

To: "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] Drill bits
From: "Blake Bowers" <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Wed, 24 Mar 2010 09:26:31 -0500
List-post: <">>
A cutting torch works as a great drill for me.

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heaven knows we need them down here!
Be an organ donor, sign your donor card today.

----- Original Message ----- 
From: "Jim Thomson" <>
To: <>
Sent: Wednesday, March 24, 2010 3:38 AM
Subject: [TowerTalk] Drill bits

> Date: Wed, 24 Mar 2010 04:11:35 +0000
> From: Guy Molinari <>
> Subject: [TowerTalk] Drill bits
> To: <>
> Message-ID: <BAY129-W14493CAE03D374CEF078CDE8250@phx.gbl>
> Content-Type: text/plain; charset="Windows-1252"
> Hi all,
>    I don't know why this is so hard.   I'm trying to drill out some hole 
> on some 3/8" steel plates that I'm going to have galvanized.   I bought a 
> 13/32" drill bit and it worked great for about 10 holes or so.   The 
> problem is that I have about 140 more to go.   Any recommendations on a 
> good quality drill bit?
> 73,
> Guy, N7ZG
> ##  13/32 = .40625"     3/8= .375"     .40625- .375 =  .03125"      That's 
> a big difference in diameters... even with  galvanizing.   I think the 
> galvanizing is only  aprx .004"'  thick.    If these holes are for 3/8" 
> bolts, perhaps you should be using  a  25/64"  drill
> bit??      I have tried them all... and was not impressed with the 
> titanium bits.   The packaging on the cobalt bits warns of not overheating 
> cobalt bits.     I worked on loan at our tool crib at work one summer, abt 
> 30 yrs ago.  The Dormer brand, and also the Butterfield brand HSS drill 
> bits   [ both made in the UK]    didn't fare too well.     I ended up 
> lately, using Zirconium bits.  They appear to last a long time, and also 
> have  THREE sides to the shank, so they never slip in a chuck.
> I don't have my book handy either, but for 13/32 holes in 3/8"  thick mild 
> steel plate,,,, it has to be slow... I think around  300 rpm or less. 
> How hard is the plate ??  As noted, you need lots of cutting fluid. 
> Overheat the bit.. and it's toast, it will have lost it's temper.... 
> permanently.
> Plan  B  is have em all punched.     I bought one of these  small roper 
> whitney #5 jr  compound hand punchs  for 1/8"  thick and less... 
> 6061-T6.... but they only go up to 9/32"       I have a requirement to 
> punch a lot of  3/8"  holes in 3/8" thick  6061-T6 plate....  so bought a 
> bigger roper whitney punch.... think it was a model  #16 or #17..... with 
> a 3.5"  throat.   Think my new punch is 7-9 tons.      It  will punch 
> holes up to 9/16".    When punching holes in 6061-T6.... only 60%  of the 
> tonnage is required  VS  mild steel  of the same thickness.
> If your local machine shop wants a small fortune to punch  140 x 
> holes..... I would be inclined to buy/beg/borrow a  larger  roper whitney 
> punch.    My new one has a 25" steel forged handle.. and is bench mounted. 
> It's a   cam action arrangement.  The secret to using the punch is to 
> bring the work piece    up into the center punch mark.. and not the other 
> way around..... but this is not always possible.     I'm sold on punchs. 
> We used electric-hydraulic punch's at work yrs ago, and punched literally 
> hundreds of 3/8" holes in 1/4...3/8" thick mild steel.   If ur just 
> drilling 20 x holes or less... a drill bit will  suffice... but with 140 x 
> holes.. a punch will make short work of it.  Drill presses are slow and 
> cumbersome as is.  Material  has to be precisely aligned, everything 
> clamped down, check, and make sure nothing shifted a fraction of a mm. 
> Then add lubricant, drill, then clean up the mess.. undo 3 x clamps,  and 
> repeat  for next hole.   Bottom line is... I can pu
> nch 15 x holes  faster that I can drill  just one.   The punched holes are 
> always dead on, and clean holes.
> The punch must have the  correct diam  die  for the thickness  of steel to 
> be punched though.   The thicker the steel, the dies have to be oversized 
> even more... or they will bind.   Oversized dies  will not work on thin 
> stuff... you will get ..'roll over'  on the edges.    I just  came back 
> late today from the metal store.. with a trunk  full  of  6061-T6  3/8" 
> plate.. for boom to mast plates... and also a bunch of  4"  channel 
> 6061-T6.  [ 40m brackets, since the F-12 flat plates ones all bent 
> slightly, 340N]     The new punch will make short work on the new plates. 
> I have also used punched holes.. as pilot holes, that are in turn drilled 
> out to a bigger diam.    This is in cases, where I didn't have the correct 
> size large  punch + die... or the larger punch  was beyond the tonnage 
> capacity of my punching tool.
> I wish I had bought one years ago.
> Later... Jim   VE7RF
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