[TowerTalk] Drill bits

[Jim Thomson]

Date: Wed, 24 Mar 2010 04:11:35 +0000
From: Guy Molinari <guy_molinari at hotmail.com>
Subject: [TowerTalk] Drill bits
To: <towertalk at contesting.com>
Message-ID: <BAY129-W14493CAE03D374CEF078CDE8250 at 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 punch 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