Date: Wed, 24 Mar 2010 04:11:35 +0000
From: Guy Molinari <email@example.com>
Subject: [TowerTalk] Drill bits
Content-Type: text/plain; charset="Windows-1252"
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?
## 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
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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