[Land-speed] Not LSR Question, Need to cut threads to make a 3/8 bolt

[Ed Weldon]

Dale--there are several possibilities here.  But let me step you through the
way I have put coarse threads on 3/8, 7/16 and 1/2" diameter rod when only
simple tools are at hand.

First take the rod to the sander or grinding wheel and grind a shallow taper
(like 10-30 degrees) on it down as far as the minor diameter of the thread
(around 5/15 for your 3/8-16 example)

Next mount the rod vertical as tight aas you can get it in a bench vise
(vertical is important as you will see)

Find a die that is new and sharp.  Preferably a round split die rather than
the solid hex chaser dies.

You'll need a die wrench with a 10 or 12 inch T handle to get good enough
leverage so you can guide and control the cut.

Mount the die in the wrench but don't tighten the set screws any more than
the minimum needed to hole it in place.  That way the split will be open and
the die will cut the least amount of material on the first cut.

Go hunt up some kind of tapping fluid or at least some oil to act as a
cutting fluid.

Now put the die and tap wrench on the tapered end of the rod with the
handles horizontal. Start turning it with both hands pulling equally at
perfect right angles.  It will start cutting and require more torque as you
cut down into the full diameter of the rod.  Try your best to keep the
wrench and your handle pulling even and at right angles.  Brush on some of
your cutting fluid.  If the force suddenly increases as you're turning the
wrench it's likely  a chip is jamming things.  Reverse a half a turn or so
to clear the chip and then go forward again.  If you start to get more deep
threads on one side of the rod and shallow threads on the other slow down
and apply some extra down force with your hand on the side that is cutting
shallow. (No do you see why I said to clamp the rod in the vise vertically?)

After you get a good first cut tighten the die to cut a slightly smaller
diameter and repeat the cut.
It may take a bit of practice to get uniform threads.

Other comments-- You'll have a tough time finding undersize rod stock at the
hardware stores.  This is primarily an industrial item.  Thread rolling
stock for manufacturing 3/8-16 fasteners would be perfect.  If you live in
an industrial city a little digging would probably find you some.  You might
try ebay or hunt for a shop that does speciality thread rolling  for custom
fasteners and see if they have scrap end cuts available.  Most machine shop
tool suppliers including the big mail/internet order outfits like MSC sell
water and oil hardening drill rod.  23/64 diameter O-1 should cost around
$1.50-$2.00/foot and work well for most 3/8-16 fastener applications except
maybe highly torqued engine bolts.

Ed Weldon


----- Original Message ----- 
From: "Dale Krumheuer" <dmirror3 at yahoo.com>
To: <land-speed at autox.team.net>
Sent: Monday, June 18, 2007 1:25 PM
Subject: [Land-speed] Not LSR Question,Need to cut threads to make a 3/8
bolt


> This sounds so eay yet I don't want to buy the wrong size steel rod stock
(again). I need to cut thread to fit 3/8" 16. I blundered and bought 3/8
inch stock yet its obviously too large for my die. What size stock should I
use ?
> Dale Krumheuer