I need help is there a standard size hole in tap guide blocks?
I found a couple on ebay but would like to make my own. I've been
looking for plans with little luck I found a 4 hole version.
Should be hea treated ?
The ones I've fund on ebay were Aluminum or 1018
Flexbar makes one out of 4010 that is het treated. Seems like this
would be better, but is it necessary ?
If so I probably would skip making one since I don't have the means of
heat treating at my disposal.
Mixed emotions on one that is heat treated. If you get careless with a
hard one, you can do minor damage to the major diameter of a tap, so it
might be better to sacrifice the hole size from several repetitions of use,
slowly enlarging the hole as you turn your tap. Unless you're involved in
some serious tapping, using it daily, I dare say that will never be an
issue.
Hole size? The smartest thing you can do is mic the taps you'd like to
use and size the holes accordingly. The major diameter of taps is greater
than nominal, so you'll find them slightly oversized. Measure the body, or
shank of the tap. Make your hole such that the guide can be slipped off
with the tap still in the hole if necessary. You may find you need a
bastard size, but the closest size you have at your disposal will work,
providing a little extra clearance, or you could bore the holes if you're
not in a hurry. With the number series, you shouldn't have much trouble
selecting a drill that will provide the proper clearance, but larger taps
can be a problem. If you drill only, double drill to insure hole size and
roundness.
Taps in the number series, below a #6, have a body diameter greater than the
major thread diameter, so the tapping block won't be able to be lifted off
without removing the tap from the hole. You might decide to make the pilot
size the body size in that instance.
Harold
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Two types of the type of tap guide you are describing.
First type guides off the threaded portion of the tap. Easy to
make and use. I have seen these both flat and with a V for
tapping cross holes in a shaft. Most likely better off if not
hardened.
Second type guides off the shank of the tap above the threaded
portion. The tap shanks are a standard size and this is most
likely a better type if you do lots of small holes as the shank
is bigger in the small taps [ i.e. < #10] You can harden but no
real need.
see:
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a whole bunch more
google for "tap shank dimensions" or "tap shank diameters"
The commercial units are finely machined and the holes laid out
in a artistic spiral pattern but from a utility standpoint a
simple block with a straight hole a few thousandths over will get
the job done.
This was one of the first projects in my machining classes. It
was always a revilation to the younger students that you could
make rather than buy tools.
Uncle George
I'm almost positive that the Workshop Series - Making Small Workshop
Tools has all the info you need on making tapping guides.
I made some a few years and have used them without any dramas
ever since, they are made of some mild steel rod, squared off in the lathe,
with a hole about 1/64 larger than the tap nominal size drilled through the
centre. Length varies but mine long enough so that all the thread on the
tap is inside the guide before I start. Diameter also varies, seems like
I used about 3 times the hole diameter to the diameter of the guide with
a nice little "step" on the bottom of about 5 times the hole diameter.
The photo doesn't enlarge so you can't see a lot of the details. Has
several different bushings that you can swap in, the bottom of the
holder has a V-groove in it, very handy for tapping rounded surfaces.
Would be easy enough to make if you've got a mill or a shaper.
Was a lot cheaper when I bought it, but if you value your time, it's
still a bargain.
Stan
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