On Feb 20, 12:15*am, Harry K wrote:
On Feb 19, 1:53*pm, DerbyDad03 wrote:
On Feb 19, 4:15*pm, Smitty Two wrote:
In article
,
*DerbyDad03 wrote:
The decimal equivalents for F & G size drill bits are as follows
F * 0.2570
G * 0.2610
I've got an old Hanson 5/16-18NC Tap that has "G drill" printed on it.
When I used it, I used a G sized bit.
I need to do a bunch of tapping and decided to start with a fresh tap,
so I picked up a 5/16-18NC Tap and Bit combination by Irwin. It came
with an F size bit which is also what it says on the Tap.
BTW...the F size is what the charts say for a 5/16-18NC Tap.
Other than calling for different bit sizes, there are 2 differences
between the Taps:
Minor: The old one says "Hanson", the new one says "Irwin Hanson"
Major: The package for the new one states that it "Starts Straight"
and there is a noticeable difference in the taper of the shaft. The
newer one does not taper as sharply as the old one therefore it fits
more firmly in the hole. (No, it's not a "bottom tap" in case anyone
was thinking that).
So I wonder...why did the old Hanson call for a G drill, which is
larger, and have a deeper taper, thus making it sloppier when starting
in the hole?
The new one is a breeze to work with but I changed 3 things
(sharpness, hole size, taper) and that's a lot a variables to
consider.
.004 diameter is .002 on a side, so that's not a lot of difference
between the F and G. Machinists use different tap drill sizes for
different materials, and depending on the "% thread" or "thread class"
callout if there is one noted on the print.
Number of threads of taper on a tap also vary, as you note, between
taper, plug, and bottoming taps.
Obviously, starting the tap straight is critical, and various methods
are used to assist with that, the simplest being a block of steel with
appropriate holes for various tap major diameters. The "starts straight"
label on the package sounds like advertising hype to me.
"The "starts straight" label on the package sounds like
advertising hype to me."
I'd tend to agree, but I will admit that the new tap - with the lesser
taper - works pretty darn well.
It almost looks like it's a bottoming tap with the first 3 or 4
cutting threads ground almost down to the flutes, then a couple of
cutting threads that "taper up" towards the full sized ones.
On the older one the flutes themselves are tapered.
I just pulled out the mics...the new one has a tip diameter of .245".
The old one measures .215".
So it looks like they are using the wider shaft to help keep the tap
straighter in the hole.- Hide quoted text -
- Show quoted text -
Hmmm...senior moment here. *There is a regular tap with the long
taper, the bottoming tap with almost no taper and one in between but I
can't recall the name of that one. *From your descritption it does
sound like the middle type tap vice a regular one.
Harry K
This is pretty confusing.
If I look here, it looks like my new tap is a "intermediate tap"
except that the picture of what they call the plug tap looks more like
a bottoming tap, so I don't trust their descriptions. I though a plug
tap came to a distinct point.
http://www-mdp.eng.cam.ac.uk/nagty/r...g/tapping.html
However, if I look here it looks like my new tap is a taper tap. Key
point: The Plug tap has much more of a taper than a Taper tap. Go
figure.
http://upload.wikimedia.org/wikipedi...x-TapTypes.gif
The packaging for the new tab simply says "Self Aligning Tap" with no
mention of Taper, Plug or Bottoming.
So I'm going to combine the two sites and assume that both of my taps
are Tapering taps because neither one comes to a point. I'll further
assume one of 2 things:
Either the new one is an "intermediate taper" tap or Hanson has
modified the basic shape of a taper tap to hopefully make the tap more
"self aligning" as claimed.
Of course, none of this really addresses the issue as to why the drill
size changed from a G to an F. I'll guess that Hanson decided that a
smaller hole would make for better alignment. As long as the user is a
bit more cautious when tapping, the result will simply be deeper
threads.