[Dave99]

I'm tapping a ton of 1/4" aluminum 6061 parts for 6-32. I've been
using a #36 bit, but the threaded holes seem a little more loose than
they should be. They do work, but I'm wondering if a #37 would be
better. Before I break a tap, I figured I'd ask here and see if
anybody has routinely done that before or if there's a better idea.

Thanks,

Dave

[Lloyd E. Sponenburgh[_3_]]

Dave99 fired this volley in news:974c16a8-21b8-44a9-
:

I'm tapping a ton of 1/4" aluminum 6061 parts for 6-32. I've been
using a #36 bit, but the threaded holes seem a little more loose than
they should be. They do work, but I'm wondering if a #37 would be
better. Before I break a tap, I figured I'd ask here and see if
anybody has routinely done that before or if there's a better idea.


It's probably the tap, unless it's a very high-quality one. It could be
dull. Even more likely, you're overdoing it, and not clearing the chips
often enough. They'll make even a good tap cut oversize. And 6061 is
just gummy enough to "gum up the works".

However, the grind on your drill bits is every bit as important. If the
tip is the slightest amount off-center, or if one cutting edge is doing
all the cutting, you'll end up with an oversized hole.

For critical threading (especially small sizes), I'll usually run a new
(good) tap through a couple holes with a little medium polishing
compound, to remove any burrs.

If you want really accurate threads, you might consider a thread forming
tap, instead of a cutting tap. Because there are no chips to interfere
with the working surfaces, the holes end up tapped to exactly the
dimensions of the tap.

And of course, keep your tap perfectly aligned to the axis of the hole,
or you'll cut with difficulty and cut oversized.

LLoyd

[[email protected]]

On Jan 22, 12:41 pm, Dave99 wrote:
I'm tapping a ton of 1/4" aluminum 6061 parts for 6-32. I've been
using a #36 bit, but the threaded holes seem a little more loose than
they should be. They do work, but I'm wondering if a #37 would be
better. Before I break a tap, I figured I'd ask here and see if
anybody has routinely done that before or if there's a better idea.

Thanks,

Dave

You might want to check the actual screws going into the holes. If
they are coming from China, etc, they may be the problem. I have found
socked head cap screws to fit much tighter than off the shelf machine
screws.

Paul

[spaco]

Good advice already.
Note that the tap drill tables you usually see are for a 75% thread
anyway, so going one number drill smaller sure isn't going to hurt as
long as you can get the tap through. There's only about 2 1/2 thou
difference between #36 and #37. Are you using a "gun tap"? This kind
"shoots" the swarf ahead of the tap, so there shouldn't be too much to
clean out.
I agree that a little troubleshooting is in order, ie: measure
screws, check tap and drill bit for size and sharpness, centering of
drill point, etc..
Are you using a lubricant? I use diesel fuel, since it's handy and
similar to kerosene. You need to keep galling to a minimum.
Is it possible that you are using a bottoming tap instead of a plug
or taper? That might mush up the threads somewhat.

Pete Stanaitis
-------------------

Dave99 wrote:

I'm tapping a ton of 1/4" aluminum 6061 parts for 6-32. I've been
using a #36 bit, but the threaded holes seem a little more loose than
they should be. They do work, but I'm wondering if a #37 would be
better. Before I break a tap, I figured I'd ask here and see if
anybody has routinely done that before or if there's a better idea.

Thanks,

Dave

[John Martin]

On Jan 22, 3:41*pm, Dave99 wrote:
I'm tapping a ton of 1/4" aluminum 6061 parts for 6-32. I've been
using a #36 bit, but the threaded holes seem a little more loose than
they should be. They do work, but I'm wondering if a #37 would be
better. Before I break a tap, I figured I'd ask here and see if
anybody has routinely done that before or if there's a better idea.

Thanks,

Dave

Try some smaller bits if you wish and see if things change. I often
drill with smaller drills than for 75% threads, sometimes going right
to 100% threads. I know it's unnecessary, and wouldn't be tolerated
in a production environment, but if it makes me feel better, so what?
It's been a long time since I've broken a tap. This is all hand
tapping, though. You do have to be careful, and feel what the tap is
telling you.

That said, 6-32 is a tough one. The threads are quite coarse for the
diameter, giving a root diameter to nominal size ratio that is lower
than for most other common screw threads. It's weak. Go carefully.

You may find that the drill size has little effect on the fit of your
threads - it could be undersize fasteners or the tap itself. You
might try an H2 instead of an H3 - you should be able to find both in
6-32 without any trouble.

John Martin

[Dave99]

Thanks for the help... Upon further investigation... I examined a few
different screws by holding them up to the light in front of the holes
before tapping. I wasn't able to see light on any of them. If
anything, it looked like the #36 holes might actually be a hair
smaller than the shank of the screws. So it must be something in the
tap process. As it turned out, I'm using screws with small nylon
locking strips. I found them at a local surplus and they're pretty
handy little things. The addition of the nylon actually makes it
workout pretty well in the end.

But since I'm on the subject... What is the best process for dressing
threaded holes that have been made in round stock? I'm putting these
6-32 holes through the sides of 1/4" and 3/8" round stock. Then those
pieces go in holes with tight tolerances. If there's a little lip
remaining on the edge of the holes from the tap, it sometimes prevents
the round from fitting in the hole. What I've been using is just a
countersink on each side of the hole. That cleans it up a bit and kind
of makes an oval shaped opening. The down side is that it can make the
start of the thread a little screwed up, so it's not always easy to
start the screw. This isn't a problem for me, but other people
assemble these parts.

Thanks,

Dave

[Lloyd E. Sponenburgh[_3_]]

Dave99 fired this volley in news:59b1900a-5a1f-4698-
:
But since I'm on the subject... What is the best process for dressing
threaded holes that have been made in round stock? I'm putting these
6-32 holes through the sides of 1/4" and 3/8" round stock. Then those
pieces go in holes with tight tolerances. If there's a little lip
remaining on the edge of the holes from the tap, it sometimes prevents
the round from fitting in the hole. What I've been using is just a
countersink on each side of the hole. That cleans it up a bit and kind
of makes an oval shaped opening. The down side is that it can make the
start of the thread a little screwed up, so it's not always easy to
start the screw. This isn't a problem for me, but other people
assemble these parts.

Were it me, I'd counterbore the tapping hole before tapping. A good,
sharp counterbore won't leave shucks for a burr.

The other rational approach would be to mill a small flat on opposing
sides before drilling. This has the added advantage of allowing you to
spot the drill dead on center, since you can drill with the same setup
used to mill the flat.

LLoyd


LLoyd

[Roger Shoaf]

Dave,

One thing you might consider is to use a finer thread than 6-32.

The 6-32 thread is a kind of force fit, not leaving much on the ID of the
screw. It is by far the most often broken tap and the weakest screw for
this reason.

Since it is aluminum, if you have to use 6-32 I like the idea of the thread
form taps.

--

__
Roger Shoaf

Important factors in selecting a mate:
1] Depth of gene pool
2] Position on the food chain.




"Dave99" wrote in message
...
I'm tapping a ton of 1/4" aluminum 6061 parts for 6-32. I've been
using a #36 bit, but the threaded holes seem a little more loose than
they should be. They do work, but I'm wondering if a #37 would be
better. Before I break a tap, I figured I'd ask here and see if
anybody has routinely done that before or if there's a better idea.

Thanks,

Dave

[Dave99]

Thanks for the tips... For some reason I never even thought to
countersink first. I suppose I could try 4-40. My thinking was just
that, it being a softer metal, that a larger thread was the way to go.

DD

[Lloyd E. Sponenburgh[_3_]]

Dave99 fired this volley in news:c54a1902-a0fe-433f-
:

Thanks for the tips... For some reason I never even thought to
countersink first. I suppose I could try 4-40. My thinking was just
that, it being a softer metal, that a larger thread was the way to go.

Not "countersink", Dave; Counter_bore_. Different tool.

LLoyd

[Lew Hartswick]

Dave99 wrote:
Thanks for the tips... For some reason I never even thought to
countersink first. I suppose I could try 4-40. My thinking was just
that, it being a softer metal, that a larger thread was the way to go.

DD
You could use either 5-40 or 6-40 also. They are standard taps.
the finer thread makes it easier to tap also.
...lew...

[Martin H. Eastburn]

This is Al isn't it. Seems to me that a finner pitch tap would drill
a hole. The force on the soft metal would tear out the threads as it went.

The idea of fine pitch was to have multiple - 3 or more - into the metal.
e.g. sheet or small brackets.

What is the real facts - please.

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Lew Hartswick wrote:
Dave99 wrote:
Thanks for the tips... For some reason I never even thought to
countersink first. I suppose I could try 4-40. My thinking was just
that, it being a softer metal, that a larger thread was the way to go.

DD
You could use either 5-40 or 6-40 also. They are standard taps.
the finer thread makes it easier to tap also.
...lew...