Reaming

Charles Vincent wrote in
t:



"In drilling the experimental holes to establish drilling technique,
the 120° (probably actually 118 0 ) twist drill appeared to produce
the smoothest hole. The 60° twist drill was about equally effective,
but offered no apparent advantages over the more common 120° drill. A
hole drilled with a machine bit with a slow spiral did not appear to
differ materially from one drilled with a machine bit with a fast
spiral, or from one drilled with a Foerstner bit."

and

"The machine bit and the Forstner bit had a tendency to produce
large chips which sometimes wedged underneath the horizontal cutting
edge. Some of the chips were complete washers in form, the full
diameter of the drill in size, up to 1/32 inch thick, and strong
enough to remain intact when the bit was withdrawn. In a few cases a
chip became wedged between the side of the bit and the wall of the
hole and scored the wall."


Thanks, this is exactly what I discovered. It's good to know I'm going
down the correct path.


Couple of things I'm still uncertain of, though. The steel parts have
quite a tight fit on the bolts. Obviously any paint on the inside of
these holes is simply going to be forced out when I push a bolt through.
this is normal?
Also, there's a small ridge formed on the edge of each hole. I figure
it's OK to leave the excess material there for a couple of reasons, one,
it provides more material for the bolt to rest against, and two it
won'ts interfere with tightening the bolts down since there will only be
a washer up against the hole anyway.
If it is poor practice to leave the ridge on the edge, what's the best
method for getting rid of it? Aside from a special machien, I thought of
carefully cutting it down with a large dril bit, but I'd be afraid of
doing some damage to the part.
Any suggestions?

On Aug 28, 1:30 pm, Fortunat1 wrote:
Charles Vincent wrote . net:


...


Couple of things I'm still uncertain of, though. The steel parts have
quite a tight fit on the bolts. Obviously any paint on the inside of
these holes is simply going to be forced out when I push a bolt through.
this is normal?

Others may have a better answer, like they did about the drill bits,
but I would mask off the inside of the holes so as to not get paint
on them and use never seize on the bolt shaft. A little dab will do
ya.

There are some places where never seize should not be used. A
fellow I know used it on his spark plugs on his Stinson. Normally
that's OK (I think) but his heads had been rethreaded with helicoils
and the helicoils backed out when the engine was running.

Also, there's a small ridge formed on the edge of each hole.

I think that's called a burr--sometimes called a wire-edge.
It is metal that has been cold-rolled around the corner
on the edge during drilling. Usually it is much bigger on the
exit side than on the entrance side. If drilling down a pilot hole,
that effect can be minimized by drilling part-way through from
each sides. Without a pilot hole alignment is too difficult.


I figure
it's OK to leave the excess material there for a couple of reasons, one,
it provides more material for the bolt to rest against, and two it
won'ts interfere with tightening the bolts down since there will only be
a washer up against the hole anyway.

I don't follow you here. Doesn't the burr stick up above the flat
surface?
Won't that interfere with proper seating of the washer?

If it is poor practice to leave the ridge on the edge, what's the best
method for getting rid of it? Aside from a special machien, I thought of
carefully cutting it down with a large dril bit, but I'd be afraid of
doing some damage to the part.
Any suggestions?

Draw filing is a technique wherein the file is held with both hands,
one
on the handle and one on the tip and drawn across a flat surface as
if slicing with a drawknife, to remove high spots. I've never gotten
the hang of it myself. The parts could also be lapped on wet/dry
sandpaper on a very flat surface like a one-foot square marble
tile, or a good quality table-saw or jointer table. Of you could
use a fine rat-tail, cylindrical or half-round file, through the
hole.
A hand grinder,even a dremel, used very carefully would do the
trick too. A conical stone would do a nice job.

Using a very large countersink bit would do it too, a very large
drill bit would do the same but is more likely to grab and tear.

I don't think that slightly chamfering the holes would hurt at
all. The sharp edge or wire is a stress riser that is relieved by
chamfering, though in this case I don't think it is a serious
issue.

If you practice on scrap, you won't have to practice on your
project!

--

FF

Fortunat1 wrote:

Thanks, this is exactly what I discovered. It's good to know I'm going
down the correct path.

You are drilling the cleanest hole, but still may not be going down the
right path. The report I quoted was written before the invention of
modern epoxies. I think that coating oversize holes in the wood with
epoxy will give you a stronger structure by further reducing the bearing
stress on the wood, but that is just my opinion.


Also, there's a small ridge formed on the edge of each hole. I figure
it's OK to leave the excess material there for a couple of reasons, one,
it provides more material for the bolt to rest against, and two it
won'ts interfere with tightening the bolts down since there will only be
a washer up against the hole anyway.

Assuming it is not just an ordinary burr, it sounds like one of the
following things is happening:

A)Your drill bit is dull, particularly on the edges of the flutes and
you are applying too much pressure to the drill to make it cut, causing
the hole to pucker.
B)The reamer you are using is dull, or the drilled hole is too small for
that reamer and the reamer is cold working the hole rather than cutting.
In my experience, this will create the pucker you are describing.
The cold worked hole will also close up slightly when the reamer is
removed, creating the tight fit you are describing.

If it is poor practice to leave the ridge on the edge, what's the best
method for getting rid of it? Aside from a special machien, I thought of
carefully cutting it down with a large dril bit, but I'd be afraid of
doing some damage to the part.
Any suggestions?

I personally would not be comfortable leaving the ridge, particularly
since I do not know what it looks like. If it is an ordinary burr, I
would use a deburring tool.

Charles

Charles Vincent wrote in
:

Fortunat1 wrote:

Thanks, this is exactly what I discovered. It's good to know I'm
going down the correct path.

You are drilling the cleanest hole, but still may not be going down
the right path. The report I quoted was written before the invention
of modern epoxies. I think that coating oversize holes in the wood
with epoxy will give you a stronger structure by further reducing the
bearing stress on the wood, but that is just my opinion.



You're probably right, but the way I see it is that airplanes just like
this have been flying wth their original spars since the flood, so if it
was ood enough for them it's god enough for me. Also, this is a plank
spar, not a capped spar, so there iis plenty of meat there. I'll
certainly keep the epoxy thing in mind in case I screw up some of the
holes when drilling them out for fittings, though. Nice to know there is
a fix for any mistakes.

Yes, pucker is a better word for it. the drills are nice and sharp and
I'm getting a good cut there. I've been cutting them out to 7.7 mm and
then reaming to 5/16th. You're right, some of the holes are cut pretty
clean, but the reamer soon produces the rounded pucker as you so aptl
put it.

If it is poor practice to leave the ridge on the edge, what's the
best method for getting rid of it? Aside from a special machien, I
thought of carefully cutting it down with a large dril bit, but I'd
be afraid of doing some damage to the part.
Any suggestions?

I personally would not be comfortable leaving the ridge, particularly
since I do not know what it looks like. If it is an ordinary burr, I
would use a deburring tool.


OK, it's not a burr, it's more the pucker you describe. does this mean
the part is trash, or can I leave it or should i try a deburring tool on
it? The reamers are new and seem nice and sharp, I am getting swarf, but
not as much maybe as you would expect..

Fortunat1 wrote:

Yes, pucker is a better word for it. the drills are nice and sharp and
I'm getting a good cut there. I've been cutting them out to 7.7 mm and
then reaming to 5/16th. You're right, some of the holes are cut pretty
clean, but the reamer soon produces the rounded pucker as you so aptl
put it.

You are using the reamer to cut .009 inches of material. Generally, I
don't try to do more than .002 to .003. As far as correcting the parts,
you need guidance from someone else. With the metal cold worked like
that, I personally would look closely(with a magnifying glass or an
industrial microscope since I have one) at the edges to see if there are
any tiny cracks. I expect there are.

Charles

Charles Vincent wrote in news:yX0Bi.47964$Um6.15150
@newssvr12.news.prodigy.net:

Fortunat1 wrote:

Yes, pucker is a better word for it. the drills are nice and sharp and
I'm getting a good cut there. I've been cutting them out to 7.7 mm and
then reaming to 5/16th. You're right, some of the holes are cut pretty
clean, but the reamer soon produces the rounded pucker as you so aptl
put it.

You are using the reamer to cut .009 inches of material. Generally, I
don't try to do more than .002 to .003. As far as correcting the parts,
you need guidance from someone else. With the metal cold worked like
that, I personally would look closely(with a magnifying glass or an
industrial microscope since I have one) at the edges to see if there are
any tiny cracks. I expect there are.

Oh dear, which means I've just wrecked a whole lot of parts. I'll have a
looksee with a magnifying glass. I did try to cut them out to 7.9 mm, but I
was afraid it might be too deep a cut and that the triangular hole cut by
the drill might leave it's remains around the edges.

Fortunat1 wrote:


Oh dear, which means I've just wrecked a whole lot of parts. I'll have a
looksee with a magnifying glass. I did try to cut them out to 7.9 mm, but I
was afraid it might be too deep a cut and that the triangular hole cut by
the drill might leave it's remains around the edges.

Don't make any assumptions based on my comments. I am unfamiliar with
the plane you are building, I do not know the metal variety you are
working with and have not seen the parts. Finally, I do not have
experience building enough airplanes to rely on experience when
answering you. Metalworking I do know about, so I could make a pretty
good guess as to what your problem was and the probable ramifications. I
suggest you talk to the designer of your airplane or another builder of
it.

Charles

Charles Vincent wrote in
:

Fortunat1 wrote:


Oh dear, which means I've just wrecked a whole lot of parts. I'll
have a looksee with a magnifying glass. I did try to cut them out to
7.9 mm, but I was afraid it might be too deep a cut and that the
triangular hole cut by the drill might leave it's remains around the
edges.

Don't make any assumptions based on my comments. I am unfamiliar with
the plane you are building, I do not know the metal variety you are
working with and have not seen the parts. Finally, I do not have
experience building enough airplanes to rely on experience when
answering you. Metalworking I do know about, so I could make a
pretty good guess as to what your problem was and the probable
ramifications. I suggest you talk to the designer of your airplane or
another builder of it.


Well, both the guys who had a hand designing this thing are dead, so
that's going to be a bit difficult! (Neither in a Hatz, BTW)
The material is 4130 steel which is a relativley high carbon steel if
you're not familiar with it.
Seems to me you've hit the problem on the head first time out. Your
experience is obvious!

I had a look with a not too powerful magnifying glass and couldn't see
any obvious cracks. There's the occasional scratch in the holes in the
direction of the cut, presumably from a bit of swarf getting caught in
the reamer. The ridge around the edges mostly stand up about .002 or so,
and maybe a little less than that in thickness. They're more regular in
appearance and much thicker than you'd see from drilling, for instance,
but they're still not so perfect around their edge you could tell a
crack from just an irregularity.At least I couldn't.
I do have someone who can look at them here, though, so that's what I'll
have to do to be sure.
Thanks for the heads up on that! They say you make two airplanes when
you make your first one, the one you fly and the one you throw away..
;(

Fred the Red Shirt wrote in
oups.com:

On Aug 12, 11:09 am, Fortunat1 wrote:
...
I'll just have to get a good
quality reamer and prepare each hole carefully. I'll see if I can get
a
drill bit that brings he holes a little closer to the final size.

May I suggest you get more than one drill bit, for the same
reason you need more than one reamer?

.What is the annealing temperature for 4130? You can drill through
a bandsaw blade by spot annealing it, that is you chuck a blunt rod
like a nail with the point ground off into a drill press bring that to
bear
on the spot to be drilled until it gets good and hot, then let it
cool
slowly. Now the spot is annealed and a hole can be drilled with
an ordinary bit.

So I wonder if re-drilling the holes will heat them to the annealing
temperature? Or would it be feasible to spin a rod in the holes
to heat them by friction to soften them? Or would that just
work-harden the surface....

Don't know the answer to any of these questions, but since any sort of
heat treating, whether it be normalising or tempering, is well beyond
what I'm able to do in the shop just by eyeballing the color of the
steel.

One thing I don't underdstand is that I work hardened a small part by
getting a little over enthusiastic with a drill bit. I tried heating the
same part up to red hot and then let it cool slowly thinking it would
bring it back to the normalised state, but it seemed just as hard to
drill as it was before I cherried it.

Charles Vincent wrote in news:yX0Bi.47964$Um6.15150
@newssvr12.news.prodigy.net:

Fortunat1 wrote:

Yes, pucker is a better word for it. the drills are nice and sharp and
I'm getting a good cut there. I've been cutting them out to 7.7 mm and
then reaming to 5/16th. You're right, some of the holes are cut pretty
clean, but the reamer soon produces the rounded pucker as you so aptl
put it.

You are using the reamer to cut .009 inches of material. Generally, I
don't try to do more than .002 to .003. As far as correcting the parts,
you need guidance from someone else. With the metal cold worked like
that, I personally would look closely(with a magnifying glass or an
industrial microscope since I have one) at the edges to see if there are
any tiny cracks. I expect there are.

OK, looked at the holes using s 10X microscope and they're not exactly
mirror finished, but they don't look too bad for the most part. I didn't
find any cracks, but I did find some microscopic chatter marks, scrapes and
chips along the edges. Also found a couple of gouges that ran across the
holes from edge to edge that could best be described as a "step".
None of these imperfections were deeper than say, .002, if even that deep.
I do have my "guy" comong over to have a look, but from my description on
the phone he thinks they're probably OK.
It's all learning, eh?