Reaming

"Morgans" wrote in
:


"Fortunat1" wrote

Not according to the info I have, anyway. I can't see the friction on
the plates giving much strength at all. One of the engineering
manuals i have is pretty specific about how the size of the bolt
makes a large difference in regards to how much material it's pulling
(iow a small bolt will pull through the wood more readily than a
large one because it's applying the same pressure over a smaller
area) Same manual goes to pains to point out that the hole should be
as perfect as possible a fit in order to spread the
load as evenly as possible over the material it's resting against.
Seems to
me I may have seen something similar in an old Sport Aviation and
maybe one
of the Bengelis books.

Is your engineering manual wood aircraft specific?

Yes, and also Tony's book shows wood.


I am NOT sure of how this applies to your situation, but I KNOW that
with wood propellors, the amount of torque (squeeze) is critical in
not having the prop slip. If the torque is not maintainted, it will
allow the prop to slip around until it bears against the bolts and
failure occurs. Anyone else?

Well, the load situation in a wood prop is a differnet kettle of fish as
far as load goes. The load is delivered in pulses and in both directions
at thousands of times a minute.
The hub is much thicker and much more rigid than the plates I have in my
wing (which are just .090 4130) and it's not hard to imagine that the
plates wouldn't be applying that much pressure between the bolts.
Also, some of them aren't all that big ( a couple of the plates attached
to the drag and anti drag wires only have about 2 sq inches of area) so
I can't see them doing al that much to keep the wing from sweeping
itself in a dive from friction alone.

It would seem like the way I have heard that many people do it, is to
fill the space between the bolt and the wood with epoxy. It spreads
the loads, and prevents wood to steel contact, which is critical to
prevent corrosion and decay.

Well, obviously I'd protect it, but I'm not going to rely on epoxy to
bear a load. If I can't get the holes 100% I'll bush them.




But your question brings up a good point. How tight a fit do I want
in the wood and the steel? Too tight will mean I won't be able to fit
the bolts through the steel after painting. I wouldn't be as worried
about the wood as the pourousness of the wood would allow for some
retention.

"Fortunat1" wrote in message
.. .
Well, obviously I'd protect it, but I'm not going to rely on epoxy to
bear a load. If I can't get the holes 100% I'll bush them.

Micarta bushings are the most preferred way to install a steel bolt through
wood, especially in a spar. My three-piece Emeraude spar would have required
54 bushings which, given my budget at the time, was way beyond the pale.
Carefully drilled holes and varnish were the order of the day.

Rich S.

"Rich S." wrote in
:

"Fortunat1" wrote in message
.. .
Well, obviously I'd protect it, but I'm not going to rely on epoxy to
bear a load. If I can't get the holes 100% I'll bush them.

Micarta bushings are the most preferred way to install a steel bolt
through wood, especially in a spar. My three-piece Emeraude spar would
have required 54 bushings which, given my budget at the time, was way
beyond the pale. Carefully drilled holes and varnish were the order of
the day.


Hmm. Well, the plans don't call for bushings. All of the high stress areas
have ply doublers and I'm using Birch instead of mahogony, so they should
be tough enough. Off the top of my head, I'd need about 80 bushings for the
Hatz. So I guess I'l just be as careful as I can cutting the holes. Just
looking through Bengelis' book, I see he recommends using a twist drill to
cut the holes, presumably to their final size, wheras I'd planned on
reaming using the plates themselves as a guide. I figured I'd get the
cleanest hole this way.

"Fortunat1" wrote

Hmm. Well, the plans don't call for bushings. All of the high stress areas
have ply doublers and I'm using Birch instead of mahogony, so they should
be tough enough. Off the top of my head, I'd need about 80 bushings for
the
Hatz. So I guess I'l just be as careful as I can cutting the holes. Just
looking through Bengelis' book, I see he recommends using a twist drill to
cut the holes, presumably to their final size, wheras I'd planned on
reaming using the plates themselves as a guide. I figured I'd get the
cleanest hole this way.

Yep, you could spend time reaming 80 holes, or be on the way to having the
whole thing done by doing something else.

IMHO, reaming in wood is taking it one step further than needed. How much
would the strength be improved by reaming? Not more than a couple percent,
at best, I'll bet.

On the using epoxy as a hole filler and wood protector; I did not mean to
imply to do a sloppy job drilling, but that epoxy does fill any
irregularities. It probably has a higher crush strength than the wood, too,
so it would spread the load evenly to the wood very nicely.

All the above is worth what the price for it was. Right? ;-)
--
Jim in NC

Fortunat1 wrote:
"Rich S." wrote in
:

"Fortunat1" wrote in message
.. .
Well, obviously I'd protect it, but I'm not going to rely on epoxy to
bear a load. If I can't get the holes 100% I'll bush them.
Micarta bushings are the most preferred way to install a steel bolt
through wood, especially in a spar. My three-piece Emeraude spar would
have required 54 bushings which, given my budget at the time, was way
beyond the pale. Carefully drilled holes and varnish were the order of
the day.


Hmm. Well, the plans don't call for bushings. All of the high stress areas
have ply doublers and I'm using Birch instead of mahogony, so they should
be tough enough. Off the top of my head, I'd need about 80 bushings for the
Hatz. So I guess I'l just be as careful as I can cutting the holes. Just
looking through Bengelis' book, I see he recommends using a twist drill to
cut the holes, presumably to their final size, wheras I'd planned on
reaming using the plates themselves as a guide. I figured I'd get the
cleanest hole this way.

I would test that theory first. Reamers may or may not give a good
finish on wood. That was one of the reasons I quoted the study I did.
The twist drill gave the best hole finish.

Charles

Charles Vincent wrote in
:

Fortunat1 wrote:
"Rich S." wrote in
:

"Fortunat1" wrote in message
.. .
Well, obviously I'd protect it, but I'm not going to rely on epoxy
to bear a load. If I can't get the holes 100% I'll bush them.
Micarta bushings are the most preferred way to install a steel bolt
through wood, especially in a spar. My three-piece Emeraude spar
would have required 54 bushings which, given my budget at the time,
was way beyond the pale. Carefully drilled holes and varnish were
the order of the day.


Hmm. Well, the plans don't call for bushings. All of the high stress
areas have ply doublers and I'm using Birch instead of mahogony, so
they should be tough enough. Off the top of my head, I'd need about
80 bushings for the Hatz. So I guess I'l just be as careful as I can
cutting the holes. Just looking through Bengelis' book, I see he
recommends using a twist drill to cut the holes, presumably to their
final size, wheras I'd planned on reaming using the plates themselves
as a guide. I figured I'd get the cleanest hole this way.

I would test that theory first. Reamers may or may not give a good
finish on wood. That was one of the reasons I quoted the study I did.
The twist drill gave the best hole finish.


OK, I went out and tried both. The nice fresh twist dril gave an
excellent hole as did a slightly enlarged hole using a reamer. I found I
had to feed the twist drill at a very steady pace to get the best
finish, but it definitely does the job. Whagt I'm still having trouble
with is getting the hole absolutely concentric with the steel plates on
either side. Clamping the plate and using it as a guide to ream the wood
seems to be a bad idea. the steel steers the reamer and the reamer
starts to wander. Drilling the wood through the already finished steel
plates seems like a very bad idea, so now I'm at a loss. What I've
already tried is getting a piece of tubing, grinding the O.D. to the
size of the finished hole and sticking it into the hole in the steel
plate. I then use a bit that's the same as the I.D. of the tubing and
drill an undersized hole. then, without moving the work, I drill a
second, larger hole just a couple thou under the required finished dia..
Tehn I reamed. Obviously, since there's about 4 or five holes in each
plate, I'm going to need to repeatedly drill accurate holes in the wood
Suggestions?

I'm going to need to repeatedly drill accurate holes in the wood
Suggestions?- Hide quoted text -


Me thinks you are making this way too complex............IMHO

Unfortunatly, you alreay reamed the holes in your fittings. The easy
way is to drill the holes 1/64 undersize, clamp the fittings where
they need to go and drill both fittings and the spar at the same
time. Use either a drill press or a hand drill with one of the home
made jigs to find the hole on the back side. If you want, put some
cheap hardware grade bolts in each hole as you drill to keep things
together (you can even drill the spar by hand one full size smaller
and use cheap bolts to hold the assembly aligned for the drilling)

Take the whole thing apart, ream the holes to final size, treat/paint
the fittings and assemble with a bit of West System in the holes. Add
some flox if you really made a mess of the holes.

As long as the bolts fit nice and snug in the metal the wood can be
pretty sloppy and the West will fill in the assembly will be as strong
or stronger than one with a perfectly fit wood to bolt hole. The only
down side is that it is a more or less permanant joint............but
then how often does one need to remove metal spar fittings?
===============
Leon McAtee

" wrote in
oups.com:

I'm going to need to repeatedly drill accurate holes in the wood
Suggestions?- Hide quoted text -


Me thinks you are making this way too complex............IMHO

Unfortunatly, you alreay reamed the holes in your fittings. The easy
way is to drill the holes 1/64 undersize, clamp the fittings where
they need to go and drill both fittings and the spar at the same
time. Use either a drill press or a hand drill with one of the home
made jigs to find the hole on the back side. If you want, put some
cheap hardware grade bolts in each hole as you drill to keep things
together (you can even drill the spar by hand one full size smaller
and use cheap bolts to hold the assembly aligned for the drilling)

Take the whole thing apart, ream the holes to final size, treat/paint
the fittings and assemble with a bit of West System in the holes. Add
some flox if you really made a mess of the holes.

As long as the bolts fit nice and snug in the metal the wood can be
pretty sloppy and the West will fill in the assembly will be as strong
or stronger than one with a perfectly fit wood to bolt hole. The only
down side is that it is a more or less permanant joint............but
then how often does one need to remove metal spar fittings?


Well, too late now but I tried this and dismissed it early on. At least
I couldn't get it to work.
I found the hole on the back side fitting wasn't as accurate as I'd
like. Also, I'd rather not resort to filler if I can help it at all. In
fact, I think I'd discard a spar first and use it for something else.
I've been experimenting this afternoon. and discovered that if I place
the spar, with one fitting correctly positioned on top absolutely square
in the dril press and then carefully brought the drill bit down into the
hole and turned it by hand until it bites a bit.When the bit is in far
enough I switch on and go right through. Worked perfectly and the holes
line up on both sides perfectly with nice snug holes all around.

On Aug 16, 10:44 am, Fortunat1 wrote:
"Morgans" wrote :







"Fortunat1" wrote

In either case I'd drill out to a sixe
under the final dia and then use the reamer to cut the final bit of
wood away. Any pitfalls with this plan?

Sounds to me like you are seriously splitting toadstools.

If you were to just drill the wood so the bolt fits, and then put some
epoxy or varnish or whatever you want to use to make sure the bolt and
wood do not interact, won't that fill the voids?

I always thought that the strength in a fitting like this was in the
squeezing of the fitting on the wood, not the sheer of the bolt
against the wood.

Not according to the info I have, anyway. I can't see the friction on the
plates giving much strength at all. One of the engineering manuals i have
is pretty specific about how the size of the bolt makes a large difference
in regards to how much material it's pulling (iow a small bolt will pull
through the wood more readily than a large one because it's applying the
same pressure over a smaller area) Same manual goes to pains to point out
that the hole should be as perfect as possible a fit in order to spread the
load as evenly as possible over the material it's resting against. Seems to
me I may have seen something similar in an old Sport Aviation and maybe one
of the Bengelis books.
But your question brings up a good point. How tight a fit do I want in the
wood and the steel? Too tight will mean I won't be able to fit the bolts
through the steel after painting. I wouldn't be as worried about the wood
as the pourousness of the wood would allow for some retention.- Hide quoted text -

- Show quoted text -

"FRICTION is FICTION", or so it says in my engineering textbook.

I think I should add my experience with wood spars. On the wood
winged homebuilt I constructed ( a Coot, designed by Molt Taylor who
also designed and built several experimental aircraft including the
Aerocar), the 4130 wing attachment plates were attached with 1/4" AN
bolts. The bolts went all the way through the spar and plates on each
side. The spruce spars were drilled with 5/8" holes that had 5/8" 2024
aluminum bushings with 1/4" holes epoxied into the spruce spar caps.
Micarta would work fine for the bushings also, you just need something
stronger than the wood. This is the proper way to attach highly loaded
metal plates to wood. The safety of the joint depends on how much
bearing stress the wood has to support. The Coot was a cantlever wing
that had very high bending loads at the attachment. Anything less than
the approach taken by Mr. Taylor would have been unacceptable. The
5/16" hole through the wood you are dealing with has a specific amount
of load that it can safely carry. Trust me, it is nowhere near what
any metal will support. The strongest wood there is (Hickory) has a
tensile strength of about 1400 to 1500 psi. It's bearing strength is
only slightly higher.
The information you have that says don't rely on clamping
pressure to carry the load is correct. The adage of "Friction is
Fiction" is one structural engineers use to explain that carrying a
load using friction is not an acceptable way of constructing a
structural joint, period. No argument.
What aircraft are you building? Whether or not the 1/4 and 5/16"
holes you have will be sufficient depends on how much load they must
carry, period. A 1/4" hole in wood will not carry much. If it is a
strut type wing (ala Cessna Skyhawk) that will be a big help. I can't
imagine a cantilevered wing where 1/4" holes would be OK at the wing
attachment. The Coot had I believe, 18 seperate 5/8" bushings in the
root of the main wing spar. As for getting proper clamping pressure
for wooden props, this is important because without it, the wood would
deform too much if allowed to by not holding it in place with
pressure, thereby weakening the joint. Friction exists and carries
load for sure, but it can easily change over time and then what are
you left with? Friction is never counted on to carry load. If the
shear or tensile or bearing strength is not sufficient, then you are
just asking for trouble.
Epoxying the bolts in place is a good idea also. Getting the
holes straight, smooth sided, properly aligned, and especially, the
correct diameter is an even better one.


Regards,
Bud

wrote in
ps.com:

On Aug 16, 10:44 am, Fortunat1 wrote:
"Morgans" wrote
:







"Fortunat1" wrote

In either case I'd drill out to a sixe
under the final dia and then use the reamer to cut the final bit
of wood away. Any pitfalls with this plan?

Sounds to me like you are seriously splitting toadstools.

If you were to just drill the wood so the bolt fits, and then put
some epoxy or varnish or whatever you want to use to make sure the
bolt and wood do not interact, won't that fill the voids?

I always thought that the strength in a fitting like this was in
the squeezing of the fitting on the wood, not the sheer of the bolt
against the wood.

Not according to the info I have, anyway. I can't see the friction on
the plates giving much strength at all. One of the engineering
manuals i have is pretty specific about how the size of the bolt
makes a large difference in regards to how much material it's pulling
(iow a small bolt will pull through the wood more readily than a
large one because it's applying the same pressure over a smaller
area) Same manual goes to pains to point out that the hole should be
as perfect as possible a fit in order to spread the load as evenly as
possible over the material it's resting against. Seems to me I may
have seen something similar in an old Sport Aviation and maybe one
of the Bengelis books.
But your question brings up a good point. How tight a fit do I want
in the wood and the steel? Too tight will mean I won't be able to fit
the bolts through the steel after painting. I wouldn't be as worried
about the wood as the pourousness of the wood would allow for some
retention.- Hide quoted text -

- Show quoted text -

"FRICTION is FICTION", or so it says in my engineering textbook.

I think I should add my experience with wood spars. On the wood
winged homebuilt I constructed ( a Coot, designed by Molt Taylor who
also designed and built several experimental aircraft including the
Aerocar), the 4130 wing attachment plates were attached with 1/4" AN
bolts. The bolts went all the way through the spar and plates on each
side. The spruce spars were drilled with 5/8" holes that had 5/8" 2024
aluminum bushings with 1/4" holes epoxied into the spruce spar caps.
Micarta would work fine for the bushings also, you just need something
stronger than the wood. This is the proper way to attach highly loaded
metal plates to wood. The safety of the joint depends on how much
bearing stress the wood has to support. The Coot was a cantlever wing
that had very high bending loads at the attachment. Anything less than
the approach taken by Mr. Taylor would have been unacceptable. The
5/16" hole through the wood you are dealing with has a specific amount
of load that it can safely carry. Trust me, it is nowhere near what
any metal will support. The strongest wood there is (Hickory) has a
tensile strength of about 1400 to 1500 psi. It's bearing strength is
only slightly higher.
The information you have that says don't rely on clamping
pressure to carry the load is correct. The adage of "Friction is
Fiction" is one structural engineers use to explain that carrying a
load using friction is not an acceptable way of constructing a
structural joint, period. No argument.
What aircraft are you building? Whether or not the 1/4 and 5/16"
holes you have will be sufficient depends on how much load they must
carry, period. A 1/4" hole in wood will not carry much. If it is a
strut type wing (ala Cessna Skyhawk) that will be a big help. I can't
imagine a cantilevered wing where 1/4" holes would be OK at the wing
attachment. The Coot had I believe, 18 seperate 5/8" bushings in the
root of the main wing spar. As for getting proper clamping pressure
for wooden props, this is important because without it, the wood would
deform too much if allowed to by not holding it in place with
pressure, thereby weakening the joint. Friction exists and carries
load for sure, but it can easily change over time and then what are
you left with? Friction is never counted on to carry load. If the
shear or tensile or bearing strength is not sufficient, then you are
just asking for trouble.
Epoxying the bolts in place is a good idea also. Getting the
holes straight, smooth sided, properly aligned, and especially, the
correct diameter is an even better one.


Thanks, even more good info!

It's a Hatz. As far as I know nobody who's built one of these has done
anything but drill unbushed holes through the wood. There are ply
doublers at the wing root and strut attach points, but the majority of
the load is carried through the cellule by the wires, fuselage and
struts, leaving the spars to take up the loads at these points. In other
words, there's nowhere near the loads put on these fittings that would
be put on them by a similar fitting taking a cantilever wing's load or
even that of a stutted monoplane. As far as I know no hatz has had an
inflight failure, though a related design, the Kelly D, has. If I
understand it correctly, the Kelly D's spars are much shallower than the
Hatz's and the airplane in question did not have one of it's ply spar
doublers glued on correctly which has certainly motivated me to get this
right.
The bolts holding the plates to the spars are all 5/16 as are the bolts
hinging the wings to the fuse and ceter section. The struts are all 1/4
bolts.