Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Ryan
 
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Default Roughing out 4" hole in .750 thick aluminum.

I have a task which requires boring four 4" holes in .750 plate aluminum,
with 10 plates in total to do. I have a boring head and / or flycutter, so
the finish cut will be no problem, it is just going to be a real chore to
rough them out I suppose. Short of using a jig saw (which I am not
convinced would work too well) what would be the best way to approach this
task? I would like to use the milling machine for the roughing, so that I
can rough the hole, then finish bore in 2 steps. Would a trepanning tool be
the best bet? If so, can someone suggest a particular model, keeping in
mind this job is meanial, therefore tooling costs are a concern.

Thanks in advance,

RB



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JMartin957
 
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Default Roughing out 4" hole in .750 thick aluminum.

Good point...

Have 10x50 table vertical milling machine, do not have cnc, nor a rotary
table. Will look into the holesaw type cutter, did not think they made one
that big,

RB




Starrett makes holesaws to 6". Others probably do also.

John Martin
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Ryan
 
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Default Roughing out 4" hole in .750 thick aluminum.

I should have looked before inserting foot in mouth...

thanks,

RB



"JMartin957" wrote in message
...
Good point...

Have 10x50 table vertical milling machine, do not have cnc, nor a rotary
table. Will look into the holesaw type cutter, did not think they made

one
that big,

RB




Starrett makes holesaws to 6". Others probably do also.

John Martin



  #4   Report Post  
Brian
 
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Default Roughing out 4" hole in .750 thick aluminum.

I find drilling small holes in the kerf really helps on the chip clearance
with holesaws in aluminium. If I had that mill, I'd be tempted to put a
trepanning tool together and try that.

Brian


"Bob Swinney" wrote in message
news:AVTXa.73038$YN5.55452@sccrnsc01...
Ryan sez: "Will look into the holesaw type cutter, did not think they

made
one
that big,.."

They do, though. Not too long ago I cut a 4.5 inch hole in a piece of 3/4
inch mild steel plate. I'm not saying it was fast. The main thing is to
keep the chips from accumulating in the kerf. Blow or brush them out
frequently. Wear safety glasses if you blow - hi-velocity chips are just

so
much shrapnel.

Bob Swinney

"Ryan" wrote in message
...
Good point...

Have 10x50 table vertical milling machine, do not have cnc, nor a rotary
table.
RB



"Torsten" wrote in message
...
Depends on what tools you got.
A cnc could just cut out the center.
Manual machine maybe cut it out on a rotary table.
Other option would be a holesaw type of cutter single or multyflute.

A lot will depend on your machinery and tools.

"Ryan" wrote in message
...
I have a task which requires boring four 4" holes in .750 plate

aluminum,
with 10 plates in total to do. I have a boring head and / or

flycutter,
so
the finish cut will be no problem, it is just going to be a real

chore
to
rough them out I suppose. Short of using a jig saw (which I am not
convinced would work too well) what would be the best way to

approach
this
task? I would like to use the milling machine for the roughing, so

that
I
can rough the hole, then finish bore in 2 steps. Would a trepanning

tool
be
the best bet? If so, can someone suggest a particular model,

keeping
in
mind this job is meanial, therefore tooling costs are a concern.

Thanks in advance,

RB











  #5   Report Post  
Jon Elson
 
Posts: n/a
Default Roughing out 4" hole in .750 thick aluminum.



Brian wrote:

I find drilling small holes in the kerf really helps on the chip clearance
with holesaws in aluminium. If I had that mill, I'd be tempted to put a
trepanning tool together and try that.


I've never done one quite this big, but before I had CNC, I did set up
to trepan
out some 2.5" or so holes. At very low RPM, it cut long, stringy chips that
were mostly pulled up out of the hole, so chip clearance was not a big
problem.
It went through on power feed rather quickly. I just ground a special tool
to use in my boring head.

Jon



  #6   Report Post  
RWatson767
 
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Default Roughing out 4" hole in .750 thick aluminum.

Ryan
Roughing out 4" hole in .750 thick aluminum.


I have a task which requires boring four 4" holes in .750 plate aluminum, with
10 plates in total to do

How big are the plates?
Bob AZ
  #7   Report Post  
jim rozen
 
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Default Roughing out 4" hole in .750 thick aluminum.

In article , Ryan says...

I have a task which requires boring four 4" holes in .750 plate aluminum,


Holesaw. Get the best bi-metal blade you can, mount it up
in a bridgeport, and use WD-40 for the cutting fluid.
Retract feed frequently to blow out chips. You can
cut from both sides, just pick up the pilot hole from
the first side.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

  #8   Report Post  
richard
 
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Default Roughing out 4" hole in .750 thick aluminum.

"Ryan" wrote in message news:
Short of using a jig saw (which I am not
convinced would work too well)

I have done stuff like that with a drill and file, a pain.
a jigsaw is fine on metal, though even on alluminium i use proper
hacksaw blades, the things they sell for metal are overpriced and the
few I have been given were crap - still Sandvik don't know how to make
a hacksaw blade anyway;-).
Yes i modified the jigsaw so i don't have to grind a bayonet on the
blades.

I chop out bit's for motor bikes with a jigsaw and 1/2"
plate is no problem, i cut blanks like your on about and get circles
within a
64th without any problem.
The way I cut a hole like that is.
Scribe the circle and drill some holes -equally spaced about the
inside of the scrap bit- big enough to get the saw blade through, four
or five holes will be enough.
Criss cross the waste with the saw till some big bits fall out.
Then cut almost to the circumferance[scribed line], cutting at an
angle to the radius and keep making cuts like this all the way around
the inside of the circle, cutting at an angle to the radius.
The plate should look like a cross between a negative of a circular
saw blade and an odd comb at this stage.
Then repeat the above bit, cutting at the opposite angle to the
radius, so the bits fall out and your left with a round hole with
little bit's to file or bore out.
It's very simple and with a jig saw you can get very close to a
circle, or any other shape you want. the number of cut's you make 'at
an angle' will determine how long it takes, go around the circle once
making say eight cut's, this will get the big pieces out and then
repeat with the cuts closer to get closer to a round hole.

The only thing to watch out for is the foot of the jigsaw marring the
surface,
it isn't to bad if you make sure you don't get swarf under the foot.
They cut much better at slowish speeds, don't push to hard the hss
blade will chop through the cheapo rear blade support. cut dry, wet
lubricant will just make a mess.

When you want to make a straight cut try a woodworkers circular saw
if you haven't used one on alli you will be suprized how good they
are...

--
richard
  #9   Report Post  
Ron Coffey
 
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Default Roughing out 4" hole in .750 thick aluminum.

You might try "treepanning" ( I think that is spelled right !)
just a thought,
Ron
"Michael" wrote in message
.. .
Ryan, i did an almost identical job, 10 pieces in 1" AL, except i was
cutting an arc rather than a complete hole. As others have suggested, i
used a hole saw in the mill at a low speed (not because of theoretical
cutting speeds but because its a bit of a hairy cut to make). There was
enough clearance in the saw to cut the 1" at one go (3.5" hole saw)

Here's a caution for you....Most of the hole saw arbours I could find or
were presented to me by tool store counter help do not hold the saw

rigidly
which it must be to use on the mill. Starrett's A17-12 does hold the saw
rigidly, or make your own. I'm no hole saw expert, but i speculate that

the
most common app for hole saws is blasting through wood on a construction
site, i guess ease of changing blades matters more than a little wobble.

you'll get probably the worst finish ever created in your shop, so buy a
smaller dia hole saw and finish up with a boring head. in my limited
experience, these hole saws are not precision cutters, then again maybe i
bought the wrong one. the set of the teeth seem incorrect leading to a

lot
of rubbing on the outside dia of the saw and the butt weld of the rolled
portion is visibly out of alignment. its only going to be cutting on a

few
teeth so feed was determined by feel. oh well, that's what the boring

head
is for.

hope it helps


"Ryan" wrote in message
...
I have a task which requires boring four 4" holes in .750 plate

aluminum,
with 10 plates in total to do. I have a boring head and / or flycutter,

so
the finish cut will be no problem, it is just going to be a real chore

to
rough them out I suppose. Short of using a jig saw (which I am not
convinced would work too well) what would be the best way to approach

this
task? I would like to use the milling machine for the roughing, so that

I
can rough the hole, then finish bore in 2 steps. Would a trepanning tool

be
the best bet? If so, can someone suggest a particular model, keeping in
mind this job is meanial, therefore tooling costs are a concern.

Thanks in advance,

RB







  #10   Report Post  
Kent Frazier
 
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Default Roughing out 4" hole in .750 thick aluminum.

This is the best advice.
Use eye protection someone else said and is the only thing I can add.

"jim rozen" wrote in message
...
In article , Ryan says...

I have a task which requires boring four 4" holes in .750 plate aluminum,


Holesaw. Get the best bi-metal blade you can, mount it up
in a bridgeport, and use WD-40 for the cutting fluid.
Retract feed frequently to blow out chips. You can
cut from both sides, just pick up the pilot hole from
the first side.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================





  #11   Report Post  
dann mann
 
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Default Roughing out 4" hole in .750 thick aluminum.

You could have some gun nut friend let loose on it with his Browning.




  #12   Report Post  
Bob Swinney
 
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Default Roughing out 4" hole in .750 thick aluminum.

Jim sez: ..."and use WD-40 for the cutting fluid ..."

I respectively question the logic of using WD-40 as a cutting fluid. Why
WD-40? Yeah, I know it is kerosene based but why not use just plain
kerosene? I know kerosene is a recommended cutting fluid for aluminum. Or
better yet, "Liquid Wrench", also kero-based - it comes in a spray can
version also. Are you sure you aren't confusing the washing action (chip
removal ?) of spray-can WD-40 with cutting fluid efficiency?

Bob Swinney

"jim rozen" wrote in message
...
In article , Ryan says...

I have a task which requires boring four 4" holes in .750 plate aluminum,


Holesaw. Get the best bi-metal blade you can, mount it up
in a bridgeport, Retract feed frequently to blow out chips. You can
cut from both sides, just pick up the pilot hole from
the first side.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================




  #14   Report Post  
William G Darby
 
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Default Roughing out 4" hole in .750 thick aluminum.


"Jon Elson" wrote in message
...


William G Darby wrote:

I also like the idea of trepanning!

You could drill a hole at the center of the hole location and use a bolt
through the hole into a Tee slot anchor with a threaded hole to receive

it,
in order to form a pivot for your plate to rotate on. (like a rotary

table)
Pick up the hole center and traverse your table two inches away from it
(making allowance for the diameter of a slot cutter)

Take great care not to let the plate get away on you. Also a bolt with a
smooth shank would be best and cut to a length such that it bottoms out

and
locks up at the right depth. A bar clamped to the plate to provide better
rotational control would provide additional safety.


This sounds EXTREMELY dangerous!



Yes it could be dangerous!!!

But I would not use a big end mill and I would not try to hog into a 3/4"
cut either. That would be asking for trouble. I would go with a 1/4 slot
cutting EM and I would start with about an eighth inch depth and more if the
set-up felt right******

OK I just got back from the mill. I cut a 4.25 " dia hole in a bit of scrap
half inch plate and once I got the bugs out, it went along fairly smoothly.
The first thing I will say is that this method is a lot of work and
dangerous, but you do not need much equipment to get a big round hole or
disc.

I used:
1/2" drill
1/4" slot cutting EM at 5000 RPM
one Tee slot nut
one 3" piece of 1/2" threaded rod
two 1/2" nuts
one short heavy coil spring

I anchored the threaded rod in the center of the bed in the Tee slot nut.
Drilled a half inch hole where I wanted the center of the hole on the plate
to be. Then placed the plate over the threaded rod followed by a washer, the
spring another washer and two nuts locked against each other.

Picked up the center of the threaded rod and did an X move of about 2.25
inches

On my first attempt I had set the speed at 5000 but was getting only 1000
RPM. This had the effect of severely shaking the set up and unknown to me
the threaded rod slacked off and allowed my center to move enough for me to
notice it.

On the next and final go I got the RPM up to speed and planted that threaded
rod deep enough into the Tee slot nut sos it'll never come out. After that
it was clear sailing there was very little rotational pressure on the plate,
so it was not in the least difficult to control the rotation. At the same
time I was fully aware that the rotation had to be controlled at all times
least it be allowed to free wheel. (BAD) )^:

So the method is doable, and yes it is dangerous but I at no time was the
least bit concerned for my safety. Somewhat like operating anything else:
most anything can tear your hands off if you do not know what you are doing
or are inattentive.

I am including a few pictures of the set-up to you Jon and anyone else that
cares to see it.

Bill Darby






With a 3/4" plate, and a big end mill
hogging into a 3/4" deep groove, I doubt you could hang onto it.

Trepanning with a hand-carved single-point cutter in a boring head will
be a LOT
safer, and all you have to do is feed the quill.

Jon



  #16   Report Post  
JMartin957
 
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Default Roughing out 4" hole in .750 thick aluminum.


Run the saw fast and use plenty of WD40. Peck, and blow out
the chips every 1/8". Should take a minute a hole, tops, with a
bimetal hole saw. Less time if you use one of those nice carbide
hole saws.



With aluminum, little need for the carbide unless you want it just for the
larger gullets - which is an advantage.

Just make sure you're talking carbide teeth and not carbide grit. Doubt that a
carbide grit saw would get through a single hole in aluminum before it loaded
up.

John Martin
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