Machining HDPE question

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I need to machine some HDPE to hold a bunch of specialized tooling for
automation cell at
work.  I need a 1.5D x 1.1 DP hole about 36 times.  I bought a 1 1/2" and 1 3/8"
spade
drill like the one you would use a hand drill to drill through pine.  

My two thoughts were that the 1.5" one might do the job or the 1 3/8" one would
make me a
nasty hole I'd hit with an offset boring head to finish.  The work will be done
on a
Bridgeport.

Thoughts, tips, tricks, warnings welcome.

Wes

Re: Machining HDPE question
Wes wrote:
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  Watch the rake on your cutting edge . If you allow the bit to self-feed ,
it will - all the way thru your stock . Cut the centering spur off the bit
and machine the cutting edge flat and square , it'll make a right purty hole
just a hair smaller than your cutter and a big pile of stringy shavings .
Don't try to clear the swarf until you're done cutting if you want to keep
your fingers . I use this stuff for one of the suspension system components
I make for the rubbermount Harley touring bikes .
--
Snag
Wannabe Machinist



Re: Machining HDPE question

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I wouldn't get near that bundle of chips with the spindle running if my life
depended on
it.  Wow is all I can say about chip production.

Wes

Re: Machining HDPE question
Wes wrote:
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I see you've some experience with this stuff too .

--
Snag
Wannabe Machinist



Re: Machining HDPE question

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One test hole.  What ever tooling I use, I'm moving a trash can next to the
bridgeport for
the chips.

Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes."  Dick Anthony Heller

Re: Machining HDPE question
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A plunge router and a suitable circular jig would be my choice for
this.
Wood-cutting router bits are usually OK for plastic, but there are
specialty
sharpened ones available, too.   Steel or carbide spiral upcut is
what I'd choose.

A spade bit will wander, doesn't self-feed at a reliable rate, and
isn't stellar
at chip clearance, either.

Re: Machining HDPE question
8d80-3c9919b1ea60@u13g2000vbo.googlegroups.com:

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And my choice would be a Forstner bit.  I make holes in HDPE a few dozen
times a year.  Twist drills won't do.  Spade bits make for rough holes.  
Forstners - fed at slow rpm and an adequately fast feed rate to prevent
softening of the work - make for a smooth hole in one cut.

LLoyd



Re: Machining HDPE question
On Thu, 23 Sep 2010 19:51:39 -0500, "Lloyd E. Sponenburgh"
<lloydspinsidemindspring.com> wrote:

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What he said, plus compressed air as a coolant/chip remover. Machining
plastic is the ONLY time I'll use air on a machine..........

Bob

Re: Machining HDPE question
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Use sharp bit and very fast feedrate!

i

Re: Machining HDPE question
"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

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I got a smooth bottom but rough sides using the spade bit on a sample.  For the
application it likely is good enough but I do like to do decent looking work.

The Forstner likely would be better.  I may just order a forstner bit.  McMaster
has HSS
or carbide edged, which would you choose?

Wes

Re: Machining HDPE question

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HSS will last for hundreds of holes in natural HDPE, but carbide is
better in the black material -- some of the pigment particles are large
enough to be abrasive.

There's an outfit up the road from us that will make any sized Forstner
for you custom.  I've seen such on-line, too.  They're only marginally
more expensive than top-of-the line bits in standard sizes.

LLoyd

Re: Machining HDPE question
"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

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I took your suggestion and used a Freud carbide tipped forstner bit.  1.5"
diameter holes,
32 mm deep, 40+ in all.  If I pecked right the currlies flew off, if I pecked
wrong, I had
to stop the mill and pick the wad off.  

What would you consider slow?  I was doing about 900 rpm, feed tended to be
agressive in
order to get chips that would break off when I retracted.

Hole finish was way better than that spade drill.

That was fun.


Wes

Re: Machining HDPE question

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I run about 700rpm doing holes that large, and feed as fast as the bit
will go through the work without hogging.  With standard rake angles
you're going to get on non-custom bits, you really need to clamp the work
down well, and use positive feed, or 1) the work will climb the bit, or
2) the bit will self-feed at way to high a rate to break off the chips.

Most of my HDPE holing is in the range of 10mm to 22mm, so I run more
like 1000rpm on those, but the other rules still apply.

I also check my bits for running true before using them.  The odd bit
(even the good brands, and ALL of the Chinese junk) will be slightly
larger at one gullet, or have a slightly deeper cutting blade on one side
than on the other.  The tend to score the wall of the hole.  With a
really good bit, I can get a hole in HDPE that almost looks polished.

LLoyd

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