Machining HDPE question

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Wes wrote:

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
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Wes wrote:

I see you've some experience with this stuff too .

--
Snag
Wannabe Machinist
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Use sharp bit and very fast feedrate!

i

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.