HDPE

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HDPE

Postby bdring » Sat Jan 08, 2011 6:37 pm

I use HPDE for some of my parts. It is a great material, but it is difficult to find at a good price. I have found that a good source for it is plastic cutting boards from stores like Walmart or Target. The problem is the quality and consistency. The thickness can very from store to store. I like at least 3/8" thick, but often settle for thinner.

Some of the translucent white ones tend to be a little stringy when cutting and spirals can get caught on the router bit. This can ruin parts if it rubs and melts. The more opaque white is my favorite, but it is harder to find. It make chips rather than spirals. After not finding any of the white this week, I started searching on line.

I ended up at cuttingboardcompany.com. They sell commercial sized board 18"x24" for about $25 at 1/2" thick. Also, there is no trough at the edge which is normally just wasted material for me. They sell them in a variety of colors. This helps restaurants segregate food types. I bought 4 sheets of the blue (cooked foods), but was tempted by the red (beef) and yellow (poultry) for the cautionary look for the tube brackets.

I test cut some parts and it cuts like a dream. Pure chips, no spirals. I cut it with a 1/8" 2 flute bit, a cutting speed of 50 inches/minute, plunge of 20 ipm and a depth per pass of 0.13.

hdpe.JPG


Note: The stringy material tended to have most of it's trouble on the plunges. Ramping down into the material helped a little.
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Re: HDPE

Postby hoda0013 » Sat Jan 08, 2011 10:30 pm

I'm not sure if this is actually HDPE, or if it cuts well with an endmill, but it might be worth a try and the shipping is free and it comes in many different sizes.

http://cgi.ebay.com/1-2-X-24-X-54-BLACK-KING-STARBOARD-POLYMER-HDPE-/260368776070?pt=LH_DefaultDomain_0&hash=item3c9f303b86#ht_827wt_698
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Re: HDPE

Postby bdring » Sat Jan 08, 2011 11:00 pm

Good find

It is hard to tell exactly, but it looks the same. The price is almost exactly the same, but I paid about $6 a sheet for shipping. It looks like they only stock black and white.

I like my blue, but maybe next order I will give their black a try.
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Re: HDPE

Postby trwalters001 » Sat Jan 08, 2011 11:25 pm

How does it cut with the laser?
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Re: HDPE

Postby bdring » Sat Jan 08, 2011 11:40 pm

I did not try it. I have heard it does not do well. It melts badly and get discolored. I have never tried anything that thick either.
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Re: HDPE

Postby Tweakie » Sun Jan 09, 2011 10:43 am

The laser penetrates the stuff beautifully but it melts back into the kerf and is virtually impossible to cut. I suppose experimentation with air assist pressures and gasses may be successful but I gave it up as being a bad job.

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Re: HDPE

Postby bdring » Sun Jan 09, 2011 11:57 am

Let's build a laser guided water jet. That ought to do it. :D

http://www.synova.ch/english/synova.html
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Laser-Guided Water Jet

Postby trwalters001 » Thu Jan 20, 2011 4:12 am

That's really cool!

I wonder what wavelength laser they're using? It couldn't be CO2 because water absorbs 10.6 microns.
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Re: Laser-Guided Water Jet

Postby r691175002 » Thu Jan 20, 2011 6:37 am

trwalters001 wrote:That's really cool!

I wonder what wavelength laser they're using? It couldn't be CO2 because water absorbs 10.6 microns.


Their technical specs say 532nm and/or 1064 nm.

I know that 1064 is a commonly available diode wavelength as well as the lasing wavelength from nd-yag (which is almost certainly what they use as it is pulsed). I can't imagine that they would intentionally use 532nm although I have read that at high enough power densities laser wavelength can double as many materials are optically non-linear. According to sams faq, people blinded by infrared often see a flash of green because the fluid in ones eye doubles the frequency into the visible range.

They list laser diode pumps as a future improvement so they are probably running flash lamps into a rod of nd-yag. They also claim 200W of cutting power; however they also list a typical co2 system as requiring 1500W so one might be able to use less.

This looks a lot more plausible as a diy project than a true water jet because the pressure is much lower and you don't have to deal with abrasives. I'm not sure what the technical difficulties are in machining a nozzle that can produce a narrow stream of water though (they claim 0.005mm). I'm guessing it would have to be a laminar flow nozzle which would probably require EDM or some other expensive process.

To be honest, the attainable energy density one would get from keeping the beam completely internally refracted would probably be worth the added expense. The technology looks really damn good. With a narrow enough water jet powers of 10-20W should be able to cut fairly well.


The name is dumb though, it should be a water-guided laser not laser guided water.
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Re: HDPE

Postby trwalters001 » Fri Jan 21, 2011 3:35 am

I used to work on a water-jet system. The nozzle had an orifice made of sapphire. They came in boxes of a dozen. Just screwed into the nozzle housing.
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