Wow, I posted a reply here, yesterday afternoon and it's now gone. It actually bumped this thread to page #3. From the chat, I see there were some forum problems, yesterday.

Anyway, it was a question on UHMW PE. Would that be even better than HDPE or not, for making nuts?

 

Well, I already bought me a cutting board and I have to know if it's HDPE or LDPE. So I decided to try a simple density test, to see if it is easily checked. If you want to skip all the technical stuff, then just jump to the end.

The density data for the two is:
LDPE is defined by a density range of 0.910 - 0.940 g/cm3
HDPE is defined by a density of greater or equal to 0.941 g/cm3

I needed a liquid, with the right density; to do a buoyancy test. But I lack the right measuring equipment. So I will have to rely on data. Found this website, with the need info: http://tlc.ousd.k12.ca.us/~acody/densitylesson2.html
They meausre Isopropyl alcohol as having a density of .87 g/cm3. I assume this is the off the self rubbing alcohol (70%),like what I am using, as the pure stuff is less dense (.79 I think). A 50% mix with water gives a density of approx .94 g/cm3, the exact dividing line between LDPE and HDPE.

To verify the liquid is at the correct density, I needed a known samples of each material. This is easy because containers are labeled with a recycle triange, material#, and as it turns out they were even stamped with the text, LDPE or HDPE respectively. My HDPE sample was from a milk jug. My LDPE was from a yellow, ice tea jar top. I placed both samples in the liquid. The yellow LDPE floated. The HDPE was actually close to neutral buoyancy and tended to stay where you put it. In other words the HDPE was the exact density of the liquid. So the test works.

So I cut off a piece of my cutting board and it's a tiny bit less bouyant than the yellow LDPE, but definitely a floater. That's pretty good proof, that my cutting board is made from LDPE.

Here is a pic of the results: Attached files

 

Kyyu,

Good test. This lets you know what you’re dealing with.
Also note the minute you start to machine it you know what type of material it is, as LDPE melts and wraps around your tool and spits melt-y type chucks of material out. And the cuts look like crap quite frankly.

On the question regarding UHMW PE:
You have to be real picky and choosy here. There are many grades of all types of plastic and this is one type of plastic you want to get your info on before placing an order.

It's assumed the UHMW PE is great due to its abrasion resistance and impregnated oils but this is only the skin of the surface.

If you want to make your own liners, nuts, slider rails etc. Do your research. No one likes to spend $50-$100 on material just to find out it works for a minute and ends up being a disaster. Also you guys need to know that it is important that you machine your threads correctly. When using 1/4 hardware store typical type all thread for your drive or any other type of all thread that lends it's self to flexing that simply using the all thread it's self is not the route you want to go to tap the plastic. This will be a nice fit and you will get ok results but you feed/rapid speeds are going to suffer. You want the Nuts to be able to rock left to right and up and down on the thread but when you go to push and pull the nut back and forth there should be no play.

Getting these things just right can really be a pain and right when you think you got it you find something else isn't right.

I had to design and have a custom tap made for the ones I do, and that’s after spending many dollars trying to find the right tap which I never did and I bought taps from every where but taps are made for bolts and nut, either to tight or to lose. Do your research or other wise you'll more than likely find you self back where you started.



Eric

 

Nice test, Kwok. I'll have to replicate your method to make sure my cutting board is the HD type. But then again, I could just put a piece in the lathe and as Eric says, I'll find out soon enough.

Yoram

 

Thanks for the info dbtoutfit. I will have to press on. That's why these forums are so great. We can share our failures and success. I just went ahead and ordered a HDPE cutting board from usplastic, 1/2" x 12" x 18" ~$18 shipped.

Tiger Pilot, let us know what you find out. I wouldn't be able to tell that way, not having cut either of the two materials.

btw, I did another test and found the exact density of my cutting board. Again, not having the right equipment, I figured I could us an eye dropper. Put 15 drops of rubbing alcohol in a container. Put the cutting board material (here after to be refered to as cbm) and the yellow LDPE in there. Obviously they both sank because of the low density of the alcohol. Then I put drops of water in until they started to float. I got the cbm neutrally buoyant with 5 drops of water. So it was 3 parts alcohol and 1 part water:

So the cbm density = 0.87gm/cm3 + [(1gm/cm3 - 0.87gm/cm3) x 1 / 4]
= 0.87 + [ (1 - 0.87) x 0.25 ]
= 0.90 gm/cm3 :ugeek:

-Kwok :mrgreen:

 

My cutting board came in the mail, today. Is it me or is everything lately, shipped by ground, getting here in two days? Cut off a test piece and it sinks like a rock; so it's the good stuff!

-Kwok

 

That is so cool - I never thought about testing the density of the material like that!
Now, where is that stinking eye-dropper? :geek:

 

I have a quick update for y'all. I finally got my SmoothStepper and hooked it up, using my Dell Latitude D800 laptop. My SmoothStepper board is powered directly by the USB cable from my laptop (although you can use a regulated 5V power supply if you want.)
After connecting everything, tuning and recalibrating, my PP is essentially running at the same speeds that I could obtain with my P4-2.6GHx desktop, without neutering the network or anything else. In fact, I've intentionally been working on the tuning with my Network card installed, with the 'Net and one folder on my desktop accessed from the laptop, at the same time.
The SmoothStepper doesn't seem to care - it just drives the PP like it's supposed to.
Last week I downloaded a program called RMClock.exe that allows me to force the CPU to stay busy, in "high performance" mode, so I'm going to try that next, to see if I can increase the results farther. Using it to test, I learned that my CPU can (and will) drop from 1.7GHz down to 560MHz up to 16 times per second, and that was another part of what was driving the Parallel Port signal crazy. Since the SmoothStepper runs from the USB port, it may make no difference - - - but I'm a geek so I have to try it. :geek:
Anyway, after adjustments (saw a couple missed steps) I'm now set at
X= 1049.39 Steps, 60 Vel, 20 Accel
Y= 17186.79 Steps, 45 Vel, 15 Accel
Z= 18032.37 Steps, 35 Vel, 15 Accel
and I'll leave it there while I make blue dust for a couple weeks.

 

Hey, here's something I just found, cutting the Tensor-28. FFF is not flat, nor is it a constant thickness.
Well, when a thin (~5mm) area coincided with a narrow (2" wide) upward wave, the sheet lifted off the X-roller so well, the 3/4" pipe wasn't heavy enough to hold it down, so the sheet STOPPED MOVING! No, the sheet wasn't snagged anywhere - the roller was just barely touching at all.
I removed my 3/4" pipe (remember those screws in the side of the lid?) and removed one of the shaft collars from the 1/4" shaft, to slide one end of the shaft just inside the PVC end-cap. Then I poured the pipe full of sand and, after a bit of cussing, finally managed to get the shaft to come back out of the hole, to put the shaft-collar back on. I was going to use BB's, but I couldn't find them. I figure I got about 2 pounds of sand in there (forgot to do pre / post weigh measurements).
The upshot is, that sheet fed through the PP like it really should, when I cut sheet 2 of the Tensor-28.
Not everyone will have this problem, because I raised my top surface by 1/8" to reduce the amount the feed roller was lifting the sheet upward. As a friend at work says, "Every solution creates its own set of problems."
By the way, I also had to recalibrate my X-axis, because a 40.000" command caused the sheet to move 40.375", after the fix but before recalibration.

 

You might tread lightly here. Too much weight and you will have problems too.

I have a third roller installed just for this problem and when I installed it as a 1" roller instead of a 3/4" roller, the extra weight of the roller caused additional problems and I had to change the roller out for a smaller diameter ie: less weight rod.

 

Flashsolutions, I thought of that, but I added weight to the roller directly pressing above the feed roller. The extra 3rd roller presses down on the flat table, hence extra friction / drag.
If I ever start running "squishy" foam, the extra weight will possibly cause some distortion, so maybe sand is better than steel or lead shot in this instance. Anyway, it worked, and that's what I wanted to tell folks about.

 

Ahhh! Yes, makes sense. I didn't realize that was the roller you were talking about. Not sure how that will affect EPP foam cutting. Let us know how it does when you run some EPP thru it.

 

(copied from another post) . . . . the wiring for the LED array was furnished by this website: http://led.linear1.org/led.wiz

I used 8 of the 10mm superbright LEDs available from Radio Shack @$2.79 ea. Yowza!
More photos - I'll edit the post later.







Attached files ="http://www.phlatforum.com/xenforo/converted_files/2983=1100-2909-08.JPG">

 

More photos




Attached files

 

Good work Dorsal, looks great. I'm glad the Filter worked out too.

Eric

 

Thanks for the compliments guys!
Mark, the SmoothStepper is working great, now that I got the diode/capacitor filters soldered on. The RF interference is also the reason for the wire-mesh (metal window screen) covers over the holes. With the screws installed, the mesh is electrically connected to the box, and the Faraday cage is complete.
Michael, some older laptops have fully functional parallel ports, and others have PCMCIA slots that are fully functional. I think the better pcmcia or cardbus-to-parallel adapter cards would have worked, but a good one is only $25 less than the SmoothStepper. You would need to run the "Drivertest.exe" file in the Mach root directory to know for sure.
From what I've been able to read, the cheap Chinese adapter cards will NOT work to drive any router, mill, lathe, hotwire or laser machine with a parallel-port interface - - they are only adequate to run a parallel-port printer from a laptop, to print out your horoscope or letter from Grandma.

 

Oh - my tables aren't wooden, they are made of some 1/2" Gator-board that I had salvaged. Gator-board is EPS sheet with 1/32" plastic sheet laminated on both sides, so it's very stiff and light, but needs a saw to cut cleanly. It had some 3/4" EPP strips bonded on one side, with some phenomenally resilient adhesive, so I just left that on the underside of the tables.
When I added the 3/16 HDPE sheet to the top of the table, I needed to slide them "up" to match the new height, so I had to slot the holes for the screws. The pieces of 1/4 MDF were scraps that I glued on to keep the screws from crushing the slotted areas of the table "legs".
btw, they work very well, as I often set my laptop up there when I'm just reading emails or watching some "RC-porn" (videos of anything radio-controlled).