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trilect
12-15-2004, 02:14 PM
Well I've managed to get some extra cash and started putting together a shopping list.

I'm basing my first router on the free plans posted on this forum with a couple differences.

3/4" HDPE at 250.00 for a 4'x8' sheet
ordering a xylotex 3 axis controller and 3 double shaft motors from the same place

ordering mach2 with a 100 dollar cam program mentioned in another thread.

thinking about using drill rod in place of the gas pipe. (I can't find gas pipe of any quality)

I might try to increase the size of the bed to 36 x 48 (experimenting with 1/4-20 acme thread rod)

I'll make lots of pictures and have lots of questions.

ViperTX
12-15-2004, 02:39 PM
Is cost the main reason why you are going with HDPE instead of aluminum? Don't forget the power supply for the steppers.

ger21
12-15-2004, 02:43 PM
thinking about using drill rod in place of the gas pipe. (I can't find gas pipe of any quality)

I might try to increase the size of the bed to 36 x 48 (experimenting with 1/4-20 acme thread rod)



Whether drill rod, or gas pipe, it's gonna flex quite a bit at that length.

trilect
12-15-2004, 04:43 PM
Is cost the main reason why you are going with HDPE instead of aluminum? Don't forget the power supply for the steppers.


I don't have any decent machines to cut aluminum or work with it. I thought about casting many of the parts in green sand but I'm limited to the size I can pour at the moment.

As for the flexing issue, I'm thinking about some sort of stiffening system, something tack welded to the center of the rods on the rods edge connected to an adjustable mount inside the base. I'll be using rollerskate bearings at first and should have a clearance problem.

yukonho
12-16-2004, 02:55 AM
Your machine is WAY too big for the components you are planning to use. Cut it at least in half, preferably even smaller. I have a 10 X 20 machine now after my first 16 X 36" machine was a flexomatic. The 10 X 20 is solid and a much better machine all around.
May as well use Mach 2 for free until you find that you need more lines of code, then buy the full version.
Why not use 3/4" MDF. About 1/5 the price of your HDPE, and probably more rigid too.
1/4-20 is going to be pretty slow and will whip a fair amount too. Try 3/8 X 12 or 1/2 X 10 Acme precision lead screw. It is not that expensive and WAY better than threaded rod.
Please, do your homework before you start or you will only be disapointed. Judging by your post, it looks like you have only begun to plan this machine. Take your time and ask LOTs of questions, and heed the sage advice of those who have built machines.
colin

trilect
12-16-2004, 08:49 AM
I'm a hands on sorta guy, I don't really know what to ask until I run into a question.

I'm thinking about the flex, I had actually thought about setting up a couple bearing rails with different lengths the loading them up to monitor the flex, then adjusting the length down till I get a happy medium, same with the lead screw I do intend on using acme rod.

I used to make speaker boxes with mdf, I don't like the stuff and I think I'm allergic to something in it. I like how HDPE looks I've used it before and your right it flexes a bit more than mdf of the same thickness you really need to stack a few thinner pieces together to make it more rigid.

This will be my learning machine, I'm building with the intent on building a better one later, using this machine to form the forms for future part molds :)

coherent
12-16-2004, 09:00 AM
Just my 2 cents for what it's worth (most likely not 2 cents)... I'm not sure what you mean by not having any "decent" machines to cut aluminum. A carbide tip blade in a table saw will cut aluminum very nicely. Just go slow and just like with hardwood, don't set yourself up for a "binding" situation. I (and many others) have done so many many times with outstanding results. I've seen folks build a complete machine out of aluminum, mdf and hpde using nothing but hand held tools like a sabre saw, skill saw and drill. You just have to take your time and measure twice, cut once. Using stuff like extruded aluminum or aluminum channel will really simplify getting a ridgid, straight machine, but MDF will work fine for smaller designs. You can make your bearing mounts and such out of the hpde, but for larger structual parts it cost more, and is less ridgid than MDF. Use c-clamps and a straight edge with the tools listed above to get good, straight cuts. If you have a table saw and a drill press, so much the better. I've seen small machines that cut beautifuly that use skate bearings, gas pipe, angle iron or even drawer slides. It all depends on your budget and skills. Like the others have said, if this is your first machine and you don't have a mill or previous cnc or engineering/building experience of this nature, start small, and you'll end up with something usable that works and learn loads in the process... then go ahead and build larger. But, if you have an umlimited budget and can get stuff like high dollar bearings and rails, 80/20, ballscrews, all machined, cut, tapped, threaded to your specifications, then by all means go big... go really big! But obviously for most of us, the building and learning is half of the fun of this as a hobby. Ebay is a great source for parts, but rarely will you find things the exact size, shape or type and so although it's a great place for parts, plan on continious changes and modifications to your design to accommadate surplus parts. Folks here can and will help with any problem or question you have. So plan well, get creative, ask questions and have fun!
-Marc

ger21
12-16-2004, 09:03 AM
Here's a link to a short video showing how much flex you can get if your not careful.

http://www.mikenchell.com/teardrop/rodflex.mov

I believe he used 3/4 drill rod for the x, and 1/2" for the y. You can see both flexing in the video.
A link to the machine build thread. http://www.cnczone.com/forums/showthread.php?t=2763&page=1&pp=40

It's a similar design, thought you might be interested.

trilect
12-16-2004, 11:51 AM
That flex is pretty bad, It will be fun to work out. I was looking in my scrap heap the other day and found some bad struts off some car I worked on long ago. The rod in the struts looked about 3/4" diameter. I think I might use these on my y axis or z axis, its really hard metal and I can only cut it with my diamond wheel.


Its funny that you mentioned table saw and drill press, I think santa is bringing me one of each for xmas along with a dado blade.