Newbie questions

[Dan S]

Hello everyone.

I just want to say this website is awesome. I found it a few weeks ago while surfing the net. I have wanted to build a cnc machine for years. I’m a soon to graduate college student, so it will be a few months before I can start building, so I’m just working on the design of my machine. I want my machine to be capable of the following.

X = 24”
Y = 12”
Z = 6”
cutting speed 50 ipm
3d milling in balsa and other soft woods
.005” accuracy

I Plan on using a large 1.5-3 hp router for the cutting head, and mdf reinforced with angle iron for the frame. I’m not sure what other parts I need so I have some questions. Any comment or suggestions would be greatly appreciated.

1. If I use large steppers 175-250 oz/in and Xylotex boards, will my machine be able to do 3d milling in balsa and pine at 50 ipm or do I need to use servos and gecko drives?

2. At 50 ipm can I use delrin for drive nuts or do I have to go with metal of some kind?

3. I plan on using drill rod for guides, but what should I use for bearings? Linear ball bearings, delrin, bronze iolite?

When I have made some progress on my design I will post some images here.

-Dan Sherman

[Mr.Ed]

Looking at your questions, i would say you're no newbie !

Ed.

[NeoMoses]

Although I've personally never built a stepper system, I would think that you could achieve 50 in./min. with good sized steppers.

For linear motion, try ebay... there's no guarantee, but I would bet you can find THK rails or good thompson linear bearings in sizes that would work for you for little money, and it'll save you a good deal of time trying to find something that will work.

Hope it helps, and keep us updated on your progress.

Oh, yeah, Welcome to CNCZone!!!

[Dan S]

Hello Ed, NeoMoses

O I’m a newbie Ed, as my dad would say I know just enough about cnc to be dangerous.
Thanks for the welcome NeoMoses.


I will be spending allot of time on ebay in the future I think, trying to find guides and bearings and motors etc, i'll go blind for sure.



http://www.herbach.com/Merchant2/mer...Code=DCPMFIELD
I noticed this little motor the other day I thought it would make a great little servo to run with a gecko if I ran it with a 4:1 reduction. Anyone think this would work?

-Dan

[HomeCNC]

That would work for your needs. At 4:1 ratio that motor will give you about 340 oz/in peek and be turning the screw at 812.5 RPM. If you use a .2 pitch ball screw you will have a maximum speed 162.5 IPM but that also depends on the encoder count you get and how fast your PC will be that sends the steps.

[balsaman]

For a machine that size I would go with steppers and a xylotex board. You may get closer to 30-40" per minute rapids with that setup tho. I would go with 100-150 oz motors. Your motors should be in the 6 volts or less range, up to a couple of amps. Get nema 23 size. You will need a 24 volt powersupply. Bigger oz/in motors doesn't always mean more speed, so don't fall into that trap. Use a 10 pitch leadscrew with nema 23, or 5 pitch if you go with the heavier nema 34 sizes.

These are all suggestions, and not based on any mathematical formulas, but they are what I would do.

Yes, you can do 3D milling with a xylotex.

Eric

[marvinstov]

Hi Balsman and Dan S,

My experiences so far.

I have two machines, one home made 14x24x5 and a "Cheap CNC" 24x12x4. I use Xylotex controllers on both with a 30V power supply. With the motors that Jeff (116 oz/in) sells with the board I am getting around 50 ipm rapid speeds. Could get more if I had better lead screws. That is all with a 133 mhz pentium. I tried the motors that came with the "Cheap CNC" (145 oz/in) but got better performance with the 116 oz/in. Jeff says it is due to the wire size used in winding the coils. The 145 oz/in motors were rated at about 0.92 amps, the 116 oz/in motors are rated at 1.75 amp.... bigger wire... lower inductance...quicker charge time. In my opinion, the whole Xylotex setup is hard to beat for a machine that size. Cheap to get started, reliable, and cheap to repair or replace if needed.

Marv

[Dan S]

Thanks for the advice everyone. I am learning more and more every day. I have decided to go with servos, I need all the ipm I can get. My other hobby is r/c model yachts, and I want to be able to mill the wood parts and, small mold pieces for them. Going with servos and geckos will cost a little more, but if I ever want to go bigger or faster I will have the drives already.

Jeff, Eric I just love your machines; I hope my machine will be half as nice as yours.

Right now I’m just looking for some decent low cost servos, under $100 for 3, then I will have to scour ebay for rails and screws.

Good news I finally found an avatar that’s perfect for me.

-Dan