Greetings and CNC build soon to start, advice needed.

Hi everyone.

I am Nick from Greece.
I want to warn every member that this thread might contain very silly and hundred time answered questions.:loyal:

I am an aircraft engeener and maniac selfbuildingmyownstupidthings guy! resently , one year ago, I enter the world of cnc, I bought a new old stock desktop cnc with cutting area 420mmX320mm and replace the motors,controllers and interface in order to make it work.
Υesterday that cnc went to a new house,with the money I get and some designing help from a friend that design 3D printers, I will start soon my cnc router build.
The idea is to build a machine with external dimensions 1500x800mm, steel frame (to lower the cost) two motors at Y axis one at X one at Z, the purpose of the machine will be woodworking and mild metal cutting.
The friend-designer suggest the design below, I know that this is something it has been used at the past at MechMate machines but I do not know if there are any disadvantages since this is not a design that I usually see, what do you guys think?
Another question has to do with the ball screw according to their length, I am thinking to use 1610 ballscrews am I going to have any problem at Y axis since this is going to be the longer one?
Motors are going to be steppers, Nema 34 637oz for X, two Nema 34 1204oz for Y and one Nema 24 566oz for the Z, any suggestions and thoughts are welcome.

Cheers, Nick!

Hello Nick and Welcome,

Ok straight to the questions.

1610 is too small diameter at this length. You will get screw Whip at higher feeds. Better choice would be 2010 or better still 2020.
Reason why 2020 is better is because you can use ratio on the screw so it lowers the screw speed but still gives same speed as 2010. The ratio also gives another two advantages.? It increases motor torque so can use smaller motors. Lowers resonance to the motor/drives giving smoother performance.

This brings me nicely to your Motor choice. Nema 34 motors are not the correct choice for machine this size and type. They require much higher voltage to get decent RPM which you'll need for router. This means larger more expensive drivers and PSU.
3 or 4Nm Nema 23 are more than strong enough for router this size and if used with ratio like suggested then give excess power.

The Design I can't comment on because not really enough detail to see correctly. However I wouldnt use round type rails as they tend to wear quickly, lot less accurate and need lot more attention compared to square type . Which require very little attention and are super accurate/stiff.

Would also forget any idea of cutting Mild Steel with that design. Steel needs much stronger machine that what you have there.

Thanks for the reply Jazzcnc, very informative.
It seems that I lost four months waiting a decent cnc plan, at least you help me not to drop money to a machine that won't do the job.
Now I do not own a cnc anymore and I do not have a plan either.:frown:

Maybe I have to change the title to "Greetings and cnc build Not soon to start!":wink:

After Dean's suggestion and some study , I am going for 80x80x3 steel tubes, EGR20 linear rails and 2020 ball screws, for the 1500mm long axis and 1210 for the rest.
I am going for a stiff design so I can work on wood, main purpose and to be able to do some aluminum cncing also.
Am I on the right track now?

I keep reading , my brain has boil:kiwi-fruit:

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Originally Posted by Nickhofen

I keep reading , my brain has boil:kiwi-fruit:

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Excellent. Now a test to see if it is working...

You probably want to machine construction foam up to 300mm thick, 20mm aluminium sheet, maybe with alternate heads for 3D printing, plasma and laser cutting. I mean, you want to keep your options open, right?

Now I am burned!!! Lol

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Originally Posted by Nickhofen

Now I am burned!!! Lol

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i've about the same dimensions take a look at my build log here
http://www.mycncuk.com/threads/8717-...irst-cnc/page3

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Originally Posted by pierantoine

i've about the same dimensions take a look at my build log here
http://www.mycncuk.com/threads/8717-...irst-cnc/page3

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Hey thanks,I'll check it tonight after kids go to bed!:thumsup:

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Originally Posted by Nickhofen

Hey thanks,I'll check it tonight after kids go to bed!:thumsup:

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if a 2:1 ratio why not a 1620 or 1610 if you wants better precision...

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Originally Posted by pierantoine

if a 2:1 ratio why not a 1620 or 1610 if you wants better precision...

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That is another question for my potfolio I guess.:calm:

Design of the x axis, I prefer to build it tapered and to use bolts ,with minimum welding, since it is one man job and better to handle, plus I want to avoid metal stress.
Please feel to coment the design.X axis is made from 900x90x90x4mm steel structural sections.
Attachment 22238
Attachment 22239

At front and back of the steel tubes I will place two steel plates 5mm to stiffness the structure ,also the two plates ,left and right, are going to be 5 -7 mom.