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Homemade CNC

Homemade CNC

Homemade CNC

(OP)
So I am designing a simple CNC Mill/Router just for an easy side project. I have it modeled but I am wondering what would be an acceptable THREADED rod to use to drive my axis. I realize that the BEST solution would be a BALL SCREW but those are super expensive. Right now I am thinking 3/8 - 16.

Any input would be appreciated!!
Thanks,

RE: Homemade CNC

I would consider using an Acme Thread instead of a normal screw thread for something like this, particularly if you're looking for smooth and consistent motion considering that there could be significant thrust load on the 'knuckle' if this is to be the primary feed screw.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
UG/NX Museum:   http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.
 

RE: Homemade CNC

I agree completely with John:

A screw thread ("V" or Whitworth etc...) has a tendency to bind, whereas the ACME thread promotes sliding even under load.

Adriaan.
I am a Mechatronics Engineer from South Africa.
www.martin-electronics.co.za

RE: Homemade CNC

Goto a junk yard and get yourself a few screw jacks. They have decent acme screws and can be picked up for a few bucks each.  

RE: Homemade CNC

Can you use a double nut to take up the slack? with one snugged against the other and the thread... this might minimise movement.

Dik

RE: Homemade CNC

Dik,
Anti backlash nuts are made specifically for these applications (low  cost/precision lead screws) and essentially function like two nuts with a spring between them. Not as good as a ballscrew still, but effective. Available here from Nordex http://www.antibacklashnut.com/

Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations

RE: Homemade CNC

How accurate do you think you really need to be?

A timing belt may very well be capable of the accuracy necessary, at much lower cost.

RE: Homemade CNC

(OP)
Thanks!! From reading this I will probably go with an ACME precision Rod. I don't really need tight tolerances but if I can might as well do it right the first time.

RE: Homemade CNC

How about scouting around E-bay and buying a used one!!  You know it probably works(test it) and will save you a ton of time and money??

RE: Homemade CNC

(OP)
I'm in it for the fun :), I just want to build something cheap too.

RE: Homemade CNC

What are you planning for the interface to a CAD program?

RE: Homemade CNC

(OP)
I am just in charge of the mechanical part. My buddy has sourced all the stepper motors and motor controllers required to manipulate the CNC. I just need to get it work.  

RE: Homemade CNC

Check out https://sdp-si.com/eStore/

I have used some components from them before. Seems ideal for a home project as you describe.

I would also love to have my own personal CNC Milling machine. Here is one on the American market http://www.taigtools.com/cmill.html

For sure, I will get or build one some day smile. Good luck with yours.  

peace
Fe (IronX32)

RE: Homemade CNC

Having recently completed my first 3-axis CNC router, go with the ACME lead screws. They're not that expensive to buy in lengths up to 6', and there are multiple sources of supply for adapters between your input shafts and the lead screw, whether of the single-start or multi-start variety.  Note that I did not say adapters between your steppers and your leads crews--you always want to include some kind of thrust bearing between your steppers and the loads they're driving.

All that said, the main thing is to just get it working.  After that you can use each new iteration of your machine to fabricate ever-more accurate components for the next!

Have fun...there's nothing like the first time you cut a part on your very own CNC!

Take care,

Tom
 

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