Could this rod be used?

http://www.clasohlson.no/Product/Product.aspx?id=388148

It's in Norwegian but I guess you get the point?

And another thing...

Instead of using alum-angles or the like with a 90degree bearing setup, could you use square steel tubing with a configuration like a rollercoaster? one "wheel" on top and one at each side? (this is for the x-axis i'm thinking now)

Sorry for the possibly stupid questions, but my brain said that it could be more stable than the usual setup...

Christian...

Hi Christian,

I'm based in Sweden. I used the standard 1 metre rod from Clas Ohlsson.

Regards,

Michael

Yes you can use standard thread screws, but it is a better idea to use trapezoidal thread (acme) screws. These are specially designed for linear motion, where as standard screw rods are meant for fastening.

I think that trapezoidal thread will run smoother and faster with less axial play (more accurate).

Trapezoidal thread is not expensive, but the Trapezium Bronze or Plastic Nuts are more expensive then standard thread nuts. You can get good New Trapezoidal rods and Nuts on German Ebay, try searching on German Ebay for “TR12x3” or “TR14x4”. Both are good sizes for medium sized CNC machines.

http://search.ebay.de/search/search.dll?from=R40&_trksid=m37&satitle=TR14x4&category0=

You can also find good (cheap) solutions (easier than the rollercoaster idea) the for the Linear Guides or Linear Rods try searching on German Ebay for “Linearkugellager”

http://search.ebay.de/search/search.dll?from=R40&_trksid=m37&satitle=Linearkugellager&category0=

I could not find a Norwegian paper about Trapezium Thread but here is a swedish paper about DIN103 Trapezoidal Thread http://www.translev.se/katalog2/H.pdf

Greezt,

Markus

Try this Swedish supplier (Gothenburg) for trapezoidal rods and nuts:
http://www.wiberger.se/templates/gaengstaenger.htm

I've also been playing with the idea of three ball bearings and a supported steel rod for linear guides, still just on the drawing table:

http://gardsjoteknik.eu/cnc/Assem1_2.jpg
http://gardsjoteknik.eu/cnc/Assem1_front.jpg
http://gardsjoteknik.eu/cnc/Assem1_finished2.jpg

Hope you get the idea.

/Pär

I use a similar arrangement to what you suggest and it works acceptably though I have twin drive screws on the wide axis which eliminates twist so side load is minimal. If you are not supporting the beam from below remember that the taller the cross section is for a given weight the stiffer it will be in that direction. I use 2 inch by 2 inch box to stiffen is under the weight of the moving gantry.

This might help minimize sag:
maximum deflection=W*L^3/(48EI)
for a box section
I=(b*d^3-b1*d1^3)/12 ( note, linear with width cubed with hieght )
b=outer hieght
d=outer width
b1=inside hieght
d1=inside width
E=young's modulus
L=length between supports
W=weight to be supported by the beam

You need to make sure the units work out for your unit system ( I work in english units ). The result may be conservative depending on your supports but will help in design choices.

Hi I would like to introduce myself to the group. My name is Andrew Whyman. I have started to build a gantry milling machine & I have got a lot of ideas from your photos & postings which I would like to thank you all for.
Regards Andrew