View Full Version : Design issues with linear motion...

03-01-2011, 06:09 PM
Hello all,

I'm in the process of designing my first CNC router table. Please bare with me as I don't have an engineering background, so if what I ask comes across as 'simple' in anyway I'm sorry.

I'm currently looking at the 'PDJinc.' router table as a rough design guide (can be seen on the website), but there are a few changes that i would like to make in order for it to suit my budget and fulfill functional requirements.

Nothings been finalised yet, but I am hoping to build the machine roughly 6'x4'ish. The machine designed by PDJ uses linear rails and bearing blocks. These are hellishly expensive and for this reason i cannot justify using them. So the next plan is to look at using round rods and bushings. But I have read that they must be supported over a long length to avoid any deflection.

If I increase the thickness of the rod to say 1" could I stop any deflection or would it definitely have to be supported? Not sure if any other members have experienced problems with this at all?

If I did have to include supports along the rod, how do i come about them? Is it something i would have to put together myself or do any of you know a manufacturer that produces precision rods with supports?

Again, apologies if this all sounds rather amateurish, but expect more questions like this. Much more.


P.S. Will only be cutting wood.

03-01-2011, 06:49 PM
I think a 1" rod of 6ft will bend no matter what else happens, just not stiff enough!
The deflection over large distances IS the main problem with router tables etc which is where the open linear bearing come in so you can increase the height of the side plates to limit deflection etc
Most of the professional units have the running gaer fixed in some way to a 6 legged table and all this does not come cheap.
Have you thought of using simple bearings running against some square tube or some such, a cheaper alternative.


03-01-2011, 11:37 PM
To give you some idea i''m using 30mm round rails at 1.5m which is just about acceptable but bigger is always better.

04-01-2011, 11:13 PM
linear rails or round supported rail and open bearings are the only ways to get a 6' length without going to excessive thickness.... if you want a cheaper option look at vgroove bearings on angle plate or skate bearings on angle plate.... look at blacktoe and mechmate designs for ideas...