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cnc smoothrods are not parallel? Answered

Hey guys i am 19 years old and a few of us are trying to make a CNC.

well we are planing to use smooth rods for support .well the problem now is when we make the arch for y axis the holes that we made for the smooth rods to go through is not perfectly parallel ,so this resulted in the smooth rods to be slightly non parallel 4-5mm over 1 meter that's the error.Well my IITan friend is so stubborn in saying that this small error will make the carriage to stall.

So if there are any experienced personel please clarify this doubt for me, because this error wont matter so much according to my calculations.

thank you for looking into the matter


how thick/long are the rods? Is this a cutting machine, or a plastic printer?

Your going to have problems - linear bearings have very little play - if they did they wouldn't be much use.

Your run out will cause jamming.

In addition linear bearings need a very smooth surface to run on effectively. Your going to have to smooth off the surface of the rods you have to get it to work. Generally silver steel is used for bearing surfaces. It is hard and true.

Here is a trick since you are using particle board.

Clamp them together before you drill out the holes.


That's what I should have done,when I was making the arch,thanks anyway.

Now the only option left is to drill another pair of holes.

Plus I have another problem,when we purchased smooth rods .To reduce costs we purchased low grade smoothrods which unfortunately stalls the linear bearing sometimes.

There are a number of different linear bearings.

Teflon, brass, or roller bearing.

Teflon and roller bearing's work best with white lithium grease.

Brass bearings work best with oil or graphite grease.

Many liner bearings are sticky at first and need to be worked in with fine liquid compound. Especially if the bearings are pressure fitted into the bearing seat, it compresses the inner diameter. In some cases the bearing needs to be reamed with a special bushing ream.

This is of course assuming the bearing seats and the bearings are aligned.


If you have 4-5mm play in the guide rods it won't bind however it will vibrate because it is loose.

Although 4-5mm over a meter seams small, to a machine it is like trying to fit a 5 foot rod into a 4 foot hole.

Lets say at one end of the guide rods they are 5cm and at the other end it is 5cm 5mm and your tool mount is guides are 5cm.

It may slide from the 5cm side to maybe 1/3 of the way to where the guides are 5cm 2mm apart and the guides bind.

To a machine it is a funnel it will slide until it binds.

However that doesn't mean you can't still use it if you can make one end of one guide float so it doesn't bind.