View Full Version : How to set paralellity and 90 deg - ty of axis ???

jlagran he
12-12-2004, 08:35 PM
Hi.. I just finished my CNC Router frame (all iron)..
and the Stepper motor already insatalled..
look at: www.geocities.com/rcaeromodel
just klik "CNC"

But, I need to setup :
1. the parellity of two rails of each axis
(how to avoid coned? and twist , not in a plane? of two rails), and
2. the 90 degree ty between two axis
(to make sure an axis is 90 degree toward other axis)

Please help, anyone have experience setting this rails?
Is there any special tools?
I try to use water pass, but its not realy accurate..
any idea?


12-12-2004, 10:22 PM
looks like your machine is bolted together, so you should be able to use dial indicaters to bring the two y rails to run parallel, you can then use shims to bring them up parallel in the vertical plane. once that is dialed in do the x axis and then the z. You can purchase inexpensive dial indicaters, (unless you want .001" inch acuracy)
what kind of precision are you looking for?

jlagran he
12-13-2004, 12:16 AM
Thanks for fast reply..

Dial indicater yes.. I'll use it.

maybe 0.05 - 0.1 mm (0.002 - 0.004 inch) precision is enough for just cutting balsa for RC aircraft.
I'll by cheap dial indicater, china made, I think it's enough.

How about your?
What precision/accuration can be expected from a homemade CNC router?
anyone ?

12-13-2004, 09:04 AM
I'm not sure what's welded and whats bolted, but anywhere alignment is critical, bolted should offer some room for adjustment. Even if you use something like 80/20 thats fairly aligned to start with you need to be able to fine tune. Some good things to remember that might help:
-If you are hand drilling/cutting (not cnc machining/milling) use a cad program if possible and use 1 to 1 printouts taped to your material to check, mark or to center punch any drill or cut points.
-Drill mounting points (Like in opposite ends of the same axis, screw etc) at the same time by clamping the like parts togetger and then drilling through both. Then you know they will line up exactly.
-When assembling, slide the axis to one end without parts/rails mounts tightened down. Then tighten down that end, then slide to the other end and tighten down the other.
-If not precision milled/drilled, make your holes for mounting slightly oversized to allow room for fine adjustment.
Sorry to those that this stuff is obvious... just my 2 cents

12-13-2004, 01:19 PM
So, the key idea is to set one rail and then adjust the parallel rail. For the gantry you adjust one rail so that it is orthoganal to the table rails, then you adjust the 2nd gantry rail to be parallel with the first gantry rail.

In time you will add fine adjustment screws to help you set the alignment....

12-13-2004, 04:51 PM
It's like anything else I suppose, how accurate do you want it? In general there is usually one rail which is considered the "master" and it is ussually bolted/welded ect down and the second rail is dialed in to match it The master rail can have precision blocks behind it to ensure it is not "bowed", the slave rail can then utilize what you are suggesting, loose over sized holes, I personally like using "jacking scres" which are a block of metal bolted beside the slave rail (on at each end) a threaded hole in the middle accomodates a bolt that can be turned up against the slave rail to push it around.(as viperTX is suggesting) The advantage is you can adjust in little amounts using dial indicaters and achieve precision. I would then shim under the rails to bring them up to the same plane vertically. Repeat for each individual axis, Then bring the entire x axis to the y axis and then the z axis to the x axis, and then ofcourse re-check again....
There are many other ways to do achieve this, but I personally like this way, as it is the method I use at work and am most familiar with.