Apparent Step Errors MKII

Hi All;

Looking for some advice. I have been building the MKII brain using the MESA cards RodW was able to supply. In doing so I thought I would do a bit more fine tuning on the table itself. It is becoming apparent there is a design flaw, leaving coordination of X-Y out and holes being less than perfect (see images). I am using IGUS bushings and wonder if they are causing too much drag on the movement of the gantry?

I have employed a 4:1 reduction as suggested by Tommy but now also thinking that I either try changing the IGUS bushes over for 608ZZ bearings and mounting blocks to hold the 10 bearings or if I need to junk the design and start again. Rod you were spot on when you said building one of these tables is not a poor mans sport

Thanks all

John

Are you thinking of replacing a linear bearing with a radial bearing for Linear movement ?

Without any pictures and or details of your linear movement setup it's kind of hard to suggest anything.

Thanks for that;

I guess I am proposing that the current IGUS bearings could be causing drag on the X axis and that by replacing them with roller bearings may alleviate the issue of the apparent out of alignment circles.
Pic 3 and 6 show the IGUS bearings which are really low friction collars.
If I can show any more information to assist please let me know.

Regards

John

The squares look ok.

Ok I guess I misread, it's not the linear movement setup, it's the gear mount setup that you think maybe the issue ?

Have you considered the pen mounting maybe causing issues, it could be moving on the change of direction ?

One of the axles do not look like the best material, which could be causing issues.

Yes changing from a bush to a bearing would be a good idea. Have you thought about pillow blocks ? They maybe the easiest option for a retro fit.

Thanks;

I'll try 3D printing a few blocks to see if that helps and if so will machine them out of Aluminium. The circles are almost as described in the cut outs I made in some 4mm plate. If you can think of anything else, please let me know. Much appreciated!
Cheers

John

Thanks Tommy, so I am clear, you suggest not tension springs for the longer belt, just pull them as tight as you can?

As to the reduction belt, would an offset idler system be OK? I am thinking of a 6201Z bearing with the following sort of arrangement.

Thanks

John

Something like this seems to work ok for tensioning the belt.

forum.linuxcnc.org/media/kunena/attachme...10314_105843_748.jpg

It is a clamp/tensioner in one. I cut a short length of belt and have set the belts face-face one tooth out of phase. The two pieces of steel then clamp on two nice flat surfaces.
M6 fine threaded bolt welded to the clamp part, with two nuts allowing the clamp to be locked tight once tensioned.

Looking at your initial reduction I have to agree with Tommy, it looks very loose. How about just slotting the stepper motor mounting holes and pulling the belt tight before locking the motor in place.

Another thing to check is that the pulleys are properly tightened/doweled into place on the shafts. I had some interesting results before figuring that one of my pulleys was slipping on the shaft.

From pics in your other thread, it's hard to see, but are your belts horizontal across the width of the plasma cutter? If not, at the extremes each step won't give you precisely the calculated distance as the belt is not pulling along the line of action of the torch