Apparent Step Errors MKII

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10 May 2021 02:51 #208446 by jnwinkie
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

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10 May 2021 03:43 #208451 by BeagleBrainz
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.
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10 May 2021 04:19 #208454 by jnwinkie
Replied by jnwinkie on topic Apparent Step Errors MKII
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

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10 May 2021 04:33 #208456 by BeagleBrainz
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.
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10 May 2021 04:44 #208459 by jnwinkie
Replied by jnwinkie on topic Apparent Step Errors MKII
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

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10 May 2021 09:36 #208469 by tommylight
The reduction belt is way to loose so it will cause backlash that will end up showing in the parts made, and no springs on long belts, moving a lot of mass so springs will be springy at every direction change and it will also show on parts.
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24 May 2021 06:56 #210038 by jnwinkie
Replied by jnwinkie on topic Apparent Step Errors MKII
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
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24 May 2021 11:17 #210047 by tommylight
Overtightening belts will cause them to fail, they should be tensioned by feeling so they do not flex much when pressing on them, and there is no slack.
Adjustable idler will work fine.
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24 May 2021 13:03 - 24 May 2021 14:29 #210055 by samforsey12345
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
Last edit: 24 May 2021 14:29 by samforsey12345.
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24 May 2021 15:57 #210071 by tommylight
If i remeber correctly, the belts on reduction are loose on your machine, that requires slots on the motor mounts or adjustable idlers.

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