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Set your 12 o'clock position with a level... because


#1

About setting the 12 o’clock position with Ground Control,
Do you see what I mean?

12oClock

I find it difficult to visually set it straight.
Now you might wonder “How straight is straight enough?”
Well 1/12 of a sprocket tooth distance is 3 degree. That is:

12oClock_ticks

And this causes about 0,5 mm chain position error on a sprocket. If both sprockets have an error around 3 degree off. They either go opposite (one too high, the other too low) and the X, Y workspace is shifted like this: X shifted to the right from 0,55mm to 0,75 mm, and Y warped near side edges by 0,3mm.

Or sprockets have errors in the same direction (both too high, or both tool low). and the X, Y workspace is shifted like this: X expands 0,2mm to 0,3mm, and Y dips (or raises) at center top by 1,5mm.

That maybe not so much for you. But if you seek accuracy, everything adds up. And that one is scaling up if the 12 o’Clock error is greater that 3 degree.

But there is an easy solution to tune in better that 0,5 degree: using a LEVEL. :slight_smile:

Well here I suggest to use a level like this.

Note 1: This picture is NOT showing a chain exactly positionned as in the calibration task. Normally the chain tip would be lying on the sprocket. But the point here is to seat the level on the top link while you tune 12 o’Clock position to get the bubble centered on the level.

Note 2: When you calibrate 12 o’Clock, you want to place the second link of the tip of your chain on the 12 o’clock top position. Then attach that second link to the sled. Here is an example on the ring kit:

And make sure to attach your chains together with a safety solution like this to prevent accidents when chain tip snaps off.

Here is a nylon rope, as thick as would fit the narrowest chain link, that I installed lately, (shown in a simulated chain snap condition):

Overall, using a level is easy and makes your maslow more accurate. Once this 12 o’Clock is set accurately. You can start exploring you chain tolerances.


Creating the 12O'Clock calibration level in FreeCAD
List of sources of error
Soft Coper Clad Z touch plate
Most Critical Measured Dimensions
Accurate MaslowCNC manual calibration, how to
Sprocket's question
#2

This post inspired me to create a 3D printable tool to help set the 12 o’clock postion. Here it is on Thingiverse: https://www.thingiverse.com/thing:3361094

(and a picture)

It fits on top of the sprocket and has a space for a bubble level to be glued into it. It also places the bubble level 3 inches away from (the center of) the sprocket for increased accuracy of the level.

I also wanted to mention that you want to set the 12 o’clock position in relation to the top beam (so the the top tooth of the sprocket is exactly perpendicular to the top beam). So if your top beam isn’t perfectly level, then that could also be a source of inaccuracy when using a bubble level to set your 12 o’clock position.


List of sources of error
#3

Oh, and I also wanted to mention that there are a couple of other 3D printable calibration aids on Thingiverse that use a plum-bob technique to get the 12 o’clock position.

Maslow Motor calibration aid
Maslow Motor Calibration Tool


#4

Nice custom tool!

This was discussed a bit a while back and I think the consensus was that you want your frame to be as level as possible so gravity pulls how the chain sag compensation thinks it will.


#5

Hi @BradM,
To comment on your last point:

My experience is using a level to get a good horizontal potision of the frame is fine. And once it “looks” level, it is good enough. In any case, a fair top beam level will not warp the workspace distances.

But adjusting the sprocket 12 o’clock to a known exact position with the level will make a significant contribution to the MaslowCNC acccuracy through the entire workspace as shown in the above color diagrams.


Creating the 12O'Clock calibration level in FreeCAD
#6

This is another method that’s been discussed and that I have used in the past.

I do like your method though with the level on the two points. I wonder since they are so close if you can dial it in accurate enough.


#7

I like your design. Where did you get the bubble level you used? I want to print one of these to verify my setup.


#8

I bought a 10 pack of them from Amazon here: https://smile.amazon.com/dp/B0153BGY0U/


#9

Thanks


#10

Very cool! Is the purpose of putting the level several inches from the sprocket just to be able to better eyeball that the sprocket is vertical?


#11

By putting the level farther away, it should tend to amplify the angles. This will let you get closer to true level. If you could make the tool even larger, the precision will increase even more.


#12

Hmm I don’t think that’s true but could be wrong. But sure seems good to be able to sanity check that things look sane


#13

When I created it my thoughts were exactly what @MartinJ says above.
But now that you ask and I think about it, 1 degree is 1 degree. Whether the level is half and inch away or 12 inches away, the level is only going to rotate 1 degree. But it does give you the benefit of being able to better visualize the position of the sprocket. When you move the motor 1 degree, the tip of one of the “teeth” moves 0.065 mm. But at 3 inches you see it move .2 mm. It “amplifies” the movement by ~33%.


#14

And it looks cool! I’m going to print one this weekend


#15

I’m going to print one as well. I’m only about half way through configuring anyhow, but I may as well go get it all as close to right as I can. Mind you I have to wait for the garage to warm up above the sub freezing we’re at now for anything to happen, but having that hanging where I can see it every day will be a great motivator for when I can get back out.


#16

That tool idea is very nice :+1:.
I ended up digging into FreeCAD to make a CNC version of that Thing.
Here is what it looks like out of the chips.

And finally you’ll find here the FreeCAD project under a GPL licence.

Enjoy and share your thoughts in the 12O’Clock Level FreeCAD Topic of the Maslow Forum :slight_smile:

FreeCAD_capture


List of sources of error
Accurate MaslowCNC manual calibration, how to
#17

Yes please!

Edit: Tonight? No pressure :wink: . Just have 2 days off and the surroundings and adjusting the cut-out for my ‘level’ is minutes, but the sprocket would take me days.


#19

and a dropbox or so?
Edit: is it to big for email?


#20

Here it is the FreeCAD project under a GPL licence.

(I edited the first post too)


#21

Hope you don’t mind i’ll check the licence an other time :slight_smile:
Would never sell something that will give me an advantage to test fork firmware and GC with the best start for a manual calibration with my 3rd sled.
Thank you!

Gero

Edit: is this 0.17 or dev 0.18?
Edit 2: The workflow ->inkscape ->freecad would interest me.