Tip 3: Repeatable accuracy - straight bed

So this tip is one of maybe 4 tips about how I was able achieve repeatable accuracy. I now have accuracy to the millimeter that is repeatable for 1,000s of movements.

I expect some of these tips are known to some of you and some folks won’t need the level of accuracy I’m talking about, but you still may get some benefit from knowing this stuff.

If you have ordered the new Farmbot Express this may not apply to you as that version wasn’t designed for the level of accuracy I talk about above.

This was the first tip I was given when I got a Farmbot - wood is your enemy…

It is much better to mount your Farmbots linear rails to metal because it is usually straighter than wood and less likely to worp over time from moisture, temperature fluctuations and sun exposure.

I was told to use lengths of aluminum angle and mount the Farmbots X axis linear rails to that. But any lengths of straight metal which isn’t prone to rusting will do. At the moment I am using linear rail for the bed because I can source that cheap.

It’s also important that the 90 degree angles on your bed are exactly 90 degrees. To achieve this make sure the beds X axis sides are exactly the same length, same goes for the Y axis sides.

I recently somehow bent one of my gantry plates and that didn’t help accuracy lol, so check the 90 degree angle in the gantry plate is also correct.

Also it’s good to use a spirit level to ensure the bed isn’t warped. I think that is also specified in the Farmbot documentation.

Hey Whitecaps,

Can you provide us with some photos of your build?

Others may benefit from being able to see your set-up.

Marc

Sure @Marc here’s a pic I took when I was beginning the build that demonstrates what I’m talking about.

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Awesome Build! Thanks for letting us know exactly how you have done it!

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It looks like you put the Farmbot linear rails on another set of linear rails… but how did you mount the 2nd set of linear rails to the wood? Without completely F’ing everything up?!?

yes, wood is your enemy… I wish that was the first step in the instructions… so many headaches to be avoided…

Hey @TroyD I don’t mount it to wood.

Again many people don’t need this level of accuracy and I also have other posts coming that even if you aren’t mounted to a bed that isn’t 100% accurate will show you how you can improve accuracy.

I have seen another picture of a build on the forum that better demonstrates this. It places a metal bed on top of soil, note they didn’t fill the bed with soil, it just sits on top. I searched for this pic but couldn’t find it sorry. If someone can post a link to it that’d be much appreciated.

The original tip I was given was to use angle \ L shaped rail, rather than linear rail and then mount that to wood using cheap brackets, everything bought at the hardware store.

Another option is to mount the farmbot linear rails on spikes, then line up pieces of string that are perfectly perpendicular, hammer the spikes in along the lines and do a 90 degree + spirit level check. Note the join in the linear rail may need to be enforced to ensure they stay straight. I have never tested this option. I think laying the metal bed on top of soil is probably easier.

Hope that helps.