Hello
You could extend these rails to get alot more travel.
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Not sure these bits are really providing any extra suppprt
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I think these are the motors for the bed, I'm thinking that you've just not drawn the supports for them. If you moved them to the bottom facing up you could get more gantry travel.
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If your gantry went all the way forward it would give you two advantages, you could fix work to the front of the machine, so that you can work on all 6 sides of things and you could possibly mount a 4th axis on the front in the future.