Mendel90 variant - help request!

Hi all,

I'm currently designing a printer that is a variation on the mendel90. Within this design I have used a lead screw and nut arrangement for the x axis motion, while keeping the other axes as normal (y - belt, z - threaded rod)

Are there any mechanical implications I should be watching out for, or reasons why this wouldn't work?

(The only consideration I can see that will need addressing is the number of steps needed per unit travel, that will have to be changed in the firmware - but this is a coding issue)

Thanks in advance

Can I ask why you're replacing just the x-axis with a lead screw? If it's to improve accuracy only doing the X-axis only gets you half way there. I'd actually look more at replacing the threaded rods for the z-axis over the x and y.

The thought behind this decision is based on possible future extruder iterations that could generate a lot of heat, so we thought that the belt could deform/melt over the period of a long print. As a result, we thought that a lead screw would be more suitable.

By the time the belt would get hot enough to melt, your x-axis carriage would have long deformed. Plus, as long as you aren't idling with the heat on, the belt is going to be constantly moving. How much it moves obviously depends on the print, but it's still moving, circulating air, and is in open air anyways. Many people have commented about running their printers almost continuously. I'd think that if there was a issue with belts melting a different material would be chosen.

The other issue is switching to a leadscrew is going to require considerable redesigning of the x-axis ends, the x carriage, and x motor mount.

What are you extruding, and what is the design of the hot end?

Unless your leadscrew has a high lead like 20mm / rev you will probably need to reduce the max speed, acceleration and jerk settings as well.

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Thanks for the input, guys. Since making the original post, I have gone back on the lead screw decision and will probably stick with the belt transmission for the x and y axis

cdru, you're right. I think it was an ill informed decision that was made a while back - we were being overly careful. A belt will be fine.

A2, one of our ideas was to use a screw extruder to extrude wafer paste (essentially starch, but other ingredients can significantly affect the rheological properties of the mix). We have since gone off this idea for multiple complicated reasons (I spent a week reading about this stuff and talking to knowledgable people about it), not to mention that the extruder would be monstrous!

nophead, this was my worry. Since we're on a tight budget, we'd be buying a standard lead screw so the whole thing would probably be a lot slower. Also, to keep the same speeds would cause greater thrust on the motor (for high lead screw), which it isn't really made for.

To throw another variable into the mix, we're making the whole thing out of laser cut wood, which requires some redesign. This is due to all the 3D printers in our university constantly being in use or down - so it could be a useful idea for someone who wants a printer quickly, and as access to a laser cutter. Thinking of going with melamine coated MDF to add a little spill protection.

A2, I forgot to mention that a screw extruder for starch gelatinisation needs 15-20MPa of pressure, and 150/175 degC in the metering section.