Values for gears etc


#1

Hello,
I would like to calculate the step rate for motor:

What is the ratio of the gear box connected to the NEMA17?

What is the number of teeth / ratio on the two visible gears?

What is the pitch of the lead screw?

What are the specs of the ‘discov3ry’ branded syringes ? (inner diameter or ml per mm, etc)

Thanks,
Ian.


#2

Oh and what is the deg per step on the motor.
ie how many steps per revolution.

Thanks


#4

Hi Ian,

What do you need all this info for? It should be easy to count the gears on our product – the cover comes right off. And our cartridges can be easily measured, as can the lead screw.

Regards,
Charles


#5

Hello @Charles_Mire thank you for replying

Like I said ‘all this info’ is to calculate the step rate for motor

Its a pain in the arse to pull apart everything to measure/count when I thought it would just easier to look it up. Having failed that: ask for the information. [ You don’t buy a toaster (or any device) requiring dismantling in order to make it useful. ]

I haven’t seen any related detailed information and plan to be a bit more sophisticated than the guess work that is available.

and, I thought by asking, things would be documented for others in future.


#6

Hello @ian

The reason I was asking why you wanted these values is because when you use the “M92 Exxxx” gcode command (where xxxx is the steps/mm), the xxxx value can vary depending on the printer. It’s roughly 10 times the value used for printing filament. For the Ultimaker printers, we use “M92 E2000” – but we’ve had some customers who have needed to use “M92 E10000” for the same material just because they are using a different printer.

We designed the Discov3ry so as to allow for a great deal of tolerance with the material being printed, and the success of a print depends on a number of factors, not just the step rate of the motor. We’ve provided a lot of guidance through this forum, our blog, and our YouTube channel, and our customers have been able to make great use of our technology with the broader information.

So is there a specific reason you need all these exact details? Because maybe there is a use-case scenario we haven’t thought of where we could provide better clarification, and it might involve more than just engineering details.


#7

Hello @Charles_Mire

I don’t mean to dismiss the information that otherwise provided, it just doesn’t answer what I’m looking for. Namely an accurate guide to steps/mm that is derived from the original questions I asked, as calculated below. I’m a little thrown by the silence and then cagey-ness towards finding out authoritative values.

steps_per_mm = motor_steps_per_revolution * gear_box_ratio * gear_ratio_2 / lead_screw_pitch * over_stepping * normal_filament_cross_section_area / plunger_surface_area
where
gear_box_ratio and gear_ratio_2 expressed as many turns to drive the output once


#8

I should also point out use normal filament diameter in slicing software. Not the diameter of the plunger.


#9

The diameter if the plunger is definitely not the right value to use for slicing, nor is the plastic filament diameter. Use 3.125 mm, which is the internal diameter of the tubing for the Discov3ry.

The unknown factor in your equation is material compressibility. Even if you hardcode all those elements in your equation, the paste material compresses, and this compression coefficient is different per material. Pressure must get built up to overcome this compression and induce flow through the tubing. There is resistance to the flow in the tubing, which is a function of the internal diameter and the length (so don’t use a 6-foot section of tubing). The final part in getting the material to print properly is choosing the appropriate nozzle diameter. If too small a nozzle is chosen, the material simply will not extrude fast enough to print, if at all.

Ideal paste materials for 3D printing must exhibit shear thinning. Then the viscosity of the material is the second most important parameter. Both of these parameters together influence the flow of the material, and the steps/mm just becomes a more abstract detail.

Are you building a custom printer and trying to hardcode all these values in?


#10

I don’t know how to reply to this without sounding like I’m being a troll, or how to better ask for the information I desired than I already have.

So I’m moving on.
Have fun,
Ian.