Want to speed up feedrate, question about figuring that out

Want to speed up feedrate, question about figuring that out

sockles 07 Jul 2012 04:18

Im currently at 30mm/s at 1.577 flow. I'd like to speed it up a little bit and I remember back in high school learning about proportions.

I'm using MK6.

Since i'm using a stepper motor, can I just do a proportion say,

30mm/s 40mm/s
-— = --- And get 2.103 flow
1.577 ?

Would this approach work?

Re: Want to speed up feedrate, question about figuring that out

sockles 07 Jul 2012 10:05

Sorry that didn't come out as well as I wanted it too

30mm/s OVER 1.577 EQUALS 40mm/s OVER (?)

(?) = 2.103 flow

Re: Want to speed up feedrate, question about figuring that out

sockles 16 Jul 2012 14:57

Bump, anyone?

Re: Want to speed up feedrate, question about figuring that out

dnewman 21 Jul 2012 06:05

RepG's Print-o-Matic uses the following formula to compute the flow rate

(area of extruded noodle) * (length/second) * (60 second/minute)
--------------——
(area of filament) * fudge * (length of filament/revolution of gear)

fudge is 0.85 for ABS and 1.00 for PLA.
nozzle diameter used for area of extruded noodle (pi * d * d / 4)
feed rate (mm/s) used for length/second of extruded noodle
filament diameter used for area of filament (pi * d * d / 4)
diameter of gear used for length of filament/revolution of gear (e.g., the circumference, pi * d)

So, as you can see if you increase the feed rate by a multiplicative factor X,
then the flow rate increases by the same factor X.

Notes:

Odd thing is that RepG uses a default of 10.58 mm for the gear diameter BUT all the docs for the pinch gear state 10.56 mm (and I measured mine closer to 10.53 mm).

While RepG uses the nozzle diameter for the area of the extruded noodle, the extruded noodle actually has a larger diameter owing to extrudate swelling (aka, die swelling). You may get better results measuring the diameter of the extruded noodle at the target feed rate (the swelling is feed rate dependent).

Dan

Re: Want to speed up feedrate, question about figuring that out

Jetguy 22 Jul 2012 03:45

Odd thing is that RepG uses a default of 10.58 mm for the gear diameter BUT all the docs for the pinch gear state 10.56 mm (and I measured mine closer to 10.53 mm).

You're not thinking correctly here. Just like a toothed pulley, the effective diameter is larger than the real diameter. The reason is that the middle of the filament is the "true" effective distance. If you used a paper thin belt on a flat pulley, then yes outside diameter is very near effective diameter but when teeth and thick belts or filament are used, then it's entirely different.
For example, the pulleys used for X and Y axis are 17tooth 2mm GT2
From SDP SI website (FYI a good source when building your own bots and believed to be a major supplier to MakerBot Industries), the specs are
Part Number A 6A51M017DF0604
Unit Metric
Pitch 2 mm (GT2)
No. Of Grooves 17
Material Aluminum Alloy
Belt Width 6.00 mm
Bore Size 4.00 mm (Note they have been out of the 5mm bore size used by MBI for a while)
Flange & Hub Configuration 2 Flanges/With Hub
Pitch Diameter 10.80 mm
Outside Diameter 10.30 mm

That should stand out a .50mm diffference in diameter.

So the distance calc is simple with GT2 2mm belt 17 teeth or 17 2mm cogs is 34mm per per rev. Or use the PI* D method 3.14*10.80mm = 33.912mm

It then becomes obvious why you cannot just measure the diameter and expect it to be true "effective" diameter when calculating for volume of filament input. There is a significant "fudge" factor going on. It's true for the belts and it's true for the filament. Only through testing can you determine the "effective" diameter. One easy way to make the pinch wheel with a line and then feed it filament and measure exactly how much filament gives you exactly 1 rotation. Divide that number by 3.14 and that gives you the effective diameter.

Last edited on 22 Jul 2012 17:17 by Jetguy Show more