Frame brace and Feet for the Mendel

brnrd

Frame brace and Feet for the Mendel
September 28, 2011 01:07AM

Registered: 13 years ago
Posts: 1,780

I posted some additional printed parts at thingiverse.com that might be of interest to others: A frame brace to stiffen the Mendel frame that can be installed on the orginal Sells or the Prusa Mendel and push-in feet for the Sells Mendel.

IMG_1680_preview_medium.jpg

IMG_1685_preview_medium.jpg

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hardtoe

Re: Frame brace and Feet for the Mendel
October 04, 2011 03:10AM

Registered: 12 years ago
Posts: 74

I printed out one of the frame braces, going to see if it helps my current print.

SFACT closed up two of the holes for the zip ties on the long end, not sure why, the STL model had them open. I also had to ream the slots for the 8mm rods, just too tight otherwise.

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brnrd

Re: Frame brace and Feet for the Mendel
October 04, 2011 07:11AM

Registered: 13 years ago
Posts: 1,780

Your flow rate might be to high. Did you enter the measured diameter of the feed in SFACT? Also, how did you calibrate your firmware value for extruder steps per mm?

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hardtoe

Re: Frame brace and Feet for the Mendel
October 04, 2011 12:45PM

Registered: 12 years ago
Posts: 74

after i made the print, I marked my filament and extruded 10mm. it was a bit over, about 10.5, so i reduced my steps per mm by 5%. my filament diameter is set to 2.8mm in SFACT, but i haven't measured it myself. i should probably pick up a micrometer today and check it out.

there's also the packing ratio in SFACT, right now it's the default of 0.85, not sure how I would calibrate that.

Edited 1 time(s). Last edit at 10/04/2011 12:45PM by hardtoe.

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brnrd

Re: Frame brace and Feet for the Mendel
October 04, 2011 01:37PM

Registered: 13 years ago
Posts: 1,780

Since you already set you steps per mm to the measured value, you don't need to worry about the filament packing density ratio. Just leave it at 1. If you printed with it at 0.85, that might be the reason that you were extruding too much.

Also, if you don't have a caliper to measure the diameter, it might be good enough to use the specification from the manufacturer.

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dean448

Re: Frame brace and Feet for the Mendel
October 05, 2011 07:46PM

Registered: 12 years ago
Posts: 139

I understand the feet.. but don't get the need for the frame brace. Is the flex coming from the printed corners? Very high print speeds? Can't be the threaded rods...

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brnrd

Re: Frame brace and Feet for the Mendel
October 05, 2011 10:43PM

Registered: 13 years ago
Posts: 1,780

In the original Mendel, the motherboard sheet which mounts on the front across the threaded rods and the stepper controller sheet which mounts in the bottom threaded rods provide side-to-side stiffness. If they are not mounted, you can actually see the frame vibrating in that direction once your feed rate gets beyond 30 mm/s. With RAMS and other electronics, there's no need to mount the motherboard sheet in front. The frame braces take the place of the motherboard sheet and cuts down on the vibration.

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Nudel

Re: Frame brace and Feet for the Mendel
October 09, 2011 10:19AM

Registered: 14 years ago
Posts: 689

Have you tried moving the top vertices closer together, to make a sort of trapezoid-form? For me that extra tension made a world of difference in the stiffness of the frame.

--
-Nudel
Blog with RepRap Comic

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brnrd

Re: Frame brace and Feet for the Mendel
October 09, 2011 06:36PM

Registered: 13 years ago
Posts: 1,780

I read about this approach but I didn't want to disturb the frame and also lose some build space in the x and z axis.

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Dale Dunn

Re: Frame brace and Feet for the Mendel
October 10, 2011 09:15AM

Registered: 13 years ago
Posts: 485

Spreading them apart should have a similar effect. Or, try moving the bottom vertices instead. I haven't tried either.

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dean448

Re: Frame brace and Feet for the Mendel
October 11, 2011 07:45PM

Registered: 12 years ago
Posts: 139

Since we seem to be talking about other approaches... I do notice some slight vibration in my frame probably due to motor commutation, I'm guessing. a vibration could become a flex if it hits the right harmonics. One concept to consider is to put a small antenna that could absorb/counter the vibration. It has to be farly flexible.

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brnrd

Re: Frame brace and Feet for the Mendel
October 18, 2011 12:55AM

Registered: 13 years ago
Posts: 1,780

I don't think the vibrations need to hit the right harmonics in order to cause the frame to flex. When do you see vibrations? I've noticed that vibrations can occur when the carriage/bed changes direction while doing the infill. The other time is when the x and y motors start and stop while going around curves, arcs or cicles due to segment pause.

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