Poll

Will they make it?

Yes
7 (10.3%)
Yes, but the printer will be a heap of crap
28 (41.2%)
No
33 (48.5%)

Total Members Voted: 66

Author Topic: Delta FDM 3D printer for $179  (Read 55964 times)

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Offline janoc

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Re: Delta FDM 3D printer for $179
« Reply #75 on: March 01, 2017, 04:27:40 pm »

Have you ever set Z0 incorrectly? While I agree the steps are probably detectable and noisy - the impact of the glass is pretty violent. I guess it is how you do the signal processing.

A violent impact into the printing surface is likely the last thing you want on any machine where you want some semblance of accuracy and of long term stability. You want to go slow and gently and ideally avoiding any contact at all - that's why various probes with flexible tips are used on CNC machines instead.

Accelerometer would completely suck for this - how would you detect where the vibration from the motors stop and the impact to the surface starts? Especially as the motor is likely still "pushing" when you hit it. This would be both inaccurate and messing up the (already poor) mechanics of the machine.

The simplest way to do this is a contact probe or the various inductive or capacitive sensors. If the bed is non-conductive then optical sensor could be used too.

And if your have a semi-decent machine, you don't need automatic bed leveling at all. You level the bed once and it stays put for a long time. My self-assembled Mendel90 doesn't have it and I have never had a problem. But the Mendel is a fairly rigid and reasonably designed machine where it is not difficult to keep the parts square to each other (unlike the various Prusa i3s and similar). The automatic bed leveling on the consumer printers is mostly a kludge working around the mechanical inadequacies of the design that won't stay square.

« Last Edit: March 01, 2017, 04:29:28 pm by janoc »
 

Offline Assafl

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Re: Delta FDM 3D printer for $179
« Reply #76 on: March 01, 2017, 06:27:59 pm »
Yup. When well calibrated it works fine. I use 1515 beams with linear carriages and it keeps square (on a mini Kossel). Still use the auto leveling. Don't know why. Use resistive pads under the glass to detect the touch. Works well.

The SNR on the accelerometer will depend on how well it is coupled to the nozzle.
 

Offline PlainName

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Re: Delta FDM 3D printer for $179
« Reply #77 on: March 01, 2017, 09:46:53 pm »
Quote
an accelerometer would make a bad job of a auto-levelling sensor

I might be wrong, but I think an accelerometer for auto-levelling is a good tool for the wrong job. You don't want the bed to be perfectly level relative gravity, you want it to be perfectly parallel to the rails the hot end is running on.
 

Offline janoc

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Re: Delta FDM 3D printer for $179
« Reply #78 on: March 02, 2017, 08:12:29 pm »
Quote
an accelerometer would make a bad job of a auto-levelling sensor

I might be wrong, but I think an accelerometer for auto-levelling is a good tool for the wrong job. You don't want the bed to be perfectly level relative gravity, you want it to be perfectly parallel to the rails the hot end is running on.

No, the idea was to detect the contact with the surface (and thus the printing surface not being perpendicular to the Z-axis) by detecting the impact, not to to measure the angle. That would be useless, indeed. Furthermore, common cheap accelerometers likely don't even have enough resolution for doing such measurement with useful accuracy.

The surface impact could be detected, but accelerometer is not the right tool for that job neither if you want any accuracy and reproducible result.
« Last Edit: March 02, 2017, 08:14:41 pm by janoc »
 

Offline PlainName

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Re: Delta FDM 3D printer for $179
« Reply #79 on: March 02, 2017, 09:03:07 pm »
Quote
detect the contact with the surface

Ah! OK :)
 


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