Any way to test repeatability of axis limt switches?
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Markforged printers, at least the one I saw demoed at the Makerspace, rezero X and Y at each layer change. That would require very high precision in the X and Y endstops to ensure that the layers get stacked properly. I'm not sure what advantage it confers, but I recently converted my printer to optical endstops and intend to try that scheme out to see what it does. I'll be mounting a gauge on the printer to see if I can measure repeatability of the X and Y endstops, though print quality will probably reveal more than a gauge can.
If the machine doesn't skip steps, rezeroing at each layer change seems pointless. Maybe they do it to allow the print to cool a little between layers instead of printing a sacrificial object that would waste their relatively expensive material.
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@mrehorstdmd said in Any way to test repeatability of axis limt switches?:
If the machine doesn't skip steps, rezeroing at each layer change seems pointless.
Absolutely.
Re-hitting an endstop during a print... that strikes me as something that has only downside...
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@Danal said in Any way to test repeatability of axis limt switches?:
@mrehorstdmd said in Any way to test repeatability of axis limt switches?:
If the machine doesn't skip steps, rezeroing at each layer change seems pointless.
Absolutely.
Re-hitting an endstop during a print... that strikes me as something that has only downside...
I had to do it on the first printer I built, in 2010. I couldn’t afford fancy aluminium pulleys for my T5 belt, so had to bootstrap something to print pulleys. I ended up using plastic pallet strapping on rubber pulleys as the X and Y belts! I had to home every layer, as it would slowly shift. I managed to print two very rudimentary pulleys that were just capable of holding the T5 belt. Then iterated a couple of times until I had a good pair of them.
Ian
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@mrehorstdmd said in Any way to test repeatability of axis limt switches?:
rezero X and Y at each layer change
That makes sense if you assume you're going to get layer shifts and missed steps. I don't see why you'd want to do that otherwise.
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No this took an interesting turn! Always interesting to see what the commercial folk have done, and to try and understand it. That said it's not always the right thing!
In this case perhaps their stepper drives or stepper drives and machine setup couldn't allow accurate missed step detection mid build. This behaviour gives almost the same result and as others say allows the user to print smaller items without needing the dupicate items to stop parts getting too hot.
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Perhaps it's all all about claimed positional accuracy. Just like a stopped clock that tells exactly the correct time once every 12 hours Vs a clock that is 1 second fast or slow so never shows the correct time.
So in marketing speak, one can claim a positional accuracy that is consistent for every layer. The fact that it's only accurate at the very start of a layer and can drift all over the place is irrelevant in marketing speak
(In case anyone has problems with my sense of humour, this post is not to be taken seriously.)
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@deckingman you may think your joking but having worked in the field of commercial manufactures of AM machines I can state that this has been the state of affairs in times gone. There were some real dishonest marketing ploys out there. There were some really slippery characters out there who could always justify their claims but in really tenuous manners. Stuff like build rates were quoting the rate at which a laser process material as it was moving over the bed, not average for a while build. These build rates making spongy crap parts, rather than the parts used to qualify the high density figures. Strength figures from processing parameters you would never use because the parts look crap.
Just to be clear, for those who know me, and know companies I have worked for, I am not saying this was their behaviour. I've been to many academic conference and trade show and seen many different manufacturers and researchers engage in similar tactics. One reason I have grown to love open source as there is far more emphasis on sharing information and results and less dishonesty as it's too easy to be disproven by others with spare time!
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@DocTrucker I can give lots of similar examples. Resolution vs accuracy is always a good one.
When I had a proper job, the engineering consultancy company that I worked were told by one of their clients (a UK engine manufacturer who shall remain nameless) that we had to use a particular piece of equipment to measure ignition advance, because the display showed two decimal places rather than the single decimal place that our default equipment used. So in the eyes of the client, that equipment was 10 times more accurate. But that piece of "more accurate" equipment only used a 60 tooth encoder and interpolated between pulses to calculate the ignition advance (which it displayed to 2 decimal places). So at best, it only received a pulse every 6 degrees whereas the ("10 times less accurate") equipment we used at the time, used a 360 tooth encoder so received pulses every degree making it potentially 6 times more accurate than the piece of crap they insisted we use.
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I'll run two prints today, one homed at the start only and the same print with rehoming at each layer change, and post some photos. We'll see what happens. I expect some blobbing at the seam in the rezeroed part, otherwise, ?????