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Inconsistencies in x-axis (short) on Sophia #1143

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amcewen opened this issue May 31, 2019 · 5 comments

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commented May 31, 2019

Sean S reported problems with Sophia's accuracy, on the Google Group:

I used the Sophia laser cutter on Thursday last week and just got around to using the stuff I cut. There seems to be something wrong with the accuracy. Has this already been noticed and dealt with? I think the Y axis (long) is okay but the X axis (short) isn't/wasn't. A hole separation was expected to be 138 mm but was actually 144 mm. You can also see that the holes are kind of elongated in the X direction. I also have a piece where larger holes were cut and the ends of the circles don't meet the starts.

This ties in with Emma having problems with it ghosting during an engrave at Maker Night too. @magman2112 reckons there's a problem with the belt and the tensioner wheel.

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commented May 31, 2019

Having watched the kind of issues Sophia has I think the best repair would be to the sled to remove skipping and misalignment issues - this isn't at all difficult, but will take a bit of time and would probably be best undertaken once Monty(*) comes online. A bit of something "compliant" to make new wheels out of would be a good first step - 1" thick polythene, or delrin being first choices Bar or slab would not matter as both could be turned down. Rebuilding the sled as a 3-wheel zero backlash design would be a significant upgrade and is far easier than it might sound.

(*) a better name for Morris?, (who should only formally christened once up & running.)

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commented Jun 10, 2019

Improving the carriage would be good, but as you say, progress on Morris/Monty/Hugo/... is taking priority.

In the meantime, can we get a minimum fix (given it's possibly the idler wheel rather than the carriage) done so that we can start using Sophia more. In particular, @jackie1050, @dazz-ling and I were just discussing how it would be better to run inductions on Sophia to stop everyone from just booking Gerald because they're not familiar with Sophia, but we can't do that with Sophia in her current state.

Maybe something for the rest of the @DoESLiverpool/laser-maintenance crew to look into?

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commented Jun 13, 2019

With much help from @magman2112 the sled on Sophia has been rebuilt, it is now a 3-wheel design with spring-loaded tensioning. Following a quick align and test it was cutting 50mm squares within 0.2mm on both axes and with a bit more tweaking will get even better.
There has been a price to pay however - due to an unforeseen lack of clearance between the sled and the Y rails the cut-able area is limited - about 23mm less front -to-back than previously. Some countersunk screws and a bit of 1mm steel plate to remake the third-wheel mount will resolve this, but for now, it's working again.
The idler wheel on the X axis still requires work but for now it appears to be working, so I propose leaving it alone until after the big laser is commissioned and doing it properly then.

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commented Jun 14, 2019

Thanks for the update. @dazz-ling is going to mark the bed and make a sign to put up next to Sophia to warn people that the bed size is a bit restricted.

@amcewen amcewen added the Broken label Jun 18, 2019

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commented Jun 18, 2019

Although the new sled has made the carriage lots better, it hasn't addressed this issue :-(

I've just tried cutting a Museum in a Box design, and over 165mm it lost 3mm on one part of the box and 6mm across the same distance on another piece of the box. It's also not a consistent, the two tabs on this photo should line up against the ruler...

DSC_0121

Marking it as broken as I don't think it's usable for people at the moment

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