Another UK build

Another UK build

Postby timrwilliams » Sun Mar 02, 2014 6:43 pm

Greetings -

Well, I didn't plan to build another printer. But when I saw the fun you are all having, and had contact with my compatriot ChrisK, of this forum, and seeing his pictures, my resolve fell apart.
But first I had to enlarge the build platform of my old (2006/7) Mendel to take the larger arm prints and sort out a way of securing prints. I eventually settled for printing in PLA, cold on glass with a PVA coating and a 10mm brim. After several false starts and a couple of aborted prints, I have ended up with a reasonable set of parts (my impression so far!) . There are one or two slight lifts and I had to resort to some epoxy resin but the arm meshing and hub movement seems good.
I have been using a heated machined metal plug to form the bearing seats to avoid the splitting that others report can occur.
Drawing breath after biggest print run I have ever done, I was thinking what extruder to use.
I have had some success with Airtripper Bowden direct drives on a couple of other column deltas I have built,but I noticed that ChrisK's pics showed what I think is a geared extruder. I know the objections to geared Bowden drives but I thought I might try one out. Does anybody have any views/experience here.

Nicholas - thank you for some interesting/challenging designs, and thanks to all for their direct/indirect
encouragement
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Re: Another UK build

Postby tommythorn » Sun Mar 02, 2014 7:09 pm

Excellent and good luck.

I'm puzzled by the adhesion problem people are having as I have the opposite problem: I've broken two slave arms trying to get them off my print bed! The only relevant factors I can of: printing on fresh blue 3M printer tape on a leveled 1/2" acrylic bed, 205 °C first layer, then 195 °C, QU-BD premium PLA. I even stopped using a brim. (My GUS efforts are on hold until I resolve some mechanical problem with the mother printer).

You don't mention it, but GUS has a native filament drive design which you could consider as well.
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Re: Another UK build

Postby timrwilliams » Tue Mar 04, 2014 10:14 am

Thanks for the link to the Simpson extruder, it looks a useful compact unit. I have been trying to machine my own hobbed gear recently, so I will give it a go.

I know what you mean about blue tape adhesion. I was getting the print plus tape lift off metal/glass!. I was looking for a medium 'stiction' and PVA/glass seemed to work for me with large prints. But of course you are right - bed levelling is the essential start.

Regards
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Re: Another UK build

Postby timrwilliams » Thu Mar 06, 2014 3:19 pm

Progress has slowed a bit, but still steady.
The print colours are not meant to be unduly patriotic, just the way the printers were set up.
Red/Blue - PLA, White - ABS.
Now for some stringing.

Regards to all.
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Re: Another UK build

Postby timrwilliams » Sat Mar 15, 2014 8:56 am

Well- One segment strung. It took two attempts and four hands but seems to work smoothly.
It was good to have some guidance from posts on this forum, hopefully the next two will be easier.
The engineer in me wants to put in some bearings/guides for the strings or possibly some PTFE bushing -
I know there is not a lot of clearance for this. Does anyone have any thoughts or is this not necessary in practice.
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Re: Another UK build

Postby NeoTheFox » Sat Mar 15, 2014 9:19 am

Nice build so far! What strings are you using? It looks twice as thick as mine.
And for the new arm design featuring guides for string refer here - Possible New Arm Mockup. There is a concept and discussion on it.
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Re: Another UK build

Postby timrwilliams » Sat Mar 15, 2014 10:56 am

I'm using 90lb breaking strain Spectra - 0.5mm diameter. Mainly because I have a lot in the spares box!

Thanks for the link. The only thing I might try with this design is a thin PTFE fixed sleeve with shallow grooves. I am fortunate in having access to a lathe to produce this. It is probably easier to try during assembly of the next arm rather than a retrofit.
The Spectra does seem to have a waxy finish so I guess friction is not a great issue and I may be unnecessarily concerned.
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Re: Another UK build

Postby Nicholas Seward » Sat Mar 15, 2014 11:30 am

I have discovered that the filament will flatten over time and the friction goes up as its contact area widens. For me the region between the motors being too hot and the motors skipping is too small to make me happy. For the record, I use weaker than normal steppers and am able to find something in that region.
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Re: Another UK build

Postby Nicholas Seward » Sat Mar 15, 2014 11:31 am

I have discovered that the filament will flatten over time and the friction goes up as its contact area widens. For me the region between the motors being too hot and the motors skipping is too small to make me happy. For the record, I use weaker than normal steppers and am able to find something in that region.
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Re: Another UK build

Postby timrwilliams » Sat Mar 22, 2014 7:38 pm

Well - It's taking shape.
I have only tested it with single arm motor drive so far.
For information, I machined thinwalled (2mm) PTFE bushes with 1mm grooves for all the
8mm stringing bolts. I think you can see some of these. I don't know if the measurable reduction in friction is important, but it certainly made me feel happier.
Now for three motor drive.
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