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Ball spacing - Fisher Delta 3D

Posted by cparsons 
Ball spacing - Fisher Delta 3D
November 01, 2016 02:53AM
I started my build last night and am progressing fairly well, but have a couple of issues?

Fairly trivial but the RepRap 'badge/logo' doesn't clip in, just falls out and will need to be glued, or
I might make a new one a bit bigger so that it is an interference fit!

Main issue is setting up the spacing across the balls to be 57mm across - the build instructions
say at least make them the same measurement, to a tolerance of 0.25mm but I think the only
way I am going to achieve this is to loctite the screw thread and screw them in and out to get them
all the same (including the effector assembly) which will end up being around 58mm I would think and then
let the loctite set to hold them in place?

Is this what others have done - or have I missed a trick? I did wonder if it was worth buying
another set of balls to see if there are any that are machined a bit more accurately?

The variation at the moment is 57.07, 57.96 and 57 67 on the columns

I have to say the rest of the kit is very well engineered smiling smiley

Edited 1 time(s). Last edit at 11/01/2016 03:08AM by cparsons.

Chris Parsons
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e. parsons.cj@gmail.com
m. 07966 754528
h. 01392 278549
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Exeter and District Model Engineering Society
Newton Abbot and District Model Engineering Society

Pilot of G-EFOX and Mixed Gas Rebreather Diver
Re: Ball spacing - Fisher Delta 3D
November 01, 2016 04:13AM
Yes, you need to use Loctite or similar or they will come un done during use. I used calipers to set mine and it was very fiddly.

When I built mine I had to file the threads to reduce some a little to get them correctly spaced.

If I understand correctly the better these are set the better the prints will be. I'd also make a set of carbon fiber rods, the acrylic ones seem to fail almost everyone, there is a lot of discussion how to make them on this forum.


DC42 Kossel 330mm x 2meters
My Thingiverse Creations
Re: Ball spacing - Fisher Delta 3D
November 01, 2016 07:19AM
Thanks, I think I will get the printer working and then looks at what you suggest - although it looks like the sockets for the CF rod are problematical, the sources quoted seem to have dried up

If the acrylic connectors are so poor why on earth do the kit suppliers keep selling them, and not research better alternatives - would help those getting started like myself!

Regards

Chris
Re: Ball spacing - Fisher Delta 3D
November 02, 2016 03:15AM
I got mine from eBay, and I see they are also available direct from the manufacturer. The other benefit (apart from reliability) is they are quieter than the acrylic.


[www.mugenuk.co.uk]

[www.ebay.co.uk]


DC42 Kossel 330mm x 2meters
My Thingiverse Creations
Re: Ball spacing - Fisher Delta 3D
November 02, 2016 03:42AM
Thanks very much - I saw the eBay ad but they only had one left, but I have now ordered two packs direct from the UK manufacturer smiling smiley

I will need 3mm carbon fibre rod to fit these, yes? Any idea what length? I am in the office and cannot measure the existing rods
and would like to get this ordered too, looks like this is fairly easy to get from eBay.

I guess I can rough up the end of the rods and use epoxy glue to attach them, bearing in mind I will need to make up an appropriate jig
to stop shrinkage as the epoxy dries?

Regards


Chris Parsons
-----------------------------------------------------------------------
e. parsons.cj@gmail.com
m. 07966 754528
h. 01392 278549
-----------------------------------------------------------------------
Exeter and District Model Engineering Society
Newton Abbot and District Model Engineering Society

Pilot of G-EFOX and Mixed Gas Rebreather Diver
Re: Ball spacing - Fisher Delta 3D
November 02, 2016 04:28AM
Sorry to follow up my own reply, but I had a sudden thought and checked the GitHub repository,
and yes, the CAD plans are there for the rods...as well as everything else smiling smiley

I have drawn a dimension to the hole centres and they are 160 mm apart so 1 m of carbon fibre
rod will make 6 rods with a bit left over (160 * 6 = 960), and I guess each rod will have to be slightly
shorter anyway to allow for the end fittings?

Sound like a plan?


Chris Parsons
-----------------------------------------------------------------------
e. parsons.cj@gmail.com
m. 07966 754528
h. 01392 278549
-----------------------------------------------------------------------
Exeter and District Model Engineering Society
Newton Abbot and District Model Engineering Society

Pilot of G-EFOX and Mixed Gas Rebreather Diver
Re: Ball spacing - Fisher Delta 3D
November 02, 2016 06:05AM
My method for making the shorter arms is to use some stainless grubscrews screwed into the rod ends (Not fo adjustment mind just to give a good surface for the glue) I think the mugen ends are for M3 and then you can use some 5od 3 id Carbon tube into which you can glue the grubscrew mounted rod end? This should give a stiffer rod than 3mm Carbon rod.

You may be able to find it at a Good RC Model Shop or there are a couple of UK Based manufacturers of the stuff

Easycomposites and also Carbon Tubes The only killer with these 2 is that carriage will probably cost more than the Tube

also found this Ebay seller Ebay Carbon Tube

HTH

Doug
Re: Ball spacing - Fisher Delta 3D
November 02, 2016 07:28AM
Im using 3mm carbon fibre rod from a kite shop and I dont think it needs to be any stiffer. I did need to use a 3mm drill bit to open the ends out a little to make room for the glue. Make sure you make up a little jig to hold them all the same length. I used a scrap piece of 2x4 and two 5.5mm drills. Once glues they slide over the drill tightly and I put some grease proof kitchen paper between each. I have been running my printer with these for about a year and so far no complaints.


DC42 Kossel 330mm x 2meters
My Thingiverse Creations
Re: Ball spacing - Fisher Delta 3D
November 15, 2016 05:15PM
I made up a set from solid carbon fibre rod but ran into a problem that when the ball ends were glued on, the pneumatic pressure resulting from the little air inside the end was pushing the end back off the rod and making it very difficult to get accurate length consistency, I had to wait for the epoxy glue to set hard before I could make another on the jig. I have since purchased carbon tube to make up another set, hopefully avoiding that problem next time.


SSMagic

Fisher Beta, upgraded to Fisher 1 with heatbed and full fan control
Re: Ball spacing - Fisher Delta 3D
January 29, 2017 04:56AM
I realise this topic is a couple of months old now but I'm not sure the point about the ball spacing was answered fully....
The ball spacing is one of the most critical things to get right on a delta. I suspect it's probably the biggest contributing factor when it comes to people being disappointed with their prints.

The common misconception seems to be that as long as the spacings between the balls on the head are the same, and separately the spacings of the balls on the towers is the same, then all is fine - this is wrong. The spacings that need to match are the pairs of balls that are connected together by the rods - ie. the spacing of the balls on a tower with the spacing of the corresponding balls on the head. The balls must also be centred too, ie. there must be an equal length between the ball and the carriage (for example) on each side.

I would also say that the recommended tolerance of 250 um is way too large. Unless you're happy with sloppy prints, I'd aim for sub- 100 um differences. I have a Fisher beta at home for personal use, and have helped build and maintain a further 6 (betas and 1s) for work and colleagues.... and other that the 1st (which was later stripped and re-built), all have had maximum variations on the order of 50 um.

As far as the arms go, like DADIY said, the stock arms are pretty poor - the acrylic used is too thin and brittle. I'm lucky enough to have access to a laser cutter so I made some re-designed arms using some thicker acrylic that use hacked up parts of the old arms between as spacers. I've never had a set of these arms fail; some have been in service since the first batch of Betas (which, IMHO, are much better than the later Fisher 1). If you do end up using acrylic arms though, I would highly recommend covering the balls with white lithium grease for lubrication. It stops the arms squeaking and it doesn't attack the acrylic like other lubricants.

Edited 1 time(s). Last edit at 01/29/2017 08:03AM by bluesign2k.
Re: Ball spacing - Fisher Delta 3D
January 30, 2017 03:16AM
Ok, I have made the carbon fibre replacement rods - and yes, they do look a lot more elegant than the originals although it was quite difficult sourcing the end fittings. Yet to see how well the epoxy holds but it is good so far...

I am thinking now reading the last post perhaps I ought to be checking the ball spacing again (it is certainly not as precise as detailed!)

Best approach? Do you think I could get away with doing this 'in situ' or strip the printer down again *sigh*

I seem to spend more time taking it to bits than actually printing sometimes - and if I print something 4 or 5 times I will be lucky to get once successful
print - they certainly need a lot of fiddling

Chris
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