In a pickle! Can anyone help re: FreeCAD & Resin printing? (Bit 'off topic'.)

[eeedelli]

Hi Folks,

 

I’m afraid I’m in a bit of a pickle! (Quite a lot of a pickle, actually!)  I’m hoping someone can help me out here. It’s a bit off-topic but also rather ironic that it’s happened now, given that I host the monthly Zoom meetings for West Lancs O Gauge Group and we were only taking an initial look at 3D printing for modellers last month - something I've not really got into yet. Hopefully, there will be someone on here who can help. It’s also forced me into a rapid ‘baptism of fire’ with FreeCAD after years of 2D designs on an ancient copy of AutoCAD.

 

Anyway, I’ve recently been working on my 1989 Volvo 740 where a variety of faults finally caused removal of the instrument binnacle. The odometer had been dead for many years (a regular problem with this model) and the addition of a completely erratic fuel gauge and, finally, intermittent loss of gauge lighting (both also well-known stock faults) finally forced me to take action.

 

I’ve re-soldered and flux-washed all the dry joints on the fuel gauge and lighting dimmer PCBs and successfully tackled replacement of the disintegrated odometer gear wheels using the after-market kit available for that problem.  However, the final move of replacing the pointer on the speedo galvanometer shaft after reassembly, met with disaster.  It was so tightly fitted that it required two diametrically opposite screwdrivers beneath to carefully lever it off in the first place. Consequently, replacement required a fair amount of pressure, which bent the ~0.6mm wire spindle. In attempting to straighten it, the inevitable happened, leaving the final 11mm of the wire separated where it emerges from the central shaft tube, complete with the splined end attached to the broken wire. (I’ve since wiped a needle file over the splined end and had it in and out of the pointer’s central boss a few times and it seems to have completely eased off.) The top sleeve bearing has been removed in this picture, for clarity.

 

 

 

 

Hindsight is a wonderful thing but I now realise I should have gently tapped it on rather than trying to press it on. Unfortunately, I’ve not had any success locating a replacement, which is hardly surprising after such a long time – it seems everyone was after them years ago as replacements when the odometer failed, rather than dismantling and replacing the gears. (It’s 'unicorn time'!)

 

Looking at it, the simplest way to repair would appear to involve cutting down the height of the tube by a few mm to allow a new 10mm extension to be placed over the existing tube with the upward extension reduced to similar dimensions as the original tube (space for a fractionally larger diameter) and with a centre hole to take a new shaft wire. (See turquoise component in right hand diagram, below.) The existing tube is only 1.2mm diameter and the central wire spindle is just 0.6mm. The splined end has proved impossible to get off the existing wire so will need to be replaced too.

Looking at some specs of resin printers, I’m not sure whether even those would get down to a fine enough resolution to do things like the splines, as the parts are so tiny (though any semblance of splines would probably work because the plastic of the central boss on the pointer already has the female shaped spline cut away and that would probably cut into the new plastic centre piece). Likewise, is it possible to ‘print a hole’ of just 0.6mm diameter for the wire without it filling up with resin? Perhaps the diagonal nature of the slicing would allow for that, as it effectively turns it into an ellipse whose longer measurement would be greater than that? (I don’t think a filament printer would get near that, would it?) Even a part-filled smaller hole would act as a guide for a tiny drill for hand finishing, if required. There's no torque placed on these components - they're just moving a pointer round on the end of the shaft, so I think resin 3D printed parts with a spot of LocTite to fix them would be perfectly ok in principle, so long as it's possible to make such small components.

 

These are images from the 3D FreeCAD files that I’ve just knocked up as my first attempt at 3D CAD. The extension tube is 10mm overall length, with a 0.6mm through-hole and a recess of 1.7mm diameter at the bottom end to slip over the cut-down original metal tube. The splined end is 7.6mm overall length with the splined part being 2.54mm, the plain part 1mm diameter and there's a 0.6mm through-hole for the wire.

 

 

I’ve yet to work out how to drill the brass rivets off the case without damaging the plastic it’s riveted to, as well as unsoldering the delicate coil springs from the supply leads.  This is going to need a steady hand!

 

Any thoughts on the dimensional tolerances and feasibility etc. for 3D resin printing?  Also, could anyone help me out by printing a few of them in the hope that they'd work (maybe 2 or 3 of each - in case I damage them!)?  Obviously I’d be happy to pay a suitable sum towards resin and postage etc.   

 

My rather battered but still much loved and loyal ‘daily shed’ is now off the road until I can get this sorted!

 

Thanks,

David.

[JCL]

Hi David,

Although there are differences between brands/formulation, resin isn't generally known for its durability. I'm probably teaching you how to suck eggs here, but have you tried the forums on the Volvo Owner's Club website?

https://www.volvoclub.org.uk/

[eeedelli]

I have indeed. (I'm in the owners' club.) The general opinion was that I'm not going to find a replacement and that has, sadly, been the case (even with the specialist breakers). Basically they all went years ago.

 

We did discuss using a watch repairer but I've tried a few and it seems they don't do fine lathe work - it's all replacement of standard parts, testing for waterproofing, new watch straps, re-glazing etc. and that's about it. There's also the cost, even if I could find one - I should imagine they'd want to charge more than the value of the car whereas 3D printed parts would be minimal.

 

Is the durability an issue of stability over the long term (in which case, how are people coping when it comes to building rolling stock etc) or are you thinking of actual 'wear and tear'?

 

I did wonder about that but there's no real torque on either of these components. All they've got to to is be rotated around with a pointer on the end in fresh air and the only part that would rub would be the metal wire against the top bearing tube, which matches the original design. Neither the extension tube nor the splined end have to rub or drive anything that would resist them. That's why I was assuming it would be something that might work quite well in resin.

[JCL]

Ah, that's a bit of a sod. In that case, to answer a couple of questions,

 

Any thoughts on the dimensional tolerances and feasibility etc. for 3D resin printing?  For the Anycubic Mono X, (and my old Peapoly Moai), the tolerance is 0.2mm. However, this can be affected by the settings used to do the print. If the print is over exposed, then more resin will be deposited, if under exposed, less will be deposited.

 

I'm afraid I can't help you with the printing (I live in Canada), but you could try @Knuckles of this parish who sometimes takes on commissions. Maybe instead of just doing one, do the one you want, and then do one "either side of that" with slightly smaller and larger dimensions.

You've nothing to lose, so it's certainly worth a try.

[eeedelli]

9 minutes ago, JCL said:

You've nothing to lose, so it's certainly worth a try.
 

Yep - That's pretty much the point that I've got to! (Any port in a storm!) 

 

Thanks for the idea of 'bracketing' the dimension.  I'll see if I can tweak the 'theoretical' one, though doing those splines was a bit of a pig!  (There doesn't seem to be a radial array setting in the sketch part of FreeCad.)  I noticed that many use Fusion360 but (a) I note that they only say it's free for 12 months and (b) I gather they've cut back on what you get and can't even export DWG/DXF any more, which would be no good if you want laser cutting etc, so I opted for FreeCad.  I'm currently surveying the foothills of a mountainous learning curve, it seems!

 

Ta.

[PaulaDoesTrains]

3 hours ago, eeedelli said:

(There doesn't seem to be a radial array setting in the sketch part of FreeCad.)

 

Use a Polar Pattern. Design the feature in Sketcher, then Pad/Pocket it in Part Design then use Polar Pattern also in Part design.

[eeedelli]

2 hours ago, PaulaDoesTrains said:

 

Use a Polar Pattern. Design the feature in Sketcher, then Pad/Pocket it in Part Design then use Polar Pattern also in Part design.

Oh, right. What do you use the polar pattern in part design 'on', if you see what I mean? (The single already pocketed implementation?)

 

The only way I found to do it was to add a new datum plane to the underside of the section where I wanted the splines and then use the sketcher on the new plane to create the circles which could then be extended along to pocket out the splines. This is the first couple of hours of 3D CAD I've done - all very different to the old AutoCAD I've used for 2D drawings for years.   I'll need to poke around a bit, I suppose.

[tebee]

19 hours ago, eeedelli said:

I have indeed. (I'm in the owners' club.) The general opinion was that I'm not going to find a replacement and that has, sadly, been the case (even with the specialist breakers). Basically they all went years ago.

 

We did discuss using a watch repairer but I've tried a few and it seems they don't do fine lathe work - it's all replacement of standard parts, testing for waterproofing, new watch straps, re-glazing etc. and that's about it. There's also the cost, even if I could find one - I should imagine they'd want to charge more than the value of the car whereas 3D printed parts would be minimal.

 

Is the durability an issue of stability over the long term (in which case, how are people coping when it comes to building rolling stock etc) or are you thinking of actual 'wear and tear'?

 

I did wonder about that but there's no real torque on either of these components. All they've got to to is be rotated around with a pointer on the end in fresh air and the only part that would rub would be the metal wire against the top bearing tube, which matches the original design. Neither the extension tube nor the splined end have to rub or drive anything that would resist them. That's why I was assuming it would be something that might work quite well in resin.

 

 

You need a watch maker rather than a repairer - I had an uncle who was one, but he retired about 18 years ago and is in his 80's now - I don't think there are many left !

 

Resin - think people are referring to the fact that most resins tend to be on the brittle side. However there are specialist resins that are more resilient - this is one I've used -  https://siraya.tech/collections/europe/products/tenacious-eu-1kg-by-siraya-tech

[eeedelli]

That's interesting - thanks. Just looking around, there does seem to be an increasing range of materials becoming available. 

 

I think, as a first attempt, even bog-standard resin would be worth a try as there are no forces imposed on these parts during operation - they just sit there and get rotated with the pointer waving about in fresh air on the end of them.

 

Yes - a watchmaker would make more sense than a watch repairer, though probably even harder to find. However, I think printing these is likely to be far more economic, if anyone is prepared to have a go at helping me out with such small parts.

[Quarryscapes]

2 hours ago, eeedelli said:

That's interesting - thanks. Just looking around, there does seem to be an increasing range of materials becoming available. 

 

I think, as a first attempt, even bog-standard resin would be worth a try as there are no forces imposed on these parts during operation - they just sit there and get rotated with the pointer waving about in fresh air on the end of them.

 

Yes - a watchmaker would make more sense than a watch repairer, though probably even harder to find. However, I think printing these is likely to be far more economic, if anyone is prepared to have a go at helping me out with such small parts.

 

If you have the designs ready to print (STLs), I can print for you in eSun Tough Resin if you like. 

Edited May 29, 2021 by Quarryscapes

[eeedelli]

6 minutes ago, Quarryscapes said:

 

If you have the designs ready to print (STLs), I can print for you in eSun Tough Resin if you like. 

 

@Quarryscapes     Thanks!  

 

It looks as though I just 'export as' .STL - Is that right?  I assume that all the slicing and diagonal supporting stuff would have to be done by you to suit the characteristics of your printer?  (This is all very new to me!)  I've not tinkered with the intended sizes yet to produce ones that are slightly larger/smaller (to allow for any printer errors). Presumably it's worth trying the 'correct' size first anyway and bunging the calipers on them to see how they turn out?

[PaulaDoesTrains]

15 hours ago, eeedelli said:

Oh, right. What do you use the polar pattern in part design 'on', if you see what I mean? (The single already pocketed implementation?)

 

The only way I found to do it was to add a new datum plane to the underside of the section where I wanted the splines and then use the sketcher on the new plane to create the circles which could then be extended along to pocket out the splines. This is the first couple of hours of 3D CAD I've done - all very different to the old AutoCAD I've used for 2D drawings for years.   I'll need to poke around a bit, I suppose.

 

OK, for the sake of argument, let's assume that you made the basic cylinder by drawing a circle on the XY plane then padding it. What you do then is create another sketch on the same plane representing one of the splines.Note that the sketch will have to  a closed shape. You then pocket that sketch to create your 1st spline. Now make sure that the pocket is selected in the tree view and press the Polar Pattern icon. Fill in the number of splines and you're done.

[Quarryscapes]

1 hour ago, eeedelli said:

 

@Quarryscapes     Thanks!  

 

It looks as though I just 'export as' .STL - Is that right?  I assume that all the slicing and diagonal supporting stuff would have to be done by you to suit the characteristics of your printer?  (This is all very new to me!)  I've not tinkered with the intended sizes yet to produce ones that are slightly larger/smaller (to allow for any printer errors). Presumably it's worth trying the 'correct' size first anyway and bunging the calipers on them to see how they turn out?

 

I'm not familiar with that software, so don't know the menu operations, but if you're seeing "export as STL" I imagine that should do it. If you want to share as a STEP or even whatever the native file format is, I can more readily tweak any bits that need tweaking should the need arise (and I can pull accurate measurements from it, STL can only give me the max bounding box).

[eeedelli]

31 minutes ago, Quarryscapes said:

 

I'm not familiar with that software, so don't know the menu operations, but if you're seeing "export as STL" I imagine that should do it. If you want to share as a STEP or even whatever the native file format is, I can more readily tweak any bits that need tweaking should the need arise (and I can pull accurate measurements from it, STL can only give me the max bounding box).

 

Ah - yes, it seems I can supply in STEP and STL (and a range of other things) plus the raw FCstd format.  Here's the full range it lists, in case you can spot anything else that might be useful:

 

 

Ta.

D.

 

[eeedelli]

57 minutes ago, PaulaDoesTrains said:

 

OK, for the sake of argument, let's assume that you made the basic cylinder by drawing a circle on the XY plane then padding it. What you do then is create another sketch on the same plane representing one of the splines.Note that the sketch will have to  a closed shape. You then pocket that sketch to create your 1st spline. Now make sure that the pocket is selected in the tree view and press the Polar Pattern icon. Fill in the number of splines and you're done.

 

Ah ha!  Yes - thanks for that. It took me a little while to actually find the polar pattern icon as it was hiding in an extension menu off the side of the screen (which I've now dragged on to a second menu icon layer) but I think I've got there!   That's brilliant - wish I'd known that before I did it all manually, so I'll go back and amend the original one, I think.

 

Ta!

[Quarryscapes]

Lets go with STEP. I've got the eSun tough in the printer already, currently printing some bits. It's translucent blue but I shouldn't think that'll matter much!