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Post by Roger on Oct 4, 2020 20:30:19 GMT
.................... Painting has to be the most soul destroying part of Model Engineering. I can see why some people loath it. Painting is one of those phases of the different skills required to complete a model (frames, motion, boiler, platework, assembly and paint) any one of which can be the reason why a model never got finished. I never looked forward to painting until I got it to work to a reasonable degree. I've always painted the assembly rather than the separate components prior to assembly. We spend ages making parts to the correct sizes so adding a layer of paint between the faces somewhat negates the effort. Masking off the contact faces can be a pain and the source of problems later as there is no effective seal on the joint. To deal with the paint shadow around bolts and rivets I go round with a fine modelers brush and put a thin coat of paint on the heads and then spray while it is still wet. Although there are many ways of skinning cats ............. Pete Hi Pete, That's an interesting idea for the paint shadow. Is it just a shadow from the spraying angle? If that's the case, it ought to be possible to overcome it by spraying perpendicular to the surface. I might look at seeing if I can get nearer to that angle when spraying. My impression was that it also had something to do with the surface tension, but that may be wrong.
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Post by Roger on Oct 4, 2020 21:42:39 GMT
This is the X-Mirrored part using the reversed tool paths. I'm surprised to have got this far in just one day. This just needs parting off and then I can look at making the fixture to hold it while I machine the outsides. Those will take a fair bit longer because there's more 3D machining and it won't be held down as firmly. I've been preparing the other tool paths for the threaded end caps and the overflow valve too, so I'm going to have a busy week machining. 20201004_223630 by Roger Froud, on Flickr
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Post by doubletop on Oct 4, 2020 22:18:05 GMT
Painting is one of those phases of the different skills required to complete a model (frames, motion, boiler, platework, assembly and paint) any one of which can be the reason why a model never got finished. I never looked forward to painting until I got it to work to a reasonable degree. I've always painted the assembly rather than the separate components prior to assembly. We spend ages making parts to the correct sizes so adding a layer of paint between the faces somewhat negates the effort. Masking off the contact faces can be a pain and the source of problems later as there is no effective seal on the joint. To deal with the paint shadow around bolts and rivets I go round with a fine modelers brush and put a thin coat of paint on the heads and then spray while it is still wet. Although there are many ways of skinning cats ............. Pete Hi Pete, That's an interesting idea for the paint shadow. Is it just a shadow from the spraying angle? If that's the case, it ought to be possible to overcome it by spraying perpendicular to the surface. I might look at seeing if I can get nearer to that angle when spraying. My impression was that it also had something to do with the surface tension, but that may be wrong. I've found that some paints just don't like sharp edges. A good example is the current incarnation of Hammerite Smooth in spray cans, it hates sharp edges. I think the problem with bolt and rivet heads isn't the spraying angle its because a boundary layer of air forms a vacuum at the intersection and the paint just can't get in there. A bit like wind flowing over a hill at the base the wind speed can be quite low. And a complete change of subject but related to boundary air flow. hackaday.com/2020/09/24/dynamic-soaring-545-mph-rc-planes-have-no-motor/ Check out the section on the physics. Pete
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Post by Roger on Oct 4, 2020 22:55:04 GMT
Hi Pete, That's an interesting idea for the paint shadow. Is it just a shadow from the spraying angle? If that's the case, it ought to be possible to overcome it by spraying perpendicular to the surface. I might look at seeing if I can get nearer to that angle when spraying. My impression was that it also had something to do with the surface tension, but that may be wrong. I've found that some paints just don't like sharp edges. A good example is the current incarnation of Hammerite Smooth in spray cans, it hates sharp edges. I think the problem with bolt and rivet heads isn't the spraying angle its because a boundary layer of air forms a vacuum at the intersection and the paint just can't get in there. A bit like wind flowing over a hill at the base the wind speed can be quite low. And a complete change of subject but related to boundary air flow. hackaday.com/2020/09/24/dynamic-soaring-545-mph-rc-planes-have-no-motor/ Check out the section on the physics. Pete I guess this is why it's recommended to spray at as low a pressure as possible so that the paint just floats down gently with as small a dynamic force as possible. The problem with that strategy is you don't get the spray atomised in small enough droplets. I suppose we're trying to do the impossible really, ie have the paint just drop straight onto the surface even when there's a corner or a rivet. And that's without any of these other surface tension issues. Frankly, it's a nightmare. That's a really interesting article, mind boggling what they can achieve like that.
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Oct 4, 2020 23:16:32 GMT
Hi Pete, That's an interesting idea for the paint shadow. Is it just a shadow from the spraying angle? If that's the case, it ought to be possible to overcome it by spraying perpendicular to the surface. I might look at seeing if I can get nearer to that angle when spraying. My impression was that it also had something to do with the surface tension, but that may be wrong. I've found that some paints just don't like sharp edges. A good example is the current incarnation of Hammerite Smooth in spray cans, it hates sharp edges. I think the problem with bolt and rivet heads isn't the spraying angle its because a boundary layer of air forms a vacuum at the intersection and the paint just can't get in there. A bit like wind flowing over a hill at the base the wind speed can be quite low. And a complete change of subject but related to boundary air flow. hackaday.com/2020/09/24/dynamic-soaring-545-mph-rc-planes-have-no-motor/ Check out the section on the physics. Pete I’m sure that’s right. It is all do with the air current. There will be refraction as well, which must be why you can get half a coat of spray on surfaces that the nozzle can’t possibly “see”. I also use the paint brush trick. If you pick over the work with a fine brush before it dries, you can often get rid of annoying bubbles as well as filling in any small shadows; sometimes you can even lift off stray bits of dust if your painting environment is less perfect than Roger’s! Only works with enamels though, solvent-based paints dry too fast. Gary
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dscott
Elder Statesman
Posts: 2,438
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Post by dscott on Oct 4, 2020 23:41:11 GMT
What a shame we cant combine what happens in rotational molding, and electrostatic dusting of grass for model railways? Typed in Electrostatic Painting and there is loads on it. Turns out you can use liquid paint or powder. Over-spray is kept to a minimum. The downside they say "Is that unfortunately items being sprayed have to be Metallic!!" Shame it was going so well he jokes.
I got into serious trouble from the first Wife upon our arrival at her sisters new house in Philadelphia. "2 Two TWO days to paint the whole house?" she learned. "Ours has taken months!" YES The team arrive and mask up the electrical switches and lights. About two hours to fill and sand down. Then the whole house is sprayed YES EVERYTHING. The second coat is applied the next day. Then the glass is scraped and the masking comes off. Next day new carpets and flooring goes down. My problem was going for a difficult Livery. We all learn from our mistakes.
Best regards David and Lily.
PS Our Daughter would love this story!!!
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Post by doubletop on Oct 5, 2020 3:42:06 GMT
What a shame we cant combine what happens in rotational molding, and electrostatic dusting of grass for model railways? Typed in Electrostatic Painting and there is loads on it. Turns out you can use liquid paint or powder. Over-spray is kept to a minimum. The downside they say "Is that unfortunately items being sprayed have to be Metallic!!" Shame it was going so well he jokes. Best regards David and Lily. Back when I didn't really know what I was doing I had tried painting my Rob Roy frames with Hammerite Smooth. I had wanted something durable but it was hopeless with the edges thinning out. I stripped it all off and had them powder coated. Using high-temp tape I had to mask all the areas where any dimension critical components were to be mounted, cylinders, valve chest, saddle etc. I got the durable finish but powder coating isn't recommended for any prototypical work. It would be hard to get dual colours to work. Pete
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Post by Roger on Oct 5, 2020 7:14:46 GMT
One trick I've not seen mentioned elsewhere is the use of low tack masking tape to remove dust. Tack cloths are probably good enough for most applications and they certainly do remove a lot of dust. However, if you want to get it all off, firmly pressing down and pulling off masking tape will do a much better job. If you buy wide tape it doesn't take long, and it saves a lot of frustration.
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Post by jon38r80 on Oct 5, 2020 9:33:28 GMT
Electrostatic painting is used in the car industry to reverse the paint phenomenon of thinning at edges. It used to be a problem in that industry that the paint meniscus thinned coverage at edges which was why cars in my youff always rusted at panel edges, something quite rare these days. Because of the charged paint particles you now get thicker paint at panel edges bit like iron filings at magnet poles. Probably not beyond your electronics expertise Roger
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Post by Roger on Oct 5, 2020 10:11:45 GMT
Electrostatic painting is used in the car industry to reverse the paint phenomenon of thinning at edges. It used to be a problem in that industry that the paint meniscus thinned coverage at edges which was why cars in my youff always rusted at panel edges, something quite rare these days. Because of the charged paint particles you now get thicker paint at panel edges bit like iron filings at magnet poles. Probably not beyond your electronics expertise Roger It's not impossible to do, just impractical I'm afraid. You need scary voltages for this to work, and the gun has to be at those elevated levels for it to work. I was involved in the repair of the spray turbines at Honda in Swindon, so I know what's involved. It's not something you want to be doing at home in my opinion.
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Post by jon38r80 on Oct 5, 2020 22:39:39 GMT
Having done a quick read on the internet I understand your point about the voltages, not really something for home brew although the currents are tiny and that’s thbit hat kills if you get it through your ticker. It appears that it’s not much help in corners either due to the Faraday cage effect (at that point the explanation lost me) I think that adds weight to the tiny brush solution.
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Post by Roger on Oct 6, 2020 19:52:02 GMT
Slow progress because I've had a lot of commercial work to do that's been taking up machine time. There's a bit of a pause in that now, so here's the fixture for the second operation. The fixture has M1.4 holes for the mirrored part too. Here I'm counterboring one fixing hole to create the lug in this position. I'll leave 1.2mm thick for the lug and then screw it down with a bolt and do the same for the other three. I need to get close to these with small cutters, so I can't leave them too tall. They stand far enough away from the injector profile to allow me to get in close. It's not the quickest of operations because it's not held that firmly, and I don't want it to move. 20201006_203357 by Roger Froud, on Flickr 20201006_222854 by Roger Froud, on Flickr
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Post by Roger on Oct 7, 2020 20:17:24 GMT
This is a typical sight when returning to a job I've left running... 20201007_083300 by Roger Froud, on Flickr ... this time it's hiding some pretty messy machining. 20201007_083817 by Roger Froud, on Flickr Just a few burrs to clean up then. 20201007_103246 by Roger Froud, on Flickr It was roughed out with a 2mm cutter, so that couldn't get into all the nooks and crannies. Here I'm using a 1mm PCB 2-flute very gingerly to get down into those places. 20201007_150249 by Roger Froud, on Flickr You can see it's cleared out behind the overflow flange on the left. 20201007_163814 by Roger Froud, on Flickr Here's a 1mm ball nosed cutter starting to clean up the mess. Here's a video of that process. 20201007_170414 by Roger Froud, on Flickr It's not too bad, but I thought I'd give it a finishing pass at 90 degrees to see if that made a difference... 20201007_195131 by Roger Froud, on Flickr ... which it didn't really. I need to reduce the step over from 0.1mm to half that. Anyway, here's a video of it doing some of that. 20201007_195747 by Roger Froud, on Flickr So, not too bad for a first effort really... 20201007_202704 by Roger Froud, on Flickr ... only there's a problem with gouging on the underside of the outlet where the tool path has gone awry. 20201007_203112 by Roger Froud, on Flickr If you look at this closeup, you can see there's a triangular shape where you can see the model surface, and that's where the blue cutter centre line paths dive below the surface. Looking at the model closely, I can see what happened. I reduced the body diameter when I got the drawing for the 8X injector, and that left the necked part just short of the body. That tripped up the maths in the CAM module, causing the issue. Gouge by Roger Froud, on Flickr So I made that 0.5mm longer so it blends with the body, and that's solved the issue. It's made a nasty hollow in the part, but I can fill that with Silver Solder or just leave it and use this one on the RH side of the locomotive where it's on the back. We'll see. I might make another one, depending on how successful this first attempt turns out to be. Although the run times are long for these jobs, the main work I have to do is in the path preparation. Once that's proven, it's not a vast amount of effort to make another one, just a bit of a delay while it's machining. Gouge removed by Roger Froud, on Flickr
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Post by Roger on Oct 8, 2020 20:30:57 GMT
Here's the mirrored half of the injector getting the second operation... 20201008_102648 by Roger Froud, on Flickr ... I wonder why they call it Roughing? You can see how the milling cutter has managed to unscrew one of the fixing bolts! 20201008_134355 by Roger Froud, on Flickr This is the first one I made. If you look at the flange, you'll see that there's a witness on the top back face where the edge is slightly thinner. That's because the 1mm ball nosed cutter isn't long enough. This wouldn't normally happen on a proper CNC machine because this is really a 5-axis job. By that I mean that you'd be able to turn the vertical faces over slightly so the spindle was at say 5 degrees. That allows you to use a 1mm ball nosed cutter that's supported by a long shallow tapered shank. I don't have that luxury, so I have to create the vertical surfaces with a longer cutter. However, I don't have any, and I'm not sure if they're even available. 20201008_134927 by Roger Froud, on Flickr So I decided to just grind away the tapered part that's causing the issue using a diamond wheel... 20201008_134325 by Roger Froud, on Flickr ... so it looks like this. Obviously this it a lot less robust than it was, so I need to go a lot slower else I'll break it. Still, it's stronger than it would be if the flutes went all the way up to the shoulder. 20201008_134557 by Roger Froud, on Flickr So far so good, but it's going to take a few more hours to finish. I could probably go a bit faster, but at this stage it's safer to just let it finish. 20201008_184334 by Roger Froud, on Flickr
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dscott
Elder Statesman
Posts: 2,438
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Post by dscott on Oct 9, 2020 0:30:33 GMT
For wonderful INSPIRATION I still have an almost monthly visit to Item number 3209 on Station Road Steam. 1500 The Builder becoming friends with Louis Raper who built superb models Professionally. They have his 5800 in 7 1/4. I am still saving up... He was in turn friends with Ken Woodham. What a team to be inspired by.
The amount of swarf we produce and what we are left with is sometimes frightening. These are looking superb Roger.
David and Lily.
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Post by Roger on Oct 9, 2020 7:05:53 GMT
For wonderful INSPIRATION I still have an almost monthly visit to Item number 3209 on Station Road Steam. 1500 The Builder becoming friends with Louis Raper who built superb models Professionally. They have his 5800 in 7 1/4. I am still saving up... He was in turn friends with Ken Woodham. What a team to be inspired by. The amount of swarf we produce and what we are left with is sometimes frightening. These are looking superb Roger. David and Lily. Hi David, I copied all those photos some time ago as a cross reference, and my conclusion is that it's very close indeed to 1501. I don't know if it was ever intended to run though. I enquired as to who bought it, and they either didn't know or didn't want to tell me. It would have been interesting to have had a little more information about it and find out if it was ever finished. It's an absolutely superb piece of work. You're absolutely right about the amount of swarf. It's not exactly an efficient way to make injectors. It is going to be remarkably strong though, even with the very thin sections in places. Let's hope it works!
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Post by Roger on Oct 9, 2020 21:17:01 GMT
Ok, these are a bit rough, but I just want to assemble them and figure out whether the machining dimensions for the threads and 'O' rings are going to be satisfactory. It I can end up using this, then that's great, but I fully expect to have to make a few changes and then make two good ones. 20201009_101743 by Roger Froud, on Flickr I'm protecting the channels I can't access with Tippex to keep the Silver Solder away from those surfaces. Everything else is reachable from the outside. 20201009_102459 by Roger Froud, on Flickr I should have bolted these and used 0.8mm rivet holes not 0.85 because the fit was a little sloppy. That meant I had to squeeze the two halves to line them up better, and that caused this flange to gape open slightly. I've wired it, but ultimately had to give it a gentle squeeze with pliers while it cooled to make sure it stayed closed. I've wrapped thin Silver Solder through the bolt holes and also through the bores to give it something to start with. There's no way to lay the wire along the joints, so I'll have to feed some in too. 20201009_111243 by Roger Froud, on Flickr 20201009_111649 by Roger Froud, on Flickr 20201009_112500 by Roger Froud, on Flickr This end didn't quite take at the flange joint... 20201009_145919 by Roger Froud, on Flickr ... so I had to do that again. 20201009_162225 by Roger Froud, on Flickr 20201009_162252 by Roger Froud, on Flickr Anyway, it looks like it's sealed everywhere... 20201009_162324 by Roger Froud, on Flickr ... this side is less messy. I'll probably shot blast it when it's finished. 20201009_162335 by Roger Froud, on Flickr I created a block and then did a Boolean Subtraction to remove the shape of the injector. I created a third Configuration of the model with a few extra bits added and all the holes removed so it left a clean cavity in the shape of the injector with a few extra clearances. I've 3D printed these out of PLA which is pretty rigid. 20201009_195319 by Roger Froud, on Flickr 20201009_195346 by Roger Froud, on Flickr I'm now sorting out the machining programs for the four sides so I can do each one on the mill.
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Post by mugbuilder on Oct 9, 2020 23:28:01 GMT
Mind-boggling work there Roger. Absolutely superb and way beyond what the average model engineer could manage. What I can't figure out is why you have so much trouble with painting when all other aspects of the job are done so well. I think that you may be too fussy and expect too much of yourself. I expect that you are trying too hard and overcomplicating things a bit. This 'Speedy' is going to be a joy to behold when finished even if the paintwork is not up to your expectations. Barry
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Post by delaplume on Oct 10, 2020 0:18:34 GMT
Hi Roger........I'm told that there's no such thing as Subtraction in Boolean Mathmatics ??......
OK, that's me way outside my comfort zone !!.......LoL !!
Seriously though, that's a very impressive looking 8X injector....fingers crossed that it works ok...but I'm sure it will........
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Post by dhamblin on Oct 10, 2020 6:52:16 GMT
If there is any natural justice then the level of thought and work put in here deserves to succeed. It certainly looks like a great start.
Regards,
Dan
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