tender Posted October 12, 2012 Author Share Posted October 12, 2012 If you can build a Highlevel Chassis you can do P4. Well, hopefully that will the case by the end of this exercise, but yet remains to be seen, thanks for the encouragement. But I'd be very wary of plunger pick-ups. They make remarkably good brakes and prevent compensation/springing from working properly. Will That's not a very helpful statement, Will, you make it sound like an unquestionable fact. Perhaps "If not fitted carefully, they may make remarkably good brakes and prevent compensation/springing from working properly" would be more honest. After all, the same could be said of any form of wiper or or other method that adds friction. My 48XX is hardly the only example that runs quite well without such problems. Nick Mike Sharman once estimated that plunger pickups in 4mm were like putting a jack between the back of the wheel and the frame of a prototype loco and pumping it up hard! I've used them in 7mm with no problems, but in the smaller scale I do find they exert too much braking pressure, and they seem rather fiddly too, though that may be my fat fingers. Best to try them out and see how you get on; if they don't work for you then there's nothing lost except a modelling session or two! I did say be "very wary" not "don't" and it was late at night I was going for a good one line-er. However if you would like a bit more balance. I had one loco that ran well with them, in rigid OO using one side only insulation (pick ups one side only). It did tend to accumulate a ball of fibres on each pick up but that was not a significant issue. However rigid live chassis locos were not for me so I tried again when I moved on to a dead chassis loco (pick ups both sides) with full compensation. This did not give a happy, or working, result. I'm happy to agree that there is an adjustment issue here, but 1. I'm not at all clear that chopping the right amount of an already very small springs is a process that is going to be achieved reliably 2. these springs operate over quite a short range, so the difference between no contact, a gentle touch and firmly applied brakes is quite small. 3. and then you have to consider the impact on a sprung/compensated axle that moves relative to the chassis. Fitting them anywhere but on the axle centre line risks having a significant impact on the way the springing/compensation works. I'm only too aware that you should equally consider the like impact of ordinary rim scraper pick-ups too. After all I run CSB sprung locs's these days with the pick-ups bearing on the top of the wheels and hence forming part of the suspension! (I've been waiting for somebody to pick me up on that but nobody has, yet). None the less the distance across which a well designed rim scraper pick-up applies a relativity uniform and controllable pressure is huge compared to that available from a plunger pick-up. Oh yes, be careful the electrical connection isn't also effectively part of the spring acting on the plunger. When you can get plungers working then they do make a very tidy solution. But fool proof they are not. Will Ok, lots of debate here and I can appreciate what is being said regarding the pros and cons of plunger type contacts. Being new to this I don't know what the alternative is, maybe someone could offer a suggestion with a picture perhaps? Ray. P.S What's a CSB sprung Loco? Link to post Share on other sites More sharing options...
Will L Posted October 12, 2012 Share Posted October 12, 2012 ... P.S What's a CSB sprung Loco? Now there's a question. CSB = Continuous Spring Beams. For a relativity short description see http://www.scalefour...hp?p=6054#p6054 Will. Link to post Share on other sites More sharing options...
buffalo Posted October 12, 2012 Share Posted October 12, 2012 ...Ok, lots of debate here and I can appreciate what is being said regarding the pros and cons of plunger type contacts... There's plenty more that could be said but it's probably time to let you make a bit of progress. If you do decide to go for plungers, just ask because there are ways of preparing them that help to minimise the issues that Will mentions. Just ignore the Mike Sharman quote, though. The great man was really having an off day when/if he came up with that nonsense ..Being new to this I don't know what the alternative is, maybe someone could offer a suggestion with a picture perhaps?... P.S What's a CSB sprung Loco? Apart from Will's excellent scalefour link there are many examples of CSB on here as well as discussions of various pickup methods. The search mechanism may help. Nick Link to post Share on other sites More sharing options...
Trebor Posted October 12, 2012 Share Posted October 12, 2012 for in depth information on CSB's you could look at http://www.clag.org.uk/beam-annex3.html a wealth of information to digest on the subject. regards Link to post Share on other sites More sharing options...
Miss Prism Posted October 12, 2012 Share Posted October 12, 2012 Fitting them anywhere but on the axle centre line risks having a significant impact on the way the springing/compensation works. Will omitted an important word in describing plungers, and the above should read: "Fitting them anywhere but on the vertical axle centre line risks having a significant impact on the way the springing/compensation works." Link to post Share on other sites More sharing options...
Nigelcliffe Posted October 12, 2012 Share Posted October 12, 2012 Alternative pickup methods..... There are lots, but sticking with what probably works easily with a High Level kit, without massive modifications, then, I'd suggest what I have done on my 0-4-0's from High Level. Fit a very small piece of double sided thin printed circuit board to an obscure part of the frames, on the outside. I use very thin PCB of around 0.3mm or 0.5mm thickness. Make up some pickups from fairly thin phosphor bronze wire (Eileens sell it). The pickups I make have a small coil wound into them to provide springing pressure onto the wheel tread; see very rough sketch below for pickup from two wheels: I tend to fit this towards the top of the frames, so it is hidden under the footplate. Paint it after connecting wires to the PCB. Using double sided means it can be soldered to the frames on the back, or it can be stuck onto the frames with adhesive. Link to post Share on other sites More sharing options...
jjnewitt Posted October 12, 2012 Share Posted October 12, 2012 I'd like to put a vote in for the coiled wire pickup method as mentioned by Nigelliffe, this is standard on all my locos and I find works well. I use 33 SWG phospher bronze wire which is availiable from Eileen's. This is an example as fitted to a hacked up Bachmann Class 47 drivetrain that went into a homemade P4 sprung bogie but the same principle applies whatever the model. I make the coil in the pickup the same way as the working coil springs for my bogies. Just wind the wire around the shank of a suitably sized drill bit held in a pin vice, three or four turns should suffice to get enough spring. If you put a bend in the end of the wire before you turn the coils and feed this into the jaws of the pin vice then it will hold the wire taught while you merrily turn away. Link to post Share on other sites More sharing options...
ozzyo Posted October 12, 2012 Share Posted October 12, 2012 Will omitted an important word in describing plungers, and the above should read: "Fitting them anywhere but on the vertical axle centre line risks having a significant impact on the way the springing/compensation works." Are you sure on that one? Would the horizontal C/L not be better? OzzyO. Link to post Share on other sites More sharing options...
Horsetan Posted October 12, 2012 Share Posted October 12, 2012 Are you sure on that one? Would not the horizontal C/L not be better? Which one is correct? I'm confused now. Link to post Share on other sites More sharing options...
Will L Posted October 12, 2012 Share Posted October 12, 2012 Will omitted an important word in describing plungers, and the above should read: "Fitting them anywhere but on the vertical axle centre line risks having a significant impact on the way the springing/compensation works." I agree I could have been more specific but I would have said the missing word was Horizontal. In that position theoretically at least any twist on the axle resulting from the plungers bearing on the rim being unbalanced will be resisted by the wheel bearings/frames which (should) have no give in that direction. In any other position some of that twist can be translated into vertical movement of one end of the axle. Perhaps a more practical objection is that should the plungers be a bit tighter than one would wish, they can prevent the wheel axle reacting fully to the weight on the stringing/compensation, leading to lifted wheels and unexplained derailments. Plungers mounted on the horizontal axle centre line will minimise this effect. This was the failing i found in my second failed attempt to use the things and exactly why I wouldn't recommender them. Link to post Share on other sites More sharing options...
Flymo748 Posted October 12, 2012 Share Posted October 12, 2012 And for further explanations of how to fit pick-ups on Very Small High Level locomotives, there is a thread about it here: http://www.scalefour.org/forum/viewtopic.php?f=20&t=1948. It includes my contribution which is one of the wound variants, under a High Level Pug chassis. There are several useful tips there and a good discussion of the pros and cons of different arrangements of wipers. Nothing on plunger pick-ups though, I'm afraid ;-) HTH Flymo Link to post Share on other sites More sharing options...
ozzyo Posted October 12, 2012 Share Posted October 12, 2012 Which one is correct? I'm confused now. vertical is above and below the C/L and horizontal is to the L/H or R/H of the centre line. So how would you mount the plungers at rail hight, or above the frames with a large wheeled loco? OzzyO. Link to post Share on other sites More sharing options...
buffalo Posted October 12, 2012 Share Posted October 12, 2012 I agree I could have been more specific but I would have said the missing word was Horizontal. In that position theoretically at least any twist on the axle resulting from the plungers bearing on the rim being unbalanced will be resisted by the wheel bearings/frames which (should) have no give in that direction. In any other position some of that twist can be translated into vertical movement of one end of the axle... Yes, I read it as horizontal and I broadly agree that they should be positioned close to this line. However, you are missing the point that your argument applies only to a single-sided pickup arrangement and, in that case, the unbalaced sideways force may be more of a problem, particularly if there is side-play on the axles. If the pickups are placed symmetrically on both frames then the forces are roughly balanced. In practice, plus or minus 15 degrees around the wheel circumference is good enough to keep the very small forces* reasonably balanced. Given typical suspension movements of plus or minus 0.5mm at most, this is something of a red herring. ...Perhaps a more practical objection is that should the plungers be a bit tighter than one would wish, they can prevent the wheel axle reacting fully to the weight on the stringing/compensation, leading to lifted wheels and unexplained derailments. Plungers mounted on the horizontal axle centre line will minimise this effect. This was the failing i found in my second failed attempt to use the things and exactly why I wouldn't recommender them. So, what you are saying is that if you set them up wrongly, then things might go wrong. I could equally say that if you put the fulcra of a CSB system in the wrong places then it won't work as expected. Neither are valid criticisms of the method, just of the particular mis-application of the method. So, can we get back to showing Ray some different ways of doing things, rather than trying to prove that because you didn't get it right the method must be flawed? Nick * typical compressive force on a Gibson plunger varies from 3-10gF over its working length, a trivial amount compared to other forces at work in a suspension system. Link to post Share on other sites More sharing options...
tender Posted October 12, 2012 Author Share Posted October 12, 2012 Wow, lots of posts here so I'll just update where I am today and add some more comments/questions later when I've have more time to digest. Thanks to Mike(meg) and Miss Prism, 4 Hornblock assembly's now complete and all sliding smoothly in the etch. Regarding the positioning of the plunger type contact, it seems to me to make more sense to position them on the horizontal C/L (i.e.left or right) as if vertically positioned (up/down) isn't there a danger that the contact will slip of the rim of the wheel (or into the centre) as the compensation rides up/down? But then again I'm the noddy here so could be totally missing the point. Ray. Sorry Nick, your post slipped in front of me. Link to post Share on other sites More sharing options...
tender Posted October 13, 2012 Author Share Posted October 13, 2012 Forgot to post a picture of the Hornblocks yesterday, so here it is. Spent last night reading the links to the Scalefour website regarding CSB's. I must say i like this idea so have been looking to see if it's possible to convert the 14xx chassis to this system. Looking at the hornblocks i have, there is a small turned ring on the face of the block so i'm presuming this is for locating an additional etch for the spring wire to pass through (as shown here http://www.scalefour.org/forum/viewtopic.php?f=19&t=947&start=50 under the heading The Etched Bits, by Will L), maybe someone can confirm this for me. Seems the only other thing required is the Handrail knobs (mentioned by Will L) for the fulcrum points and a selection of guitar strings. Presumably the original pivot bars for the front and rear wheels and the compensation beams supplied with the High Level kit would become superfluous. It all sounds relatively straightforward, but then there's that spreadsheet (here http://www.scalefour.org/forum/viewtopic.php?f=19&t=947&start=25, again mentioned by Will L) for working out where to put the fulcrum points and getting the balance right. And how do you work out the axle loading before you've even built the model? Maybe i should just stick with the High Level instructions for this first build, unless somebody has already done it and can advise one way or the other! I've also been looking at the alternative suggestions for the pickups. Quite a few are based on a wound coil of phosphor bronze with the end resting perpendicular to the rim edge of the wheel. I would have thought that this would have worn through pretty quickly. I think i'll give the Alan Gibson contacts a try as i already have them, i can always retro fit the alternatives suggested later if required. Ray. Link to post Share on other sites More sharing options...
Coombe Barton Posted October 13, 2012 Share Posted October 13, 2012 I've also been looking at the alternative suggestions for the pickups. Quite a few are based on a wound coil of phosphor bronze with the end resting perpendicular to the rim edge of the wheel. I would have thought that this would have worn through pretty quickly. I think i'll give the Alan Gibson contacts a try as i already have them, i can always retro fit the alternatives suggested later if required. Too many people, on here and at demos at exhibitions, have warned me off these. I also have a squad of them, but am putting their purchase down to experience and using PB wire. Link to post Share on other sites More sharing options...
Nigelcliffe Posted October 13, 2012 Share Posted October 13, 2012 Maybe i should just stick with the High Level instructions for this first build, unless somebody has already done it and can advise one way or the other! Build your first High Level following the instructions. Then it **will** work. You will gain experience and understanding of how a good design goes together. Then, if you want to, try modifications from the instructions. Chris at High Level is one of those producing parts for CSB's. So, some of his designs are suitable for such systems. But, bear in mind that a lot of the parts and assumptions are for P4, which has a lot more space between the frames than OO due to both the difference in track gauge and the thinner wheel section. You asked a question about wheel movement on a pickup for compensation, and loosing contact with the wheel. It should not be an issue. If a wheel moves more than 0.5mm on normal running on the track, then your track needs fixing. The idea of suspension/compensation climbing over matchsticks is a comic demonstration of an underlying principle, not an illustration of what you should be doing on your railway. - Nigel Link to post Share on other sites More sharing options...
Miss Prism Posted October 13, 2012 Share Posted October 13, 2012 Spent last night reading the links to the Scalefour website regarding CSB's. I must say i like this idea so have been looking to see if it's possible to convert the 14xx chassis to this system. You don't need a 'CSB' for a 4-coupled. A couple of springy equalisers will do the job. (In effect, these are merely the kit's rigid beams made thin enough to flex vertically.) With springy equalisers pivotting on their midpoint, the static force on each axle will be equal regardless of where the loco centre of gravity is. (Unlike the proper 'CSB', where more attention has to be paid to balance.) Looking at the hornblocks i have, there is a small turned ring on the face of the block so i'm presuming this is for locating an additional etch for the spring wire to pass through (as shown here http://www.scalefour...&t=947&start=50 under the heading The Etched Bits, by Will L), maybe someone can confirm this for me. Chris Gibbon will give you some etched carriers if you ask. Presumably the original pivot bars for the front and rear wheels and the compensation beams supplied with the High Level kit would become superfluous. Yes. You could keep the trailing axle rigid, or mount it on its own springs. It all sounds relatively straightforward, but then there's that spreadsheet (here http://www.scalefour...&t=947&start=25, again mentioned by Will L) for working out where to put the fulcrum points and getting the balance right. No spreadsheet is necessary for the 4-coupled, because a CSB (if you choose that option) will be symmetrical. Look at the Symmetrical 2-axle case. For a coupled wheelbase of say 29mm, the distance between each axle and its outermost fulcrum should be the same but could be anything between 9 and 11mm - it doesn't really matter. Don't try to be too clever and put a CSB over all three axles. And how do you work out the axle loading before you've even built the model? The advantage of the springy equaliser route is that you don't have to know it. Whatever route is taken, you'll need to pay some attention to final balance. Link to post Share on other sites More sharing options...
Will L Posted October 13, 2012 Share Posted October 13, 2012 Forgot to post a picture of the Hornblocks yesterday,.. Don't forget to mark the two parts of each set so you keep them together. Don't assume that they are interchangeable, they probably are not. Spent last night reading the links to the Scalefour website regarding CSB's. I must say i like this idea so have been looking to see if it's possible to convert the 14xx chassis to this system. Glad you like the links, but my view, for what its worth, that for a first build it's worth going with the kit instruction. The 14xx was a fair choice as a first build and what you need to get you going is a success. I'd save your first CSB for a classic 0-6-0. Will Link to post Share on other sites More sharing options...
buffalo Posted October 13, 2012 Share Posted October 13, 2012 ...Maybe i should just stick with the High Level instructions for this first build, unless somebody has already done it and can advise one way or the other!... I agree with Nigel and Will here, stick with the instructions for this build. Although, in theory, an 0-4-2 could be treated as an 0-6-0 for a CSB, in practice it will not be anything like as straightforward as a real 0-6-0. I've also been looking at the alternative suggestions for the pickups. Quite a few are based on a wound coil of phosphor bronze with the end resting perpendicular to the rim edge of the wheel. I would have thought that this would have worn through pretty quickly. I think i'll give the Alan Gibson contacts a try as i already have them, i can always retro fit the alternatives suggested later if required. Firstly, the coiled phosphor-bronze wire approach as ably demonstrated by Justin is an excellent solution and I wouldn't worry about it wearing out. If it does, then it is easy to replace. Mine only get limited running, so perhaps others with more long-distance running can comment, but I doubt that wear will be an issue with any approach. However, if you do decide to go with the plungers, as the only one around here who seems prepared to support them, I'd better give you a few hints as to how to make them work well. Hopefully, others may find these comments useful as well. Firstly, the set on the right are the Gibson type straight out of the packet. Those on the left are a much older type whose source I cannot remember (I've had them for about 30 years), but I'll return to them briefly later. The first thing to notice is that both the brass plunger and the plastic bush are a bit rough. They're not all this bad, I've deliberately chosen bad examples to illustrate the point. Cleaning them up is essential if you are to get smooth working and I suspect some folk go wrong by not doing this carefully enough. The plunger has a small pip on the tip where it has been parted off after turning. Clean this off by rubbing on a bit of fine wet/dry paper until you have a nice smooth curve on the face that will contact the back of the wheel rim. More important is the slight lip that usually remains from turning at the other end of the large diameter section. The one in the photo even has some nasty swarf in this area. Any lip or swarf must be removed, you should aim for a small radius on this step to minimise the chances of the plunger snagging in the bush. The bush has some moulding flash on both inside and outside faces. This also needs cleaning. I thin the outer face by rubbing it on wet/dry, clean out the bore with very light use of a drill bit (1.7mm IIRC), then use a larger, say 3mm, bit to cut a very light chamfer in the outside end of the bore. For working on both plunger and bush, it is helpful to hold them in a pin chuck. The results should look a bit like this: When fitting the plunger, use as fine a wire as you can find (I use wire sold for DCC decoder fitting) and make sure it is free to move without snagging on anything. Bend the tail of the plunger so that it keeps the thick part inside the bush, then always use some form of heatsink and solder as quickly as you can when attaching the wire to the end of the tail because the bush is easily melted. Here's an example where I got it wrong. The damage wasn't immediately apparent, but only appeared after several hours running: You'll notice a second, shorter spring in the second photo. I've included this because folk often mention shortening the spring to reduce the pressure. The first thing to realise about this is that in theory it is nonsense. The only ways to get a softer spring are: 1. use a thinner wire, or a material with a lower modulus (e.g. phosphor bronze is less stiff than steel) 2. use larger diameter coils 3. use more coils Shortening a spring reduces the number of free coils so increases its rate (makes it stiffer). However, it's not that simple in practice because a shortened spring may be acting over a range where the compression force is lower because it has not been compressed as far as a longer one would be. So, does it work? What is the effect of shortening springs in this case? I set up a plunger in a chuck so that it was free to move and measured the force required to compress it to a typical working position. I measured the force over the full range of the plunger, but chose for comparison a position with about 0.75mm of the plunger sticking out from the bush. This is about what I would use on a P4 model. Using the normal spring, the force on the plunger ranged from 3 to 8 grammes over the full length of plunger movement. At the 0.75mm position it was 6gF: The shortened spring had three coils removed and the results for the same experiment gave a range of 0 to 11 grammes over the full range and 6.5 at the 0.75mm position. Hence, I conclude that you might get a lower force when the plunger is further extended, but that is probably only possible in 00, perhaps EM. With the limited space between frame and wheel in P4, you are more likely to get a stiffer spring! So, why did I include that older unidentified plunger in the first picture? Notice that it has a steel spring with very small diameter coils so we would expect it to be quite stiff. Using the same test setup as above and measuring at the same 0.75mm extension, the force was 15.8gF. Still nothing like putting a jack behind the driving wheel but nevertheless somewhat higher than the Gibson plungers. Maybe these, or even an even stiffer predecessor, were what Mike Sharman had in mind when he made that oft-quoted comment? Nick Link to post Share on other sites More sharing options...
tender Posted October 13, 2012 Author Share Posted October 13, 2012 Don't forget to mark the two parts of each set so you keep them together. Don't assume that they are interchangeable, they probably are not. Yes, thanks for reminding me of that Will. I've already found just turning the block through 90deg can make a difference. Build your first High Level following the instructions. Then it **will** work. You will gain experience and understanding of how a good design goes together. Don't try to be too clever and put a CSB over all three axles. Glad you like the links, but my view, for what its worth, that for a first build it's worth going with the kit instruction. The 14xx was a fair choice as a first build and what you need to get you going is a success. I'd save your first CSB for a classic 0-6-0. Will I agree with Nigel and Will here, stick with the instructions for this build. Although, in theory, an 0-4-2 could be treated as an 0-6-0 for a CSB, in practice it will not be anything like as straightforward as a real 0-6-0. 'Ah, well, it's no use prevaricating about the bush...' All this good advice is leading me to the same conclusion, stick to the instructions and save CSB's for another day. Firstly, the coiled phosphor-bronze wire approach as ably demonstrated by Justin is an excellent solution and I wouldn't worry about it wearing out. If it does, then it is easy to replace. Mine only get limited running, so perhaps others with more long-distance running can comment, but I doubt that wear will be an issue with any approach. However, if you do decide to go with the plungers, as the only one around here who seems prepared to support them, I'd better give you a few hints as to how to make them work well. Hopefully, others may find these comments useful as well. Firstly, the set on the right are the Gibson type straight out of the packet. Those on the left are a much older type whose source I cannot remember (I've had them for about 30 years), but I'll return to them briefly later. The first thing to notice is that both the brass plunger and the plastic bush are a bit rough. They're not all this bad, I've deliberately chosen bad examples to illustrate the point. Cleaning them up is essential if you are to get smooth working and I suspect some folk go wrong by not doing this carefully enough. The plunger has a small pip on the tip where it has been parted off after turning. Clean this off by rubbing on a bit of fine wet/dry paper until you have a nice smooth curve on the face that will contact the back of the wheel rim. More important is the slight lip that usually remains from turning at the other end of the large diameter section. The one in the photo even has some nasty swarf in this area. Any lip or swarf must be removed, you should aim for a small radius on this step to minimise the chances of the plunger snagging in the bush. The bush has some moulding flash on both inside and outside faces. This also needs cleaning. I thin the outer face by rubbing it on wet/dry, clean out the bore with very light use of a drill bit (1.7mm IIRC), then use a larger, say 3mm, bit to cut a very light chamfer in the outside end of the bore. For working on both plunger and bush, it is helpful to hold them in a pin chuck. The results should look a bit like this: When fitting the plunger, use as fine a wire as you can find (I use wire sold for DCC decoder fitting) and make sure it is free to move without snagging on anything. Bend the tail of the plunger so that it keeps the thick part inside the bush, then always use some form of heatsink and solder as quickly as you can when attaching the wire to the end of the tail because the bush is easily melted. Here's an example where I got it wrong. The damage wasn't immediately apparent, but only appeared after several hours running: You'll notice a second, shorter spring in the second photo. I've included this because folk often mention shortening the spring to reduce the pressure. The first thing to realise about this is that in theory it is nonsense. The only ways to get a softer spring are: 1. use a thinner wire, or a material with a lower modulus (e.g. phosphor bronze is less stiff than steel) 2. use larger diameter coils 3. use more coils Shortening a spring reduces the number of free coils so increases its rate (makes it stiffer). However, it's not that simple in practice because a shortened spring may be acting over a range where the compression force is lower because it has not been compressed as far as a longer one would be. So, does it work? What is the effect of shortening springs in this case? I set up a plunger in a chuck so that it was free to move and measured the force required to compress it to a typical working position. I measured the force over the full range of the plunger, but chose for comparison a position with about 0.75mm of the plunger sticking out from the bush. This is about what I would use on a P4 model. Using the normal spring, the force on the plunger ranged from 3 to 8 grammes over the full length of plunger movement. At the 0.75mm position it was 6gF: The shortened spring had three coils removed and the results for the same experiment gave a range of 0 to 11 grammes over the full range and 6.5 at the 0.75mm position. Hence, I conclude that you might get a lower force when the plunger is further extended, but that is probably only possible in 00, perhaps EM. With the limited space between frame and wheel in P4, you are more likely to get a stiffer spring! So, why did I include that older unidentified plunger in the first picture? Notice that it has a steel spring with very small diameter coils so we would expect it to be quite stiff. Using the same test setup as above and measuring at the same 0.75mm extension, the force was 15.8gF. Still nothing like putting a jack behind the driving wheel but nevertheless somewhat higher than the Gibson plungers. Maybe these, or even an even stiffer predecessor, were what Mike Sharman had in mind when he made that oft-quoted comment? Nick Hi Nick. I'm glad somebody likes them, I always look on wipers on RTR as my worst nightmare, their so easy to damage when stripping down a loco. When i first saw the Alan Gibson plunger contacts I thought what a great idea. Obviously reading here not to every[most]bodys taste. Anyway, i'm going to give them a try so your comments re preparing and setting them up are going to come in realy useful. Like i said earlier if it does give problems it shouldn't be too difficult remove and retrofit a coil wound PB contact. Not so the other way round. So, whats progress today. Well not a lot, apart from cutting out the frames and cross members from the fret, then realising that i need a selection of very small drills to drill out the tiny holes in the etch (to accept the various bits of brass wire later in the build) before bending up. My drill set only goes up in 0.5mm increments from 1mm so not much use there. Not the sort of thing you get from B&Q so another internet order required. You'd think that living near a city such things would be freely available, but not in remotest N.Wales. Moving on I thought i'd make up the rear wheel carriers. These are three bits off etch laminated together to make something similar to the hornblocks for the rear wheels. On reading the instructions i came across a phrase (technique) i'm not familar with, Quote 'sweat all the layers together using the minimum amount of solder then try the assemblies in the frame to ensure they are a smooth sliding fit.' so hope somebody here can explain the process 'sweat'. Ray. Link to post Share on other sites More sharing options...
RMweb Premium MPR Posted October 13, 2012 RMweb Premium Share Posted October 13, 2012 Hi Ray, Nice to see a High Level 14xx kit being built - it reminds me I've got one I really must get round to... Regarding "sweating," it is a technique to join pieces without adding solder when making the joint. Each piece is "tinned" on both sides (i.e a thin layer of solder is applied to the individual pieces), the parts are aligned, then heat is applied from the iron to reflow all the solder and make a good joint. The keys to completing a successful sweated joint are the same as any other soldering operation 1) Scrupulous cleanliness of the pieces - clean with fine emery or glass fibre brush if there is serious oxidation of the surfaces. 2) Clean iron and fresh solder application to the iron (again to limit surface oxidation) 3) Liquid flux on the\workpiece You are aiming to get a very thin layer of solder on ALL the joining surfaces -if you can't get 100% coverage when you wipe each surface with the iron, it probably isn't clean enough. When making the actual joint,remember you are trying to get the whole area of the joint above 145C to allow everything to flow - a well tinned bit has a much bigger surface area in direct contact with the material, and in the initial stage of heating, liquid flux will conduct heat much better (before it boils off). An oxidised bit is also a much poorer conductor of heat. It's a good idea to start with the tip at the edge - for small joints the initial touch may be enough, otherwise move the iron around the edge - you may not even have to touch the middle (and have to clean where you've touched). If you've got it right, steam will quickly flash from the joint followed by a silvery gleam around the edges as the solder is drawn by surface tension out to the edges. Good Luck! Martin Link to post Share on other sites More sharing options...
RMweb Gold The Fatadder Posted October 13, 2012 RMweb Gold Share Posted October 13, 2012 Interesting thread as I have one of these as a first p4 chassis build Interested to read the feedback on plunger pickups, as I'm also not a fan of wipers, and given the complexity of a split chassis build was very tempted by plungers Link to post Share on other sites More sharing options...
Miss Prism Posted October 13, 2012 Share Posted October 13, 2012 I would like to clarify my understanding of the situation of the effects of plunger pickups on spring-suspended wheels. A plunger pickup exerts a force F at point A on the horizontal axis of a clockwise-rotating suspended wheel. A reaction force uF on the wheel is produced at point A, where u is the coefficient of friction between the plunger and the wheel tyre. The direction of this reaction force is opposite to the direction of the wheel at that point. This reaction force will produce a moment at point O. The magnitude of the moment is uF x distance OA. The moment will make the wheel want to rotate about point A instead of point O. The centre of the wheel will therefore want to move upward at point O, i.e. its downforce on the rail will reduce. If the plunger is applied at point B on a clockwise-rotating wheel, the reaction force will make the wheel want to move downward at point O, and its downforce on the rail will increase. In this way, a plunger will load or unload the suspension according to which side of the wheel it is placed and the direction the wheel is rotating. Is the moment significant? Let's put some figures to it. Nick has explained the plunger force will itself vary, but let's take his typical mid-travel value of 6g. For a typical coefficient of friction between phosphor-bronze and steel of 0.35, the reaction force uF will be approx 2g at the tyre, which will produce a moment of approx 18gmm at point O for a typical sized driving wheel. Countering this moment will be the springrate of the wheel itself, typically 70g/mm in 4mm scale. What we can conclude is that the moment will not affect the wheel unduly when the wheel is fully loaded, but it will affect the wheel loading significantly when it is toward its unloaded state. (The height difference between a wheel's fully loaded and fully unloaded states will be less than 1mm.) For a full chassis of several sprung axles, the effects of a series of plungers will become unpredictable at the least, and will prevent the spring system operating ideally. The plunger position providing a zero vertical moment at point O will be given only by mounting it on the wheel's vertical centreline. Unfortunately, the most convenient position for a plunger is on the wheel's horizontal centreline, and the most inconvenient position for a plunger is on the wheel's vertical centreline. A classic modeller's dilemma. Much the same critique can be made of non-plunger type tyre pickups of course. (Cue the split-axle fans.) Link to post Share on other sites More sharing options...
tender Posted October 14, 2012 Author Share Posted October 14, 2012 Hi Ray, Nice to see a High Level 14xx kit being built - it reminds me I've got one I really must get round to... Regarding "sweating," it is a technique to join pieces without adding solder when making the joint. Each piece is "tinned" on both sides (i.e a thin layer of solder is applied to the individual pieces), the parts are aligned, then heat is applied from the iron to reflow all the solder and make a good joint. The keys to completing a successful sweated joint are the same as any other soldering operation 1) Scrupulous cleanliness of the pieces - clean with fine emery or glass fibre brush if there is serious oxidation of the surfaces. 2) Clean iron and fresh solder application to the iron (again to limit surface oxidation) 3) Liquid flux on the\workpiece You are aiming to get a very thin layer of solder on ALL the joining surfaces -if you can't get 100% coverage when you wipe each surface with the iron, it probably isn't clean enough. When making the actual joint,remember you are trying to get the whole area of the joint above 145C to allow everything to flow - a well tinned bit has a much bigger surface area in direct contact with the material, and in the initial stage of heating, liquid flux will conduct heat much better (before it boils off). An oxidised bit is also a much poorer conductor of heat. It's a good idea to start with the tip at the edge - for small joints the initial touch may be enough, otherwise move the iron around the edge - you may not even have to touch the middle (and have to clean where you've touched). If you've got it right, steam will quickly flash from the joint followed by a silvery gleam around the edges as the solder is drawn by surface tension out to the edges. Good Luck! Martin Thanks for the explanation on 'sweating'. Before I make a hash of it, I thought I'd put up a picture of the bits involved just in case there's something else i need to consider. It all looks a bit frightening to me considering this has to slide smoothly in the frame. On the left are the four components to be 'sweated' together. The right most component is the four bits dry assembled. What worries me is that the faces of the two outer bits when tinned will make the channel formed by the narrower middle piece a too tight a fit when slid onto the frames. Is it just a case of going for it and cleaning out the channel after soldering or is there an easier solution. Ray. Link to post Share on other sites More sharing options...
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