ozzyo Posted November 1, 2012 Share Posted November 1, 2012 So, how do you stop the crank pins unscrewing when you tighten the nut up against the crank pin bush? Ray Hello Ray, if its a screw that goes in from the back of the wheel, some people melt in a small staple that fits into the screwdriver slot. On Slater's wheels I use Loctite 290. OzzyO. EDIT for PS. if the bush that the coupling rod runs on is also screwed it should act as a lock nut. Link to post Share on other sites More sharing options...
PenrithBeacon Posted November 1, 2012 Share Posted November 1, 2012 ... Doesn't that make the screws a loose fit, my wheel were pre-drilled and the crank pins (screws) cut themselves in. I did countersink the back a bit for the head of the screw. ... Ray. No, not in my experience. The top of the threads 'catch' the o/d of the hole and screw into it just fine. Although many, but not all, AG wheels do have a hole for the screw moulded in, my experience is that this hole is too small and is smaller than the root diameter of the screw. I think that this is the cause of the 1mm screw 'crankpin' 'going in' as it where at an angle and not perpendicular to the wheel. I think it also has to be borne in mind that the plastic is very soft and hence very ductile. I think that this property makes it susceptable to 'creep' and the moulded and drilled hole will close to a degree over time. I have to say that I scrapped a good many AG wheels until I worked out a method of dealing with this problem and that method included the purchase of a drill press to get the crankpin hole and the axle hole square to the back of the wheel. I have needed this machine for years and I finally took the plunge simply because I couldn't see the solution unless I laid out the dosh. Regards Link to post Share on other sites More sharing options...
Horsetan Posted November 1, 2012 Share Posted November 1, 2012 ..... Although many, but not all, AG wheels do have a hole for the screw moulded in, my experience is that this hole is too small and is smaller than the root diameter of the screw. I think that this is the cause of the 1mm screw 'crankpin' 'going in' as it where at an angle and not perpendicular to the wheel. I think it also has to be borne in mind that the plastic is very soft and hence very ductile. I think that this property makes it susceptable to 'creep' and the moulded and drilled hole will close to a degree over time. I used to try to get round this by "starting" the crankpin screw at both front and rear faces of the wheel centre. Sometimes this worked, but not always. The more recent AGW wheels I have used seem to be better at permitting a properly-mounted crankpin screw; is this due to a change in the formulation of the plastic? The drill press is useful if you've got room on your desk for one. Then you'll wonder how you ever coped without it. If you really wanted, you could try re-drilling the crankpin hole in order to use Ultrascale crankpins, as Dave Bradwell occasionally recommends. I will have to try this eventually on the AGW 5ft driver intended for the BR 9F. Link to post Share on other sites More sharing options...
tender Posted November 1, 2012 Author Share Posted November 1, 2012 EDIT for PS. if the bush that the coupling rod runs on is also screwed it should act as a lock nut. Hi OzzyO. The bushes that the coupling rods run on have a plain clearance hole in the crankpin. Anyway, moving on, I now have the coupling rods fitted and the crank pins are no longer fouling the chassis. However I still have one stiff spot. It occurs when the left side coupling rod lies through the centre line of the axles with the crankpins facing the rear. The compensation also becomes stiff at this point. Rotating the wheel through 180 degress so the crankpins face the front and its okish. I'm wondering if I have the holes in the coupling rods too snug a fit, but thought i'd ask here first just in case i'm barking up the wrong tree. I don't want to open them up and make them sloppy if not necessary. Ray. PS. i should add i assembled the wheels with a GW quartering jig so I'd be suprised if it was a quartering problem. Link to post Share on other sites More sharing options...
Will L Posted November 1, 2012 Share Posted November 1, 2012 So, how do you stop the crank pins unscrewing when you tighten the nut up against the crank pin bush? Any reason why it should? The moulded hole in the wheel (or the the hole you have to drill if there isn't one) is sized so the steel crank pin must cut it's own thread on the way through. If you've managed to get the crank pin to go through any other way than strait down the hole, do tell us how, so we can avoid making the same mistake. All I know is that left to their own devices they follow the easiest path through, which, given the depth of the hole is more than twice the effective diameter of the pin, is to follow the line of the hole. I haven't ever had had one go any way other than strait down the hole. Of course if you've made the hole over size by sticking a drill though first.... Having cut their own thread through about 2mm of plastic, the crank pin is now held quite tightly in the wheel, No way should running a proper crank pin nut down the crank pin generate enough force it to turn back. You should only need to apply any real force one you are locking the nut against the bush and the crank pin can't turn back then. Your problem stemmed from using sleeving as a temporary nut. This will have a tight grip on the pin and thus getting this on is well able to turn the pins back. I use plain 14ba nuts at this stage as they are easier to get to grips with than the Gibson round ones, particular if you have a 14ba nut spinner (GW do just the thing). Will Link to post Share on other sites More sharing options...
Jol Wilkinson Posted November 1, 2012 Share Posted November 1, 2012 Hi OzzyO. The bushes that the coupling rods run on have a plain clearance hole in the crankpin. Anyway, moving on, I now have the coupling rods fitted and the crank pins are no longer fouling the chassis. However I still have one stiff spot. It occurs when the left side coupling rod lies through the centre line of the axles with the crankpins facing the rear. The compensation also becomes stiff at this point. Rotating the wheel through 180 degress so the crankpins face the front and its okish. I'm wondering if I have the holes in the coupling rods too snug a fit, but thought i'd ask here first just in case i'm barking up the wrong tree. I don't want to open them up and make them sloppy if not necessary. Ray. PS. i should add i assembled the wheels with a GW quartering jig so I'd be suprised if it was a quartering problem. Try slacking off and then retightening the crank pin nuts in this position. The CP bushes probably have a few thou play on the CP and can end up being slightly off centre. If you get a build up of tolerances, then it sometimes shows as being tight in one position. The bush bore can also be eccentric, as these small items aren't always that accurate. Try different bushes on that coupling rod. It's all a bit of trial and error, but you are probably looking at .005". If that doesn't work, open out the CP holes in the rods very slightly, until the problem goes. Link to post Share on other sites More sharing options...
Will L Posted November 1, 2012 Share Posted November 1, 2012 ...However I still have one stiff spot. It occurs when the left side coupling rod lies through the centre line of the axles with the crankpins facing the rear. The compensation also becomes stiff at this point. It's not unusual to get a stiff spot of that sort on first assembly. This is because there are a lot of possible sources of error that can add together to produce a miss match between the distance over the crank pin holes in the connecting rod, and the equivalent distance over the crank pins. So long as there isn't an obvious significant error in the works, then opening up the crank pin holes is the way to go, though don't go too far down this rout if things aren't obvious improving as there will be something else that isn't quite right. In practice most stiff spots can be solved by opening up the crank pin holes, if there is enough meat in the coupling rods for the size hole you need, but it isn't very satisfying from an engineering point of view and very sloppy holes mean the driven axle can turn a significant distance before the rest join in, which isn't pretty.. Just seen Jol's advice, which is a good starting point as the crank pin bush is often overlooked as a source of error. Just remember that cutting your teeth on a 4 coupled loco is a good thing as this problem only multiples with additional axles. Will Link to post Share on other sites More sharing options...
ozzyo Posted November 1, 2012 Share Posted November 1, 2012 crank pin holes in the connecting rod, and the equivalent distance over the crank pins. So long as there isn't an obvious significant error in the works, then opening up the crank pin holes is the way to go, though don't go too far down this rout if things aren't obvious improving as there will be something else that isn't quite right. In practice most stiff spots can be solved by opening up the crank pin holes, if there is enough meet in the connecting rod Just remember that cutting your teeth on a 4 coupled loco is a good thing as this problem only multiples with additional axles. Will Sorry to say this but opening the holes in the connecting rods wont help at all as these are on the inside of the frames between the driven axle and the cross-heads. But opening up the holes in the coupling rods can help. The best things for doing this are the tapered broaches that you can get from Eileen's Etc. OzzyO. Link to post Share on other sites More sharing options...
Will L Posted November 1, 2012 Share Posted November 1, 2012 Sorry to say this but opening the holes in the connecting rods wont help at all as these are on the inside of the frames between the driven axle and the cross-heads. But opening up the holes in the coupling rods can help. The best things for doing this are the tapered broaches that you can get from Eileen's Etc. I stand corrected, and I've done it before too. You'd think I'd learn. Obviously I can't deal with too many words starting with the same letter. For the sale of clarity I've corrected the original post too. Oh, and those little tapper broaches were one of my best buys ever. Will Link to post Share on other sites More sharing options...
R A Watson Posted November 1, 2012 Share Posted November 1, 2012 I may have told this story before, but, during my time coach painting on the Dart Valley Railway (before it opened for services) we had the job of painting one of the 14xx locos. As it was in ex B R condition it was very tatty and as part of the final finish we removed one of the side rods to remove the digs and blemishes. After placing it across two rails the day was spent polishing to a mirror finish, when we came to refit it it was found to have expanded in the heat, this was during the summer,and was too long to fit back on only the application of large quantities of water which somewhat negated the finish we were trying for shrank it sufficiently! Your problems must be minor compared to this at least you can just use a small reamer. Waly Link to post Share on other sites More sharing options...
tender Posted November 1, 2012 Author Share Posted November 1, 2012 It's not unusual to get a stiff spot of that sort on first assembly. This is because there are a lot of possible sources of error that can add together to produce a miss match between the distance over the crank pin holes in the connecting rod, and the equivalent distance over the crank pins. So long as there isn't an obvious significant error in the works, then opening up the crank pin holes is the way to go, though don't go too far down this rout if things aren't obvious improving as there will be something else that isn't quite right. In practice most stiff spots can be solved by opening up the crank pin holes, if there is enough meat in the coupling rods for the size hole you need, but it isn't very satisfying from an engineering point of view and very sloppy holes mean the driven axle can turn a significant distance before the rest join in, which isn't pretty.. Just seen Jol's advice, which is a good starting point as the crank pin bush is often overlooked as a source of error. Just remember that cutting your teeth on a 4 coupled loco is a good thing as this problem only multiples with additional axles. Will Sorry to say this but opening the holes in the connecting rods wont help at all as these are on the inside of the frames between the driven axle and the cross-heads. But opening up the holes in the coupling rods can help. The best things for doing this are the tapered broaches that you can get from Eileen's Etc. OzzyO. I stand corrected, and I've done it before too. You'd think I'd learn. Obviously I can't deal with too many words starting with the same letter. For the sale of clarity I've corrected the original post too. Oh, and those little tapper broaches were one of my best buys ever. Will I may have told this story before, but, during my time coach painting on the Dart Valley Railway (before it opened for services) we had the job of painting one of the 14xx locos. As it was in ex B R condition it was very tatty and as part of the final finish we removed one of the side rods to remove the digs and blemishes. After placing it across two rails the day was spent polishing to a mirror finish, when we came to refit it it was found to have expanded in the heat, this was during the summer,and was too long to fit back on only the application of large quantities of water which somewhat negated the finish we were trying for shrank it sufficiently! Your problems must be minor compared to this at least you can just use a small reamer. Waly Well I have a set of them tapered broaches but have been holding off using them to open the coupling rod holes until I found the route of the problem. This I have now found (I think), although I've no idea what has caused this. The two pictures below show the distance between the crank pins (with the coupling rods removed) rotated so they are at their closest . The left side The right side As you can see there's a discrepancy of about 0.3mm. Indicating 1. I've got a dodgy set of wheels 2. The hornblocks are misaligned on one side. As the hornblocks were assembled in one of them expensive jigs, I can't see how it can be 2. The only way of checking this is two remove the wheels and check it on the jig again. So, how do I get the wheels off the axles without damaging them or making them loose on the axles when reassembled. Ray. Link to post Share on other sites More sharing options...
Horsetan Posted November 1, 2012 Share Posted November 1, 2012 ...how do I get the wheels off the axles without damaging them or making them loose on the axles when reassembled. You may find a GW Models wheel pulling tool useful. Just as well you don't resort to pinning wheels to axles, otherwise you'd be really stuffed. Link to post Share on other sites More sharing options...
Will L Posted November 1, 2012 Share Posted November 1, 2012 As you can see there's a discrepancy of about 0.3mm. Indicating I'd have said that was a difficult measurement to pull off with certainty For instance, can you be sure the axle blocks are in the same hight in the horn cheeks? I'd want some verification before taking big decisions on the basis that its right. If you can get at the axles I'd try to get a direct measure on them too, perfectly where you can see with the axle block bottomed out when the measurement is made. But assuming you can verify the measure. 1. I've got a dodgy set of wheels 2. The hornblocks are misaligned on one side. or another possibly 3 The one or more of the axle blocks got turned top to bottom even if you did ensure they remained paired with the correct horn cheek etch. There are almost certainly others As the hornblocks were assembled in one of them expensive jigs, I can't see how it can be 2. I wouldn't reject it as a possibility there are ways of getting it wrong even with the jig, but it could also be 3 which could have the same effect The only way of checking this is two remove the wheels and check it on the jig again. So, how do I get the wheels off the axles without damaging them or making them loose on the axles when reassembled. This is why its a good idea to arrange things so the axles can be always be dropped out. While fitting wheels once only is the objective, so long as you chamfered the axles ends before you started you will probably get away with it, but do get the loctite in the joint when you put them back on again. To remove the wheels, support the back of each wheel both sides of the axle and tap the axle through from the front. I'd use a couple of metal rulers across the open jaws of a vice Will Link to post Share on other sites More sharing options...
tender Posted November 2, 2012 Author Share Posted November 2, 2012 or another possibly 3 The one or more of the axle blocks got turned top to bottom even if you did ensure they remained paired with the correct horn cheek etch. To remove the wheels, support the back of each wheel both sides of the axle and tap the axle through from the front. I'd use a couple of metal rulers across the open jaws of a vice Will Hi Will, I don't understand your 3. If both frames were assembled with the hornblock etches soldered in position in the jig with the axle blocks on the fixed pins I don't see how the distance between one set has increased by 0.3mm on one side. This is what I want to check by removing the wheels Your method with the rulers sounds like a good idea, why didn't I think of that. I've dropped the coupling rods (with bushes) back on the jig to check the spacing of the pins and they both fit perfectly. Too late to do anything now, so will see what tomorrow brings. Ray. Link to post Share on other sites More sharing options...
Michael Delamar Posted November 2, 2012 Share Posted November 2, 2012 Hi Ray. just throwing this in, I would hazard a guess it could be a smidge out of quarter, does sometimes happen with the quatering jig, this could give the effect you are having. wouldnt take the wheels off yet but gently adjust if possible, keeping those moist fingers off the tyres if you can. cant be certain because of angle of the photo etc but it looks like it here. . id wait for more experienced of the forum to advise first . (edit) ignore that as tosh, you couldnt check the quatering in the way photographed because we dont know what the other side is doing, however it does still look like it might not have been lined up when measured, as Will said itd be hard to measure accuratley in the way you've done, I do think it could still be slightly out of quarter though. Link to post Share on other sites More sharing options...
Will L Posted November 2, 2012 Share Posted November 2, 2012 Hi Will, I don't understand your 3. If both frames were assembled with the hornblock etches soldered in position in the jig with the axle blocks on the fixed pins I don't see how the distance between one set has increased by 0.3mm on one side. This is what I want to check by removing the wheels Unfortunately the axle hole isn't necessarily spot dead centre in the axle block. The block will fit the etched guides two ways. Once you have soldered the etch to the chassis with the axle block one way up, if you assemble the axle with the axle block the other way up, the result may not quite match the jig. I'm not saying this is the definite cause , it's just another theoretical possibility. Just like off set holes in the crank pin bushes, wheels with slightly different crank pin throws. crank pins not in strait, wheel not quartered exactly the same, and coupling rods not exactly matching the chassis sides (jig or no jig). Anybody think of any more? The hard truth is that there are tolerances on all of these even on the best run workbenches, before you begin to think about actual errors. Whether your chassis runs smoothly form the word go or if it need a tweak or two before it will, depends not just on how these tolerances and errors net together. Though clearly the right methods, the use of jig, and pure good old experience will hopefully minimises the errors. In practice for the chassis to run without stiff spots, the clearance between the coupling rod holes and the crank pin bushes has to be greater than the sum total of all the tolerances as they affect your chassis. How much you open out the coupling road hole and how much time you spend tracking down all other possible sources of error is up to you, but for them to work with nice sliding fit is asking quite a lot. If and when this all gets a bit much and you wonder why you bothered, just remember there are lost of chassis running around very nicely to prove that it can be done. Have fun Will Link to post Share on other sites More sharing options...
Michael Delamar Posted November 2, 2012 Share Posted November 2, 2012 just wondering how free the wheels run? Im not saying this is the problem but did you take anything off the inside of the bearings? hold ends of axle by finger and thumb and dangle the chassis swinging gently too and fro, if it the chassis doesnt return to the 6 o clock position on its own then its too tight. was also thinking the chassis may have a slight bend or twist in it, but I would have thought with it not being a solid chassis itd be fine. Link to post Share on other sites More sharing options...
ozzyo Posted November 2, 2012 Share Posted November 2, 2012 Hello Tender, if you can do it try checking the crank-pin centres at the other end of the throw and at top and bottom dead centres. Then if you can check them in the normal running position as well. I would not expect to see any differences at top and bottom dead centres. I hope that what I've said makes sense. OzzyO. Link to post Share on other sites More sharing options...
tender Posted November 2, 2012 Author Share Posted November 2, 2012 Hi Will, thanks for your explanation. Here's the logic why I think the axle blocks should be in perfect alignment. Looking the my very crude diagram. The three circles in the middle represent the three 1/8" pins fixed in the jig. If the hornblock/axle box is soldered to each frame while the axle boxes are on the pins and the end of the frame is butting up against the third pin i don't see how there can be any significant error regardless of how offset the hole in the axle box is as the hornblock etch would be offset by the same amount when soldered onto the frame. I've now taken the wheels off one side of the axles and remeasured across the axles. There is still a 0.25mm discrepancy between the left and right side. (so my crude method of measuring in my previous post wasn't far out) Conclusion - must be something wrong with the jig. Well not quite, I've had another look at it and there is good bit of wobble in one of the pins where it is threaded into the block. On close inspection the pin wasn't seating properly so I've given the thread a good clean out and it now appears to be OK. I suspect it had moved while switching from one frame to the other. Guess I should have checked by refitting the coupling rods on the ends of the pins before soldering up the hornblock etches. I'll have to put this down to Noddy error. So where to go from here. Three options as far as I can see 1. refit the hornblock - could be tricky now it almost complete 2. Make a new coupling rod with the holes 0.25mm wider apart 3. Elongate the holes in one of the existing coupling rods Any other suggestion? Ray. PS OzzyO, Michael - just noticed your post while typing this. Link to post Share on other sites More sharing options...
RMweb Premium Pannier Tank Posted November 2, 2012 RMweb Premium Share Posted November 2, 2012 As the hornblocks were assembled in one of them expensive jigs, I can't see how it can be 2. The only way of checking this is two remove the wheels and check it on the jig again. So, how do I get the wheels off the axles without damaging them or making them loose on the axles when reassembled. Ray. Wasn't there an issue with one of these jigs in that as you tightened the axle pins on the alignment jig they were no longer vertical? Link to post Share on other sites More sharing options...
buffalo Posted November 2, 2012 Share Posted November 2, 2012 Wasn't there an issue with one of these jigs in that as you tightened the axle pins on the alignment jig they were no longer vertical? I seem to remember the odd post or two about this from people who didn't really understand how to set up one of these jigs. IIRC it was a case of screwing the axle pins into an Avonside jig, then adjusting the spacing with the clamp screws loose. When the clamp screws were tightened the play was taken up and the pins moved. What wasn't understood was that the adjustment should be done with the clamps slackened just enough to allow the saddles to move, not slop about. Then when tightening the clamps to continue checking the fit of the rods on the pins, adjusting the separation as needed. The correct way is probably obvious to many of us, but not so if you've little or no previous experience of mechanical adjustments. Nick Link to post Share on other sites More sharing options...
tender Posted November 2, 2012 Author Share Posted November 2, 2012 just wondering how free the wheels run? Im not saying this is the problem but did you take anything off the inside of the bearings? hold ends of axle by finger and thumb and dangle the chassis swinging gently too and fro, if it the chassis doesnt return to the 6 o clock position on its own then its too tight. was also thinking the chassis may have a slight bend or twist in it, but I would have thought with it not being a solid chassis itd be fine. Without the coupling rods (or even leaving the right hand side connected) the chassis can be pushed along the bench by just the touch of a finger with all wheels turning nicely, so I don't think there's a problem there. Hello Tender, if you can do it try checking the crank-pin centres at the other end of the throw and at top and bottom dead centres. Then if you can check them in the normal running position as well. I would not expect to see any differences at top and bottom dead centres. I hope that what I've said makes sense. OzzyO. I made four measurements with the crank pins in different positions, there was always a 0.3mm (+/-0.1mm) discrepancy left to right side. Wasn't there an issue with one of these jigs in that as you tightened the axle pins on the alignment jig they were no longer vertical? I've not noticed that, but will check. I seem to remember the odd post or two about this from people who didn't really understand how to set up one of these jigs. IIRC it was a case of screwing the axle pins into an Avonside jig, then adjusting the spacing with the clamp screws loose. When the clamp screws were tightened the play was taken up and the pins moved. What wasn't understood was that the adjustment should be done with the clamps slackened just enough to allow the saddles to move, not slop about. Then when tightening the clamps to continue checking the fit of the rods on the pins, adjusting the separation as needed. The correct way is probably obvious to many of us, but not so if you've little or no previous experience of mechanical adjustments. Nick Think this was pointed out in a recent MRJ which had a review of three jigs. I checked the spacing with a coupling rod before soldering up the first frame but forgot to check again with the second, I think the wobbly pin was my downfall, I wont let that happen again. So to reiterate my options. (or other suggestion) 1. refit the hornblock - could be tricky now it almost complete 2. Make a new coupling rod with the holes 0.25mm wider apart 3. Elongate the holes in one of the existing coupling rods Any takers? (I fancy three, there's always two as a fall back, think I'd rather start again than to attempt one.) Ray. Link to post Share on other sites More sharing options...
ozzyo Posted November 2, 2012 Share Posted November 2, 2012 So to reiterate my options. (or other suggestion) 1. refit the hornblock - could be tricky now it almost complete 2. Make a new coupling rod with the holes 0.25mm wider apart 3. Elongate the holes in one of the existing coupling rods Any takers? (I fancy three, there's always two as a fall back, think I'd rather start again than to attempt one.) Ray. Hello Ray, option one is the best, but the hardest one as well. But you do have option four. Fill in one or both holes in one of the coupling rods and then re-drill them, it's a bit like option two but with less work. You will have done this, but have you checked that both rods are at the same centres? OzzyO. EDIT for this, if the rods are laminated you could unsolder them and cut them to set them at the right centres, this will work best if the centres are to close together. Link to post Share on other sites More sharing options...
Michael Delamar Posted November 2, 2012 Share Posted November 2, 2012 I've now taken the wheels off one side of the axles and remeasured across the axles. problem here is now how does one quarter the wheels using the GW jig as the spring in the jig wont locate with the wheel that is fitted to the axle. so may have to take the other side off too . Link to post Share on other sites More sharing options...
tender Posted November 2, 2012 Author Share Posted November 2, 2012 problem here is now how does one quarter the wheels using the GW jig as the spring in the jig wont locate with the wheel that is fitted to the axle. so may have to take the other side off too . I guess pushing the axle just part way back out of the wheel will be enough to relocate the wheel in the GW quartering jig. Link to post Share on other sites More sharing options...
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