Any Question Answered

[Izzy]

Didn’t quite understand what was meant by rod reversing, thanks to Don’s post now do. But whatever, that they appear to work one way, but not another, would seem to indicate that there is a mis-match somewhere, that one or more measurements are not the same. It might be anywhere though, and a very small discrepancy. The thing is a 4 coupled wheelset can take/absorb far more in the way of error/discrepancy than a 6/8 coupled. 

 

Going back to the wheel crankpin issue, quartering is not the same as crank throw, and I just wonder if the hole is not just out of position relative to the spokes but in throw distance which is a bigger problem. 

 

Izzy

[Donw]

3 hours ago, Izzy said:

Didn’t quite understand what was meant by rod reversing, thanks to Don’s post now do. But whatever, that they appear to work one way, but not another, would seem to indicate that there is a mis-match somewhere, that one or more measurements are not the same. It might be anywhere though, and a very small discrepancy. The thing is a 4 coupled wheelset can take/absorb far more in the way of error/discrepancy than a 6/8 coupled. 

 

Going back to the wheel crankpin issue, quartering is not the same as crank throw, and I just wonder if the hole is not just out of position relative to the spokes but in throw distance which is a bigger problem. 

 

Izzy

 

What I was saying about getting them all in line will show up the crank throw  as a missmatch between the wheelbase and the rods. If you then move them from say 3 o clock round to 9 o clock the error will show up differently  as the effect of the crank throw will have reversed. So if at 3 o clock the right hand half of the rod looks 0.5mm bigger than the wheelbase moving it to 9 o clock will show it as 0.5mm smaller and you know the crank throw is 0.5mm to large on the right hand wheel.

 

Don

 

I think I have said that wrong. It is much easier to see than explain. You can see which side the hole in the rod is compared to the crankpin. It is worth trying because you may see that expanding the hole slightly one way will fix it.  

Edited July 19, 2019 by Donw
poor eplanation

[Nigelcliffe]

With tight rods there is the "how much slop should be in the holes?" question.    Some very good loco builders produce locos which seem incredibly sloppy when one inspects them, yet they run superbly.  Others are very precise with very little slack in the build.     

 

So, if its not horribly difficult, it might be worth making a duplicate set of rods and enlarging the holes in stages to see if more slop gives good running.   Trouble with enlarging holes is that its easy to make them larger, much more work to make them smaller again!

 

  

[Valentin]

On 31/05/2019 at 14:42, Argos said:

Has anyone had any success with the new 3d printed universal joints?

 

I'll freely admit to being quite a ham-fisted modeller but have broken 3 joints now.

Two whilst installing them into the socket (and have had to drill them out) one while cutting off the sprue.

 

They feel too brittle to use.

If anyone had had success could the share their secrets?

 

I've also had one of the socket break whilst running with a wire installed.

 

Again I refer back to my ham-fisted comment rather than this being a criticism of the product. 

 

I tried one of these UJ's today. I don't remember last time I was so frustrated. In my opinion they should be withdrawn from the shop. The design is excellent but unfortunately the material is not good enough for purpose.

 

The first "ball" broke just after a few minutes of rolling the engine when I accidentally knocked the engine of the rails; it fell down on one side next to the track - not a drop, not a hard kick just the kind of accident that happen all the time with no dramatic consequences. When I put the engine back on track I noticed the broken joint. Unacceptable.

 

The second "ball" broke during more extensive testing. The locomotive run beautifully around a circular track, at different speeds, for an hour or so; I was stressing the motor by suddenly changing the direction and increasing / decreasing the speed. After one such change of direction, at high speed, the UJ broke. This is also unacceptable.

 

Tomorrow I will go back to the standard UJ, with looped wire.

Edited July 19, 2019 by Valentin
UJ, not UK :)

[2mm Andy]

32 minutes ago, Valentin said:

 

I tried one of these UJ's today. I don't remember last time I was so frustrated. In my opinion they should be withdrawn from the shop. The design is excellent but unfortunately the material is not good enough for purpose.

 

The first "ball" broke just after a few minutes of rolling the engine when I accidentally knocked the engine of the rails; it fell down on one side next to the track - not a drop, not a hard kick just the kind of accident that happen all the time with no dramatic consequences. When I put the engine back on track I noticed the broken joint. Unacceptable.

 

The second "ball" broke during more extensive testing. The locomotive run beautifully around a circular track, at different speeds, for an hour or so; I was stressing the motor by suddenly changing the direction and increasing / decreasing the speed. After one such change of direction, at high speed, the UJ broke. This is also unacceptable.

 

Tomorrow I will go back to the standard UK, with looped wire.

 

Valentin,

 

Thanks for the feedback. I'll raise the issue with the Products Officer and Sales Officer at tomorrow's Association committee meeting. It maybe that printing the UJs in a less brittle material is the way forward, but will report back in due course.

 

Andy

[Nick Mitchell]

27 minutes ago, Valentin said:

The first "ball" broke just after a few minutes of rolling the engine when I accidentally knocked the engine of the rails...

...The second "ball" broke during more extensive testing... After one such change of direction, at high speed, the UJ broke....

 

Hi Valentin,

Out of curiosity, may I ask about the hole you drilled in the ball part? Did you drill into the wider part of the shaft only, or did you drill through the bit where the shaft narrows and into the ball as well? Also, what was the diameter of your hole?

 

The one and only one of these I have used (on the Jubilee, installed about 10 months ago) is still intact. I drilled just into the thicker part of the shaft. I have had it "fail" twice in that time, with the cyano glue "letting go" of the steel shaft where is is glued into the printed part.

 

I wonder if it would be feasible to 3D print these parts in brass or steel?

 

Nick.

 

[2mm Andy]

10 minutes ago, Nick Mitchell said:

 

I wonder if it would be feasible to 3D print these parts in brass or steel?

 

Nick.

 

 

I'm not sure if they would meet the print bureau's guidelines for minimum wall thicknesses, detail thicknesses, etc, but it might be possible to 'lost plastic' cast in brass from a 3d printed master.

[Valentin]

Hi Andy, Nick,

 

 

Thanks for your input.

 

The wire (guitar string) I have is about 0.27 mm. I hand-drilled, only through the "fat" part of the "ball", using a 0.3 mm drill bit. As the plastic is somehow transparent I was able to see how much I was drilling, and I was going very slowly.

[Nick Mitchell]

19 minutes ago, Valentin said:

The wire (guitar string) I have is about 0.27 mm. I hand-drilled, only through the "fat" part of the "ball", using a 0.3 mm drill bit. As the plastic is somehow transparent I was able to see how much I was drilling, and I was going very slowly.

Sounds like you have done exactly the same as me... which makes me worry how long mine will last. I have tested it quite extensively, but it hasn't had long term sustained running. I'm lucky in that I have the wherewithal to make my own brass versions of these, but I suspect for many people the 3D printed parts are so much neater and easier than the available alternatives.

 

1 hour ago, Valentin said:

Tomorrow I will go back to the standard UJ, with looped wire.

If you're going back to the wire loop, one improvement I stole from Jerry (after seeing it on his demo stand at York in 2018) is to make the loop captive at one end - like in the picture below. That the 3D printed balls click into the sockets and don't fall out is another desirable feature.

[Donw]

It occurs to me that as the wire loop can twist  slightly it may have the action of absorbing some of the shock of abrut stops or changes of direction . It may be that such shocks affected the 3D printed version.  

 

Don

[queensquare]

7 hours ago, Nick Mitchell said:

Sounds like you have done exactly the same as me... which makes me worry how long mine will last. I have tested it quite extensively, but it hasn't had long term sustained running. I'm lucky in that I have the wherewithal to make my own brass versions of these, but I suspect for many people the 3D printed parts are so much neater and easier than the available alternatives.

 

If you're going back to the wire loop, one improvement I stole from Jerry (after seeing it on his demo stand at York in 2018) is to make the loop captive at one end - like in the picture below. That the 3D printed balls click into the sockets and don't fall out is another desirable feature.

 

Like most good ideas, particularly relating to loco building. I pinched it from John Greenwood!

 

Jerry

[Caley Jim]

A wire loop in a slot is far simpler than faffing about with drilling bits of plastic and supergluing them on! 

 

Jim 

Edited July 20, 2019 by Caley Jim
Edited for predictive text errors (again!)

[queensquare]

42 minutes ago, Caley Jim said:

A wire loop in a slot is far simpler than faffing about with drilling bits of plastic and supergluing them on! 

 

Jim 

 

I agree Jim. I use a loop in a slot at one end with the captive loop at the other.

 

Jerry

[-missy-]

If we all still had the attitude of you two we would all still be making things by filling lumps of Brass.

Shameful attitude towards people who make an effort to try and help others and improve the hobby in my opinion.

[Valentin]

-missy-, I am sorry I started this dispute - I cannot stress enough how grateful I am for all the efforts made by the Association members to design and develop new products. I was so frustrated with the 3D printed universal joints, I just had to cry my dissatisfaction with the material they are made of - as I mentioned before, the design is great and they are very easy to assemble, easier than making precise loops in a string wire.

 

Anyway, after about an hour of working on a new UJ I got this:

 

Video Clip 1

 

Video Clip 2

 

I wonder why the engine wobbles...

 

[Argos]

4 hours ago, -missy- said:

If we all still had the attitude of you two we would all still be making things by filling lumps of Brass.

Shameful attitude towards people who make an effort to try and help others and improve the hobby in my opinion.

 

I'm taking a guess that I am one of the two in question?

 

if so how does my post display any "attitude"?

 

I took pains to point out I am quite a ham fisted modeller and was not criticizing the product.I

 

As with Valantin's response above I am eternally grateful to those who dedicate time and effort into the Association's products.

The hobby would a poorer place without them.

 

 

Edited July 20, 2019 by Argos

[Donw]

I dont think any disrespect was meant to those who do so much to help us. However it is surely valid to discuss the technical merits of various solutions. The use of a UJ in our application is to allow the motor shaft and the shaft carrying the worm to be at different angles so the loco can go round curves.  It is a fact that  where the  two shafts either side of the UJ are not at the same angle the speed of both shafts cannot be constant and there is a sinusoidal variation between them.  It does seem to me that the thin wire UJ  solution has merits in that the thin wire can twist and will absorb much of the stresses involved and may also absorb the sinusoidal variation .

 

There is a short bit of video here https://www.youtube.com/watch?v=LCMZz6YhbOQ that shows how this occurs. It also indicates that a second UJ can restore the constant  speed but this only works if the input and output shafts are parallel.

 

Don  

[Caley Jim]

I think the two being referred to were Jerry and I. I can see the merit in trying to create a product to, for example, simplify making uj's, but I think there are times when things tend to get too sophisticated. I'm a great believer in the KISS principle. 

 

Jim 

[EHSUK2001]

I see no criticism of any person or persons here, only of the material a particular product is currently manufactured from. It’s probably too brittle for its intended purpose and perhaps a more forgiving material is required?

 

A large batch of 3D printed figures from Shop 3 have recently been replaced by the manufacturer, due to them being far to brittle.

[CF MRC]

On 18/07/2019 at 23:08, justin1985 said:

Well, I don't think the suspect wheel turned out to be a problem, but this chassis really isn't rolling, and I can't work out why!

 

I carefully marked the suspect wheel, and now it's in the chassis (on rear axle) it quartered with no problems on the jig. Running with rods reversed and fitted on the central (geared) axle and the rear axle, it rolls absolutely flawlessly. However, with the rods reversed the other way and running on the central and front axles (i.e. the shorter wheelbase on the 57xx) - or indeed with them fitted to all wheels - I simply can't get it to do more than a 1/3rd revolution. 

 

All of the wheelsets are visually in quarter, and all slide effortlessly back into the quartering jig. With the rods fitted to one side, the ones on the other side drop on virtually effortlessly - which I understand to be another test of quartering? So I'm struggling to think that quartering is the issue.

 

 

None of the muffs are pinching. I'm not sure that any of the crankpins are still 100% perpendicular to the wheels, but any that were a bit out have been tweaked back into something very close to perpendicular.  The crankpins were, I think, an old bag rather than new shop stock - they measure out at about 0.51 or 0.52mm. The connecting rods were opened out with a 0.6mm drill. I couldn't see any evidence of the frames not being parallel. 

 

 

The wheelsets aren't quite pressed into gauge yet - temporarily at "Irish Broad Gauge" as Tim was calling it, to give a better chance of adjustment or being able to get the wheels back out without more damage, if needs be. Basically I left the aluminium hair clip between the inside face of the wheels and the frames when pressing them in using the jig. The central geared axle is perhaps a tad tighter (done first, before I realised the clips would make a nice temporary spacer).

 

Can I at least take the fact that the central and rear axles run well with the rods  reversed and on to rule out the problem being with those, and therefore the problem must relate to the front axle?

 

I'm reluctant to start opening out or drifting the connecting rods holes any further, without being sure that that's the issue. Is there anything else I should check?

 

J

Returning to Justin’s chassis, if the back half is OK and the rods bind on the front wheels, try slightly altering the quarter on one of the front wheels.  If you look with a glass you might see that the crank pin sits tighter against one end of the hole than the other  when rotating - move the wheel in its muff a gnats whisker to even up the pin in the hole - I don’t believe that quartering jigs are infallible. 

 

Another thing to try is to swop over the two front wheels and see if that has an effect.  Do the rod holes line up perfectly with one another?

 

Tim

Edited July 21, 2019 by CF MRC

[Ian Smith]

The fact that you are trying each end of the rods independently and have a problem should rule out that the crankpin holes in the rods are not in line but I would check anyway by placing one rod over the other to ensure that the holes are all in line, then inverting one rod and sighting the holes again - the holes should all line up in both scenarios.

By holding a straight edge against all 3 pins on one side, a further straight edge can be used to check that the pins on the other side are all in alignment - this check should be made at both 3 and 9 o'clock. Also at 6 and 12 o'clock. Any discrepancy in the latter would indicate a longer/shorter throw on one axle.

[justin1985]

Many thanks for all of the replies. I've been very busy over the weekend and only just had a chance to have another fiddle with it.

 

On 19/07/2019 at 09:50, Caley Jim said:

Are you sure that the rods are dead straight and haven't got accidentally bent? That's one of the reasons, apart from my compensated system, that I use jointed rods. Another thing is that I've found that if you turn it back and forth between the right spots they sometimes work their way out. 

 

Jim 

 

Yup - checked they're straight, and flat. Holes also line up neatly between both sides. It is possible to force it to rotate when it binds, but I it takes more force than I'd think would be a case of just needing a little freeing up like this. 

 

On 19/07/2019 at 13:12, Donw said:

The pinch point is usually when the cranks are at 3 0 clock or 9 0 clock. I would try taking the rods off one side  move the wheels so that the side with no rod is at 3 or 9 the crankpins should now be in line with each other and the axles centres. A thin straight edge across them should show up if one is not in line which suggests a quatering error. If they are all dead in line  the problem may be an incorrect crank throw on one wheel or mismatch between the rods and the wheel base and holding the rod to the crankpins while they are inline should show this up.

 

Don

 

Tried this and the rule is in contact with all three pins on the side with no rods, if the rods are on one side only. Trying it a few times, it sometimes looks like the central crankpin might be a tiny tiny fraction lower than the two ends on some revolutions, but not others. But we're talking less than a rizla thickness - 0.1mm or less?

 

On 19/07/2019 at 10:26, Chris Higgs said:

How does it roll if you put a rod on only one side? If it is a crankpin throw wrong, then this should bind up on one side or the other.

 

If the rods run OK on each side with the other one off, but bind when both are on, then it pretty much has to be quartering.

 

Chris

 

Not sure if this is exactly what you meant Chris, but I've just tried rolling with one side on, and the other rods side reversed so only the known "good pair" is connected on that side (then switching sides). Surely if it only had one rod it would always bind after a revolution or two? 

 

Setting it up with "one full, one reversed", it seems like one combination of right hand side rods on entirely and left hand rods reversed (only on rear/longer pair) rolls smoothly really easily. The other way around (left hand side rods connected and right hand side reversed, only on rear pair on that side) is really difficult to get to roll without binding.

 

Am I right in thinking that has isolated the problem to being the front left hand wheel (i.e. binding only occurs when that wheel has a rod on it). Does that make sense? So the problem is isolated to the crank throw, or the fit of the rod (?), on that particular wheel?

 

In terms of trying alternative rods, does anyone know if the ones on the old Farish replacement etch fit Chris's etched chassis for the 57xx? I know I have this etch somewhere (used the 4F rods from it) but can't seem to find it right now to check.

 

Thanks again

 

Justin

[Izzy]

I believe the rods are exactly the same dimensions, just a bit bigger and with larger holes, as per the 3/4F, J94/08 etc. If they don’t allow the chassis to run then the quartering/throw would certainly seem to be the issue.

 

Just as a (very crude) test/fix you could try bending the crank pin on the suspect wheel a bit, towards/away from the wheel axis or left/right. As a pin with a different throw would describe a circle around the axis of the correct throw it might show if this was the problem. Or if the pin wasn’t truly vertical to the wheel face then the described circle will progressively increase the further away from the wheel face. It’s all nip & tuck this lark......

 

Izzy

[CF MRC]

It’s well worth getting an eye glass (loupe) and looking at the position of the crank pin in the hole as it rotates. The first option is to try tweaking the position of it by altering the quartering, as I mentioned above.  The next option is to use a small round file and ‘stretch’ the hole away from the bind. 

 

Tim

[2mmMark]

On 20/07/2019 at 17:52, -missy- said:

If we all still had the attitude of you two we would all still be making things by filling lumps of Brass.

Shameful attitude towards people who make an effort to try and help others and improve the hobby in my opinion.

I make quite a lot of stuff by filing it out of brass, steel, nickel, aluminium, tufnol etc. but in my defence, I am doing it digitally.  Sometimes I cut or burn one of my digits or even accidentally glue it to something , which is quite annoying.