P4 Q Class from PDK kit (go to p. 6)

[DLT]

Interesting build, I'll catch up later.

Cheers, Dave.

[islandbridgejct]

Quentin,

 

I'll be going down a similar road to you as soon as I can make the time, so it's interesting to see a beginner's steps.

 

Keep up the progress reports, and good work so far!

 

Alan

[Portchullin Tatty]

The AG lock nuts are a real pain to keep on--they unscrew themselves quickly. Ah well, at least it won't be too hard to to remove the side rods when it comes time to paint the wheels.

 

 

-I should've bought a wheel press. I saw an NWSL one at a show last month before I'd done the wheels. That would've helped enormously. 

 

I'm also finding that it takes more weight that I'd thought it would for the wheels to grip the rail--the CSBs seem to be causing trouble here. At least the additional weight needed will help with haulage capabilities.

 

Quentin

 

Quentin, looking good!

 

Picking up on a few of your points:

• I (and a lot of people besides) don't us the alan Gibson crankpin nuts in the build until the very end.  Instead, use some insulation from some electrical wire.  Slide it over the thread and it will do the same job nicely.  Get the wire insulation that is thick enough to be bigger than the crank pin bearing.
• It is certainly quite difficult to mount Alan Gibson wheels without using a wheel press - so one is a worth while buy.  If you don't have one, assemble them in a vice is the best advice and take a lot of care (as you appear to have done) to ensure it is square to the wheel in both plains.  Another big bit advice on assembling wheels on the axle is to deburr the end of the steel axle and even put a very slight taper on the outer 1/2mm - this helps the assembly, reduces the prospect of damage of the wheel boss and helps keep it square.
• Try and remove the wheels from the axles as little as possible, as the plastic boss to the wheel does damage itself.  CSBs help a lot in this respect and I can build a chassis without removing the wheels from their axles at all except for the driven axle, where I get it as a rolling chassis and have to take off the wheel to get the drive gear/gear box on.
• With regard to needing a lot of weight on the chassis, you can change the guitar wire for a grade down.  However, if you can get the weight in, this may be the best course.

Good luck and keep up the good work.

[mightbe]

I'd like to say progress has been made and that the problems have fixed themselves. Errr, no. 

 

What I finally discovered is my chassis's roll-ability is significantly reduced by the CSBs--I finally went for broke and pulled them out and hey presto, everything is smooth and free and the chassis easily rolls down a slight gradient.

 

Have others found this? Do CSBs really only come into their own with the whole body on? I can't even let the chassis (alone) roll by propelling it--the second my hand isn't exerting any downward pressure the chassis seizes up and there's a split-second of light skidding.

 

Anyone have any solutions?

 

The calculations were all done to optimise operation for 12 thou or 13 thou steel wire, depending on how much weight I added (I admit, I only have a dim idea of what the loco might weigh when it's finished). I found some posts on the Scalefour forum about loco weight and tractive effort to base my predictions off of (IIRC an LMS 4F was one of the locos mentioned--a very close cousin)

 

Using .012" steel wire meant the springs were fully compressed the entire time, and would therefore only 'push' downwards. .013" wire means that once the body is on the chassis won't roll very freely--it has to be given horizontal 'help' at all times. The exact moment you stop pushing the drag beam the entire thing comes to a halt within about an inch. I would've expected maybe 6 inches of travel or more? Truth be told I don't know what normal CSB behavior looks like! 

 

Should I try an even thicker (i.e. stiffer) gauge of steel wire to see if it transfers the weight better, or a thinner one to cut my losses? :/

 

Quentin

[DLT]

Quentin,

 

drill through the upper frame rivet holes, push in a short piece of wire until it projects the right amount and solder/glue (thin superglue may be easiest.

 

Jol

 

I did something similar with my whitemetal Q-Class a few years back.  I cut several brass rods to the right length and pushed them through both sides.  This makes it easier to keep them in position while you solder them.

See photos at bottom of this page:  http://www.rmweb.co.uk/community/index.php?/topic/2359-dlts-sr-locos-e1r-class-by-sef-revisited/page-7

Hope this helps,

Cheers, Dave.

[billbedford]

Have others found this? Do CSBs really only come into their own with the whole body on? I can't even let the chassis (alone) roll by propelling it--the second my hand isn't exerting any downward pressure the chassis seizes up and there's a split-second of light skidding.

 

 

Yes, any sprung system will only work satisfactorily if it is properly weighted. You don't need you with the frames with the body, a dummy weight which is close to your expected final weight will do just as well. The fact that your frames work well without the spring wires shows there is nothing intrinsically wrong with the frames. You need to try the frames again with a weight and the spring wires, first without the coupling rods and then withy them.

[Dave Holt]

I'm struggling to understand why the CSB would affect the free rolling of the chassis unless the wheel base is changing slightly, depending on where the axleboxes are in the horn guides. Have you checked that the horn guides are all square to the axle centre line?

Regarding spring deflection and ride height, my understanding is that CSB's are usually arranged to have a static deflection of 0.5 mm for the weighted loco, so must be set up 0.5 mm below the normal ride position when in the unloaded state. If 12 thou springs fully bottom out at your estimated weight something is wrong with the initial set up.

Dave.

[mightbe]

Dave, thank you! 

 

One of the rear hornguides was about 5 degrees off-kilter, I was able to safely melt the solder with a mini butane torch and got it out. I then cleaned up everything and re-placed it mostly by trial and error/guesswork. Getting it vertical was no issue, but getting it right in line with the other was a bit of a task.

 

It now rolls better than it did (still not perfect..). Sometimes during tests it looks like the wheels lose traction right when the momentum is nearly spent--they stop rolling and slide for the last ~1/4"every couple times.

 

Would this be down to the nickel silver rail? Or am I up a certain creek without a certain paddle?

[Dave Holt]

I think you're expecting rather a lot for an unweighted chassis to run perfectly well from new. The very slight binding you describe could be a minute error in wheelbase or quartering, which may well bed in with a bit of running or require slight enlargement of the crank pin holes in the rods - but beware excessive clearance here.

If you put a weight on top of the chassis, does it run better? If so, I'm not convinced you have a problem, since you wont be running the loco without its body, I assume?

Dave.

[mightbe]

The project has progressed! Here a few (cruel) photos:

 

 

 

Things are still "chunked"--cab roof is just held with sticky-tack at the moment, the firebox and boiler are still separate units. The firebox will need some remedial work with milliput. 

 

-----------------------------------------------------------------------

 

 

I've discovered that the cab floor is far too long to let the loco and tender be coupled at a realistic distance. Does anyone have drawings that show its dimensions? As seen in the pic, the floor has to go clear to the wall for the loco and tender to sit at a reasonable distance. Mind you, there are parts that go there!

 

Quentin

[Horsetan]

^^

 

Well, that doesn't look bad at all for a first effort in P4. The basic structure is all there.

 

I've recently picked up the predecessor of this kit, which was produced by Crownline - they share the same designer: Paul Hill. There isn't a huge degree of change in the design, apart from the fact that the Crownline chassis was a fold-up, "OO" only and uncompromisingly rigid, so it will need work to make it usable in P4.

 

I was slightly amused to find whitemetal splasher tops in the Crownline kit - it would have been simpler to stick with etched ones, as you get slightly more clearance.

 

AGW's 5ft North Eastern wheels are just a touch out - crankpin in line instead of pin between and no bevel, but the right number of spokes. (The next step up would be the 5'2" Stanier-bevelled ones which on the face of it tick all the boxes, but the diameter is too big.)

 

If "Wild Bill" Bedford is monitoring this topic, the "Q" is another wheel design he might like to have a look at for his wheel production experiments.

[mightbe]

It sounds like they haven't updated the kit at all then! What you describe is exactly what came in the box. Haha

 

Quentin

[Horsetan]

It sounds like they haven't updated the kit at all then! What you describe is exactly what came in the box. Haha

 

The common factor is Paul Hill who now owns and runs PDK, after taking over from Dave and Sheila King who hired him when they ran Crownline and subsequently worked with him again when they set up PDK. Paul's no-frills design style is very distinctive.