PRMRP 7mm Class 50

[Hull Paragon]

When I work out how to paste my written text into these fields I'll start! (Scroll down for the main content! I found out how to do it!)

Edited September 30, 2017 by Hull Paragon

[PaulWarb]

Hi
 
I'm no expert but I think it should work if you go to Options (far right icon top row) and tick Paste as plain text.    Then go to the Twitter icon   t   and select notice or twitter - paste the text in the large box and hit OK.

 

I hope this works - if not I'm sure someone else will correct this and tell me I have got it wrong!!!

[MGR Hooper!]

When I work out how to paste my written text into these fields I'll start!

What did you want to paste? Maybe an admin can help.

[Luke Piewalker]

I've had to use Ctrl-v to paste here

[Hull Paragon]

Thanks. I can do it now. I have just set up the post and after 30 minutes of fiddling around, I pressed a key and the whole lot disappeared.....so I will have to start again!

[Hull Paragon]

I have been an avid reader of much subject matter on RMWeb in the past so I thought it was only right that I try to adjust the balance and post my experience to possibly help or guide others.

 

Before I begin my effort, many thanks to those who have taken the time to write about their experiences with J71s, Bogie Van Bs, B1s, point construction and almost everything else…….my post won’t be as accomplished as theirs but I am sure that there will be those who can guide me as I publish instalments. Please feel free to comment/advise/criticise/praise if you feel the need. I will try to respond to any comments as and when I can.

 

My specific interest is 7mm around the start of the 1960s with a slant on the railways of Hull around that time. After years of thinking about it, I have eventually started to build a layout, a loco and some rolling stock. Slowly but surely I believe I have managed to improve…….

 

There has been a huge amount of dialogue within the Gauge 0 Guild about the future of the hobby. Costs are one of the usual concerns and the problems of younger modellers finding enough disposable income (as well as space) have been discussed. It follows that lower cost kits and ready to run locomotives have a possible role in ensuring the hobby continues to flourish. PR Model Railway Products (PRMRP) are one manufacturer which provides low cost kits. (It is another matter if younger persons can develop the skills to build them!)

 

This series of posts are about the PRMRP Class 50. I know it’s not Hull in the 1960s but I am building this one as a gift for someone………

 

There isn’t a great deal of information on the construction of PRMRP 7mm diesel kits so after starting, I thought I’d share my progress. I have built etched brass stuff before but I am a long way from being proficient so what follows is not how to do it:  just a journey.

 

I know that PRMRP get a lot of criticism in the railway blogs, and I am well aware that the kits are not top dog…..but I am not a top dog builder so it seemed a reasonable project…..relatively low cost and if I improve my skills (and patience) I can always go back (if necessary) and upgrade the basic build with, say, cab details and other accoutrements?

 

It’s a long story but I already have a Class 31 for which I have bought specialist motorised bogies so I have the necessary bogie etchings which are common to all the PRMRP kits, as well as motors and gears etc. I asked Peter Besant if he could supply a Class 50 without etched bogies and he kindly offered a discount and brought one to Telford where I picked it up.

 

The kit comes as a number of etched brass sheets with a body in one piece. The body is pre-shaped. Mine had a number of creases which proved difficult to remove satisfactorily despite Peter’s advice to tweak them out using a round metal bar. All other bits and pieces are in sealed polythene bags. Unfortunately, I decided to write this after I started so there are no photos of everything as it was in the box……sorry!

 

The instructions are sparse so it’s a bit of an adventure sorting everything out and making sure it’s in the right place. The drawing is small and poorly reproduced so I scanned some from Diesel Rail Main Line Diesel Locomotives by Colin J Marsden and Graham B Fenn. (I found a brand new copy recently at my local railway (Mid Hants) and paid the princely sum of £1 for it). I enlarged them on Photoshop so that they are near as damn it to scale, before printing them off. I also have access to a Class 50 on the railway. 50027 Lion is one of the preserved locos there so I was able to add a load of close up detail photos to the file.

 

An example:

 

 

So much for the introduction. On to Part 1! The bogies………and apologies for the varied quality of the pictures.

 

The inner bogie frames are flat and must be set to the right length before being bent to shape. The sheet is marked with half etched lines parallel to the ends and these are used to set the correct length of the frame. (If I hadn’t already started the frames this would be a little clearer). The following picture shows a couple of the lines on the right after the excess length was removed. The instructions give the dimensions for each class of diesel, and show which half etched line where the break must be.

 

 

The frame is then bent into a ‘U’ shape which is reinforced with spacers.

 

As I said earlier, the frames are universal for all diesels so each frame has different axle spacings depending in the class you are building.  The distances are set by utilising sliding saddles with the axle holes in. Once the distances are set, the saddles can be soldered in place giving even more rigidity.

 

Here are the separate pieces bent to shape. Notice the shape of the spacers which have an inset to allow for Delrin drive chains. (More of this later). I fixed the spacers in place before the saddles.

 

 

I found setting the correct axle centres (relatively) accurately to be quite difficult. The saddles can’t be fixed in place until this is done. I set the distances on my Hobby Holidays loco frame jig. This fixed everything in place at the right location and I soldered everything using a gas torch.

 

 

The end result. The bearings are still to be fixed in place.

 

 

I have read a lot about Delrin systems and although I have no personal experience, while (whilst?) I was at Telford I came across some 7mm belt drives on the M&M stand. They are supposed to be quieter so I decided to give them a go. After fiddling around for a while I found that they were an exceptionally tight fit and as well as setting the saddles on the jig, I also checked the belt drives to make sure they would go on before everything was set in stone. I’ll find out when I fit the axles into the bearings).

 

The belt…..

 

 

The belt drive check set up…….

 

 

The axle centres are set to the correct distance but the belt is very tight and I’m slightly worried that there will be too much friction and also the possibility of distorting the bogie frame. I’ll test the drive as soon as the bearings are soldered into the frame to make sure the motor can drive the axles smoothly without overloading.

 

The white metal bogie outer frames are in two pieces which need to be soldered together. In the photo, the lower pairs are in two halves, the top pairs are assembled. The spigots on the bottom part locate into half round slots in the rear of the top half.

 

 

I almost always solder white metal parts together with low melt solder and a gas torch. With care it is much easier than trying to get heat into large parts with an iron.

 

The finished article (except for some minor flash still to be removed and the blue tack holding the two parts together).

 

 

Day 2

 

I put the bearings into the frames and fitted the axles. The pulleys slipped and I added the worm wheel to the driving axle. With the belt fitted, I pushed the axles through the opposite bearings and was about to fit the motor when I noticed that the worm wheel was off centre by some distance.

 

 

 

I contacted Malcolm at M&M and he immediately agreed to send me two of his narrow pulleys in exchange for the oversize ones so thanks to him!

 

The next job is to solder the outer frames to the stretchers, and fit a plate onto the inner frame, then drill the relevant holes so that the outer frames are removable..........

[Fastdax]

This series of posts are about the PRMRP Class 50.

 

 

Thanks for starting this thread Paragon. I'll soon be doing a PRMRP conversion of a Triang Big Big Hymek, using the same bogie etches as you have shown.

 

I have also got hold of the M&M Models drive belt kit with narrow pulleys, so I'm very interested in how yours will go together.

 

Following with great interest!

 

Your photos add a lot of interesting detail. Any chance of making them bigger?

 

Thanks,

Duncan

[JeffP]

Very interesting, thanks. The belt drive looks like a lot of faffing around, but can't be any worse than Delrin.

[Hull Paragon]

Thanks for starting this thread Paragon. I'll soon be doing a PRMRP conversion of a Triang Big Big Hymek, using the same bogie etches as you have shown.

 

I have also got hold of the M&M Models drive belt kit with narrow pulleys, so I'm very interested in how yours will go together.

 

Following with great interest!

 

Your photos add a lot of interesting detail. Any chance of making them bigger?

 

Thanks,

Duncan

I'll try to post bigger pictures....I set these up at 10cm and processed them in Photoshop to reduce the file size. I'll try 20cm with the next batch and see what happens.

 

Ray

[Hull Paragon]

Very interesting, thanks. The belt drive looks like a lot of faffing around, but can't be any worse than Delrin.

 

It's not too bad...as long as it works when I get the motor fitted I'll be happy.

 

Ray

[Pete Harvey]

The M&M belt drives are a very good product and give a more positive drive than the delrin chain, but it does tak some thinking out to mount them properly.

 

[mike knowles]

I've recently helped with fitting the belt drive system to a set of JLTRT Western bogies. Using the narrow pulley on the driven axle allowed the use of the preferred Roxey Mouldings gearbox. However as you found, when installed, the belt was a very tight fit and the friction was such that very poor running resulted and the motor quickly became very hot. To get round this the bearing holes in the chassis were elongated to effectively reduce the axle spacing by about half a millimetre (not enough to be noticeable) and the problem was solved. The bogie now runs smoothly and freely. One big advantage of the belt system over the delrin chain is that the belt drive sprockets are fixed to the axles by grub screws rather than relying on a tight fit between the axle and the delrin sprockets which either makes assembly tricky or worse still if you open up the hole in the sprocket too much it then slips on the axle!

[JeffP]

I wonder if the belts will stretch with time, like a car fan belt does?

[Hull Paragon]

The M&M belt drives are a very good product and give a more positive drive than the delrin chain, but it does tak some thinking out to mount them properly.

 

SH101789.JPG

This looks very neat Pete

 

Ray

[Hull Paragon]

I've recently helped with fitting the belt drive system to a set of JLTRT Western bogies. Using the narrow pulley on the driven axle allowed the use of the preferred Roxey Mouldings gearbox. However as you found, when installed, the belt was a very tight fit and the friction was such that very poor running resulted and the motor quickly became very hot. To get round this the bearing holes in the chassis were elongated to effectively reduce the axle spacing by about half a millimetre (not enough to be noticeable) and the problem was solved. The bogie now runs smoothly and freely. One big advantage of the belt system over the delrin chain is that the belt drive sprockets are fixed to the axles by grub screws rather than relying on a tight fit between the axle and the delrin sprockets which either makes assembly tricky or worse still if you open up the hole in the sprocket too much it then slips on the axle!

I am waiting for the replacements pulleys from M&M so I'll soon find out. I had assumed that I would have to elongate the bearings and you appear to have confirmed this....

Ray

[Hull Paragon]

I wonder if the belts will stretch with time, like a car fan belt does?

I don't know. However, if anything goes wrong, the only way to replace them will be to remove the outer frames so that the inner frame can be dismantled....hence my desire to make the assembly removable.

 

Ray

[Hull Paragon]

Day 3

 

Day 2 sort of fizzled out! I then spent a day on the railway where I took some more pictures of the body shape on Lion. I don’t need these yet but I will when the body is folded later on.

 

The pulleys haven’t arrived yet so I concentrated on setting up the stretchers with the outer bogie frames.

 

Am I the only person in this hobby who can’t do a 10 minute job in 10 minutes? As well as not wanting to make too many mistakes, I want to get everything lined up properly…..and this is the root of today’s (long) delay.

 

The axle centres are 47.25mm giving an overall front axle to rear axle dimension of 94.5mm. This dimension is pretty much set in stone as the belt drive is designed for these centres. (However, the centres could be slightly reduced to slacken the belts if they prove to be over tight). The problem is that the bogie frames are too long. I measured the centres at 96mm. The photos don’t show this too well due to parallax error unfortunately.

 

 

This means that there is a misalignment of the axle boxes/wheels. This misalignment will be exacerbated by reducing the axle centres to accommodate the belts. No amount of filing the ends of the castings can change this. In the end, as I couldn’t see a reasonable solution, I went ahead with the axles slightly out of line.

 

The stretchers are bent along the half etched lines. There are indents on the back face which align with the inner bogie frame ends. I guesstimated the centre line and marked the drilled holes for the fixing screws. I also formed some end panels from scrap to solder inside the frames for the stretchers to bolt onto.

 

 

 

 

 

Eventually I set up a rather Heath Robinson arrangement to line up one of the bogie ends with a stretcher .......

 

 

and holding my breath, I soldered them together with low melt and a waving gas torch. (I took the picture before I cleaned it up!)

 

 

Tomorrow I will solder the rest of the bogies and stretchers together, line up the axle centre height and mark the panels for the fixing screws.

[The Nth Degree]

Ray, did you find you had to file back the outside of the bearings to get the wheels to fit comfortably on the axles? I'm currently playing with an old RJH Class 40 kit but the back-to-backs are very tight.

 

Currently suffering from a bout of manflu so I'll post a couple pics of my drive chassis when I'm feeling up to it.

[Hull Paragon]

Ray, did you find you had to file back the outside of the bearings to get the wheels to fit comfortably on the axles? I'm currently playing with an old RJH Class 40 kit but the back-to-backs are very tight.

 

Currently suffering from a bout of manflu so I'll post a couple pics of my drive chassis when I'm feeling up to it.

I had to do a number of things to get it sorted out.....see below......

[Hull Paragon]

Day 4

 

An interesting morning.  First of all I needed to get the drive sorted out.  After setting up the worm/worm wheel alignment (crudely) it then became apparent that the belt drive would rub against the worm and, one assumes, rapidly wear and/or break. This was caused by the bearings pushing the pulley too close to the centre of the axle. Nothing was fixed at this stage so I took the bearings and held them in a drill chuck and sawed off the excess. Putting it all back together and putting power on resulted in a red hot motor! Nothing turned. It was clear that both the worm/worm wheel mesh and the belts were both too tight.

 

I decided to move the drive axle 0.5mm away from the motor (to the rear) and move the axle at the front end 1mm to the rear. The end result, I hoped, would be to release the pressure on the worm and to slacken the belts by 0.5mm. I then soldered the bearings in (hoping that I had got my dimensions right), and re-assembled it all. This time, everything worked reasonably well. It’s not quiet but I will oil all the surfaces and drives which should help.

 

 

This view shows the cut back bearings at the bottom. I also added spacer washers to the drive axles to prevent any lateral movement and effectively lock the worm wheel on the centre axis. One is just about visible between the wheel face and the bearing in the bottom left of the picture.

 

I thought there might be a problem with the axle lengths and after soldering the second bogie side to the stretcher, I checked……..and I was right. The inner frame will not sit inside the outer frame unless the ends are cut off the axles. So I cut the ends off the axles!

 

You can see this on the right hand side with the shortened axles on the left.

 

 

Eventually, I have reached a point where the inner frame is almost finished……which sort of translates into ‘I’m not taking it apart anymore!!’ The centre bearings are loosely fixed in place to allow coarse vertical movement. I’ll put a spring of some kind on the axle at some stage in the future.

 

The only other problem I had was the failure of the grub screw in the narrow pulley. It has just about tightened enough, but if I can’t fix it, I will drop some nail varnish or something on the joint to add a bit more friction.

 

[Hull Paragon]

During the afternoon I finally soldered the outer frames to the stretchers. The whole process is a bit fiddly as there are no reference points, but it is still relatively straightforward once you have it all set up.

 

After setting up the inner and outer frames together, again without a reference, I drilled holes in the end plates and (eventually) screwed the whole lot together. It still needs some work but essentially it’s finished. Sounds contradictory but at least I know what I mean!

 

 

The stretcher looks a bit out of line but it has to come off again as I realised that this stretcher should be at the other end. I also drilled large holes so that there is quite a bit of adjustment available.

 

 

This is the first time I have done one of these. The lessons learned on this one will make the second one a bit quicker and, I hope, a bit better. I now know the dimensions for the axle centres and I know the sequence of events. However, the misalignment of the outer frame axle boxes  with the main axles is immensely annoying especially as I had to adjust the axle centres the wrong way to get everything working properly. Setting up the motor gearing, the drive belts is very fiddly and I lost count of the number of times I did it, took it apart and then did it again. I'm not an expert but I have a little experience. I cannot imagine a beginner doing this bogie. Unless someone knows better of course........

 

I still have to put the air cylinders on but that shouldn’t create too much trouble……the etched steps need to be done too.

 

I’ll be back when the second bogie is done and I make a start on the body.

[The Nth Degree]

I will probably file some flats on my drive axles to hold the gear wheel and pulley sprocket in position. There'll be less reliance on a firm nip from the grub screw, especially in the aluminium of the pulley.

[Hull Paragon]

I will probably file some flats on my drive axles to hold the gear wheel and pulley sprocket in position. There'll be less reliance on a firm nip from the grub screw, especially in the aluminium of the pulley.

 

That is sound thinking........it didn't occur to me but makes good sense......thanks

 

Ray

[The Nth Degree]

Any news Ray? You were giving me some impetus to carry on with my Class 40 bogies.

[Hull Paragon]

Any news Ray? You were giving me some impetus to carry on with my Class 40 bogies.

Good morning! I'm still here but the short delays have turned into slightly longer ones....however I have made some progress on the 2nd bogie!

 

Ray