Trueness, or otherwise, of Gibson and Romfords

[97xx]

Just been rebuilding a scratchbuilt chassis I made as a teen for an equally scratchbuilt 36xx. It had a bit of a 'lope' - long wheelbase of the 2-4-2 (and thus 0-4-0 chassis for modelling purposes) accentuated what was a slightly out of square Romford. Try as I might I could not 'true' it - even skimmed a thou or so off of the boss to ensure a new face. Think the tyre was the culprit, being slightly out of truu on the (insulated) diecast rim. Couldn't budge it to do anything.

 

Gave up and as I wanted to change a few other bits ended up buying Gibson wheels, rods, crankpins and plungers.

 

Fitted the Gibsons using a milling vice and jig to assure 100% squareness. All usual precautions to ensure eased and cleaned axle ends etc.

 

Well, they're not square. Both axles have a slight wobble on at least one wheel. That's problem one. Pressed the axle out and retried, no better.

 

Second problem was having faffed about with the rods, it became clear that the 'nut' that holds them on was bored off-centre. Doing it up therefore nipped down the rod to the top hat bush. Opened it all out a tad and ended up with a working chassis.

 

My question is - are these Gibsons ever ABSOLUTELY square? To be fair, probably two of my four are - and before anyone asks the two that are not weren't the last man on to the axle. This was all done VERY carefully. 

 

Second question - should I have bought Romfords? Although given the mixture of diecast boss, steel axle and nickel silver rim AND insulator, plus the fact that one wasn't true on my original build tempted me to try Gibsons for first time.

 

Finally any advice on squaring the Gibsons up? They just seem to 'spring' back to whatever out of true they were...!

 

Thanks.

 

 

 

 

[97xx]

As an update, pulled out a set of spare Romfords (wrong spoke count which is why I bought the Gibsons) which I have now fitted using same technique as a test and they have come up almost perfectly true. Certainly good enough.

 

I trued the Romfords again using mill vice technique but in two steps:

1. Presssed onto axles between mill vice jaws, with parallels in vice to support axle square

2. Plus could take an additional step in that I could true the actual rim using a thick disc against each between the vice jaws - the point  being that as it had a hole over the boss it was truing by applying force to the actual rims.

 

With the Gibsons you can't do step 2 with discs as the wheel simply slides further onto the axle, reducing the b2b measurement. 

 

The bottom line seems to be that if you don't get right first time with the Gibsons, you're a bit snookered. I did btw leave them overnight to see if they 'settled' as I have heard this can happen with the plastic centre/steel axle.

 

A digression, but I also noticed that the steel rim and brass pickup sparked heavily - completely absent from the N/S Romfords now on.

[Steamport Southport]

Never had a problem with Gibsons. They don't like being taken on and off though. 

 

However if you are using them you might want to try a GW Models wheel press and quartering tool. Advertised in the MRJ but I haven't got the last couple of issues and don't know the current price or availability due to the virus.

 

I don't think his details have changed from this post.

 

https://www.rmweb.co.uk/community/index.php?/topic/148707-gw-models-wheel-press-quartering-jig/

 

A bit more discussion here.

 

https://www.rmweb.co.uk/community/index.php?/topic/19209-gw-models-wheel-press-and-quartering-jig/

 

 

 

Jason

 

[Tim V]

A tip with the Gibsons is to ensure that you have put a relief on the end of the axle - a slight taper, just to take off the right angle. This ensures the axle goes in without shaving a bit off the inside of the boss.

[97xx]

12 minutes ago, Tim V said:

A tip with the Gibsons is to ensure that you have put a relief on the end of the axle - a slight taper, just to take off the right angle. This ensures the axle goes in without shaving a bit off the inside of the boss.

Yes I did that per the instructions.

 

Thanks regarding the other options for assembly.

 

I have seen all the various wheel presses, and agree the GW one looks good - and in fact with all my machinery I very nearly made one. However it was nothing I cannot achieve with the mill vice, which is minutely controllable and 100% square. 

 

I may mount up some redundant wheels on an axle in the mill and do some trueing tests.

[harry lamb]

You should visit the online 'MRJ' index and seek out Chris Pendlenton's articles on wheels and crankpins. Mr. Pendlenton and his friend, the well known etched 4mm. chassis and kit manufacturer Dave Bradwell have much experience in the improvement of the AGW wheelsets. Albeit to EM/and P4 gauges but similar work can be applicable to 'OO' I should imagine. As an aside, you may also wish to invest in the 'long wait' and order some Ultrascale wheels. These are quite expensive but of excellent quality and well worth it if you are just doing the odd engine! They also provide a consistent and well designed c/p system which is about as good as there is available and true! But the waiting list is about a return trip to Saturn ! But they are worth it in the long run! However, not forgetting the 'Exactoscale' range, which unfortunately have now gone to ground, are the finest scale wheels in the smaller gauges bar 2/3mm. but the axle setting system, in which I found no bother, left quite a bit to be desired! Not an insurmountable problem I would have thought but there you go. I am looking forward to their return. These wheels are, visually, the very best of 4mm. scale wheels of both traction and trailing vehicles. Regards. HL.     

Edited June 14, 2020 by harry lamb
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[Mark]

Have you checked the tyres are properly seated to the plastic centres. This used to be a general problem but has improved a lot with the current owner. If they aren’t then check for any residual parts of the spruce on the insert and clean it off. Also check in the tyre itself to make sure there is no debris preventing the tyre sitting down correctly. When you are satisfied glue the tyre on with loctite.

 

When you press the wheel on the axle make sure you press against the face of the tyre and not the boss in the middle. That will ensure that if there is any wobble between the tyre and the insert the tyre itself will end up perpendicular to the axle.

 

Regards

 

Mark

[97xx]

Thanks for the various comments.

 

I've run the wheels up on an axle in the mill, and measured with a dial gauge:

• Axle true (to take out any machine or axle inaccuracy)
• Wheel rim runout (i.e. sideways B2B error)
• Wheel rim true (i.e. circularity error)

. Then removed the tyre, cleaned off the sprue evidence (which was indeed present) and repeated.

 

Before:

• Axle < 1 thou
• Runout  5 thou
• True 5 thou

After:

• Axle < 1 thou (same)
• Runout 5 thou
• True 2 thou

So, the sprue residue affected the circularity which seems to make sense, but hasn't improved the runout.

 

Let's ignore the very small axle/machine error to make it simple.

 

I suppose the runout, although it looks offensive, only affects B2B, and if we assumed both wheels as poor and with their errors 180 deg opposite, that's 10 thou which is 0.25mm on the B2B. Small I know, but it still looks a lot!

 

The circularity at (therefore under) 2 thou is good.

Edited June 19, 2020 by 97xx

[PenrithBeacon]

Never used Romfords because I've always modelled in P4.

 

My method with AGW wheels is to hold the axle in the drill gun and chamfer off the ends of the axles. Then I use the GW press held in the vice and fix the wheels as tightly as I can to the press with draughting tape then offer up the chassis axle by axle and squeeze the press by hand.

 

This method does depend on the axles being the right length to give the correct B2B, and it does work after a fashion, in that it can result in a wobble free assembly but in any case it massively reduces the wobble.

 

Regards

Edited June 19, 2020 by PenrithBeacon
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