Alan Gibson driving wheels

[PenrithBeacon]

Can anyone offer advice on how to get the crank pins on Alan Gibson driving wheels square?

 

MTIA

[alastairq]

article in MRJ #200 [this month's] by Chris Pendlenton....covered this sort of problem...

[PenrithBeacon]

article in MRJ #200 [this month's] by Chris Pendlenton....covered this sort of problem...

 

 

Thank you, I'll buy the mag.

 

Regards

[Torper]

If the crankpins are not square, then the driving wheels are defective and not fit for purpose. Send them back for replacement - much easier than Chris Pendleton's method!

[Grovenor]

If the crankpins are not square, then the driving wheels are defective and not fit for purpose.

Not always, the earlier wheels in AGs list, where the tooling was taken over from Studiolith, you have to drill the crankpin holes yourself so you have no recourse if you don't drill them square. You need to use a drill stand and make sure the wheel is properly supported. It also helps to get all the wheels with the same throw if you make up a jig.

See Crank pin throw jig

Regards

Keith

[bertiedog]

I think it's a wee bit unfair to Gibson to suggest that the wheel moulding does not have an accurate positioned hole, they are now moulded in, but there was a period when the Gibson style metal crankpin collars were not very true, having the hole drilled in the metal bush a bit off centre. They offered replacements and recent ones are OK.

• But best check the collars by putting on, say, a needle, and spinning around, they should run true. If out of true you will get slight binding, even with correct quartering.

However the scale size Crank-pin system is very small, Gibson chose a small BA size, and it can be increased in size to 12 BA. but you will have to make your own collar from fine brass tube, not easy without a lathe. You can also use Markits 10 BA bolt on type if you want, drilling out the hole and tapping 10BA

 

With the original Gibson scale parts, assemble first to check fit, de-burr etc., and then take apart, then glue with epoxy the main bolt into the wheel boss hole, adding the collar to the outside with a spot of glue. Check the throw is the same on all wheels a small gauge, it can be filed from scrap brass or aluminum. It's more a "check" than vital, but best to be safe, than sorry.

 

The rods should be a good fit on the collars, not too tight or too loose, you can always open out with a taper broach if too tight, but you can't tighten them!!!!(well, you can, but only with a bush soldered in and re-drilling)

 

Virtually the same advice applies to Ultrascale wheels, there are lots of alternative crankpin methods.

 

Stephen.

[artisan100]

Just a small correction, Bertiedog, but the current Gibson crankpins are not a small BA size, but are threaded M1. That's according to their list anyway.

 

Geoff

[meple]

Just a small correction, Bertiedog, but the current Gibson crankpins are not a small BA size, but are threaded M1. That's according to their list anyway.

 

Geoff

 

 

14BA and M1 threads are virtually identical. The normal modeller would not be able to tell which was which.

 

Consider the use of Exactoscale crank pins. The collar is threaded and so holds the screw (M1) tightly and in alignment.

 

 

[bertiedog]

The small differences, (pitch and diameter, plus angle of contact), added to tolerances may explain why I had to replace the bolts on the last set, 14BA are smaller and finer pitch, but a nut of 14BA generally fits the 1% larger 1mm thread, but very tightly.

 

Trouble is such tiny metric bolts are not made in huge quantities and tolerances can be a bit loose from some suppliers of such fine metric thread sizes. BA bolts come more from Specialist suppliers like EKP Screws, and are to tighter tolerances on sizes

 

I would advocate using 12BA with smaller retaining nuts, made by running a 12BA tap through a brass 14BA nut. This gives a nearer scale appearance, especially if the nut is thinned down in thickness as well, by filing down with a fine finish needle file.

 

At present the 12BA and 14BA taps and dies are cheaper and more easily available than 1mm as well. Small metric taps are not so widely distributed, and tend to be supplied in HSS types, doubling the price or more. Metric model engineer Tap and Die sets rarely go as small as 1mmx.25pitch, although at the moment small metric watchmakers sets down to .6mm are available very cheaply from Ebay suppliers like Proops.

 

The problem that appeared with the top hat shaped bearing collar, was the back was not flat, and the hole eccentric, but this has been addressed by Gibson. The eccentricity was only a few thou, but you could get the tolerances adding up across the whole set of wheels and binds occur, even when appearing to be correctly quartered, as it alters the throw of the crankpin.

 

Over the years the best crankpins were Hamblings, which are now Markits type, but these used collars rather than nuts to retain the rod but the advantage is that the crankpin is firmly screwed home with a 10BA thread into a tapped hole on the wheel. The Markits can be threaded of course, and a nut added, metric or BA.

 

Stephen.

[John_Hughes]

My understanding is that the BA threats actually are metric; can someone please confirm or deny?

 

Ta!

[meple]

My understanding is that the BA threats actually are metric; can someone please confirm or deny?

 

Ta!

 

 

Yes they are metric but the thread form is different from the ISO metric thread.

 

BA has an angle of 47.5 degrees whereas ISO has 60 degrees. The BA thread is also round topped (crest) whereas the ISO is square topped.

 

This means that the BA thread (14) has a pitch of 0.23mm and that of the ISO (Coarse) of 0.25mm. It's unlikly that you will come across a fine 1mm ISO but if you did its pitch is 0.20mm, which means that it would not fit a BA but the Coarse thread will (over a short distance such as a nut).

[ThePipersSon]

Going back to the OP. I had difficulty getting the crank pins square because, when you drill the hole for them, it emerges on the other side of the wheel on the edge of the raised boss. Thus when you try and insert the crankpin, it doesn't go in straight.

 

My solution was to remove some of the raised boss, until the crankpin was entering a flat surface. It seems from MRJ article that Chris Pendleton had to do the same.

 

I'm sorry I don't have any photographs of it, but I don't possess a digital camera.

[Horsetan]

Going back to the OP. I had difficulty getting the crank pins square because, when you drill the hole for them, it emerges on the other side of the wheel on the edge of the raised boss. Thus when you try and insert the crankpin, it doesn't go in straight.

 

My solution was to remove some of the raised boss, until the crankpin was entering a flat surface. It seems from MRJ article that Chris Pendleton had to do the same.....

 

You can to a certain extent countersink the back of the crankpin hole in addition to removing the section of boss that encroaches onto it. The result should be a more tailored level seating for the M1 or 14BA screw.

[bertiedog]

As indeed the Gibsons are now metric the nuts are going to have to come from them if they are .20 fine, but they are .25, (just checked a bolt from Gibson). The last wheels I had through from them were pre-drilled, has this changed?

 

The BA threading system was a Victorian idea, to give tight fitting, and fine adjustment for instrument retaining screws. It was during a period when it was intended to "go metric", and the committee decided to base on the Metric standard, as they looked upon this as more "scientific" ......?

 

It uses a formula to step each size rather than solid numbers, leading to awkward thread pitches that can't be done on a conventional lathe, you have to use a thread chasing lathe, or resort to dies or die heads in lathes.

 

They chose metric 6mm thread by 1mm pitch as the nominal source at 47.5 angle,(it's near to a 1/4inch size), The angle remains constant for all sizes as usual with threads. A 6mm x1mm metric thread matches to 0BA, except for the angle of contact,(60^o with metric, and a square top to the thread).

 

The pitch constantly gets smaller as the size goes down, unlike the ISO metric threads, maintaining the same mechanical and frictional contact across the range of sizes. The rounded form top helps with maximum grip.

 

The whole system was declared redundant by British Standards, but survives today for many uses like models and instruments, the area it was designed for.It is very unlikely to ever fall out of use in practice. I was assured in 1967 by Dormer Drills that it would be impossible to purchase taps and dies for it beyond 1970......but they still available!!!!, as are Watchmakers threads, RA microscope threads, Clock swiss fine, Imperial Acme, Imperial buttress threads, Whitworth, all meant to be long gone but still here on the market.

 

Stephen

[lonesome_whistle]

The last wheels I had through from them were pre-drilled, has this changed?

 

 

Stephen

 

Some of the wheels are pre-drilled, other are not. As alluded to earlier in the thread by Grovenor, it probably has something to do with the age of the patterns. Certainly the 4'7" GW drivers do not come with the crankpin hole in place. Getting the crankpins true is certainly a problem I have encountered particularly with the wheels that do not come with the hole pre-installed (I'm not sure whether they are drilled or moulded in). The link provided by Grovenor provides a solution but even with the hole drilled true it is important to countersink the hole and remove the boss where it encroaches on the head of the crankpin screw. It is a bit of a faff and probably much easier accomplished with some sort of jig.

[PenrithBeacon]

Thank you, I'll buy the mag.

 

Regards

 

Well, I finally got a copy of the mag but had to go to Smiths in Watford! I took a look at the article and decided that the method described had more to do with model engineering that the sort of modelling I aspire to.

 

I really cannot say, hand on heart, what actually goes wrong and why, but I would imagine that as these wheels have been on sale for ages now and there must have been many thousands sold that there must be a solution.

 

The wheels do come with a drilled hole. They also come with screws which are intended to act as crank pins and the destructions say that the screw must be screwed into the hole and there is no need for the hole to be tapped. OK, so far so good. The problem is that as I attempt to screw the screw into the hole there is no way that I can ensure that the screw goes into the hole square. Whether that means that the hole is originally out-of-square and therefore the screw is following the original 'pilot' hole or that I am screwing the screw into the hole out-of-square and the material, a very soft plastic, is permitting this is more difficult to determine.

 

Thanks for the ideas above, I'll look into them.

 

Regards

[bertiedog]

Well, I finally got a copy of the mag but had to go to Smiths in Watford! I took a look at the article and decided that the method described had more to do with model engineering that the sort of modelling I aspire to.

 

I really cannot say, hand on heart, what actually goes wrong and why, but I would imagine that as these wheels have been on sale for ages now and there must have been many thousands sold that there must be a solution.

 

The wheels do come with a drilled hole. They also come with screws which are intended to act as crank pins and the destructions say that the screw must be screwed into the hole and there is no need for the hole to be tapped. OK, so far so good. The problem is that as I attempt to screw the screw into the hole there is no way that I can ensure that the screw goes into the hole square. Whether that means that the hole is originally out-of-square and therefore the screw is following the original 'pilot' hole or that I am screwing the screw into the hole out-of-square and the material, a very soft plastic, is permitting this is more difficult to determine.

 

Thanks for the ideas above, I'll look into them.

 

Regards

 

Well, you have hit the problem in one, yes, it is Model Engineering, but really it's very minor and very easy, to drill the hole at right angle, and take a bolt through accurately.... Within any home mechanics capabilities.

 

Where you have got a problem is the screw is acting as a tap, deforming and cutting it's own thread as it goes through the plastic, and if it starts the thread out of true it will remain so. Taps come in a set , with a first tap with a lead in to aid alignment, this guides it, and it is followed by a full sized tap to complete the thread.

 

The hole should not really need to be tapped, but a clean clearance over the thread, open up with a taper broach or stepped sized micro drills until the screw just enters the hole. If the hole is already there then work from the back of the wheel not the front. The boss at the front should have a flat parallel surface(Y) to the back, if domed or raised in any way, smooth carefully with a fine needle file till true.

 

The bolt should not be tight or too loose. If you do the opening up with step sizes or drills, then the drill will follow the hole and remain true, if un-drilled it will just need care and accuracy to drill a pilot hole, and open up gradually till correct. A pillar drill would help, or an attachment for a hand drill to drill at right angles reliably. Practice "off hand " drilling at right angles by estimate, practice helps! You can use a guide block with a true hole in it, but it will have to be made on a pillar drill.

 

The coned seating for the screw head can be cleaned up at the back with a larger twist drill head. Go in far enough to recess the coned head just below the surface.

 

The screw is fitted and the top hat bearing slipped over the bolt, and as long as the back of the top hat bearing is true and the face of the boss true, flat and parallel with the back of the wheel, the bolt will be pulled tight by the nut and washer, and should be at right angles straight away.

To assemble finally, epoxy glue must be used, a long set type, or good quality 5 minute type like Araldite or Loctite. Superglue gel could be used, but epoxy allows adjustment whilst setting, if out you can correct it .

 

A smear of epoxy glue is added to the screw and the hole and the screw put in to place, a smear added to the front and the top hat bearing dropped on to the screw. Keep the top of the thread clear of glue.

 

The nut and washer is then fitted, and gently tightened till the glue sets, and then the outer washer and nut can be removed, and that's it, the top hat bearing will be in the right position, tight on the bolt which will be securely fastened to the wheel at right angles.

 

The alternate is to tap the hole 14 BA or 1mm x.25, with the tap held at right angles by eye, or through a block of wood or metal drilled to clear the tap, the block rested against the back of the wheel and the tap inserted through the hole to enter the hole in the wheel.

 

If it is tapped it goes not need glue, but I would add it anyway to make sure the bolt is firmly mounted, especially important on a crank axle, where the valve gear will be bolted on to the crankpin end. In this case there must be no rotation at all, or the valve gear will tie itself in knots.

 

Stephen

[PenrithBeacon]

Thanks, I'll see what I can do to implement the advice. I would imagine that the 'Alan Gibson Workshop' owners look at these threads, perhaps they could modify their product to some degree even if it's only changing the destruction leaflet.

 

Regards

[micklner]

Using these for first time , no real problems. Can anyone confirm you Loctite the outside " retaing nut" to the screw and then remove the thread back to the outside nut . Presumably you file the thread flush with the outside of the nut. ??

 

thanks

[garethashenden]

Using these for first time , no real problems. Can anyone confirm you Loctite the outside " retaing nut" to the screw and then remove the thread back to the outside nut . Presumably you file the thread flush with the outside of the nut. ??

 

thanks

Either Loctite or a very careful application of solder, then trim screw and file back.