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Axle will not fit in bearings, what do I do?


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I’m currently building a chassis kit for a Pacer and have hit on a problem.  Some of the axles will go through the top hat bearings, but some do not.  The difference is tiny, probably less than one tenth of a millimetre, but what do I do to solve the problem.

 

Any help appreciated.

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Probably obvious questions but is there a burr on the axle stopping it going through, or is it the axle which is too large in diameter, or the hole in the bearing which is too tight? Could you heat up the bearing, or cool down the axle, or both, would that give enough leeway?

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On the assumption (!) that this is a one-off project and you don't wish to invest in broaches, etc., then one way is to wrap a piece of went and dry abrasive paper round a smallish diameter rod and work it to and fro and round and round until the axle enters. But do check for burrs on both the axle ends and the bushes too.

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31 minutes ago, decauville1126 said:

On the assumption (!) that this is a one-off project and you don't wish to invest in broaches, etc., then one way is to wrap a piece of went and dry abrasive paper round a smallish diameter rod and work it to and fro and round and round until the axle enters. But do check for burrs on both the axle ends and the bushes too.

 

Buy the broaches - they are absolutely invaluable.

 

Regards,

John Isherwood.

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15 minutes ago, cctransuk said:

 

Buy the broaches - they are absolutely invaluable.

 

Regards,

John Isherwood.

But how do you get a broach into a top hat bearing?

 

BTW I cannot understad the OPs question

" Some of the axles will go through the top hat bearings, but some do not"

Axles don't go through top hat bearings, a ground point goes into one.

Edited by melmerby
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19 minutes ago, melmerby said:

 

Axles don't go through top hat bearings, a ground point goes into one.

 

I thought that they were called pin-point bearings if they supported a ground point axle and top-hat bearings if the axle went all the way through..

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The through axle ones i've always thought of as axle bushes.

When I asked for "top hat" bearings at Alan Gibson I got what I expected but I must confess the packet says "pin point bearings"

 

Putting "Top hat" in to a search comes up with those for pin point axles more often than not.

Edited by melmerby
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5 hours ago, ColinK said:

I’m currently building a chassis kit for a Pacer and have hit on a problem.  Some of the axles will go through the top hat bearings, but some do not.  The difference is tiny, probably less than one tenth of a millimetre, but what do I do to solve the problem.

 

Any help appreciate

 

 

1 hour ago, melmerby said:

But how do you get a broach into a top hat bearing?

 

BTW I cannot understad the OPs question

" Some of the axles will go through the top hat bearings, but some do not"

Axles don't go through top hat bearings, a ground point goes into one.

 

I think as said before there is some confusion over terminology Top hat bearings can either be the pinpoint type usually used for coaches and wagons, where the end of the axle is ground into a pinpoint and fits into (not through) the bearing. Or a mainframe bearing bush where the axle goes through the bearing

 

To ensure the inside diameter of a mainframe bush is a minimum required size you would use a parallel reamer, rather than a tapered broach, though a very light touch of a broach may assist an axle to be inserted into a bearing

 

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Thanks for the replies and apologies if my use of ‘top hat’ has caused confusion - that is what I thought they are called.  The photo below might help. There are four sets of these, one for each axle.

 

C762BF0D-CED6-44FC-BC6D-7085E4D206DA.jpeg.7a4206a832453ce0e216a4ba99278095.jpeg

 

Each side has a brass bearing with a hole through it and a flange on the outside.  I have soldered these into the etched chassis.

 

As the hole in the bearing is too big for the axles, a brass reducing bush goes inside the bearing, I have glued these in place as per the instructions.

 

I can understand that an axle will not go through both bushes if I have not lined them up properly, but that is not the problem. An axle will go through some of the individual bearings, but not all.  I’m assuming that the hole in some of the bearings are fractionally too small and that I need to open them out very very slightly.

 

I hadn’t actually thought of reducing the axle diameter, but that might be easier for me - I’m fine at making scenery and buildings, but making moving parts is a new area for me.

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Personally I wouldn't entertain reducing the axle diameter, it could lead to other problems.

 

Broaches are definitely be the best solution, they are invaluable for making etched kits and a really useful addition to your tool collection. They usually come in sets according to size range. Assuming this is a 4mm chassis you are going to need one that ranges from 3-4mm for a 1/8inch axle. About £9 from Squires (page 90 in their online catalogue). You can buy broaches in sets which works out more economical if you want to invest in a larger range.

 

Edited by nickwood
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1/8 th inch straight reamer.

 

 

 

Never use a tapered broach one side of the hole will be wider than the other, due to the taper shape. Use a taper on holes e,g on the etch so that the bearing is at ight fit into the etch before soldering. if you make that hole oversize nothing will line up level, when the wheels/axles are fitted.

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Colin

 

In hind sight it might have been better to check each bearing prior to fitting, however when fitting the bushes into the bearings you must ensure firstly that all axles will go through all the bearings, then when fitting the bushes into the bearings you must ensure they are parallel with each other.

 

The tool you now need is a parallel reamer, its a bit like a drill but not only more accurate but will ensure the 2 holes will be parallel with each other

 

Agreed broaches are extremely useful in opening up holes in etches, but unless the broach is parallel along most of its length it is not the tool you require, the broaches I have are tapered and therefore will give you a tapered hole.

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3 minutes ago, micklner said:

1/8 th inch straight reamer.

 

 

 

I don't think it's ⅛" as the normal axle bushes have been reduced (to 2mm?)

I assume these are for 3' 7" or similar diesel/coach wheels.

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If those are 2mm reducing bushes and you have neither reamers nor broaches then here's a dirty trick. Put a spot of toothpaste in the bearing and fit a cocktail stick in the mini drill or by hand. Run it through the bearing till the axles just fits through. 

 

Longer term both parallel reamers and  broaches are very useful. 

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3 hours ago, rdr said:

top hat refers to the outside shape of the bearing, cylindrical body with a large shoulder and no through hole. I would expect there to be two different versions for solid or pin point axles.

Shouldered bearings......

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I think it's worth pointing out to the OP that a new reamer will cut oversize because of burrs that are left over from the manufacturing process.

To remove these put a layer of toothpaste on a leather belt, insert the reamer into a drill and wrap the belt around the reamer. Run the drill for a few minutes and it should remove the burrs.

Cheers

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Sounds like a quality control problem with the axles,  Normally a few thou is neither here nor there with rolling stock wheels as they run in  outside bearings. Any variations just mean some of the wheels slide in and out a bit easier as you adjust the back to back.   If you are using pin point or extended axles then you can't really complain, but if they are sold for inside bearings then its not merchantable quality.  I would try to match the axles to the bearings to see how many combinations you can make work. It makes a difference if you just bought the right number of axles for the model, or if like me you have lots of the things lurking in your scrap box, but it may be possible that all the axles can be matched to sets of bearings.  If not if you keep the bearing/ axle combinations which work together it may be that only one or two rogues remain.   My next move would be stick the axle in the chuck of the Black and Decker drill and gently apply a cheap flat needle file to the spinning axle.  After a trip to A+E and cresting a pile of ruined axles  I would source some more axles until I found some at the other end of the tolerance range which will actually fit..   

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If a given axle enters some of the bearings and not others, then the sleeves in the bearings are out of spec and should be replaced. Possibly you bought a packet of them and have spares already, so you can pick out the ones that are good. 

 

It looks like the 1/8" bearings are soldered in to the carriers and the reducing sleeves are glued inside those. I'd unsolder the 1/8 bearings and replace them with proper 2.0mm bearings that don't need the sleeves. Alternately, heating the assembly would break the glue and let you get the sleeves out but would probably unsolder the 1/8" bearings at the same time.

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10 hours ago, DavidCBroad said:

.   My next move would be stick the axle in the chuck of the Black and Decker drill and gently apply a cheap flat needle file to the spinning axle.  After a trip to A+E and cresting a pile of ruined axles  I would source some more axles until I found some at the other end of the tolerance range which will actually fit..   

Some emery cloth will do it and probably give finer control & better finish.

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