Problems with gearbox binding up

[Blandford1969]

Hi All,

 

I am looking for some advice, i have always tended to use motor mounts rather than gearboxes (yes i have been living in the old days, but have just ventured into gearboxes for the first time). I have built up a Comet 50 to 1 gearbox, when the gear wheel is not tightened the motor turns, but it does sound like it is pulsating. When I have tightened it up it just does not want to go at all.

The chassis runs freely so i do not think that is the issue. I did have some fun trying to get the gears central against the worm.

 

Can anyone help me to see what I have done wrong?

 

Kind regards

 

Duncan

[Kenton]

Sounds like they are too tightly meshed.

You should be able to pas a piece of thin tissue through without ripping it to shreds.

A 50:1 is starting to get to the finer end of single stage - the higher the ratio the more difficult to set up.

Is the axle rigid?

 

How is the gear locked on the axle? - If a grub screw then you need to be aware that it will push the gear off so that it is not centered on the axle - it will rotate in concentric fashion and therefore bind.

 

When you say trouble meshing the gear to the worm - do not force it - they should roll on to each other - check that they have not been damaged.

[Blandford1969]

Thanks for the reply, yes the axle is ridgid and yes it is with a grub screw. I will try playing with it again

 

Kind regards

 

Duncan

[artisan100]

Hi Duncan,

 

Firstly, don't worry too much about the worm being not central on the first gear. As the gears are helical cut it doesn't have to be.

 

Solving motor/gearbox problems is usually a step by step process. The GB1 is a two stage gearbox, so we just have to work through the geartrain piecemeal to find the problem.

How does the motor run when there's only the layshaft and worm in place?

If that's OK, how does it run when the driven axle is in place but the combination is not installed in the loco?

If the above are OK and the chassis is free running then you should be alright with the gearbox in the chassis.

 

The likeliest cause of a problem is the worm binding on the gear on the layshaft. If the motor mounting holes in the gearbox have been opened out slightly off centre, or if the fixing holes in the motor itself are marginally out of position then it will be enough to cause binding. It can sometimes be cured by rotating the motor by 180 and then trying again, but usually it's a case of slightly enlarging the holes in the gearbox and moving the motor (and hence the worm) slightly further away from the gear on the layshaft.

 

Contact me if you have any further problem.

 

Geoff

 

(Comet Models)

[bertiedog]

Arrangement by Comet, Copyright Comet

Provided for Reference only do not copy.

I assume that you are referring to the above 50:1 Comet gearbox with a Mashima attached.

The key is order of assembly, the axle is usually last, with the upper worm gear adjust first, outside the Chassis.

The intermediate gear should revolve freely and run true, no wobble of any kind, and then the motor is adjusted by enlarging the motor mounting holes and moving the motor towards and away from the gear, so as to get a smooth contact without any trace of bind.

This may take a couple of attempts to get right. The motor can be left running to bed it in a bit and re-adjust etc, then add a spot of loctite to each screw done up tight.

Next the axle gear is mounted and the box put between the frames, and the mesh should be all right first time, but it is better to pre-test outside the frames, and adjust the lower bearings to get the mesh right. The holes may need enlarging and when correct the bearings soldered in final place, checked and taken apart to assemble inside the loco frames.

At this point it should all work fine, without any binds or wobbles, but before the fitting, check the chassis is really free running, the quartering is 100%, and no rods binding anywhere, completely free rolling.

An old trick for checking the gear mesh is real cigarette paper jammed between the gear faces, this leaves about 3 thou gap, and should be all right, but frankly if the gears are true it could go tighter. Too tight and rhythmic binding occurs as the motor turns the gears, too loose and it wears and may be noisy.

If you have already assembled the lot it may have to come apart and re-do again, best to get it right now, before further finishing etc, it always pays to get the unpainted loco running and indeed run in before final strip and paint.

Hope this helps, if further queries just post with pictures if possible. The Comet gears and gearbox are first rate items and should work fine, but do check for flaws in the gears just in case a bad gear has got supplied. No point in trying to get a flawed wobbly gear set to work, they won't!!!

Stephen.

[bertiedog]

Hi Duncan,

 

Firstly, don't worry too much about the worm being not central on the first gear. As the gears are helical cut it doesn't have to be.

 

Solving motor/gearbox problems is usually a step by step process. The GB1 is a two stage gearbox, so we just have to work through the geartrain piecemeal to find the problem.

How does the motor run when there's only the layshaft and worm in place?

If that's OK, how does it run when the driven axle is in place but the combination is not installed in the loco?

If the above are OK and the chassis is free running then you should be alright with the gearbox in the chassis.

 

The likeliest cause of a problem is the worm binding on the gear on the layshaft. If the motor mounting holes in the gearbox have been opened out slightly off centre, or if the fixing holes in the motor itself are marginally out of position then it will be enough to cause binding. It can sometimes be cured by rotating the motor by 180 and then trying again, but usually it's a case of slightly enlarging the holes in the gearbox and moving the motor (and hence the worm) slightly further away from the gear on the layshaft.

 

Contact me if you have any further problem.

 

Geoff

 

(Comet Models)

Posted my reply whilst you posted so I hope nothing overlaps!!

 

Stephen.

 

 

[Blandford1969]

Thanks Stephen and Geoff,

 

I will go through the steps you have both kindly given. I think it is binding on the layshaft so will try rotating the motor and opening the holes and then seeing if that works. I have got some more time to play with as this is now destined for a SEF U, which i will do a thread on.

 

Thanks also for the offer of further help.

 

Kind regards

 

Duncan