Association gears mesh problem

[Velocemitch]

A spot of help and advise required if I may..

I'm just coming back into modelling after a break of 10 years or so (might be more???). I used to model in 2mm and had some reasonable success with track and locos etc, so part of todays project is to check if I can still do it. I have picked up a part completed Fencehouses Jinty chassis kit, which I had started but never finished. All seemed to be going quite well, but I have hit a puzzling snag. I can't get the 64DP gears to mesh, the kit uses a 13t and an 18t set, which checking the mesh centres is 6.15mm. I have checked the hole centres on the frames and they are good as spot on. The muffs appear to be concentric (I've tried two sets), yet the gears just will not mesh properly. Almost like there is some mistake in the machining. 

Some times they feel normal, but other times they just snag like there is grit in the teeth!. there doesn't appear to be a point where this happens (ie if there was a high spot in the gear teeth).

I can't see any issues with the chassis, it seems to be aligned right and I've also tried meshing the gears just outside of the frames using some long axle shafts, tried both sides too to rule out one frame being different to the other.

The gears will have been purchased when I bought all the parts maybe in about 2007, not quite sure of the date. I wonder if there was a faulty batch or something?

I've never had any real issues with gear meshing before, especially on the 64dp sets, which are usually pretty forgiving.

[Jan W]

Did you check the gears for burrs?

Could it be that there are small burrs on the edges of the teeth?

It could explain why the grinding doesn't always occur.

A slight sideways movement can bring the offensive edge above the other gear.

 

Jan

[Velocemitch]

3 minutes ago, Jan W said:

Did you check the gears for burrs?

Could it be that there are small burrs on the edges of the teeth?

It could explain why the grinding doesn't always occur.

A slight sideways movement can bring the offensive edge above the other gear.

 

Jan

Yes checked that thanks, they seem clear enough. 

 

[Yorkshire Square]

The 13T 64DP gear actually had the general dimensions of a 14T gear so your clearance centres should be nearer 6.5mm.

 

I'm not familiar with the Fencehouses Jinty chassis - are you referring to the Masterclass/Farish conversion chassis? What are the specified centres/gears in the instructions? Have the holes for the frame bushes been open out true? Have you tried 14T and 18T M0.4 gears?

 

Some photos might help.

Edited January 1, 2022 by Yorkshire Square

[2mm Andy]

Reading the above I had a feeling of deja vu, so I checked the box where my part completed Fence Houses Jinty chassis has resided for the past few years, and I found that the gears I'd put in the box were a 14t and a 16t (both probably 64dp). It looks as though I'd realised there was a problem and swapped the gears for some that worked. I've just checked them in the chassis and they seem to mesh ok if possibly a little loose (meshing centres should be 6.08mm including a running clearance).

 

If you can't source any more of the 64dp gears (the Association doesn't stock them any more although they are still available from Ultrascale if you want to potentially wait 8 months) then the nearest equivalent is the 14t and 16t M0.4 gears which have meshing centres of 6.13mm including a running clearance. You'll need to change the gear muffs to 3-102a and 3-102b though as the metric gears have 3mm diameter holes instead of the 1/8" that the DP gears had (and which the skew cut wormwheels still have).

 

I hope the above is of use.

 

Andy

 

 

Edited January 2, 2022 by 2mm Andy

[Velocemitch]

Andy I think this explains it, I’m sure I wasn’t going daft. The kit instructions are quite clear with 13t and 18t, but it’s obviously not going to work. It seems to be a mistake in the kit.

looks like I’m going to have to change the gears. I hadn’t realised the muffs had changed, I wonder if this will make things awkward for the worm meshing, as the hole in the gear will be too large to suite a 3mm muff. I might need to reduce the diameter of an older muff local to the new gear.
better rejoin the association now as well!

[2mm Andy]

7 hours ago, Velocemitch said:

Andy I think this explains it, I’m sure I wasn’t going daft. The kit instructions are quite clear with 13t and 18t, but it’s obviously not going to work. It seems to be a mistake in the kit.

looks like I’m going to have to change the gears. I hadn’t realised the muffs had changed, I wonder if this will make things awkward for the worm meshing, as the hole in the gear will be too large to suite a 3mm muff. I might need to reduce the diameter of an older muff local to the new gear.
better rejoin the association now as well!

 

The axle muff shouldn't be a problem - you can purchase 1/8" dia. muffs (shop code 3-102a) that are turned down at one end to 3mm dia. to fit a metric gear. They come in pairs, so you could use the other one to fit the metric gear on the centre axle.

 

Andy

[MrSimon]

Hi,

 

I used a 3-390 14t spur gear after finding the 13t didn’t reach - there wasn’t any calculation there I was just trying what was in my box.  It works ok (although the chassis is currently in the sulking tin after a slight rods mis-hap…)

 

Hope that helps 

Simon