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Comet 4F


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Hello all, I haven't been in touch for a while so I thought I'd give you an update.  I can't start building the layout yet, I'm waiting for some work to be done on the house, however, I've been busy populating and lighting all my coaches.

Having done that, I decided to have a go at building a 4F chassis, quite a leap for me, I've never done anything like that before.  I really like the 4F and would like one that would pull well, so I ordered the Comet chassis and the Canon motor and gearbox.  Hopefully I can put some weight in it to aid adhesion and pulling power.  I spent the afternoon/evening on it, struggled a bit, some of the bearings came loose, but I managed to get to the stage of testing, (pic' added) only to find I'd lost the grub screw from the layshaft!!:o

Ahh well, roll on  Monday so I can order another.

 

Cheers

John

4F Chassis.jpg

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Fitting the Comet sprung hornblocks, although not essential for OO or EM, would considerably improve the ride and pick-up.  They are quite easy to fit and you can still drive the centre axle.  Heres my 63xx chassis with the centre ones fitted, awaiting the outer ones.  The etched springs can just be bent to allow the hornblocks to be installed then bent back to retain them.

 

IMG_1199.JPG.441a894176c39f190a256dfd4ee708bf.JPG

 

 

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Mate, I would put this in kitbuilding and scratchbuilding, in the skills and knowledge section . will get more views than the model engineering section.

 

Edited by mswjr
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Hi, yes, I thought about it, but as it's my first attempt decided to try the easier option first.

The instructions aren't very thorough and a picture of the braking system would be very helpful if anyone has one.

Thanks to all for the input.

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1 hour ago, PenrithBeacon said:

IMG_20191217_171215.jpg.40938e2c602dd85308b0462452e032fa.jpgPerhaps I'm misunderstanding the photos, but I thought the Comet hornblocks are supposed to slide up and down in the chassis cutouts? At least, that's how I've done it.

 

 

Yes that's correct.  The black marker may be confusing the picture.

 

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A glutton for punishment, I've done 12 now, liked the first one so much, just kept going on - but for 2 layouts! But all with rigid chassis, yes I'm lazy, take the easy way out, but make sure my track is as near perfectly flat as possible. Gone from Comet gearbox to High Level.

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On 22/05/2021 at 20:27, Jeff Smith said:

Maybe a Mod could move it!

 

The way, I understand, is to "report" one of the posts which will bring it to one of the Mods' attention who hopefully will move it to the kit building section. I'm sure you will get far more help and advice there. I'll report it now.

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On 22/05/2021 at 00:08, SuperD said:

Hello all, I haven't been in touch for a while so I thought I'd give you an update.  I can't start building the layout yet, I'm waiting for some work to be done on the house, however, I've been busy populating and lighting all my coaches.

Having done that, I decided to have a go at building a 4F chassis, quite a leap for me, I've never done anything like that before.  I really like the 4F and would like one that would pull well, so I ordered the Comet chassis and the Canon motor and gearbox.  Hopefully I can put some weight in it to aid adhesion and pulling power.  I spent the afternoon/evening on it, struggled a bit, some of the bearings came loose, but I managed to get to the stage of testing, (pic' added) only to find I'd lost the grub screw from the layshaft!!:o

Ahh well, roll on  Monday so I can order another.

 

Cheers

John

 

 

I have had your thread moved, John to the kit building and scratch building section as you will get far more attention and help here and more people will see your build and hopefully give you some useful advice.

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You can see from the pic' that I've fitted the motor and I've run it now that I have the grub screw.  It's nice and smooth, though not as fast as I expected.  The gear sets are not quite central on the worm even though I've followed the instructions with the thinner bearing.

I've managed to get hold of some wheels (Andrew's out of stock) and I removed the motor, fitted the wheels and checked it for free running.  The middle wheels don't touch the track unless I press on it and I have to lift the track about three inches before it moves (this is under it's own weight).  So....do I remove the wheels and broach the bearings a little, I don't want any sloppiness in it?

Any help/advice would be appreciated.

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A few points:

 

1) I think Rice's "Locomotive Kit Chassis Construction" is excellent.  It is a bit dated and, alas, out of print.  However, there will probably be copies around.

 

2) The old Comet site had some useful downloads that Wizard appear to have discarded.  Here's the one on chassis construction:

 

Building loco chassis the Comet Way.pdf

 

It was publicly available on the old site, so copyright shouldn't be a problem.

 

3) Rice recommends, IIRC, that for a rigid chassis, the center wheels should be higher than the others by the thickness of Sellotape.  This provides some small compensation for minor track irregularity.

 

4) Axles should fit in the bearings so that they slide out under their own weight.  Broach the bearings until that happens and the chassis should run freely.

 

John

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There was one axle that didn't fall through without a push, so a touch with the broach and all fine.  I then laminated the Coupling rods and put them on using the plastic insulation tip. :yahoo:...... Amazed...still free running.  Flush with success, I fitted the motor and put the chassis on a plinth with the wheels hanging free.  Gently turned on the power............nice smooth running and very quiet.........Mmm, nothing to this modelling lark, I'll have a coffee and let it run for a while.

Return to find it's a bit jerky, I feel at the motor and its really hot.

It's a bit like golf... just when you think you've cracked it, you have your worst ever round...

Coupling rods are off.  I'll see what tomorrow brings.

Cheers

Edited by SuperD
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You don't say which wheels you are using.  My preferred brand is Markits because quartering is a no brainer.  If you are using Gibson or similar, quartering needs more care.  Make sure you have that right.

 

I would take the GB out, reattach the rods (articulated?) and run the chassis along the track, look for a once per rev binding.  The rod holes could need a touch of the broach to fix this.  Do one hole at a time until it feels right.  Loose rods are not desireable.

 

John

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7 hours ago, SuperD said:

There was one axle that didn't fall through without a push, so a touch with the broach and all fine.  I then laminated the Coupling rods and put them on using the plastic insulation tip. :yahoo:...... Amazed...still free running.  Flush with success, I fitted the motor and put the chassis on a plinth with the wheels hanging free.  Gently turned on the power............nice smooth running and very quiet.........Mmm, nothing to this modelling lark, I'll have a coffee and let it run for a while.

Return to find it's a bit jerky, I feel at the motor and its really hot.

It's a bit like golf... just when you think you've cracked it, you have your worst ever round...

Coupling rods are off.  I'll see what tomorrow brings.

Cheers

Panic not, SuperD. Your centre drivers will be hanging down, compared to the fixed outer axles, if you're running it dangling in the air as described. This may well account for the overheating of the motor, as the mechanism is perhaps binding slightly at one or more crankpins at certain points on each rotation of the wheels, especially once things warmed up, because the centre axle is low.

 

Sprung/compensated chassis should be run in on a rolling road, or a continuous run of track. Try your chassis on a length of plain track & see how it goes. (Use some long leads to connect the motor to the controller, as you've not got any pickups fitted as yet).

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Don't forget some light oil on the wheel bearings and the gears.  This will make a tremendous difference.  Also if they are one piece coupling rods there will need to be a slight clearance at the crankpins, especially if any of the wheels have any slop.  Finally, it is a good start to be able to move the chassis freely but they sometimes behave differently under power, however driving the centre wheels should minimise this.

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14 hours ago, MarkC said:

Panic not, SuperD. Your centre drivers will be hanging down, compared to the fixed outer axles

You're looking at the wrong chassis, the one built by SuperD is all rigid.

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Hi all, thank you very much for the input.  I ran it this morning with rods off and got the same result.  I'm using Romfords by the way. After a bit of head scratching I realised that one of the brass bearings had come loose, I don't know if this was because of the heat generated. Anyway, a bit awkward because I did the soldering before I folded the gearbox but I've redone it.

While I had the motor out I put the rods back on and tried it for free running.  It wasn't as good as the first time and there was a slight bind every revolution.  I'd drilled the rods as instructions at 1.2mm and my next drill is 1.5mm, a little more than I would like.

However, I did the outside wheels, but no improvement.  So we'll see what tomorrow brings.

Cheers

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You didn't mention using the rods as a jig to set the bearings.  It is crucial that the bearing centers are identical to the rod centers.  I had a set of these:

 

alignmentjig.jpg

 

These are on the London Road Models site.

 

Don't use a drill to enlarge the holes in the rods if that is what you think needs doing.  A broach is the correct tool giving you very fine adjustment.  Try to open them ever so slightly and try the chassis each time until things work.

 

Another tip is to get a length of 1/8" steel rod, about 8 - 12" and slip it into the bearings.  Hold the chassis on a cutting board marked with squares, and check that the frames are perpendicular to the rod.

 

John

 

Edit, one more thing.  You say the wheels are Romfords.  These and Markits use the same axle design with square boss and nut.  However, in my experience Romfords are not as fine as Markits.  If you are using code 75 track, the flanges could hit the chairs.  Markits have mostly superceded Romfords nowadays.

 

Edited by brossard
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I have used a number of methods constructing chassis over the years. The Iain Rice book was my standard reference work some years ago. I currently use a Poppy’s Jig. I can  recommend it. I’m currently constructing a number of LMS 460 comet chassis., using both their canon motor  and  Taff Vale models alternative. In both cases with Comet gearboxes and drive extenders. My preferred gearboxes are High Level, currently unavailable.

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10 hours ago, Nile said:

You're looking at the wrong chassis, the one built by SuperD is all rigid.

Meh! You're right. Oops. However, my point about testing such chassis remains :)

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Good morning all,  I used the Comet jig and the axles fall straight through under gravity. which I don't think they would if it wasn't square, but that system looks interesting, I'll have a look.  I'm using some Romfords from the auction site. I can't get hold of any Markits at the moment.  This is a problem in so far as three are uninsulated and I don't want to go "live chassis", so I'll change them when I can get some.

Back to the free running... I've already drilled the outside holes, I didn't realise that there was a broach so small (1.2mm) I must get one. But, try as I may, I cannot get this to run smoothly under it's own weight, so I lubricated it and put the motor in and tried it...........

I intended posting a vid' but the file's too big......it runs really smooth and quiet.

So my next hurdle, when I get some wheels, will be how to fix the rods on the crankpins without upsetting anything as it is now.

Thank you all for the support so far

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