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The basic frames

Posted by Kenton , 20 October 2009 · 1,020 views

kitbuilding frames chassis
So the indecision is silenced and off we go...
I guess most of those who know me guessed which way was most likely but the discussion on what is the best suspension for an 0-4-0 will no doubt continue well after this kit is complete.

The best place to start with any loco kit build is with the the chassis (sorry frames). Getting these straight and true is essential and if not made as such will ruin the rest of the kit build.

First identify the parts required using the instructions and the parts list then find them on the fret ??“ easy, as they are clearly numbered. Using fine tin snips, I then removed the parts from the fret - I may have mentioned before that some care has gone into the location of the fret tags in this kit so that they do not interfere too much - though there are a few very small parts where this has been beyond any amount of design. Once removed from the fret, tidy up the edges with a fine flat file.

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The first thing to note is that there are 7 frame spacers. (three different sized, folded: 3a rear upper, 3b middle lower, 3c front upper; two identical straight: 3d and 3e rear and front lower; one with an etched centre line: 3f this takes the knife edge 5 above the rear axle; and finally an odd shaped spacer 3g, with two hooked corners, and the location of which I was unable to deduce from the drawings.)
There are also EM spacers supplied on the fret for those who desire to build this for that gauge. With the exception of one other component, discussed later, that is the only difference between the builds as far as I can see.

Starting with the frames [1] the merest whisper of a 5-sided broach is all that is required to enable the bearings to be inserted into the front and jackshaft axle holes. Remember, these should be a tight fit, and it was likely only the etching cusp that prevented them sliding in without further work. They were soldered in place with the bearing flange facing the back of the wheels.

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Starting with the middle lower spacer [3b] fold along the half-etched line. Do not strengthen these folds with solder at this stage. Solder the spacer in the half-etched recess on one of the frames. Then inserting 1/8" rods (the axles will do - but longer rods would be better) through the bearings just soldered, align the frames and solder the other frame side to this spacer.
I would normally suggest at this stage placing the frames on a flat glass surface to check alignment, however the frames do not have a flat side so the next best thing is to place the wheels on the axles and then test the alignment. The frames will tilt back slightly on the jackshaft axle but this doesn't matter as long as all 4 wheels are touching the glass. Gently twist the frames until they are all touching and check that the axles are parallel (this is where long rods helps) and that they rotate freely.

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This use of glass is easier to see live than in a photo.

When satisfied, the wheels were removed. Do not forget to do this at each stage, they are plastic spokes and I didn't want any accidents with all the heat.
Fold-up and push the upper rear [3a] and upper front [3c] spacers into their half-etched slots in the frames and then solder in place. Checking each time the squareness of the construction as above.

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The following little gadget is quite useful for removing wheels, a wheel puller:

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Now insert the flat lower rear [3d] and lower front [3e] plain spacers. These are quite difficult to force between the frames and care should be taken not to twist the frame or to buckle the spacers. Again check the squareness and re-adjust before soldering in place. The frames are now quite a rigid structure.

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Next, add the horizontal compensation beam spacer [3f], it has a centre half-etch line which should face towards the axle. Then solder the knife edge [5] into the half-etch so that the arrow points either up or down. A thought raced across my mind as I wondered what state this would look following many 100 hours of pressure against a rotating axle. Posted Image

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Sorry about the mess in there - photo taken before cleaning.

This was possibly the most difficult step in this stage of construction. Keeping the knife edge vertical in the middle of the spacer was challenging. I can see it would have been even worse if I had not had the zapping power of the RSU and at least 3 hands. I can only suggest possibly adding this to the spacer before inserting the spacer using higher melt solder. But even then there is a good chance of it falling off during soldering. At least doing it the way I did, there is no risk of the spacer falling out as it is sprung into the frame half-etch. I have a soldering iron with a fairly long 2mm tip but that would not have reached the join.
Check the height of the knife edge by placing an axle through the rear axle holes. It should rock on the edge in the upward direction by about 2mm.

The decision having been made to use the compensation system as supplied, I did decide to add an axle bearing to each swing arm. This is not suggested in the kit and may prove to make the compensation slightly stiffer - be that on my head only. The swing arms are made up with pairs of part [2] overlaid. Use a well greased axle (in my case following reaming of the axle hole, the clean bearing) through the axle holes and a short scrap length of brass wire through the pivot hole to keep the pair aligned as they are soldered together. Be aware that they do become "handed" if adding bearings and I would suggest that the bearing flanges face the frames.

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The swing arms are attached to the rear of the frames and need to be inserted between the spacers to do so and are arranged with the flatter side uppermost. Using a pin (a Peco track pin seemed appropriate - so they have a use after all :D ) solder each pin as a pivot through the arm to the frame. Some solder mask and care is required to solder this pivot pin to the frame as the arm should still rotate freely on the pin. The arm should run parallel to the frame or the bearing will bind on the axle. Tidy up the face of the frames with a file to remove any pin protruding.

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Finally, we are left with spacer [3g]. There is no identification of this part or specific instruction on its placement or use in the text. I believe it is used as a motor support. If this is indeed the case I am leaving it off for the present as it is likely to be surplus or will interfere with the High Level gearbox/motor.

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That completes the frames for now and I am very happy with the way it all went together without any additional fettling. But I mustn't forget to give it a thorough wash to remove any residual flux.

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Given the wheelbase is held from the fixed front axle by the pitch of the coupling rods, and that hornblocks have been intentionally omitted on the rear axle, what function do the 'swinging arms' provide?

A distinct wobble Posted Image

... sorry shouldn't be so flippant ;)

The front axle is fixed but as you can see on the latest blog page the swing arms give an amazing amount of transverse movement. Far more than I envisaged, but that could be my construction at fault. I cannot see it being any other way. The coupling rods are not going to do anything to help or they will be so tight that no movement will be possible. There is no doubt that the suspension does work with about 2mm in either direction about that knife edge.

I first tried a wire across the frame for the rear pivot points as previously discussed. (going against the instructions) This was even worse, so I reverted to the instructions. The pin could perhaps be a bit tighter to the frames, but having soldered one solid... :( Perhaps a crankpin/16BA nut+bolt might have been better and to some extent adjustable.

I think the lack of a bearing face outside the frame only helps to exaggerate the transverse movement - hopefully this will be corrected by packing with washers - something that would also have been required with hornblocks - but I don't really like to do that.
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Michael Edge
Oct 22 2009 12:25
The beams are supposed to be fitted against the frames, no mention is made of adding bearings as in this kit they are doubled, this gives adequate bearing surface. If bearings are added they should be on the inner face. I have found that using screws for these pivots leads to greater wear from the screw thread turning in the frames, pins or rivets are better.
Your unidentifiable frame spacer is in fact a scrap piece, the original drawing was modified to shorten one of the spacers, to preserve the tags this piece was left in.
Michael Edge
Michael thank you very much for your comments - very much appreciated.

The beams are supposed to be fitted against the frames, no mention is made of adding bearings as in this kit they are doubled, this gives adequate bearing surface. If bearings are added they should be on the inner face.

I did indicate my addition of bearings was a personal deviation from your instructions, the outcome being "on my own head" whilst giving my reasons. But it is a point well worth repeating.

I have found that using screws for these pivots leads to greater wear from the screw thread turning in the frames, pins or rivets are better.

Nice to know that alternatives were looked at. My suggestion with using screws was more intended at getting around the problem I had with using pivots and not soldering them solid. I had not thought through the additional problem which they would introduce of wear or working loose.

Your unidentifiable frame spacer is in fact a scrap piece, the original drawing was modified to shorten one of the spacers, to preserve the tags this piece was left in.

:D :D you got me on that one Posted Image

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