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A new 'Old Engine' - GWR 184 - part 6

MikeOxon

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blog-0323800001417381779.jpgAlthough this may seem a short post, it represents a very big step for me! I had been seriously concerned that I would not be able to construct a chassis with sufficiently well-aligned axles, within the constraints of my own abilities and my lack of any real workshop facilities - just a desk and Dremel drill on a stand.

 

 

 

 

 

 

 

 

 

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My work-desk

 

When one builds a kit, the designer has already made lots of difficult decisions for you. A scratch-builder has to think out every little step for himself - what metal to use for the frames, where to position the spacers, and so on. I decided to cut my frames from 1mm x 6mm brass strip and to hold them apart by three Markits-type spacers. Since one of the driving axles is close to the centre point of the frames, I had to decide where to place the 'middle' spacer. I chose to put it ahead of both driving axles, in case the space between them was needed for motor mounting purposes.

 

Next decision was how to align the frames for drilling the axle and spacer-mounting holes. I have read the suggestion to solder the two frames together, so decided to follow this approach. My iron is a fairly basic Maplin 'solder-station' and, by trial and error, I have discovered that a temperature setting of 285°C works well for me, when using lead-free solder, without too rapid tip-oxidation while 'standing -by'. I've no idea how accurate the temperature read-out is, so other irons may differ. There are convenient buttons on the controller, to switch to pre-set temperatures, and I usually switch to 200°C if I'm not using the iron for a reasonable period. This keeps it warm between uses, without much oxidation. I clamped the frames together, applied some phosphoric acid flux to the ends, and soldered them together. This was fine for holding them when drilling the 2mm pilot holes but, when it came to opening out the axle holes to full size (1/8"), the drill tended to push the frames apart a little, so perhaps I should have soldered them together all along their length. I wasn't sure that my iron had the 'beef' for that and whether I would get them apart again!

 

I measured the positions as accurately as I could with a metal rule (marked in 1/2mm graduations), scribed guidelines with a small diamond scriber, and then centre-punched the holes for drilling. I used a 2mm drill in my Dremel mini-drill, mounted on its vertical stand. I aligned the drill by eye and held the parts in position with BlueTac and adhesive tape - supplemented by my fingers. Eye protectoirs are essential, since tiny specks of brass do fly about when drilling. I applied a drop of very light oil, which seemed to help the drill to go through quickly and cleanly. Once all the holes were completed and I had checked that they all seemed to be in the right places, I applied the soldering iron again, to separate the two frames. Then I cleaned up all the faces with needle files.

 

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The spacers screwed in easily and seemed to be well-aligned (I have yet to counter-sink for the screw-heads) but I knew that the acid test would come when it came to fitting the axles through their bearings. I had to use a larger power-drill to open out the axle holes to 3.5mm and then I used a circular needle file to open out the holes very carefully, until the bearings were a firm push fit (with pliers). I smoothed off the ends of the (Alan Gibson) axles and gentle tapped them into the bearings. Everything worked --- they slid into position smoothly between the frames. To say I was relieved would be a great understatement. Actually, I was b----y amazed :)

 

With that hurdle crossed, I can turn my attention back to the 'body' and , in particular, to obtaining the various fittings that need to be added. One very prominent fitting on many of these early engines can be seen just behind the chimney. I remember, many years ago, that I found it quite difficult to identify this item, so I'm happy to pass on that it is a displacement lubricator for the cylinders. It was placed in that position for ready access to a steam supply but later, the fitting moved to the sides of the smokebox. Later still, these lubricators were controlled from the cab and led to another fitting that puzzles some visitors to GWR footplates. There is an item in the roof that looks rather like an electric cooker element but it is not there for crew comfort - it is the condenser for the displacement lubricator in these early 20th-century engines.

 

Mike

 

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A very satisfying feeling indeed when you have made a chassis and even better when it works! Just one thing though, you don't have to open out the holes while soldered together - as long as you have  pilot holes through the two halves they can be opened out later.

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A very satisfying feeling indeed when you have made a chassis and even better when it works! Just one thing though, you don't have to open out the holes while soldered together - as long as you have  pilot holes through the two halves they can be opened out later.

Of course!  Thank you for that - one of those things that is obvious afterwards but I was so concerned not to take anything apart until I was sure.

 

Now I've done it once, I'm sure it will seem quite straightforward next time but I wanted to convey something of the tension of doing things for the first time :)

 

Mike

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The drill stand makes this really achievable. Congratulations on your first chassis!

 

Did you make the coupling rods at the same time, or do they exist already? The 'secret' to a great chassis is to drill frames and coupling rods whilst all parts are sweated together ;-) 

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Thank you, Rich - I still can't believe it's rolling beautifully!  I had ordered some 8' rods from Alan Gibson but it turns out that he's out of stock, so I'll have to make some.  I had read that idea of drilling them all together but too late now!

 

I had only 'tacked together' the body with UHU for the earlier photos, so now I'm cleaning up and preparing to solder the parts together.  Apart from those coupling rods, I'm now on familiar ground :)

 

Mike

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Congratulations Mike, it certainly looks neat. As Richard says, the stand looks very useful. I take it the actual drill is a handheld one, which can be mounted in the stand?

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Agree with Rich if you intend to buy in coupling rods use them as a guide to drill the frames then open out the holes in the frames.

 

I find Lead free solder doesn't flow as well. Leaded solder is still available.

 

Don

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.......................I take it the actual drill is a handheld one, which can be mounted in the stand?

My drill is a Dremel 8200, which mounts onto the stand.  The drill is 'cordless', which is a slightly mixed blessing when the battery goes flat at the wrong moment!  I also have a very small 'cheap n cheerful' 12v drill that is useful for jobs like drilling pilot holes under the baseboard.

 

 

Agree with Rich if you intend to buy in coupling rods use them as a guide to drill the frames then open out the holes in the frames.

 

I find Lead free solder doesn't flow as well. Leaded solder is still available.

I'll bear in mind those tips for aligning rods for my next build!

 

I agree about lead-free solder - horrid stuff that goes all stringy.  Apparently, it's banned for defence and aerospace work in the USA because of the potential for growth of tin whiskers, which can lead to short circuits.

 

Mike

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A bit of potentially useless information....

 

When I was involved with machining brass and bronze components (some 40+ years ago!) we had drills with the cutting areas ground at different angles compared to the drills used for steel. There are tables in the Machinery Handbook specifying the correct / recommended angles for drill points for various materials.

 

It's almost certain that your drill set are correct for steel but not for brass, hence the problem with "bits flying"

I would think it is almost impossible for an amateur to re-profile a 2mm drill.!!

 

I do remember that using a correctly profiled drill cut more readily and made a much better, cleaner hole than a "Steel Profile" one. We were using drills in the 12mm to 25mm range!

 

I should confess that I didn't do the drilling myself.... I was part of the design team who got the blame if things went wrong!!

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Thanks DonB.  I'm sure that 'real' engineers use all sorts of specialist tools to achieve optimum results in an industrial environment.  As a 'part-timer' I generally make do with what I can get off the shelf at Screwfix, or wherever, but I do appreciate that the correct tool for the job can make a big difference.  I have read that grinding small flats on the cutting edges of HSS drills can help a lot when drilling brass.

 

My first test holes were a bit rough, until I used a lubricant.  I believe that paraffin is best for brass but I used a very light oil, which helped a lot.

 

'Bits flying' was a bit of an exaggeration but I wanted to emphasise the importance of eye protection - it only needs one small speck...

 

Mike

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I did learn how to sharpen drills with a sort of twisting motion but unless you get the centre sopt on it will cut oversize. It is good for those drills where you use either a broach or a reamer to open it to the correct size. If the hole size is critical use a new drill.

Actually Mike have you got a set of Jewellers broaches I wouldn't be without mine.

Don

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Hi Don,  As I understand it, the requirement when drilling brass is to blunt the drill a little, so that it doesn't cut a spiral into the brass. 

 

I can see that broaches will be useful.  As I learn more about scratch building, I realise that drawings and precise dimensions are only a guide and that the real fit is achieved with files, sandpaper, broaches, and the like :)

 

Mike

 

p.s. and when the above tools fail, it's time for the fillers :)

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I may have it wrong but I thought the idea was to have a shallower angle on the drill so it didn't bite into the brass so much. My warning was that doing so to the drill it is easy to get the tip off centre and end up drilling oversize. I should have a small booklet on drills with useful info somewhere which I hung on to from work. To be honest I don't think is it that critical for us as we are usually drilling through fairly thin pieces.

Lubrication does help if nothing is too hand a bit of spital is often useful.

Don

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