JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,907
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Post by JonL on Dec 12, 2018 13:56:42 GMT
I'll shortly be attempting the connecting rods and associated motion work on the Britannia. Does anyone have any top tips to bear in mind before I crack on? I've never done anything like it before and want to avoid making silly errors if possible. Not Britannia specific obviously, just tips for making the rods/bearings etc. I don't have a mill, just the ML7 and a Vertical slide.
Thanks in advance
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Post by Deleted on Dec 12, 2018 14:30:13 GMT
Hi Nobby IMHO the most important thing is getting the center's spot on and equal to not only each other but also the axle center's. Personally I wouldn't start without having a proper way of measuring the critical distances. This can be via cheap digital scales or DRO. Some will say you can do this just with the machine dials..this very much depends on the quality/graduation of your machine. Next is to plan your steps, some setups won't be possible after doing others so think it through carefully. I did cover in some detail how I did mine, you'll find the index on page 1 to show you what pages to look through.. Imho this is one of the most critical parts, get this right and things should work out well later in the build. Good luck..oh and my coupling rods were my first go at such things...just take it one step at a time... Pete
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Lisa
Statesman
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Post by Lisa on Dec 12, 2018 14:32:59 GMT
If you look back in my Blowfly thread (the first few pages), you'll see how I made my coupling and connecting rods; in 3 pieces silver soldered together, which greatly reduces the amount of work when you don't have a mill (or, for that matter, even if you do!). There's also some pic's of my rather rough but functional adjustable coupling rods, for getting the centres right and drilling the crankpin holes.
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Post by mr swarf on Dec 12, 2018 15:34:53 GMT
Before you start give a little thought to the steel you will be using. I used some BDMS once to make a rod & it ended up like a banana when I unclamped it from the mill. Black has less stress in it but you have to get the scale of first. Paul
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,907
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Post by JonL on Dec 12, 2018 16:20:23 GMT
I do have the pieces roughly cut to size from Model Engineering Laser (yes, cheating....), its getting the critical distances that worries me a little.
Measure twice cut once I guess...
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Post by delaplume on Dec 12, 2018 16:33:58 GMT
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Post by delaplume on Dec 12, 2018 17:04:49 GMT
Hello Paul, I'm assuming you already have your axle boxes fitted in the horns in the mainframe and that the axles have a reasonably good centre-drilling in their ends ?? To reproduce the actual pitch between axles on my loco I use a set of Trammels.....In our case these will transfer a "real time" dimention rather than the theoretical one as given in the drawings............The use of pre-turned "Buttons" with centres in can give an existing hole in the embryo rod a place for one of the trammel rods to register...
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stevep
Elder Statesman
Posts: 1,070
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Post by stevep on Dec 12, 2018 17:55:04 GMT
On one of my engines, I made dummy two-part adjustable coupling rods, which I adjusted on a pair of axles until everything went round smoothly. I then used them to transfer the dimensions on to the actual rods. I actually used hardened sleeves, and drilled through, but the alternative would be to use buttons to transfer the dimensions on to the rod, and then set the rod up on the milling machine.
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Post by ettingtonliam on Dec 12, 2018 19:54:14 GMT
I've been out of locos for some years, went on to traction engines and stationary engines, but I recall making a jig consisting of a piece of BM flat, drilled to take a silver steel stub which was a close fit in an axlebox bore. At the other end was a slot in to which fitted another silver steel stub, threaded at one end to take a nut which clamped it to the flat. Both stubs were drilled and reamed to suit the size I needed to drill the coupling rods, and I hardened them. In use, the stubs were slid into the bores of adjoining axleboxes, and the nut tightend up. When removed it was used as a drilling jig for the coupling rods. This way, the rods exactly matched the spacing of the axleboxes. Even if the axlebox spacings vary, this method copes, and doesn't need measuring equipment. I suspect that it dates from the LBSC era, but is effective never the less.
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Post by delaplume on Dec 12, 2018 20:16:33 GMT
I've been out of locos for some years, went on to traction engines and stationary engines, but I recall making a jig consisting of a piece of BM flat, drilled to take a silver steel stub which was a close fit in an axlebox bore. At the other end was a slot in to which fitted another silver steel stub, threaded at one end to take a nut which clamped it to the flat. Both stubs were drilled and reamed to suit the size I needed to drill the coupling rods, and I hardened them. In use, the stubs were slid into the bores of adjoining axleboxes, and the nut tightend up. When removed it was used as a drilling jig for the coupling rods. This way, the rods exactly matched the spacing of the axleboxes. Even if the axlebox spacings vary, this method copes, and doesn't need measuring equipment. I suspect that it dates from the LBSC era, but is effective never the less. Yes, I "like" this because of its' practical approach.... As you say it reproduces the varying pitches as found on your individual loco. and thus guarantees that the rods and wheel assembly will rotate.......which is what is required after all............. My trammels will give the same readings but won't act as a drilling jig as well...... .I can imagine that it did indeed come from the pen of LBSC, just the sort of practical help he would give the "raw tyros".......Much to the chargrin of his "admirer" ...the little hot pepper that was K. N. Harris.... Thanks for posting, much appreciated
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,907
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Post by JonL on Dec 12, 2018 20:28:33 GMT
I was thinking of using a home-made trammel arrangement using the indents I made in the axles for the rotating centre in the tailstock when I remachined them. That would give me the distance between centres and therefore the ideal length of the connecting rod?
I am not really sure how tight a fit to make each bearing; I want them to be free moving but not sloppy I guess?
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Post by ettingtonliam on Dec 12, 2018 21:14:41 GMT
Free moving would be right. Don't forget that in use, due to the springing, the axles will move vertically independent of each other, and there has to be enough clearance in the coupling rod bushes to allow this to happen without binding.
After WW1, when a number of companies were struggling for work due to the cancellation of the munitions and armaments orders, and the loco works were flat out catching up on neglected maintenance, orders for large numbers of locos were given to companies with little or no previous loco building experience. Woolwich Arsenal and Armstrong Whitworth come to mind. When delivered, built to armaments standards, they were simply, far too tight, and had to be taken into the loco works to be eased off before they would run properly. Nothing like a bit of slack in the right place, the art is in knowing where and how much.
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don9f
Statesman
Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 960
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Post by don9f on Dec 12, 2018 22:13:03 GMT
I've been out of locos for some years, went on to traction engines and stationary engines, but I recall making a jig consisting of a piece of BM flat, drilled to take a silver steel stub which was a close fit in an axlebox bore. At the other end was a slot in to which fitted another silver steel stub, threaded at one end to take a nut which clamped it to the flat. Both stubs were drilled and reamed to suit the size I needed to drill the coupling rods, and I hardened them. In use, the stubs were slid into the bores of adjoining axleboxes, and the nut tightend up. When removed it was used as a drilling jig for the coupling rods. This way, the rods exactly matched the spacing of the axleboxes. Even if the axlebox spacings vary, this method copes, and doesn't need measuring equipment. I suspect that it dates from the LBSC era, but is effective never the less. This is basically what Les Warnett described for machining the coupling rods for his 5” 9F and it worked well for me. Also on a different project, I had the problem mentioned above of BMS distorting slightly during machining, so would recommend “normalising”. Becomes more of a problem with longer rods....they can actually “grow” due to the relief of stress etc! Cheers Don
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Post by ilvaporista on Dec 13, 2018 8:30:47 GMT
I used our wood burning stove to normalise material before machining which involves removing lots of material. Leaving the material in overnight allowed a gradual cool-down and the steel was found in the ashes the following morning. No distortion after machining the rods but I did not do one with and one without this treatment so I can not be certain of the process. However I had to machine an old chain sprocket which was almost untouchable with HSS, a cooking overnight made it nice and soft and another cooking the following night after machining to red heat and then plunged in oil brought it back to semi hard. A tip if you try this is to do the oil plunge outside and not in the living room, every time I walk near the stove with metal in hand my wife reminds me of the smell that took a few days to shift.
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,907
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Post by JonL on Dec 13, 2018 14:12:21 GMT
I think what is worrying me most is judging how much free play to dial in. With the axles at full articulation there is an awful lot of geometry change, enough to make me think that if I try to encompass it the rods will be almost slack on the pins.
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Post by mr swarf on Dec 13, 2018 15:04:30 GMT
You need to make your rods with the holes at your exact axle centers spacing. The free play will be gained later by slightly easing the leading & trailing bush's. Paul
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Post by Deleted on Dec 13, 2018 15:05:16 GMT
I think what is worrying me most is judging how much free play to dial in. With the axles at full articulation there is an awful lot of geometry change, enough to make me think that if I try to encompass it the rods will be almost slack on the pins. All I can advise is make the bearings a good sliding fit (no rock), the OD,s into the rods are best to be a drift fit. Assuming that all 'centers' are spot on, the wheels should turn when all axles are at the same height. This may be good enough..any tight spots when axle heights differ should disappear during the running in process..if not you can always open the effected bearing up a little until the loco is free running...that should do the trick. Pete
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stevep
Elder Statesman
Posts: 1,070
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Post by stevep on Dec 13, 2018 20:24:04 GMT
A famous TV presenter on matters steam and mechanical engineering once gave a talk to the Basingstoke club (when I was a member there), and he said "you always need to leave room for the oil".
So, not too good a fit.
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,907
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Post by JonL on Dec 13, 2018 22:13:57 GMT
Excellent advice all; thank you very much.
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Post by delaplume on Dec 13, 2018 22:17:10 GMT
Quote}-- "you always need to leave room for the oil". Absolutely !! Oil, no matter how thin is a measurable, physical entity and you must make allowances for it......... Just to help you visualise this}---From my own MoD Apprentceship when hand fitting with Engineers Ruler and "Firm joint" Calliper ...We had to get to between + 0.005" and + 0.010" before being allowed access to a Micrometer for finishing to size..........This was done by realising that on a ruler with 1/100"'s the gap between each black line was the same as the line's thickness.....ie each line was 0.010" thick.....So by splitting the line when reading the Calliper you could be +0.005" or - 0.005".....and 5 thou allowance is more than enough for that oil clearance.. Just a pointer for you}---- When trying your rods on the rolling chassis make sure you have locked the boxes in their approx. running position ( probably half way ? ) and that you roll the chassis on a section of firm, flat track each time.....This will negate any clearances in the boxes at the moment of testing but--- upon their release --- will add a few extra thou overall and should give a nice, sweet-rolling assy... Other things to consider}---- a) What method did you use to ensure each of your 6 crankpins were at an IDENTICAL pitch from their axle centres ...and that they are at a true 90 degrees from the wheel's FRONT face ?? b) Similarly how did you 1/4 the wheelsets such that they are the SAME as each other ??..Note}--- you are allowed a few degrees off either way from the required 90 degrees so long as ALL 6 have the same error....
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