Minnie 1" Traction Engine

I hadn't intended to start this project for another year or so, or at least until my Princess Royal build was well underway, but anyway: I obtained some parts and the original book for the 1" Minnie traction engine recently, so thought I'd put this thread as a sort of placeholder, and to ask any preliminary questions (of which there will be a lot).

Since I've got all four part machined wheel rims, and a full set of laser-cut spokes and strakes, I might even make a start on the wheels quite soon. I'd need the hub castings, and some advice on riveting, but at least it would be a relatively quick win and I'd have something nice to look at while contemplating ordering a boiler...

The book won't lead you far wrong except the gear centres are already bored to finished size so Masons gear centre marking tool isn't universal without mods.

I’m thumbing through the book now. The gear centre device looks clever, sure it can be modified quite easily though?

One question that immediately springs to mind - are there any good ‘how to’ guides for riveting - for example the wheel spokes will need a lot. Is it basically cold forming a domed rivet into a countersunk hole and then machining flush? Presumably mild steel rivets are available for this, and the domed tool that corresponds to the head? Is it a fairly straightforward process?

The other thing is forming keyways in hubs and gears - can it be done in the lathe using the power feed, or do you use the hand wheel? Are inserts or tools for this available?

Thanks.

Should have mentioned - if anyone has any spare castings or other 1” Minnie parts for sale I’d be interested - anything considered.

Thanks.

Following my asking for ideas a while back on cutting keyways, it's not really good for the lathe to use it as a key-way shaper. It tends to put a rather unfair strain on it, somewhat different from normal turning loads. It can be done, on small key-ways, with fine cuts, but it's not a habit to cultivate.

It can only be done by hand on a conventional lathe because the drive to the saddle is via the mandrel - but I would advise not even thinking of doing it under power.

However, by sheer chance an hour or so ago I was thumbing through a random bound volume I happen to have, of Model Engineer & Electrician (as ME was called then); and encountered an ingenious solution to this.

The writer made a key-way cutter in the usual way: a bar with a projecting cutting-tip; like a boring-bar but with the cutting edge facing forwards. This is held in the tailstock chuck.

The part to be keyed is set on a thick "table" as he called it (plate rather like a chuck back-plate) mounted on the faceplate or 4-jaw chuck, and the tool fed through it by using the tailstock hand-wheel, taking a few thou at a time.

That's the internal keyway. For the external one he set the cutter in a radial hole in the table, and fed the work into that.

In both cases the cut is advanced by adjusting the protrusion of the cutter from its bar; and the thrust was taken by the tailstock whose line of action is much closer to the cut. He was using a Drummond lathe, he wrote, about the size of a Myford 7.

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The same volume also shows a rather neat key-way cutter in which the tiny cutter pivots on a pin to relieve it for the return stroke; but in practice a rigid mounting never seemed to hurt. The key-ways in hefty great full-size lumps like locomotive driving-wheels were cut on slotters that didn't appear to have any such relief.

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If you need re-bore or recess the centres of a gears the problem is holding it accurately without harming the teeth.

The obvious is wrapping it in a steel or aluminium strip and clamping it in a 4-jaw chuck, or clamping it by the face to a faceplate; and to centre it with the DTI running very carefully against a close-fitting bush protruding from the existing hole. Of indicate off the teeth but be careful not to let the probe catch between the teeth.

Another is to mount a thick mild-steel or aluminium disc on the faceplate, and leave that undisturbed through-out the rest of the task. Starting with the smallest wheel, bore the disc to hold the gear by a gentle push-fit, locking the gear in place with clamps acting on its face. After machining that wheel, re-bore the plate to take the next one up...

(That would also work for holding things like pulley sheaves.)

Follow Mason's way of forming the keyway on the Crank shaft gear cluster and you won't go far wrong and no strain on any machine. The others are quite small and short so can be planed with the carrage. But with cheaper broaches being available from some of the ME suppliers worth thinking of getting the proper item.

As for riviting there are very few that will need a CSK hole, a few at the top of the smokebox spring to mind but the rest will want a formed "snap" head to match the supplied had at the other end. So plain lightly deburred holes.

Softjaws are ideal if you need to chuck the gears to work on the bores and just a couple of simple bushes will allow Mason's depthing tool to be used. Though as most of us now have mills one gear can be held in the spindle and rotated against the previous which is better than trying to pick up a scribed line left by the depthing tool.

Edited By JasonB on 22/02/2021 07:44:21

Cutting keyways,working days long ago,the company used to cut the occasional keyway in gears,on an 8 inch Wilson lathe using a toolbit held in a boring bar,we were trained to cut by winding the saddle forward,then wind the cross slide forward to relieve the tool from rubbing on the return out of the bore,if not the spring and rub on the tool wood break the cutting edge of the tool,first time I got the job I did as I was told and it went ok ,then got distracted and forgot to wind the tool forward on the return and promptly broke the cutting edge ,the tool was either 3/8 ot 7/16 wide and a bit less than 1/32 was broken right off across he cutting edge.Annoying as it took some time grinding a square toolbit too a very accurate width,only did it once and never forgot it. I can say that if you had a stack of steel gears,up to 1 1/2 inch thick it was hard work winding that big saddle back wards and forwards.i agree with the above comment that big slotters never appeared to have any form of tool back stroke relief unlike a shaper clapper box,any one on here worked on a big slotter,slotters were a rare sight in the south of England the only one I ever saw was in Portsmouth tech.Probably were used in the Southern railway works or dockyard but there was never a chance to look round. Now to get to the point I have an American book on machine practice and this shows how to cut keyways in gears etc, it recomends pointing the cutting tool upwards so the clapper box is not effective,and this practice is recomended to reduce chattering and poor surface finish,I tried this on my 18 inch shaper ,with the clapper box locked and it works there is no cutting edge damage to the tool,yet do the same in a big lathe and the tool edge disappears. Just do not know why. By the way how could be power feed be used to cut keyways in the average lathe ,power feed requires the spindle to be rotating.Traction engine alloy wheel rims ,be careful when rivetting,I was trying to get a good snap head form when rivetting over on the inside and cracked the rim,made new rims from steel.

Some old timers used to run a belt from the countershaft to a pulley attached to the first gear in the train on the change gear quadrant. This was usually done to provide finer feed than the standard change gears allowed but it could be adapted to power the leadscrew without rotating the chuck. You would have to take off the main belt between the countershaft and headstock spindle. And make sure quadrant was positioned so gears are not engaged with the headstock spindle gear. So when you start the motor, the countershaft turns and powers the change gears via the second belt to the pulley there. I suppose if you had reversing motor you could even power back feed.

I've shown these photos recently but perhaps worth repeating:

Len Mason's own design for slotting in the lathe:

Taken from Len's "Using the SMALL LATHE" which I think is a rather under-rated book, perhaps because of the title which really refers to amateur sized 3 or 3 1/2" lathes rather than industrial machines. It is available as a re-print from TEE Publishing **LINK**

HTH,

Rod

Edited By Roderick Jenkins on 22/02/2021 11:11:37

When l started my Minnie (still unfinished) l built a hand-operated Slotting Attachment, described in ME, which was mounted on the lathe saddle, l ran a Drummond "B" at the time. l later modified it for an ML10. l can't remember which issue it was described in though but likely to be late 80s/90s.

l also attempted to make the Hand Rivet Squeezers described by A Mellor in ME for 15/5/87 and 6/5/88.

l seem to recall that these were specifically for the Minnie TE.

Hope this might be of some help.

Again, read the book. It'll tell you the rivets are copper and the only single sided snaps are for the strakes, which you have to do first after you make the special rivet snap tool.

There is a standard for rivets of 1.5 times the diameter to form the head, but that varies due to the hole size. Buy your 1/16 drills in 10's and get the drilling and wheel templates right, making extra spokes is more than a little tedious.

Further:- The hand-operated slotting attachment, by R J Cochrane appeared in ME V 152 No. 3720 of 1984 and l needed to make a pattern and get the casting done locally. A useful accessory indeed.

Small imperial Snapheads actually need 1.427D to form the head but treat that as a starting point and do a few practice rivits as actual hole size and the individual snap can vary.

Strakes are best done with a steeper csk so use a centre drill for those to get 60degrees rather than 90.

I also started to make a hand slotter, Minnie is long since finished but the slotter is not.

Do a lot of practice rivets:

Shorten each rivet by a known amount per step until it looks right. Then shorten all rivets accurately to the same length. That way one achieves consistency:

I chose to make my own fixtures and rivet snaps:

Finished rear wheels:

Andrew

Thanks all - as I mentioned, I'm thumbing through the book, reading the bits that get my attention rather than in full detail.

Andrew - the wheels look great. How did you make the concave die? Perhaps hammering a ball bearing into some hot bar or something like that?

Do the rivets need to be heated before installing?

Do you use Loctite on the rivets to take up any radial gaps?

Also, regarding the wheels and the model in general, is a dividing head worth investing in, or would marking out and hand drilling be suitable? I think marking out is the method used in the book, but using a gear wheel to get spacings. I've never done this before.

For PCDs on the 10V cylinders, I used co-ordinate drilling using the DRO, but that's a lot of co-ordinates to find and go-to for all four wheels.

Anyway, I'll read the full wheel assembly chapters and take it from there. Apologies if any of the above questions are answered in the book - just asking.

Unless making one of the large scale models the rivits are not heated as they would loose the heat by the time you had got them into the hole and the snap will also act as a heatsink. As supplied they are annealed so should be soft enough to set cold.

No Loctite. As the head is formed the shank of the rivit will also expand outwards to take up any difference between it's diameter and that of the hole, hence my comment earlier that you may need a little more length if the fit is slack.

There are a number of ways to do the wheels, as you have a DRO you could step out the middle spoke hole using the PCD function or co-ordinates from Zeuz book and then make a jig to locate the other two spoke holes off the central one. If splashing out on new equipment I would say a rotary table will get more use than a dividing head for things like milling the slots in the hubs, curved cuts in the expansion link etc

Thanks Jason. I meant a rotary table.

Any recommendations for these? I’ve heard stories...

I spotdrilled and then used a ballnose slotdrill in the lathe. With a range of metric and imperial slotdrills one can get pretty close to the actual size. Odd sizes, particularly 32nds or even 64ths, are often on Ebay at minimal cost.

I CNC milled and drilled my own spokes. The rivet patterns are copied from full size rather than the drawings. For the front wheels the 3 holes are on an arc, not a straight line. On the rear wheels the 4 rivets are zig-zag, not in a line. The rivets are 3/16" which is conveniently close to 2BA. The holes in the T-rings were marked out by hand. I scribed a circumference around the T-ring with oddleg calipers at the distance in determined by my 3D CAD model. I also knew the theoretical distance from spoke to spoke from the CAD model. I set that distance on dividers and stepped round the previously scribed line until I go back to the start. If everything didn't quite line up I adjusted the dividers and had another go. Once marked out I spot punched and drilled free hand using the vertical mill. I used a fixture to fit the spokes on each side in turn:

The hub is sitting on a spigot screwed to the plate. The rim is centred on the hub as best as possible with a rule. Note the 2BA screws. Once a set of spokes are fitted it is simple to drill through the other holes on the spokes. I drilled the spokes and T-rings 4.7mm, ie, a tad undersize. When riveting was underway I ran a 3/16" drill through each hole in the spoke/rim before fitting each rivet. Generally after drilling the rivets needed a slight tap with a brass rod to get them inserted.

Fitting the spokes on the rear wheels was similar except that the rims needed blocking up different amounts on each side, and on each wheel. Since the rear spokes are on the inside of the T-rings one can't spot through for the additional holes. I used a fixture based on a spare spoke and a block that straddled the fitted spoke. A 2BA bolt held everything together for drilling each spoke:

Generally the wheels won't fit on my 12" rotary table, but I did fudge it to drill one row of holes in the rim as a starter for the rear wheel strakes:

It isn't obvious if the spokes are a 1/16" or so out, but a 1/16" offset on the strakes would be glaring.

When setting the rivets the expansive force generated by the shank can be enough to distort the T-ring:

My methods are pretty crude, but probably better than the original builders used.

Andrew

OK thanks Andrew. I'm really trying to get a feel for the level of accuracy required for wheel drilling. It seems from what you've said, and from the bits of the book I've read, that marking out/templating is sufficient, as opposed to needing c. 0.001" accuracy for engine/linkage parts. I suppose when you're ultimately dealing with jigged bits of bent metal this makes sense.

I suppose I could also do a 2D CAD drawing of the initial hole patterns and print on thin card, then temporarily glue to the wheel and lightly mark through to the rim. I could then check and correct with dividers before drilling the centre holes for each spoke as you did.

The strakes and spokes I've got are laser-cut, but TBH I've not looked to see if they've got any holes in them.