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Member postings for mgj

Here is a list of all the postings mgj has made in our forums. Click on a thread name to jump to the thread.

Thread: My teeth do not mesh!
05/12/2011 17:47:01
Sturminster Newton still has a working flour mill- it uses a cast iron water turbine, but elsewhere the gears are all hardwood - elm I think. For good reason - risk of explosion with metal gears.
 
The turbine has lignum vitae bearings - I forget how long htey lasted underwater, but a very long itme.
01/12/2011 23:19:53
Well you have several choices.
 
1 Remake the hotrnplates and get a tight mesh. Personally I wouldn't bother with that.
2. Do the calculations and see if you can fit one more tooth in on one of the gears. Wouldn't bother with that either at this stage.
3. Redo the calculations and fit a close but different ratio using 2 different gears. Problem with that is that small changes in ratio actually make quite a difference in running.
4. Try the eccentric bushes route , if its a real problem.
5. Finish the engine and see if its a problem. If it isn't, which is the most likely outcome, forget about hte problem. If it is, wel lyou still have (1,)2,3,4 above to try.
 
Like Stub Mandrel suggests, a dose of forgetfulness might be best. They'll be a bit noisy, thats all, but then straight cut gears always are, so thats hardly dramatic. Not going to break, and will transmit drive.
30/11/2011 22:33:46
Brilliant- fit where they touch. Bet they clank a bit too.
Thread: Ground or silver?
30/11/2011 18:24:45
Well that either means its spot on, or else it only fits where it touches!
 
I guess spot on, but it really takes something to hold the total error to within the reaming allowance of a standard H5 reamer, across 5 axles.
 
You have done very well.
 
 
Is that from brand new before running in, or after a little service. I'm hoping ot complete MM by Xmas.
Thread: Tipped Tools
30/11/2011 18:18:31
Could be. OTOH the Myford handles WNMG inserts beautifully.
 
Not often you find 3/8 negative rake tools, but these I bought from Myford with the lathe many years ago.
 
The WNMGs are an industry standard, so I can buy them singly for about £5 each, and that gives me 6 edges since they are double sided. (5mm .8mm nose radius). Very cheap - magic for castings.
 
Cut beautifully on a small lathe.
 
Most of the tipped parting tools use negative rake inserts, to prevent dig ins. All the Chronos ones come with ISCAR GTN2 clones as standard, and they are negative rake. you can get positive rake tips if oyu want. I can't remember hte numbers, but then, personally I wouldn't want positve rake on a parting tool. - zero at best or slight negative. Stops that inwards vector which causes did ins andf makes everyone chase around with rear toolposts.
 
Negative rake ground (HSS) tools are (or have been) recomended for copper - always use them on bronze, and zero rake on brass.
 
Horses for courses.
Thread: My teeth do not mesh!
30/11/2011 12:47:11
Remember too that the originals were built by blacksmiths, and many of the gears were cast, and worn. Precision involute gears they probably were not.
 
So as long as the sides of the teeth engage, they will transmit drive, and you will get that nice clang clang of a real traction engine out of it.(and probably for the same reasons too!
 
If there is a problem, and they actually miss or skip, can you machine up a couple of eccentrics (one eccentric and part off of course) and pop them in the housings and adjust out some or all of the slack that way.
Thread: Tipped Tools
30/11/2011 02:39:52
Well I have to say I use SECO tips on both the 6" and the Myford. Intercahngeably with HSS, at HSS speeds and feeds, when it suits. I get a very good finish, and I regard Ok for dimension as +/- .0002".
 
I do have a Quorn and ground HSS - mostly now for specific shapes and profiles. With a high rake angle I can take about 200 thou on a single cut on the Myford feeding by hand, without causing it pain, so that deals with roughing steel.
 
I have heard all this stuff about being only suited to CNC rates etc. Perhas it does. but not in my workshop.
 
Tipped parting tools are a can't live without item.
Thread: First steam test of 3 1/2" William
29/11/2011 22:39:51
You could have pressurised on an air compressor (or even off an old tyre) and gone round each joint with detergent in water. Its not perfect, but it will find most leaks.
 
Easier on the fingers too!
Thread: Ground or silver?
29/11/2011 22:34:34
Which is better- well case hardened mild. Much harder surface, which is what we are interested in, than silver steel in its normal state, a lot easier to machine and a great deal cheaper.
 
Why get PGMS. An ordinary bar of plain mild in a reamed bush is fine. You may have to be a bit more precise if you are using ball or small roller bearings. Bit of slack (as long as its not too much) won't harm - how accurately have you made the frames/axle boxes, beause if you aren't accurate to within a thou or so, there is a good chance it can bind. (less than the reaming tolerance).
 
Perhaps one needs to work it out. You have 2 or 3 axles. You have the axle boxes in their sliders, you have the axle in the axle boxes. You then have the wheels quartered, and connected by the conrods. Your reaming clearance is a thou per bush. So if you are to get your con rods to slide over the crankpins (both sides) the total error can only be 1/2 thou, or its going to bind.
 
If you can do it with a DRO and work to inside a thou, then one can be very precise. If you are on mandraulic dials, one might be more realistic.
 
My little Metre Maid fortunately (went the unadjusted machined route), and one can just just detect a very small tight spot - nowhere near enough to stop the wheels rotating, but with care you can feel it. That was PGMS, and that took real care to get that. But it will be fairly quick to run in. Which is a lot better than the alternative.

Edited By mgj on 29/11/2011 22:35:12

Thread: Cutting Tool Steel
29/11/2011 12:03:11
Shortening, and roughing. Use mine to put aproximate angles on sq HSS before grinding.
 
Biggest I go to is 3/8 sq.
 
I will see you at MEX - I doubt I shall miss you.
29/11/2011 00:08:21
I think if I were in this game I'd try one of two approaches.
 
If I had cobalt endmill, then that is the best and quickest way to reshape. And if CS says it works, he of the tangential tooling, praise be upon him, you can bet it does. I keep meaning to get a couple for roughing all my tool steel (but since I don't use so much these days...)
 
Failing that, I would rough out with the 1mm cutting discs in an angle grinder - fast (very), waste little material and put little heat into what is being cut. And they don't take the angle grinder under gyro forces. Then I'd grind with a proper tool and cutter grinder - or a grinding wheel if I didn't have the other..

Edited By mgj on 29/11/2011 00:09:05

Thread: Displacement lubricator
22/11/2011 18:13:55
Dennis - agreed, your manifold valve should also serve as an oil cutoff, but its not so positive as a cutoff in the oil line.
 
2 points - if you have a leak you have no means of stopping a flood (how far do you take insurance?). Also steam pressure decays, so when you shut off steam, you will still get some oil shoved along until pressures equalise.
 
How much and will it matter? Probably on my litlte 5" gauge Metre Maid with its baby 3/32 lines, not hardly. On a bigger engine with more volume in the lines, you might well cop for a faceful after a halt. I don't know is the short answer, so someone more knowledgeable than I must advise.
 
I have valves in both lines, steam and oil, and an NRV in the oil line - I believe that is normal practise., and it is what other very experienced club members have advised, so I pass it on on that basis.
 
Glycerin for the sight glass, if you don't have it already, comes from cooking accessories/spices etc in any supermarket. Its used for special icing - so baking type stalls.
20/11/2011 23:35:32
I am told (and am installing on mine) that its a good idea to put an NRV in the steam line between manifold shut off valve and oil tank. What can happen if one is not fitted is that, on cooling down, if you fail to open open some other valve like the blower, the vacuum will suck oil back into the manifold and possibly from there into the boiler, which is a bit less than favourite.
 
Its also wise to fit a separate oil shut off valve. The needle valve can then be left set for the oil feed control, and when one is stopped, you just shut the globe valve, which doesn't disturb the steam setting, and prevents filling hte steam chest with oil. I am told.
 
You have some sort of condensing coil somewhere between steam feed valve (manifold) and oil tank? I have 12" of pipe zigzagged on a black painted plate on the side of the cab, but possibly with a 7 1/2" model there is enough pipe to ensure condensation anyway. Whatever, you need to be sure you are feeding water under pressure, and not steam into the oil tank.

Edited By mgj on 20/11/2011 23:36:21

Thread: BW Electronics DROs
19/11/2011 22:41:52
Allendale have now brought out magnetic scales which are very neat and very small. They come in 2 ranges I think. One reads to some fantastically small amount, the other to the normal .0002" (.0004" doubled) Which is what many of the glass scales read to, and theye come in a range of sizes.With the magnetic strips,housings and heads I beleive they really have solved the problem of fitting a quality DRO onto something Myford sized, and probably on 3 axes. What I want to find out is whether you can put one of the super ones on the x slide, and ordinaries on the others, because the super ones are a tad pricey. My economy DRO box may not take too kindly to varying ranges on different axes - so I need to ask.
 
If I am not teaching my granny - one does have to calibrate the scales, (or the output to the box to be precise) but once one has that offset sorted, one can take one mike reading an inch away form the finished diameter, and provided things are rigid, it will be spot on at the far end - to the point that I have got a bit casual about micrometer readings. Which will bite me one day, but so far it hasn't.

Edited By mgj on 19/11/2011 22:46:36

Thread: How heavy is my loco?
16/11/2011 22:17:05
Tony - you really want the weight on each axle, and to balance it if possible. You get better traction that way. EIM had an article on it, but if you can't weigh each station individually, you can weigh one then the otehr and if you know hte mass of the whole machine you can take moments and derive the detail for each axle, and the CG location, and how much lead to add where, without having to go back to the scales
 
As owners of Caterhams and other proper machinery with engines in the back will know, for optimum performance you cannot just tweak the spring pans/preloads and level the machine. That levels the machine but it doen't alter the weight balance or load on any axle, and if one is metaphoricaly rumbling about with one leg in the air, it doesn't do a great deal for adhesion.
Thread: what does this mean on a drawing
16/11/2011 10:20:54
Also you will find that reamers and the like are classed as Hx as well. The standard I think is an H5 IRRC, but you can get what you wan't - if you want to pay for it.
Thread: Heating equipment for boiler making
15/11/2011 11:00:54
Terry - thank you for that contact. The soldering burner will be very handy when doing TE tenders.
 
------------
You will need a cyclone type burner to deal with silver soldering in confined spaces. That is not cheap or expensive - that's a specific type of burner. Sievert do them for certain - others probalby.
 
You also need the right regulator. You could I guess, do a boiler with a 2 bar regulator, but I would think that most people doing that sort of work would use a 4 bar one.
------------
 
 
Thread: Silver solder or copper rod?
13/11/2011 23:49:17
F750. The 8 lbs didn't include the bloody 2 2 x16 gauge rails that were forced on us by the rules, but were utterly useless in a monocoque. The 40 lbs did, and got there by very careful use of the rollover hoop, round not sq tube, and keeping it very thin, and the car very small. (Most of the body was less than the height of the wheels, and they were 20" in dia) And virtually no brackets - just threaded tubes brazed (no nuts and centre drilled out allen bolts sized to a maximum stress loading.
 
Thats not a rolling chassis - thats a basic coffin/spaceframe - you have to put engine gearbox fuel tank etc etc.
 
1/2" aerolam board - its a honeycomb of paper with very thin glass reinforced epoxy outers. You make it up in a series of diaphragm bulkheads - ie thick wall with big oval cutouts.Probably been superseded by something else now
 
40lbs Not F1 at all BTW. (And we were a lot smaller than even the present F1 cars) Easy to move about the workshop! Thats a steel spaceframe in 20g round steel tube. That wasn't the lightest chassis about - one or two others were lighter, but at the expense of rigidity, so they didn't handle so well. Which is why I went to the Aerolam board, and I lost quite a few lbs.
 
Keep the suspension bolts to 1/4" dia, turn down the starter motor casing, ali flywheel, ali disks, magnesium wheels -
 
How heavy did you think a racing car was? Most of them, without an engine, you can easily pick up the chassis/monocoque even pretty well fitted out. - or could. I'm a bit out of date now.
13/11/2011 19:00:23
That was because you used Reynolds tubing, like we did on the racers. If you elded it it went allbrittle and fell apart. Now I suppose, they MIG or TIG up bike frames in ali, and my last car was all honeycomb board stuck together with one of the 3M glues and an activator! .Mind you, it brought the chassis weight down from 40lbs to about 8 with a consideralbe increase in torsional rgidity, so it wasn't all bad! (Just added a bit of local strengthening around the hard points where suspension was mounted.
 
----------------

There is a specific SS alloy for silver soldering tips onto tools. .If you have a silver solder that can be used with a soldering iron, are you sure it isn't one of the Comsol types, which I think contain a bit of silver, but are nowhere near as strong as proper silver solder.
 
I would email CUP alloys because a lot is about to change with the move to Cd free alloys.
13/11/2011 09:02:06
Richard - I believe you are right about the joint design issue. A lot of those joints were just butt brazed, so I was told. I actually saw that on an F750 racer as well. The scrutineer told the man to take his car away.
 
Some tubing of course you cannot weld without subsequent heat treatment, and you either braze or use so called manganese bronze "welding", but it is a form of brazing.
 
I believe they also ban riveted joints- when a properly designed riveted joint is IIRC as strong as and less prone to fatigue than a welded joint.
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