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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.

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Thread: Lubrication
08/02/2012 19:14:50
My Little Samson is lubricated from above and that works fine. Even the bearings which carry an upthrust from the gears are also lubricated from above, and they are always good and oily. Equally Sweet Peas axleboxes are lubricated from above and they last very well.
 
If in doubt, turn a shallow groove in the bearing and then oil from whichever direction you want? Install an oil cup with a small hole, and a wick or felt pad, and the thing will last forever - if its big enough. If not the groove will act as a reservoir.
 

Thread: getting there..... now for the slide valves
07/02/2012 18:31:47
You want the absolute minimum of clearance, while allowing the slide valve to move vertically, as the others have said. Excess clearance = lost motion and less precise timing (as does poor dimensioning). I worked to .001 plus the calculated allowance for steam at operating temp for expansion, because it mustn't jam. The expansion figures are in The Model Engineers Handbook, as are the steam temperatures for given pressure. .
 
You also want a really good finish on the portface, because that, or the film of oil on it, is the seal between exhaust and live steam, and you don't want live steam headed for exhaust, and not bothering with the cylinders in passing.
 
Check also that the valve does not lift at all when it is moved by the rod.
Thread: Boiler feed pump
02/02/2012 23:00:52
Depends a bit on what you are making, but the .8mm wire is very good for general purpose pipework, rod fork ends etc. Some alloys are better at fillet forming, so its a good move to have a couple of alloys available, plus some higher temp stuff so you can step in sequence without melting work already done.
Thread: One screw two directions, same time
31/01/2012 23:02:07
The Rarden 30mm cannon has a similar device. One thread winds the gun back to cock and feed, and the other winds it out to battery - part of the unjamming drills. But there is a third mode - when you have wound the gun back and "cocked" it, it shot forwards under spring pressure to battery along the gaps in the diamonds. How that one worked I don't know, but somehow the nut could slip between the point of the threads, and not when you wound the handle?
Thread: Drilling brass - seizing
31/01/2012 15:55:11
I think all modern drills are ground with back taper, so they should clear. I always bang heaps of coolant on to limit expansion - nothing special, just the ordianry 20:1 mix of cutting oil and water, but lots of it.
 
Like you fear caused me a lot of grief - I approached gently and all that stuff. And its exactly what one shouldn't do, because a soft approach allows the drill to catch and then drag the holder forwards into the backlash. Once I kind of understood hte logic, stopped drilling pilots and deep centres, and banged the drill in firmly to get the holder pushed back agin that feed nut, and hard ernough to keep it there all my drilling in bronze problems went.
 
(You won't achieve a high feed rate - what you will achieve is a an end load controlling the drills advance)
 
I don't claim its the best, or even the only answer, but its done me OK both drilling tough materials, and parting for a while now.
Thread: Black Five, Jinty or 4F - 3½" or 5" gauge - for a Beginner?
30/01/2012 15:02:57
Well whatever you get, might I suggest one that has a reputation for accurate drawings. Its a real pain ot build something with great care, only to find it doesn't fit!!!.
 
I'm aftraid I'm a Sweet Pea man. Well Metre Maid, because I preferred the 060 layout and I had never built a loco before.
 
Simple to make, cheap(er) boiler, darned good drawings, excellent book. Everything is fairly easy to get at and maintain, and being "narrow" gauge, everything is chunky and easy to hold, so one is not trying to munch metal that flexes and bends. Pipework is pretty simple too. And it has a reputation for pulling like hell and thats no bad thing for a punter who is not so experienced managing tiny fires. (I'm OK with a 3" TE, but having driven the odd 5" on occasion, these small fires need a bit more managing. )
 
Next loco will be a Schools class, inside cylinder and all the grief that goes with it - and busted 10 Ba bolts too. But for the moment, plain Jane Metre Maid seems a darned good starter for 10!
 
How long to build. 17 July 2010 I started. It will be going for its hydraulic test shortly, and completed and  in steam end of Feb. I'd have done it a lot quicker if the boiler had arrived on time.
 

Edited By mgj on 30/01/2012 15:08:46

Thread: Drilling brass - seizing
30/01/2012 13:51:04
Sorry - to be sure - I wasn't suggesting using an endmill in rotation. Specifically Andrew said he had no boring bar of a size. So when I want a little boring bar and I don't have one to size, I just take an endmill, mount it in the tool post and use one tooth as a boring bar.
 
Endmill isn't turning - its just the unwitting supplier of a tooth. You have to offset the toolpost a touch to give a whisker of clearance.
 
This will probalby work in Andrews case because the job is a bearing shell, so the hole will be fairly short. Unless one has a long series endmill of a size and hte job warrants such a length.
29/01/2012 23:11:26
Trouble is Andrew, you now have a pilot, so the most resistanceful part of the bit (the chisel point) is not helping you by slowing the advance of the drill. You are cutting on the flute edges only.
 
I would suggest you just bore it to size. You may not have a boring bar, but I bet you have a slot drill or end mill that will go in the hole. Mount that in the toolpost and bore with that - set up to cut on one tooth. Cheapest small dia boring tools around (not my original idea unfortunately), but it works a treat with indexable or ordinarly slot drills/ end mills.
 
The other thing is that with biggish (3/4 drill bits) jamming and jumping in the work is that you can score the MT in the tailstock, or "disalign" the work in the chuck, because forces are quite high. However, if you have to keep drilling, then now you MUST back off the drill. Slower is not necessarily better - the greater the angular velocity the less the effective rake, so by going very slow you are "sharpening" your drill and increasing the bite at each rev, which increases the forwards thrust. Get the speed up, back off the drill and use the quill lock to apply a drag. If thats the route you want to go, then counter intuitively, its a case of more bottle, more throttle, so long as the drill is set right. .
 
Might be best to get the hole to about .005 undersize, and then with a shed load of coolant to stop any temperature rise and "side/flute" grabbing, ream like that. I always believe that its very unwise to ask a reamer to take more than a few thou, esp in a bronze where temps can rise and cause that sort of grabbing.
 
All the best - I shall be starting my 4" LS short, so I have this to come.
29/01/2012 20:21:09
Like Andrew, I believe that one must keep the feed rate up. If you feed slowly, the drill can catch and pull forwards. If you feed faster than the drill is trying to feed itself , then there is a resistance to forwards movement, and the drill (and parting tool since the same rule applies) won't grab - it cant, because there is a reaction resisting movement, so it isn't going to jump forwards. Times to watch are when you start the hole into a centre hole, or at the end on breakthrough. Both times are when one should advance the drill very smartly to reduce effective rake.
 
(The faster you feed, the less the effective rake of course. )
 
All that is happening is that one is pushing the drill - so its pushed hard against the feed nut. Allow that forwards pressure off, the drill will try to self feed - , it was against the feed nut thread, but now its free to jump into the clearance in front of the feednut, And so it does, grabs a large chunk and presto - one jam up or a jump forwards out of the taper.
 
Andrew - big holes in bronze - same rule. Don't drill a pilot - just a minimal centre with a centre drill to make sure it starts right - make sure you have to push hard and apply loadsa coolant with a razor sharp drill (4 facet) off the Quorn. Never jammed yet, always cuts to size. Like you I don't like reaming bronze - I drill close to size, and then use a very sharp new ground boring tool, and that seems to work perfectly.. Personally I always use coolant in bronze, (and always with brass to keep those chips under control. Just makes the machine a lot easier to clean)
 
I used to drill pilots and the things jammed, unless one backed off the drill (aka blunting it) and since I don't use a pilot, I take great care to ensure my drills are ground exactly symmetrical on the grinder, so they cut straight and to size.
Thread: Stress relieve in castings.
25/01/2012 17:42:30
Armour castings like tank turrets and hulls are left outside for 6 months or so. Its a lot cheaper to leave them outside than it is to reheat and cool slowly in a furnace.
 
Outside is better than indoors because of the greater thermal range.
Thread: flatness of faceplate ?
20/01/2012 22:41:27
Don't forget that it will never be truly flat because if the lathe is set correctly, it should turn very slightly concave.
 
And as Jason said, it would be someone being a touch unwise if they just put a faceplate (or a chuck backplate) onto a lathe and expected it to be true.
 
Still 1 mm is a bit more than one might have expected, but it won't matter so long as the outer edges remain thick enough to remain rigid in use. So that might be a machining allowance?
Thread: NEW MAGAZINE FOR MODEL ENGINEERS
08/01/2012 10:40:20
I wonder whether this is worth the time - chasing links, researching I don't know what, etc. I read a couple of posts at the front, and the last.
 
If the mag comes out, it will come out, and it will, I daresay be advertised. If not it won't.
 
I feel my time is better spent munching metal?
Thread: Silver Soldering
07/01/2012 09:31:55
Tubal Cain is very good on it in his book. He advises, similar to the jewellers, the use of prepositioned bits of SS where ever possible, and I find that a very succesful technique - its actually the best way if possible or circumstances permit, because the SS won't melt until the metal is hot enough.
 
A few centre pops are a pretty good way of ensuring a small gap between two bits of metal.
Thread: Quality of Engineer's squares
06/01/2012 18:20:16
I agree about the limitations of making cylindrical squares. Technically you don't need to clock the thing at all. - as long as it holds parallel.
 
But reality intervenes.

Ideally one wants to clock the thing true and set it parallel in a fixed steady with a proper DTI - I did that with my Quorn spindle, and eventually got it true to .00002 in 4"., before machining the bearing seats. Madness approached.
 
So you have to accept a point where good enough is good enough, and one can make it as well as it need be.

Edited By mgj on 06/01/2012 18:20:54

05/01/2012 22:30:20
I have a mild disagreement - the turnaround method described by Terry is very good, but the most accurate way to check a square is to use the lathe bed (or other suitable) as a reference, and put it up against one of Michaels cylindrical squares, which are so easy to make. Some kind of light behind is best.
 
Put a bit of (true) bar of sensible size into a 4 jaw, and clock up true. Face the end, and then turn a recess. How deep doesn't matter, but about 1/8 is fine - to relieve the base is all that is needed. Just make sure that the edge of the recess is as thin as is sane - say 1/16". Dismount from the chuck and wrap carefully, because it will be square to within pretty much nothing. If one thinks of geometries of generated circles its easy to see why.
 
That was in ME years ago, when it still did tooling and printed in hot metal/B&W!
 
I accept that the thing can only be truly accurate if the edge is infinitely thin, such that it represents 2 points, but we don't need to worry about that, especially as we can't achieve it, but it will be the rightest angle one has in the workshop, or is ever likely to posses.
 
A 3/4/5 triangle is also absolutely a right angle, but there is the possibiltity of introduced errors if ones drilling and measuring are not spot on. Still, made properly such a triangle should be very accurate.
Thread: Finishing leaf springs
05/01/2012 17:43:53
Why bother with popping it in the oven. Its bright drawn mild so it isn't heat treatable. You might remove the stresses from manufacture, but you are not going to alter its mechanical properties by that.
 
Put them together dry, and if they are a bit firm you could try reducing the damping (interleaf friction) with some grease, or possibly some tufnol leaves. Its all to do with the stress you operate at - there is a quite a bit of spring in mild, especially over a short travel.
 
I did that for my Little samson. the drawing called for spring steel - it got plain mild, and they work fine, relatively lightly (stressed) loaded over a short travel.
Thread: Piston rings or graphite packing ?
04/01/2012 22:19:43
Model Engineers Hand book. Tubal Cain. Absolutely all the info on Imperial and Metric o rings you will ever need.
 
And on piston rings!
 
And on just about any other bit of useful Workshop Data an ME will need.
Thread: Rivet snap dimensions
04/01/2012 17:43:27
No disrespect, but on the basis of that, I think a dolly with 2 slots in it might be a more speedy answer.
 
I bet that would squeeze a rivet a trifle.
03/01/2012 22:42:58
Jason - thanks. I had seen that, and thats why I was going for this very massive dolly guide.
 
What I'd like to be able to do is rivet the spokes to the ringsand then weld the rings in. That would simplify things (back wheels), because the guide won't need to bridge the second ring, so one would probalby get a better squeeze. I think I'd make a pattern to compare the bent item against as well, just so as to be able to make the odd scientific adjustment.
 
(After looking at your link - he uses a bridge dolly with 3/16 rivets, and that has worked very well and i think his dolly is less massive than I was planning, so there is another option)
 
Edward in his book has a good idea for a spoke bender which could easily be made to have stops on it, so it would actually bend pretty accurately. Have a trial run/assembly and then a happy afternoon TIGging in the rings!
 
We have diverted a bit from rivet heads, but its all part of the process - of TE wheel riveting. Maybe not loco sized rivets.

Edited By mgj on 03/01/2012 22:43:12

Edited By mgj on 03/01/2012 22:48:07

02/01/2012 22:05:23
No Jason,I'm going for rubber tyres from your lad Alan at MJ. Woodblock would look lovely, but I think on tarmac they would get to seem pretty untidy in moderately short order. I could well be wrong. Also remebering the fun at school sliding around on those old parquet floors, I wonder how much grip wood block would provide on grass?
 
I had my tees rolled up ready to weld, all 4 for £160, but thought they were undercharging so I gave then a couple of hundred. Considering what some charge I felt that was pretty reasonable. (Paid handsomely because the perch braket cost £10 including material, and I'll only pay a tenner for geting a few other bits bent up.)
 
A weekend will see them as "wheel blanks" . I'll get a Clarke cheapie press, and make a dolly guide up from 1" x 3" steel section, (as on TT) and I think I shall use Edwards conical squishing system. If it takes a bit longer to produce a decent job, then fine - I have the 3" and shortly Metre Maid to keep the fires burning. That 3" has been a real winner - took a bit of sorting through my inexperience, but its a super engine now.
 
I shall have an experiment with chisels, and if I can't make that work quickly and easily then I shall use your rivet grip and the bandsaw. That Arrand gadget looks very good, but they will charge, and I already have a bandsaw, so the bandsaw idea wins in my workop. If I had't got a bandsaw or a power hack, then the Arrand would be very attractive.
 
Thank you all - I have learned a lot.
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