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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: Paint ????
23/05/2011 17:27:46
Dear old Blackfriars gloss enamel produces a very hard wearing finish. Very good paint, doesn't mind a bit of heat, and brushes out very smoothly..
If I were spraying, which I shall be shortly, I'd use car 2 pack. Mixed properly its of thee right viscosity, sprays beautifully, dries quickly and is diamond hard. As long as you just go for a wet film. Leave it 5 and recoat, its difficult to get a run, and you get a briliant shine without polishing. Lechler stockists will match a colour, (I expect the others will too) if you have used some other paint for brushing. 2 pack can be used as a one pack for touching in. Just atkes a bit longer to set.
Do it outside on a warm dry day, and then take it in to set. Wear a mask.
Without doubt the best and easiest to spray but a touch pricey. But then you gets what you pay for, and the special "thinners" and other additives which are common to all mixes can be stored for a long time. Clean with gunwash grade cellulose thinners of course. Never used these sexy base coats, but then on both (ali) racing cars and model aircraft one wanted to keep the weight down - still managed ot stick and not peel off

Edited By mgj on 23/05/2011 17:28:12

Thread: Tooling questions for a KX1
22/05/2011 22:36:47
Steve, you know the cutting speed in fpm for your saws, and you know their diameter, so I'm sure you can work out whther 250 rpm is too fast or not (and whether hte work is regulasr of genuinely occasional.
I must admit, when I went looking for a mill it was the slowest speed it would do that I was interested. If you intend to generate large (relativley) radius surfaces like say a boiler saddle, or whatever then possibly 250 is way too fast, though carbide indexable radial bars are available.
I want to build a 4" TE next so a big sweep matters. But for a clockmaker I imagine its less important, with relatively small dia form cutters in brass. Start driving medium sized BP cutters in steel and iron and its a different story.
I think you have to decide on thee basis of what you make, and not on what others may make.
ER chuck - the 32 is more flexible because it will carry bigger tooling. If you want to run short cutters, make a sub carrier, and you'll get the clearance that way.

Edited By mgj on 22/05/2011 22:37:35

Edited By mgj on 22/05/2011 22:39:12

Thread: Headstock Tachometer
22/05/2011 22:26:22
Hardly worth the trouble to build anything special. A dab of white paint and hand held impulse/optical tacho and you have your answer. You don't want to put any effort into it, because once you have a reading and mark as Steve has implied, you never need the tacho again. Not that one ever really needed it in the first place, because the tool is either cutting properly or its not, and it won't take long to get oneself sorted.
At the end of the day, does one actually need to know revs at all - I have a geared head on one lathe, and pulleys on the other, and I have no idea what each ratio provides, but I know what settings cut right at what diameters.
But, if you really want to find out, they do them for testing the speed of electric motors. (and all sorts of other ranges) so Scrrewfix might well stock. The model aircraft ones with a digital readout (available from most model shops) are about £15 -£20, and they will give you a reading at 600 rpm on a 2 blade prob. 4 or 8 bits of reflective tape on your chuck and you are well in the range of one of those at lathe speeds.
Calibrate against 50hz.
But are you sure that it is time or money usefully spent?

Edited By mgj on 22/05/2011 22:27:50

Thread: Warco VMC drawing
19/05/2011 06:06:15
Have you tried Warco?
Thread: Why did my Flywheel Wobble?
19/05/2011 06:03:32
i'd agree - it was most likely bent in the initial clamping.
One point that is important is only to use 3 clamps.Because then it will, like any 3 legged object, find its own "level" and it is very difficult to bend it. (Unless one overtightens on the spokes)

Edited By mgj on 19/05/2011 06:05:19

Thread: square head bolts
17/05/2011 11:33:57
Or use it as the excuse needed to buy a self centering small 4 jaw, which is quite a useful thing anyway.
You could also make a split bush to take a length of the right sized square bar. Being split and fairly thin walled, if you use it to hold the bar in the 3 jaw, it will be held tightly and centrally enough for the purpose.
Saves a lot of milling etc.
Thread: Allchin 11/2" scale
16/05/2011 18:51:28
Jason our posts actually crossed. I can see the difficulty - you post wasn't up when I replied, so please don't think I was cutting across you, and your knowledge is greater than mine..
We have to accept dodgy drawings - so one is never knackered till the fat lady sings as it were.If you don't have dimensions, somehow you have to find them, by whatever means? Or cut and shut till it does work.
No one is completely stymied!

Edited By mgj on 16/05/2011 18:52:25

16/05/2011 16:21:18
Chin up Bernard- you don't have a problem.
You know the distance from the centre of the crank to the end of the pump. So now you can take off that, the length of the ram forward of its pivot. Now you take off that 1/2 the travel of the ram = the eccentric offset. (I imagine both eccentric and ram are dimensioned) Knock up a rod to fit . First time you try it out, you may have to shave a bit off the nose of the pump ram, if it fouls. Or you can give it .010" clearance from the outset. Either way will work, which is what matters.
If you can't get those dimensions now, then fret not. Just wait till you have enough of the engine erected and you can .
Actually that is a better way of doing it than making it precisely to drawing - you want the minimum clearance volume in that pump so it can clear airlocks - so you were going to do it that way anyway????
These things are not that critcal. The originals were made with blacksmith technology, and at your worst you will do better than that!

Good luck.
Thread: What Collet type, 5C or ER25
16/05/2011 10:52:27
Kai - you won't go direct D1-4 to ER32.
Warco/chronos/Chester all do what they call ER32 collet chucks. You then get a separate back plate,like any chuck, and put the collet chuck on the backplate. I would try to go for the ER32. They cost little more and you can fit a lot more in there.
The coolant pump - at 400V - is that for 3 phase, or do you want a single phase pump for home use?
do you want a 6 station tailstock turret. fine for repetition work, but I doubt many of us have really been lost without one!
A digital indicator -thats a dial indicator? The digital ones are good - I have one by Mitutoyo. Nowhere near as easy to use for centering etc as an ordinary needle type. Analogue needle type is much more useful, and probably cheaper! Get a good Mitutoyo needle DTI - far better.
I don't see a drill chuck for your lathe tailstock/morse taper. I'd rather have that than a tailstock turret. Nor for the mill. Thats a drilling chick, not a milling chuck. Nor if you have 4MT tapers, do I see any adapters to hold the MT2/MT3 drills, unless the lathe came with an MT4-3 adapater , in which case you will need an MT3-2 adapter plust a tool ejector wedge, which will serve for both head and tailstock - I guess your tailstock is 3MT..
A 75mm boring head. Very nice, and I have bought one, but its not something you are likely to need when you start. If you wanted to save some money, you could easily wait for that. As a modeller, it is not something you will need that often because usually you could do the same work in a 4 jaw chuck in the lathe. But yes, eventualy they are nice to have - but not essential for a beginner.
16/05/2011 08:35:08
A D1-4 to ER32 is easy enough to come by. Yyou will need a backplate as well.
A DRO - I have a hybrid system - I have a proper DRO on the table on 2 axes, and a digital indicator on the z axis. I had already fitted the indicator so I thought it wuld be OK. It is, but I really wish I had all mu ino on one panel, and most DROs will use the 3rd axis for co-ordinate milling in 3 d. Which is not often used, but useful when you do want it.
Doing it again on a budget, I'd fit a 3 axis control box, and then I could add the scale later. I have now ot buy a 3 axis box and a scale which is silly, considering a 3 axis box is only about £20 more expensive than a 2 axis one. Bad decision on my part.
I agree about the centring indicator. I had not looked at them before, and I'm off to buy one - very sharpish.
Edge finder - Starret make a very good spring type for about £10. I wouldn't bother with anything cleverer than that.

Edited By mgj on 16/05/2011 08:36:12

Thread: Eccentric Turning
15/05/2011 23:25:28
It is a nice piece of work
Alan its a horrible design of casting, because if you turn it round to turn the other eccentric, then you lose the centre pop and that critical relationship. So I turned the 2 from the same side. To retain the valve rods I cut a groove in the eccentrics and machined the rod ends with a raised internal "fin". You could just use a circlip and put grooves in both I suppose.
The trick is that it doesn't matter where the first eccentric to be turned is, in relation to anything else. What matters is the relationship between the eccentrics. "TDC" can be found with a dial gauge, but with an eccentric you need to be a touch more careful than with a cam.
Its a horrible bit of design, and as I said, knowing what I know now, I'd make 2 eccentrics and pin them later into 1 unit, or even key them onto the crank, once I hade the valve timing properly adjusted.

Edited By mgj on 15/05/2011 23:27:01

Thread: What Collet type, 5C or ER25
15/05/2011 22:40:14
Are 5c collets suitable for holding milling cutters?
I beleive not but am not certain.
ER collets are, definitely, so may be used both in a mill and as ordinary collets in a lathe. They will also hold drills very accurately in tool and cutter grinders - the range facility being very useful.
So the probability is that an ER system is better, more versatile bet.
Milling. Do you need coolant - yes. Or mostly unless your cutters will be tipped or rapidly disposable. However, you don't need some special pump system - you can start with  simple gravity feed from a 5l can hanging on hte wall. Pumps are better, of course, but not essential.
Do you need a power feed. No but it is very nice.
Do you need a DRO, no, but it is VERY VERY nice. Some people would say yes.
Do you need a dividing head. Yes in time, but a DRO will have a dividing faciltiy which will cope with most requirements, and for the time being unless specifically gear wheels are your interest, (eg clock making) a simple spin indexer will do for most of the rest (cylinder head covers, and anything which requires division of holes of that type.
Do you need a rotary table - yes for certain things and when you make them (traction engine expansion links etc) then you will know about it. You can rotary mill rod ends, but you can also make filing buttons on the lathe and do a good a job. Not part of a beginners arsenal, but useful. Buy later.
Edge finder - yes, but then they are not expensive.

Edited By mgj on 15/05/2011 22:43:07

Thread: This months MEW are 3 CNC features two too many
15/05/2011 13:53:04
Well it doesn't IMO have much with my psychology, or developments a coming or even with whats gone, or even whether CNC is a worthy successor to manual metal munching..
Personally I buy a magazine because its contents interest me. However marvellous CNC may be (I used to do a lot of control engineering and guidance theory, so unfamiliar, Luddite or reactionary I am not) personally I find it just plain dull.
And when I see a page of code, "Wow awesome" is hardly my first response. More like "Wonderful" in that wifely tone we know so well, and for the same reasons.
For those that like it, good for them, its not for me to criticise or interfere. I'm just not going to pay for a magazine full of it.
Given the response in this thread as a whole, that is possibly a hint our beloved Editor might want to take. If his polls and survey say otherwise, then he has a judgement to make, and he will know soon enough whether he jumped the right way.

Edited By mgj on 15/05/2011 13:54:05

Edited By mgj on 15/05/2011 13:55:47

Thread: Correcting pilot error
15/05/2011 13:36:24
Would it be possible to weld (mig ideally) fill, or silver solder fill and just start again.
You haven't specified what the object is, but if its feasible, adding metal for a fresh start is often a better solution than trying to take it out.
Sometimes, if strength is an issure, then a rough old screw thread carved in there will give a mechanical lock too- for SS or even loctite.(bush). Weld of course it will all be melted anyway.
Thread: Eccentric Turning
14/05/2011 12:13:59
You could well be right. - I could see the plate holds the boss well. I often use a grub screw and 603 retainer, and then heat to release - I guess I'm too lazy to make a plate! (I will put that in the memory banks against the day, because it will come. A t version of such a plate could be used for turning crankshafts at reduced overhang where one wouldn't want grub screw marks.)
Jason - dead right, that the same setup as mine, just scaled up a touch. That pair of eccentrics is/was a single casting!)
Perhaps my passion for being accurate in this case was because I had a 2 cyl engine, so sameness of the 2 components angles was very important.
Doing it again I certainly would just make 2 separate eccentrics out of bar. That design is very awkward indeed to get all to thickness, machining one disc behind the other. Or else you have to turn it round and reset. (The design I had was just 2 eccentrics and a boss, like a couple of coins one on the other, and a small boss 3/4" long in total if I remember right. Anyway that sort of size so there was no real holding length or boss - hence the mandrel suggestion)
If one didn't want to have the units separate when installed I'd still make them separately and then pin them together at the right angles.

Edited By mgj on 14/05/2011 12:15:05

Edited By mgj on 14/05/2011 12:18:30

14/05/2011 06:50:56
You don't have to be that accurate. Don Ashtons book says that the lead of a launch link engine is typically between 21?? and 27 deg. And if you are a bit out, you can restore the timing by shaving a bit of lap off. (or adding a bit) Not ideal, but it will still run fine. On my traction engine I had too much lead even though I set (keyed as per drawing) the eccentrics very accurately to 21 deg of advance. I could have shimmed the rods, but it was easier in the installation to alter the valve. Wicked lazy I know, but it runs perfectly. - so well that it will just tick over under no load on the tiniest leak through the regulator (if you put it in gear). Critcise the regulator if you will, but the rest is pretty good!.
So if you know what the lead is, its more important to get it the same forwards and reverse than actually to a given amount, though perfect is best of course.
I did a Stuart Launch engine and I am assuming these are the same type with both eccentrics and the boss all cast as one unit? Marked the crank bore on the casting and bored/reamed that.. Marked the first eccentric centre. Put the thing in a dividing head and rotated the assy to the right offset to mark the second eccentric centre. Now you have 2 pop marks to dividing head accuracy one in each eccentric, its a simple 4 jaw job, settiing the 2 popmarks true in turn using the normal 2 centre technique with the assembly mounted and locked on a dummy crank.
If you don't have a dividing head, then draw the angle 4x full size with a protractor and shrink it in a scanner. That'll come out pretty accurate, and one can mark out from that.
PITA of a design. If you get bored with it, just make the 2 eccentrics separately, and set fwd and reverse independently to zero lead in full gear by moving the eccentrics as normal. Unless you intend to cross the rods when a smidgen of lead might be useful, since it will reduce towards mid gear. Thats what I shall do with the next TE. Not cross the rods of course, but set the valves by rotating the eccentrics - because there is a far better chance of getting better valve setting, and you can eliminate to a degree errors introcuced by small dimensional inaccuracies.(perfect being better!)
Thread: Cutting a 365 tooth gear
13/05/2011 18:58:15
What kind of head do you have? If its a complete VDH you can do it using the secondary worm and work in angular measure, which will save making a plate
Thread: Setting topslide to an angle
12/05/2011 07:04:35
You can also, with a taper turning attachement, do it properly- the advantage being a very long measuing base leg. 10" on the Hemmingway one. Also I've never moved a topslide by hand when trying to be accurate - I find a light soft faced hammer and a gentle bump to be hte most effective. Light taps and you can apply an offset very easily, and very accurately.
I suspect that if one does it trial and error off the scale it is quite easy to get it wrong, because without an accurate vernier life won't be easy. But, over 10" and working to say 1/3 of a thou, you tend to be pretty right first time, for most tapers.
Thread: Castings
11/05/2011 21:50:53
Listed in the Blackgates Catalogue.
On my list of things to do after a 4" LS traction engine so I checked availablitiy. They said, only a few weeks ago that they carry the castings as stock. Model Engineers Laser do a fair few laser cut parts too.
Labels and nameplates - try Diane Carney, who seems to have the production of photo etched scale nameplates very firmly under control. I'm sure if you said you wanted this or that from the class that is all she would need. ( She has just done a nameplate for a Metre Maid for me, and though a very simple job, it is perfect.
Thread: Setting topslide to an angle
11/05/2011 19:47:51
You can also do it with a calculator. You measure the rubbing distance for a DTI - the length over which you can measure on your top/compound slide. (Accurately with a pair of calipers)
Then you do your basic trig -the leg of the slide is the hypotenuse, and the offset you will measure/set is the opposite.
Therefore opposite /hypotenuse = sin theta.
So sin theta / hypotenuse = offset to be measured on the clock..
If you want to get really passionate about it you can use a genuine DTI rather than a basic clock.
Its all you are doing with a sine bar- if you want to pay for one.
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