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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: HELP HELP HELP - Warco 1224 Gear Head Lathe
12/10/2009 18:48:34
I beg to differ.
 
It is quite plain that the beds of these medium sized lathes can be and are twisted in the mounting process. All anyone is doing in the shimming process is getting back to straight, to make up for wobbly floors, errors in the making of  cabinet stands etc. It's just that the average model engineer doesn't have access to a calibrated high grade engineering level - a carpenters level is nowhere near good enough. Nor do we have industrial grade stands, most do not use levelling jacks and mats, nor the means to get them so mounted, and many equally don't have floors guaranteed level. And I reiterate, one is not twisting a bed, one is using a cutting process to ensure there is no twist in there, and that the bed is mounted as straight as it was when it was ground..
 
Even my Chinaman has a register and jacking screws, so the facility to adjust the head is there if I wish, but I would consider it very foolish to level a lathe, moderately crudely, and then assume that the head was out - because:
 
1. Even the most destitute Chinaman has access to measuring kit that we don't.
2. Fooling about with head alignment, without being certain of what one is doing, may result in a head aligned with the bed, as mounted, but with that all important concavity dialled out.
 
Unless one has good reason so suspect something. Here I agree, if a spindle has gone in on the piss and the head adjusted to compensate, then surely that would colour ones perspective, and needs restoring and sorting. But that is not normal.
 
Errors induced in initial mounting are.
 
Bigger lathes may need aligning differently - of them I have no experience and claim little knowledge, other than at work we straigtened a Colchester Master? - huge old thing with a 6 foot bed  and a 24" faceplate, but not much worn - with a few shims under one corner.
 
However these 6" inchers  can be twisted and can be straightened. And you know when you have it right, because all the drag in the saddle disappears with the crossbind removed. Also of course, do not doubt that you can move the head of a Myford if you want. Four allen bolts ( easily reached) is all it takes - as long as one feels that is wise..
 
Further I actually took my own advice and reset the Chinaman the other night. Without touching the headstock, the thing is straight to .00005" in 12" (Yes really - 5 hundredths of a thou according to Mr Mitutoyos digital mike) By good fortune I admit because it was the first try - and best to quit while one is ahead. The concavity is about .001 in 9".
 
( I apologise for not knowing my Colchesters - but this is a seriously full sized machine)
 
 
Thread: Drilling problem
11/10/2009 13:40:21
The trouble with 4 facet sharpening is that its expensive, and now everyone on CNC uses specialist short spotting drills and that sort of thing. I much prefer stub drills for almost all drilling - they don't wander.
 
As you say Chris - that's where I got into 4 facet sharpening. However Harold Halls more basic jig and sharpening system would be better for most I think. The Quorn allows you to make your own reamers and spiral this and thats and spiral flute taps etc etc. But there is a lot of work and expense for facilites which most wouldn't use. ( I built all the accessories and most remain pristine, brand new and unused from 15 years ago! Its only worth making them at the time to ensure that centre holes are all absolutely the same distance apart)
 
The sharpening process is pretty easy. The only problem with  these things is that you need some sort of degree scale - beyond the 45-90 -45 marks - for many designs I think. They are not difficult to do, but you do need a dividing head, or perhaps a rotary table. On that note, if anyone needs a blank divided and graduated, let me know - as long as it comes on mandrel ready to mount. To pop a blank into an arbor and hold in a collet to knock out 360 divisions is no great trouble, so long as it doesn't become a flood.
 
As for spending ones money on a set of Dormer or Osborn drills. Well a set of drills going up by .1mm is a good thing to have, but as model engineers do we need quality? If one has sharpening faciliites I'm not sure one does, unless one is getting into drilling very tough stuff. If I had to choose, I'd rather put my money into a good quality chuck and taper.
 
Geoff, I may be teaching my Granny, but if a drill jams in a brass/bronze bush, almost certainly it was too sharp and it pulled forwards. Zero rake for brass and copper and bronze if you don't want jam ups.Sure it could have been some other problem, but probably it was used out of the box? (Yes, being properly blunt generates rubbing and overheating but some kind of coolant or RTD solves that)

Edited By meyrick griffith-jones on 11/10/2009 13:45:25

10/10/2009 19:26:39
Mike - the angles, like any drill grinding are not critical. However you set, like any other drill a half of 118deg = 59deg (or 90-59= 31 depending on how the grinder is set), because one is going to grind the 2 halves separately.If you want a drill for sheet metal, then you'd set a different 1/2 angle of course.
 
Then in "pitch"  you set the secondary clearance. In the Quorn book I think it says about 25 deg. I do 20, simply because in upside down mode I can only get 20. Anyway, enough to ensure the heel clears.You grind both tip faces till you have cleaned all up, and then a quick clean at the same infeed.
 
Then set the primary clearance of 10deg., and grind that. The trick is to grind only so much so that the back edges of the primary lands intersect - exactly - its quite easy to do by eye. What that does is give you the effect of two chisels edge to edge, and exactly cenred. Importantly, at the join there is a tiny point, so in effect you have a built in centre drill and thats what makes them run so true. And when sharp, they cut so fast that in brass you have to blunten them - because unlike a commercial drill bit, there is no chisel point - which isn't a chisel point, its a graunching point. (Zero rake for brass is the technical term, but blunten them is what you do!!)
 
Sorry but I don't have a pic for you, but I think Harold Halls book on tool sharpening has the detail and also a method of making the holder to do the job. (The same holder also does endmills and slot drils as well)  Its worth doing, because they are far better and sharper than brand new ones and particularly good for small lathe owners where power is at a premium.
 
I don't know the articles Chris is talking about,  but I'm sure they'd be perfecty good too.
10/10/2009 14:25:23
But - with respect a reamer will follow a hole. You can make a D bit to dead size out of silver steel - that should straighten a wandered hole - within limits of course!. Or take GHT's advice which is to bore to near size after drilling, and then ream the last .005".
 
Which doesn't help much in our small sizes where you cannot get a boring tool down the hole.  Back to 4 facet sharpening and a tool and cutter grinder of some sort.
 
If it is small and deep and has to be straight and to a size, then I use a 4 facet sharpened drill bit, and a SS d bit down it to finish. (Or build things that are big enough not to have holes that small in them)
Thread: Rear mounting parting-off tools
10/10/2009 11:35:29
Chris - only you can say.......
 
I tried these rear tool posts in the Myford during my 20 year parting nightmare.... but I did find, compared with a larger lather, the RTPs do make it all a bit cramped.
 
John, you experience mirrors mine. I used a Dremel to cut that scoop and use the tool in the front toolpost. Result is the same.  I have collected up quite a few of the Myford/Dickson type tool holders for hte QC system, over the years - and I'm like Chris. You never seem to have enough, but that's why I'm all front toolpost..
 
I reckon that kit Q cut is great. Actually I was offered second hand a standard Sandvik blade for peanuts, which takes the same tips. Idea was to drill a couple of holes in it, and mount it on a bar- same sort of arrangement as the KQC, and in theory cheaper than buying a Sandvik holder for the blade. This is when I found that the Sandvik steel was tough. But seriously tough. All the way through. I think RHA steel armour isn't as tough. Having blunted the drill and resharpened it twice, I ended up having to buy a solid cobalt one. The system now works very well on the 6" lathe, but for the convenience, I think the proper holder might have been better!

Edited By meyrick griffith-jones on 10/10/2009 11:35:58

Thread: Drilling problem
09/10/2009 22:08:31
Have you actually checked that table and quill are set square to each other? That's one quite easy way of getting an oversize entry if the hole is a bit deep. And that it is tight and didn't tilt in the drilling?
 
If you extend the quill and lock it, clean the table off, then bring it up and  put a setsquare against the quill Tell you straight away.
 
if you don't have a large enough square, if you set up as large a dia bar in the 4 jaw as you can, CLOCKED TRUE, and turn a recess in the base to leave a thin ring (skim the surface of the ring true of course), that will stand square, and might perhaps save buying a big square for a one off use.  

Edited By meyrick griffith-jones on 09/10/2009 22:11:00

Thread: Rear mounting parting-off tools
09/10/2009 21:53:06
Chris - as a matter of interest, are you using Quick change toolholders? If one is not, then I can see a use for a back toolpost, despite the problems of spiking both work and self with extraneous pre-set tools. (Depends on size of lathe I suppose, and I daresay one gets used to it too)
 
With any of the quick change types it's the work of a couple of seconds to change a tool which "arrives" all set at centre height, so the back toolpost is probably much less useful.  - in my case my 60deg chamfer tool is also the bevelled face parting tool used to make sure whatever is being chopped off on the right comes off cleanly..
 
 

Edited By meyrick griffith-jones on 09/10/2009 21:53:32

09/10/2009 18:33:24
I know thats the conventional wisdom, but in fact if a tool is mounted a touch high on the front, or  a touch low at the back the tendency to dig deeper is just the same, because either way its being dragged into the work.
 
I struggled with a  couple of rear toolposts and used blades of 1/16. 3/32 and 1/8, and they were all just as darned bad as each other. (flood with coolant, cut wide slots, steep rake angles shallow rake anges and so on, front toolpost or back.) I could never, in 20 years, reach this nirvana that others seemed to, of being able to part off at high speeds and feeds.
 
UNTILL I bought a Kit Q cut from Greenwoods. And then looked at the geometry of that Sandvik tip, and then bifurcated with the Dremel the cutting face of ordinary HSS blades. The difference seems to be that the chip is actually rolled in on itself, so coolant gets in there and it never jams in the groove. (Nemett in ME recommended the same thing if I recall)Also with the commercial tipped blades, the carrier is significantly narrower than the tip so the back clearance is built in.  Not that that is essential - one of my tipped tools is actually designed for 3mm tips, though I am using 2.5mm wide tip, and the clearance is minimal.
 
Since then, tipped or HSS blades, I have never had a jam up, and the days of inching in, slow speeds and extra wide slots are gone. 600rpm, front toolpost with the Dickson type holders and feed in - and the bar parts off.2 1/2" diameter bar, single deep slot, lots of coolant, straight in, mirror finish. (TE eccentrics) I've parted off 3/12" bar in a single slice, but that wasn't an interupted cut of course.
 
You don't HAVE to build a rear tolpost. I have a proper Myford one, and an Ivan Law designed one. You can have both free gratis and for nothing if they;ll fit your lathe. They really are that useful (and have gathered dust for 4 years!!) But if you want them, by all means have them, but when you fnd out how useless they are, please don't post them back.
 
I suspect that the success of back parting toolposts has a lot more to do with chip clearance than geometry. Operating from the front toolpopsts should in fact be more rigid because all is being pushed down onto the bed. At the back it's all being lifted and any slack will be magnified. And the chip clearance issue has been very effectively addressed by the modern tip shape  - these tips just fold it up, roll it up and spit it out
 
 
The only thing I do  is of course is to make sure that the toolposts is genuinely square to the work.
 
Glanze from Chronos also do a very nice tipped blade. In some ways its more versatile because it is a blade in a clamp type holder so you can keep it short for every day, and extend it when you need it. The Kit Q cut is fixed length, (but with less forward overhang)  but its Sandvik tips cut more freely despite being .5mm wider.
 
 
Thread: Milling collet arbor jammed in milling machine
08/10/2009 17:57:16
Ah - well that's because you are not the right Christopher, for which I apologise.
 
I agree, it could be a little bit of hike to the Houndstone Trading Estate from the Smoke, especially as i think you have such places up there. 
 
Chris H though might find it useful.

Edited By meyrick griffith-jones on 08/10/2009 18:01:53

07/10/2009 22:47:53
Well, if you do get any spare bits, just be sure to tip them in - they'll find their own level somewhere.
 
Missed this one - so belatedly good for you. Now you do know your way around the machine, you'll be a lot less frightened of it - thats for sure.
 
Oh and Chris, your nearest supplier of good bearings/belts/ power transmissions helicoils, oil seals etc, if you need him is on the Houndstone Trading Estate. (with apologies to Grannies if necessary) They are very good and will get bearings ground to non standard sizes etc.  Premier Power Products.
Thread: Please hellp
07/10/2009 18:20:15
Ring Myfords and explain the problem.
 
They can give you an answer on the spot, and will have parts on the way inside a day. (take credit cards too!)
 
0115 9254 222 will get you reception.
 
Might be worth slackening the belt a little? And grooving the top face of the parting tool.?  Must have been quite an impressive jam up?

Edited By meyrick griffith-jones on 07/10/2009 18:26:26

Thread: Steam turbines
06/10/2009 18:42:29
Fred, I think that building to an established design would be a good idea.
 
In this one I am lucky, in that my MSc was in guided weapons, so gas turbines and aerodynamics was bread and butter. I have the necessary equations available, but i also know enough to know how little I know about it when it comes to designing from scratch. (or how much one needs to find out!)
 
 Still , one of the curses of any turbine is blade flutter (for which there are several causes) and one of the fixes for flutter is rigidity, since flutter is actually twisting under aerodynamic load. If you are going the bladed route, you might wish to think therefore in terms of titanium. While it is a nightmare to machine to good shapes, being notch sensitive, (and boy you do not want notches or poor surface finish in stressed titanium),nevertheless it offers a very high stiffness to weight ratio. From a performance point of view, that would be a better bet that steel or ali
 
No disrespect, but to go from scratch, when it would seem from your original post that the mathematics of aerodynamics and strengths of materials may not be your routine bedtime reading - its all getting a bit exotic, and someone else's (proven) design might be wiser?
 

Edited By meyrick griffith-jones on 06/10/2009 18:43:10

05/10/2009 23:00:07
Busting load - will be the tensile stress at the root of each bade. The load which generates that stress will depend on the size and shape of the blade. Then you have to determine the thrust on the blade because you have forces in 2 directions.
 
The centrifugal force is solely  dependent on velocity and blade mass so you can work that out in 2 seconds. But you need root area to convert that into a stress, and allowable stress varies, in old units from about 18tons tensile for cooking mild, up to to 50 tons tensile (from memory) for some of the MARAGING steels (martensitic age hardening)- depending on conditions - as does their suitability.
 
The aerodynamic force is a little more difficult, partly because aerodynamic equations tend to be relatively complex, and partly because the standard equations may not apply - they are for wings of relatively high aspect ratio, and you are talking in turbine blades of very short fat wings. (very low aspect ratio)
 
And you may well also have to make some compensation for temperature or creep - see below.
 
Importantly in any short fat wing, much in the way of losses is determined by spillover due to the pressure differential between the front and back of the blade - you lose effctive area. The way to stop that is to fit a plate to the wingtip (see all the F1 cars) - in a turbine that means a very close fit between blade tip and casing. You have to allow for and include blade stretch. 
 
To work that out you have to allow for both the increase in diameter due to simple thermal expansion, and due to centrifugal loads. And all that presupposes that you know quite a bit about your materials, and the conditions inside the turbine?
 
So anyone who offered a one liner would be very unwise.
 

Edited By meyrick griffith-jones on 05/10/2009 23:01:01

Thread: riviting
04/10/2009 22:01:30
Have a look back on the beginners forum. There is a thread on riveting, There may be enough in there to give you a few ideas which might help.
 
I agree - its is a pain in the fundamental, and it needs 3 hands, but I don't live in Shropshire.
Thread: Wheel cutting
02/10/2009 17:55:07
Or fit a DRO, and switch between radius and diameter at the touch of a button!
 
And metric and imperial.
Thread: HELP HELP HELP - Warco 1224 Gear Head Lathe
01/10/2009 23:08:06
You are quite right - It could be the topslide.
 
I never use it while turning. - I set length to a shoulder on the saddle with a saddle stop, get the topslide so it doesn't overhang, and .005 short of target, and lock it. That gives me maximum rigidity and the least possibility of any chatter, or problems while parting off. Do all my turning with the topslide locked and then finally move it forward the 5 thou  needed to get the shoulder length right, and then wind out to give a clean face. The topslide is set parallel with a DTI and never moves .
 
So with that method of working its not part of the equation.
 
On the Myford I have one of the Radford topslides from Hemingway. That has a tenon to set it parallel, and there is no taper turning facility - it doesn't rotate at all and it is guaranteed to be parallel. (If I want a taper I either use a home made taper turning attachment, or replace the original Myford topslide temporarily. the advantage of hte Radford is that the topslide never fouls the tailstock - one of the banes of Myford ownership if the topslide is set straight.)
 
So apologies for not mentioning it .
 
But, with respect, I'm not so keen on your system of aligning the topslide because you cannot guarantee that anything held in a 3 jaw will be true.  His Warco has a topslide with a flat ground face that should be parallel to the topslide dovetails. So all he has to do is put a magnetic base on the lathe bed, and the foot of the clock on the side of the topslide and wind the whole saddle back and forth. Adjust the topslide till there is no indicator movement. After that one can use a setsquare agin the topslide to set the toolpost for say parting off - if youhave a quick release toolholder block to square up on.
 
If you are doing it on a Myford (or any other lathe with no flat face on the topslide),  hold the clock in a toolholder (or remove toolpost and use magnetic base on the top), DTI foot against the side of the bed. Move topslide forwards and back. Rotate topslide till there is zero movement and lock down.
 
 

Edited By meyrick griffith-jones on 01/10/2009 23:09:53

01/10/2009 18:11:11
Peter - bit chunky compared with a Myford- as I found out when mine arrived!! Kind of out of my experience too when it came to finding space for it.
 
 
Traction engine 42. Are you sure the headstock is not aligned. I know that not all Chinamen are identical, but if you go to the back and open up the cabinet door, on mine plainly there is a machined right angle which locks up against the back of the lathe bed. Thats not to say that swarf or some other problem couldn't  exist, but I think you'll find a proper regisert in there.
 
One can check on the 90 degrees if you are sure your faceplate is true. Take  a DTI across the facepalte. You should pick up a small "error", because the lathe should be set to turn ever so slightly concave by a couple of thou per foot or less. But concave it should turn. So if the headstock deviates more than that, then you might start looking harder.
 
However this lathe hasn't been set up, so there is a good start. I might, if I was being thorough, take the chuck off the camlock face and ensure there there was nothing AT ALL (not even the smallest smidgen of a flake of brass - the common culprit) trapped between chuck and mounting face. And I'd  also check the taper rollers were propery adjusted and locked up.
 
Also, if Ant don't mind, I suspect that a bit of unsupportive practise has been going on. If you habitually work with long overhangs then taper is inevitable, not from the lathe, but from spring in the work. (This is a nasty dirty habit which one ought to be out of a bit sharpish). But, an unaligned lathe bed combined with an unaligned tailstock can make things worse. So for me, first get the lathe straight, then align the tailstock, and then use the tailstock for its intended purpse - supporting any and all work where the overhang is longer than about 1.5"
 
The Rollies Dad system looks fine doesn't it?. I'm not sure it would be so accurate as a test bar in the morse taper, but I bet it would get you close, perhaps very close. It is after all the collar method without the cuts, and using an average error. At its very basic, it has to be a lot better than nothing. 
 
Lathes cutting straight from new? Well to misquote Tubal Cain. A lathe bed is ground straight, then you start hanging offset weights like motors and gearboxes on a long slender body. Then you put it on a mounting platform locked to an uneven floor. Of course its going to be pissed, totally pissed, and the longer the lathe bed, and the heavier the lathe, the more flexible and the more pissed its likely to be. A little lathe like a Sherline or Cowells hasn't got enough weight to really flex anything. It's also very short so its relatively very rigid, so you can easily get away with it. A Myford is pretty assymetric, longer, and very slim so you won't. My 12/37 is so darn long I can flex it quite easily with a spanner on a bolt - one handed with no effort. With a laser aligner you can see the displacement  in the bed as you jack it.
 
So they need setting up, and more setting up the bigger you go.
 
Ain't rocket science people. 
 

Edited By meyrick griffith-jones on 01/10/2009 18:34:15

Edited By meyrick griffith-jones on 01/10/2009 18:36:03

Thread: Myford ML7 spindle nose dimensions
30/09/2009 19:41:39
Still got the streaming cold
 
I really got myself into a tiswas over this one.
 
Anyway mine did fit fine first time, so perhaps the doing is easier than the writing. Apologies.
Thread: HELP HELP HELP - Warco 1224 Gear Head Lathe
30/09/2009 19:37:03
Not that critical Ant. Just a cotton reel shaped thing. As long as you have a couple of raised collars to skim on about what 8" apart and about 1/16" high and 1/42 wide is plenty.  Sort of ruler measurements.
 
Metal dia about 1 1/2" - 11/4 on a biger  lathe. Anything that's rigid enough not to spring under load. I have a bit of 1 1/8 ali HE30 from my racing days, so thats good enough, but if it has to be steel, it has to be steel.
 
Big heavy lathe - hold shims in long nosed pliers while you slide them under the foot - watch your fingers.
 
One point. The machine is secured to the floor? Cork tiles makes good cheap damping, and stops a lot of drumming in hte cabinets.
 
Its all a bit experimental - you have it bigger at the chuck end. Slacken off, pop a strip of  .010  brass shim either side of the mounting bolt, say 3/4" wide, under that back foot there, tighten down firmly and see what difference it makes. It ain't that scientific!

Edited By meyrick griffith-jones on 30/09/2009 19:37:44

30/09/2009 17:08:25
You probably could - but its not so simple on these bigger Chinamen because the mountings for the bolts go into slots on top of the pedestals/cabinets. On top of the plate in which the slot is located is a rubber pad to stop coolant going down the slot, so you'd have to make a plate, then lift the lathe off its mounts and then secure the plate and a gasket. . Then you can start jacking. But then you are supporting the weight of a very substantial lathe on 4 very thin bolts so there is then relatively little vibration damping.

So what you gain on the roundabouts, you lose on the swings! Its not actually that bad, because once you have done it, shims don't drift!
 
He's talking about a Warco 12/24. So he can get a couple of feet in between centres, and turn 17-18" diameter with the gap removed. Played the same trick getting a Colcheter into a friends place. Its just one of those things you have to do if you are getting into machinery of that size and power.
 
For Tubal Cain the standard modellers lathe was probalby a Myford or an Emco  I don't know about an Emco, but a Myford 2 people can lift and position.(with red cheeks)

The Myford uses long bolts though mounting pads with built in O rings to seal:and there is a built in adjusting nut and a locking nut. You are quite right, it does make it very easy. These 6" lathes are rather bigger lumps and while you can use the same principle, the mechanics are touch more serious. Like you need a crane or hoist to get it installed and once installed or assembled dismounting it completely is certainly doable, but its not likely to be a popular option!

Of course the best thing would have been to have made sure the floor was perfectly level to engineering limits in the first place!
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