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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
30/09/2009 13:08:32
Ordinary turning there is no way I'd not use a rotating centre for something 12" long. Then because of the runout in a live centre, I'd change to a dead centre for the last 2 cuts. And if it were thin, then i'd be using a travelling steady as well.Its far too much overhang and it is bound to spring. So its not a valid question, if you'll excuse me putting it that way
 
But yes I do get that sort of lack of taper because both tailstock and lathe bed are properly adjusted. In fact on the Myford, currently the taper is 0. (but that won't last!)
 
The point is that you cannot take a bar and simply put it in a 3 jaw and expect it to run true to critical limits.
 
Towever if you TURN a diameter on it then that diameter will run true (and you cut the excess off having found your sculpture within the bar as it were) 
 
So stick a rigid bar in the 3 jaw. Rough turn 3 hollows, so you have 2 widely spaced collars. (With a rotating centre installed if it were me) You want a cotton reel shape.
 
 Remove the centre and now lightly skim the collars to a good finish using power feed, WITHOUT moving the infeed, so you are testing the alignment of the bed.(Hence the ali and light cuts) ABSOLUTELY at the same setting.. They will indicate 0 runout. Now skim them again (.02mm), without altering the infeed inbetween and measure with a MICROMETER. If the one further from the chuck is bigger you need to move the toolpost towards the work - not by using the infeed, but by putting a shim under the front foot of the bed. If the outer collar is smaller, its a bit of shim under the back tailstock foot to move the tool away. Reskim remeasure, readjust. until its right. A good game played slowly, buty once it is right, any future adjustments you can make by a nipping up on the holding nuts usually. I've never had to add extra shims.
 
The assumption is that the headstock and hence axis of the bar/collars remains still, and you twist/straighten the bed by moving the tailstock end. (Not the tailstock but shims under the mounting points at the tailstock end, so the whole bed is moved. With a lathe like a 1224, you will need to slacken the mounting bolts at that end , and then with a hydraulic jack, lift the bed a smidgen, slide a shim under, drop the bed and retighten and then recheck). That in turn moves the saddle relative to the CL of the bar or spindle bore and takes out any taper. If you have a 24" lathe and you are working at the 12" point, then very crudely, if the difference in diameter is .001", the difference in radius is.0005. You are at the halfway point, so you need about .001 of shim. And if you are working 1/3rd of the way down the bed, then pro rata. Thats just a very rough starting guide and allow a whole evening for the exercise!!!!!!.
 
You can do a rough check with a test bar mounted in the morse taper (NOT a 3 jaw) and a DTI in the toolholder but you do have to finalise by cutting collars.
 
Once you have the lathe straight, then you can put a test bar between centres and clock on it, to take out any tailstock misalignmant. Once you have done that, you will find that you can set something to run true in the 4 jaw, put a clock in the end of the bar and run the tailstock centre into place, and you will get no movement on the clock
 
 
When you check in the future, you can certainly put the same bar in the 3 jaw, but you must skim the collars true and then take the cuts.
 
The actual diameter of the collars is unimportant - its the DIFFERENCE that you are taking out.
 
I may be teaching my Granny, (and I aplogise if so) but I think there is a little confusion, and perhaps also a touching faith in what a 3 jaw self centring chuck will do .
 
Runout is radial misplacement.  - hold something in the 3 jaw that is truly round, and the clock will indicate movement. The bar is not CENTRALISED  or not aligned with the axis of the lathe. Its wobbling to use the real technical term. So a 3 jaw is very convenient, but not accurate enough for critical work. If you can find your dimension within the bar as above, or its not critical - like a simple locking pin then fine. (there are specialist 3 jaws like the Griptru, and very expensive high precision ones, but the above is true for the normal common or garden 3 jaw that most of us use or can afford)
 
Collets - .probably centred repeatably to 1/2 thou?. Good 3 jaw .002-.003 TIR I guess when new, and a lot less if it has been overtightened or jobs grasped in the tips of the jaws. If it has to be something that is dead true, like a crankshaft or bearing housings in an axle tube, you can't turn it end for end in a 3 jaw and expect it to be straight enough to fit a set of reamed bearings and all to spin true. It won't. You have to set it true in a 4 jaw, or mount it betwen centres for that sort of work. 
 
PM me and I'll give you a phone no if you need a bit of help - its a simple job, just a bit of a pain first time out..
 

 
 
 

Edited By meyrick griffith-jones on 30/09/2009 13:13:35

Edited By meyrick griffith-jones on 30/09/2009 13:16:23

Edited By meyrick griffith-jones on 30/09/2009 13:19:30

Edited By meyrick griffith-jones on 30/09/2009 13:21:28

Edited By meyrick griffith-jones on 30/09/2009 13:24:05

Edited By meyrick griffith-jones on 30/09/2009 13:28:04

Thread: Myford ML7 spindle nose dimensions
30/09/2009 12:07:36
Damn -put it down to a streaming cold and late at night. the thread is 1.250 x12 whit and not 1.125x12. Should have known because I only did one only the other day.
 
Got myself totally crossed up there.Pity there isn't a delete post facility.
 

Buy a Model Engineers Handbook (3rd edition)by Tubal Cain. The dimensions are in there as is all the threading data.

Edited By meyrick griffith-jones on 30/09/2009 12:09:18

30/09/2009 00:18:35
Can you correct the dimensions - I've put the decimal point in the wrong place. +2 tenths of a thou to + 5 tenths. Apologies

Edited By meyrick griffith-jones on 30/09/2009 00:18:52

Thread: HELP HELP HELP - Warco 1224 Gear Head Lathe
30/09/2009 00:15:00
Dias - that's the standard shimming test.  Myfords have rather nice screw jacks for the purpose, but most lathes needs shimming.
 
Turn 2 collars - sharp tools small cuts, preferably in aluminuim, on a rigid bar (1 1/12" approx depending o nthe lathe)  say 6-8 " apart or more depending on the size of the lathe. Distance is not not critical. same setting - and don't remove form 3 jaw.
 
If the diameter further from the chuck is the smaller of the two diameters, then you need to move the work AWAY from the tool. So shim under the front mount, tailstock end. If its the larger dimension, you need to move it towards the tool - so you shim under the back mount, tailstock end. Headstock end is not moved.  Eventually you get the 2 collars the same size and your lathe is set right.

Edited By meyrick griffith-jones on 30/09/2009 00:15:59

29/09/2009 23:59:25
You have done the standard turning turning test on 2 collars and shimmed under the feet of the lathe accordingly?
 
You have runout on your spindle? Seriously? Detectable runout with a DTI against the inside of the morse taper, or on the Camlock taper?  (Not on a bar held in a chuck of course which will runout all over. <2 thou runout is good for a good 3 jaw, and I bet our cheapo Chinese 3 jaws do a lot worse than that.) Bearings checked and adjusted?.
 
You should have sensibly, zero runout.
 
Mounting in a three jaw chuck shouldn't affect trueness. That doesn't mean a 3 jaw will hold truly concentric - it wont, but if you turn a dia (ie skim a surface) that should be true and not runout, as should any other circumferential point on the same bar machined at the same setting. What you can't do is clamp a test bar in a 3 jaw and draw any conclusion as to the truth of the lathe. You can set it to run dead true in a 4 jaw if you wish, and then clock off that, but not a 3 jaw.
 
Checked the tailstock is aligned if you are using that to support your bar. Very occasionally the tailstock may be low or high, but more likely it will be out side to side.
 
The way to do the adjustment is to do the standard tuning test and shim till that comes out right. Then put a test bar between centres head to tailstock, and adjust that out. Wise to use a soft centre in the nose of the lathe and skim that new and in situ before doing the test.
 
Tools are good and sharp, and you are not measuring after some mega deep cut? Doesn't sound like it if the large dimension is nearer the chuck.
 
Are the chuck jaws allowing flex, even though hte lathe is straight? That would normally give the larger dimension further out, unlike yours.
 
 
So do the tests and see what happens. My 12/37 was a mile out plonked on the workshop floor, as  delivered. Properly adjusted, and I just reset it the other day, its turning parallel to better than .025mm in 12"  They do move about a bit, and I do mine every sort of 6 monthly or so.
 

Edited By meyrick griffith-jones on 30/09/2009 00:01:32

Edited By meyrick griffith-jones on 30/09/2009 00:06:42

Thread: Myford ML7 spindle nose dimensions
29/09/2009 23:28:37
The register diameter you can measure, and the depth will be measurable too, less an allowance for the threading runout groove. You will need to turn to 1.250  +.00002/ +.00005 if you want it to really run true. (Keep it well oiled with 3:1)  As long as it clears the actual depth of the register is not critical.
 
 The ones I have cut for mounting stuff on a VDH, and putting a boring head into the Dore Westbury have had registers about 1/2" long. The one supplied on the BS0 dividing head, which is perfectly secure is not much more than 3/8" long. 
 
The thread is 1 1/8  x 12  55deg Whit form, but you wil need to ensure the crests are truncated a fraction, to be sure it doesn't hang and the register and back flange are doing the aligning..
Thread: Small Milling Machine
28/09/2009 17:55:51
I would think that probably the best small mill you can get is a Dore Westbury  Mk11 - if you can be sure it was made well. (And if it wasn't you can take it to bits quite easily and sort it out) And you can find one.
 
Many have power feed + auto knock off. Many also have the low speed gearbox which gets you down to a sensible speed for flycutting on a large radius. Thrust bearings in all the handles, large feed nuts. Astonishingly versatile little machine and purpose designed for the model engineer.
 
Spares  - well you can make anything yourself, on a 3 1/2 inch lathe.
 
And no, mine is not up for sale - too useful.
Thread: End mills in a drill chuck
26/09/2009 20:21:40
John - I agree 100%
 
The point I was making was simply that just because one might be using a  milling cutter in a drill chuck, that doesn't  mean that one is doing something unsuitable - and htat perhaps one ought to specify what one is up to. You yourself have said "serious" radial loads, and the poster said "very light" milling. A thin skim in brass being one thing, and for sure, a drill chuck in good nick, properly secured, and you'll get away with that. Walk into NIMONIC and you certainly won't. 
 
I think also when it comes to radial and vibrating loads with drill chucks , very often there are 2 tapers involved, and not just one - unless your drill chuck is fitted for a drawbar and dedicated for use in a mill. (or more rarely it is one of the expensive monolithic ones0
 
Further, most drilling machines do not have the right bearings for milling - or may well not.
 
So all in all, I rather agree that milling in a drill or drill chuck is not a great idea, in general, but not always.
26/09/2009 15:31:35
john - I believe you are talking of putting a radial load into a drill chuck, which agreed, is unwise in the general run of things.
 
That's rather different from putting an axial load from any form of cutter into a drill chuck which was designed to carry axial loads.
 
Are you sure that you don't have the signs in the axial loads the wrong way round, at least in steel. You need to apply a thrust to drive a drill bit or slot drill. (about 80lbs force to drive a sharp 1/4 bit).
 
As for supported unsupported - well not necessarily - depends on the strength of the chuck. Granted the forces in the jaws are not constant of course, but no one said they were - they are in fact cycling - reaching a maximum as the load is being taken on one jaw, and then being shared between two - in proprtion to the angular difference. (I have no doubt that we can can work out our sines and cosines as well as the next man). But that doesn't mean that the grip on the tool MUST be reduced below an unacceptable minimum.
 
As for walking out - you don't feel that might be more a phenomenon of worn chucks jaws of any sort which allow axial moment   - rather than a cycling of forces in the jaws of a chuck in good condition? Actually you can get walking out in chucks which wholly support the tool - such as ER32 collets - it they are not tight enough.
 
And no - milling cutters don't always generate radial forces. Not on plunging cuts.
 
And there are plenty of pretty flat tipped drills too - many gun drills for a start, and sheet metal drills - or drills ground for drilling into sheet.
 
So again - its not about milling or drilling - its about the direction of the forces being generated. And to some degree the magnitude of those forces vis a vis the strength and rigidity of the set up as a whole.

Edited By meyrick griffith-jones on 26/09/2009 15:32:51

26/09/2009 10:29:28
Define milling.
 
Then define the directions and types of load.
 
Then look at what milling chucks will take, and what drilling chucks should take, and it becomes pretty obvious what you can and cannot do with a drill chuck.
 
But if someone is seriously attempting to suggest that the load with a slot drill/end mill cutting a flat bottom hole or  spotfacing is in any way different from the loads generated by an ordinary drill bit, then they need to do a little explaining of just how? (Except that an endmill may generate less vibration - in a pre drilled hole. If you are going straight in you'll need a slot drill of course. Nor are we discussing run out)
 
So perhaps we should be a little more specific and not attempt to apply generalities which in truth do not exist.
 
Plainly it is nothing to do with whether a cutter is short and fat, or long and thin - it is to do with the forces generated , and their vectors.

Edited By meyrick griffith-jones on 26/09/2009 10:32:05

24/09/2009 18:22:29
I never used one for milling, but I have often used one for spotfacing with a slot drill.Never even budged a chuck on its taper.
 
I wouldn't do that now - nothing to do with a conversion of St Paul - just that I now have a mill with a dove-tailed column, so the repositioning problem has gone away . Its easy to lift the head whereas on the previous round column machine, you'd lose position.
Thread: graphite year stuffing
24/09/2009 18:16:20
Niloch - thank you. I had looked in the Screwfix catalogue, but didn't realise that the cord was ptfe.
 
Great help - and cleaner than greasy hemp!
23/09/2009 21:04:12
Thanks - I'll try that
 
Sometimes, given the simplicity of other peoples ideas, I feel I haven't considered my options very well .
Thread: Artillery
23/09/2009 21:00:54
What do you need to know.
 
Depth - typically .008 on dia for our sizes such as 30 cal = .308 groove to groove ..303 =.311 groove to groove. .303 land to land. .270/277 etc.If you look up SAAMI they will give you all the tolerances etc
 
Typical steel in US nomenclature is 4130. There will be a UK equivalent. Its not a "special" gun steel. (there isn't such a thing really) Its just a medium carbon, workhardening engineering steel like many others.
 
Twist rate depends on velocity and projectile length. The longer the proj (length to diameter ratio) the greater the twist rate. The higher the MV the lower the twist rate, so you need to get this right. It varies considerably, so you would need to look at something in your class. Long arms with an MV of about 2500-300fps are about 1:9 - 1:10 twist rate.
 
How to make - well you can hammer forge onto an externally rifled mandrel with a rotary hammer if you are a professional, or for a one off you'd be best off making a broach of the right size with offset cutters, and a guided tail of the right twist. Or you can single point cut and index. The cutter is on the end of a rod, and the rod is externally" "rifled" and passes through a stationary "nut". Whip it up and down the barrel.
 
If you want to make an accelerating twist, then you have to cut the rifling with a cutter moving down an externally rifled guide connected to a cam, and at a point part way down the bore the cam comes in and turns the guide, accelerating the twist towards the muzzle. ADEN guns had that.
 
In principle its not that difficult. The barrel doesn't even have to be terribly straight. You don't want it lumpy along the bore, but a (little) bit of a banana doesn't matter, so long at it remains consistent (tank barrels warp by whole inches along their length due to differential heating in a breeze). For the initial drilling op you want a deep worm gun drill, which are easily bought on special order - I have several, not for guns I might add, but for drilling various deep straight holes in milling machine quills etc.The automotive industry uses them a lot for doing oil holes etc.They are in the catalogues of people like Dormer - specialist, hardly rare, but not the easiest of things to use.
 
In this country at least, if it were recognisably a pistol, and rifled, you might have a difficulty with the legalities. And proof? However, thats an area I am simply not competent to comment on and you would need to ask an expert. (never tried, got no interest)
 
A word of warning, or a suggestion. If you are going to make one of these things and actually fire it using a nitro propellant, be aware that loading a pressure vessel up to 19tons/sq inch near ones face is a potentially hazardous activity. Worth making sure you have the maffs right before proceeding? (Especially with things like locking lugs on which the integrity of the whole affair depends)
 

 
 
Thread: graphite year stuffing
23/09/2009 20:13:39
Chris - where do you get that because thats exactly what I was looking for. But none of the big plumbers in Yeovil stock it.
 
There is gas type ptfe tape which is quite a bit thicker than the standard,  which could well work too, but that string is the stuff.
 
LSM stock gland packing, but its really a bit thick for this sort of application.
23/09/2009 17:48:45
This is a bit like stuffing glands on boat propellor shafts. I'm using the  dirt cheap hemp yarn and grease on my piston rod because I can't be bothered with graphited and I can thus argue it's more prototypical.
 
Wind  some round the rod, so its going to fill the hole reasonably, overlay with grease, tighten gland outer till assembly doesn't leak, and is not too tight. Victorian technology - not very complex!  (They used a lot of tallow - but that smells) If it does leak a bit - see all sorts of steam engines at the steam fair, and:
 
a Don't worry.
b Tighten a bit more
c If that creates too much friction, loosen a bit, and if it leaks a smidgen:
d Don't worry.
Thread: Milling collet arbor jammed in milling machine
22/09/2009 21:49:25
Well it wasn't me that said that about rules- someone much wiser. Dr Johnson I think.
 
And I agree entirely with your suggestion as to who may or may not have had whatever kind of wit. Certainly not Circlip (whom I am still blessing in fact as I sedately cut out brown paper gaskets. ).
 
As for this problem - I hope otherwise, but it sounds, given the (severe) hammering the top of the taper has had, that it has been expanded or bruised in some way.  It could well be that one should be looking for a press of many tons. Once you get into bashing bits of machine tool with lump hammers you tend to be in trouble!
 
I hope I'm wrong, but it all sounds a little Neanderthal to me - I have a little 4oz ball pein in the workshop, and it makes me wince when I tap anything with that, without an aluminium drift in between.  Nor do I think I have ever needed to...........
Thread: Lathe Advice Needed
22/09/2009 18:12:17
Can you mill on a Bantam? I'm not familiar with them, but if costs/space mean you need to have one machine tool then you will need a lathe with a tee slotted cross slide - or be prepared to modify a cross slide.
Thread: Milling collet arbor jammed in milling machine
22/09/2009 18:05:47
Depends a bit on exactly where the slot is placed, but for sure you don't want to go beasting the top of the taper, then expand it, and find it is imperially jammed - which it may be already..
 
I'd be inclined to screw or palce a bit of steel in there above the millling taper. Copper/brass or any of the soft metals will deaden the shock and its shock that needs to be generated. Get the wedge tension on, and then apply a bit of a tap from a drawbar type thingy from above in the direction you need the chuck to go, after warming the spindle (not the quill or chuck).
 
If that fails try the vibration system.
 
If that fails its a new spindle and bearings
 
As for the physicists - hopefully one won't be caught by surprise, hopefully the drawbar is loose and clear of the head, hopefully you will be a minimum revs, hopefully you'll have a bit of wood between chuck and bed, hopefully the drop permitted will only be about .25 of an inch so all is contained, hopefully one will be near the e-stop/isolator, and hopefully one will be ready to wind said chuck out if hte work a bit quick. One can of course wait for a accident to turn into a drama if one wishes.
 
Rules as they say, being for the guidance of the wise and blind obedience of fools.
 

Thread: Artillery
21/09/2009 23:16:26
I doubt they'd be interchangeable Dougie. I'm no expert on vent tubes other than the 120gun uses a magazine of electrically fired vent tubes.
 
Basically the vent tube had an earthed body and an insulated centre contact - it looked like a .50" cartridge - more like one of the Infantry COMBAT/WOMBAT 50 Springfield spotter rounds than a 50 BMG. That got fed (or not as was often the case)from a rifle type magazine  into the nose of the FNA - the rather antiquely named Firing Needle Assembly. (Rather like a Mauser bolt face on a vertically sliding breech) A central contact would then make electrical contact, and you would pull the trigger when ready. That lit the gunpowder in the tube.
 
As far as I know the mechanical vent tubes used a hammer or lock to fire a small primer which fired the  gunpowder charge in the tube. (going by the US M110 - 155mm Counter Battery and 8" howitzers.) So the probability is that the mechanical systems woulnd't have had any electrickery to the breech - just a lanyard. Some of the bigger guns had hydraulic breech opening mechs.I think the rotation of the breech locking mech would cock the vent tube firing lock, but the vent tube itself would be manually loaded and manually extracted.
 
Gunpowder was used because its very "flameful" and full of burning particles which are good at penetrating the cloth covering igniter pads on bagged charges.
 
Everything I know about vent tubes!!!
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