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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: Cutting tip for hole cutter
31/05/2011 19:25:32
Ian I agree - I just superglue such items tt a bit of wood, or between 2 bits, and then chomp the hole.
 
Having said that, I'd rather if the thing permits use a conecut, or mark out the hole, and chomp with an air nibbler and then just trim the edges
 
Trepanning I've always found one of those things thats nice in theory, but best left to someone else to do.
Thread: Machining what am I doing wrong?
30/05/2011 23:40:16
I'm sure its something to do with the headstock bearings being differently loaded - in one case they (it is)are in compression and in the other under tension. It might be worth adjusting them up, because , machining away will pull any clearance forwards and allow a touch of movement in the front bearing.

What type of centre are you using in the tailstock?
Thread: Three Jaw Chucks
29/05/2011 22:59:46
Or it could have been stripped down for cleaning and not put back in the right order with the right pinions in the right places.
 
However, unless the jaws are allowing material to wobble- causing chatter etc, then it probably doesn't matter, because one shouldn't be relying on a 3 jaw for repeatability. Nor collets if you want real precision, because even they have an error. A 4 jaw is the only way to reset properly (or a Griptru, or slacken chuck backplate and clock) because with a decent DTI you can reset to the limits of surface finish.
 
The chosen route all depends on what the job has to do when complete.
29/05/2011 22:05:16
I did have the figures, but if you look at Workholding in the lathe by Tubal Cain, he goes into the errors in 3 jaws.
 
I think, for a standard quality 3 jaw, using the preferred pinion, about 5 thou is all that they guarantee new, at a distance form hte face. See the appropriate DIN standard which many work to..
 
If you were .020 out then either the chuck is not set properly in its backplate (unlikely in view of its other results) or possibly you had a flake of swarf in somewhere - possibly even internally. Or maybe you didn't use the preferred key.
 
Could one expect repeatability of .002 every time (using any key?) No. (unless you were lucky)
 
I have a brand new Pratt Super Precision chuck. The error on that varies between 1.27 thou to about. .0004" using the preferred pinion on bars. About 1/2 thou on 100 mm rings on the same preferred pinion.
 
Thats a new instrument of a grade somewhat higher than the standard chuck (and it had to be reworked twice to get it into the SP tolerance so it took some weeks to be delivered)
 
Would you do better with a new chuck from RDG and ARc euro. Possilby - BUT, what are you to gain? No one in their right mind takes a bar and puts it into a 3 jaw and regards it as true. If you need a bore concentric with a circumfenrence, you either turn them at the same setting, or you reset in a Griptru, collet or 4 jaw.
 
For rough work, yes you can turn end for end or reset, but if it matters, as in an axle tube with bearings at each end and you want to be able to slide and axle through, then no you most certainly cannot, not even with an SP chuck, unless you are very lucky, because the error is greater than the reaming allowance oversize.

Edited By mgj on 29/05/2011 22:08:22

Thread: Badger's Bum Trials
29/05/2011 13:17:04
agreed.
 
Its like GTN tips. They are a negative rake parting tip. Dimensionally and in the catalogues they are interchangeable with GFNs - they look so similar. In fact the difference being that the GFNs are positve rake, whihc is a huge difference in characteristic.
 
If you look at SECOs on line cataloge they list in CCMT -06 30-40 different tips. Iscar about the same
 
Tips are a bit of a minefield!
29/05/2011 09:41:17
Thanks for that- I have long colums of print and an invitation to ignore or restore members? Apart form that!! its an excelelnt post.
 
Clealry Sumitomo are better in htis instance, and better wet at all speeds - and that speed isn everything. Buto f course that doesn't mean to say that would be true for all materials.
 
What isclear is there is a difference between tips, I love SECO, but when I next buy some I will try these Sumitomo jobs - though I was looking faround Ebay for APKT milling tips, and see that ISCAR are sellincg CCMT0602 04 tips very cheaply. SECO wil chip too , but one is dealing with a brittle sintered material and that can happen.
 
There is probalby a great deal of difference between HSS - some being good, some being bad. Some being well ground, and some not. I will post a pic of what I reckon an HSS knife tool should look like a bit later.
 
Incidentally, one of the advantages of tipped (indexable) tooling which no one mentions is the shape of the holder. The cutting tip is alway clear of the shank so you never have to adjust the toolpost angle - you can set it square and swap between a knife or parting tool without any changes in set up. And it will face across any size of disc without fouling.
 
Chris - you got squished too!


Edited By mgj on 29/05/2011 09:47:41

Edited By mgj on 29/05/2011 09:48:42

Thread: Gib Strip Material
28/05/2011 09:26:40
Soft material will surely load with abrasive dust and become a lap?
Thread: Machining what am I doing wrong?
26/05/2011 22:54:03
There is a very good reason for that tip radius - its all about crack propagation from sharp corners in things subject to oscillating stresses like long thin crankshafts?
 
A radius also dramatically increases strength , in highly loaded shoulders like screws etc. You are talking of a factor of around x3 (don't quote me on that since memory fades, but it is by a masive margin.)
 
Why would one want a mirror finish in a cylinder bore? Seems a little unusual when its normal to go for a slightly rough finish to allow for bedding of the rings, a means of retaining oil and to ensure it glazes properly. Perhaps I have it wrong, but the normal way of finishing a cylinder is to go slightly undersize (by say .0002") and then fine hone to exact diameter - at least for ringed engines anyway. However, I am not party to the drawings, so I could well have it wrong.
 
Also all this super sharp HSS that I have been shown, and again I may have this wrong, has generally simply been high rake angles. You can have super sharp highly polished lower rake angles which also give a superb finish, but it doesn't look so sharp. The only advantage of a high rake angle generally is that a forwards vector is applied to the tool pulling it into the work. Too much is disastrous, but enough does one a favour by unloading the feed when taking big cuts.You don't need super sharp HSS when finishing - rather you want a precise nose radius. (see The model Engineers Handbook amongst others)
 
For example, fresh grind a tangential tool (relatively high rake) in its jig on a fine stone, and use it on free cutting mild, and the chances are you will get a finish like a badgers bum. Break the tip with a stone and apply a nose radius, and the finish should be superb. Start using it in tougher steels of course and one needs to reduce rake anyway, and a tool ground for such a purpose will look pretty blunt. It will also take more power to drive it, and it should give a good finish, - but it will appear pretty blunt.
 
Im afraid I rather disagree too about freehand grinding. I'm sure some can do it, and when one wants a say a form toool with a given radius and relief, can whip one up freehand on an offhand grinder, with all the angles correct and the whole cutting surface in one plane. I'm quite incapable (and the photos of those who say they are not are hardly impressive in that direction either) - so I use a free hand grinder for rough shaping only. After that it goes on the Quorn, and it comes out right first time, with a mirror ground finish, which is, in general repeated on the work.
 
I don't have a photo of a lathe tool, but there is one of a decently ground drill in my albums, just to make the point, though being a drill it wasn't finished on 100 fine grit finishing stone used for lathe tools.
 
So when it comes to sharp, and reliable shaving cuts, it comes down, so the experts like Tubal Cain et all say, down to correct rake angles and a high polish and nose radius on the tool.
 
Talking of which - were I cutting a .180" wide but  deep  slot which is what a main jounal is, I would simply use a 2mm wide tipped parting tool. They are so deep that one has enormous rigidity, and being in a single plane you don't have to worry about the holder hitting anything. There is a built in tip radius, and with the right tips, ( since there are roughing tips and fine finish parting tips, and of course it will all set up square very easily) it wil lcome out all shiny in one. And with that shallow rake angle and looking blunt, ones chances of a ruinous dig in are very small. 
 

Edited By mgj on 26/05/2011 23:01:14

Thread: ISCAR tipped parting tool
26/05/2011 18:13:10
Half the world uses GTN 2 Clones About £50 for a box of 10.
 
Chronos do them of course for the Glanze parting tools, or I use Zenit GTN2 Z7. Thats a 2 mm wide one, but they come in several widths, and straight or left or right hand cutting.I get mine from DHS tools, but I can't believe that Buck and Hickman or JML etc don't also do them. RDG have started advertising a parting tool, and that looks very like a GTN tip in it.
 
I've seen Israeli Carbide (ISCAR) advertising them on e bay as well, selling direct.

Edited By mgj on 26/05/2011 18:15:08

Thread: Machining what am I doing wrong?
26/05/2011 18:05:26
My experience is mostly in 220M07/ EN1A and with that you can take shaving cuts with carbide as easily as with HSS. So you can on the Myford.I don't like to, but you can.
 
Commonly used inserts - no idea. Chronos were supplying tools with SECO inserts, which is how I met them. Greenwoods were supplying Sandvik tips, and DHS my local toolshop is a Sandvik agent, but gets me SECO. I also have Stellram non ISO tips. you can't tell hte difference between any of htem in free cutting mild, apart from hte Sanviks which don't like so much feed. (Taht doesn't apply to .8mmradius tips) Take your pick.
 
At the end of the day, the material has no idea wheter its being cut with carbide, HSS or a hacksaw. The difference is to do with rake angles.
Thread: Slide Valve Operation
26/05/2011 17:55:33
Alan - do you mean a larger inlet port diameter into the steam chest, or into the cylinders.
 
Mostly the ports into the cylinders are smaller than the exhaust out of the cylinder, in part because the exhaust is carrying twice the mass and much more by volume than are the inlet slots (which also double as exhausts). The port into the steam chest may be fairly large to ensure a reasonable reservoir of steam under pressure to fill the cylinder x2 because its double acting, and in the event of a sudden increase in demand. The size of the hole into the chest doesn't matter so long as it is is large enough to cope with maximim mass flow because it plays no part in valve timing. - think of the steam chest as an extension of the boiler.
 
Aslo of course pressure velocity and temperature are to some degree interchangeable, , so within reason, like any fluid, when it arrives at a smaller hole, it just speeds up, and when it gets into a bigger pipe it slows down. Thats not strictly true, because there are limits and penalties in the exchanges, but its good enough for our purposes.
Thread: Machining what am I doing wrong?
25/05/2011 22:31:50
Andrew - thats putting it very politely.
 
I can get a mirror finish at 4-500 rpm (use for almost everything because I like it on the big lathe. 600 on the Myford), and Morrison Edgeplus. Feed for finishing will be .005 per rev.
 
Tips are either Sandvik or SECO with .4mm radius. I did try some other ones and I didn't like them - bought them recently from Chronos. I normally take 2 final cuts of .010 to finish Thats .020 on dia. And genuinely I don't do better with HSS, either in a tangential holder or a conventional knife shape with more conservative rakes. I don't have the ability to measure surface finish to CLA.
 
However I have found that HSS at higher rake angles is more flexible in its use, in that it will tolerate higher feeds and cuts. Sandvik tips particularly don't like being pushed outside their recommended feed rate, SECO don't mind, and will take a bigger cut and greater feed than the Sandviks. And the chipbreaker is better too - I don't like long curling chips!! (Get them when I'm taking 250 thou on radius on the Myford with HSS and high rake angles - PITA) the only trouble with a conventioanlly ground HSS tool is hte trouble regrinding, compared with just changing a tip.

Korloy I haven't used, but clearly tips differ in their performance. However for JSKs purposes, I would still argue that he's better off getting things sorted with carbide and amateurs/beginners rates than with possibly blunt HSS.
 
The interesting thing you didn't perhaps mention was thermal stability. You start turning metal at the speeds you mentioned, and it gets pretty hot - enough to make a difference on diameter? Certainly if you have a few passes to make to form a deepish shoulder?
 
There can also be other factors too.
The chuck - mine happens to be a brand new Pratt in the big lathe, and the Myford also has P&B chucks.
 
Headstock bearings. On the Chinaman at least I have some brand new (and epically expensive) precision taper rollers from Germany. Long sad story but they made a difference. The Myford is still on its old bronze cone, but the tail end bearings are new and very smart, and it is very well adjusted.
 
So lets just say then that carbide can perform very well in "amateur" conditions, depending on the circumstances. That avoids an argument

Edited By mgj on 25/05/2011 22:34:08

24/05/2011 22:54:51
If they screech = tailstock in for support? Thats the common one.
 
Technically you should use the tailstock and a running centre all the time. None of us do but any appreciable overhang out of the chuck and its a good idea.
 
Screeching (or chatter?) is a function of the undamped natural frequency of the set up, so you can change Fn, and remove the chatter.- generally by stiffening the setup and thereby increasing Fn. It's caused by rapid (high frequency) small movements, and because the work is moving away from the tool and springing back, the cut is inconsistent and the finish usually lousy.
 
Another way of getting rid of it is often to shorten the overhang of the tool from the toolpost. That overhang should always be the minimum possible for the job in hand.
 
Oh and reduce revs and (often) increase feed a bit.
 
Glad things are getting better.
Thread: Paint ????
24/05/2011 22:41:13
Hugh - cellulose are excellent - provided you get the viscosity (thinning) right.
 
That depends on how fast you move the gun and how far the gun is from the subject - to a point. A bit of practise, but you want to spray a WET FILM. Too dry and it loooks sort of dry and won't melt to a good shiny surface. Too much and it will run. Also don't be in too much of a huury to get the paint on, and don't dwell. Put a film on, let it go off and then put the next film on (start off, run on, run off) and build it up like that so it doesn't slump.
 
And with cellulose don't do it when its damp or it can bloom which is a pain.
 
Personally I don't like spraying cellulose, but then I have got used to 2 pack which is so much easier. but I did do one racer with it, and it came up like glass. Can you still buy cellulose like that? I am not sure i'd agre about cellulose being easier. I can understand your concerns about health, but easier? Still give it a go. You can, done right, get a very good finish out of a can in fact.
 
Colluurs - they are all car colours but most suppliers can match a colou, and there is a huge range, going back to the year dot.. Halfords certainly can, and on the spot. At a price but one or two of their touch up bottles would certainly do a model.
24/05/2011 22:41:00
Hugh - cellulose are excellent - provided you get the viscosity (thinning) right.
 
That depends on how fast you move the gun and how far the gun is from the subject - to a point. A bit of practise, but you want to spray a WET FILM. Too dry and it loooks sort of dry and won't melt to a good shiny surface. Too much and it will run. Also don't be in too much of a huury to get the paint on, and don't dwell. Put a film on, let it go off and then put the next film on (start off, run on, run off) and build it up like that so it doesn't slump.
 
And with cellulose don't do it when its damp or it can bloom which is a pain.
 
Personally I don't like spraying cellulose, but then I have got used to 2 pack which is so much easier. but I did do one racer with it, and it came up like glass. Can you still buy cellulose like that? I am not sure i'd agre about cellulose being easier. I can understand your concerns about health, but easier? Still give it a go. You can, done right, get a very good finish out of a can in fact.
 
Colluurs - they are all car colours but most suppliers can match a colou, and there is a huge range, going back to the year dot.. Halfords certainly can, and on the spot. At a price but one or two of their touch up bottles would certainly do a model.
Thread: 1440 lathes
24/05/2011 17:14:09
I wonder if there is a lot of difference in quality between makes of Chinaman. I bought one off The Engineers Toolroom, and some said that that was a quality version.
 
I must admit the price was reasonable, but looking at other lathes by Chester and Warco,I cannot see much difference in finish etc, and one or two minor differences in design detail. Of course, one doesn't know the difference in terms of accuracy, so I can only say that this one, after a bit of careful setting up and some fiddling with a cross slide gib, has been absolutley spot on, and you can hit dimension =/-.002" all day every day.
 
There is no doubt that my Chinaman wouldn't stand the rigours of production forever like a Harrison, but then it will never have to. If I had wanted a top grade production type lathe, I would have bought that instead.
 
Chester has a very good 61/2 - 7" that might be worth looking at. They called it the Coventry I think. Warco were out of stock in that size this morning on their website- I happened to look,
 
(By setting up I mean shimming under feet to get it set straight in response ot a turning test. I doubt you can drop any lathe on the floor and expect it to turn dead straight as is, can you?)

Edited By mgj on 24/05/2011 17:16:18

Edited By mgj on 24/05/2011 17:16:55

Thread: Paint ????
24/05/2011 12:36:50
John I can agree. I did my TE with ordinary brushed Japlac and there not a brushmark on it. The only trouble with the long drying paints is dust, and in that what you wear when you are painting. Your suggestion of warming both paint and object is very good. Using a quality enamel you should NOT expect to get brushmarks.
 
Contrary to what many would say, an exhibition grade finish isn't actually that difficult, provided one pays attention to detail and is thoroughgoing about preparation. It can be a bit of a longwinded process in the preparation, but difficult - no. Its pretty mechanistic. You just do what you have to do, and it will work, especialy with high grade modern paints. With 2 pack its dead simple, because you get such a superb and durable finish straight off the gun, and you don't have to worry about viscosity, because it will be right if mixed properly.
 
One of the tricks is masking off. Finding a decent edge masking tape is not so easy. The commercially available DIY rolls are fine for attaching newspaper, but I found it tolerable useless for doing a paint over paint edge. Specialist auto paint suppliers do stock special tape for that which will stretch and flex to accomodate curves. The ordinary Tamiya stuff from model shops is pretty good too - thin enough not to leave a lumpy edge, and won't allow bleed under, and peels off very cleanly and easily too. Available in 10mm and 6mm wide. So I did edges with that, and then used ordinary for all the "filling".
 
Going on from Ramon's point - most of these paints will adhere very well so long as there is a good mechanical key and a non greasy surface, but I only stated that to make apoint. Here weight is not a problem so it makes sense to etch prime. I would disagree slightly in that from what I learned from the paint specialists in DQA, the degreased and abraded surface is far far more important than almost anything else.
 
As for 2 pack - sure its unpleasant stuff, but we are not professionals and we are not using it continuously indoors. Like you Ramon, I mixed it in a well ventilated place, and wore a mask, and stood downwind and sprayed out of doors.
 

Edited By mgj on 24/05/2011 12:38:56

Thread: Sieg Super X3 advice needed!
24/05/2011 10:42:25
I would bet that machine will work inside a thou - mostly its down to the operator, and a state of mind. Not a state of mind about fanatical accuracy for accuracy's sake, but because if you machine a slot or something, the bit you have made has to fit something else, and things work better if they are straight and level and to depth and dimension. So you can, for example, allow for expansion when things get hot, so they work first time as intended. And so forth.
 
Which saves a lot of grief and wasted effort - it also allows you to make certain things. Certain parts of Stirling engines have to be made to very fine limits. Certain parts of Ramon Wilson's small 2 strokes need to be dead on, or they'll never start. So being able to work inside a thou is not to be sneezed at, and it keeps the scrap bin empty.

Going on from that, 2 points.

It is as easy towork to a dimension as not - all you have to do is set the dial correctly?
 
If you have an accuracy problem, generally the job has not been secured properly, or the dials/leadscrews are not too hot, in which case it is very easy on most mills for £20 -£30 to fit the digital vernier type readouts in lieu of a full DRO if that is acceptable, and then all one has ot do is be able ot control backlash.

As for this machine being OK or not and subject to upgrade in the next few minutes - unfortunately no one can help you on that. You have to decide what you want to make on it, and then work out, in general terms, the largest component you are going to have to fit on it. (or accept that for certain things you will have to sub out)

Have you actually handled one of these machines or gone to see one in the flesh at an exhibition? Do you like it?

There is I suppose a general suggestion one can make about milling machines- you get the biggest, heaviest, most stable with the longest table that you can fit in the workshop, becaue one can normally always do a small job with a big machine, but it is less easy to do a big job on a small machine, and, other things being equal, surface finish is usually dependent on mass and the ability to absorb vibration.
Thread: Paint ????
23/05/2011 20:47:20
Almost all non ferrous requires an etch primer I think, but then if you speak to the paint kings they will also say that most metals require first a hot caustic degrease, then shot or suitable blasting and then another degrease before anything is applied. That is of course a cousel of perfection, and it is surprising to learn that paint will adhere very well in the absence of a lot of these treatments..
 
If the metal surface is good and well degreased and the paint chosen correctly you don't NEED an etch prime, or indeed any primer depending on the durability required and future use.
 
See comments about racing components.
 
However, for our purposes a good degrease followed by an etch prime and prime is a good idea, but I have seen some try to etch prime as if it is a primer, and paint it "wet". It isn't a primer in the conventional sense - its a chemical surface treatment, and one really wants no more than a mist, just enough to discolour the (well degreased) surface. Then you apply the proper primer, not just when its touch dry, but generally some hours after that, to allow the etch to do its bit, etch prime being an acid. It should be noted that etch primes performance is often badly degraded by grease spots/finger prints etc, so a good degrease is a very very good idea.
 
The OP mentioned spraying - Sealey do a very nice gravity fed touch up gun with fan spread control for about £25. you can mix up very small quantities(20-50cc) of 2 pack using a hypodermic syringe (sans needle), and cover a sane area with it, without wasting paint. And its very easy to clean too.
 
 
Thread: Machining what am I doing wrong?
23/05/2011 18:33:13
I beg to differ about carbide and feeds and speeds. Use it all the tipped tools at exactly the same speeds that I use with HSS - works perfectly, with several different makes of tips in both positive and negative rake configurations. For those who don't believe, go try it.(Yes I know carbide will go a lot faster, but its nonsense to suggest it HAS to - especially on a lathe where coolant is being used, for the very good reason that the coolant can go everywhere which is messy and uncomfortable)
 
As for all this advice to use HSS, well that's fine if he has a means of grinding it and the skill to grind it, at least adequately. If not, he's much better off with indexable carbide tips because he should have a tool which will cut and is of known quantity - and dare I reiterate, doesn't need to be run at warp speed to cut effectively.
 
So as with all things, let us start at the beginning.
Head drive belts are properly tight and not permitting skidding?
Are the lathe bearings good and not allowing deflection.
Is the chuck in good nick and not permitting movement (try the 4 and 3 jaws)(you are giving the chuck jaws something to grip ie your test bar extends right to the back of the chuck jaws?)
Is the tool at centre height.
Is the tool holder holding the tip securely and correctly - we had a case where the tip holder was causing rubbing. Look at it carefuly when iti s in place and you should see only line contact - if it is above centre usually you get rubbing. If below centre you can get tearing. check against a point cnetre held i nhte tialstock.
If you have a 1" bar are you cutting at about 4-500 rpm with a feed rate of about .005" per rev. (or metric equivalent) Because that will give you a good finish especially in 220M07 or free cutting mild..
Are the saddle and cross-slide gibs properly adjusted after having been degreased from new.
Is the feedscrew nut properly secured and is not permitting the x slide to bounce back and forth. And is the other end of the feedscrew properly adjusted by the handle.
When testing is the tailstock engaged to provide support.
Tool overhang?
Toolholder securely locked in place?
Ccorrect tips - you are not using some funny tip designed for some strange metal - ie you have a steel cutting general purpose grade?
You are using coolant - yes?(At which point a lot of people say they cut dry. Good luck to them, a dose of coolant produces a finer finish and tools last longer. My definition of a good finish is =/-.002" on diameter, and a mirror shine. )
 
If you have all those addressed, and it is still doing this, then you have a problem, but not until..
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