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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: Parting off help!
28/06/2021 10:51:41

It is the lack of rake that makes life easy. I only use 4 deg (in the main) because I have toolholders that hold the blade at the optimal 4deg, so the top is ground flat and the toolholder does the rest. Grooving and everything else is done with zero rake.

I don't like having a rear toolpost fitted because on a small lathe it gets in the way, for me anyway. The only reason I tried it, was because of parting problems, and it offers no advantage - and you wouldn't expect it to. If one resolves the forces the diagram is exactly the same, front or back, and in particular the backlash space is on the work side of the feed nut either way round. (One day I will get round to making a backlash eliminator of the Myford! It has been on the to do list for 10 years now!)

So the concern is a component of the force on the cutting tip acting to drag the tool tip forwards into the work: if you have positive rake such a force exists by definition, and if you have negative rake such a force doesn't exist. But clearly some positive rake is helpful in promoting a nice clean cut and a good finish. But not too much. Hence limiting it to around 4deg.

That's for general purpose steel, but more grabby materials like bronze and copper need to be treated differently and the recommended angles are different. I normally use a commercial tip for them, because of the negative rake: that works without getting too involved with specialist tools.

DMB - the decent tapered Eclipse H5 blades are available - at a price. MSC do them. Interstate seems to be pretty good too. Seems to be a lot of "HSS" around much more cheaply, but it is I find, rather useless.

Edited By mgj on 28/06/2021 11:00:54

27/06/2021 23:47:17

Might be worth being careful how much rake you add - the more rake the more inwards force exerted by the cut there is, and the more prone to jamming.

4 degrees positive seems ideal, though the commercial tips tend to use a small amount of negative rake - negative rake generates an outward force of course, so they are very unprone to jamming or chatter. They also recommend mounting the little GTN series tips slightly above the c/l.(Largely stopped using them since they offer no advantage over the Eclipse blades at 4 deg positive)

I gave up using a rear toolpost - just took off the top rake, and used Eclipse 3/32 blades at the normal turning speed in the Myford turning 220M07 and haven't had any chatter or jamming problem since.

 

Edited By mgj on 27/06/2021 23:51:08

Thread: Master key - precision chuck.
13/06/2021 22:08:10

John - yes thank you. That is a very good old wheeze. I seem to remember reading it in The Amateurs Lathe by Sparey in around 1980 when I bought the lathe. Tubal Cain also mentioned it in some publication - perhaps the First Edition of the model Engineers handbook.

Poor man's Griptru, and it works well. Best, for repeatability if you always use the same socket to tighten.

12/06/2021 17:24:25

Thank you all. I have been away for a few days.

I know a 3 jaw is never the greatest for accuracy, and I also understand the difference between accuracy and repeatability. However, there are many jobs where an accuracy of just under a thou is acceptable, and having paid the cash, and never abused this chuck, I would like to be able to use it to its limits.

I shall give Pratts a bell.

04/06/2021 15:41:08

Old Mart thank you - that is exactly the faff I was on about. It isn't just about holding a single diameter bar. And indeed, on this chuck, the internal and external "best" sockets are different.

Depending on which measurements one is taking, in addition to a test bar, you need a fairly stout ring that won't deform, and at about mid range. This is a 6" chuck so a ring of wall thickness of around 3/4" and 4" id, turned truly concentric on both ID and OD is what one is on about.

So one needs a chunk of ali or 220M07 a couple of inches long and 6" or near in dia. Then I have to bore a 4" hole in it.

That to me is a bit of a faff, and not quite a simple as some have supposed. Especially as Messrs PB have already done the work!

So, back to the question - does anyone know the convention and my thanks to Neil Wyatt for the suggestion.

03/06/2021 18:21:56

Jason - no. Mine doesn't have that zero on it.

Zan, Thank you - I have a ground test bar.

I suspect a large ball bearing race would be a good external check.

03/06/2021 14:11:40

Jason - yes. The jaws are marked, like that, but which socket, for the chuck key, refers to which jaw? So is no 3 socket left or right of no 3 jaw?

With all the internal and eternal jaws, there is a lot of fiddling to find out by trial and error!

best. M

03/06/2021 13:01:42

I have a Burnerd super precision chuck (not a Grip - Tru). It is just a precision 3 jaw.

It came new with a bit of paper giving the master sockets, one for internal and one for external tightening, and for the 2 different sets of jaws. (and all the run-out for each).

The problem is, which socket is which. The jaws are numbered, but looking at the front of the chuck from the tailstock, is the master socket to the left or the right of that jaw? Because the sockets are not numbered.

Anyone know the convention?

Thread: A Welding Problem - Steel Type?
03/06/2021 12:49:19

I did once have a problem with a SIP that was difficult to control.

Turned out I was using .6 mm wire rather than the .8 for which the machine was intended (though a .6 tip was supplied with it) . The controller card didn't give me enough feed, even at maximum, so it kept burning back. You could weld, but it wasn't great, and I could never balance feed and amps properly.

Might be worth checking, because the right wire restored normal service perfectly.

 

Edited By mgj on 03/06/2021 12:49:58

 

Edited By mgj on 03/06/2021 12:51:50

Thread: Spindle not running true
30/03/2018 18:22:22

I'd agree with Jason - if it was OK before and you didn't brutalise anything when it was apart (includes misplacing shims and so forth), then I'd look at what has changed.

I would check the assembly very carefully, and I think I'd have a scout about to see if there is a blob of paint interfering with anything, or preventing some housing from closing up as it should.

I think it would be most unwise to start hacking at metal until you identify what is wrong.

 

Edited By mgj on 30/03/2018 18:22:43

Thread: Teflon Spray ?
08/09/2012 12:11:37

One of the reasons many of these products don't perfom as well as one might expect, and others seem to get them to work well, is because occasionally people don't think about what the material is doing and how it works. It is important to use them intelligently,

If you have a thin type penetrating oil which disperses water out of a crack. (WD, 3 in 1 and many others) thats grand, but the water hasn't gone away (as a matter of principle) Its simply moved elsewhere. Eventually the oil will float (depending on evaporation rates of the wateretc etc.)

So the trick, in watery conditions like the bore of a steam engine, or tools in a poly bag full of damp air, is to dry the water off and respray. (With say a loco, its easy - pump the stuff in, spin the wheels a few times, and then respray, and no risk of a cylinder full of heavy oil creating a hydraulic lock next time. )

------

Again, I think it most unwise to say what will or won't stick to what, not unless one actually knows the subject. The chemists these days really have their act together, and just because a material is ostensibly slippery, it doesn't mean to say that it won't stick to something, using electrical bonds and the like. For instance preservative greases can look the same as any other grease, but have very poor charactristics under load. Some oils can be very good at rejecting water, cling to surfaces but reject small particles, and not be made of "oil" at all, but for example glycol.

So generalisations can be - misguided or possibly just out of date.

08/09/2012 09:20:27

Obviously your rust is different from mine. Keeps bores perfecty clean and stops rings sticking. But like all of the lighter low viscosity materials, its best if left alone and not rubbed off. Still if people don't like WD40, they would be better off using something else. At the end of the day, all that most of these oils do is provide a simple barier between oxygen and air.

If I wanted to keep tools and the like clear for extended periods then I'd use a proper ph controlled preservative grease like the military PX7. Or something really heavy like chainsaw oil because that really sticks and you will need white spirit degrese properly, but it isn't ph controlled.

 

Incidentally Geoff, I didn't think that an IC engines rings depended much on oil. A lot of IC engines have oil scraper rings precisely to remove (almost ) all of the oil from the bore. The advantage of WD40 in those circumstances is that it removes the old oil possibly - darned good thing - it will be acidic, and contain a fair proportion of fuel, (up to 10-15% by volume for a relatively unworn engine, more for an old design) and replace it with a fresh light preservative, which will stop them sticking. But of course one doesn't then want to turn the engine over.

 

What happens when you use the choke/ECU on start up, if the rich mix doesn't wash the bore clear, or nearly so?

Edited By mgj on 08/09/2012 09:21:04

07/09/2012 18:45:29

Well WD40 bonds at a molecular level with the substrate and displaces water. I use it squirting a blast into cylinders to prevent water rusting the bore. You know it will bond with hte base iron very aggressively.

But its not a lubricant as such, as Coal burner said. Teflon is,

 

Will WD40 prevent rust - very effectively, and for years. Obviously Because if a molecule has had its bonds taken up with a non oxidising agent, they are not available to be taken up by oxygen atoms.In principle at least. Thats pretty basic chemistry - and most oils don't work that way - they just coat (or that used to be true, less so now).

However before one says Teflon is this and something else is that, one wants to know what the properties of the carrier are. - since in general teflon will reprent a very small proportion of the total volume. So before saying the one stuff is better than another, one really wants to look at the tech spec, and see what it was made to do, and use it for that purpose.

Edited By mgj on 07/09/2012 18:46:56

Thread: Dormer drill bits
06/09/2012 17:02:16

Possible best to ring Dormer and get a definitive answer?

Thread: Elephant Hawkmoth
19/08/2012 09:05:55

Well as a failed humming bird hawk moth photo taker, I like it.

We always used to get the HBHMs on the valerian outside my window. Every year. Wonderful to watch them. But not this. They are susceptible to cold winters and we are on the limits of their range.

Hopefully next year.

Thread: Whistles
18/08/2012 22:15:12

I rather agree.

I have a couple of traction engine whistles in service. They are adjustable, in that the bell screws down for tuning.

You can set them on air, but they always require a bit of additional tweaking to get them working really well on steam. So if you are going to set a whistle on air, you need to be sure you have set it right in the middle of the range, because it can end up sounding pretty feeble on steam.

There was a good article on sizes and dimensions. The original was published as an SMEE article, but it then appeared in ME quite recently under the heading of "Wheezeless Whistles". It will contain all that one needs to build a good whistle.

Edited By mgj on 18/08/2012 22:15:47

Thread: Parting problems
16/08/2012 20:32:25

I'm sorry but it is simply not true that a rear mounted parting tool moves away from the load. That old chestnut has been around for years, and I am afraid that a lok at the vectors involved prove that is oversimplified and wrong If it was right the tool wouldn't jam up at the back - and it can.

Draw it up - its easy to see.

img.jpg

 

The force acts at right angles to the face of the tool - on the top rake.So it has 2 components - some downwards(at the front) and critcally, some inwards Put that point above centre at the rear and you create a situation where you have an inwards force pulling into thinner material if things go wrong so its tending to unload. Put the tool below centre then you have an inwards force digging into thicker metal.

Do the same drawing from the front, and you can see the forces are the other way around but otherwise identical. And you would expect that since the tool and the job have no idea where they are.

What  is needed is an argument that explains how it jams both front and back, and why its less likely to jam at the back. And thats pretty simple, once you look at the mechanism.

Waht you have to do is take off the inwards force - take off the rake, you remove the inwards vector and it doesn't jam. Look at the commercial indexed tools and they are all almost zero or negative rake.

How does it work - You dig a tool into the material, you generate that inwards force, but the feed is greater than that inwards force so the tool is kept under control in the backlash gap - its jammed against the feed nut, and it cant move forwards. Reduce the feed, the cut is insantaneously identical, but that pressure is removed - it is now free to pull in, which it will in the backlash in the feed nut. Which is why most of the time these jam up occur when the operator is being careful

If you get rid of the rake and maintain a steady feed, you find that jam ups are a thing of the past. I have apile of tools and kept putting on rake, because it looked sharper. Bought about 10 different models to try to solve the jamming problem. The identical tools, reground don't jam any longer - no top rake. And I don't part off from t he back any longer. If anyone wants a genuine Myford rear parting toolpost they can have it. It is perfectly useless and offers no advantage. PM me!

 

Why doesn't it jam up at the back so much - less feednut backlash, because normally that face on the screw is only ever used to retract a tool under no load. But put enough rake on and it will jam at the back, and very easily - that I promise. Got that tee shirt.

 

BTW tools have to be straight etc as well - thats understood. As is the fact that tools must give vertical glearance. I do agree though that the Sandvik 2.5mm tool as fitted to the Kit Q Cut cuts better than the GTN2 fitted to the Glanze and others.  But not by much, and hte GTN is a lot cheaper and made by many people.

Edited By mgj on 16/08/2012 20:35:06img.jpg

Edited By mgj on 16/08/2012 20:38:08

Edited By mgj on 16/08/2012 20:43:54

Thread: Frame Problem
16/08/2012 16:45:47

I'd have thought he's entitled to an answer if one is available - after all thats why he posted the question. Still one continues to see the kind of warm and friendly attitude, allied to useful and accurate advice that persuades me to visit but rarely.

I wouldn't worry about the oil creeping - the paint isn't going to get into places, and longer term the oil in there might do good. I'd just give it a spray of oil personally and put it aside. I've used penetrating oil on the joints for good reasons. Then come the day, give it a good scrub with a brush in hot detergent and get it warm to dry. (If you are brave enough and use gloves, then very hot caustic is pretty good, but be careful - eye protection and all that stuff) Prime and top coat ASP

Priming at this stage - depends on how long you want to keep it, but most primers are porous. So there is a limitation there.

Edited By mgj on 16/08/2012 16:47:46

Thread: Turned items are not looking good ...
15/08/2012 22:10:53

I think I would look at the chuck as well. I don't think that has been mentioned, and if it has a bus pass, or not been looked after, the jaws may not be holding correctly.

Give the lathe a tune up (it probably deserves it), sharpen all and ensure you support the work properly too, with minimum overhang. But before despairing, mount a job in another chuck/collet/faceplate/4 jaw, and see. Culprit could easily be a dodgy 3 jaw.

Thread: Machinability of Drill-Rod
14/08/2012 19:18:01

Drill rod is what they call silver steel. So it will machine like any high carbon relativley high strength steel. Silver steel or gauge plate in the soft condition of course.

If you need to know precise details, then you'll need the ANSI spec for that grade which will only be a google search. If you don't know precisely which grade you have, then ask the supplier, and you can cross refence from there.

What were you going to use it for is the next question. Making tools - then probalby one ought to finish grind. If its for pegs and dowells any grade will do. If for driving pins, then case hardened mild will be an easier to machine and give a harder result.

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