Things they don’t tell you in the books so I’m asking you lot

[John CoatesParticipant @johncoates48577]

Well I must admit I had a good look at the Barker when I ventured into the garage last night between 8 – 10pm. A bit nippy but several layers and working under three lamps helped warm me up

 

Had a need to make some 5mm thick 20mm dia 8mm bored washers to help fix the new chuck to the mill table as the 8mm studs I had made had bent the thin washers I had borrowed off some bolts.

 

Thinking about what Chris S had said I rotated the top slide to 30 degrees from the lengthwise axis so it cleared the tailstock and took all my cuts with it in this position. And I must say it made a real difference to working with the lathe. Facing, turning down to 20mm dia, drilling out to 8mm, were all a doddle.

 

Other than having to swap the speed wheels over to switch between high speed turning and low speed drilling and parting, it was a lot better. But then I am slowly buying the bits necessary to go 3 phase so soon all that gear swapping won’t be a problem.

 

You guys with apprenticeships behind you have an advantage in knowing what to do and I am glad you pass this on to newbies like me. As I said, some of the basics as to how to orientate the top slide, take a cut, are missed out from some of the books.

 

John

[TerrydParticipant @terryd72465]

Hi Chris

 

I use a taper turning attachment on my Boxford, and the 1.5mm would be a roughing cut, my final finish cut would be no more than 0.1mm, sorry if I gave other impression.

 

Regards

 

Terry

[John OlsenParticipant @johnolsen79199]

I think even a fifty year old Bantam is going to be a bit more rigid than my 55 year old ML7.

 

Actually, we seem to accept that a boring tool will almost always have some spring in it, and take sometimes 3 or 4 passes before it has taken all it is going to take. So why is is surprising if an outside turning tool sometimes does that too? If the top rake of the tool is absiolutely ideal for the material being cut, then I guess the force on the tool should be about neutral, eg not pulling it into the cut or pushing it out, so it would cut to the exact size and not cut more on the way back. Realisticly this is rarely going to be the case, sometimes it will have flexed slightly in on the first pass, so will not leave the spiral, and sometimes it will have flexed away from the job. (The job may also have some spring in it.) (The ideal rake would probably also vary with the depth of cut….)

 

The bit about the top/compound slide not clearing the tailstock sounds a lot like a Myford, although of course other lathes have this problem too. It is one of those things, do you make the bits as big and strong as you would like or do you leave room to work but make them weaker?  GHT designed that slide for the Myford with the gears to at least move the handle back a bit. It is really annoying when it almost works except you can’t quite turn the handle ! A local here has had a casting done for a tailstock with more clearance. It may also be more rigid, which is another thing where the Myford could be improved.

 

regards

John

 

[Steve GarnettParticipant @stevegarnett62550]

Posted by John Olsen on 16/11/2010 09:42:15:

Actually, we seem to accept that a boring tool will almost always have some spring in it, and take sometimes 3 or 4 passes before it has taken all it is going to take. So why is is surprising if an outside turning tool sometimes does that too?

 

Simply because we know that with the boring bar, the force is being applied transversely, across the thin cross-section that isn’t supported? Not the case at all with the force applied to the outside tool, with significantly less spring. I would say that the chances of spring being the cause of axial movement of an outside tool were rather less than, say, even the slightest amount of slack in the gibs of either the compound or cross slides when taken out of cutting stress. I’ve proved to my own satisfaction in the past that this can make a difference.

[chris stephensParticipant @chrisstephens63393]

H Guys,

To comment on recent posts;

As a general principle I have my compound slide as far to the left as I can get it whilst still not exposing any dovetail. The reduces any overhang to the minimum.

Can’t recall suggesting rotating the slide to 30 degrees, but if it works I am quite happy to take the credit.

 

I thought a taper attachment would be involved, power feed does improve finish, if for no other reason than that it produces a “steady state” cut that where all bending or slackness is consistent. Hand feeding can lead to unevenness because small but inevitable pauses in handle turning. 

 

Steve has said it all, boring bars are by their very nature flimsier than turning tools, but I take John O’s point that we expect boring bars to flex and work around it. 

 

This thread has brought up an interesting point, any self taught machinist might not know what he should expect of a turning tool in the way of a finish. If you don’t know what to expect how can you try to achieve it. I do see that anyone learning from a book or magazine and only having photographs to judge by is at a loss, just as publishers have problems trying to convey such information through grainy images. It is fairly easy to portray a torn surface but a shiny one gets lost in flare. It is rather like trying to show a picture of a mirror, but without any reflection in it.

chriStephens 

 

[Anonymous]

Just out of interest, while having my 11am coffee break, I’ve measured a few of my turned surface finishes. The range was from 0.2µm Ra to 6µm Ra. This was on a mix of aluminium, stainless, EN24 and cast iron. A fingernail test against a Rubert scale confirms that the results for the rougher finishes seem about right. I’m not surprised about the rougher finishes; I’m deliberately using fairly high feedrates, about 0.2mm/rev, but the finish is appropriate for the purpose.

 

I’ve learnt the hard way that to get a good finish on steel with carbide inserts you have to run at the appropriate surface speeds, otherwise the material tears.

 

The provenance of the material is also important. The first steel (EN1A from company X) that I turned on my lathe gave a very poor finish. I tried varying everything, speed, feedrate, depth of cut, coolant – no effect. The material would turn nicely for a inch or more, and then tear. I was really disappointed and upset, having just invested a lot of money in the lathe. Coincidentally, at the time at work I was liasing with a local machine shop to get some CNC milling done. I asked them about metal suppliers and they said, unprompted ‘oh we don’t use X, their steel is rubbish, we use Y’. I bought some EN1A from Y, and what a difference! Nice finish and consistent along the whole length, about 500mm. Companies X and Y are both trade suppliers. You live and learn!

 

For roughing I’ll use a DOC of between 0.04″ and 0.15″ and a feedrate of about 0.01″/rev. Finish cuts anything from 0.001″ to 0.04″ and feedrates from 0.002″ upwards depending upon the finish and accuracy required.

 

Right, back to work and PCB layout.

 

Regards,

 

Andrew

[Ian S CParticipant @iansc]

Just been making a fairly long single throw crankshaft, 8mm dia this evening, turned between centers, now theres some spring in the works. I’v been using .200″ DOC on 1.5″-2″ MS don’t know the grade, thats with HSS tools, with carbide I up the feed and speed, and reduce the DOC to .050″-.080″ these are roughing cuts, time taken works out fairly similar, unless I’m using 4140 steel as I do quite a bit, then the carbide speeds things up a bit. Yes its the same here about the same grade steel being different from different suppliers, or some times our main supplier trys to give use the rubbish.  Ian S C

[John CoatesParticipant @johncoates48577]

Posted by chris stephens on 16/11/2010 11:22:57:

 

This thread has brought up an interesting point, any self taught machinist might not know what he should expect of a turning tool in the way of a finish. If you don’t know what to expect how can you try to achieve it. I do see that anyone learning from a book or magazine and only having photographs to judge by is at a loss, just as publishers have problems trying to convey such information through grainy images. It is fairly easy to portray a torn surface but a shiny one gets lost in flare. It is rather like trying to show a picture of a mirror, but without any reflection in it.

chriStephens 

 

 

A nail and head impact point Chris

 

Exactly what I was trying to say. All the books (WPS, Sparey, Geo Thomas) I have bought presume a basic level of familiarity with what is trying to be done that they don’t cover it. They will talk about DOC, feed rate, speed etc but it takes a lot of trial and effort (and smashed tools I found) before the learning process starts to fill in those blank bits that were probably the foundations of apprenticeships. This is probably because they are aimed at the professional engineer turning their hand to home / model engineering and are talking peer to peer. Mind you reading some of the tales about apprenticeships on the web it seems to have involved long periods doing mundane stuff before you got to get hands on with the machines.

 

Ah well back to the learning – tonight, once the kids are bathed and in bed, when the garage is nicely cool, as I’m at work now !

 

John

[Anonymous]

Hi John,

 

May be I’m cynical, but in my experience a good number of professional engineers are completely clueless when it comes to actually making things.

 

Only yesterday the managing director of the company that does some of our electronics assembly was telling me that they had turned some assembly work away as it simply wasn’t possible to assemble the items as designed. Well, not without the aid of a sledgehammer. Even more worryingly the engineers that had ‘designed’ the assemblies couldn’t see what the problem was until it was forcibly pointed out.

 

Regards,

 

Andrew

Edited By Andrew Johnston on 16/11/2010 13:20:09

[chris stephensParticipant @chrisstephens63393]

Hi John C,

Like you, I have read many books on model engineering, and none come to mind that are written by authors who have put themselves in the position of rank beginner, before putting pen to paper. This is unfortunate but understandable, once you reach a certain level you forget what it was like when you started and  are, now, more interested in showing the “clever bits” and not the mundane.

SMEE are doing their best by running short beginner courses, but to be fair this only really  covers the SE region, although some come from much further afield. At the Ally-Pally Show (sorry to mention the opposition David), this last January we had a lathe set up for complete beginners to try their hand, with some success I might add. In truth some of the children were not only complete beginners but the did not know what a lathe was for and were prompted to have a go by “gramps”!

If complete beginners are not catered for, our hobby will surely and inevitably die through natural wastage.

chriStephens 

[KWILParticipant @kwil]

I was talking recently to a member of staff from a major MOD oriented establishment who said exact;y the same as  Andrew,  their “Engineers” had designed the stuff but “they” would not go down to the workshop where it was, I presume because they would not understand the processes the workshop would have to undertake to achieve “their” designs. A bit like spanners and dirty hands I suppose.

[David Clark 13Participant @davidclark13]

Hi Andrew

I came across this once or twice.

On one occasion the design called for a 12mm threaded hole through a 12mm wide and 3mm thick bit of stainless.

I told the boss what I thought of the designer (far to rude to publish here) only to realise the designer was stood next to him.

regards David

 

[Richard ParsonsParticipant @richardparsons61721]

 

I know the feeling. I once worked for a MOD orientated outfit. Some ‘Engineer’ had designed something which just could not be made to the degree of accuracy he required. The darned things just would not work properly. Eventually they had to call in help which came from the commercial systems people (the only other people who could read their programming code. During trying to de-bug the gizmo I found stupidities in the code (comparing real to integer) screens which did not mean what they said etc. Would the Engineer answer my questions? Not on your Nelly. He complained to the Boss that if I could not understand the specification (2 pages of ramblings) why had it been given to us idiots to sort out. I could not even find out from him what the thing was supposed to do. Eventually I found that from ‘Sales’. Once I knew that I did the proper analysis, wrote the specification and had it programmed.  I even found some variables which the Engineer had ignored. Weird things ‘Virtual Stable Tables’.
Yes it works but it is still not quite as accurate as it could be It is about.  It is about 20 mm out after 14 days.  The problem is the direction and speed out galexy is moving through  space. 

The day you stop learning is the day to get your wooden overcoat.

Edited By Richard Parsons on 16/11/2010 15:38:35

[The Merry MillerParticipant @themerrymiller]

In my experience of managing teams of engineers and draughtsmen, within an R & D environment,  I found that the best  mechanical design engineers I had working for me were those who had progressed from an engineering apprenticeship into the drawing office.

They would start as a detail draughtsman  with the ambition to reach the giddy heights of a design draughtsman and subsequently become a “Design Engineer”.

 

These people were usually top of their class and were highly sought after.

 

The number of occasions when I had graduate mechanical engineers in my group I found their lack of practical experience, (in most, not all situations) to cause many embarrassing moments.

 

Len.P

[Peter G. ShawParticipant @peterg-shaw75338]

Just like to add a couple of comments.

 

I am not a trained machinist, and as a consequence, I do not know what is acceptable finish. Fairly obviously, if you can feel ridges then it’s poor, but just what is acceptable finish I do not know. I know that the finish required is dependant on the usage, eg for a bolt it probably doesn’ need to be superfine, but for a plain bearing it will need to be somewhat better. But how much better? In my situation I can only experiment and hope for the best. I suspect that there a large number of newbies who are in the same situation, hence any pictures which show a desired, and for that matter undesired, finish will be helpful. For example, Harold Hall sometime ago did some experimenting with milling and published some photos showing the different finishes achieved on a piece of steel by milling on one direction and then in the reverse direction. This, to me, was most helpful, as were the comments about blunt cutters. As is the comment above about different suppliers supplying different versions of what was supposed to be the same steel. Pity the writer didn’t feel free to say who supplied the best, although I can understand that there could be legalistic problems.

 

My second comment is about David Clark saying what he thought of the designer. Good for you David. It is high time that a few more designers were told upfront about the shortcomings of their designs, and here I have in mind a semi-circular glass cover that “Erin” has. This thing is heavy, and has a silly little square glass “knob” with sloping sides. The design is such that the base of the “knob” is wider that the tip, hence your fingers simply slide off unless you squeeze very hard to get a grip. Turn the “knob” around such that the slope was in the other direction, and it would be very much easier to use. This is an example of very poor design where the designer has been more concerned with looks than practicality. Of course, “Erin” doesn’t see the problem. Mind you, I haven’t seen it around for some time,so maybe she has quietly got rid of it!

 

There are, of course, a lot of other items that are simply poor design, but it isn’t necessarily “looks” design. For example, I had two Maxis. In general, we found them to be very good practical cars – except that there a number of poorly engineered features under the skin of the car, eg, rubber butterfly joints that failed regularly, primary drive gear oil seal which failed regularly, etc. I’m sure we can all find examples of poor design both in the engineering and in looks/usage.

 

Regards,

 

Peter G. Shaw

[The Merry MillerParticipant @themerrymiller]

As an addendum to my last post, some of the better design engineers went on to gain a degree in some branch of mechanical engineering after being sponsored by the company in that respect.

Guess what happened  next after they obtained their degree, they were wooshed off to the sales dept, (for a better salary in most cases) and so lost to engineering for ever.

 

Some did regret the move but the lure of the higher salaries and a company car was a very strong attraction.

 

Len P.

 

 

 

[Anonymous]

Peter,

 

Just because you can feel the ridges on a surface finish, doesn’t mean that the finish is inadequate. It’s what is appropriate for the circumstances.

 

If you look in my odds ‘n’ sods photo album there is a picture of a Rubert surface roughness scale. On the little rectangles in the bottom right, for milling and turning, the first few blocks have clearly visible ridges. I doubt the makers would have bothered to do this if those kind of finishes were not acceptable in some cases.

 

Surface finish is as much an art as a science, which is why there are so many ways of defining it. As I’ve recently found out even professional machinists don’t always understand it. I think it is very difficult to convey the different surface finishes via pictures. The ‘fingernail’ test is remarkably sensitive, which is why the Rubert scales were produced in the first place. See this link:

 

http://www.rubert.co.uk/Comparison.htm

 

(I don’t seem to be able to post it as an actual link, grrrrrrrrrrrrrrrrr!)

 

Regards,

 

Andrew

[ChrisHParticipant @chrish]

As a PS to the “designer is an idiot” theme, on a ship one day we had a graduate engineer, very well qualified, far superior to us poor mortal engineers with dirty hands and boilersuits who were running the place.  For his degree he had written a thesis on marine boilers.

 

Whilst being shown round the ship’s engine room he asked what these great big blocks were, 20ft square by 20ft high each, or thereabouts.  The exact dimensions are lost in time, and don’t really matter. but very big lumps of kit.  There were 2 of them.

 

That is the boilers we told him – you remember, you wrote a thesis on it………………. 

Edited By ChrisH on 16/11/2010 18:03:59

[Sub MandrelParticipant @submandrel]

One irritating bit of poor design. The Mondeo had a small tube taking coolant from the front to the back of the engine, underneath exposed to all salt spray, road grit etc. Galvanised mild steel. Apparently my experience of the tube rusting through from the outside and dumping all the coolant on the road in a few seconds was ‘normal behaviour’ for a Mondeo of its moderate mileage.

 

Neil

[Anonymous]

Hi Ian,

 

Blimey, 0.2″ DOC on steel! I’m obviously being a big girls blouse when it comes to roughing cuts on the lathe. What sort of speeds and feedrates are you running at that DOC? And how many horses power your lathe?

 

Regards,

 

Andrew

[Sam StonesParticipant @samstones42903]

For the benefit of an ignoramus who no longer has the books, what’s a DOC?

Regards,

 

Sam

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Sam, I’m taking it to mean Depth Of Cut.

 

Regards Nick.

[Peter G. ShawParticipant @peterg-shaw75338]

Andrew,

 

Thanks for that, and yes, I do understand  about horses for courses.

 

Now, back to the comments about poor design, I have three examples of what I would consider to be well engineered designs.

 

One was a Bendix washing machine which ran for 17 years without any major problems until the alloy spider which supports the drum corroded until it became so weak that it collapsed. It’s predecessor lasted 5 years before becoming uneconomic to repair. This machine I should add was hammered by our bringing up three children.

 

The second is a Mitsubishi TV bought in 1992. At 6 months old it had water from a vase poured into it, but swift application of a wet & dry vacuum cleaner followed by the use of a hot air gun and it lasted a further 17 years without a problem. Then it needed a capacitor change to restore full functionality. Just recently, a further two capacitors have failed and been replaced to restore full working. Total cost about £1 for all three capacitors. But, interestingly, all three capacitors were on a sub-board which required the removal of six or seven plugs, two screws and two clips to take it away to a place of comfortable working. Now that to me is good thinking.

 

The third is my H68V Black & Decker mains drill bought in 1986. It has been used for a lot of heavy work – masonry drilling, steel drilling, wood drilling etc, and it wasn’t until last year that it suffered it’s first failure – a short pin about 12mm long and 4mm wide. I looked at buying a replacement, but the prices for one of a similar specification – 400W+, electronic trigger controller, and a 2-speed mechanical gearbox –  were astronomical. Replacement pins not being available, I made one myself – and it now works again. Previous drills simply did not last.  

 

Peter G. Shaw

 

[Sam StonesParticipant @samstones42903]

Oh sHOnet !!!

How obvious!  Mutter mumble.

Clearly, only an ignoramus would ask such a question. Especially one who’s been applying DOC’s for about 65 years without knowing it. AND worst still, one who has been surrounded by plastics acronyms since 1950.

Perhaps for us oldies (who, like me, are too lazy to work them out), ME could collect and build a useful acronym glossary?

Thanks for coming to my rescue Nick!

Regards,

Sam

Edited By Sam Stones on 17/11/2010 21:32:55

[NJHParticipant @njh]

Hey Sam

 

Be easy on yourself – the only ignoramus is the one who doesn’t ask the question!

 (Now I knew about this as I used the DOC the other day for a FLU .) 

 

regards

 

Norman 

Edited By NJH on 17/11/2010 22:57:49

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