Turned out nice

[phileakins]

At the risk of throwing an explosive elephant into the room (and retiring smartly) one thing we have not discussed is the 'machine-ability' of metals.

As an example, I have two steel rods (different diameters) one of which machines beautifully, lovely finish whatever I do to it - the other is a b**ch to get a good finished surface on and generally looks like I've turned it with a plough: despite experimenting with tool tool angles/types and speeds!

I've read this document which shines some light on the problem - my concern now is to establish what the grade of steel (the scrounged rather than the bought variety) is without a full kit of laboratory test equipment. Indeed, is it possible? If not what the best way to guess the correct rotational (cutting) speed? There are different formulae for different steels from low to high carbon not to mention tool and stainless.

As as aside, I found this to be very useful in diagnosing my turning faults.

@ Brian - Thanks, I was hoping for illumination - and I got it! Not perhaps the one I was expecting, but one that pragmatically works. Lesson learned!

According to Antony Jay and Jonathan Lynn ('Yes Prime Minister') a courageous move was to be undertaken when all else had failed: and not even then - well done Martin.

 

[Brian McKenzie]

Phil,

I suspect your 'difficult' steel rod might be 'silver steel' (called 'drill rod' in America), which we hobbyists commonly use for axles etc for its nicely ground finish.

By comparison, free-machining steel bar (grade 12L14 or 'Ledloy' in my part of the world, not sure of the UK designation) is very easily worked and has widespread availability from both steel stockists and model engineer's supply outlets. One possible disadvantage is that its composition doesn't allow for soldering.

To improve finish along a long length of turning, you might try setting the tool at 1 o'clock position to the work. This accentuates a trailing wiping action, as in a machine with less rigidity the tool can then deflect away from the work, rather than digging in however minutely, thus spoiling the finish.
____________________
N.B. The video clip in message No.94 has the embedded title, 'Turning 304 stainless steel . . . .'
304 grade (the commonest) is what I had on hand, but do look out for and use 303 grade, which is the free turning version.
____________________

-Brian McK.

 

[Overseer]

At the risk of throwing an explosive elephant into the room (and retiring smartly) one thing we have not discussed is the 'machine-ability' of metals.

As an example, I have two steel rods (different diameters) one of which machines beautifully, lovely finish whatever I do to it - the other is a b**ch to get a good finished surface on and generally looks like I've turned it with a plough: despite experimenting with tool tool angles/types and speeds!

I've read this document which shines some light on the problem - my concern now is to establish what the grade of steel (the scrounged rather than the bought variety) is without a full kit of laboratory test equipment. Indeed, is it possible? If not what the best way to guess the correct rotational (cutting) speed? There are different formulae for different steels from low to high carbon not to mention tool and stainless.

As as aside, I found this to be very useful in diagnosing my turning faults.

@ Brian - Thanks, I was hoping for illumination - and I got it! Not perhaps the one I was expecting, but one that pragmatically works. Lesson learned!

According to Antony Jay and Jonathan Lynn ('Yes Prime Minister') a courageous move was to be undertaken when all else had failed: and not even then - well done Martin.

Start using the slowest speed the lathe will run at, turn some, then increase speed in steps until the surface finish deteriorates. Free turning steels should be ok without cutting fluid but if you are having problems cutting fluid will help. Generally the cutting speed for steel is much slower than for brass. If you find a steel that turns like brass it will be a leaded steel, 12L14 being the US and elsewhere name, can't remember the euro designation. If you get the bar end it may still have the paint colour the manufacturers use to identify the grades, from memory purple is free turning but it shouldn't be hard to find the colour code on line.

 

[Brian McKenzie]

. . . . my concern now is to establish what the grade of steel (the scrounged rather than the bought variety) is without a full kit of laboratory test equipment. Indeed, is it possible?

Yes, it is possible to identify ferrous types by a process known as the Spark test. This is very easily done using a bench grinder. The different materials when ground give off their own individual display of spark shape and pattern, unique to each type.

Googling, 'Metals Spark Test' displays some of the spark patterns, but none so clear as in the publication, 'Model Engineers Handbook' by Tubal Cain, a useful purchase for anyone employing machine tools.

-Brian McK.

 

[JimG]

I've read this document which shines some light on the problem - my concern now is to establish what the grade of steel (the scrounged rather than the bought variety) is without a full kit of laboratory test equipment.

Phil,

You can get an indication of what kind of steel you have by looking at the sparks given off from a grinding wheel. I know that I read this recently and it must be in one of my model engineering books. I'll have to have a dig through them and see if I can find the information.

Jim.

 

[Martin Shaw]

After Brian gave me a very useful critique of my tool grinding, I had another go at it and produced something that to my amateur attempts looked reasonable. I thought I would try it out this afternoon, a dismal failure, the work piece merely blunted the tool edge, disheartened the penny dropped, the tool I had so laboriously ground was in fact a carbide tipped tool and I had been sharpening the other end without realising that the manufacturesr wouldn't have used HSS for the shank, but of course mild steel. No wonder it wouldn't work. There is a benefit albeit as yet unrewarded, I think I might have grasped the basics of this grinding lark, ordering some HSS blanks tomorrow.

Phil raised an interesting point about metals, along with everything else I acquired a bucket of stock material, I separated out the brass to the workshop, but the steel remains in a heap on the garage floor. I just picked up the first suitably sized piece to test the lathe, but actually I have no idea what it actually is, mild steel I suspect but maybe not. Either way Brian is correct, Tubal Cain's book does give this info as well as a lot of other useful stuff, well worth acquiring.

Finally can I thank everyone for their support, it has been most helpful, especially when things weren't as I had hoped.
Regards
Martin

 

[adrian]

You can get an indication of what kind of steel you have by looking at the sparks given off from a grinding wheel.

You can also get an idea what steel you have by filing it with a cheap needle file. If it files the metal then it's mild steel, if it blunts the file then it's probably silver steel, if it blunts your decent files then it's probably tool steel/gauge plate!

 

[Martin Shaw]

Just a quick update. The lathe is all working, sort of. I'm still not happy with the rigidity, nor with the cutting abilities, which I'm sure is mainly down to the tools rather than the lathe. I think adjustment of the gibs is going to be necessary fairly frequently until it all settles down. Brass isn't too bad but steel is still pretty hopeless, according to literature a 1mm cut should be perfectly possible, hmm some way to go here. Ah well plenty to play around with.
Regards
Martin

 

[JimG]

Martin,

Are you using any cutting fluid when working on the steel? I find that the fluid helps a lot getting a good finish on steel. I apply it neat with a brush. Also, is your steel free cutting - EN1A? This steel has a small percentage of lead in it to promote good finishes and works very well on small lathes. Using other steels can give problems when trying to get a good finish.

I wouldn't expect to get a good finish from a 1mm cut - I would probably make a 0.8 - 0.9mm cut then finish with a 0.2mm or o.1mm finishing cut to get a good finish.

Jim.

 

[Ian_C]

Just caught up with this thread. Congratulations! A lathe massively expands the scope of what you can do. Don't expect much material removal rate from a small lathe, especially in steel. Better to just be patient and take small cuts. I have a shonky old Hobbymat and I've got used to taking off about 0.2mm per pass. Turning down from a sizeable bar is almost a Zen exercise- like water dripping on rock we will eventually arrive at the required diameter. Small tool helps too, and if you're not comfortable grinding HSS blanks or tools then a small indexable insert tool is a good way to go (you can buy them down to 6mm or 8mm square shanks).

Pay attention to gib adjustment. Worth taking some time over this. And it helps on small lathes to lock off the slide on the motion you're not using to keep things stiff.

Should mention that setting the tool tip accurately to centre height helps with cut and finish as well. Sooner or later you'll acquire a quick change tool post with height adjustment - and you'll wonder how you ever managed without one. Saves tons of time and faff.

I'll mention my experience of Sieg as a caution. All the Sieg machines are made in China. I have professional experience of engineering in China and what you don't get from China at that price point is craftsmanship. I have a recent Sieg milling machine and it's a decent, solid piece of kit. But....as delivered it was essentially unusable and I ended up stripping it down to components and completely cleaning/rebuilding it. That's fine if you have the tools and an engineering background. I imagine the Sieg lathes would be similar; you'll get plenty of cast iron in the right places for your money but you'll need to strip and rebuild to make it work well. Buying a Sieg from Axminster doesn't make it any better either!

Yes, you will end up with a milling machine too at some point. Seems to be the law! And that will again massively expand the scope of your modelling. Then you'll fit DRO and wonder how you managed without it. And then you'll contemplate a small CNC machine. Believe me it just happens like that.

 

[JimG]

You can get an indication of what kind of steel you have by looking at the sparks given off from a grinding wheel. I know that I read this recently and it must be in one of my model engineering books. I'll have to have a dig through them and see if I can find the information.

Found it - in Tubal Cain's Model Engineer's Workshop book



Jim.

 

[Martin Shaw]

Ian

Not all of my recent machine tool activity is in this thread, so actually I bought a SX2P mill first since I already had a Cowells lathe. As you rightly point out it is well enough made and no I didn't expect a Bridgeport for the money but I seemed to get it to a workable state far easier than the lathe. If you look in my "A5" thread you'll see some pics of enlarging bogie cutouts in frames done on a rotary table in the mill, which turned out pretty well, and I was modestly proud of. I chose Arc as a supplier because they seemed well thought of, the mill came in an R8 variant with brushless motor for quietness sake. I didn't have any existing tooling to match and it was the biggest both for access into my workshop and the pocket.

I had decided on the particular lathe but Phil brought a 10% discount offer to my notice and given what else I wanted to purchase it made sense to go for it. I have been exploring the gib issue on the model engineer forum and it seems I am far from the only one with this problem, which seems to be Sieg generated rather than an issue with the importers. The cut depth is partly due to the lack of rigidity in the whole saddle assembly, but also I'm sure due to my inexperience in grinding tools. I'm certainly didn't expect to become expert overnight, but I did feel the machine should be a bit more ready to use than it is.

Jim
The bit of steel I was testing with was lifted off the garage floor, what grade it is I have no idea. Cutting oil has yet to be acquired although for the small stuff I'm doing and on the right grade of metal it should cut well enough dry, all the other parameters being optimal of course, which they're currently not.

Thanks both for the thoughts.
Regards
Martin

 

[Martin Shaw]

There has been nothing much from me in the last six weeks due to life getting in the way, I won't bore you all with the details but September was c**p.

Just before Telford I had a discussion with Arc about the rigidity of the tool post and why I was getting a severe juddering at about a 1000rpm. The rigidity issue was eventually informed by a discussion on the model engineering forum which suggested the fit of the gibs was poor and the need to lap the dovetails. Out with the Brasso and much boring to and fro got them to an acceptable point, no rock in the slides but still twiddleable by the handles. They're still not perfect but usable.

Arc suggested that the judder might be caused by a set of particularly loose deep groove ball bearings in the headstock and recommended changing them to angular contact bearings, which were ordered to be delivered on my return from Shropshire. Now I'm old fashioned enough to think that machines should be maintainable without completely dismantling them, not this beast, so the headstock was stripped right down, the old bearings removed which was a bit of a challenge, and the new ones installed, which was an even greater challenge. I reassembled it sufficiently to test, with the sad realisation that all that effort had changed nothing. I then unplugged it, threw a dust sheet over the top, and got on with something vaguely more rewarding.

Some weeks passed and I thought that a more scientific approach than spanners was needed. I ran it for 30 mins to warm up the bearings and at that point there was no end float in the spindle and the bearings were still nicely tight which ruled out that. I clocked the register on the spindle and the run out is no worse than 0.01mm, or 0.4 thou if you want, so pretty acceptable. I fitted the 3" 3 jaw chuck which fits the spindle snugly, chucked a piece of bar and turned it concentrically. It clocked exactly zero run out, not the merest flicker, so the lathe in that form can produce perfectly acceptable work.

Trying the backplate for the 4" chuck, there is a slight but noticeable difference between the diameter of the spindle register and the recess in the backplate, and when the lathe is spun up the wobble at 1000rpm returns. Obviously bolting the chuck on as well merely amplifies the out of balance. It seems that the 4" backplate is the culprit. There is I think an oversize recess for the spindle register allowing it to be mounted off centre, and because it's a universal design for 3 and 4 jaw chucks the drillings are not equispaced which may also have a bearing. More discussions which I don't hold out a lot of hope for frankly and I think the answer is to take the spindle and chucks to a local precision engineering establishment and aske them to make bespoke backplates.

Way up thread

You are right to some extent, but it does seem a lot needs to be done to make the lathe usable. You clearly have the necessary skillset, but if a beginner bought one and then could not use it then the hobby could easily lose someone.

In all honesty if I had realised what I was letting myself in for I would probably have spent the money getting the Cowells remotored, and Neills right, it could well put someone off.

Onwards and hopefully upwards
Martin

 

[JimG]

Trying the backplate for the 4" chuck, there is a slight but noticeable difference between the diameter of the spindle register and the recess in the backplate, and when the lathe is spun up the wobble at 1000rpm returns. Obviously bolting the chuck on as well merely amplifies the out of balance. It seems that the 4" backplate is the culprit. There is I think an oversize recess for the spindle register allowing it to be mounted off centre, and because it's a universal design for 3 and 4 jaw chucks the drillings are not equispaced which may also have a bearing. More discussions which I don't hold out a lot of hope for frankly and I think the answer is to take the spindle and chucks to a local precision engineering establishment and aske them to make bespoke backplates.

Martin,

If it's a new lathe and chuck can you try negotiating a swap for another chuck in the hope that you might get a replacement with a more accurate fit on the register. It might be worth a try and a lot less expensive than getting bespoke work done.

I had a similar experience to you some years ago in trying to get an ER25 collet holder to fit directly on the register of my ML10. I got as far as three attempts by the supplier to send me one that was a good fit on my register but with no luck. All were oversize and the holders were tending to tighten up on the screw thread and be off-centre by quite a bit such that the collets were way further out of true than my three jaw. I eventually gave up and got a backplate from Myford which fitted well, and got a collet holder to fit the backplate. But there was a fair bit of email group exchanges at the time about the fit of these collet holders and I know that some people did manage to get products which actually fitted the Myford register. I think you might be suffering from the modern tendency for the quality checking being done by the purchaser.

Jim.

 

[Martin Shaw]

Jim
Thanks for your thoughts. I don't believe that the 4" chuck is itself the problem, the 3" one that fits directly onto the spindle is accurate enough, more that the backplate isn't as precisely made as it should be. I'm certainly going to have a talk with Arc about the way forward.
Regards
Martin

 

[Martin Shaw]

I had a discussion with Arc about the problem which in all honestly wasn't particularly helpful so I decided to contact the model engineering world. A gentleman suggested that plugging the unrequired holes would help. The chuck mounting holes are 9mm dia counterbored 14mm half way through, so not difficult but not easy either. Meanwhile another gentleman suggested the converse, bore additional holes either side of the common hole, the backplate is universal for 3 jaw and 4 jaw chucks. He suggested holes 0.7 of the dia of the existing. The rusty geometry persuaded me to calculate the volume of the counterbored hole and convert that into a dia effectively of 0.7, 8.12mm as it happens, so I settled on two 8mm holes either side of the common one.

The backplate set up on the mill and swarf being produced, even with some oil and taking the feed slow it would be easy to stall. I drilled it at 250rpm which is possibly a bit slow but no horrid noises were produced.


The modified one on the right showing the new holes. Anyway I put it all back on the lathe and lo and behold, great joy emanated from the workshop. There is still a slight wobble around 1300rpm but considerably less than there was, the bouncing around at 900ish has completely disappeared, and at last I can use the b****y thing for it's intended purpose. I will do the same mod on the backplate for the 4 jaw chuck but since that's almost always unbalanced anyway it's less critical. That's taken me very nearly 4 months of admittedly on/off effort to get this far, I'm somewhat under impressed.
Regards
Martin

 

[JimG]

Martin,

That's excellent, and with quite a simple method to resolve the problem. It sounds as if you are not the first, and probably not the last, to have the same problem. It could be worth letting Arc Euro know your solution in the hope that they might be able to persuade their supplier to modify the chuck back plates, although I believe it can be quite difficult to get Far Eastern suppliers to consider changing their products.

Jim.

 

[David Taylor]

I'm impressed you found and fixed the problem. Good news and I'm glad it is working properly at last!

 

[Martin Shaw]

Jim
I believe that Arc have the backplates made to their specification rather than importing it, and perhaps reasonably from a cost perspective have it as a universal item for both 3 and 4 jaw chucks. As I have found it falls between the cracks in both instances and bespoke items dedicated to each type of chuck would be better. I can't see any major barrier to this other than stockholding and when all said and done it is no more than a steel disc with holes in it. I will be letting Arc know my findings.
Regards
Martin

 

[Steve Cook]

A good solution to the problem Martin - seeing both backplates side by side, one can see how its out of balance in terms of material mass.

Out of interest, have you had to machine the mounting face for the chuck on the backplate, with the backplate mounted on the lathe? On my previous lathe (an ML10), I was given a four chuck to use with the three jaw. On mounting the four jaw it had an horrendous wobble, it turned out that that chuck had not been fitted to that lathe before. I split the chuck from the backplate, turned the backplate in situ, then bolted the chuck back up - no more wobble.

It might be worth running a DTI over the mounting face to check that it is running true, I never did on the ML10 as the wobble was visual. On the current ML7, every backplate has been turned in situ to suit each chuck, thus maximising accuracy.
Steve