What Did You Do Today 2020

What's the leadscrew pitch?

Neil

And second prize goes to...........Neil, for an interesting idea. The leadscrew is 4tpi, so pitch is 1/4". But why second prize? That's because it's an industrial lathe, so the leadscrew is reserved for screwcutting. The power feeds are driven by a key that slides in a slotted shaft.

It has prompted me to go an measure the bands though. They're nearer 5mm apart, but are inconsistent. Some are 6mm, and some way more than that. The finish does seem to vary slightly within each band. I don't know if the same occurred when roughing as the finish was awful; torn and rough as a badgers rear end.

I don't generally have this problem with EN1A. I have seen something similar once before when I was starting out. The material was supposed to be EN1A, but it would turn beautifully for a varying distance and then suddenly change to rough, and then back again. I got thoroughly depressed and was considering following the advice of the late JohnS, vis take up knitting. The steel was bought from an engineering tool shop in Cambridge. At the time I visited a local machine shop to discuss getting a box CNC machined for work. I mentioned my problem and they said "we don't buy from X, their material is crap".

Andrew

I once had a similar problem on my Harrison L5A, I tried just about everything to no avail.

It eventually turned out to be a faulty cage in the front taper roller bearing, new bearings were fitted 25 years ago and it has been OK ever since.

Phil

What pitch is the rack along the front of the bed?

Would be interesting to try a straight cut once you have finished doing the chimneys to see if you still get the pattern

A rough estimate of rack pitch is 5.5mm, which corresponds to Mod1.75, give or take a bit.

Andrew

[ At the risk of attracting ridicule from Hopper ]

Have you considered the possibility that the gear driving the slotted shaft is slightly eccentric ?

This could induce a number of interesting cyclic variations.

MichaelG.

Maybe just changing feet while I open my mouth here, but...

I do not know that lathe at all, but is that a taper turning guide/attachment/mechanism hanging from the rear?

If not, how did you cut the taper - using a taper guide plate of some sort? What keeps the cross slide bearing up against the guide? Or does the lathe have a change gear set that drives saddle and cross slide synced somehow? I would presume the finish has something in whatever mechanism controlled the taper section..

Both feet firmly in mouth now..

Joseph

the device at the rear of the lathe is a Colchester-Hepworth hydraulic copying attachment. You can see one in action on Keith Fenner,s Colchester-Clausing lathe on his you tube channel.

I don,t know its details but the rear mounted tool post follows the path taken by a stylus in contact with a previously prepared pattern mounted at the rear of the lathe bed as the saddle advances.

HTH

Dave

In a word 'no', but I haven't seen the effect before, either sliding or facing.

Andrew

DD is correct, it's a hydraulic copy unit. The tool on the back of the cross-slide is driven by a double acting piston. The T-shaped extension below the tool slide carries a stylus that replicates the shape of the tool. Through a series of valves and channels the tiniest movement of the stylus unbalances the piston so that the tool slide moves until the pressure on both sides of the piston is equalised. The effective gain is high so there's almost no error in following the path. The movement of the tool in and out is controlled purely by the template. The axial movement is controlled purely by the lathe feed mechanism. The slide is at an angle to the work so that at the end it can move perpendicular to the work. If the slide was perpendicular the feedrate would need to be infinite.

The shape and, to some extent, surface finish is determined by the quality of the template. Although my template is filed as I don't need great accuracy it would be surprising if I'd got a small ridge almost exactly every 5mm. Especially as I finished by draw filing in short lengths.

I've used the unit on other parts and not seen the same effect, albeit the parts were much shorter.

The mystery remains unsolved.

Andrew

Andrew,

Many thanks for the pictures. I have seen a similar effect previously on some questionable grade material so my guess would be an inconsistent material, several of your comments would support that particularly I think where you referred to the roughing cuts and a similar change in performance with the 'torn' finish. I doubt it is anything to do with your machine given you have not noticed a similar effect previously, I am sure I have read accounts of instances where you have used the hydraulic copy attachment for other components previously on TT? The fact that it appears visually regular but when measured confirms it is more random would tend to support that. I don't remember if you have a hardness tester but it might be interesting to take some comparative hardness readings between the more pronounced areas of the finish? I can't really think through how impurities may be unevenly distributed through the bar from melt to final rolling but I suspect it could be to do with the composition and the action of the working to produce the bar.

I have a friend who has a business running several automatics and he has commented in the past of having batches of bar, supposedly of a standardised quality that gave this kind of finish on the components which caused them to be rejected which was fixed by nothing other than changing the source of supply without any resetting of the machines (this was all bright bar). On tracing back the material the poor finish batch was from an Asian source, the good replacement from Germany. There is often comment re steel from Asia being poor due to its recycled origins, I do find that difficult to understand sometimes as a solid with the supposed same chemical composition from different sources (according to the material certs) but there does seem to be something in it - behaviour of boiler tubes in service with unexplained rapid and localised pitting being another example.

Just my thoughts.

Paul.

Tried to do some more programming of the Omron inverter. Did a few hours on autocad. Went to bikers café with friends. Now on here.

You have just quoted something that I said on another thread. Yes the steel from other countries can be rubbish. It has all sorts of crap mixed in with it. China buy every bit of scrap they can & recycle it & so do India & others. We buy things made there & get along with it , but at the end of the day it is substandard.

All steel producers use remelt as much as possible, since it saves a lot of energy compared with reducing virgin ore. It's rather jingoistic/xenophobic to assume that 'foreign' product is likely to be worse than Port Talbot of Scunthorpe product...

I was thinking more of West Yorkshire foundry in Leeds where I worked on electrics for a few years & yes Chinese steel is crap & so is Indian steel. Xeno or not. Don't know if you go that far back but Mexico started making the body shells for Ford around 1985. They fell apart in a few years. I know I spent many hours welding them back together.

Edited By Steviegtr on 12/01/2020 23:33:11

I think that is a generalisation, I also said I find it difficult to understand why that should be so! I don't believe that all steel produced outside of Europe is "crap". As to car bodies, is it that all bodies made today that don't rust are made from 'new' European steel? I find that hard to believe. I think that is more to do with improvements in paint technology and probably assembly standards. It's many years since I studied metallurgy and it's not an avenue I persued in my career so most of what I learnt I have forgotton! I do believe standards can vary between batches even from the same mill but I don't believe that every piece of steel originating outside Europe and the America's is substandard. There were operations in the UK (Sheerness Steel being one) that operated entirely on recycling scrap granted though they produced mainly low grade materials such as rebar and not bright products destined for machining operations. I do believe however there are variations in standards (and that can be form whatever origin) but only a full analysis would provide any evidence to support Andrew's experience and my hypothesis and the source of origin would need to be determined. Who knows where it was really manufactured!

Paul.

An interesting analysis. Car bodies do not rust anymore because they are zinc bath dipped. They used to say the best cast iron was from Detroit.

Material certification is no guarantee that the material is what it purports to be, aircraft manufacturers have been scammed with substandard material submitted by so called preferred suppliers. You have to rely on instinct, if a material comes from a source that you have had no problems with in the past and it machines as you would expect it to do, then that is really all you can hope for.
Dave W

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In the real world ... for Steel, this is probably as good as traceability gets: **LINK**

https://www.aisc.org/steel-solutions-center/engineering-faqs/2.1.-material-identification-and-traceability/

MichaelG.

Not quite true, car bodies are pressed from Zinc plated steel, "Zinctec" being one name for it. Along with much better joint sealants, better design and very much better paint systems car body corrosion is no where near as bad as it was.

Having said that Porsche, some years ago, hot dipped (galvanized) the bottom 6 inches of complete body shells to stop the appalling corrosion they suffered from. The last 100 (150?) Reliant Scimitars also had galvanised chassis.

What Detroit did with cast iron was to develop techniques to enable casting in very thin sections, they probably used good quality iron but the skill was in their casting techniques.

John