Cast Iron Straight Edge

Parts are heated in a stress-relieveing oven to a specified temperature over a specified time period then controlled cooling. Any good heat treatment place will do it.

My spindle moulder came from a "Well known and respected" maker,brand new.

First time I used it,I found that the two fences were not in line with each other. This was due to the horseshoe casting being faulty. I believe that this was due to stresses which were not released because it was not left long enough to "weather". It seems this is no longer done,for cost reasons,I suppose.

Returning it to the makers was not an option,due to cost,so I took it to a local machine shop to have the faces ground true. I was told that there was quite an error,most likely caused by the casting being machined while too fresh. The unit did not strike me as being a very good design,since it went from fairly thick sections to very thin ones,not a good idea ! I was advised to "keep an eye on it" since it might go off a little more later on,but if it does,bring it back and we will skim it for you" Fair deal !

They said castings are treated using "New methods",which dont always work,they believed the old way was better.

A good observation by Larry above about the design going from thick to thin and the designer not realising that might be a problem. I think we will see more of this as companies rush out designs by the youngest (cheapest) graduates who can knock out impressive CAD renderings but have no experience.

But then again they can probably click a button and much like FEA get a computer simulation of how a part may move.

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... and any informed engineering decision then gets over-ridden by the bean counters

MichaelG.

Hello!

A friend and I are looking to get smaller (30cm or so), knife edge cast iron straight edge castings. My friend has managed to locate a seller in the US but for many reasons I would prefer to get them from within the EU.

Does anyone know of a seller of either raw castings, semi finished or finished straight edges as per my description above?

Best regards

Karl

Edited By Neil Wyatt on 23/01/2019 16:44:44

I should add that my above post was posted as it’s own thread before it was kindly moved by Neil Wyatt. I have since read this thread.

Just buy a length of standard rectangular cast iron and machine it from that.

Andrew

I used to machine parts for Bridgeport in my apprenticeship, the castings came in from the foundry across town Mansfield, then we checked fettling and roughed out on a planner or shaper. They were then taken outside and a date stamped on. We just left them outside in the rain, sun and snow to weather. They were left for up to 18 months but usually only a year. They came in to re-machining and although they were rusty it was only skin deep perhaps 15 to 20 thou. They were 're planed drilled and final ground for despatch to Leicester.

David

I did that, it bent like a banana though I did try to mill it from round, not square. I then got hold of some dovetail pieces which were slideways off an old machine and scraped one of those as a prism for doing cross-slide dovetails. That worked well but 6 months later it had developed a 2 tenths bend. Didn't take much scraping to fix it but I remind myself to check it on my plate each time I get it out to use it.

Edited By Pete Rimmer on 23/01/2019 19:17:28

Both are good suggestions but I wouldn’t know where to get either. I don’t know of any larger machine being scrapped and none of the Swedish metal vendors I’ve come in contact with carries cast iron in bar stock. Any suggestions for the UK market? Germany?

Natural "weathering ' iron castings was a very good way of stress relieving iron castings there was the daily temperature cycle and then the annual cycle from winter to summer temperature cycle,this produced very stable casting in good quality iron and was quite common practice 50 years ago, the very best makers of precision tools would leave them out longer,iwas informed jig borer makers would leave them up to 3 years, its no good telling the buyer of a very expensive tool expected to be accurate to within 2 tenths of a thou over the capacity of the machine that its not as accurate as specified because the accountants did not like the slow procees,I once was in technical contact with a swiss jig boring company,their machines had a normal life of 40 years before reconditioning was reqired ,when a borer table was machined and scaped in a minimum of 3 millimeters was machined from the table as it was found that a stress was built up in the surface of the table dues to years of clamping work to the table and they found that it was essential to remove a least 3mm to remove this local stress.The company where I did my training made a range of optical benches up to 2 metere long and these castings spent a long time in the stores prior to machining and were used in a first in first out arrangement. The problem with car cylinder blocks is that the bores tend to go out of round as the motor industry did very little in in stabilising the castings in the 1960s it was found that if the cylinder head of one popular car was removed for say a decoke ,some of the engines would tend to burn oil,and it was believed at the time that the removal of the head removed a clamping force ,the block relaxed and the internal stresses released tended to cause bore ovality.When of a visit to Massey Fergusson at Coventry I found that there was no stress relieving of the iron castings,but on the other hand ,all steel bar material and steel forgings were stress relieved at red heat and there were massive chain bed furnaces which must have cost a fortune to run. Years later I was involved in machining LM25 gravity die castings which had recieved a very precise heat treatment and the metalurgy was strictly controlled,plus machining was under temperature control, I found that even with this control about one in a hundred castings distorted slightly when the clamps were released after machining,I would add that the clamps were not causing the distortion,eliminating distortion caused by internal stress be relieved during machining can be a problem,Perhaps with modern very accurate manufacture very few assemblies are dismantled during the life of a product and a bolted up assembly has no chance to distort,Cars for instanceare now rarely decoked or totally stripped.

Last weekend I had a visit from a Norwegian friend who was over for the Ally Pally show and we were discussing this very thing (the difficulty in finding used straight edges). He told me that by far the easiest place he knew of to find cast iron straight edges was Sweden.

If you're in Sweden and struggling to find them I don't know what I would suggest.

Edited By Pete Rimmer on 23/01/2019 20:57:58

One of the guys who has already commented on here messaged me regarding making castings as someone else asked him about this a month ago, Personally I'm after a bevel edged straight edge for the purpose of scraping ways, maybe 50cm/24inches something that sort of size, I'm waiting to hear from him to see if what I want is similar to the other request he had, if this is something that would interest you, I'm sure he could put your name down for one.

Cast iron rounds, squares and flats are readily available in the UK. I use M-Machine Metals in Darlington, but there are other suppliers. The material is often listed as GR17, or grade 250, about 17 tons per square inch tensile strength.

Going to get spendy if you want 24" (60cm) rather than the originally mentioned 30cm.

Andrew

Another supplier is United Cast Bar they also do GD250. Call them up and talk to one of the sales team, they might have a piece on the shelf. They also have a Kendall milling machine so they can pre-finish any part you order. I bought 3 metres of iron bar from them for the scraping class and they did give a good service.

United Cast Bar (UK) Ltd
Spital Lane
Chesterfield
S41 0EX.
Telephone: 01246 201194
Fax: 01246 540434

I found a place 'west york steel' https://www.westyorkssteel.com/cast-iron-bar/ who have a variety of different grades of Iron Bar, if you're more enlightened on this subject than I, which grade would be most suitable for making into a straight edge? and why?

Anyone else feel free to enlighten me on this subject if you can

So now we have sown doubt on the stability of anything made of cast iron what do you use as a dead cert reference? From anecdotes on this forum of granite distorting if not cared for correctly you will need to prove the truth of anything regarded as a standard.

Mike

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An autocollimator may be the best we've got.

MichaelG.

The sensible person would always check their straight edges before use especially if there's been a long interval since last use. I have an as-new 48" cast iron straight edge that I don't use but check the others against. The only thing that tells me that this 48" is not moving is that the other straight edges all check against it. If one day one of them didn't, I would check another. Two straight edges are not going to move the same so the second check would identify which part has moved.

Really though if they are correctly stored a commercial straight edge should stay straight fairly indefinitely. It's tools you make from cast iron that you should be careful with checking before use. As for granite moving over time, I never experienced that nor met nor talked with anyone who did. worn, yes but warped no.