A few old photos from Craven Manchester - Page 2
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  1. #21
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    But all those backsides sitting on the Vee ways will warm them up and you'll never get consistent bluing

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  3. #22
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    Would they be flaking for oil retension, or scraping for flatness. What does the straight edge used for bluing a surface that large look like, or would it be measured optically with an autocollimator or theodolyte?
    Mark

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  5. #23
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    Quote Originally Posted by rotarySMP View Post
    Would they be flaking for oil retension, or scraping for flatness. What does the straight edge used for bluing a surface that large look like, or would it be measured optically with an autocollimator or theodolyte?
    Mark
    Now, that I can tell you as best I have gleaned from Chris.

    From my discussions with Chris - the 'roughing' areas were defined by a scraper hand traveling down the bed with a 30" to 36" x 4" wide I beam shaped parallel - Craven cast quite a few early ones with circular holes in the vertical web to reduce weight, later ones with 'egg shaped' cut outs - theses became affectionately known as the 'Happiness is Egg Shaped' masters. The very early paralells were a true cast I beam - I have one such in my shop 5" deep and 3.5" face width 48" long. Heavy is an understatement dates back to pre-1900's we think.

    (Machine sections from the 'planer' were generally within a 0.001" of finish or they were sent back, however, in the later years Craven offered a rebuild service and worn machines were assessed in a similar way):-

    So the chap in charge - wondered along the bed with the SE 'floating over the surface and 'hinging it' one handed ! to get an idea of where the bed 'wanted a good bashing' (i.e. a few thou' off) these were marked up with chalk. Once it got 'about right', the spirit level was employed over the SE parrallel. To get it better, when it was looking like within a few tenths of the desired surface, the scraper hands had small 'intensifying plates' I have one which is 17"x10" wide, with a pair of handles across the narrow ends, dovetail edge down one long side. These were used along with Engineers Marking Blue to bring the PPI to the desired level.

    Lots of other things happened - tight wires, trammels and a host of other methods were used in the initial stages and experienced hands to ensure that the finished item could be extracted from the rough castings and still be in spec' - when Chris talks about headstock castings weighing 40mt or more and being a bit tight on final dimensions so a specific chap was called over to ensure they 'got the part out' - I think there was far more 'art' to the manufacturing than at first meets the eye.

    As for 'bums' warming the bed and causing distortions - quite possibly - but not likely of important in the 'bashing out phase.

    The use of autocollimator was not common, the use of levels far more.

    Chris had me 're-scrape' the 68"x3" SE I had prepared to within 0.00025" overall as he didint like my finish on his SE. He insisted that I do it with only a shorter 30" SE parallel and the levels - just to ensure I got the message he went and scraped out a couple of hollows over its length to -0.001". When I had it done, the 0.0002"/10" level shows no more than half a division of movement over its length. I then checked this with the autocollimator given to me by Demon73 (cheers again ) - after mapping it, it shows 0.00018" total deviation. Locally, the scraping depths are less than 0.00015" and Chris is of the view it needs further refining to smooth it out ! Tolerance on the larger machines at Cravens was 0.0001"/12" for bearing faces.

    I wonder how many of the younger scraper hands stuck it out for the long run like Chris ?

    Finally, the scraping / flaking for oil pockets - there were a few hands that specialized and in fact were requested for certain finishing jobs - these guys as described by Chris were physically powerful guys, that produced 'curls' in may cases '1/2" wide and upto a couple of thou' deep' grunting audibly with each cut. The patterns were all done by eye and a small arc centred around the scraper across the shear /way. 'Craven Roses' were produced from 4 curls meeting so you got a cross of 4 curls from the 4 passes of curls over the entire bed. There were other styles and each hand produced their own signiture when required.

    It was not unheard off for a bed section to have been completed and some error elsewhere require that it be re-done - usually an adjacent section was 'out' and it was easier to redo a bed section than for example a headstock / tailstock or saddle etc. Chris recalls on one such occasion, having to take 4 heavy cuts over an area of 'curls' (oil pocket flaking ) to get below it. Now I have watched Chris take some heavy cuts to demonstrate 'how' - I measured the depths of those 'bedding curls' at 0.0015" x 5/8 wide at the centre of the curl. He is 73 now, and by his own admission, not the man he was in his 20's, doing it all day, for weeks at a time I guess you develop the technique to shift material with an effective technique. I cant duplicate the depths after 7 months that Chris can achieve apparently effortlessly now !

    Sorry if this is rambling and of little interest.

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  7. #24
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    Thank you, very interesting. I'd not heard of the "Craven cross" pattern but wish someone had a photo of it. I picture something in my mind but I'm not sure if it's correct. And I'm even more impressed by scrapers doing what I'm picturing. To be an attractive pattern I'm imagining it symmetrical. And while most machinists I think develop a certain amount of ambidexterity from running handles and things with each hand, the prospect of making nearly identical right and left curls sounds daunting. And then further to set left and right, then another at right angles just boggles the mind.

  8. #25
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    Another thought. Would Chris be able to make an example of that pattern for the record and to add to this fund of knowledge?

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  10. #26
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    Quote Originally Posted by TGTool View Post
    Another thought. Would Chris be able to make an example of that pattern for the record and to add to this fund of knowledge?
    I will try and get a few sample photos and upload them when I next get Chris in the workshop.

    Mat

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  12. #27
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    I think you would have more thermal effect from a window letting in sunlight than the behinds of a dozen skinny kids on a 100ton plus machine!

    You need to extract as much information from chris as possible as I don’t think there are many men left with his true heavy experience and knowledge (and witness)of the machine builders art.

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