South Bend Heavy 10

  1. Pete.

    Pete. Member

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    Here are the basic tools I use for scraping. Two hand scrapers, an ink roller, canode blue, a surface plate and a pot of brake cleaner. I've got loads of other including a biax power scraper but these are all you need to get going, plus a couple of medium grit stones.

    IMAG3116.jpg
     
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  2. rtbcomp

    rtbcomp Moderator Staff Member

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  3. Pete.

    Pete. Member

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    So today I've been scraping the compound flat ways and the swivel. First I ran a stone over the flat ways and straight away I see some damage caused by adjusting the compound angle by hitting it. This is always a bad idea - use a block of aluminium if you must tap it round because here is what happens - you raise the corner of the part and the top way is lifted off the bottom way (and break the edges off the part).

    sbheavy10scraping01.jpg

    So I stoned the corners down a bit and you can see the effect has been more than you might at first think.

    sbheavy10scraping02.jpg

    Cast iron is very malleable and the raised lump goes a long way. So I stoned it a bit more , a bit too much as it happens because I went too far on the right hand side, possibly because I'm right -handed and rolled the stone a little. Anyway the result is a bit of extra scraping.

    sbheavy10scraping03.jpg

    I kept going until the ways were flat and here are the two halves ready for assembly later:

    sbheavy10scraping04.jpg
     
  4. Pete.

    Pete. Member

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    Now for the swivel. First run a quick 2-way scraping pass over it so that it prints. The flat top of the corss slide is very good and only takes a few passes to get a nice print.

    sbheavy10scraping05.jpg

    The underside of the compound was not so good. It only prints over 3/4 of the circumference.

    sbheavy10scraping06.jpg

    I scraped this one four or five times and eventually it came in with a nice full contact, so these two parts are also now ready to go.

    sbheavy10scraping07.jpg

    You can really tell the difference after scraping a swivel or a slide, because the difference between moving freely and locked up solid is a tiny fraction of a turn on the locks, or gib adjusters. With a worn part you feel a bit of 'spring' in the allen key as you tighten it up.
     
  5. Brad93

    Brad93 M J B Engineering

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    How do you know, when scraping, that two dovetails are the same height?

    In my head there is nothing to stop you scraping one lower than the other?
     
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  6. Pete.

    Pete. Member

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    Mostly it doesn't matter. Especially on a lathe and more especially when doing work like this because you're taking so little off. What matters is that the ways match. Also you have to bear in mind the scale that you're working to. Can you hit a tolerance of a thou on a milling machine? Yeah if you're careful. When scraping you'll have to go over it 5-10 times to take a thou off. You have to work quite hard at messing it up badly.
     
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  7. Pete.

    Pete. Member

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    Last bit tonight and now I'm thoroughly knackered. Here's the bottom of the cross-slide. Even though it looks perfect to the naked eye - if you looked at this part you'd say it was very low on wear (which it is), but the spotting blue tells a story. The casting has stress-relieved over a long period and it's riding only on the inner edge of the ways. Not great for rigidity and the gapped edges attract the ingress of dirt.

    sbheavy10scraping08.jpg

    Not much contact there so I break out the Biax scraper and hit it a few times, probably taking off half a thou where it blues up.

    sbheavy10scraping09.jpg
    The face is coming in but it's still not touching on the corners.

    sbheavy10scraping10.jpg

    A few more goes and we're getting there. This would be a lot of work by hand, glad I got the power scraper. It's important when you get to this stage to make sure every scrape is an individual mark. If you join the scrapes together you'll never finish the job.

    sbheavy10scraping11.jpg

    Pretty good now. Needs a final touch but I'm saving that for later. The blue is drying out on the plate giving a bit of an iffy print but I'm running short and I don't want to clean it up when I'm finishing for the evening.

    sbheavy10scraping12.jpg

    So I've set up the saddle to scrape the flat ways and ran a quick couple of passes so it'll hold the blue. You'll remember right at the start that the survey showed the rear of the ways to be un-worn but the front 2/3 to have a bit of wear. This is the result. The straight edge is bridging the gap because it's riding high on the un-worn bit (on the left in this pic). It's important to only scrape this area until it starts printing in the middle because that's going to bring that 1-2 thou wider reading on the survey closer to the rest of the measurement, and save on time hand-scraping the dovetail later.
    You'll also notice that I had to scrape the ridge off the sides of the ways where the slide didn't fit full width so it would let me print it on my straight edge.

    sbheavy10scraping13.jpg
     
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  8. Dennis Aspö

    Dennis Aspö Member

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    There are ways to do it though in some cases, here's a video (two parts) where an indicator is used to get the dovetails true height to each other.

    Indicators and surface plates seem to be the most important tools. But this procedure would not be possible on all compound slides, on this model the top of the compound is flat and seems to be a precision machined surface itself so it can be used as a reference surface. My compound is round on top, older machines seem to be part works or art instead of tools, with all the rounded impractical surfaces that are no good for work like this.

    But if you can get the relevant reference surfaces of the parts you are working to register against your surface place you should be able to get it true and even to that surface.



    I am no expert though, don't even own a surface plate yet, just find it a very fascinating subject.
     
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  9. Brad93

    Brad93 M J B Engineering

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    That guys got some skills that’s for sure
     
  10. Pete.

    Pete. Member

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    You CAN do it for any surface but my lathe doesn't have the wear to even give it a thought. I did map the compound base and found it very good as in the photo here. There's no way that the small amount of scraping I need to do is going to upset the geometry.

    sbheavy10compoundbase.jpg

    If there was say 15 thou wear in the front of the slides I would be step-scraping to bring the back of the ways down to the height of the front first.

    Milling machines are a different animal altogether. You absolutely MUST consider the planarity (and perpendicularity) carefully when you're scraping every part of those, because the slides move the part, not the tool.

    We are both students of the same teacher. He's super-enthusiastic and makes great videos on how to achieve text-book results which is great for spreading the knowledge and keeping people captivated on youtube. I'm not knocking that in the slightest but I'm 20yrs older and want to get on with doing stuff in the real world rather than achieving perfection. There's room for both schools of thought.
     
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  11. Brad93

    Brad93 M J B Engineering

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    I see. Certainly very interesting and a subject you could probably get lost in.

    Fancy doing mine when you’ve finished your lathe haha.
     
  12. slim_boy_fat

    slim_boy_fat Forum Supporter

    I'm quite adept at that, but I've had decades of practise. :ashamed: :laughing:
     
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  13. Brad93

    Brad93 M J B Engineering

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    @Pete. what sort of stone do I need to sort this taper out?
     
  14. spencer 427

    spencer 427 Member

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    You probably need an Indian stone if it's only very small imperfections to stone out.
     
  15. Pete.

    Pete. Member

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    You gotta be extremely careful using a stone on any taper. Certainly don't do it with the spindle running. I think that I would get an old backplate and use it as a lap with some diamond paste. That will quickly take down any bumps without altering the basic taper.

    I'd take a look at it certainly. Even a quick job can make a huge difference to the rigidity.
     
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  16. mm289 Member

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    520
    Dover, Kent
    Knowing a little bit about scraping (as you know) I am seriously in awe of how quickly you get these results - you are a machine:clapping::clapping::drunk:

    Cheers,

    Paul.
     
  17. Pete.

    Pete. Member

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    Cheers Paul, though you shouldn't sell yourself short not many people can scrape a surface plate to workable grade after just one day's tuition like you did.

    Anyway, here's where I'm at. I've got to tackle the dovetail ways now (a job I hate doing because the parts are hard to hold and the work is fiddly but hey-ho, it's gotta be done.

    sbheavy10scrapedparts.jpg

    I have to adjust the width of the vee ways as you can see the are .02mm wider at the back than the front, we knew that from the initial inspection. To do this I will scrape both way from the left edge her eto the middle twice, then from the left edge to about 1/4 of the way once, and see where I'm at. It should leave a tiny dip towards the middle but that's ok, it's better than a crown which can yield a false print if I'm not careful with the bluing.

    I'm running short of canode blue which is a pain because there's a production shortage so everywhere is selling out of the smaller bottles. I've had to buy a gigantic 32oz bottle from America which is going to cost 80-90 quid by the time they've billed me for import and VAT. I'm thinking of getting a bunch of small bottles and selling some on, because 32oz is about a 20 year supply at the rate I use it.
     
  18. spencer 427

    spencer 427 Member

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    I struggled to get any. I managed to get a couple of tubes of Stuart's blue.
     
  19. MattF

    MattF Member

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    I've thought that quite a few times too. But anyhows, getting back to technical stuff.... :D
     
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  20. spencer 427

    spencer 427 Member

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    I struggle with that to
     
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