Help me judge my bearing quality progress
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  1. #1
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    Default Help me judge my bearing quality progress

    I recently bought a Rockwell 14 by 40 and the wear on the bed is minimal maybe cause it has hardened ways. However the cross slide had some binding in some areas. Turned out it the slide is convex and ways are concaved. I have read MTR cover to cover several times and scraped for flatness and square a good bit but not for sliding bearing. MTR outlines to start at the CS and I am following that plan. From these pictures can you judge how far from complete I am. I have an average of 10 ppi but not all over. The bearing points are mostly in the center. It is hard to tell from a picture and I know I am not finished, but how much% should the points cover. Thanks.
    img_20140614_210833_394.jpgimg_20140614_210817_107.jpg

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    I think the answer is 50%. Your not far away, because you have coverage end to end. What radius tip are using there? I'm thinking you now go to a smaller radius, and start splitting those larger blue patches up to bring your point count up.

    What are you using to knock the burrs off? See how you have not a lot of contact for what looks like an 1/8" wide land down the inside and outside edge of each way. If you are using a stone, that might be causing that.

    Regards Phil.

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    Yes Phil you are correct. I was riding the edges too hard with the stone and after realizing that I am stoning much more carefully. Thanks for the feedback.

    Edit: I am using a 3" radius edge. I have a 1.5" I could go to now.

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    Great advise Phil. I moved to the smaller radius and cut the spots in half instead of scraping them off and more and smaller points began to appear. I guess that is why the transition from roughing to finishing is important to get correct.

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    Many assume slip stones or sharpening stones are flat and they rub it to remove the burrs and the edges like Phil say's gets rolled off. Many of the old timers tried to keep their stones clean, so they advised to store them in a coffee can filled with mineral spirit's. I advise against doing that as the stone cuts more when wet. Carefully lay the stone on a granite plate and hinge it. I would say 75% of the stones I have seen are concave on one side and convex on the other. If they are real bad i break them in 1/2. . I always show this in the class as I pass out a tapered slip stone to them and first have them come to the surface plate and check that. many times you can spin them like a top toy. I tell the students: After you scrape brush or vacuum off the chips, wash of the blue left on and then run you fingers over the burrs and then stone it a little bit and feel it again. ust to remove the burrs and not the high spots you just made.

    When your scraping you need to be a detective and think about when the machine is being used, where does the dirt get into the ways? The ends and edges, so you want to the edges on the outside and ends hitting to keep out the crud. I wish you would set a starrett surface gage on top of the way and put a .0001" or .0005" indicator on the blue spot on the same way and move the stem in and out of the low spot to high spot. You will need to see .0002" to .0005" difference. Check 4 to 6 places. Just looking at it, it appears the depth is to shallow. When you scrape does it seem to come and go? good one scrape and bad the next? This happens because your not scraping deep enough (the industry term for not enough scraping depth is "chicken scratching"), using a dull blade or stoning to hard. . Be sure you hinge or check for the airy points swivel while bluing the compound on the plate. It should pivot on each end approx 30% from each end. If it swivels in the middle that means the way looks like the bottom of a rocking chair and as you rub it side to side and you get a false reading. As it rocks it blues up giving you false reading. So far so good. Rich

    PS: I give the students a good stone when they take a class, or a new one that might be bent...lol

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    On the mention of oil stones. I thought I'd share this. Its one of the best Gizmo's I've ever knocked up.

    I got a 12" dia slice of cast iron, and milled this pattern in it, then ground it. With a bit of valve lapping compound, it does a great job of dressing a stone and making it flat. Its also cleans and opens up the face. Particularly good if I've been scraping steel. It pulls out the crap that embeds in the stone.

    p1000684.jpgp1000682.jpg

    Regards Phil.

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    It looks as though sloping face of the dovetail hasn't been touched yet ,is it best to completely finish the horizontal face first or rough in the slope once the horizontal faces are near.

    Excuse my terminology ,in fact please correct it.

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    If it was me, I'd complete the flat surfaces. You have to have a datum, and the flat is it. If you go back to them later, and rework them, you change everything else ever so slightly.

    The other reason, is a lot of time, you will measure the leading edge of that dove tail over rollers, and the bottom of the roller sits at that datum / flat plane.

    Having said that, if you knew it was bad and had a lot of wear, probably wise to rough both features in, in case it moves.

    Regards Phil.

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    I'm using much smaller stones! Say as big as the last two joints of your finger.
    If you start stoning, you hear/feel that it is scratching. As soon as that scratching is gone, you are done stoning. That are just a few strokes.
    If the spots look blurry, you are stoning too much. To get a feel, start stoning very little with little pressure. When rubbing the part on the granite plate and it sounds/feels scratchy, it wasn't enough.

    Learn to listen to the sound and feel while spotting and deburring!

    While scraping, it lay the stone into a can of petroleum (diesel fuel if you want). From time to time, they go into an ultrasonic cleaner.


    Nick

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    Quote Originally Posted by machtool View Post
    On the mention of oil stones. I thought I'd share this. Its one of the best Gizmo's I've ever knocked up.

    I got a 12" dia slice of cast iron, and milled this pattern in it, then ground it. With a bit of valve lapping compound, it does a great job of dressing a stone and making it flat. Its also cleans and opens up the face. Particularly good if I've been scraping steel. It pulls out the crap that embeds in the stone.

    p1000684.jpgp1000682.jpg

    Regards Phil.
    That's nice Phil.

    I use one of these with a few drops of high-flashpoint solvent. I give it a few swipes then wipe the stone off.


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    I scrolled down to see Peter beat me to. I use a pocket diamond like these Diamond Whetstone Sharpener | DMT® - Diamond Machining Technology this is for smaller surfaces of course, as that's all I'd ever do. Just wondering what the thoughts are on something like these though?

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    Quote Originally Posted by Pete F View Post
    Just wondering what the thoughts are on something like these though?
    They certainly clean and open up the face of a stone. Our mate GQ had one here on loan. But heres the BUT. They cant be flat assuming the pressed metal constuction. It makes no difference to an edge of a blade. But it cant be flat. They do a great job on my pocket knife.

    Call me anal, but I like a flat stone. I've been known to put them in a toolmakers vice and kiss them on the grinder.

    A point I neglected before. You occasionally see lapping plates on Ebay /Auctions even down here. There usually cheaper than used surface plates. No body lapp's anymore.

    If you get the chance, pick up one of those just to tune up your stones.

    Regards Phil.

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    I have seen a east German scraper use a sharpened bearing race once
    Would that be good or bad practice ?

    Peter from holland

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    Just to be sure I understand correctly Phil, you're saying that the stone used to deburr the piece after scraping needs to be absolutely flat (or as flat as realistically possible)? I'm surprised about that as I didn't think it really mattered Maybe I misunderstood. That happens. Often.

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    We may have gotten off subject a bit, but while we are on the topic I have always been told that to flatten a stone you rub it against another stone. The lapping plate seems like a great idea also.

    Charles

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    The sharp edge of the Biax radius gage is used to de-burr and not use a stone. I have never had much luck flattening a stone as it seems to dull it and they get high in the middle. I would suggest the next time you flatten them, check them for hinge. I agree with Nick sound is important in many aspects of scraping and 1/2 moon flaking. Ask my students as I teach that all the time. Rich

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    Quote Originally Posted by machtool View Post
    On the mention of oil stones. I thought I'd share this. Its one of the best Gizmo's I've ever knocked up.

    I got a 12" dia slice of cast iron, and milled this pattern in it, then ground it. With a bit of valve lapping compound, it does a great job of dressing a stone and making it flat. Its also cleans and opens up the face. Particularly good if I've been scraping steel. It pulls out the crap that embeds in the stone.

    p1000684.jpgp1000682.jpg

    Regards Phil.
    That's very similar to the cast iron laps used in optics for grinding and polishing prism/flats: they just have a pattern like a chocolate bar milled into them.

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    I flattened my stones by using sand blasting garnet grit and oil on a glass plate.. It is amazing how quick it flattens down...

    I do use a silicon carbide stone though...

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    RC,
    Would you share that procedure in a new thread or here.....I would like to see that. Have you ever measured how flat glass is by the way? Rich

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    Quote Originally Posted by Richard King View Post
    RC,
    Would you share that procedure in a new thread or here.....I would like to see that. Have you ever measured how flat glass is by the way? Rich
    It is the same as what Phil is doing, just using glass rather than cast iron. It's a good idea to have a plate that's a good bit larger than whatever you're flattening so you can spread the wear around as evenly as possible in the interest of keeping the lapping plate fairly flat. I think the grooved iron might be better as it gives any large particles and the extra swarf somewhere to go. I use the same setup for my stones also. The stones can also be lapped with diamond hones (companies like DMT make big ones - 4" x 10" - that work very well, Atoma is also a very good brand) which are quite flat. Personally I prefer the loose grit method, as I have found it to leave the cutting surface of the stone more "open." I use diamond plates to flatten sometimes if in a hurry, but much prefer the cutting action of a loose grit lapped stone.

    One more little trick if you use glass: before you begin to lap, wet the glass and stick a sheet of silicon carbide wet-or-dry of the same grit or finer than the loose grit you will be using to the glass. Put your loose grit on top and lap - this way you will stay flatter longer.

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