turcite thickness / compression
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  1. #1
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    Default turcite thickness / compression

    Hi,
    working on a VN22LU saddle. The lower sub-saddle of the universal rides on the
    knee top surface dovetail.

    The casting itself has worn due to chips and lack of lubrication, and is about .005"
    out across a diagonal, relative to the reference surface (original scraping of the
    universal saddle's pivot joint).

    Here's a picture of the underside face. Some scores which are an additional .004" low
    as well.

    vn-lower-saddle-1.jpg

    Since I need to remove .030" or more from the knee anyway due to scoring there, I'll
    have to build up the underside of the sub-saddle.

    My question is: with turcite type products, should I mill out the .005" unevenness of
    the saddle, then apply turcite?

    Or, is it no problem to have turcite to .030" in some places, .035" in other places?

    I suspect the answer is: turcite might compress by a very small amount, but this
    level of unevenness is irrelevant, particularly on an old mill. But I wanted to check
    while I am setup to mill the surface if I should. I will have to prep it for turcite
    adhesion regardless...

    Thanks!
    -Phil

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    I don't think compression is much of an issue.
    Take the amount of square inches, then divide that into the total
    supported weight, and I would be surprised if there was any compression.
    I would expect the loading per square inch to be very low.

    Paul

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    Not an expert in Turcite or similar polymers. However, my understanding is that the surface must be machined flat, left with a rough surface, be clean from dirt and oil, so that the epoxy glue forms a thin, uniform layer, to guarantee uniform adhesion and mechanical properties of the repair.
    While the glue cures, the piece should be coupled with the mating component (e.g. saddle on bed) preventively coated with releasing agent, loaded to a specified minimum pressure. If coupling with the mating component is impractical, one could machine to tight tolerances a replica of the mating surface and attach them rigidly applying even pressure during curing time.

    After curing, the Turcite shall be machined/scraped to perfect fit to the mating surface.

    Both for the curing and the finishing of the job, it is implied that the mating surface shall be even (i.e. pristine or perfectly evenly worn) and reconditioned to proper standards first.

    Paolo

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    Just stumbled on this thread always interested in what 'peeps" get up to with Turcite.

    The Turcite material won't compress or plastically deform or flow - while being clamped. (like what Toolnuts is saying).

    It's almost annoying how much force can be applied to a polymeric layer before it compresses or any dimensional change in thickness (at room temperature) is appreciated.

    In Cinematic lenses some manufacturers use "Plastic" type shim stock "gasket " as lens shims that are designed to hold micron level tolerances - Drives me mad but seems to work :-/

    Interesting how (in theory) that turcite can be wet ground and scraped (with super sharp tools ?)

    That epoxy layer if compressed with mating components and release agents should level out pretty well ?

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    One other question-

    I will fill the oil grooves with epoxy in applying the turcite and then recreate them on the turcite surface... this is straightforward.

    However as you see from the picture there are two sets of
    3 socket head cap screws which attach stub gear shafts on the top surface of the sub-saddle.

    I can only imagine needing to access them again if there is
    Major wear to those gears or shafts which seems very unlikely
    With proper lubrication, which will be fine now since I’ve
    Re-run all the lubrication lines.

    That being said, epoxying in those SHCS makes them nearly impossible to access. On the other hand, having access holes through the turcite might
    increase the chance of turcite release?

    Thanks
    Phil

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    I don't know about your whole Turcite idea as opposed to just machining and scraping it back flat with the least amount of material removal. Scoring is great to be stopped from further scoring, which obviously you're doing, but scoring technically only reduces bearing load surface. Even heavy scoring can be a small part of the total load plain. The thing is with any change of height, especially on a saddle, there are so many other things that also have to be redone to maintain alignments. Mating screw nut mounting heights are just the start of it. Anyway... to each their own plan I guess. Machining back and replacing height with Turcite is not a terrible idea. Just not sure I would do it myself on a cool old battle ax like that.

    What I'd mostly like to mention is well one. Yes you should keep access to all mounting screws when adding Turcite. Either that or do a pencil rub of your entire saddle surface and keep it in a "In my whole life I'll never forget where I put this" kind of place.

    Something else I noticed is the wear you have from one corner across diagonally to the other is coincident with the oil galley design. Meaning the areas of greatest wear are also the areas furthest from a distribution point of lubricant.

    It's safe to say that many oil galley designs have been tried and failed over the years. This looks like one of them. If anything I would add a vertical or near vertical line extending from the last part of the V on both ends across the saddle one more time. Remember not to run your grooves off the edge anywhere. The groove on the right in your picture looks like it runs off, but I'm thinking that might also be serving a gib or the likes of. Also remember that if symmetrical like this groove design seems to be, you'll have to start one groove where the oil feed hole is, but you might want to reverse the design and not cut your new Turcite grooves directly above the old ones. Sound like creating weak points to me. Unless of course the old grooves get machined away with your Turcite idea.

    My 2 cents to the cause.

    Dave

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    Quote Originally Posted by 13engines View Post
    I don't know about your whole Turcite idea as opposed to just machining and scraping it back flat with the least amount of material removal. Scoring is great to be stopped from further scoring, which obviously you're doing, but scoring technically only reduces bearing load surface. Even heavy scoring can be a small part of the total load plain. The thing is with any change of height, especially on a saddle, there are so many other things that also have to be redone to maintain alignments. Mating screw nut mounting heights are just the start of it. Anyway... to each their own plan I guess. Machining back and replacing height with Turcite is not a terrible idea. Just not sure I would do it myself on a cool old battle ax like that.

    What I'd mostly like to mention is well one. Yes you should keep access to all mounting screws when adding Turcite. Either that or do a pencil rub of your entire saddle surface and keep it in a "In my whole life I'll never forget where I put this" kind of place.

    Something else I noticed is the wear you have from one corner across diagonally to the other is coincident with the oil galley design. Meaning the areas of greatest wear are also the areas furthest from a distribution point of lubricant.

    It's safe to say that many oil galley designs have been tried and failed over the years. This looks like one of them. If anything I would add a vertical or near vertical line extending from the last part of the V on both ends across the saddle one more time. Remember not to run your grooves off the edge anywhere. The groove on the right in your picture looks like it runs off, but I'm thinking that might also be serving a gib or the likes of. Also remember that if symmetrical like this groove design seems to be, you'll have to start one groove where the oil feed hole is, but you might want to reverse the design and not cut your new Turcite grooves directly above the old ones. Sound like creating weak points to me. Unless of course the old grooves get machined away with your Turcite idea.

    My 2 cents to the cause.

    Dave
    The supply of oil to this part of the machine really is poorly designed IMHO.

    A single bijur metered oil line drips from the upper saddle through the casting,
    and onto the top of the lower saddle, where there is another oil channel in a semi-circle
    (corresponding to the 90degree maximum swing of the universal table).

    upper saddle:
    vn-oil-distribution-2.jpg
    lower saddle:
    vn-oil-distribution-1.jpg

    That semi-circle in turn has a drilled hole that delivers oil down to the saddle/knee
    interface oil groove pictured at the top of this thread.

    So I agree that the wear does appear worst the furthest from the oil distribution
    point. It also is at the rear, and next to the gib, which could have been over-tightened,
    or the saddle lock (which presses on the gib) could have been partially or fully engaged
    while using power traverse for a long time?

    As for your original feedback on the necessity of scraping, the scoring that is really a problem is on the top of the knee itself.

    dovetail-wear-3.jpg

    I have considered filling those scores with Score-Ex, but it's quite a big area and I'm a bit skeptical it will stay adhered, even following their application notes. So I'm expecting to scrape this down (considered having it ground, but expensive).

    So if I take the knee down by .030" or so, I can add it back via turcite on the sub-saddle and end up back at a height where the gears feeds to the table will align.

    -Phil

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    If it sounds to good to be true then it is. I have nver had much luck with Score Ex. Oh I uded to be a distributor for Devitt machinery the importer of Moglice and Score Ex. If your going to fill a score buy some Devcon Plastic Aluminum as it is shinny like cast iron, the plastic steel and score ex is brown. Milling or grinding may seem expensive, but the fillers will eventually come out and your worse off then before you filled it. If I were you If you cut holes in turcite I would fill it with a filler as you said leaving it open is another place oil and coolants can work away at the expoxy and the turcite will fail. Paolo is right. Machine or scrape the metal flat before gluing it on so you won't loose any valuable thickness if you don't. I use .047" or .062" Seldom ever use .030" as it is hard to cut oil grooves in it with-out going through it. I use Rulon 142 and you can get loads of info on this web-site. Bearing Manufacturer | Bearing Supplier | TriStar Plastics

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    Quote Originally Posted by Richard King View Post
    I use .047" or .062" Seldom ever use .030" as it is hard to cut oil grooves in it with-out going through it.
    richard, if you go through it when cutting oil grooves what problems will it cause? delamination?

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    Yes...between the epoxy and the material. I have seen this on many Taiwanese machines that cut the groove through the turcite pulls loose. I found this PDF about it. look at last paragraph on page 9 https://www.aetnaplastics.com/site_m...Brochure_1.pdf

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    Quote Originally Posted by Richard King View Post
    Yes...between the epoxy and the material. I have seen this on many Taiwanese machines that cut the groove through the turcite pulls loose. I found this PDF about it. look at last paragraph on page 9 https://www.aetnaplastics.com/site_m...Brochure_1.pdf
    Richard, thanks for linking the brochure. It was interesting to read. It said a bit more about oil grooves:
    ”Milling completely through the material into the metal saddle is not recommended. For any pattern chosen, it is extremely important that the milled grooves maintain a generous, smooth radius which blends the top of the groove back to the surface of the material without creating any sharp edges.”

    I was planning on milling the oil grooves, so even though I have .030” Turcite, I could control the depth so as not to go through. But I haven’t a clue how I would get a generous smooth radius with a .020” depth of cut. I suppose I could use emery cloth to radius the edges.

    Another thing the brochure said was that the turcite should go on the moving part. Often it is the stationary part that has the most wear and ends up with the most metal removed after scraping, especially if the moving part is longer and extends out beyond the stationary part. Does it ever make sense not to follow that rule, and put the turcite on the stationary part?

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    In general the moving part is the shortest part and therefore the turcite always stays covered
    That is the important part
    Not a good idea to glue turcite on the bedways of a lathe and expose the turcite to all the chips
    BTW Turcite is best pull scraped

    Peter

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    Quote Originally Posted by Peter from Holland View Post
    In general the moving part is the shortest part and therefore the turcite always stays covered
    That is the important part
    Not a good idea to glue turcite on the bedways of a lathe and expose the turcite to all the chips
    BTW Turcite is best pull scraped

    Peter
    The part I was asking about is the column top on a Deckel mill. The horizontal Y axis ram is longer, and is the moving part. The column top is shorter and always covered by the ram.

    I’ve heard before that turcite should be pull scraped. The question I have is whether the pull scrapers used for turcite are sharpened like woodworking pull scrapers (burnished edge with a slight hook)?

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    Quote Originally Posted by rimcanyon View Post
    I was planning on milling the oil grooves, so even though I have .030” Turcite, I could control the depth so as not to go through. But I haven’t a clue how I would get a generous smooth radius with a .020” depth of cut. I suppose I could use emery cloth to radius the edges.

    It's called a 2 flute HSS ball end mill. Should cut like butter. Just determine the width of the groove you want and dig out your chord-of-a-circle calculator and find the smallest ball end mill that will give you the width you want and the depth you're stuck with in a single pass.

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    Quote Originally Posted by rimcanyon View Post
    The part I was asking about is the column top on a Deckel mill. The horizontal Y axis ram is longer, and is the moving part. The column top is shorter and always covered by the ram.

    I’ve heard before that turcite should be pull scraped. The question I have is whether the pull scrapers used for turcite are sharpened like woodworking pull scrapers (burnished edge with a slight hook)?
    This is a situation that I would do it otherwise Turcite on the stationary part. That is why I tend to say turcite on the smaller/shorter part
    The few times I did pull scrape turcite I used my normal scraper Perhaps not ideal but it works

    Peter

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