Problem Measuring Dovetail Parallel on Compound -- Scraping in the Compound - Page 3
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  1. #41
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    Quote Originally Posted by JST View Post
    You may be better served by making something such as Rich King suggested (and both he and I illustrated). It does the job, it is simple, and it has a very large number of other uses as well. It will repay the trouble of making it in many ways.

    Neither of us posted a good picture of it for your particular use, but I would think you could easily see how it works.
    JST,thanks. Hmmm. I hear your caution on going the route I was considering. You are right that it is quite possible to see how the King-Way design would work for my application. I did find quite a bit more information and images (thanks to those who embedded images rather than linked,often broken) about it at King Way Alignment Tool

    One question about the K-W is whether the wide base gets in the way in tight places or at the end of ways. Perhaps there is a special narrow base for those circumstances? Maybe I am making up problems? I suppose an advantage of the broad base is that it averages the surface measurement over the the length of the base rather than being point readings.

    Denis

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    Quote Originally Posted by stephen thomas View Post
    Besides the purpose built rig showed earlier in this thread; I have used the old Federal clamp on bracket with a .0001 indicator, and a stub with a ball in it on the other end (clamp end). Not the most rigid setup, but it works over pins if you are careful & only need to do this stuff once ever few years.

    smt
    Stephen, I see you were posting while I was typing. Here you are posting a somewhat different opinion. I feel like I am at a tennis match. I respect both opinions and appreciate them. I likely would be only doing this operation occasionally, so that might argue some for the simpler if less versatile device. Or maybe I should be thinking of designing a "simple" device which would be designed to, at a later date, incorporate some of the refinements of the K-W if needed.

    Denis

  3. #43
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    Denis-

    Forgot to mention i really like your earlier suggestions for extending the utility of the rig I showed. But so far, I also have other (simple) options for things that can be done over pins, so less compulsion to move in that direction. But it could happen.

    smt

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    You have options with the "base", which I assume means the "tube" part. It mounts on the rod several ways.

    It can sit on a V-way (opening is down).

    It can go "in" the side of a dovetail way, with opening away from dovetail.

    The opening can surround the dovetail, as in my picture, when dovetail has the flat way on itself.

    One side of the opening can ride on a male dovetail while the OD rides on the flat, when the flat is the surface out of which the dovetail extends. That's likely the best here.

    And, of course, more than one size of "tube" can be made, to fit many sizes.

    The indicator can be situated any way you like to reach the surface in question.

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    It was not easy for me to decide which measuring device to go with. Both major options noted above in this thread had appealing features. I decided to go with the King-Way A-sized device. Attached are pics with notes on materials choice and part sizing. I already posted some info in the general-archive on the base. Not wanting ot double post, here is a link to that information. The base was by far the most time-consuming piece to make. King Way Alignment Tool

    In a related thread I have been getting info on the Starrett 57s snug. I am in the process of making a re-scaled version of it to fit a 1/2" rod on the tightening-screw side. Starrett 57S Snug Assembly drawing or photos question.

    Denis
    Attached Thumbnails Attached Thumbnails king-way-1-.jpg   king-way-2-.jpg   king-way-3-.jpg   king-way-4-.jpg  

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  7. #46
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    Default another dovetail measuring tool

    I am working on a SB 10L lathe, scraping the compound rest and ran into pretty much the same problem, no great way to measure parallelism of the base and fit of the gib. I could not get a good sliding fit for the length of travel. I took a several days to design and build a fixture based loosely on the kingway concept, a bit smaller for the smaller parts. An aluminum base holds 2 dowel pins that are 1/4" dia with a gap between them of 0.400". I wonder how this gap and radius compares to the Kingway? I liked this design better than some of the fixtures shown in the book because it allows me to run the indicator very close to the end of the dovetail.

    I fixtured the dowels parallel and glued them in place with red threadlocker. I do not think they really have to be perfectly parallel, they should still repeatably rest on the two planes. The base can be rotated to change which dowels contact, either one at the bottom of the dovetail or one on the top and the other on the side. The base can be removed from the fixture and reversed for use on inside or outside dovetails.

    I quickly found the gib to be about 0.003" too thick at one end, scraped it down while checking for flatness and got to a reading of +/- 0.0005" I reassembled the slide with oil and it works quite smooth along the entire working length. This made me happy. I have been following the book Machine Tool Reconditioning by Edward Connelly he does not say what the target should be for accuracy other than in the section on indicators where he mentions a 0.0005 indicator is good for most work?

    The other thing I have run into is that the gib is now too loose so I fitted a 0.005" shim behind it, would it be OK to just glue the shim to the backside of the gib or should I be be thinking about building a new thicker gib?
    Attached Thumbnails Attached Thumbnails p9070546.jpg   p9060538-small-.jpg   p9070542-small-.jpg   p9060532-small-.jpg  

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  9. #47
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    Do not glue the shim in place
    Thickness of the glue layer will not be constant
    It only matters when installing It is static furthermore as it is at the back of the gib
    I sometimes bend over one end of the shim to hook behing the gib

    Peter

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  11. #48
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    Quote Originally Posted by Peter from Holland View Post
    Do not glue the shim in place
    Thickness of the glue layer will not be constant
    It only matters when installing It is static furthermore as it is at the back of the gib
    I sometimes bend over one end of the shim to hook behing the gib

    Peter
    I was thinking of using just a little bit of the threadlocker glue then assembling and tightening the gib to squeeze out the excess and hope there is not too much excess. I really like the idea of the hooks on the end of the shim, thanks for that. I wish I had thought of that earlier, I would of made the shim a little longer LOL.

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    You could softsolder on a piece of 2mm square brass on the last 2mm That would not matter that much But i would give it a try as it is and see how it goes

    Peter

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    Nice Job! I would not be afraid to leave the shim loose in there as where is it going? Or glue it to the backs side. What sort of material is it? No glue, Starrett shim stock 1/2" wide would work. Or some .005" Plastic shim stock or Phenolic. You should also check the the surface where the back die of the gig rests. It is usually high in the middle. Or the small end is dinged up when someone was tapping it out. Another simple way to check those small slides is on a surface grinder table or mill. Indicate one side and move the indicator to the other side. I would try to hold .0002" co-planer. Leave the gib loose .0005" to .001" for the oil wedge or film. If your rebuilding it for your use, I can see no need to worry about a shimmed gib. Are you going to use it now and then or as a production machine? Home use, a loose shim will stay in there for as long as you will own the machine.

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    Thanks for the comments and encouragement. I am trying to learn about scrapeing and this will be my first tool reconditioning, a home use lathe for sure. I did use steel shim stock and cut a notch in it for the adjusting screw (same notch the gib has) so it really can't move too far anyway. The glue may be a case of me overthinking things. I did scrape all surfaces to try to get them flat however I did not have a proper tapered edge straightedge so I used the unworn taper attachment dovetail to spot the insides. I do have some other decent square edge straitedges and a granite surface plate to work on the level areas. I have ordered a tapered edge NOS straitedge from ebay (Russia) so it will be interesting to see what that looks like and I can recheck the dovetails.
    I am curious about how to best set the gib force, it seems like it is hard to get a feel for it after the leadscrew nut is installed. Right now I can tip the compound and it will slide by gravity the entire length with no noticable shake so I think I will mark and measure the adjustment screw and put it in the same place after reassembling with the leadscrew. I could also assemble it dry, tighten up the gib snug so it does not slide, then back it out from there the distance that gives me the 0.001" to 0.0005" you recommend based on the known taper of the gib, then reassemble with oil. Is there a better idea to know what the oil gap is?

    I had not thought about using the milling machine to measure the dovetails but I do like designing and building tools so I should be all set now.

  16. #52
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    I was going to be doing a class in Springfield VT, but we had to cancel it because of Covid. One of my better students lives in NH and is a member here. Warren Jones. He goes up to The Gear Works in Springfield where we were going to hold the class. Maybe you could meet him there sometime and he could show you. I'll email him and see if he can come here and comment.
    Rich


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