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Thread: Calipers, Digital Dial?

  1. #61
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    Quote Originally Posted by ian maybury View Post
    I was brought up on both systems, and even worked for a couple of years way back as a machinist using both. There's situations where i'm much happier with mm (as in drawing/laying out work), and others where i'm more intuitive with inches.(household sized measurements and believe it or not thou based fits etc in engineering) Inch fractions i understand, but they really cause me problems in that other than very simple addition or whatever requires a pencil and paper.

    What i'm maybe saying is that there's no definitive answer - that it's mostly a matetr of what we learn and become proficient enough in that it's intuitive. Trouble is as we get older it's harder to change/learn new stuff in the deeply embedded way we do when younger...
    And that's the crux of the matter. As far as digital calipers, I do wish manufacturers would forego 1/128ths. I just have to move the head until I see a figure that is usable.

  2. #62
    Robert, I find caliper accuracy quite necessary in a few woodworking operations. My most common example is when turning the open end of my tool handles where a blade goes into a hole and a brass ferrule goes over the outside. I test every handle OD for a +.001" -.005" fit so that the ferrule slides on and with a slight bit of epoxy fits firmly without play. Experience has told me that undersizing the OD by anything more than -.010" is both detrimental and poor workmanship. There are occasional other situations where super tight tolerances are necessary but are fit tested rather than measured. Generally, a properly fit mortise and tenon joint is within .005" and if you go as loose as .010-.015" the fit is noticeably sloppy. As much as possible in furniture work I avoid measurements altogether and use a story stick.
    Dave Anderson

    Chester, NH

  3. #63
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    Interesting Dave. Brian is running a post discussing the handle he is working on for his new Gennou head, similar to the one Derek made for his. Dave mentions "turning the open end of my tool handles", which sounds like he is turning tool handles on a lathe?

    I am interested as I am thinking about some sort of lathe to help with chair parts and tool handles. I prefer to do as much of this work as possible with hand tools, still working to the tolerances Dave mentions probably isn't going to happen with just hand tools. In the class I took a couple weeks ago at Country Workshops we made short wide spindles for Welsh Stick chairs from splits out of red oak. We made roughly square pieces from the splits, then octagons with spokeshaves. We roughed out tapered spindle shapes on a lathe as we formed the tenons on each end. We finished the bodies with spokeshaves to leave them a little rough but finished the tenons on the lathe to get a more precise fit.

    I have been wondering about the precision we make tapered tenons to. In the class I took recently with Chris Schwarz he explained that the reason tapered tenons driven into corresponding mortises in the seat of a chair or bench are strong but do not split the wood they are being driven into has to do with the different woods used for the various parts. The chair legs are typically very hard wood (tenon) where the wood used in the seat (mortise) is typically a softer wood. The idea being that the harder wood tends to embed in the softer wood rather than split it. If the hard piece can compress the wood in the softer piece, might the precision of the fit be less significant?

  4. #64
    You and CS are correct in the sense that with either a round tapered tenon or a faceted tapered tenon the softer wood of the seat deforms when the harder legs are driven into the tapered mortise. What I meant on precision fitting is that we work to very tight precision tolerances most of the time when making furniture with either hand or power tools but often don't measure, but rather adjust to fit. In most things we can actually get a better fit and work to a tighter tolerance with hand tools than with power tools. An easy example is the absurd notion of trying to remove .001-.003" from the edge of a board with a table saw, planer, or power jointer. A hand plane of almost any type would do the job quickly, easily, and without setups and adjustments to the machines.
    Dave Anderson

    Chester, NH

  5. #65
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    Dave,
    I find caliper accuracy quite necessary in a few woodworking operations. My most common example is when turning the open end of my tool handles where a blade goes into a hole and a brass ferrule goes over the outside. I test every handle OD for a +.001" -.005" fit so that the ferrule slides on and with a slight bit of epoxy fits firmly without play. Experience has told me that undersizing the OD by anything more than -.010" is both detrimental and poor workmanship. There are occasional other situations where super tight tolerances are necessary but are fit tested rather than measured. Generally, a properly fit mortise and tenon joint is within .005" and if you go as loose as .010-.015" the fit is noticeably sloppy. As much as possible in furniture work I avoid measurements altogether and use a story stick.
    THANK YOU
    I am sick to the teeth of arguing that one so I kept quiet.
    + 1 on the usefulness of story sticks . . . also go/no go "gauges" ; self made or otherwise.
    PS: the Mitutoyos I spoke of way earlier on are for my metal working but find use in the wood shop, just not for their ultra precision obviously.
    Sharpening is Facetating.
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  6. #66
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    Hilton,
    Your plastic one is no doubt easier to read than my brass one.
    There is a brass one with a white strip with black graduations I almost bought hoping it would be easier to read but I don't really need it right now.
    I am adverse to plastic calipers (just a personal phobia; I'm in counceling for it making great progress . . . in a controlled environment where I feel safe I can hold one in my hands now for almost a minute) . . . but they have their place especially if fiber reinforced.

    PS: obviously the plastic caliper is perfectly useful for the purpose you use it for.
    Allow me to give an example of why I am ascared of plastic in semi precision situations :
    We had a batch of assemblies that used to be made for decades and decades out of aluminum ; they had hardened steel shafts and adjustable hardened bearings. From the factory the bearings were always just put together but not adjusted. Every mechanic was expected to adjust the bearings to a zero play setting with only a very small or zero amount of binding (after all they were going to break in some). Play was unacceptable though.

    There was a big blow up. I was in charge of inspection. There were a lot of assemblies (plastic ones only) that had a fair amount of play upon final inspection. Here I am going around telling some of the best people in the business that they didn't know what they were doing and that they were lying to me when they said they had adjusted the assemblies for zero play.

    Long story short. I put several of the dambed things on the roof in the sun. All had zero play when I put them up there (adjusted at shop ambient about 70°F or lower) It was only 90° to 100°F on the roof. Every one of them had very significant play.

    Plastic machine parts peeesses me off.

    PPS: the adjustments were often done early in the day when the shop was cool and beings there was no air conditioning (swamp cooler) by after noon the shop was around 90°F so the bearings developed play from the plastic moving. Only 20 or 30 degrees. The difference between inside a trouser pocket and room temp.
    Last edited by Winton Applegate; 03-31-2015 at 3:05 PM.
    Sharpening is Facetating.
    Good enough is good enough
    But
    Better is Better.

  7. #67
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    Quote Originally Posted by Winton Applegate View Post
    There was a big blow up. I was in charge of inspection...
    LOL, Somehow, I can picture this.








    Edit = you know I'm just kidding Winton, I couldn't resist
    Last edited by Pat Barry; 03-31-2015 at 7:28 PM.

  8. #68
    Quote Originally Posted by Robert Engel View Post
    Really? If there's a 1/64th gap I submit you will have a snug fit, so how can .020 be that sloppy?

    1/64th = .016, so for the sake of argument, permit me to revise the .020 figure.
    I mean, you have to have some room for the glue, don't you?

    My point is, we are woodworkers, not machinists.
    Our building material is alive and moves and shrinks and expands, so cutting and fitting beyond 1/64 is a waste of effort.
    If I make a tenon that is 1/64 undersized, it is going in the burn pile or getting a shim glued to it.

    If your dovetails have gaps of more than about .005, they will look pretty sloppy (and that's a generous number).

    An edge joint that has an .015 gap in the middle is a recipe for failure, even if you manage to pull it together with clamps.

    A door stile that is twisted by .015 will throw off the flatness of the whole door.

    My point is, we work to tolerances of much closer than .015 all the time. Whether we need calipers for that is a different question--only one of the situations I listed above would involve calipers, and it certainly doesn't require them. I use calipers because I used to be a machinist and they're practically surgically attached to my hand, but in most cases you can achieve the necessary precision without them. But the precision is definitely necessary if you are trying to do fine work.
    "For me, chairs and chairmaking are a means to an end. My real goal is to spend my days in a quiet, dustless shop doing hand work on an object that is beautiful, useful and fun to make." --Peter Galbert

  9. #69
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    I couldn't agree more. For general carpentry, a 1/64 gap seems small, dead on even. For furniture and other fine wood working, 1/64 is a HUGE gap.

    I use variety of methods to insure accuracy. One of them is a dial caliper with 1/64" increments. However, it's pretty easy to judge 1/2 and 1/4 of that on the dial without dedicated marks.
    Quote Originally Posted by Steve Voigt View Post
    If I make a tenon that is 1/64 undersized, it is going in the burn pile or getting a shim glued to it.
    ...
    My point is, we work to tolerances of much closer than .015 all the time.
    -- Dan Rode

    "We are what we repeatedly do. Excellence, then, is not an act, but a habit." - Aristotle

  10. #70
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    Quote Originally Posted by Daniel Rode View Post
    ...For furniture and other fine wood working, 1/64 is a HUGE gap.

    I use variety of methods to insure accuracy. One of them is a dial caliper with 1/64" increments. However, it's pretty easy to judge 1/2 and 1/4 of that on the dial without dedicated marks.
    I tend to agree in principle with this sentiment about wanting your fine work to be well fitted, however, I suspect that we achieve tighter results through a practice of check and trim rather than using a fine caliper. I may be the oddball here but I rarely use my caliper. In fact, I only recall using it in the past year to verify the size of a bolt I cut off my truck in order to find a metric replacement. I have never used one of my calipers for woodworking, not even for setting my power tools (ie depth adjustment , etc). Even for the job Dave described above you don't need a fancy caliper.

  11. #71
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    I don't measure everything I'm building with calipers, but yes it's very likely that a great deal of it is much closer than 1/64

    Quote Originally Posted by Robert Engel View Post
    Really? If there's a 1/64th gap I submit you will have a snug fit, so how can .020 be that sloppy?

    1/64th = .016, so for the sake of argument, permit me to revise the .020 figure.
    I mean, you have to have some room for the glue, don't you?

    My point is, we are woodworkers, not machinists.
    Our building material is alive and moves and shrinks and expands, so cutting and fitting beyond 1/64 is a waste of effort.

    As to your example, you wouldn't have the issue with a tapered sliding dovetail.
    Not everything I make is glued and tapered sliding dovetails are not always feasible....but even then they will be friction fit when they are much tighter than .020" clearance.

    A very strong glue joint relies on a tight fit, not bridging a gap.

    .020" is the thickness of a commercially cut veneer, how often can you fit that in with one of your mortise and tenons?

    Point still stands at .016"
    Last edited by Brian Holcombe; 03-31-2015 at 7:18 PM.
    Bumbling forward into the unknown.

  12. #72
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    I think it is important to recall the original context of the OP. At least in my young experience turning, it is very hard to judge the size of a round object on a lathe. I understand that normally we might test the fit and adjust by hand with hand tools. Unfortunately when the tenon being worked is in a lathe it gets a little complicated to pull it out and check it in the mortise. I have ten 9-10" spindles lying on a chair seat. I tried to get them close to the right size on the lathe using an open ended wrench and mechanical calipers. They are all significantly oversized. Once the wrench slides over the tenon being worked the tenon being worked is too small, a very hard problem to fix. With a dial or digital caliper I can tell exactly how much over sized the piece I am working is. It may even be possible with some devices to check size on the tenon turning in the lathe.

    Actually I find multiple types of tenons in Windsor chairs which require differing degrees of precision. The tapered tenons on chair legs that fit in open ended tapered mortises in the chair seat need to make contact with most of the sides of the mortises. The wedge placed in these joints helps but the joint still requires consistent pressure throughout. Driving the tenon into the mortise too firmly will crack the seat, which that late in the game is a real bummer. The straight mortises in the outside of the chair seat and in the arm/back can be much less precise as the spindles these mortises hold in place are designed to flex and move anyway. As long as the spindles do not pop out of the bottom joint, unlikely if the mortises are deep enough, close is good enough. The top joint on each spindle needs to stay put in the bow/arm but, a wedge in this joint usually assures this.

    The number of objects being fitted to mortises also comes into play here. With two tenons on rungs and spindles and tricky tapered tenons on the chair legs the extra time to fit all those pieces can become a larger factor. My issue is getting each tenon as close as possible to the correct size as early in the work as I can.
    Last edited by Mike Holbrook; 03-31-2015 at 7:37 PM.

  13. #73
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    I tried to get them close to the right size on the lathe using an open ended wrench and mechanical calipers. They are all significantly oversized. Once the wrench slides over the tenon being worked the tenon being worked is too small, a very hard problem to fix.
    Your gonna need a bigger wrench.

    There are locking jaw Crescent wrenches that can be set to any size within their range.

    Sometimes I make a gauge by drilling a hole in a piece of scrap then cut it in half.

    Here is something Junior Strasil posted that can be modified to check tapered holes:

    http://www.sawmillcreek.org/showthre...cket-Taper-Jig

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
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  14. #74
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    I used to have a digital caliper that read in decimal. I used it, but not often. A couple years ago, I picked up a fractional dial caliper and I use it all the time. For tenons, I'm likely to use it to measure the thickness of the rough cut or to compare left to right top to bottom to see if I'm staying square. It's just a fast and convenient way to measure a variety of things.

    The final fit is achieved by sneaking up on the cut, not by working to a specific measurement. Each tenon is custom fit to it's mortise. I think most hand tool woodworkers do this.
    -- Dan Rode

    "We are what we repeatedly do. Excellence, then, is not an act, but a habit." - Aristotle

  15. #75
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    Wrenches ? . . . on a Windsor chair . . . ? I Couldn't help saying that.

    I know what you mean though.

    Your gonna need a bigger wrench.

    There are locking jaw Crescent wrenches that can be set to any size within their range.


    Newbie comment here so take it as such but . . .

    and I do zero turning on a wood lathe but . . .
    and if I wanted to make round things the right size I would put it in my metal lathe and with very little concentration make it to the right size but . . .
    and I have watched enough Norm to think I know but . . .

    couldn’t/ wouldn’t a guy just set one of these things to the close to done size and another one to the done size and turn to that ? ? ? ?
    Set it with a measuring caliper of some kind that is close enough even if you just put the inside measuring jaws in the hole and lock the screw and use it to set the things above without looking at the little gradgeeeations.
    Sharpening is Facetating.
    Good enough is good enough
    But
    Better is Better.

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