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  • Evan
    replied
    Far too stiff a spring. It doesn't take much spring pressure to displace the metal when it is multiplied down to a tip that is only a few thousandths in radius. If the pressure of the spring is one pound and the tip has a contact area of .003 x .003 approximately then the pressure at the point is around 100,000 psi which is why it is able to engrave mild steel just fine as that exceeds the plastic yield.

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  • gundog
    replied
    I wonder how one of those spring loaded center punch tools would work for this?
    Mike

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  • Swarf&Sparks
    replied
    But a 1/2" to 1/4" collet adapter is readily available, even in this backwater.

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  • Evan
    replied
    I'll wait for Corrie to reply. I am interested to know why a graving tool with a 1/2" collet is needed. That isn't available commercially.

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  • Swarf&Sparks
    replied
    I think you've missed my point Evan.
    First post from a noob (with a CNC machine) and he needs someone to make a drag tool?

    If I'm wrong, I apologize to corrie, but those who have built or retro-fitted CNC, would have the means to build such a tool.

    Those who can afford off-the-shelf CNC, are unlikely to be lurking on this board. They'd be calling the supplier of the machine to order one.

    No offence to yourself, you dun damn fine work, as usual.
    Maybe I'm just getting too old and suspicious.

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  • Evan
    replied
    That's not very nice Lin. Even if I didn't know anything about machining but was somehow introduced to what a CNC can do I would buy just because they are so cool. It's a tool and one can never have too many tools... Humans are tool users. Only a few are tool makers.

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  • Swarf&Sparks
    replied
    Someone has a CNC machine that needs a drag graver, and doesn't have the tools or knowledge to make one?

    Hmmm

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  • Evan
    replied
    I almost didn't notice this thread had risen to the top again.

    This isn't a good time for shop work. I don't get near enough time for my own projects during summer as I have many other things to do. This week I will be mainly fabricating some gates for the fencing we put in earlier. When I do have some time in the machine shop I am working on an electric power unit and transmission for my bicycle.

    What I am trying to say is that I can't spare the time to make an engraving tool right now. If you are still interested come next winter let me know and I will consider it.

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  • corrie
    Guest replied
    Hello all, new here. Evan I realy like your tool holder. Would you be interested in making me one with a 1/4 or 1/2 inch collet size.If not I would understand. Where would I source the parts for such a tool holder? Thanks in advance.

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  • macona
    replied
    Couple sites that sell engraving tooling:

    http://www.2linc.com/

    and

    http://www.bitsbits.net/

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  • John Stevenson
    replied
    Dave.
    Can't post any photo's as the demo machine is in the showroom a fair distance away and this tool is with it.
    I can sketch it out later and post the sketch.
    It's quite simple, not far off what Evan has but a bit inversed, my spring is inside.
    The reason I slotted the outside, just a keyway really, is that a pin in the holder stops it turning and still allows it to float.
    Although these are hardened a carbide 4mm cutter will soon slam a keyway in these.


    You could pin the chuck and slot the body but it's then harder to strip down , my pin is an allen grub screw with the end turned down parallel.

    The spring is adjustable by a screw fitted right down inside the 7/16" UNF drawbar thread as mine is on a R8 fitting.

    As Evan says they need to be a good fit, mine runs in an oilite bush.

    They aren't new, they have been around for years. Dick Stevens did one in MEW a few issues ago but he made his collet chuck based on an Eclipse pin chuck.

    I don't have the time for this and if I can buy off the shelf reasonable then it save me money hence the use of the ER11 collet chuck as they are readily available and so are the collets.

    .

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  • davebaldwin
    replied
    Originally posted by John Stevenson

    I made one a while ago out of one of these.



    They are an ER11 collet chuck with a 16mm ground OD and a JT1 taper in the end.
    Although they are hardened it's possible to cut a slot in the side for a peg to fit and allow it to slide in a holder. My holder is a blank R8.
    .
    Can you post some pictures of what you have done? I was also curious as to why you slotted the collet chuck and not just drilled a hole for a pin? I'd have thought this would have been easier given the shank is hardened.

    Dave.

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  • Weston Bye
    replied
    Just ran across an article in the Fall 2007 Digital Machinist - "Drag Engraving Tool For CNC Mills" Though different in configuration, the tool is identical in principle to Evan's.

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  • John Stevenson
    replied
    Originally posted by Evan

    Even now anyone venturing to sea out of sight of land should carry a sextant and the ephemerids


    I've got some of their records..............


    .

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  • Evan
    replied
    I have no intention of trying to replicate an antique instrument in all respects. What I want to do is build a decent working sextant using modern methods and materials. I won't use brass, too heavy. It will be aluminum and anodized. It will also be nicely engraved, both functional and decorative. Sometimes what seems decorative is also functional, especially when it provides a more secure grip when handling the instrument.

    Even now anyone venturing to sea out of sight of land should carry a sextant and the ephemerids and know how to use them. It requires no batteries and isn't destroyed if immersed in salt water. Solar storms don't knock it out of commission. It can even be used to navigate without a timepiece, the ephemeris or even a compass. A common technique usually used before the advent of accurate clocks is to sail a rhumb line of constant latitude. Constant latitude is maintained by taking noon sights. Even a stick can be used but a sextant is much more accurate. Then all you do is aim for a point on the landfall coast that is either well north or south of your destination. That way when you make landfall you know which way to turn.

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