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Thread: trying for an elegant and effective quick change tool post

  1. #1
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    Default trying for an elegant and effective quick change tool post

    I'm looking to put together a simple quick change tool post with emphasis on ease of manufacture and positional accuracy. I'm not much worried about being able to change tools one-handed, or in record times. I want to be able to spend time setting up my tools and know they're in the same spot when I change them out.

    I came across Lew Harstwick's awesome design here at homemadetools.net. I like the idea of ground rods and V grooves.

    In trying to fit it with my wants I've decided to tackle it a bit differently, shown below:


    This is a top view. The tool holder is on the left. The two ground rods and related hardware are roughly center. The tool post is on the right. My Sieg C2 uses a 10mm stud to mount the tool post, so there's a through-hole centered on the tool post to accommodate it.

    To pull the tool holder against the post I'm looking at using a regular T-slot and T-slot nut engaged by a 10mm socket-head cap screw. This is the horizontal screw in the drawing. You can see that it is offset vertically to clear the tool post stud. You can see a similar through hole for mounting a tool holder parallel to the axis of the lathe, which is similarly offset.
    I'm thinking about changing the design to have the through-studs centered between the ground rods, which would put the tool post stud offset from the body of the tool post.
    One issue I'm foreseeing is that t-slot nuts are relatively short, which means they'd only work for a small vertical range of tool holder positions. To increase travel I'd either have to make one as tall as the tool post, which wouldn't be hard, or bore the block in several places to allow me to put the nut in a few different vertical places, depending on the desired height of the tool.

    What are your thoughts on this idea? What do you think of the through-studs, the regular T-slot nut, and the positional accuracy of the ground rod on v-slot design?

    Thanks!
    Last edited by burdickjp; 03-21-2014 at 09:52 PM.

  2. #2
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    Check out this design; I think it does everything you want:







    http://finance.groups.yahoo.com/grou...20Tool%20Post/

    Dead solid, very good repositioning accuracy (<0.001" on all three axis), really easy to make in a small/home shop, all adjustments are independent. No Vee Grooves, No Dovetails, No Keys! Just a round post with a generous flat and a screw for vertical adjustment.
    Last edited by Paul Alciatore; 03-21-2014 at 10:32 PM.
    Paul A.

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    You can't win and there is a penalty for trying!

  3. #3
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    For that design I would make only one V slot near the cutter and one flat at the back. If the 2 Vs on all the toolholders aren't perfectly aligned with the round rods, the toolholder may not seat the same every time. If 1 V and 1 flat it will always align with the 1 V. Also, I would make the T nut bigger. If the bolt for the T nut is 1/3 of the way down from the top you will still have about 2/3 of the block for vertical adjustment. You will have to hold the T nut from turning while you fit the toolholder on it unless you pin it to the toolpost with a sliding fit. In general, it seems like a workable plan;

  4. #4
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    I did see the D-shaped design, but for some reason completely forgot about it.
    Here are my arguments against it, and possible solutions:
    The tool holders themselves are more complicated. Not a show stopper, but it would be nice if the tool holders were as simple as possible, since a few of them need to be made.
    The tool holders would likely be better with a big V rather than a circle. It would then pull into the V, which would likely be more repeatable and more rigid.

    Quote Originally Posted by Toolguy View Post
    For that design I would make only one V slot near the cutter and one flat at the back. If the 2 Vs on all the toolholders aren't perfectly aligned with the round rods, the toolholder may not seat the same every time. If 1 V and 1 flat it will always align with the 1 V. Also, I would make the T nut bigger. If the bolt for the T nut is 1/3 of the way down from the top you will still have about 2/3 of the block for vertical adjustment. You will have to hold the T nut from turning while you fit the toolholder on it unless you pin it to the toolpost with a sliding fit. In general, it seems like a workable plan;
    Good point on the single V slot. I'll have to think about how to implement that while allowing the tool holders to be able to mount both parallel and perpendicular to the lathe axis.

  5. #5
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    You could put 2 Vs in the toolholder and only use one or the other.

  6. #6
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    Quote Originally Posted by burdickjp View Post
    I did see the D-shaped design, but for some reason completely forgot about it.
    Here are my arguments against it, and possible solutions:
    The tool holders themselves are more complicated. Not a show stopper, but it would be nice if the tool holders were as simple as possible, since a few of them need to be made.
    The tool holders would likely be better with a big V rather than a circle. It would then pull into the V, which would likely be more repeatable and more rigid.

    ...<snip>...
    I guess you are serious. On the tool holders, his definitely use less material. I don't know if that is better if you want rigidity. But look at the operations needed to machine them. I do use two tool grooves vs. one, but for both hooders it is a simple, rectangular slot and not difficult to make. He has two Vee grooves that must be both parallel to each other and, as already brought up, exactly the correct distance apart. Then you need to machine a Tee slot and that is at least a couple more steps. On mine, you drill a hole and bore it to size. The only thing it needs to be accurately located to is the flat that the clamp is bolted to and that is easy to mill if you follow my instructions. If you make a mistake and go too far, a simple shim will save the part. You are going to spend a lot more time making his holders than mine.

    As for rigidity, by clamping around a full 360 degrees on a large diameter post, you get what is essentially a single piece of solid metal. I doubt that any dovetail or other design I have ever seen can possibly be more rigid.

    I have used these holders for years now and can attest to their accuracy, rigidity, and durability. And they are very easy and quick to change. If you are making a bunch of identical parts that quickly becomes a very valuable feature.
    Last edited by Paul Alciatore; 08-03-2016 at 11:00 PM.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  7. #7
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    Quote Originally Posted by Paul Alciatore View Post
    As for rigidity, by clamping around a full 360 degrees on a large diameter post, you get what is essentially a single piece of solid metal. I don't that any dovetail or other design I have ever seen can possibly be more rigid.
    Please don't take my criticism as anything negative. That's not what I'm intending.

    Unless I'm missing something, it does not look like you're clamping the full circle. When you engage your clamp it's going to push against a point on the ID opposite the flat. This is best illustrated by imagining the OD of the post as much smaller than the ID of the holder. Any inconsistencies between the holder and post will cause it to contact at a different point on the ID. If there's anything in the way it will change where it contacts.
    A V, on the other hand, will draw into the same place every time. It has no choice but to. It would be more forgiving, so to speak.

    Would this cause an appreciable difference? Probably not.

  8. #8
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    The fit is fairly close and the holder, although massive, IS flexible enough to distort enough to grip all around. So it does have full contact when clamped, not just at two places. Much like clamping the head of a round column mill to the round post: you get 360 degree contact. The generous sized flat provides very good indexing action. It has no choice but to lock to the same position every time. And I have verified this with multiple holders.

    When Lew's holder is making a heavy cut, it tends to rotate (tool tip down). This produces a strong force opposing the clamping to the post. If enough force is generated, it will rotate and be pushed away from the post. Toolguy's suggestion of only one Vee groove and one flat would make this more likely to happen as the flat would not resist this rotation at all. If you make it, I would stay with the original two Vees. And don't get me wrong, it is a good design, but it has it's flaws or weak points. No design is perfect.


    Quote Originally Posted by burdickjp View Post
    Please don't take my criticism as anything negative. That's not what I'm intending.

    Unless I'm missing something, it does not look like you're clamping the full circle. When you engage your clamp it's going to push against a point on the ID opposite the flat. This is best illustrated by imagining the OD of the post as much smaller than the ID of the holder. Any inconsistencies between the holder and post will cause it to contact at a different point on the ID. If there's anything in the way it will change where it contacts.
    A V, on the other hand, will draw into the same place every time. It has no choice but to. It would be more forgiving, so to speak.

    Would this cause an appreciable difference? Probably not.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  9. #9
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    Quote Originally Posted by Paul Alciatore View Post
    The fit is fairly close and the holder, although massive, IS flexible enough to distort enough to grip all around. So it does have full contact when clamped, not just at two places.
    I was wondering about that as I was walking through the grocery store just now. Thinking can happen anywhere, I guess. Very cool.

    I finished out my initial idea:


    Things changed: perpendicular and parallel through screws are now centered and intersect, so you get one or the other, but not both. This puts the t-slot nut centered between the two rods. The tool post stud is offset. There's a screw and two thumb nuts to locate the tool holder vertically. The vertical locating screw is M6. The screws holding the rods to the tool post are M4. The through screw is M10. It'd be nice to reduce the tooling requirement to as few tools as possible.
    Last edited by burdickjp; 03-22-2014 at 01:10 AM.

  10. #10
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    While I understand the desire to spend time, rather than money, and the limits imposed by available machines you aren't going to improve on an Alorus (or it's near kin). In the same way that a big rock or a hunk of metal, hand held, can do what a hammer does, but would not do it with the precision and efficiency of a hammer. Don't try to re-invent the wheel unless you can come up with something that works better...

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