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Flexure Cut Off Blade Holder

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  • Bob La Londe
    replied
    Nothing is super critical if used in a tool holder. Get the insert edge close to the top of the nominal optimum tool size portion. Creep up on the blade fit with the dovetail cutter. Getting the face inside the blade slot parallel with opposing surfaces is nice, but not critical. You can always adjust a few thousands when clamping in tool holder by holding it against a parallel against the chuck face.

    Nothing is super critical except probably the blade fit. A sliding fit when cleaned with light resistance is probably perfect. When you get close take spring passes.

    I considerably simplified the design. I'm not concerned about the "strength" of the flexure. The clamping screws are more than adequate to provide strength. The graph size is not relevant. Its was just the handiest piece of paper. I did work from a print, but I see no reason to publish the print. Everybody's application could be a little different.

    If you wanted to make something like this to use in a 4 way tool post you could leave the nominal tool size clamping bar over size, take test cuts, and then mill a little at a time until you get an acceptable level of near zero nub.


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  • Bob La Londe
    replied
    Due to an almost comedic series of errors that long bar that was supposed to make 3 blade holders wound up being just one... and a little shorter than target length. Jack screws turned out to be completely unnecessary, and the blade was locked very solidly with just one clamping screw, although the length remaining still held three. I think if I make another (I probably will) I will leave jack screws out. If a blade binds I can always use a wedge.

    I think it was Steffan Gottswinter whose video I was inspired by to make this. I've not gone back through his channel to double check, but that rings true in my mind. I seem to recall him making a flexure holder for an import parting blade insert holder.

    I made test cuts from 1-7/16 to zero in 304 stainless. umahunter had given me two inserts to try with the blade. One was coated with what looked like TiN and one was uncoated. Both appears to be mediocre sintered carbide. The first cut with the coated insert was ok, but as I pushed the insert harder and harder it chipped welded the stainless and chowdered. The uncoated insert was used at modestly low RPM and feed per rev, and it cut from full diameter to zero very well. This is a very rigid blade holder setup inspite of being help in a toolholder. All the flex is in the lathe itself. The blade has more than 3/4 inch of stick out and I was very happy with its rigidity.

    The cut is amazingly good. At first I thought it finished with zero nub, but I can feel a tiny bit of nub with my finger tip. That's really just about center height. I just did the metal scale trick to set height, so its closer to center than I expected. It may even be on center with the tiny invisble nub just being with from me pulling off the part to quickly, or a tiny amount of flex in the machine overall. I would really like to try it with a very sharp polished insert, but I have not been able to find one for this type of turning blade. Of course I can sharpen an insert if I really want to try it.

    I had some issue seating the insert to my satisfaction. Finally I laid a lead bar across it and tapped the lead bar with a mallet.

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  • BCRider
    replied
    Primo work on both the slick little custom cutter as well as the holder so far.

    Like you I've thought a few times of doing something to permit a rear mounted tool post for some secondary operations. Using the new AXA tool post has taken away some of the urge but I still think it could be a handy feature at times. The top of my cross slide is flat so it's an option. But it's not all that thick so T slots are out of the question. Instead I've considered the option of a few threaded holes probably 3/8-16 to permit mounting a rear tool post in a couple of placement options. But I've never hit a wall where I couldn't do something or where it would save the sort of time that would be needed to justify the operation. On the ToDo List though is removing the cross slide to add ball oilers so I don't have to finger smear the oil on the dovetails. Perhaps while the slide is off I might just drill those holes. They'd be capped off to keep the swarf out with some flat head screws that would be milled off flush with the surface so they don't collect any junk.

    Jackary, nice job of that rear post! It's also pictures like yours that make me think a rear post might be a good idea.

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  • Bob La Londe
    replied
    I had to make a little 10 degree D-bit dovetail cutter. I'm not sure that was the right angle, but it seems to be. (Old broken 1/4" carbide end mill shaped on the T&C grinder.) This piece of bar is intended to make three of these. Still a bit of work to do. Next is to drill and tap for clamping screws and jack screws. Then cut the flexure. Saw cut them apart, and then do some basic clean up. The face up on the bar is the original finish. I thought about taking a skim cut, but its an unimportant surface. The fit is really darn good, but I got lucky.

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  • Bob La Londe
    replied
    Yes, I have considered making a one piece tool post to go on the back of my cross slide. I do not have a t-slot table cross slide on the primary lathe, so I would have to "decide" to modify it and figure out how to do it without risk of breaking it.

    The little turret lathe (if I ever have time to work on it) already has two tool posts on its t-slot table.

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  • jackary
    replied
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    I made this a while ago, it is very rigid the block is drilled through about 5/32" dia and slits are cut. The horizontal slit cuts into the hole and the vertical slit cuts about 1/16" above the hole. The holder can be rotated 180 degrees for a larger blade. The slits can just about be seen.The base has a slight slope enabling height adjustment.
    Alan
    Last edited by jackary; 02-19-2022, 02:08 PM.

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  • old mart
    replied
    I have had both types, and if you are intending to make the one piece type, then the clearance between the 120 degree blade holders must be a minimum to be able to slide the blade in as the flexure will be very small. The thinning down to make the flexable "pivot" should be done at a late stage and you could try tightening the clamp screws during the thinning using a blade in place to get enough flexibility without overdoing it. I would also give the clamp screws clearance holes on the top part. The one piece type that I had was an Iscar. I made the 2 piece type for a single 26mm holder and a double sided reversable 26/32mm rear toolpost, it was easier for me and did not require slitting saw cuts.

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    Last edited by old mart; 02-18-2022, 04:28 PM.

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  • BCRider
    replied
    Simple holder might not be so simple if the slot in the tool holder is not deep enough to put the gripping power of the screws out far enough from the flexure hole. Notice where the screw marks are located right over the hole instead of out towards the cutter in Noitoen's picture.

    Clearly it works but it's not the classically correct way to do things. It's like a strap clamping setup with a really poor setup that puts the clamping stud back right beside the rear support instead of forward towards the work piece that needs to be held down. I'd call it a case of "good enough is good enough".

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  • Bob Engelhardt
    replied
    That IS simple! Simple always gets high marks from me. Well done.

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  • Noitoen
    replied
    Simple holder I mentioned earlier
    You may only view thumbnails in this gallery. This gallery has 1 photos.

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  • Bob Engelhardt
    replied
    Originally posted by BCRider View Post

    ... The flexure style to combat chatter has a long history. ...
    I was wondering what the advantage was. Thanks.

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  • Bob La Londe
    replied
    I think the thought for the tool holder held blade holder is that you can set it lower on small lathes so you can use the taller blades. I actually have a tiny 2 piece somewhere for using parting blades on the 7x10-16 mini lathe with a tiny A2CNC tool post. If you look at my sketch and many of the similar tools others have posted you will notice on most the top of the blade is at about the same level as the top of the block that would be clamped in the tool holder, but the bottom of the blade is lower than the bottom of that part.

    My purpose is specifically to hold an insert blade. Taper is not an issue. They are flat with a shallow peak roof on the top and bottom. I will need to machine a slight dovetail in my holder. I'll probably need to make a tool on the T&C grinder to do that.

    Yes, I know when I count my time it would be an order of magnitude cheaper to just buy one, and I have made a point in the past to say mine is a for profit shop. Not a just a hobby shop. The thing is that projects like this hone my skills. I do have in my opinion some (just a few) master level skills at a very limited number of things. I have a lot more I don't and sometimes I just like making something and not worrying about meeting about a customer spec. I make things sometimes for the same reason other people do. Because I enjoy doing it.
    Last edited by Bob La Londe; 02-17-2022, 02:57 PM.

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  • BCRider
    replied
    Originally posted by buffdan View Post
    Winkys workshop has a video up, and plans.. Maybe?
    I watched the Winky videos a few days ago. The flexure style to combat chatter has a long history. Flexing holders seem to often show up for use on less solid lathes. But even my buddy with his SB9 is doing fine with a solid parting tool holder.

    It also comes back to how and what the lathe is mounted onto. My 12x36 in the old shop and perched on the old "tin lunch boxes on end" used to sing soprano frequently even when using back gear if I got even the least bit moderate in my enthusiasm. That same lathe with no changes other than my filled concrete construction block pedestals hardly ever even chirps when parting even on the low direct speed. Same lathe, same gib setup same tools. Just a solid and very supportive base.

    But not everyone has a really solid lathe. If I were still running the Myford 7 I'd likely be all over the Winky's flex holder and even modify the idea to work on a rear post (another apparently effective idea for lighter lathes that like to sing). But I fixed my own chatter issue with the new mount..... Which you can tell I'm still gushingly enthusiastic over. I honestly feel that a good solid and rigid beam of some manner as a lathe mount is a huge deal for any bench style lathe.

    Bob, I think your idea for a holder like that is stellar. But I do like the idea that one of the others had earlier for making a custom dovetail direct mount.

    My CAD computer is sick just now so the past week has been me on my notepad. But using the finest of GPAD (That's Graph Paper Assisted Drawing) here's a sketch that might be of interest with the same idea. Both in AXA for my own needs but certainly adaptable. I did a "tool holder" version as well as a dedicated version The dedicated version is kept pretty narrow to reduce overhang. The adjuster might need to go into the body off one side of the dovetail rather than over the tool area as per usual. As shown the saw cut for the flexure comes pretty close to the back of the dovetail.

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  • BCRider
    replied
    Originally posted by Bob Engelhardt View Post
    Here's an interesting & very simple one that uses side clamping, but with a 2-piece wedging action; the force being supplied by the holder:
    https://www.aliexpress.com/item/4001243858781.html
    I'd worry about the side pinch style you linked to. First off many parting blades are tapered and narrow at the base. So if it catches and lifts the back at all it'll lift way too easily after that. Also there will be some flex along the base so most of the pinch will be lower down. Or for the pinch to be actually equal along the whole sides of the blade there would need to be some deliberate mismatch to the tapers so it starts out tight at the top and as the outer side of the holder flexes under pressure the sides would come into full and even pressure contact at some fairly specific tightening pressure.

    Nope, I'll go for the top and bottom edge hold where the metal blocks any tendency for the blade to catch and lever itself up.

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  • buffdan
    replied
    Winkys workshop has a video up, and plans.. Maybe?

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