Flexure Cut Off Blade Holder

[Bob La Londe]

Bob, you're not wrong about seeing that style of flexure holder in the past week. I'm pretty sure it was well displayed in a YT video that I also saw. But like you I hope no one asks WHICH video. The method also struck me as being very home shop friendly.

It's worth noting that the flexure web in your sketch is only the width of the one saw cut running down from the top. And the narrow width of that means that you will need to strictly limit the amount of movement needed so that small area isn't stressed into cracking.

Your sketch also includes a height adjuster. But the sketch shows a bar which would clamp into a holder that has its own height adjuster. So really that whole top between the mounting bar and the part with the setscrews could be relieved down to just over the height of the securing bar and make for a much wider flexure joint which would give a zero risk of any stress cracking.

Yep!

The adjuster is an unintentional misdirect. I should not have put one on this part.

A buddy of mine loaned me (no particular time limit) an insert type parting blade to try out. This is the new "backup" blade in umahunter's shop, so I only need to run it back right away if he jacks up the one he is using. He has a smaller lathe and is using a 2 piece block similar to the one in post #4. I could make one like that, but I have kinda fallen in love with the flexure type holder idea.

My intention is to make a holder that is a very close fit to try it out. If I really like the blade I'll buy one (probably two so I also have a backup) with some inserts. There will not be much flex needed in the flexure.

[Mark Rand]

PeWe tools do a version for Multifix style toolposts.

https://pewetools.de/produkt/abstechhalter-fuer-26er-abstechschwert-at2090l-inkl-hss-klinge/

I've got one and it works very well.

[welderskelter]

I seen a spring type cut off tool on you tube that impressed me . Course it dont take much to impress me.

[buffdan]

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

[BCRider]

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.

[BCRider]

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.

[Bob La Londe]

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.

[Bob Engelhardt]

... The flexure style to combat chatter has a long history. ...

I was wondering what the advantage was. Thanks.

[Noitoen]

Simple holder I mentioned earlier

[Bob Engelhardt]

That IS simple! Simple always gets high marks from me. Well done.

[BCRider]

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".

[old mart]

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.

[jackary]

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

[Bob La Londe]

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.

[Bob La Londe]

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.