Thread: Too much rigidity?

I've never seen a parting tool holder break like that. I would have expected the blade to break before the holder.
Was the tool on centre? for parting it needs to be as close to on centre as you can or slightly below.The idea being if its above centre and you have a dig in it will increase the depth of cut.If its on centre or slighty below and you have a dig in it will decrease the depth of cut.
I have a couple of tangential holders which are quite good. Have attached a rough sketch. With this design if there is a dig in, the holder flexs at the top and the point of the tool moves away from the work.

regards
bollie7

Originally Posted by bollie7

I've never seen a parting tool holder break like that. I would have expected the blade to break before the holder.
Was the tool on centre? for parting it needs to be as close to on centre as you can or slightly below.The idea being if its above centre and you have a dig in it will increase the depth of cut.If its on centre or slighty below and you have a dig in it will decrease the depth of cut.
I have a couple of tangential holders which are quite good. Have attached a rough sketch. With this design if there is a dig in, the holder flexs at the top and the point of the tool moves away from the work.

regards
bollie7

That's a "swan neck" holder - something I'm definitely going to investigate following my Indian made toolholder breakage. They might be hard, but they haven't got the heat treatment quite right - it's far too brittle. Note this blade also survived unscathed.

Jordan

Looks like the business end of the parting blade moved sideways which put all the pressure on the back of the tool holder.

Nev

Originally Posted by SurfinNev

Looks like the business end of the parting blade moved sideways which put all the pressure on the back of the tool holder.

Nev

Looks like that to me as well. If it is what happened, I don't think any parting holder would hold up to that.

Dave

I think you'll find the bottom of the tool holder failed first. I assume there is a large part missing off the bottom, the black part below the 6 should continue almost all the way across to the left.

But I could be wrong

Stuart

You can see the piece I mean in the overhead shot, its down on the carriage.

Stuart

Stuart,
I see what you mean.
Bryan,
Time to use that milling attachment and make a new one.
I would say it is either Chinese or Indian tool holder that was mad out of crap metal.
If you bought it new take it back or if off ebay send them a picture.
As for your spindle adapter do you have a picture of it?

Dave

Bollie7, I'm pretty confident I had the tool on centre.

Jordan thanks, I was trying to remember who posted that breakage.

Nev & Dave, Stuart is correct. The blade pivoted vertically, breaking off the front bottom and rear top of the holder.

The holder was pretty cheap, and I don't know if I'd try to claim warranty, but I might still let them know of the failure.

Dave, re making a new holder, I'm thinking about how to achieve the right angles for a tapered blade with only square cutters. Maybe I'll just buy one.
I'll take a pic of the spindle sleeve if you like. Are you thinking about why it's coming loose?

Bryan You're worried about the bottom corner being 90deg? That might not be a bad thing as it would tend to push the blade against the holder wouldn't it? Although it would mean the blade was only supported on one corner. If you dont like this, as the holder needs an angle over 90deg you just need to make 2 cuts. I've been looking to buy one for the big blades I have, having seen this I might just make one. I made one that uses hacksaw blades and works pretty well.
Stuart

Originally Posted by Bryan

Dave, re making a new holder, I'm thinking about how to achieve the right angles for a tapered blade with only square cutters. Maybe I'll just buy one.
I'll take a pic of the spindle sleeve if you like. Are you thinking about why it's coming loose?

Yes I was thinking why it came loose, but with out seeing it it's a bit hard to work out.

With the cut off holder you could mill it out then set it up in the toolpost parallel with the main ways, make up a tool holder for a piece of HSS to put in the chuck (or between the chuck and the tail stock) with the HSS shaped to suit the angle needed and use the carriage as a shaper to take out the little bit that needs the angle. You could rotate the tool holder in the chuck to adjust the depth and with a sharp tool it wouldn't take long.

Dave

Ok I'm confused (not for the first time) so I drew a picture.
If Bryan can mill the one on the left, why cant he reset and make two more passes in the mill to square up the top and bottom?
Or are you guys talking about something else?
Stuart

The parting off tool holders i have used have had like a dovetail slot which the parting tool can slide in and out in his may be like that

The HSS blade type parting-off tool I have is held in my 4-way toolpost for rigidity.
When mounted with the base of the blade holder flat, the tailstock side of the blade tool is vertical, no cutting clearance at all.

It is easy to check the side clearance by putting the holder on a flat surface with an engineer's square against the two sides.

I put a shim behind the bottom of the blade in the holder to equalise the vertical clearance on the two sides.
One day, I will mill the bottom of the holder appropriately.

An additional change is to mill off the top of the holder towards the rear so that the back toolpost screw bears directly on the blade.

The two changes above made all the difference.

At the limit, I broke (hell of a bang) the blade when I attempted, unwisely, to part off some steel tubing.
The blade was pulled forward as it cut into the bore.

John.

John, your holder sounds similar to mine. The shim is shown as a red dot. I think I'd like to improve on it instead of reproduce it. Also I think that blade is a bit big for my machine so I'd like to go down a size. The little parting tool I ground out of a 3/8 stick seems to cut so much easier, presumably because it's half the thickness. It's just quite limited in depth.

Stuart, I'd like to know more about your hacksaw blade parter. Got any pics?

Dave, I like your 'shaper' idea. But I'm a bit limited at the moment as my apron and gearbox are both on the bench awaiting parts. I've rigged up a bracket so I can use the tailstock to move the saddle a bit, but it's a fiddle-fart, and it's certainly not up to shaping.

I've included a couple of pics of my spindle sleeve, one with the cheap chuck I was using. The chuck's never slipped at all, but it has some runout, which would contribute to vibration. The sleeve bore is MT2, finished with a reamer, and it holds very firmly. I made it that size so I could use my tailstock tooling in the headstock. The male taper on the sleeve is a pretty good fit in the spindle. It's hard to see in the photos, but the ridges of the machining marks have become polished quite uniformly over the surface. I guess the real answer is a collet chuck with a drawbar. But that's money I can't spare right now.