Parting on the Lathe

[PixMan]

The style of blade holding blocks I have for my Dorian CA quick change tool post seem to have a good design for holding straight, tapered or T-shaped blades.

See in this photo how the clamping block moves and captures the top of the blade. It seems there's enough space up there for clearance on a T blade. I have no rub marks on the lower extremity of the blades I have, so they must be holding the straight blades fairly square. Of course the insert type blades have much more side clearance because the cutting width of the inserts is a bit wider than the blade itself.



Here's the three holders I have. Two take blades of 7/8" (22.22mm) to just over 1" (26mm), while one takes the taller 32mm (1.259") blades.



I do prefer these because the center height can be set once, and it doesn't change a bit as I extend or retract the blade. Most (if not all) of the standard No.7 type blade holding blocks that come with QCTP kits are angled and that changes center height as you move the blade in & out. I hate that.

[EdK]

(12-09-2013, 08:44 PM)TomG Wrote: ...

It's like this Ed:

Tom,

Got it, thanks.

Ed

[dallen]

I have one of the standard aloris parting blade holders and I can never stop the blade from slipping.

DA

[TomG]

Is it the cam lock type with the locking screw out the back? That's what I have and it never slips.

Tom

[dallen]

thats the one I have, it always slips, no matter how tight I try to get it.

DA

[awemawson]

Tolerance issue probably. Sounds like the locking cam perhaps needs re-making ?

Andrew

[PixMan]

(12-10-2013, 10:41 AM)dallen Wrote: I have one of the standard aloris parting blade holders and I can never stop the blade from slipping.

DA

I've heard of that happening with the import ones. I do not care for either the cam type nor the single wedge type, for two reasons. First, I believe the single point of contact puts a stress riser on the blade, making it a likely failure point. Secondly, the small point of contact offers minimal clamp pressure as compared to the long line of contact in the style holder I choose to use. When tools aren't held rigid, they move. When cuttings tools move opposite of the intended, they fail.

The blocks I have are known as 7-71 and 7-71C, and both Aloris and Dorian sell them. You may notice one has a shiny new clamp block. My dad had made that because the original one was broken in half when I bought it off eBay for cheap. I can only assume the original owner tried to tighten all four screws while holding only a half long blade.

[Mayhem]

I've had good results on my friends 9" lathe using parting blades made from old carbide tipped circular saw blades. Cut them out with the plasma and then touch the tips up with a diamond file and they work well in the standard parting holder that came with is 100 series (AXA) QCTP. The problem is (as already noted) when you have to adjust the length, as height also changes.

I have two double ended Valenite VH101-32-3 parting blades that I bought (very cheaply) from Ken. I cannot recall the inserts these use right now (I'm sure Ken will though). We spent some time looking for the VGTB 16-25 tool holder, which Ken managed to track down for me for a good price.

Ken more recently gifted me a VG112 R 16-30 Parting/Deep Grooving Holder that takes VTG double ended inserts. This is my go to tool for parting hollow or small diameter stuff.

My friend in envious of these but it is proving difficult to find a similar system with a 1/2" shank for a reasonable price.

[dallen]

(12-11-2013, 08:48 AM)PixMan Wrote:

(12-10-2013, 10:41 AM)dallen Wrote: I have one of the standard aloris parting blade holders and I can never stop the blade from slipping.

DA

I've heard of that happening with the import ones. I do not care for either the cam type nor the single wedge type, for two reasons. First, I believe the single point of contact puts a stress riser on the blade, making it a likely failure point. Secondly, the small point of contact offers minimal clamp pressure as compared to the long line of contact in the style holder I choose to use. When tools aren't held rigid, they move. When cuttings tools move opposite of the intended, they fail.

The blocks I have are known as 7-71 and 7-71C, and both Aloris and Dorian sell them. You may notice one has a shiny new clamp block. My dad had made that because the original one was broken in half when I bought it off eBay for cheap. I can only assume the original owner tried to tighten all four screws while holding only a half long blade.

I stopped using the HSS blades and holder, pitched it in a drawer on the tool box, and went to a GTN insert blade that I had, with some overly wide inserts in a holder that I originally made to work on my 9" lathe, which I modified so I could clamp it in one of the BXA tool holders by silver soldering a steel bar to the side of it.

So far it works, wish I had some narrower inserts for it, but then who knows maybe Santa will drop some out of his bag as he and his team of raindeer fly past at mach 4.

DA

[TomG]

I took a closer look at Aloris AXA and it's not a cam type at all, it's a wedge type. That's what I get for relying on my memory.

It holds the blade nice and tight and doesn't move around when tightened.

Tom