CCMT boring toolpath tips ? flat bottom hole with double radius to flat walls

Hi,

This is on 4130... dimensions are in the first pic... Maybe I'm overthinking this and yes I dont have the ideal tools but I'm trying to deal with a flat bottomed hole with a radius going to 40degrees then a straight taper then another radius to 90 degrees to make the walls. I only have small CCMT boring bars (up to 16mm) and a TNMG in 19mm... and yes it would be great to get another bar for this but I only need to make 6 of these.. so.. yeah.

Attached is a crappy mspaint version of what I'm trying to make... Plus my current concept of my 4 toolpaths to complete it. Basically, use an almost flat u-drill, then bore axially to the max flat bottom depth with a sharp reverse angled retract so the tool doesn't 'wedge' when retracting (i.e. go + in Z at the end of the bore diameter on each pass). Then run a finish pass axially on the finished bore and include the first curve since it would be at the better angle on my 85 deg CCMT, with an arc out. Then start at X0 and do a finish pass outwards taking up the last bit of the U-drill tip and the deeper curve, arcing out once past the previous machined depth. Both finish passes would arc out so in theory I would have a nice blending.

BUT.. this seems lame to me.. The last path the curve is "against" the intended cutter angle (as far as I can tell), and I cant envision the 2 finish passes not burring or having a step, i.e. a shitty blend line. What would you guys recommend for accomplishing this, or am I being a cheap stubborn bastard and I should just get or MAKE one of those V shaped bars that apparently can radius... or should I just giver in one path and hole i dont bust the tool ??

Hi phatbob:
What material?
How big?
How accurate?

If it's not some totally nutso freaky hard shit, I see no reason you cannot just turn the whole finish pass in one go, even if you have to cobble up your own tool with an insert, an oxy acetylene rig, some silver solder, and a piece of suitable round bar.
Once you know where the corner of the insert is, you should be able to program it like any other shape.
Might be worthwhile to go backward out of the part from the center if you want to avoid dragging chips across your finished surfaces.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

4130... added dimensions pointer and material to the original post ... outer diam 61mm flat bottom diam 17mm (see the pic). So what you're suggesting is, make the right tool, do it in one pass as a backbore. Yeah. Im trying to avoid that (I should have said "avoid having to buy / make tool"). I only need 6 o these and prob wont ever again... that being said, what tool would be right for this in one pass anyways ??

Hi phatbob:
I like these Sandvik nosepicker inserts: VBMT11 03 02-PF
They are 35 degree diamonds, 1/4" IC with positive rake and a tip rad of 0.00787"
Way too fragile for gnarly roughing but for the kind of work I do I've found nothing better for finishing in tight places.

If I need something a bit stouter I use these: DCGT070204-MJ VP10RT from Mitsubishi.
They are 55 degree diamonds with a tip rad of 0.0156" also positive rake.
As you can perhaps tell, I do only small stuff...my machine is a 5C chucker.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Same style of machine here... using a 3" extended depth collet for this... perfect and thanks, will check em out ! Really appreciate it...

-Pbob