Grove and cut off tool question

[BillB]

Hey All, This question is out of the realm of Acorn control but is CNC machining related so I figure it cant hurt to ask since there are so many seasoned machinists in the group.

If your not familiar with my machine its a Shirlene chucker lathe with Acorn control. And as you can see I have a QC tool post mounted at both ends of the table for as much versatility as I can get for swapping tools. The mounts and mounting position are exactly the same and they both have the same rigidity.

My goal while setting up the machine has always been to have my grove and cut off tool mounted to the top tool post. I've purchased 3 more grove and cut off tools with different cut widths as well as another one I already had with the goal to swap them out on the fly.

When testing the top and bottom tool posts with all the same tools mounted in both the upper and lower tool posts the cutting is day and night. I am only manually feeding the tools at this point to test as I work this out. The bottom tool post with all 4 of the insert tool holders as well as the high speed steel cut off tools all work flawlessly and as expected. Clean cutting, nice and smooth like butter (aluminum & Delrin) When I try the same tools on the top side tool post it is a total fail. YES I've dialed in all my tools to cut on center line of the stock, And even if I'm slightly off a bit on the bottom cut it still cuts fairly well like a manual lathe you just end up with a nipple. Im running mist coolant FYI. Top tool post is a TOTAL FAIL, makes a lot of noise, lots of deflection in fact im surprised to see how much everything can move its crazy on a little machine like this.

Are the tool holders I'm using not the right geometry for a back side cut off tool? are they just not meant to X- cut off. I dont get how its any dirrent than the front holder, just upsidedown. ?
I've been trying to figure out IF there are special tool holders with different geometry for a back-side cut-off tool. All I find is Right and left hand "standard" carbide insert tool holders like the ones I've bought.
My tool post is OXA size.

IF yes can someone provide a link to the right kind of insert tool holder I need to be looking at?

Hope you guys have some input for me. Thanks

[suntravel]

I think the carbide inserts are made for steel and rigid machines.
You should use sharp ground ones for Aluminium and not wider than 2mm.

Uwe

[tblough]

As a test, I would try your insert tooling set up for the bottom tool post in the top tool post and run the spindle backwards. If that cuts fine, that will rule out any tool post or squareness problems leaving only height problems on the top tool post remaining.

For the blade type toolholders, the blades are narrower at the bottom than the top to provide side clearance on the groove. They cannot be mounted upside down in the holder, or one side of the cut will rub.

[BillB]

As a test, I would try your insert tooling set up for the bottom tool post in the top tool post and run the spindle backwards. If that cuts fine, that will rule out any tool post or squareness problems leaving only height problems on the top tool post remaining.

For the blade type toolholders, the blades are narrower at the bottom than the top to provide side clearance on the groove. They cannot be mounted upside down in the holder, or one side of the cut will rub.

That would be a good idea but unfortunately my Spindel does not run backward,

The inserts are all wider at the cutting edge than the upper and lower support blades as you called them / "clamps" by about .01-.02. For example the medium-size insert I have is .08 wide with the blades at .065. In this case both upper and lower blades are the same thickness.

I will check squareness but even so it it was slightly off would I be seeing such poor results.

any other thoughts?

[tblough]

Looking at the two grooving tools mounted on the front and rear tool posts in the second photo, I don't see how the rear one can be on center. It appears the same amount of tool height adjuster screw threads are visible on the two tool holders. I don't see how that is possible. With, I'm guessing, 1/2" shank insert holders, there should be 1/2" difference in the thread length. Is there a 1/2" spacer under the rear tool post?

[BillB]

Looking at the two grooving tools mounted on the front and rear tool posts in the second photo, I don't see how the rear one can be on center. It appears the same amount of tool height adjuster screw threads are visible on the two tool holders. I don't see how that is possible. With, I'm guessing, 1/2" shank insert holders, there should be 1/2" difference in the thread length. Is there a 1/2" spacer under the rear tool post?

So as I was trying to work this out I swapped out tools many times front to back and also flipped the tools, then adjusted the heights to be on the center line. SO the picture is taken after all of that testing, and the holders are just placed in the machine for visualization. So yes the thumb screws are not even adjusted in the picture so your probably right about being about 1/2 off. The actual adjustment puts the top of the holder about even with the top of the post and the thumb screw all the way down. Sorry to confuse you.

[BillB]

and btw: tool holder shank size is 3/8x3/8

[vw_chuck]

Does the back of the carriage have a way to stop it from lifting off the ways? I know on my lathe you can only load the tool pushing it down onto the way. If you load it the other way the whole carriage tries to lift off the ways and makes chatter. Keep in mind the carriage doesn't weigh that much on a small lathe.

[BillB]

Does the back of the carriage have a way to stop it from lifting off the ways? I know on my lathe you can only load the tool pushing it down onto the way. If you load it the other way the whole carriage tries to lift off the ways and makes chatter. Keep in mind the carriage doesn't weigh that much on a small lathe.

Not sure about stopping it from lifting, It's a new machine I would imagine the gibs are tight but I'll look. If you have suggestions LMK. What your saying makes sense I actually never imagined the forces are so high on a small lathe. its literally lifting it up the entire carriage tool post etc.

Do you have any input on the type of tool/holder and insert I have? The fact that its a standard cut off tool which from what I'm seeing seams to be designed for the front X+ side of the stock?

[vw_chuck]

I know on my lathe which is a 11x26 it doesn't even have any gibs on the Z axis. You can lift the whole carriage up if you are strong enough. Kind of crazy.


I do know that tool is the most usefull tool I own. The clamp down one can be used for grooving, turning, profiling pretty much anything in aluminum. They work great and you can get like a pack of 10 inserts on amazon for like 10 bucks. You really can't beat it.