Using a 3/8 shank tool in AXA tool holder

[JRouche]

Explain. How is a shim under the toolpost going to reduce rigidity. How would a shim under a tool not then?

That is a very good question.

The way I see it if you have to shim up a "system" the larger the contact area the better.

So some tool blocks might have more horizontal surface to shim from. Better load distribution.

If you do (shim) the tool or cutter holder that will be a much smaller surface area. More deflection, more poor cuts, more chatter, more chipping of tool tips. And more importantly? More diaper (shim under tool) changes for various jobs. I always fix the machine then the tool. JR

[The Metal Butcher]

That is a very good question.

The way I see it if you have to shim up a "system" the larger the contact area the better.

So some tool blocks might have more horizontal surface to shim from. Better load distribution.

If you do (shim) the tool or cutter holder that will be a much smaller surface area. More deflection, more poor cuts, more chatter, more chipping of tool tips. And more importantly? More diaper (shim under tool) changes for various jobs. I always fix the machine then the tool. JR

Yeah. I'm just asking. Cuz I've made cuts with a shimmed CXA post and a normal CA post heavy enough to max out the carbide on a brand new brazed 3/4" tool. 'Round about 1.5" off the diameter. Can't tell you much difference between the two. Obviously shimmed tools have been done in turret lathes for ages. So I'm just trying to see how one is better vs the other. If someone has some math or a nice FEA simulation, I'll bite. Otherwise...

[nickel-city-fab]

My rule of the thumb is the fewer the connections in any system that requires rigidity, the better. Or, Shim Happens.
I have seen guys buy tool shanks that are way way over sized for their machines,
and then mill the dovetail slot directly into the tool shank,
dispensing with the tool holder altogether. Same could be done with HSS.

[Rich Carlstedt]

The amount of shim the poster needs is a non event when it comes to lathe Toolpost footprint and rigidity

There is a greater loss of rigidity in some of the extended tool bits you see being used all the time or improper parting operations

The Metal Butcher nailed it

Rich

[BCRider]

Ya knowz... it strikes me that we're all so OCD that we wouldn't be happy until we all have the ideal tool post.

That tool post would reduce any overhang by being a monolithic block that locates the tool bit or insert within the directly supported area of the cross slide or compound and cross slide with nothing extending out past that supported area. And each block would be a custom height for the tool bits or inserts such that no shimming or any other height adjustment is required. And the block would fully support the tool bit over it's entire lower side so only the required clearance angle extends out past the block's support so the loads are primarily carried in compression through the block to the lathe.

Oh, and to avoid the weak modulus of steel this ideal tool block would be solid carbide.

Would that pass muster?

[nickel-city-fab]

Ya knowz... it strikes me that we're all so OCD that we wouldn't be happy until we all have the ideal tool post.

That tool post would reduce any overhang by being a monolithic block that locates the tool bit or insert within the directly supported area of the cross slide or compound and cross slide with nothing extending out past that supported area. And each block would be a custom height for the tool bits or inserts such that no shimming or any other height adjustment is required. And the block would fully support the tool bit over it's entire lower side so only the required clearance angle extends out past the block's support so the loads are primarily carried in compression through the block to the lathe.

Oh, and to avoid the weak modulus of steel this ideal tool block would be solid carbide.

Would that pass muster?

Neat idea, I'd be willing to bet there's a government-funded lab somewhere that has actually done this for critical applications

[The Metal Butcher]

Ya knowz... it strikes me that we're all so OCD that we wouldn't be happy until we all have the ideal tool post.

That tool post would reduce any overhang by being a monolithic block that locates the tool bit or insert within the directly supported area of the cross slide or compound and cross slide with nothing extending out past that supported area. And each block would be a custom height for the tool bits or inserts such that no shimming or any other height adjustment is required. And the block would fully support the tool bit over it's entire lower side so only the required clearance angle extends out past the block's support so the loads are primarily carried in compression through the block to the lathe.

Oh, and to avoid the weak modulus of steel this ideal tool block would be solid carbide.

Would that pass muster?

Nah, sounds weak as hell!

:P

You know...

Speaking of solid carbide... my workplace can spray carbide coatings. If I ever get rich, I'm gonna be the only man in the world with WC ways. (Just the top .030" or so. ) That and turcite, it'll never wear!

[Fasturn]

You can drill and tap the tool holder from the bottom and clamp up instead of down ? Gee.......... what a dumb idea! Now its 1/8 shim and a cup of coffee. Now go do the right thing.

[kuksul08]

Following up with the solution.

I bought a piece of precision ground 1/4" steel plate, 3" by 6". Drilled 2 dowels to locate it to the compound rest so it's not spinning around as I rotate the tool post. Lapped the top of the compound rest to ensure a perfectly flat fit. The plate only needed to be 3x3 for full support, but it came as a 3x6 piece so I left it.

Interestingly enough, by doing this I learned that the top surface of the compound rest on the spindle side of the T-slot is about .004" lower than the rest of it. I can't think of a logical reason for that. I shimmed it so everything is flat and it's rigid as ever.

Now I can use 3/8 and even 1/4" tools without shimming individually and all the tool holder adjusters work!

[mikey553]

My 12x36 has the opposite issue. The height from top of the compound to spindle axis is only 1.18. As a result of this I opted for an AXA. But technically even that is a touch too tall. So holders with 3/8 square tooling sit only 1/4" up from the top of the compound with 1/2" of dovetail above the holders. But the holders with 3/8 boring bars sit right on center in the dovetails.

My 12 x 36 lathe has 1.25" from the top of the compound to spindle axis. I have BXA tool post and many holders and I think this is the best size for my machine. I can put a 1/8" boring bar directly in the holder and still have plenty of room to spare. On the other hand I have a few oversized holders which can accept 20 mm tools and they fit just fine on the post. Yes, sometimes you need a way to clamp a big tool on a small lathe.

[Doozer]

You went way overkill for no reason.
All you need as a round washer like
spacer under the toolpost that is large
enough to fully support the square
diagonal width of the toolpost.
Your large plate is no advantage at all.

-Doozer

[J Tiers]

Those wondering what the fuss is about, and talking about how normal shimming the tool is, are forgetting something.

Let the subject of toolposts come up, and suddenly some of the same folks who say how normal shims are, will be shouting about how the big advantage of the QCTP is the fact that you can throw away all those troublesome shims. It never fails. They will be heard declaring how much of a relief it was to ditch the shims, etc,etc, etc, when they finally got RID of that 4 way post in favor of a QCTP, be it AXA, BXA, etc.

So, shims seem to be OK sometimes, and the worst torture in the world at other times.

Now I agree that with the QCTP you only need to do the shim once, when you put the tool into the holder. That's so obvious that it hardly needs to be mentioned. But it is ironic that with the QCTP, the device that gets rid of all shims under the tool, it is now considered "perfectly normal" to have to use a shim.

The spacer block underneath the post is clearly and obviously the right solution......

[mattthemuppet]

looks good to me! Having the tool post supported under its whole base certainly won't hurt either.

[kuksul08]

Yeah, I really didn't want to deal with spacers under each tool. This makes thinks so much faster.

You went way overkill for no reason.
All you need as a round washer like
spacer under the toolpost that is large
enough to fully support the square
diagonal width of the toolpost.
Your large plate is no advantage at all.

-Doozer

I thought about doing that, but sourcing a large, precision washer was no easier than a piece of ground bar stock. The spacer has to be perfectly flat so tool height doesn't change as the tool post is rotated.

[BCRider]

Those wondering what the fuss is about, and talking about how normal shimming the tool is, are forgetting something.

Let the subject of toolposts come up, and suddenly some of the same folks who say how normal shims are, will be shouting about ...... "stuff"........

Yes, we are good at splitting hairs, aren't we?

Other interest groups have their own trigger topics. For bicycles and motorcycles all one needs to do for a good long argumentative thread is ask about chain cleaning and lubing. The threads invariably turns into multi page battle zones even if the threads are only a couple of weeks apart. We might have a topic or two like that here at HSM.... maybe....