Drilling with the cross slide

[Susquatch]

Link to AXA to MT2 tool holder, appears to have oval opening for the arbor tang to prevent rotation.

That's the same as my BXA MT3 Holder. And yes, it has a slot for the MT3 Tang.

With modest pressure, mine deflects 2 thou to the rear side (away from the operator). The deflection is linear with tool pressure.

Using the BXA tool holder, the axis of rotation is offset about 4 inches rearward (away from the operator) from the centerline of the tool post. Everything is rubber. The tool post and tool holder are very solid. But a torque force with a moment arm of 4 inches is not trivial.

On the contrary, a tailstock has zero rearward offset. There is no moment arm and therefore, the deflection is zero.

Note - this is only rearward deflection. Both the tailstock and toolpost will also generate an upward deflection that is the result of the force offset of half the swing of the lathe and the vertical structural strength of the toolpost, tailstock, and lathe bed. But my tailstock and my bed are virtual beasts in comparison to my toolpost and MT3 BXA Toolholder.

Caveats:

1. Every lathe will be different. The smaller the lathe the greater the deflection. The stronger the structure the lower the deflection.

2. Any deflection will be linear with tool pressure. The amount of deflection is dependent on tool pressure.

3. I used a center mounted in the chuck and in the Morse taper and a 5" tool between them. Other geometries will affect measurements.

4. I did not measure tool pressure but tried to be consistent with a pressure about the same as I would apply drilling with a half inch drill.

5. My indicator was mounted on my headstock. Thus, it was also measuring any offset generated by any twisting of the carriage. This is probably minimal but..... Everything is rubber, and that deflection should be included too.

 

[MrWhoopee]

Aside from rapid retract for chip clearing, the biggest advantage to drilling with the carriage is the ability to use power feed.
My experience with AXA toolposts is that the footprint is small enough that it is difficult to keep them from rotating under heavy, off-center loads, such as power feeding a drill.

 

[slow-poke]

Aside from rapid retract for chip clearing, the biggest advantage to drilling with the carriage is the ability to use power feed.
My experience with AXA toolposts is that the footprint is small enough that it is difficult to keep them from rotating under heavy, off-center loads, such as power feeding a drill.

When you say rotating, do you mean the Morse Taper spins in the quill?
That has happened to me when using large bits.

 

[MrWhoopee]

When you say rotating, do you mean the Morse Taper spins in the quill?
That has happened to me when using large bits.

No, that's another issue. I was referring to the toolpost rotating about the bolt that secures it to the compound.

 

[slow-poke]

No, that's another issue. I was referring to the toolpost rotating about the bolt that secures it to the compound.

Thanks, that's good to know.

 

[Susquatch]

When you say rotating, do you mean the Morse Taper spins in the quill?
That has happened to me when using large bits.

A tang will help with that.

The load based (torque) offset I described in post 21 above is similar. In that case the whole assembly is strain bending in response to the torque load about the center bolt. Actually rotating on the toolpost center bolt like @MrWhoopee describes would be much worse.

Fundamentally, I can't recommend the practice on smaller lathes. It's much better to use the tailstock.

Further to that point, I've never felt the need for power feed when drilling or reaming. These are simple operations and manual feed using the tailstock quill has never caused me any problems nor left me wishing I had power feed......

 

[Janger]

Further to that point, I've never felt the need for power feed when drilling or reaming. These are simple operations and manual feed using the tailstock quill has never caused me any problems nor left me wishing I had power feed......

Agree, but I think anyone would want power feed if drilling 12”+ holes like historical alarms was describing or hundreds of holes as JN mentioned. I think an ELS or CNC maybe even better.

 

[Susquatch]

Agree, but I think anyone would want power feed if drilling 12”+ holes like historical alarms was describing or hundreds of holes as JN mentioned. I think an ELS or CNC maybe even better.

I suppose that is a possible need. It's just difficult for me to imagine needing that with parts chucked in a lathe. I'd think power feed would be the least of the tediousness in that situation.

But I totally agree that someone needing such repetition probably also wants CNC.

I'm just a one or two off hobbiest.

 

[mbond]

with no other tools in the shop to do it (or space to house them), you have to use the ones that you have

I have never seen a lathe where the tail stock isn't substantially more robust than the cross. And yes, the reduced eccentricity between the load and the support will produce better results. But you generally don't power drill for accuracy. Do that to get close, and then bore or ream

There is another load that hasn't been mentioned. it is the asymmetry between the forces on the bed from either the tailstock or the cross between the side facing the operator and the away side due to the torque of the spindle. It should be a second order effect - after tool pressure in both the along the bed and upwards directions - but it deserves to be mentioned

 

[Susquatch]

but it deserves to be mentioned

I thought I did mention it!

5. My indicator was mounted on my headstock. Thus, it was also measuring any offset generated by any twisting of the carriage. This is probably minimal but..... Everything is rubber, and that deflection should be included too.

But ya, minimal for sure.

Your point about the relative strength of the tailstock is really the substance of my entire assessment. Everything is rubber so it does move, but not enough to matter. On the other hand, the tool post does move - and it moves enough to matter.

 

[mbond]

Maybe you did and I mis understood.

But an indicator on the headstock will fail to measure a movement of the headstock. It will measure movement in other parts relative to the headstock

this load twists the headstock one way, and the bed and everything connected to it in the other direction. No single indicator can measure it

 

[Susquatch]

But an indicator on the headstock will fail to measure a movement of the headstock. It will measure movement in other parts relative to the headstock

You are correct. But since what I wanted to measure was how much the drill/reamer base moved relative to the spindle/headstock, I'm ok with that.

 

[mbond]

I can nit pick with the best of them

But yeah, if that's a problem, you have way bigger problems somewhere else in the setup

 

[combustable herbage]

I have one that is a AXA and MT2 and it shares drill time with the tailstock in similar fashion to others, probably 70%tailstock.
I have never had an issue with it my compound is normally parallel with the ways. I will say I can only remember breaking one or two bits using this unit with the great feed control from the qcgb of my sm10 utililathe unlike the many I have broken turning the tailstock too quick especially with those little center drills.

 

[slow-poke]

Thanks for all the thoughtful comments.

I don't use flood coolant. It's not uncommon that I need to drill quite a number of holes often somewhat deep in aluminum on the mill. Sometimes I will just use the quill, but more and more especially for deeper holes I reuse a few line program that pecks at the hole and pauses after retraction so I can clear the swarf from the drill bit and then give a squirt of A9 cutting fluid for the next peck. I find it just goes faster.

I ordered the AXA-MT2 tool holder so I will give it a try on the lathe, it will be nice to have the option.