# Machining from the cross-slide on a lathe



## Sparweb (Jul 24, 2021)

My lathe's spindle gears have a spindle lock, normally used to remove the chuck, of course.
With the spindle locked, it's pretty solid.  I can sort-of force it to rotate (maybe about 0.2 degree).

I just started to wonder if people attach tools to their QC tool posts and do machining from there onto the work still locked in the lathe chuck?
Imagine a small power drill attached to the tool post.  I could move the tip of the drill to an exact radial point form the center of the lathe, drill a hole, then unlock, rotate, lock the chuck to a new position 90 degrees and drill again.  Repeat and it gives me an easy 4-bolt pattern on a round flange.  That would save me a set-up on the vertical mill and an indexer.

Is this done?  Examples?  Bad idea?


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## mmcmdl (Jul 24, 2021)

Whatever works for ya . Think of live tooling on a CNC lathe .


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## epanzella (Jul 24, 2021)

I use a chain sprocket to index in my lathe. Turn the crank and a pin engages the sprocket and locks the spindle in place. A tool holder with a drill chuck can make any combination of holes. I have a 50 and a 72 tooth sprocket. New ones are about $10 each


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## silverhawk (Jul 24, 2021)

The hardest part will be the spindle you end up with on the cross slide will need to remain parallel to the bed, yet move vertically to get that third axis. Can it be done? Yes. It will be more work for not a lot of return, because the weak point will still be the cross slide.

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## epanzella (Jul 24, 2021)

Third axis? What for? The spindle is on center and you use the cross feed to get the radius.


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## silverhawk (Jul 25, 2021)

epanzella said:


> Third axis? What for? The spindle is on center and you use the cross feed to get the radius.


It was mentioned that the lathe spindle (holding the work) is locked, and your milling spindle on the cross slide is also locked vertically. This means the set up will only be able to control depth of cut and the distance traveled by the cross slide, or "slots", and would be limited to on-center-only. Perhaps this is what was wanted? Is the lathe spindle going do be unlocked during this operation to introduce radial movement? If that's the case, we are changing from the standard x/y/z (Cartesian coordinate system) to an x/z/a system (polar coordinate system), which works well enough if the rigidity can be improved on the cutting spindle (weak point again, same issue for keyway cutters also called milling attachments).

If we are not rotating the lathe spindle at all, we are only working in two dimensions.

Note that a 0.2 degree backlash could open the tolerance window quite a bit the farther away from center you get using the cross slide. 

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## silverhawk (Jul 25, 2021)

For simply doing bolt patterns, it should be fine. 

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## Sparweb (Jul 25, 2021)

Thank you - interesting ideas.
I'm expecting to work within the limitations of this method, so asking for 3 axes is just asking for the milling machine.  The time to use this is only for conveniences, like a simple bolt-circle, a grub screw, and the like.

Epanzella,
If I understand your setup correctly, the hand crank seen in the lower right corner draws the lever until the pin rests tightly between sprocket teeth.  That would seem to allow you to take out free play at the same time as indexing.

Silverhawk,
There are some movements that will be very hard with this method, so radial movement with the cross-slide and piercing with the X bed are the only movements I'm thinking are practical at the moment.  If the spindle is locked, then I can drill holes into the face of the work.  

You could suggest that by turning spindle I could also cut a groove, but that's easy to do using a standard cutting tool, so it's not necessary (not to mention awkward).  Other coordinated movements might be possible.  I can't visualize at the moment.  

mmcmdl,
I have seen live tooling on a CNC lathe running a few times.  Good example there.  Now I realize that must have been in the back of my mind as I was wondering about this - just didn't realize it at first.


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## Sparweb (Jul 25, 2021)

Aha:


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## savarin (Jul 25, 2021)

I use a spindle in the tool post for bolt patterns, I use a change gear in an expanding mandrel locked to the lathe spindle, I index the chuck with the change gear.
I have also used a milling cutter the same way and moved it up and down a bit at a time in the qctp with the set screw for simple milling so yes it can be done.


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## epanzella (Jul 25, 2021)

silverhawk said:


> The hardest part will be the spindle you end up with on the cross slide will need to remain parallel to the bed, yet move vertically to get that third axis. Can it be done? Yes. It will be more work for not a lot of return, because the weak point will still be the cross slide.
> 
> Sent from my SM-T500 using Tapatalk





Sparweb said:


> Thank you - interesting ideas.
> I'm expecting to work within the limitations of this method, so asking for 3 axes is just asking for the milling machine.  The time to use this is only for conveniences, like a simple bolt-circle, a grub screw, and the like.
> 
> Epanzella,
> If I understand your setup correctly, the hand crank seen in the lower right corner draws the lever until the pin rests tightly between sprocket teeth.  That would seem to allow you to take out free play at the same time as indexing.


Yes, you understand that correctly.  Turn the crank and lock the spindle. Takes out the backlash and allows simple indexing the spindle for drilling bolt circles. I don't use it for milling.


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## brino (Jul 26, 2021)

I saw it first from @Ulma Doctor here:
https://www.hobby-machinist.com/thr...post-cross-drilling-fixture.49064/post-413645

I built one too and it does come in very handy!

-brino


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## chatter chatter cut cut (Jul 30, 2021)

i have a tool post grinder [dremel tool ] the the qctp will adjust at least 1/2 inches up  from center , works for me.


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## Sparweb (Aug 7, 2021)

Thanks for the ideas!

I got it to work.
I had an old chuck lying around.  It must have been an extra thrown in with a drill press I bought at auction, because it didn't fit and I never used it until now.  It's turned out to by a trashy chuck and I won't use it again, but it worked well enough to prove that this method works.
I just had to mate it up to some 3/8" rod, and I found some bronze bushings at Princess Auto* that fit perfectly into my 3/4" tool holder, as you can see.
From this cheap and dirty proof-of-concept I'll do something a bit better for future use with a new chuck.  

*Translation assistance:  "Princess Auto" is a Canadian term.  In the USA it's pronounced "Harbor Freight".


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## matthewsx (Aug 7, 2021)

*Translation assistance:  "Princess Auto" is a Canadian term.  In the USA it's pronounced "Harbor Freight".


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