XARO: Putting Yesterday's Technology to Work

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Steggy
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XARO: Putting Yesterday's Technology to Work

Post by Steggy »

XARO: Putting Yesterday's Technology to Work

Over here, I described the JET 1236PS lathe I acquired earlier this year. After repowering the machine, and fitting it with a collet chuck and quick-change tool post, I've put it to work numerous times making things, Accuracy-wise, the machine does pretty well and I'm not having any trouble achieving thousandth-of-an-inch results in the Y-axis.

The X-axis is another matter. The carriage crank has a calibrated collar that reads out to the nearest 0.004", which is good enough for a lot of applications. However, there are some cases where I have needed to go tighter. Also, the collar is in an awkward place, making it hard to set and read, and thus a possible source of errors.

Given all this, I decided I needed some kind of X-axis readout that would give me thousandth-of-an-inch accuracy. These days, everyone is going gaga over DROs (Digital Read-Out). Not me! As my basic nature is to make things rather than buy them, I fitted my lathe with an XARO (X-axis Analog Read-Out). The inspiration for making it came from a similar device on my buddy Carl's lathe, as well as ones I had seen on lathes in years past.

Now, you may be wondering what in blue blazes is an XARO. It's really very simple: just a dial indicator (DI) with 2" travel mounted in such a way that the carriage can push on the plunger as the tool is moved toward the headstock. As the motion is directly transferred to the DI the accuracy is as good as that of the DI itself.

The mounting for the DI is made to use the bedways as the reference point so the DI's centerline is exactly parallel to that of the lathe. "Exactly" in this case amounts to being within a couple of thousandths of absolute parallelism—parallax error in that range is negligible—proportional to the cosine of the angle between the lathe's centerline and the DI's centerline. As I was designing the mounting, I decided to make it sufficiently robust to act as a mechanical stop for the carriage to assist with repeatability.

At this point, you are probably muttering something to the effect of why not use a DRO instead of technology that was state-of-the-art back when Bonnie and Clyde were robbing banks. Well, I'm old-fashioned when it comes to machine tools. I started using lathes, mills, etc., some 60 years ago, well before the advent of electronic measuring devices. I learned how to use those calibrated collars to achieve thousandth-of-an-inch accuracy. I didn't—and still don't—need a pile of transistors and integrated circuits to tell me how far to move the tool or workpiece.

There is also a matter of cost. A high quality DRO is a significant investment. Even a cheap one is relatively expensive, and as always, you'll only get what you pay for. The overwhelming majority of the "affordable" DROs come from a certain country in which quality control and customer service are not-well-understood concepts. 8)

Installing a DRO means installing an encoder, which means possibly drilling and tapping holes into various parts of the lathe, which is something I'd rather not do (unpleasant visions of broken taps come to mind). Errors in installing the encoder can translate to errors in what the DRO displays. No thanks!

Anyhow, my XARO is a really simple device. The parts used to make it are shown below.

xaro_parts.jpg

In addition to the DI, what you are seeing from left to right are the saddle, clamp stud, clamp nut, DI retention setscrew and clamp. The saddle and clamp are machined from cold-finished steel. The 5/16" stud and clamp nut are pieces I got from McMaster-Carr. The setscrew was courtesy of the local Ace Hardware store.

The stud is a type normally used in die work. It has a hex socket broached into one end to facilitate installation and removal. While a nice feature, it wasn't essential. What was essential is the stud is heat-treated and has a closely-held diameter, the latter which allows it to act as a precision pilot for the clamp. Maintaining parallelism between the clamp and saddle is important in achieving good clamping, hence the stud.

The heat-treated clamp nut is a machine tool part that conveniently uses the same wrench size that fits the nut on the carriage lock.

The JET 1236PS has inverted vee ways, necessitating that a corresponding vee be milled into the saddle. This vee accurately locates the XARO relative to the lathe's centerline and also give ample contact area to achieve good clamping to keep the XARO from drifting if bumped by the carriage. Here's a closeup of the saddle.

xaro_saddle.jpg

The clamp engages the underside of the bedway that acts as the vertical guide for the carriage. There is a step machined into the clamp to contact the bedway. Here's a closeup of the clamp.

xaro_clamp.jpg

Here is the XARO mounted on the lathe.

xaro_on_lathe01.jpg

There is about 1/8" clearance between the bottom side of the DI and the top of the quick-change gearbox. The DI, of course, had a lug on the back, which had to go. Unfortunately, the cover was designed in a way that had I cut off the lug there would have been several gaping holes exposing the DI's interior. So I had to make a new cover that would produce the required clearance.

dial_indicator02.jpg

I cut that cover from a slug of 6061 aluminum I had laying around. In order to be able to reuse the original cover screws, which are some funky metric size that no one would have in stock, the new cover had to be as thin as the old one, 2.5 millimeters in case you were wondering. I got that by using the cutoff tool to take a baloney slice from the aluminum slug after facing and turning to the required diameter. I used the old cover as a template to lay out the screw holes.

Here's a photo of the XARO in use.

xaro_on_lathe03.jpg

More photos in the next post.
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Steggy
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XARO: Putting Yesterday's Technology to Work (cont'd)

Post by Steggy »

XARO: Putting Yesterday's Technology to Work (cont'd)

Continuing, here is a photo of the interface between the XARO and the ways.

xaro_on_lathe02.jpg

As I said in the previous post, the XARO is designed to be able to act as a carriage stop. Here's a photo of it doing just that.

xaro_full_travel.jpg

Not visible is the point of contact with the carriage, which is behind the dial indicator's (DI) plunger. There is about 0.050" travel left in the DI at this point, so it isn't possible to bottom out the DI.

In the next two photos, you can see that I didn't have a lot of room between the underside of the XARO and the lead screw. It would have been nice to use a threaded knob to secure the XARO to the ways, but there wasn't the requisite clearance. Also, I was concerned a knob might not allow for sufficient clamping force. Plus the rack used to move the carriage would have been right about where one's knuckles would be to turn the knob. Ergo use of a nut and wrench.

xaro_over_leadscrew.jpg
xaro_wrench_clearance.jpg

And to finish up, a photo looking down at the XARO.

xaro_on_lathe04.jpg

Total investment in material and parts to make the XARO, including the dial indicator, was about fifty dollars.
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
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GlennW
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Re: XARO: Putting Yesterday's Technology to Work

Post by GlennW »

ZARO :wink:
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Steggy
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Re: XARO: Putting Yesterday's Technology to Work

Post by Steggy »

GlennW wrote: Sun Dec 13, 2020 6:58 pmZARO :wink:
A little swordplay perchance? :D

A YARO is on the "drawing board." It's not as critical a need though as was the XARO.
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
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GlennW
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Re: XARO: Putting Yesterday's Technology to Work

Post by GlennW »

Carriage is "Z" axis, cross slide is "X" axis.

"Y" would be a vertical axis perpendicular to the cross slide.
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Steggy
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Re: XARO: Putting Yesterday's Technology to Work

Post by Steggy »

GlennW wrote: Sun Dec 13, 2020 8:33 pm Carriage is "Z" axis, cross slide is "X" axis.

"Y" would be a vertical axis perpendicular to the cross slide.
That wasn't the way it was described back when I was taught this stuff. Carriage movement, being side-to-side relative to the operator when facing the machine, was X, same as movements on a two-dimensional plane. Cross-slide was Y. Can't say though that I've kept with all the new-fangled terminology.
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
JimF
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Re: XARO: Putting Yesterday's Technology to Work

Post by JimF »

BigDumbDinosaur wrote: Sun Dec 13, 2020 8:56 pm
GlennW wrote: Sun Dec 13, 2020 8:33 pm Carriage is "Z" axis, cross slide is "X" axis.

"Y" would be a vertical axis perpendicular to the cross slide.
That wasn't the way it was described back when I was taught this stuff. Carriage movement, being side-to-side relative to the operator when facing the machine, was X, same as movements on a two-dimensional plane. Cross-slide was Y. Can't say though that I've kept with all the new-fangled terminology.
You were taught Mill Axes,Lathe is what is described.
Patio
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Re: XARO: Putting Yesterday's Technology to Work

Post by Patio »

Nice finish on the parts. Looks real clean.
If you thread the bottom and have the clearance hole in the top part, you would be able to use a wing nut. No tools needed. Just a thought.
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Steggy
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Re: XARO: Putting Yesterday's Technology to Work

Post by Steggy »

Patio wrote: Mon Dec 14, 2020 1:18 amNice finish on the parts. Looks real clean.
Thanks!
If you thread the bottom and have the clearance hole in the top part, you would be able to use a wing nut. No tools needed. Just a thought.
I did consider such an arrangement but decided I wanted the top "clean" of protuberances that could snag things. Also, I wanted the XARO to act as a carriage stop and didn't think it would be possible to sufficiently tighten it with a knob or wingnut. As a 9/16" wrench is needed to tighten and loosen the carriage lock, I chose a stud size that would accept a nut that fits that wrench.

Something I may add to it is a hinged acrylic cover to protect the dial indicator from the lathe's "exhaust."
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
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Harold_V
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Re: XARO: Putting Yesterday's Technology to Work

Post by Harold_V »

I use a similar device on my Graziano, although it does not function as a carriage stop.

In regards to the lathe's "exhaust"----when I ran my shop for gain, I ran coolant in the lathe, which was used quite often. Coolant and long travel indicators don't get along real well, so I used to slip a plastic bag over the indicator, one that completely covered the stem and the entire indicator body.

The plastic bag would be placed over the indicator and mount, with the contact point removed. It would then be installed, using the screw of the contact to puncture the plastic bag. With the contact tightened securely, a perfect seal was created, so the bag shield was still water tight. I could run the lathe with coolant for a full day with the indicator staying perfectly dry, including the stem. I'd usually replace the bag each day, to ensure it would be clear enough to view the dial.

If you emulate this setup, you most likely will have to do a little custom trimming of the bag so it can fit over the entire indicator and mount.

Nice job on the mount.

H
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Re: XARO: Putting Yesterday's Technology to Work

Post by liveaboard »

Nice, I like it.
I have the same concerns with a DRO; I can't afford a good one and don't have confidence in a cheap one.

Of course, dial indicators cost money too.
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Re: XARO: Putting Yesterday's Technology to Work

Post by Steggy »

liveaboard wrote: Mon Dec 14, 2020 3:30 amOf course, dial indicators cost money too.
That's where eBay is your friend. You can get a 2 inch DI for a reasonable price. In fact, you could buy a lot of DIs with the money required to purchase one DRO.
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
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