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lathe recommendation needed for micron accuracy

Mark Winsor

Aluminum
Joined
Feb 4, 2013
Location
Hartford, CT, USA
Hello, I'm searching for a machine which can (really) accurately cut tapers/2d curve profiles into relatively soft materials (bronze, lead, aluminum). The challenge is that the accuracy required is +/- 0.0001" or better on the average ~1.8" inside diameter, over a ~1" length. We also need a way to inspect the parts, ideally in the machine.

Currently, we're using a Haas TL-1, and having to send parts out to a high end CMM to verify results, which are neither accurate nor repeatable.
From Haas, I think the machine accuracy is .0004, and the repeatably .0002, without considering any other error sources, so it's time to upgrade.

These are expensive parts and we're only running 1 or 2 at a time, so even if we had an in-house inspection method, guessing and checking with offsets and spring passes is not a great long term solution. A more accurate machine with some kind of in-machine inspection would be best, something like a "contour tracer" or "perthometer". Do any machines have these built in, or a probing system accurate enough? Where should I start looking as far as machine type, brand, budget?

Also, if anyone is already set up to do this type of work, especially in the New England area, I'm also interested in outsourcing.
 
Possible to leave a little extra on the part and CNC grind?
With that said, what you're asking is possible, with some $$ investment.
A very high quality lathe, and, possibly scales, a high precision chuck, and a chiller.
 
A Hardinge T42SP can handle those tolerances with no issue, feel free to reach out to me and I can send your contact information to our NE Sales Rep. Machine is equipped with glass scales, chillers collet ready spindle with .5micron or less positioning accuracy/repeatability and less than .3-micron spindle runout.

Sorry for the advert, yes, I work for Hardinge as a AE\Turning Product Specialist

Tom
 
For only a few pieces, I'd forget about the on-machine inspection and get a contracer. Too expensive, if there is even such an animal.

It sounds like material is cheap and parts small so maybe a relatively short cycle time. Cut one, check it, toss it, adjust, cut another.
 
Hello, I'm searching for a machine which can (really) accurately cut tapers/2d curve profiles into relatively soft materials (bronze, lead, aluminum). The challenge is that the accuracy required is +/- 0.0001" or better on the average ~1.8" inside diameter, over a ~1" length. We also need a way to inspect the parts, ideally in the machine.
Regardless of what you run these parts on, you're still going to have to design an entire process to thermally stabilize the room, the machine, the coolant, the measurement techniques, etc, etc. If you haven't done that, there is no way to know what kind of parts you sent out for inspection.

I can regularly hold similar ID tolerances on a TL-1 when boring bronze transmission bearings. To be clear: these bearings are pre-machined and pressed into a substantial steel gear before final sizing. The material is therefore very stable concentricity-wise. I measure on the machine with telescoping gauges and I need to be +/- 0.0002", though I can usually hit half that. Every tenth or two in size can be felt as a significant fit change on the final transmission shaft they're being mated to.

So the machine can do it, if you're careful about the setup and the process. If you're in the situation of needing to measure the parts and they're truly stable (not changing shape when they come out of the machine), your next problem will be the choice of metrology. Are you using two or three point bore gauges? Have you considered air gauging?
 
Thanks for the replies. The parts are in fact bearings that are pressed into a steel insert in an aluminum housing, then finish turned. I should have mentioned that the OD of said housing is 7.8". The shop is not extensively climate controlled, we only maintain within say 60 to 80F. If a machine has a chiller (I'm guessing this is for the coolant, and maybe it also circulates through the spindle?), does the shop still need to be better controlled than that?

It's impressive to hit 0.0001" accuracy with a TL-1, but I'm not sure realistic for us, given the profile to be cut, cost of the parts, and the difficulty of inspection on-machine. It would be worth extra $ to make the process more foolproof.

Re inspection, I don't think telescoping, bore, or air gauges are adequate, as the ID has a taper/2d crown to it of a few tenths, which can probably only be seen with high end CMM or Contracer style device.

@Tom, I have sent you a PM with my contact info. The Hardinge has the benefit of a 9" max diameter, and bigger is better for us to accommodate future larger engines.

Takamaz J-WAVE PLUS (and Miyano) looks nice but too small, is there an equivalent larger model which has no bells and whistles, but keeps the accuracy? A lot of options to choose from just based on size

I am also open to used equipment if it can be demonstrated to hold these tolerances before purchase
 
The shop is not extensively climate controlled, we only maintain within say 60 to 80F. If a machine has a chiller (I'm guessing this is for the coolant, and maybe it also circulates through the spindle?), does the shop still need to be better controlled than that?
Simple answer. Yes. Even if it’s only the machine that’s in the controlled environment.
 
Get a hold of hardinge . I believe there super precision line can handle it. If interested i have GT27SP with very low hours that I would let go cheap it has the high speed skip and probe interface for a wired probe. We used it to finish bore hydraulic lifter bodies, we abandoned the project due to other difficulties,
 
The parts are in fact bearings that are pressed into a steel insert in an aluminum housing, then finish turned. I should have mentioned that the OD of said housing is 7.8". The shop is not extensively climate controlled, we only maintain within say 60 to 80F. If a machine has a chiller (I'm guessing this is for the coolant, and maybe it also circulates through the spindle?), does the shop still need to be better controlled than that?
Sorry, I'm having to declare shenanigans on this whole thing. Absolutely, yes, a temperature swing of 20 degrees F will affect this. Absolutely the part being in an aluminum housing, with steel insert will affect this. Holding it in your hand will affect this. Holding the measurement tools in your hand will affect this.

Either you have a customer, or a requirement that has been complete BS in the past or you're about to embark on a steep learning process to get there. A 7 degree change in the temperature of the part is enough to blow you out of size by 0.0001". That applies to everything else in the chain too. Things like ball screws and the temperature of the chuck are at play.

If you're the machinist, you've been sent on a fools errand by the engineers. If you're the engineer, rethink the design because what you're chasing has obviously never happened in the past and the design doesn't need this spec.
 
I'm more engineer than machinist. The parts have been made correctly in the past, I have the CMM reports, measurements in a controlled climate. In our testing experience, parts that meet the print do not fail during testing, and those that don't... often do. I think the crown profile shape is more critical than the exact diameter, but that isn't proven yet. This is R&D work, not mass production.

I do understand what you're saying about the temperature affecting the size- that's unavoidable. In my thinking, the more accurately we can control the part (at a known temperature), the better learning we will gain about what works and what doesn't. A couple tenths could be the difference between metal on metal contact/friction/bearing seizure vs. having a comfortable oil film that runs forever.

This level of precision is new for our shop, that's why I'm asking for input. Even if we don't achieve perfection, if we can do "better", it's a good thing for what we are trying to do.
 
Small Takamaz J-WAVE PLUS or Miyano RL series will do that all day every day.
Or any small high quality lathe with gang style tooling, no turret.
+1 on a gang style lathe.

Can't afford to let a turret eat up your entire tolerance band.

The shop is not extensively climate controlled, we only maintain within say 60 to 80F.
Build an inspection type room and put the lathe in there, maybe?

Re inspection, I don't think telescoping, bore, or air gauges are adequate, as the ID has a taper/2d crown to it of a few tenths, which can probably only be seen with high end CMM or Contracer style device.
Doing this in-machine seems unlikely. I would measure a straight section of bore with a 3-point bore mic, calibrated to a custom ring gage, and trust that if the straight section is within tolerance, the rest of the profile is as well. Then verify offline on a CMM.
 
A Hardinge T42SP can handle those tolerances with no issue, feel free to reach out to me and I can send your contact information to our NE Sales Rep. Machine is equipped with glass scales, chillers collet ready spindle with .5micron or less positioning accuracy/repeatability and less than .3-micron spindle runout.

Sorry for the advert, yes, I work for Hardinge as a AE\Turning Product Specialist

Tom

I have a Hardinge T42SP. I hope the new ones have gotten way better because the older ones are a pile of shit compared to a Miyano.
 
Endless options..
Any of the high-end lathes can do this if your process is set up right.

Don´t worry about the air-co chillers and environments and stuff. Imo. Ime.
Hugging a 7" piece of metal in your hand for even 2 minutes will not warm it to any significant degree.
Metal expands and contracts in a perfectly ordered fashion.

If you pour warm water or coolant on it it will expand, but when it cools to 20C it will again be to spec.
Using a go/no go gage on it, of the same temp as the workpiece, should give you perfectly repeatable results better than 1 micron.

Example:
If the room, workpieces, and gages, were all 30C, aka too warm, they would still work, and still give the right go/no go results.
Even though they are probably about 0.0150 mm oversize at 30C vs 20C for a 1.8" bore.+/-
(TLAR estimate).

I think You could use any of the digital dti´s with spc cables to probe the workpiece.
Maybe use a known-good "perfect" piece next to the workpiece, and compare the difference. It will be at the same temp and have the same thermal errors (if any) as the workpiece.
IF a == b to a given accuracy, then a must be ok.

Contact probes are accurate to better than a micron.
You could use these, for critical features, since these are one-off pieces made in low volume as You said.

For an idea, I might take a swing at 2 microns, perhaps 1 micron (partly), reference measurements and parts qualification setup.
This would be a 40k/mo contract as ballpark -just calibrating your expectations.

Watchmakers and telescope makers have been doing sub-micron work by hand for over a 100 years.
It´s not all that *hard* but it is either laborious or expensive.
 
I'm more engineer than machinist. The parts have been made correctly in the past, I have the CMM reports, measurements in a controlled climate. In our testing experience, parts that meet the print do not fail during testing, and those that don't... often do. I think the crown profile shape is more critical than the exact diameter, but that isn't proven yet. This is R&D work, not mass production.
There are very few CMM's + operators that I'd trust to accurately measure a .0001 difference.

Having worked with CMM's myself, I know I can get it to say whatever you'd like with just a few clicks. I've also had customer's claim my parts were bad because the CMM report said a feature was off by 7inches... on a 3in long part... But the holier than thou report shall not be questioned.

If you truly care about splitting tenths, a CMM is not the way. You'd need a dedicated air or laser gauge.
 
You can get an air gauge that will measure a tapered bore, it will be custom.

 
Personally - for 1-2 pcs at a time, I'm not seeing how thermal this, or ... really much of anything else is of much value here.
???

It sounds like you may need a machine that has less than .0001 resolution for starters.
The Hardinge T series at least have this, but I can't say that I have ever had any need to qualify it.
I may chase tenths on bearing bores, but I have never tried to split them.

But with that said - for one or two pcs, I don't see that thermal stability is a concern at all?

For starters, I would say that you should have some means - other than the machine - to qualify the machine.

I would address this just like I doo bearing bores:

1) Rough it close, but ... maybe leave .050" on it yet?
2) Change to your finish tool and take it to .040.
3) Take it to .030
4) Take it to .020

5) Measure with whatever means that you have.

6) Adjust offset
7) Take to .010

8) Measure again

9) Take final pass

10) Measure before taking out
11) Measure once it is out and compare / double check the same.\


The key here is that you DOO NOT index the turret away once you are down to the adjust state.

You need to keep a stable DOC, and maybe .020 per would be better.
I typically use .020 for my apps, but I am at 10X tol as you are trying to achieve ....
Going back to take that last .0001 will not work well b/c your tool will be rubbing, and the tool pressure is not the same, so your last pass needs to be real.
A .0001" pass is only for the grinder.


Also, if you limit your X axis moves to "only as required", you can mitigate, or even nix thermal growth in the X screw even for longer jobs, but in this case, again - I don't see thermal growth as an issue.

A machine with finer pitch screws would seem to be best.

Really, any lathe with fine pitch screws in good shape, .00001 resolution on the control, trucks in good shape, and X thrusts in good shape - should be what it requires. If these pre-requisites are met, I would think that any brand would be about the same at that point.

Finishing tool would be about as essential as well, and I have no recommendation there.


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