VMC for True Position

[chris m]

Good afternoon esteemed forum members; this question has come up in the past but I figured I would cast the net out there again to see if anything new has come down the road.

 

We have parts that are regularly manufactured here which have a drawing requirement of .0008RFS between a number of reamed holes [as few as three, as many as eight] machined in a VMC and an existing bore which is machined in a previous operation. We are currently making these parts in a 10 year old, 30 x 16, CAT40, box way, X over Y table machine with no thermal comp and no scales and a Renishaw OMP400 probe. The hole positions vary anywhere from dead balls right up close to the limit and it takes a little coaxing to get the machine rolling, but I am still pretty impressed that we get the results we do.

 

The issues that I have are that I have only the [1] machine which will reliably produce these parts, though I can limp by on a couple of others if I absolutely had to, and that I am using the majority of my tolerance on a regular basis, which I don’t care for. To that end, I am looking into some new iron for this operation and I’d like any insight on the various equipment you guys have in your shops, or have seen around in your travels. I am personally thinking: 20 x 20 or 30 x 16, CAT40 or Big Plus, linear guideways, scales, thermal comp, and a .00001” programmable control.

 

Please discuss

 

C

[Guest]

quote:

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.00001” programmable control.

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I don't know that I have seen a control that will go down that far Chris, not inches.

 

One thing I have done in the past is to switch a machine over to run in Metric, your adjustment resolution is much finer than it is in inches.

.0001/.in

.001/mm = .000039/in

 

From a machine stand point you will ultimately need a "high end" machine likely in a climate control situation to reliably manufacture those closer than you currently are doing.

[Rick Henrickson 65]

makino goes to .00001

[chris m]

John, we have run in mm in the past in an effort to gain something but it has little effect on our existing machine; most likely due to the fact that the machine is as good as the resolution we have, but no better.

 

Okuma has a .00001" control option, though the machine cannot actually execute a move that small, and I think I've seen some others but not sure.

[mold100]

Makino is 5 place, the V55 will hold all day long.

[Hardmill]

YASDA, no need to look elsewhere.

 

 

PEACE

[chris m]

Corey and Steve, can you give me a little more info on your relative choices?

[Justin Beebe at Folsom Tool]

I have been holding true position of .001 on an older Makino and believe it or not on a Fadal with no problems. I am reaming both holes in the same operation making sure to approach from the same direction to eliminate backlash. When we first checked the holes the CMM was saying they were out of tolerance by .0002 but it turned out it was a false reading. We made a gage and they have been running fine on both machines.

[chris m]

quote:

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believe it or not on a Fadal with no problems

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You're right, I don't believe it, but true position of [2] holes to each other is easier than trying to put them in relative to something that's already there.

 

quote:

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We made a gage and they have been running fine on both machines

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Are you a gage house? The degree of precision required to make a gage that could actually check for a true position of .001 is pretty stupendous. If you do have the capability to make such a gage I may be interested in talking to somebody there about a couple of things I'd like to have made.

[Justin Beebe at Folsom Tool]

Chris,

 

We are not a gage house. I didn't make the gage but I can look into it for you. Our true position tolerance is also called out a MMC. The holes are:

 

.375 +.0005 -.0000

 

and

 

.500 +.0005 -.0000

 

So we have bonus tolerance.

 

How are you guys checking your true position?

 

By the way I think the reason it is holding on the Fadal is because I am establishing the position of the holes with and endmill then reaming. Once the machine moves to the position the X, Y axis never move again until both holes are finished. It just changes tools with no axis movement. You are in a much tougher situation than I am.

[chris m]

Justin, are you talking about a 3/8 hole inside of a 1/2 hole [like a cbore or port]? In this case I can understand both the gaging and the Fadal much more easily.

 

We check the parts on a nearly-new Mitutoyo CMM, which I'm not sure is good enough to be completely accurate, but it does repeat.

[Hardmill]

Yasda is gonna hit ya in the wallet bigtime,

but if you serious about holding position

there isnt a finer machine tool out there.

Ive held .0002 profile tolerance on a Yasda

that the CMM couldnt even check.

 

I got a contact for you if your interested.

 

 

PEACE

[Justin Beebe at Folsom Tool]

The parts have two bores that are in line with each other. There is a .516 slot in between them. When I get to work tonight ( I'm on night shift for a week) I will try to post a screenshot of the parts. We have a good Brown and Sharp CMM. I was told the reason that we got a bad reading with the CMM on the first part was because of the way the part was resting. The wall it was laying on when checked was not perfectly flat, and not perpendicular to the holes and it altered the reading of the true position. After putting in a brand new endmill and having a flat surface to locate the part with the next one checked out fine on the CMM. I am no CMM expert. We have a quality department that handels that. I have been told at two shops that CMM's can have issues with true position for the reason I describe above. I could be wrong maybe someone else has some input on this subject. We use the gage to double check. The parts have been working perfectly for the customer. I am always open learning more about this trade so if I can learn a more accurate way to check parts like this I am open for suggestions.

[Guest CNC Apps Guy 1]

I'll throw this profile tolerance CMM report out there for giggles...

 

 

note the consistency... that's 41-42 probe hits on the profile...

 

Toyoda FH450S in Titanium on a .035" thk wall .425 Dp.

[SIG]

What brand of machine is this?

I would consider just adding scales if your machine can already hold tol.

Is your shop temp controlled?

Do you have more error in Y than X?

[mold100]

Yasda, Seen the mystical beast one time, in a mold shop very impressive machine, however at the 35% higher cost than the Makino I ran at the time, and given the tolerance of automotive Mold work I couldnt justify going to the boss man and saying We gotta have one.

 

Also another machine that I had very good luck manufacturing helicopter parts on that was incredibly accurate and fast was a mikron HSM 700. I have nothing else good to say about that machine though I hated it.

 

Chris I ran the Makino V55 everyday for 2 years we had an intimate relationship. It was the first "high speed" machine I ran and it was 6 years ago. It reads 5 place decimals, and not doubt in my mind that it can easily hold any tolerance to the 5th place. I have ran since then a roeders, a few mikrons, a bostomatic, 2 DMG machines and now a sodick HSM, and being completely honest the Makino is superior to the later choices. Now I am aware that though it is a Top level machine there are others as well. I can also say I have ran a few Mori's and one of them now as well with the sodick, and they are very good mahines as well.

[Greg Williams]

quote:

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Okuma has a .00001" control option

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Yes that is correct. This option is normally sold on all Okuma Mold and die class (MD) style machines.

 

I would think any Mould and die class machine with scale feedback thermal comp in an air conditioned room worth it's salt should be able to do this.

[pip]

Mold 100

 

Can I ask you your opinion of the roeders.

[Steve Hattori]

We have a Hermle C40 5-axis with Heidenhain control and scales. The scales are resolved to .1 micron, and the control goes out to five decimals in inches (.00001). In metric, it does move one micron at a time. Thermal comp and a synthetic-granite base. Machine will run parts with .0001" tolerance easily. It isn't as expensive as a Yasda, but so far, the quality is outstanding.

[chris m]

Thanks for the info, guys, keep it coming if you have something to say. Greg, the machine we're looking at from Okuma is an MB-46V which has the .00001 control but I think it is an option [which I would buy]. SIG, the machine we have now is an Okuma & Howa which would be difficult to add scales to because it was not prepped for them when it was built and I don't feel that it would be fiscally responsible to put that much $$ into a mid-1990s machine even if they would retrofit it.

[mold100]

Pip,

 

Good High end machine, Pricy a few years ago It would eat a Makino SNC graphite mill, and A mikron for breakfast, however doesnt stand up to the Makino V series, or a Mori Die Mold IMO. What are you looking to Cut would be the starting place, just trodes and finishing hard steel, its a good choice, if you want to rough before HT or remove alot of steel material, wouldnt be a choice for me. I dont remember model but it had a small hsk spindle.

[pip]

Chers mold100

Cutting trodes with ours, just having a few problems with CLE on electrodes.

[Kevangel]

Chris, my only advice on trying to get the truth out of salesman on boring "true position" hole locations on VMCs, is to ask what they will put in writing. I was told scales only help with thermal growth and not true position(will help on jig bores and bridgeports)..think it has something to do with the actual drive motor and the board that controls it.. and make sure the person understands volumetric accuracy and not just moving in one direction (believe it or not, the salesman have told me "no one has ever asked me before about true position....yeah right...) I see Milltronics has gone to 40 millionths encoders and inline drives, they have some kind of accuraccy statement at bottom of model page.....I would probably buy a 20 X 40 travels and stay in the middle of travels, even my Moore jig-grinders and jig bore are effected at ends of travel, when new I think they guarenteed .0001" true position anywhere in travel, but a piece of steel added into mix...

[chris m]

Proof in the part is a given on this project. Anyone and everyone who presents a proposal will need to agree that the machine, in my shop, makes XX parts in a row to this tolerance checked on that machine with this much warmup time, etc, or it goes back on the trailer.

[CAM-mando]

quote:

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You're right, I don't believe it, but true position of [2] holes to each other is easier than trying to put them in relative to something that's already there.

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So is this a machine accuracy problem or a fixturing / probing problem Chris?

 

Is the deviation primarily from the pre-existing bore?

 

Sorry to question the obvious, I am just curious.

 

quote:

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Proof in the part is a given on this project. Anyone and everyone who presents a proposal will need to agree that the machine, in my shop, makes XX parts in a row to this tolerance checked on that machine with this much warmup time, etc, or it goes back on the trailer.

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Amen to that... I won't bore you with the details.