Inspection Sheets: Worthless?

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SteveHGraham
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Inspection Sheets: Worthless?

Post by SteveHGraham » Sat Aug 11, 2018 11:04 am

As everyone here knows, machine tools and accessories often come with inspection sheets. These things contain tables in which actual measurements are compared to specifications.

I always assumed that if I bought a chuck or something, and there was an inspection sheet with measurements filled in by hand, it meant someone had measured the item. Now somebody is telling me it doesn't work that way. I am told it means the factory measured ONE similar item from a LOT the item belonged to. So if you buy a $20,000 lathe, the odds are overwhelming that the numbers on the inspection sheet are for a different lathe, and your lathe could be a mess.

Does anyone know the truth? It seems stupid to rely on group inspections for precision tools.

I just found out that Tormach only inspects 1 in 20 mills, so 95% of their machines go out the door with nothing but high hopes to back them up.
Every hard-fried egg began life sunny-side up.

John Hasler
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Re: Inspection Sheets: Worthless?

Post by John Hasler » Sat Aug 11, 2018 11:11 am

SteveHGraham writes:
I always assumed that if I bought a chuck or something, and there was an inspection sheet
with measurements filled in by hand, it meant someone had measured the item.
Now somebody is telling me it doesn't work that way. I am told it means the factory measured
ONE similar item from a LOT the item belonged to.

And then they paid someone to copy the results over by hand 99 times?

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SteveHGraham
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Re: Inspection Sheets: Worthless?

Post by SteveHGraham » Sat Aug 11, 2018 11:21 am

Right, that seemed a little far-fetched to me.

I think someone is confusing overall quality control for products like vacuum cleaners with necessary inspection of individual machine tools.
Every hard-fried egg began life sunny-side up.

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NP317
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Re: Inspection Sheets: Worthless?

Post by NP317 » Sat Aug 11, 2018 11:25 am

I have no idea what the truth is to Steve's question.
That leaves it up to us to repeat the inspections to learn if our machines are within tolerances!

After installing the DROs on my lathe and mill, checking their accuracy against external measuring tools, and machining parts and measuring the results,
I now have confidence that both machines are within specifications from the factory.
But it took a while...

Most important: They meet my needs.
~RN

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Rich_Carlstedt
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Re: Inspection Sheets: Worthless?

Post by Rich_Carlstedt » Sat Aug 11, 2018 5:19 pm

I have seen Photocopied inspection sheets, and fiquried they were lazy and I consider them just that- too lazy to measure.
I never buy on the basis of a inspection sheet, and do my own data measuring.
What I have found is you get what you pay for, There are no shortcuts, only lesser quality for a lesser price.

Rich

Cary Stewart
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Re: Inspection Sheets: Worthless?

Post by Cary Stewart » Sat Aug 11, 2018 5:29 pm

Modern production of most everything use SPC (Statistical Process Control) along with sampling of lots. Tormac is a very reliable company so they apparently are using a sampling routine for quality control. As an example I purchased a Bison 2 3/8" dia. 3-jaw chuck for my Unimat 3. It came with a little sheet showing the measuring points and giving the tolerances. On the bottom of the sheet was a colored inspection stamp with a individuals initials. A few years later I purchased the same chuck used for my DB/SL Unimats with the same little paper with a later date and a different inspectors stamp and initials. What is happening is they do some kind of a check on each chuck very quickly which verifies that the individual chuck meets the tolerance requirements. When I purchased my first chuck new they were $124.00 each. Now they are $365.00 which is almost the same as a 6" plain back chick. I don't think the Poles like us anymore.
Cary

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ctwo
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Re: Inspection Sheets: Worthless?

Post by ctwo » Sat Aug 11, 2018 5:46 pm

The certificate must identify the specific device by serial number and date. It depends on what you are getting and from who and how they operate, as Cary said.

Steve, I bet we watched the same YT video. Do you think the Haas was individually measured and certified?
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

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SteveHGraham
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Re: Inspection Sheets: Worthless?

Post by SteveHGraham » Sat Aug 11, 2018 7:38 pm

I hope Haas checks each machine instead of waving a magic wand over each freight car and pronouncing a blessing.

The Tormach video was distressing. The buyer said he could push on the table and make a dial indicator move, and he talked about parts being off by several thousandths, if I recall correctly. I can't see blowing five figures on a machine that requires substantial rehab and then won't do any better than a converted Grizzly.

He also said that after he sent the machine back, he was out over two grand. He claimed he told them up front what he intended to do, they assured him the machine would do what he wanted, and then they sang a different tune when he put it to the test and it failed.

I haven't heard Tormach's side of the story. I hope he was exaggerating.

Interesting thing: some people have major gripes with Haas. Can it be that no one cares about quality any more?

I saw someone over at PM talking about trouble-free Taiwan CNC machines. I wonder if that's true.
Every hard-fried egg began life sunny-side up.

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NP317
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Re: Inspection Sheets: Worthless?

Post by NP317 » Sat Aug 11, 2018 10:13 pm

I just researched my lathe and mill for test spec sheets.
The Grizzly G0709 lathe has test sheets with hand entered results, and the machine serial # specified on the sheets.
The Grizzly South Bend SB1027 mill has test sheets with separately printed results, and no serial # specified.
Both test sheets have diagrams showing exactly how to perform the tests yourself.

Interestingly, the Taiwan-maunfactured SB 1027 mill has the superior manufacturing, with very little machining detritus under the table or elsewhere, based on my delivery inspections.
And it performs as well an any Bridgeport machine I have used, and that's quite a few! The SB seems to be more rigid, too.

So when in doubt, I can redo any of the tests specified and compare the stated accuracy results.
~RN

pete
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Re: Inspection Sheets: Worthless?

Post by pete » Sun Aug 12, 2018 8:24 am

I watched that same video. I'm not defending or trying to crucify Tormach. But I have some doubts about the video posters machine tool experience and actual knowledge level. About all that was mentioned was some surface finish and dimensional errors. I don't doubt that part. But I don't recall any real checking being mentioned as to what the causes might be before sending the machine back. And I sure don't take any YT video at it's face value without the poster showing he does know exactly what he's doing over many many videos. One slightly loose ball screw mounting bolt and loose misadjusted gib could create that exact problem. I don't know that was the cause but it's one possibility for an easialy fixed issue. Or maybe it really was a pos? If you don't check first about what's really causing the problem you can't say for sure the machine was poorly made or not. It's supposed to be rare, but even the very best of machines can get through QC with a problem sometimes. Pulling the table to do some checks isn't rocket surgery, and I wouldn't have hestated to do that at all. Should you have to do that with a new machine? No way. But for 2k I sure would.

Bogus test certificates? I've got a couple of them here. And years ago John Stevenson was doing cnc conversions to X3 mills and also doing stepper driven 6" Vertex rotary tables as a 4th axis for those mills. He mentioned on the HSM forum he'd once bought 20 of the 6" Vertex tables in one order and every single test certificate "had the exact same numbers" for every one of those R/T's. My off shore but still fairly expensive gage blocks came with a proper certificate showing the exact dimensions to the nearest millionth for every block. Everything looked legit. Funny thing was there were two blocks in that set where both were the exact same size. Buying a NOS set of grade 2 Mitutoyos showed about the same test certificate. The difference is I know which one I'm a bit more willing to believe.

Should you do your own accuracy checking? Think about this, even with the very best and most expensive built machines today they level, recheck ALL the alignments, then run real world cutting and performance checks on brand new machines before it's ever put onto producing parts. Not many on the forums ever mention doing much more than leveling a lathe bed or tramming a mills head in. Haas has it's supporters and detractors even on the PM forums. Just like a Tormach you get what your willing to pay for and that Haas mini mill is still there entry level machine. 45k or maybe a bit more should get you at least a half decent workable machine, but that's still chump change compared to anything that's fairly good.

That 2k "restocking" fee of Tormachs doesn't make them look very good at all. So if I was Tormach? I'd make real sure to start doing some damage control so I'd video and post what they find once they start digging into that machine. If it was a factory error that couldn't have been fixed then say so with no excuses. If that video poster could have fixed the problem with little effort then put up a video showing how to do that if an owner sees the same issue on another machine. Reading the comments under that video shows it's already cost them a few sales if any of those comments can be trusted.

Mr Ron
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Re: Inspection Sheets: Worthless?

Post by Mr Ron » Sun Aug 12, 2018 8:43 am

I have a lathe that has the wartime stamp on the bed. That was supposed to be headed for a military unit. Mine was installed onboard a navy ship. Since I bought it used, there was no inspection certificate. I would assume the lathe underwent a thorough inspection at the factory before the navy would accept it.
Mr.Ron from South Mississippi

earlgo
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Re: Inspection Sheets: Worthless?

Post by earlgo » Sun Aug 12, 2018 9:50 am

All this reminds me of long ago when the company I worked for bought sulphurated oil by the tank truck and sold it by the gallon. Each delivery from the supplier had a spec sheet proving the composition. One delivery sheet looked so familiar that the plant supervisor got out the last delivery sheet and held them up to the window. BEEP! Exactly the same graph and numbers. When confronted, the vendor admitted that he didn't test every lot. New vendor, please.

As far as inspection sheets for machine tools go, how would any shop, much less a garage shop, verify any of the readings without a lot of metrology equipment?
--earlgo
Deja Poo - The feeling you have seen all this crap before.

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