Scraping and Struggling.

[Anorak Bob]

If I set up my Mahr 1um indicator square to a 10mm rod in the dividing head and zero it I can then gently retract the stylus with the cable release allowing me to move the table up to the position of the same 10mm rod held in a collet and chuck that I trust. I can then gently release the stylus and position the spindle to zero the indicator. More accurate than a loupe. I will need to make a flat faced stylus.

What do you reckon, pissing in the wind? The setting up square will be the tricky bit.

BT

[Stustoys]

Hi BT,
I dont see how the flat faced stylus is going to make things easier. You'd need to be perfectly** square in two plains. I think you'd be better off with the normal stylus. Though I do like that you end up on center and dont have to worry about removing the offset like my idea below.

How about this, one 1um indicator on the table set against the 10mm rod in the dividing head. Another 1um indicator on the machine set against the 10mm rod in the spindle. bring the rods together until you have movement on either indicator. Repeat as many times as you like on both sides of the bar until you are happy?(if you had flats ground on the rod until they where 5mm thick that would let you be on center)

Maybe while you have it set up, turn the dividing head 180deg and see if it all comes out the same?


Stuart

[Abratool]

Bob
Been thinking about your next step & feel a pointed round tip stylus would minimise error compared to a flat type.
regards
Bruce

[RayG]

Hi BT,

A cylindrical stylus would minimize the error from not being on-center with the indicator.

Regards
Ray

[Anorak Bob]

My centering efforts have been thwarted. The plan to use the Mahr's cable release to gently lift then lower the stylus onto the test rod won't work. It lacks uniform repeatablity, 0 to 5 um variation. I have to work out another plan. I need to devise some way of rigidly fixing the indicator back to the immobile body of the mill. There is too much movement in the Noga support.

I pulled my Bausch and Lomb microscope apart in a futile attempt to create a 43x loupe. I can't hold the thing still enough and clamping it to something isn't easy.

More head scratching

BT

[Stustoys]

Hi BT,

Have you tried a DTI? The lower pressure helps I think.
I've found when you get that fine that the normal old bar and clamp indicator holders work better as you can make the arms very short(but my Noga is a copy I have no idea how good the real ones are).


"A cylindrical stylus would minimize the error from not being on-center with the indicator"
But how do you get it square the both plans?

Stuart

p.s. Some may say 0.0002" was pretty close

[Anorak Bob]

Stu,

Thanks for the response. My most accurate DTI is a 0.0001" Mitutoyo, coarse in comparison with the Millimess. I have a stout armed Eclipse mag base I will try with tomorrow.

The Israeli Noga is big, flexible and superb but I also have a couple of 19 dollar minature pretend hydraulic versions that have proven unbeatable in a number of setups. They get in where the Noga can't. 1um, 0.000039" is nudging FA. Doesn't take much to move that needle.

I will let you know how I get on.

BT

[Michael G]

I remember being told a story once by an ex toolmaker - when he was an apprentice he spent some time in his company's metrology lab. One day the supervisor announced to him that they were going to measure a micron.
I can't remember all the things they did, but the measurement was done at lunch time so the press line was not working, and I think they even stopped people walking & driving forklifts outside the lab. The lab was of course temperature controlled and the items being measured had been in that environment for some time to get a uniform temperature. They would have worn gloves and were careful where they breathed so that air currents or the heat of their breathe did not disturb things.
I also read a story where the grand old man of Mitutoyo came to their top production area to "show the troops how it was done". He blued up a surface plate, did a couple of movements to spot the item that was being scraped and then told people to leave it for 15 minutes because the heat from sliding it on the surface plate was enough to cause some distortion in the surface (we're taking a Master Master plate here).
What I'm trying to say here is that while you may have equipment capable of resolving to micron levels, unless you are being every careful, the uncertainty surrounding the measurement is probably such that you are not really accurately and repeatably getting that. In that case the gauge that reads to 1/10th of a thou is probably adequate for the work you are doing.

Michael

[Abratool]

I remember being told a story once by an ex toolmaker - when he was an apprentice he spent some time in his company's metrology lab. One day the supervisor announced to him that they were going to measure a micron.
I can't remember all the things they did, but the measurement was done at lunch time so the press line was not working, and I think they even stopped people walking & driving forklifts outside the lab. The lab was of course temperature controlled and the items being measured had been in that environment for some time to get a uniform temperature. They would have worn gloves and were careful where they breathed so that air currents or the heat of their breathe did not disturb things.
I also read a story where the grand old man of Mitutoyo came to their top production area to "show the troops how it was done". He blued up a surface plate, did a couple of movements to spot the item that was being scraped and then told people to leave it for 15 minutes because the heat from sliding it on the surface plate was enough to cause some distortion in the surface (we're taking a Master Master plate here).
What I'm trying to say here is that while you may have equipment capable of resolving to micron levels, unless you are being every careful, the uncertainty surrounding the measurement is probably such that you are not really accurately and repeatably getting that. In that case the gauge that reads to 1/10th of a thou is probably adequate for the work you are doing.

Michael

I read your post & all I could thing of was "Lets rebuild Australia"
Bring it back, please
We had plenty of know how, why did we let it all go ?
regards
Bruce

[Anorak Bob]

Michael,

I am fully aware of my limitations and and those of my equipment. I'm using the Millimess because I have it. The accuracy of the machined base was simply a fluke.

Bob.

[Abratool]

Michael,

I am fully aware of my limitations and and those of my equipment. I'm using the Millimess because I have it. The accuracy of the machined base was simply a fluke.

Bob.

I think it may have been skill,& know how.
regards
Bruce

[Michael G]

Bob, I apologise if you thought I was slighting your abilities and methods. One of the reasons that we are involved in this hobby is to try and improve and I agree with Bruce that skill and know how may be the reason things worked for you. Occasionally I encounter students how don't believe they are capable of getting things right and they attribute everything to luck too - it's a tough job convincing them that it is possible they are capable and can "own" some success.

What I was trying to say in a long winded way is that there is too much uncertainty in measuring to a micron in a home workshop. (Because of my background I tend to use specialist terms - in this case I'm meaning the likelihood of a measurement being correct rather than a false value due to measurement error, thermal conditions, technique, vibration, etc, etc,...). If that's the only gauge that you have then that's what you have to use, but with a gauge capable of that level of precision you may end up chasing your tail because you are reading values that are a result of the environment rather than the work being measured. I've done it myself - I have a very precise spirit level (0.005mm per metre from memory) and once when I was trying to level a mill table I was having all sorts of trouble because the slightest bit of grit or imperfection on the table was enough to throw things out. Switching to a less precise level let me get to good enough without erroneous readings throwing things out.

Michael

[Dave J]

Your doing some nice work as usual Bob.
The way you ended up doing the top last was the way I would have done it. I replied to the other thread about the base and doing it that way, but not sure what happened to it.
As to the micron accuracy, from what I remember of your shed it all sealed off, so you would have a better chance than most of us with open sheds chasing microns.

Dave

[Anorak Bob]

Michael,

When I purchased the Millimess indicator, it was not a purchase fueled by aspiration, pretention or illusion. I bought it because it is a requirement for the servicing of the horizontal spindle in the 13. Schaublin state in their service manual that a 0.001mm indicator is to be used when adjusting the spindle bearings. A task that I have yet to undertake.

My use of the indicator has been limited to simple positioning, levelling and the measurement of runout. I use the indicator for the final accurate realignment of the universal table. Repeatability has not been an issue in any of these functions which are really no more than observations of deflection.

At the age of 59, I still have the ability to comprehend and I do understand your comments and more importantly, why you made them.

Bob.

[Bryan]

Bob, sorry if this is a bit agricultural, but I would drill a starter hole as near as I could, leaving plenty of meat. Then bore, measure, adjust, repeat. Measure from the hole edge to the part edge with a mike.