Am I the only one ?

[DavidA]

Just wondered if anyone else had made this mistake.

I mentioned elsewhere that I have just started using my new XI L mill.

I decided to reduce a bit of steel bar by 1/10" in 0.010" stages,  just to get the feel of the machine.
The vertical scale is marked 0,  10,  20,  30 then back to 0.

Anyway,  I did my ten cuts and measured it.  Too thick.  'Strange' I thought. Then did another set of ten cuts.  Same result.

After a bit of head scratching I realised that the scale has 36 graduations,  not 40. each of 0.002";  giving 0.072" down per revolution of the scale.

I was  incrementing down by moving the scale round by whole numbers, and there are  only six graduations (0.012") between 30 and the 0 mark.

Please don't let me be the only one here to have done this.

Dave.

[lordedmond]

Yep your are the only one in the wide world that has done such thing  


Stuart


Only joking, typical Chinese dials, don't change the screw just bung on the dial to make it look OK

[Davo J]

I haven't got that machine but we all make similar mistakes.
It would be worthwhile using a vernier or digital caliper on all axis's to check the dials to see how true they are, and that way you know if you have to compensate for them.
Even on my large Chinese HM52 mill (which is the same as Chester's T mill over their) is out on the down feed collar, but a DRO has fixed that.

Dave

[andyf]

It took me a long time to work out why the topslide dial on my Chinese lathe never seemed to get things right. I knew it used the common approximation that 40 thou = 1mm, but the error was far greater than 1.5%. Finally, I realised that the dial had 50 "thousandths" graduations round it, whereas the feedscrew was 1mm pitch.   
 


Happily, my spindle gear is 40T, so it was easy to skim the marks off the dial and index 40 new ones round it.

Andy

[DavidA]

That's the next step.  Clamp on a dial guage and check what is actually happening.

Dave.

[saw]

I am in the same club 

[sparky961]

A simple solution if the dial has both metric and imperial is just to keep a calculator beside the machine and convert to metric when you need to go more than one revolution or across the zero line.  When I use this method and measure the part afterward, I find I'm much closer to the desired measurements.

Alternatively, you could start working in metric - unless you're American, in which case it would be a sin. ;)

-Sparky

[DavidA]

Sparky,

I tend to work in a mixture of Imperial and Metric anyway.  My age group seem to be more adept at this having been brought up in the cross over period.
As for the American thing,  shame on you  You'll be asking them to use Centigrade instead of Fahrenheit next.

As long as 0.001" on the dial corresponds wit 0.001" of vertical movement it isn't a problem. It was not realizing that there were not ten divisions between every whole number that caused the initial confusion.

Saw,

I feel much better now.

Dave

Apologies to my American friends;  I couldn't resist it.

[mklotz]

Apologies to my American friends;  I couldn't resist it.

That's ok.  We don't take seriously anything said by a bunch of wan guys who use a hundredweight that weighs 112 pounds.

[bigmini]

Apologies to my American friends;  I couldn't resist it.

That's ok.  We don't take seriously anything said by a bunch of wan guys who use a hundredweight that weighs 112 pounds.

Well that's including VAT or GST, or whatever I got used to converting back and forth in the workshop when we had one metric lathe and one imperial one-  The one you wanted was always tied up doing something else. Now I have a metric one and I just stick to that mostly. Unless I'm repairing something or making a part that needs an imperial thread.