5um vs1um

[Markbinwi]

The question is it worth $35 upgrade for 1 Ditron glass scale? I have a 12x36 Craftsman/Atlas lathe. Is 5um good enough?
Thanks

 

[WobblyHand]

The question is it worth $35 upgrade for 1 Ditron glass scale? I have a 12x36 Craftsman/Atlas lathe. Is 5um good enough?
Thanks

It's worth it for the X axis (cross slide). Less so for the Z axis (along the length of the lathe).

In full disclosure I got the 1um scales for both axes. Then you can easily see and measure 0.0001" increments linearly. 1um is a really small number - don't expect to machine to that level unless you are exceptionally talented and have a matching machine. When I lock an axis I can see things squirming about until it's locked. But at tenths, things are relatively stable. I shoot for tenths, but am happy within 0.0005 - 0.001". If you can't measure it, it's hard to hit your targets.

I previously had native 0.001" scales. So using only the DRO I could only do diameters to 0.002" since the DRO resolution was 0.001" on radius. Going to 1um scales on X really helped me a lot.

 

[ycroosh]

The question is it worth $35 upgrade for 1 Ditron glass scale? I have a 12x36 Craftsman/Atlas lathe. Is 5um good enough?
Thanks

In practice 5um scales are more than enough for a lathe, even on the cross slide. They will give you 0.0004" resolution on diameter. 1um scales will give you 0.00008" on diameter. I can't hit anything under 0.0005" on my lathe unless I get super lucky, and in most cases when I get to within 0.001" I do a little happy dance. Anything better than that goes to my surface grinder for grinding between centers, and even then tenths are VERY challenging.

All of the above applies to glass scales. If you are looking at magnetic scales, 1um or 5um are "marketing terms" and have nothing to do with the actual scale resolution (which is around 10um for good ones).

Regards
Yuriy

 

[Markbinwi]

In practice 5um scales are more than enough for a lathe, even on the cross slide. They will give you 0.0004" resolution on diameter. 1um scales will give you 0.00008" on diameter. I can't hit anything under 0.0005" on my lathe unless I get super lucky, and in most cases when I get to within 0.001" I do a little happy dance. Anything better than that goes to my surface grinder for grinding between centers, and even then tenths are VERY challenging.

All of the above applies to glass scales. If you are looking at magnetic scales, 1um or 5um are "marketing terms" and have nothing to do with the actual scale resolution (which is around 10um for good ones).

Regards
Yuriy

Thank you all.

 

[mksj]

I would recommend going with a 1uM (glass) scale for the cross slide, but to some degree it depends on the accuracy/rigidity of your lathe and the accuracy of the work you need. The issue with using a 5uM on the cross slide is that when using diameter mode the display increments will be in 0.0004" steps which is resolution (what it will read) but not accuracy (which is often +/- 1 digit repeatability), and you have issues with the linearity of the scale over a specified distance/increment). There is also computational error of the DRO unit, they can do some funny rounding errors. I have had both scales on my lathe, when I bought my DRO they sent a 5uM when I specified a 1uM, I kept on having issues in hitting the correct diameters on work at the 0.001" level. I finally checked the scale specifications and then replaced it with a 1uM. A 5uM scale may seem accurate enough but often I am working on tenths and the a 5uM scale it just didn't work. Magnetic scales can be appreciably worse in particular many of the Chinese ones, their accuracy tends to be quite bad.

Example below, were a series of drive pins for a Narex boring head, I made 8 replacement pins and the diameters were all within +/- 2/10ths.

 

[WobblyHand]

I agree with Yuriy. But, I have done precise parts to the tenth. It is hard. You need to do that sort of thing for bearings and for decent slip and interference fits. 99.9% of the time, I'm happy to be within that 0.001", but there are times when you need to do better. If you don't practice, it's hard to get better, and perform when it counts.

That being said, having a good micrometer is an essential part of getting there. Just because your DRO moved to where it says doesn't mean there wasn't part deflection, or movement upon cutting load. (That means you didn't actually cut 0.002", you cut 0.0013" because the part moved away from the tool.) The micrometer is ground truth. A DRO makes things a lot easier, but it's no substitute for part measurement with a micrometer. @mksj 's QuantuMike is awesome. Have one, love it.

 

[MrWhoopee]

I have 5um scales on my Heavy 10, more than close enough.

 

[ycroosh]

I have 5um scales on my Heavy 10, more than close enough.

Love your signature (both parts)