Accuracy on the lathe

[gus]

When doing precision work know when to take a break and when not to.
when the part is hot from rough cutting is a good time. when you are trying to get the last cut or two in or taking off the last few thou or the last few tenths is not a good time. it is easey to forget whether or not you dialed in for the last bit and if you are working in tenths things can change while you are on break. it does not take much to move the cross slide 1 ten thousands and that is two tenths on the diameter.
I worked in a shop where the tolerances could be plus .0003 - 0.000. a spring pass is all that is needed to take that little bit extra.

Also if you have tolerances use them . on the OD shoot for the high number on the ID shoot for the low one. You can always lapp off a little but add on tools are hard to find and expensive.
Tin

Hi Tin Falcon,

Thanks for the tip. While turning the shaft O.D. of the FireFly I.C. Engine,
I thought i got the required fit between bearing bush and shaft.Remove from
chuck and fit into bush was another unhappy story. Hot shaft and cold shaft.

Now making some DIY tooling and after these,Gus will dive in again to build new engine and get all the required critical fits.

 

[lohring]

A quick update on my cheap DRO. The cross slide scale reads radii so I did a check on it's accuracy. I had a piece with two target diameters, .980" and .590". I machined one diameter to .9805" The next diameter finished at .5895" That gives a cross slide travel of .1955". I set the scale on zero at the larger diameter and it read a travel of .194 at the small diameter. That may be good enough for some projects and is within the +- .001" advertized accuracy, but I often like things closer as in this case.

I also machined the length of the .5895 diameter section. I was not as careful as the length wasn't as critical, but the indicated length on the scale was .220" and it measured .225". This wasn't as good a test as I didn't face both ends of the piece with the scale set to zero at the first face. I just ran the tool up to the first face to set zero. However, I would expect that to be within .002"

As you can see. the accuracy isn't as good as real digital read outs.

Lohring Miller

 

[AussieJimG]

Thanks Lohring, you have just solved a small problem:

When I put two of my "tyre tread" DRO on the cross-slide at the same time, I found a discrepancy of up to 0.03mm between them. I expected plus/minus one LSD (least significan digit) because that is the case with all digital instruments. And now you have suggested an accuracy of plus/minus 0.001" (0.02mm). So worst case, I can expect plus/minus 0.06 difference.

Now I understand.

Jim

 

[lensman57]

Hi Jim,

Unfortunately this what I experinced with the cheap import digital calipers. The repeatabilty was just not there, they specify this in their charts at plus or minus 0.02 mm which is not good enough for critical work. I found that I get better precision with the Mitutoyo brand but then again it costs 3 times as much.

Regards,

A.G

 

[gus]

Hi Jim,

Unfortunately this what I experinced with the cheap import digital calipers. The repeatabilty was just not there, they specify this in their charts at plus or minus 0.02 mm which is not good enough for critical work. I found that I get better precision with the Mitutoyo brand but then again it costs 3 times as much.

Regards,

A.G

Hi A G

How much would a Mitutoyo DRO cost ? Bought a Makita Bandsaw December 2012.Maybe a Mitutoyo in 2013 if my investments gives good profit in 2013.

Or Please advise the best of the cheapie DRO. The "Heidenhan" DRO on the Leblonde gave me good results but had to watch the cutting tool.Both Leblondes sold when plant shutdown 2001.

 

[lensman57]

Hi A G

How much would a Mitutoyo DRO cost ? Bought a Makita Bandsaw December 2012.Maybe a Mitutoyo in 2013 if my investments gives good profit in 2013.

Or Please advise the best of the cheapie DRO. The "Heidenhan" DRO on the Leblonde gave me good results but had to watch the cutting tool.Both Leblondes sold when plant shutdown 2001.

Hi,

I live in the UK, anything decent costs an arm and a leg, a 12" Chinese made DRO- scale costs about £45.00, the Mitutoyo about £180.00. I managed to get a brand new Absolute Digimatic caliper for less than £60.00, the used ones are going for about £35.00~£40.00 , the Chinese calipers costs anything between £12.00 and £29.00 and they are not bad to be honest but not as accurate as a Mitutoyo in IMHO.

Regards,

A.G

 

[lohring]

The Mitutoyo DRO on my mill easily positions the table within .001". I mostly use the scales on the lathe to get close. I think the scales will be fine for lengths. They still aren't going to substitute for the new cross slide lead screw and the direct reading dials.

Lohring Miller

 

[gus]

Hi,

I live in the UK, anything decent costs an arm and a leg, a 12" Chinese made DRO- scale costs about £45.00, the Mitutoyo about £180.00. I managed to get a brand new Absolute Digimatic caliper for less than £60.00, the used ones are going for about £35.00~£40.00 , the Chinese calipers costs anything between £12.00 and £29.00 and they are not bad to be honest but not as accurate as a Mitutoyo in IMHO.

Regards,

A.G

I paid 90 Pounds for a 12" Mitutoyo Digital Vernier Caliper. All the Chinese Verniers I bought been bad.They eat batteries and when battery power is down they flash on and off. But recently I paid S$10 for a Plastic Version just for fun.
It did not eat batteries.