Digital caliper usage

[pepi]

Been using and testing with positive results. I am sure it goes against the tried and true machining methods...

So let er rip, thin skinned I am not.

Using a hole to describe the method.

Hole is 0.500
Round bar 0.750

Indicate the hole 0.500
Zero the caliper
Indicate the round bar 0.250
Machine round bar to Zero

Perfect fit....... what say you?

Pep

[Hawkeye]

That could work IF your lathe dials (or DRO) are set to measure diameter, rather than radius. Most are set up such that you need to divide the difference in your measurements by 2. If you turned your dial 0.250", you would find the round bar to be smaller than the hole.

Also, in practice, it's a good idea to sneak up on your final size by machining close to that size, then carefully measuring before closing in on the final size. When you are getting close, be sure to do several "spring passes" (re-cutting without changing your settings), to allow the 'give' in the lathe to cut what it will. Then measure and cut, taking the same number of spring passes before measuring again.

[pepi]

Mike,
I wrote that knowing most here know chopping .250 off in s single pass is out of the question.

 A better statement would had been. Work your way to zero in increments.



Thanks for pointing that out, that should have been mentioned.


Pep

[Dr Stan]

Much like setting any digital measuring tool to zero for the finished dimension when conducting inspections of the finished parts.  Should work just fine, but you also need to factor in the clearance or interference called for in the design.

[TomG]

The concept is interesting, but the execution is flawed. Calipers are not considered precision measuring instruments, especially on round parts and holes. Generally they can't be trusted to any closer than a few of thousandths on such, even in experienced hands. To get a good clearance or interference fit between a shaft and hole, you'll need to use a micrometer on the shaft and telescoping gauges, gauge pins or bore gauges on the hole.

Tom

[pepi]

Tom,
I understand what you say, the next time I play with this concept I'm going to verify. Have telescope gauges, just arrived. That's a motivator on its own. I did read the round bar after machining, it was + .0005 .(caliper)

Being new to machining for personal projects, was unaware of the known inaccuracy of the caliper.

Thanks for the advise.
Next comes knowing climb and conventional milling, like standing and walking. In other words, not thinking just applying and using at will.

:-)

Pep

[Dr Stan]

(11-14-2018, 08:30 AM)pepi Wrote: Tom,
I understand what you say, the next time I play with this concept I'm going to verify. Have telescope gauges, just arrived. That's a motivator on its own. I did read the round bar after machining, it was + .0005 .(caliper)

Being new to machining for personal projects, was unaware of the known inaccuracy of the caliper.

Thanks for the advise.
Next comes knowing climb and conventional milling, like standing and walking. In other words, not thinking just applying and using at will.

:-)

Pep

Digitals are much better than vernier calipers, AKA verynear from the "Good Old Days", but as Tom said they require correct use, effectively making sure they are square with the work, the pressure applied is consistent, etc.  It would be a good idea to compare your caliper & micrometer readings to get an idea of their/your accuracy.

As for climb & conventional milling, imagine yourself above the center of the spindle looking down.  Is the cutting edge moving away from the work (conventional), or is it digging into the work (climbing).

Dial calipers were in some ways a step up from verniers, but were easily damaged from trash between the rack & the gear.  They could also skip a tooth & be .025" off.  One shop I worked in banned them for this reason alone.