steamingbill
9th Aug 2018, 08:12 PM
Cobbled together this thing today. Very simple.
The more I think about what it does and the results produced the more I think that this gadget is useless.
Any advice - hints - recommended websites ? ............. gratefully received.
See photos - Dial Gauge Indicator mounted on long piece of Pactene with a weight at one end to standardize the pressure on the base of the pactene.
As you move it around the granite plate you can detect variations in the surface height. Holding it at the end furthest from the gauge and the weight and just pushing horizontally minimises effect of hand pressure on the measurements - which were significant prior to putting the weight in place. Taking your hand away completely removes hand pressure and ensures all measurements taken under identical conditions.
According to the data I gathered the centre of the granite plate is all within 0.03mm of itself and there is a 0.05mm dropoff all around the edge of the plate. See attached spreadsheet.
But what is it actually measuring ? The three highest points under the plastic will define a plane and assuming the base of the plastic has been cut perfectly flat, the base of the plastic will sit on that plane and the dial gauge will measure the difference between the local spot and the base of the plastic.
I wanted to see if I could estimate how flat the granite plate is - but after thinking about it I don't think what I've done is valid.
Any comments from brains trust gratefully received.
I suppose I could mount the plate on the mill table and hang a DTI off the end of the quill and move the table around under the DTI - will have a bash at that tomorrow - but that will then include any errors associated with the mill table not being perfect,I know it slopes slightly.
Bill
The more I think about what it does and the results produced the more I think that this gadget is useless.
Any advice - hints - recommended websites ? ............. gratefully received.
See photos - Dial Gauge Indicator mounted on long piece of Pactene with a weight at one end to standardize the pressure on the base of the pactene.
As you move it around the granite plate you can detect variations in the surface height. Holding it at the end furthest from the gauge and the weight and just pushing horizontally minimises effect of hand pressure on the measurements - which were significant prior to putting the weight in place. Taking your hand away completely removes hand pressure and ensures all measurements taken under identical conditions.
According to the data I gathered the centre of the granite plate is all within 0.03mm of itself and there is a 0.05mm dropoff all around the edge of the plate. See attached spreadsheet.
But what is it actually measuring ? The three highest points under the plastic will define a plane and assuming the base of the plastic has been cut perfectly flat, the base of the plastic will sit on that plane and the dial gauge will measure the difference between the local spot and the base of the plastic.
I wanted to see if I could estimate how flat the granite plate is - but after thinking about it I don't think what I've done is valid.
Any comments from brains trust gratefully received.
I suppose I could mount the plate on the mill table and hang a DTI off the end of the quill and move the table around under the DTI - will have a bash at that tomorrow - but that will then include any errors associated with the mill table not being perfect,I know it slopes slightly.
Bill