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Question on Water jet Tolerances

ross340

Plastic
Joined
Jul 10, 2017
I have a question about water jet tolerances. I just recently had a job cut and some interior holes I modeled were .030 oversize. (compared to my drawing) Which was extra shitty because it was supposed to be a bearing hole. Material was 1/4" carbon fiber. It was the first time this company has cut carbon fiber with the water jet before but it seemed to go really well, pierces looked great, no delamination or deformation. There was a fair amount of taper but didn't seem excessive. my question is, where did that .030 come from? is it because of the material? is there ever any excuse for a water jet to cut .030 off of what's shown on the file? was it a kerf offset issue? Trying to move forward, I'm just trying to figure out if I should just adjust my files to work with what comes off of his machine or should I try and pin him down about either making a mistake with the kerf offset or creating a new offset for the material? I suspect he cut "on-line" and that's where the extra .030 came from. But how do I bring that up without telling him how to do his job?
 
It sure could be a programming issue. 0.030" is a popular focusing tube ID so it could be an incorrect compensation G41 vs. G42 issue, Or maybe lack of compensation at all. It could also be the wrong focusing tube was used vs. what the programmer set the compensation too. Perhaps the focusing tube was extremely worn, I've seen them wear in an unusual oblong way if the orifice gets partially blown or cracked. It's hard telling.

The better question is why didn't the operator know to inspect the hole sizes if they are critical. Was it specified on the drawing? If I get a tight tolerance job I always put in a new orifice and focusing tube. However, a bearing fit would seem to be outside the typical capabilities of a waterjet. I feel comfortable with a +/- 0.005" diameter tolerance on hole diameters over 1 material thickness. Not taking into account that taper is present as material thicknesses climb.
 








 
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