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How does one...Rough? (self.machinist)

submitted 10 months ago by curiousPJ to c/[email protected]

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Running into a dilemma...

I have no trouble ending up with an accurate finished part with really tricky features.

BUT...BUT I can't figure how to quickly develop a roughing strategy. I'm always doing short run items so I don't have many opportunities to be hogging out material repeatedly. So, when I get a 1pc job that needs a lot of material removed, I'm very slow.

To a point, where I'm getting micromanaged.... on roughing.

I'm inclined to be safe and prioritize process stability over Material removal rate. For example in HEM, Instead of doing 10% stepovers, i'll do 6%. In turning, I'll keep DOC down on the bottom left end of recommended specs instead of burying past the insert radius. I don't get off on huge MRR like others, my moment of glory is hitting incredible tolerances on a difficult design/material.

What really scares me is... that a mistake in roughing parameters comes with bigger risk than just "tighten the bolt until it loosens up and quarter turn back". It's the part becoming a projectile/scrap, machine damage, and at worst an injury. Lathe work where I have only a fraction to hold onto and inches of material to remove....

How have you developed a 'sense' for how aggressively you can rough?

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[–] [email protected] 5 points 10 months ago* (last edited 10 months ago) (1 children)

I've been working as a prototype machinist for a few years so similar situation.

You just gotta try. If the tool says it can do it and the machine has enough power just work up to a good DOC. Trust the DRO and have at it. I've almost never had anything go flying out of a vise or chuck, but use good judgement.

I've made .1" doc in 17-4PH H900 and titanium on the lathe holding onto 1/4" of material. Never had a part go flying. Ive thrown parts in the mill but never caused machine damage, just broken endmills and scrapped parts.

On super expensive material or parts I'm slow but I can still hit .0001" tolerances with big roughing cuts.

[–] curiousPJ 3 points 10 months ago* (last edited 10 months ago) (1 children)

good judgement

What I find difficult to deal with is determining where the threshold is with work fixturing and clamping pressure without going past the limits. I feel like it's entirely based on job experience rather than theory like SFM or chipload.

I could just incrementally take deeper and deeper cuts but the stopping point for me is the fear of tossing the work. Who knows if I left another .060" of potential DOC because I was afraid. I suppose there is an accepted range of 'general' roughing parameters that conventional workholding like the .060" step on self-centering vises or a manual 3 jaw vice holding on to a thin section can handle... Although if I'm really cranking on the handles, the tool is more likely to break first than the part flying out.

There's just something that is unsettling with me when the answer seems to be...Just rough more stuff and you'll get better at it. Not arguing against it but it's because I'm one of those theory 1st guys.

[–] [email protected] 3 points 10 months ago

Yeah it's tough. There's no good rule of thumb you'll just have to push it till it fails sometimes. Careful is always better but it's also slow. Just remember a vice tightened normally is several thousand pounds of clamping force.