Estimating engineering time on machine design

I'd just like to compare notes with a few machine designers about how they figure time on machine design tasks. I personally find that about
1 1/4 hours per fabricated part is minimum to estimate for design (3D) and detailing (2D), and that's really a very conservative minimum. 1 3/4 hours to 2 hours is probably more realistic unless the task is very straightforward. Then one has to figure in time for changes and time to do assembly drawings. It's certainly not nearly as simple as that, and there are a lot of variables that can drive an estimate drastically one way or another, but that's where I begin. How about you? I'm just looking for general approach "rules of thumb" as contrast to how I start off.
Thanks for any feedback
Mark 'Sporky' Stapleton Watermark Design, LLC www.h2omarkdesign.com
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Best way is to base section cost upon similar past project sections, keep good records.
For building machines by outside vendors I figure the list parts cost +10% contingency, off the shelf and custom estimated, times 3, where x part 2 is engineering and assembly cost and x part 3 is profit margin. Add more for true developmental work and out of the normal extra's required. Build in house typically parts +10% x 2-2.5 depending on how knowledgeable workforce is.

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Although in-house may be cheaper it often can take longer and require some non resident expertise be brought in.

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