[dalianharley]

Ok this is a follow up from my previous post. I cut a part from a stock but didn't come out to the right thickness. That brought me to my next question, how to properly bring the stock to designed size?

Here is my process

1. designed a part in solidworks, let's say it's 0.2" thick

2. using a 0.5" thick stock bar to cut the piece

3. in Cam, i defined the stock to be 0.1" on top and 0.2 on bottom.

4. the stock is actually 0.496" thick

now, i don't really know how to proceed. should I mill 0.1" from both side of the stock, measure the exact stock thickness, and re-enter it in CAM, re-generate the toolpath, and cut the part?

Or should I define the stock to be 0.4" thick, then mill 0.05" from one side, measure the remaining thickness, say it's X" thick, and face the other side with calculated thickness as X" - 0.4" to bring the stock to exact 0.4" as defined.

i'm leaning more towards the latter as I don't have to re-define the stock in CAM and re-do the toolpath. pls advice...

Daz

[SCzEngrgGroup]

There is no single right answer. It depends on the part, the machining sequence, the CAM capabilities, how you're fixturing the piece, and a whole lot just on personal preference.

Regards,
Ray L.

[Hirudin]

What I like to do is...
* Find approximate stock thickness - 0.5".
* Take a minimum off the top during the first set of operations. Take, say, 0.050 off.
* Flip the part, and set my zero point based on the machined side of the stock. I'll bring my zero-setting tool (a Haimer Taster usually) down onto my soft jaws or parallels and use that reference point as my "0".

Sometimes, after setting the part offset to the parallel I'll then raise the machine up to the desired thickness and re-set Z to 0. So, for your example I would then move to Z 0.200 and reset the part offset. Obviously, the zero-point has to be set up correctly in your CAM software.

[jm82792]

(I did forget most don't use 3d cam programs, so if you have a 3d cam program, a gcode file, and don't want to remake it read on)
Okay this one can be easy if you ignore some factors or just know they already exist such as if your stock is flat, and etc.
The CAM program thinks it's .5" and it's .004" less.
You're taking a bit less of than you'd normally do, and therefore the top of the stock is not "proper" for homing/touching off.
So you touch off or offset from the bottom of the stock by .5", and then you get the proper Z home/stock surface.
Then your first pass is .004" shy of it's usual DOC, and you'll get the part you want without fidgeting with your GCode.
Now you can do this with thicker stock, and so forth. But obviously your tool engagement will vary(adjust feed and speeds for first pass if needed), and therefore if you do enough parts then you might want it to be properly done instead of a quick hack for a test.
I work almost always with wood so I can get away with a lot, but it should be applicable in your situation.

[Hirudin]

That's a good idea! Do the first side as if it really was 0.5" thick and then the second side should come out correct.