New to machining and having second op issues

Hi Guys,

I'm wondering if anyone would be able to help me or explain what i could possibly be doing wrong??

First of ( if you havent already guessed) I'm very new to machining. I literarily used CAD/CAM (Fusion 360)and a CNC machine for the first time only 12 weeks ago!. I decided to take the crazy jump without ever touching a machine and buy a new Haas VF4SS and just throw myself in the deep end. Ive seemed to pick up the software side no bother and im pretty familiar with the machine now also but on the second op I seem to be about .2mm out or offset on every cut. It seems consistent with the opposite side so if one side is out by .2,then the other seems to be in by .2 if that makes sense? Im not sure if its a stock offset issue on fusion360 I'm doing or if its a workholding issue.

Here is a typical workflow that I'm doing.

I tram in my vise on the machine. I have machined parallels in the vise to sit my stock onto and I have put a stop on one side of the vise. I then put a 123 block hard up to the stop on the vice and use the Wips (renishaw) touch probe to set my G54 XY right in the corner. Then i put the stock in the vise and set my Z to the top. At this point I also touch off all the tools ill be using to make sure all the offsets are correct.

On my CAM I begin the first op with the datum showing the top corner of my stock which relates to the XY position on the machine. I then run the program without any issue. When I flip the part i change the datum on the part to be on the model this time. Normally a similar edge to tie in with the XY on the machine, and I retouch of Z. When I flip the part however I dont really alter the stock much on cam from the first op. Should I be setting the stock offset to zero stock as the sides have now been machined??

I know a lot of guys seem to machine/ Ream holes and use the probe but surely the method I'm trying should work also? I know I must be doing something retarded so any suggestions would be greatly appreciated.

Kind regards

James

When I define the job for my second op, I reverse the z offset so the stock/model relationship is the actual result after the first op. Ex.
Op1 I set the model Z .02" below the stock top. The bottom of the model may have say .5" if stock. I duplicate the job for the second op, then just flip the Z orientation and use the model geometry for the G54 pos.

Another thing I do is set my z0 to the top of the parallel (bottom corner of stock) on op1. So when I flip the part, the z datum is already set for op2. For touching off x with overhanging stock, I use 123 block etc. I touch off y in the non moving vise jaw After I tighten the vise handle. My Kurt fixed jaw can move almost .002" depending how tight I crank it down.

ukkie said:

Should I be setting the stock offset to zero stock as the sides have now been machined??

Click to expand...

How much stock do you show on your second op model? .2mm???

I too use Fusion and never use a stock offset, I do that with my fixture offset and stop, which is a pin in a tool holder for lower volume parts.

Wsurfer said:

When I define the job for my second op, I reverse the z offset so the stock/model relationship is the actual result after the first op. Ex.
Op1 I set the model Z .02" below the stock top. The bottom of the model may have say .5" if stock. I duplicate the job for the second op, then just flip the Z orientation and use the model geometry for the G54 pos.

Another thing I do is set my z0 to the top of the parallel (bottom corner of stock) on op1. So when I flip the part, the z datum is already set for op2. For touching off x with overhanging stock, I use 123 block etc. I touch off y in the non moving vise jaw After I tighten the vise handle. My Kurt fixed jaw can move almost .002" depending how tight I crank it down.

Click to expand...

OK I'm not sure im fully following? so do you change the stock to replicate the newly cut size for the second op?

Ive just done another test piece today and I just put in the fixed sizes of the stock and then centred the part within the stock. I did the first op without any issues but the second op was off by .2mm in the Y evenly ( so it cut in by .2mm on one side and overhangs by .2mm on the other) and the X was out by .1mm evenly. To me with my very limited knowledge in this field that it looks like an offset issue. If it was vise tension or some sort of workholding, would it create such an even deviation?

Im wondering if I should set my offsets to zero in the X and Y for the second op as this will be the hard faces that will be against my hard jaws on the vise?

OK so would you recommend not using any offset on the XY for the second op?

In your case where the stock is centered, you dont need to change anything for setting up the second op z(top of parallel). As far a Y offset. I set it on the vise fixed jaw. These references that never moves. For example, I machine op1 .01 below the bottom of the model if possible. All subsequent dataums for the following operations are done. When the part is flipped over, my model point is the finished surface from op1.

Lets say you have a simple 2d part. I touch off z on the top of the parallel and y on the fixed jaw. The only reference I need to touch on op2 is x. Using the model point in op2 has the finished machined surfaces on y and z (already set in op1 as stock box point)