I am attempting to use my CNC in place of a jointer for a project, and am looking for some help understanding the logic behind where to place the contour cut toolpath. I ran a test and it didn’t go exactly how I expected, so I am hoping someone here can explain the logic of where I went wrong.
Test:
I first used a pocketing toolpath to cut out the letters SH with the correct spacing. No issues here.
Next I drew a line halfway in between the two letters so my joined area would be evenly spaced between the letters.
Using a second piece of material, I pocketed the S and used a contour cut (offset outside/right) for the line.
I re-zeroed the offcut from step 3 to pocket the H.
I clamped the material from steps 3 and 4 together and compared the distance between the pocketed letters to the distance between the pocketed letters in the material from step 1.
Results:
The letters from the clamped pieces were about 0.1" further apart than the letters in the solid piece. I did a chamfer on one of the letters, so measuring was a little difficult and maybe they were actually a full 1/8" further apart.
I assume I can fix the issue by just cutting the jointer line using no offset on the contour toolpath rather than using the outside offset, but I am hoping someone can help me understand the logic because I can’t wrap my head around why the distances don’t match up. Please explain it like I am 5 Pocket Contour Test.c2d (292 KB)
Agree with Will. If you do not have a fixed reference jig or a Bitsetter you will struggle to align projects an get exact measurements on digital calipers when re-zeroing as you described.
@WillAdams@Redlander thanks for your replies. I do have a fixed reference jig and also have a bitsetter. Re-reading my post, I can see where I misspoke and caused some confusion. I didn’t re-zero my machine on step 4, I just took the offcut and moved into the zero position against my reference jig. I can of course machine off the extra material, but was hoping to gain a better understanding of the programming so I can correctly cut these dims on the first try next time. I guess I am back to the guess-and-check method for now.
The space on the left and right side of the letters is different.
The space on the left-hand side of the H should be the same
as the right side of the S. So, when you moved your cut off over
to cut the H, it moved the distance of the left-hand side of the S.
I think that is the problem.
Jim
I don’t think so. The distance between the S&H where he’s measuring is 0.895"
The distance to the right of the S is 0.446, and to the left of the H is 0.449, a total of 0.895"
One curious thing is the difference in the measurements, 1.0205 - 0.892 = 0.1285
Pretty close to 1/8" ?? Did you measure the individual distances? They don’t look the same in the picture.
Hard to tell with certainty from the photos, but it looks like the letters when cut in mdf were scaled larger than when cut in the other material. Maybe the entire cut (not just the distance between letters) was scaled up unintentionally in the mdf.
I didn’t catch the .003 difference. I used .449 for both sides.
I did notice the number being close to .125
I thought there may be a rounding error or measurement a tad
off. I’m going to take another look.
Jim
@Tod1d you are correct, the individual distances are not the same (larger on the H piece). I also noticed that the discrepancy was about 0.125", or the radius of my endmill, so I was wondering if there was some programming logic that I messed up.
I recut the test file and cut the straight line contour on both pieces so they were cut relative to the letter placement rather than relying on the zero set-point. I still got the same problem of extra material but it was closer to 1/16", so I used Will’s suggestion and just machined off the excess.
Your math was correct in the design, within a couple thou.
My first thought was wrong tool… if you’d used a 1/8" to cut the 1/4" path it would add stock.
But then the left side would be full, rather than the right.
If your X zero was a bit to the right of the fixture, both left sides of each piece would be full??
