Maybe this is just general knowledge that I don’t have yet (or did not up until this point), but tonight I noticed that both my 1/4" and 1/16" down cut endmills cut pockets about 2mm smaller than what they were designed to be. Is this normal for a down cut tool path?
What size pockets? Cut with what feeds and speeds?
Did you try taking a finishing pass at full depth?
Upload a .c2d file and photo showing how the cut turned and details of the measurement?
The pockets ranged in size as I was trying to size them to fit the bit boxes. Here is the file that was used with the tool paths still intact. I did move the objects around as I did a final pocket test with a 1/4" up cut bit (the 201) just to check that it make the correct sized pocket.
Bit Holder Test 2.c2d (176 KB)
This first shows the size of a pocket that was designed at 14.9mm. As you can see, it was cut to 12.9 with the #251 and a 1/16" down cut bit to square the corners up some.
This next one was a 14.7mm pocket, it cut to 12.72mm.
And this larger pocket was designed at 63.5 and cut to 61.5
Finally, this is a pic of the 1/4" up cut (#201) designed at 20mm, cut to 19.88 (that could be a measuring error)
All of the main down cut pockets were cut with the #251 using 2.5 mm stepover, 3mm depth per pass, 304.8 plunge, 1524 feed rate, and 18k RPM.
Corner cleaning was done with a 1/16" down cut using rest machining at 1.587 stepover, 1.27 dpp, 1143 plunge, 1651 feed rate, and 15k RPM.
No finishing or full depth passes were made.
Is it possible that whoever sold you the downcut bits sent you metric instead?
@mhotchin is alluding to is this question that you didn’t include data for in your message.
What are the actual measured diameters of the bits in question?
Try cutting a slot and measuring it?
I guess it is possible, but one of the bits (#251) came from Carbide 3D with my 5 Pro and starter bit set. The other came from a dealer on eBay. I will measure them and find out.
I’ll try this as well and report back.
Edit: The below tests were done on a completely new CC file.
This morning it is cutting the correct sized pockets and slots, so I don’t know what the deal was. Last night while I was having the issues I even rebooted (power cycled) the CNC and VFD. Strange.
Well, maybe it is the file I’m using to do my sizing tests. I tried running that file again with some changes to the layout and pocket sizes and again it cut the pockets too small. Interesting enough, the four ~44mm circle shapes cut at the correct size. It also failed to cut eight of the other smaller holes (3.14mm -6.5mm) even though CC shows that it will cut them with the 1/6" bit.
I recreated everything in a new file and it is all cutting correctly now. I can only assume that the file was corrupted some how and was messing up the size settings.
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