I have one of the original 48x32 machines (journeyman woodworker?) and never had any issue with this before that I know of but my last project did not cut to specs.
I created a file in Vectric with 5mm x 15mm oval holes in a grid patterned array. The spacing between the holes is accurate and the overall dimensions were cut correctly. Seems to only affect the size of the holes.
I tried changed from pocket to profile and both cut the same. I ended up doing a pocket with a 0.2mm offset and it came out perfectly to 5mm x 15mm.
Could it be bit deflection from the thin bit? Since you’re cutting several holes, I assume you’re trying to max out feed rate. Try carving a few holes at your current feed rate, and another set of holes at a much lower feed rate to see if the hole diameters are different.
Haven’t thought if that. I’ll verify, but I’m running it at the default whiteside rates. Not sure if that is considered fast or not. I’ve not gotten that deep into 3D carving. Thanks for the advice.
Hi Rob - I have certainly noticed variation in accuracy when using faster speeds. With any luck I plan on doing a video about that in the coming weeks, but we have a lot of craft fairs coming up so not sure if I will have the time do do the experimentation. In the mean time I just slowed down the feed rate and all seems repeatable and accurate. If I need perfect accuracy, 60ipm with a 40ipm finishing pass; if I want to live on the edge, 80ipm with no finishing pass or finish at 80. If I don’t care so much, 120ipm no finishing pass. All for a 1/4” end mill and 0.1” DOC – would push to 0.25” DOC if my spindle could handle it (which it cannot).
Thank for that info. I’m still pretty new to CNC cutting.
In theory, if it was an issue with deflection, repeating the toolpath would eventually equate to accurate cuts, right? As the amount of material being removed would be reduced on any additional passes resulting in less deflection.
I am going to remake this project once I get a new bit. I’ll try the rates you have provided. Not sure if this matters, but I used the spiral cut feature in the pocket toolpath, I have it set to two passes for 4.7mm material resulting in a 2.35mm DOC.
What speed should my spindle (Mikita router) be running? As I noted before, this project has burnt up a brand new bit after only cutting about half of the holes.
Hi Rob - your DOC seems good to me (~0.096”). I usually ran my Makita at 2-3 all the time. Anything over 4 and it would vibrate my workpiece off the machine!
Generally, “burning up the bit” as you say probably means it’s going too fast (RPM) relative to the feed rate. I’ve found 16K RPM great for Cherry and 18K for Hard Maple; walnut doesn’t seem to care too much .
Now that I have a VFD, I do play around with the RPM to dial it in based on the sound the machine is making. Any high pitched squealing means the RPM is off relative to the feed rate. It’s far easier to change RPM than feed rate mid cut.
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