I believe my machine or software is causing a dimensional problem and looking for suggestions to troubleshoot - Help Please I created a dust shoe in Vcarve. The top and bottom will be cut from plexiglass and the center body is 3d printed. I took the dxf of the center body from Vcarve into Fusion 360 and modified it into a stl file. The top and bottom that is the exact same dimensions as the center body was cut into the plexi glass. When taking the top and bottom parts cut from plexi glass and placing them onto the 3d printed center body the plexi glass is larger longer in the Y axis than the 3d printed part. I measured the printed part in the Y and it is 326mm and the plexi glass is 328mm. If I measure the 3d printed body in Simplfy3d it matches the 326mm. This leads me to believe that perhaps the Y axis is running long for some reason and I am not sure how best to correct it - is it a software issue or mechanical issue? I am running Open Builds Black Box using the Open Builds Control to operate the MPCNC. When I first put it all together it was dead accurate in X and Y. I just checked the Y axis by doing 100mm marks and it's spot on.
Peter - I did complete the calibration upon set up (prior to any cutting with the machine) -- I then after these plexi glass cuts did Y movements at 100mm increments and they are spot on. This is why I am perplexed. This is the pen test I did as you can see - well to my best vision it appears to be spot on in all axis.
My first guess is that there are some deflections that are taking place for the forces while the routing is taking place. This machine (even though 3d printed) should be able to make these cuts once you find the sweet spot of speed vs force A suggestion would be do shallower depth-of-cuts for each pass and take your time.
the tool is rotating and pushing on the material. picture it moving in Y + direction. the front of the tool is moving right, thus pushing the tool left. it will do this all the way around your part, thus making the part larger than designed. if you go the other way around, known as climb cutting, the part will be too small. even multimillion dollar machines do this. this is why roughing and finishing passes were invented. roughing gets close with fast, heavy cuts (relative to the machine, you are not going to be cutting 2 inches deep in one pass with an MPCNC). then the finishing pass, which is very light, will finish to size. a finishing pass may take hours on a 3D part.
I am using Vcarve to design and then generate the tool paths. The cuts made were in 1/8" plexi using a very cheap HQMaster 1/8" End Mill Single Edged Flute (Amazon). These cuts I did at full depth and at a feed rate of 30mm/sec. The first photo shows the cuts were spot on at the beginning but as it cut to the furthermost part of Y+ that is where the cut was too long. X axis appeared to be fine. I am in learning "Grasshopper" mode and turns out the dust shoe design didn't work so I ended up designing another that will work some what but its not ideal but similar to the first. The cuts were better this time but still not exact. The orientation was more cutting to the X+ vs. Y+. I also changed the depth of cut to 1.25mm for two passes and I dropped the feed rate back by 25% in Open Builds Control. Makita spindle speed setting was on a 3. My Z height was off a bit so I ran both passes a second time after bringing the Z down a couple of thou. I would like to understand what can I be doing to ensure the best possible cut.... I.e. what is missing from my workflow (roughing / finishing pass - set up in Vcarve?) I am trying to learn a bit on the MPCNC before I get my new machine which is an all aluminum, lead screw driven machine on linear rails. Thanks for the comments much appreciated for any information to help me learn.
Keep in mind the MPCNC is large factors less rigid than any OpenBuilds machine so: is too aggresive! Try 0.5mm DOC at around 1000mm/min
I want to try out my dust shoe and want to cut out some table clamps out of MDF. I am going to use a 1/4" upcut bit and I am wondering what would be a not too aggressive DOC and speed giving I am doing this on an MPCNC ?
I use 1/2 the diameter of the cutter for woods and plastic. However, my CNC is much more rigid than a MPCNC. There are many factors that will limit your feed and speed. If your MPCNC is small, it is stiffer and can cut more aggressively. If it is large, then it will flex more. Also, your z-height will affect the flexing in the system as well. Basically, no two MPCNCs are alike which is why it is hard to find a good feed and speed table. You may have better luck searching the MPCNC forum. There may be someone with a similar build to yours that has it dialed in. I did a quick google search, but was unsuccessful, because even the designer could not say due to all the variation in builds. He did speak of this: Milling Basics | V1 Engineering
Thanks - I followed Meyers Woodshop using the spoilboard files for the Shapeoko XXL and then dialed back from what he used (20in/min) and I was able to cut my fence out and believe it or not it's square. Though I am ready for my new machine to arrive... two more weeks and hopefully I'll have it.
