Workholding Help

#1
Hey everyone, new to the forum and so glad I found it. I have been a reseller for a while now, but am starting to design and sell my own brand of knives. As background, I have my knife designs already done and its pretty sweet to see them carved on the CNC machine, I do all my design in Fusion 360 and so far all my knives are fixed blade knives. I have been using a simple Softjaw for the flip side but unfortunately I am running into serious chatter when I am carving the the longer knives because it isn't fully supported on backside and the machine is leaving serious gouges in my blades, which are clearly visible in the attached picture of two knives i ran yesterday.

I'm curious to learn how you all do your knife workholding/pallets to make sure your blades are fully supported while using an 3D Adaptive Tool path?? I cant figure out how to hold them down to carve the second side and still use a 3D adaptive toolpath to hog all the metal out around the top and sides and start the contour on the blade. I might need to change my Tool Paths but would love to hear your feedback on this subject.


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#2
I do my through holes first and then the profile as a second op using a fixture(locating off the through holes). I grind after heat treat but I HAVE done what you are attempting. Build a second and third op fixture (you can use one for both if you design it mirror) Put a boss with a hole in it on you blade design...on the spine side right near the tip of the blade. Then bolt through it to your fixture when surfacing (not carving) the blade surface with the ball mill. The blade cannot be cantilevered like you are trying...you will be amazed at how much quieter tying the end down is...and how much longer your end mills last...that much over-hang is beating them to death...lol. Probably not helping with material stress either.

After all said and done you simply grind off the crescent you had on there...either before or after HT. I leave mine on so I can HT multiple blades and put a bolt through it during HT...I use air-hardening (A2) so bolting them makes for less warpage...use a LOT of air to cool.

Also...it looks as if your (or your machinist...) post is set to output curves as line segments...unless you wanted it that way.(bottom side of handle) There will be a setting in your CAM program in the post processer that creates the code for you machine...usually you can change betwee arc and line segments...if it is a bit different than you drew it that will be the problem....

Hope this helps
 
#3
Thanks Ted, You are absolutely correct, this was one of my first designs and i used a splice rather than a curve, Im hoping i could make it work to get the look i am going for, rather than going back and completely redesigning the knife. I have put the small loop on the spine to hold it down and working to design the fixture now. How do you keep your tool paths away from that loop on the spline when you are carving? do you design it as a separate body or do you put something in the design that allows the tool path to be guided around the bolt that will be used to hold down the knife?
 
#4
Locate off of the through holes and bolt the piece down. Thats what i do, not saying that it is the best way but it works very well as long as the studs are not drastically undersized, i go no more than .004" undersized.
 
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