I’m printing oversized pieces and then machining them to size. I’m using Bambulab ABS in an X1 with active chamber heating. I’m using the stock filament settings for the exception of 100c bed. The filament was properly dried before printing. I’m contour machining with a waterline strategy and the step down is .005”.
I’m getting some weird color variations which is not a big deal for my application and some stringing of the filament which is a big deal. I’m attaching a picture of an area that is pretty bad. The print itself is great before I machine it and most of it is fine. It does seem the angle of the surface plays a part in it.
Machine printing ABS is not the best option…
The material is rather soft AND gets sticky once it gets too hot.
With the right, water based, coolant running you should be able to avoid most of the issues in the pic.
Don’t expect perfect results though with tools meant to work metal…
Take look at the slicer preview for this model.
You will see that, even with vertical walls, the actual contact area of the outermost wall is not much at all.
With slightly higher nozzle temps you should getter adhesion between the wall layers and reducing the speed for outer wall a bit more will also help.
If you ask me though you should still add one more step before trying the machine a test print:
Print two small test models to machine with identical settings.
One you place into a jar with some acetone that does not get into direct contact with the model.
For a quick and dirty one you could also simply brush the acetone onto the model to leave it ‘wet’.
Once looking dull and dry repeat the process two or three times.
This with chemically fuse the ABS after softening it so don’t try to machine it like this!
Leave in a well ventilated area, preferable not too cold and wet for about 24 hours.
Do a scratch test with a sharp knife - if the treated model is as hard as the untreated AND you can no longer smell any acetone give it a try.
If you can afford leave bigger or more complex parts for at least two day before trying anything fancy.
After this treatment those lines should no longer separate and the result should look much cleaner.
Try a spray bottle with soapy water while machining and you might even get a shiny finish.
Hi
Thanks for the detailed response. The acetone chamber sounds like a good idea but won’t work in my workflow. I bumped the nozzle temp up to 280C and I’m printing the part again. This is a part that I’m using to try and dial in the process so I have zero issues trying different things. Although it does take almost two spools to print all the parts I figure there is always a cost for knowledge:)
We have been giving the parts an acetone wipe and then red scotchbrite pad after it dries. Seems to be working quite well.
Probably not as sharp as it should be
Climb milling.
Mostly the results are fine I’m just trying to get a handle on what to expect with printing. Push comes to shove we can hit it with some paint. The acetone welds the strings back to the part without issue. The part has 9 walls with a .4 nozzle and a theoretical stock allowance of .04". The area in the picture is towards the lighter side as I’m still working out registration issues so I’m not sure how far into the allowance I am at that point.
If you cut plastic with too fast a cutter speed, the friction causes melting. Also, two flute maximum.
Speeds and feeds?
I machine ABS all the time, no problem. Same idea as you - print oversize and machine to tolerance. Though I’m generally must milling specific surfaces and not the perimeter of the print.
Step down 0.005 is also a lot shallower than I’d have gone. Typically, I do a stepdown that’s 1/4 to 1/3rd of the cutter diameter.
2 flute ball end .25" diameter. 5000 RPMs (max) 50 IPM. Any faster and I get enough overshoot to cause issues.
It’s making a great chip and I’m not smelling any heat so I don’t think the problem is in the machining specs.
.005" down is what I use on type1 PVC and I find that gives me an end product that requires very little hand work. These are one off items and 10-15 hours of finish run time is the norm.
Related question for you all. how are you creating your printed model with machine allowance? I do a lot of modeling but the majority of the stuff I do the model is supplied and shelling and offsetting doesn’t always work. Especially if there is a lot of fillets. Right now I have settled into using CAM to virtually machine a simulation model with .040" stock on it. I can then output that simulation as a STL. It works but is kind of clunky. Didn’t know if there was anything in the slicer other than scale that would do anything for me.
I bumped the print temp up to 280c and the results were better for sure. I feel that Polymaker ABS machines better than the Bambulab ABS. That coupled with the fact that I had my first failed print due to tunneling with the refill I’m probably going to use the Polymaker. I like the price and the concept of the refills but they are really loosely wound and I’m surprised I didn’t have a problem sooner.
Anneal the ABS part before machining. This will cause some shrinking, but you’re printing oversize. ABS has one of the largest shrinkage rates of all materials. Machining a non-annealed part can cause the stresses built up to be released causing cracking.
Good luck
