Clean Edges

[Ben Brummett]

what is the best way to get a clean edge on MDF (not Big Box Grade)
I am cutting letters mostly and getting a edge that has cut lines on them.
Have a Apire 8 software and a shopbot Alpha with Spindle and Vortex Compression Bit (.25 #3112) Cutting at 12000 RPM and 150 IPM feed rate.
Material is Plum Creek MDF .63 thick and I get 2 lines on the edge when I cut at .25 in per pass.
Sanding is taking as long as the cutting takes, any help would be appreciated.

Ben Brummett

[ohiolyons]

a photo would help.

the lines are on the letters correct? I have never seen lines on lettering before.

Profile lines on the edges on the outside edge could be handled by last pass option in a profile cut.

[Leo]

You can cut down to an onion skin, leaving .005 or so on the periphery then go back over the cut and remove the .005 at full depth. Maybe switch over to a finishing end mill

[Mobius]

Try a cleanup pass as was mentioned. Lines like you are describing can be caused by a few things. Bit deflection, spindle/gantry deflection, spindle being out of tram (not square to the table/material), material pulling up off of the table while being cut, etc.

I also find that I always get lines when I cut material with a compression spiral, unless I'm doing a full depth cut. I can cut the exact same file/material with an identically sized up or down cut 2 flute spiral and not get lines, but they always show up with the compression spiral.

[esteeme1]

Agree with all said. Something that may help is to use the offset option with the profile toolpath. Use a negative offset to cut inside the initial cut, and just enough to remove your deflection issues. Make sure to change the number of passes to one so you cut it out in one pass. If your profile size is critical run your cut with a positive offset and then zero offset for the last pass. You can set up your pass depths so your not repeating unnecessary cuts. i.e if your bit cut depth is set at .25 for the bit you are using you can set your cut depth there and then run your final pass with the selected offset.

[Adrian]

Why are you doing two passes in the first place? A ShopBot Alpha can easily cut through MDF that thick in one pass with a 0.25 bit. Use a lead-in so you're not getting the compression bit pulling in the wrong direction. Personally I would just use a downcut bit instead as compression bits aren't cheap and MDF wears them quickly. With a decent condition spoilboard you won't to do need much if any sanding on the bottom.

[bravesoul]

I mostly cut hardwood (Hickory, Oak, Maple, etc) and always use "Machine Vectors" using "Climb" then use "Last Pass" Allowance .02" and check "Reverse Direction" and it always gives me a very clean cut.

Joe

[Ben Brummett]

Thanks Guys for the help, I am starting today to see how your suggestions work out. Again thanks for the help..