Newbie here, just have a few questions that I’ve been wondering about.
Background: Shapeoko 3 with Makita router (usually just left at ‘3’ on the speed dial) and Sweepy 2.0 connected to a shop vac/cyclone system. MDF wasteboard, using double-sided tape to secure workpieces.
I’m primarily needing to make profile/through cuts of small shapes (anywhere from 1/4" to 3" across) out of 1/8" thick sheets of various hardwoods (maple, wenge, padauk, bubinga, etc.)
Currently, I’m using up cut spiral bits (1/4" shank, 2-flute, flat nose, 1/8" flute diameter, 1/2" flute length), and generally just select the #326 endmill option in Carbide Create, which seems to work OK.
Question 1) Would I be better served by a different type/style of bit for the types of cuts I’m making? If so, what would you recommend?
Question 2) From what I’ve read, a down cut bit might be a superior option for my use case; if so, (assuming the flute diameter/flute length/number of flutes remains the same), would I need to change any of the feeds/speeds just by virtue of it being down cut vs the equivalent up cut bit?
Question 3) What is the advantage of using a 1/4" shank bit, vs. investing in a smaller collet and using 1/8" shank bits (both with 1/8" flute diameter)? I guess the 1/4" shank bits have a bit more rigidity/strength, but as I don’t need to cut material more than 1/8" thick, I’m wondering if I could save money by just using 1/8" shank bits if they will provide enough strength for the types of woods I’m cutting.
I have used both the Elaire Corp and Carbide 3D precision 1/8" collets that @WillAdams mentioned, they are both great high precision (minimal runout) collets.
The 1/8"-size collet will allow you to use smaller cutter diameters, sizes that wouldn’t be available in 1/4" shank, I almost exclusively cut thin stock (less than 1/8" thick) and the smaller bits/endmills will only come in a 1/8" shank. I use 1/16" tip regularly, and have 1/32" down to micro sizes, they all come in 1/8" size only. I use Onsrud Super-O downcut in wood (a single flute bit), though they also make a good 0-helix (straight) single flute as well. The Super-O is good for wood, plastics, and aluminum so you wouldn’t necessarily need a different bit to do different materials…
About 1): downcuts are great to get a clean finish on the top edges, but then you may end up with sub-optimal finish on the bottom edges (the opposite of when using upcut endmills). I see you are cutting 1/8" thick material, you may have some luck using 1/8" compression bits at full depth (they have both an upcut section at the tip and a downcut section a bit higher up the flute, which can result in perfect finish on both the top and bottom edges. They did wonders for me to cut thin (and cheap/low quality) plywood, illustration here.
About 2): The feedrate can stay the same, as it relates mainly to the number of flutes (and indirectly to endmill diameter). However downcut have poorer chip evacuation, since they tend to push chips downwards, so when e.g. slotting they can end up getting packed at the bottom of the cut. I like to use a smaller depth per pass (than I would use for an upcut) when I use downcut endmills for that reason.
About 3): in addition to Will’s and Stephen’s answers I’ll add that for me shank diameter mostly helps to reduce tool deflection. But for cutting through 1/8" of wood, and assuming you minimize stickout and are not looking to optimizing your cutting time, a 1/8" shank will do just fine. I have a large variety of 1/8" endmills, fancy ones from Amana from the C3D store as well as cheap ones bought in 10-packs on eBay, and they all have their purpose (I will use the cheap ones for aggressive roughing or when trying out a new project the first time, since I won’t lose any sleep over breaking one or two, and then I’ll keep the Amana ones for when the prototype is OK and I want to proceed with the final cut)