What bit would you recommend for 1 to 1 1/2 inch hardwoods for small pieces?

[carolinasmith]

I just got my D-MAX running and I'm new to CNC. I had been wanting to try cutting small pieces for segmented woodworking, thinking the CNC would be way more precise than I could be with my miter or table saw. I was right!

I was thrilled when I did test cuts on scrap plywood. I did 2 inch side rhomboids that I made in Aspire (shaped like diamonds) so when you put 3 together, it looks like a hexagon with the "Mercedes" symbol). They fit together like a glove.

I will be using hardwoods (maple,walnut,cherry, purpleheart) and want to make a cutting board, so want 1 inch thick rhomboids. I had used the 1/4" Super O bit that came in a Desktop pack (7bits). Seems like a lot of wastage for small pieces. I have a 1/8" collet, so maybe I should look for a 2 inch long 1/8" bit?? What if I wanted to cut 1.5 inch or even 2 inch deep rhomboids?

What kind of bit will give the cleanest cuts (upcut, downcut,?) and any other thing to go for (flutes, I don't understand all the ramifications yet). I will be cutting on the outside of the rhomboids.

Thanks for any opinions.

[steve_g]

Carolina…

Here’s a document I edited back in 2012… it’s getting a bit dated now but still has some valuable information about router bits…

https://drive.google.com/file/d/0B8GtiBWUjRyRY01lYmNrWW5CVUU/view?usp=sharing

1/8” bits are not a good choice for deep cuts… my suggestion would be to not use them in material over ½” thick. For best cuts, generally I use an “onion skin” cutting strategy. This method cuts just off the cutting line (.01” to .02”) in a climbing direction. The climb cut has less tendency to chip out. Follow that cut with a conventional cut on the line. The conventional cut is the smoothest cut in your arsenal. Your first cut (off the line) is stepped down in whatever depth is appropriate for your bit, while the final cut on the line is done in one pass. This means your bit will have to have a cutting length the full depth of your material.

The article above will discuss up cut vs down cut and many other topics… feel free to ask for more clarification after reading the document!

SG

[carolinasmith]

Thank you for the info. I chose to cut outside the line, thinking it would give the full measurement (a rhomboid two inches each side). I am thinking if I cut ON the line, the dimensions would be shorted by the radius of the bit, as in a 1/4" bit on the line means the mid point of the bit is on the line, means 1/8" is shaved off. Is this incorrect thinking?

I don't yet know how to set up sequential cuts for the same piece for onion skinning. But for small pieces surrounded by waste, I'm guessing the onion skin technique would involve not cutting through the whole board (I don't want to use tabs for segmented pieces), because if it did, what is to hold the freed piece from jumping around when the final conventional cut is done?

[steve_g]

Carolina…
You are correct, I chose a confusing word to describe my intent. Rather than saying “on the line” perhaps I should have said “all the way up to the line”. At any rate, this illustration should make my intent clear!

Your second point regarding hold down issues is the classic CNC operator’s conundrum… traditionally, this small part would need to be cut leaving tabs in place and removing them with a secondary operation. Other choices would be cam clamps, screws, tape and vacuum hold down. None of these options are viable for this part. My personal choice, if I actually chose to make these parts on a CNC Router, would be to cut them from a board that is thicker than necessary, not cut the part all the way through and then run the parts through a bandsaw set for the correct thickness. This is the method I use when cutting small earrings…

SG

[tlempicke]

If you are using one of the latest versions of Aspire you can do this really easily.

Open the toolpath tab for PROFILE
Fourth window down the screen is LAST PASS
Check the box for "Do separate last pass"
Put in your machining allowance (.01 or so)
Check the box for reverse direction if you want to use that technique

[Burkhardt]

I don't yet know how to set up sequential cuts for the same piece for onion skinning. But for small pieces surrounded by waste, I'm guessing the onion skin technique would involve not cutting through the whole board (I don't want to use tabs for segmented pieces), because if it did, what is to hold the freed piece from jumping around when the final conventional cut is done?

I prefer doing such cuts (if the individual pieces are at least 2 square inches or so) on a disposable vac pod. Then you can clean cut right through, no tab or onion skin removal:
https://lh6.googleusercontent.com/-xA8pe3XKLfc/VtJKkocscnI/AAAAAAAAGJc/5_2a9FMWXUA/w1024-h630-no/1-DSC00320.JPG

[carolinasmith]

Thanks for all the tips, and the 2012 article was great.