Need some suggestions please…
I have a 1.25” Freud mortising bit that works great for my spoil board but not so much with hardwood. I messed around with all kinds of feeds, speeds, depth of cut and step overs and finally came up with an acceptable setting. Wondering what others have found.
Settings that worked for me…
.015 depth of cut
25% step over
100 inches/min
Makita at about 3.5
Against the grain or I get burning
Thinking if I want to speed things up without leaving burn tracks I’m going to have to invest in a better surfacing bit so if people have suggestions it would be appreciated as well.
Thanks in advance.
I found the same issue, and happened to have a 3/4 inch Freud flat bottom mortising bit…it works very nicely and I have used it on red and white oak, walnut, cherry, and soft maple. Up to about 1/16 inch (.06xxx) DOC, plunge rate 40, 140 ipm, and Makita at 3.5.
Normally if you’re getting burning when cutting, the feed rate is too low. If you’re only running a 25% step over I’d suggest going to a smaller bit with a larger step over or increasing your feed rate to maintain a higher chip load.
When I’m surfacing, I don’t normally need to run as deep as that bit CAN go, the 1/16 was just the deepest I’ve ever run it when surfacing. I often run at 40% stepover if it is a surface that is going to be reversed and held against the spoilboard without any carving in it for speed’s sake. If it is the “good” side I use a smaller stepover to find a balance between speed and sanding time later.
Stepover only effects how much scalping is left over between each pass and will not effect the burning of the wood. With a surfacing bit this is the space between the middle of the bit between the blades. If you stepover is too large it will miss this spot as it goes back and forth. That is where the scalping happens. As Derek said burning happens when the feed rate is too low. You will need to increase this to get a better chip load. I run this bit 120ipm at .25doc. 30%stepover.
Having the proper doc and not shorting that out will keep more pressure on the cutting head and reduce scalping pressure. Too many people make this smaller than it should and it causes the bit to ride up over the wood rather than make a good cut and leaves marks.
The other thing you’re introducing to the “error factor” (tolerance stack up) when using a large bit with a small step over would be magnification of any machine tramming error. If you machine isn’t perfectly trammed then the large diameter bit will magnify this and potentially end up “recutting” the part you already cut but not enough to make a chip, just heat and dust. Other than surfacing the wasteboard I’d suggest sticking with 1/2" bits or smaller with larger stepover. The main reason to use a larger bit for surfacing the wasteboard really is to reach outside the limits of the machine to flatten a slightly larger wasteboard.
