I’d welcome your comments or advice on a current issue i have when cutting some snack trays.
The wood is Ash and the pockets are being cut with a 3/4" dia radiused end mill
(A SpeTool “Bowl and Tray Router Bit”)
The radius of the Bowl & Tray Router Bit is 1/4’‘, the shank diameter is 1/4’‘, the cutting diameter is 3/4’’ which gives a central flat area 1/4" diameter.
When cutting, I’m getting slight burning on the inside edge of the pocket, particularly at the radiused bottom edge, which is very difficult or impossible to sand out.
It is particularly noticeable when the router is travelling on a roughly North to South direction.
When you are cutting are you making dust or chips?
Chips is what you are looking for. Its a combination of router rpm and feed speed. The slower you are moving the router with a higher rpm speed you can burn the material. Along with that and a dull bit you can have the problem of burning. Your North to South direction is mostly caused by grain direction. changing the feeds and speed should help.
Check your bit and make sure it is sharp just because it is new that does not make it sharp. If the bit shows signs of being hot or burnt it may have lost its edge. See if the manufacturer of the bit has any recommended feeds and speeds to start with.
You can adjust your feeds and rpm to get the chips. You can also do a finish pass of .2 to .4 mm to reduce any burning.
If you check the forums most of us bought a bowl bit for one reason or another and everyone has the same issues, check posts for an ideal starting place.
Edit: just looking at your trays I realised your stepover is going to cause a bit of a dwell effect, do you have burning usually right in the middle of where the toolpath spirals and finishes in each pocket? Because that’s an interesting form of induced dwelling caused by a toolpath that may be able to be remedied by 3d finishing paths
Drop your RPM to 10000. You should be able to cut up to 2000 mmpm (or faster if the machine takes it. My F&S calculator is going up to 200 ipm (5000 mmpm)) . Program it at 1000 & bump the feed override until it seems to be struggling. You should get chips at least 0.1mm thick
You can up your stepover to almost 1/4", maybe go 6mm
Thanks Anthony
I’m getting fine chips but will experiment with faster feed rates. The Spe Tool chart recommends 18000rpm and a feed rate of 120"/min and a cut depth of 0.125" which are both a lot higher than I’ve been using. 120"/min is about 3 times the feed rate I’m using! and seems very fast?
It’s a new bit and shows no sign of being hot and is cool to the touch when removing.
Thanks Tod
Yes looking at the Spe Tool charts they suggest a feed rate around 3 times what I’m using so will experiment with higher feed rates and lower rpm.
Re step over, I’ve tried larger stepovers but because the flat section of the bit is only 1/4" dia any more than a 1/8" stepover produces ridges on the bottom of the pocket.
You may want to set up an inner vector and a pocket toolpath with a straight end mill to hog out the majority of the material to save wear and tear on the bowl bit.
