Electric planer taking chunks of foam out

i was hoping someone could help me…

I bought a cheap ryobi power planer and it was working fine. But then one day it started taking out huge pieces of foam out of my blank. I am using xps which is very similar to poly. I know that eps can have that problem but this was strange. I thought it was because I bought a cheap planer. So I ended up getting the modified hitachi for $400.  I used it and it started taking out chunks off the foam. 

I feel that I am doing something wrong. Please help 


Welcome to Sways. Dull blades will pull & tear at foam. Like all tools everything needs maintained. Sharpen the blades or get new ones.


What density XPS are you using?

EDIT: Standard housing insulation (XPS) foam is low density and soft.

You’re not doing anything wrong, and it’s not your planer’s fault.

Extruded polystyrene foam just tears like hell under the planer. PU foam tears if you go really fast, or of your blades are very dull. EPS doesn’t tear at all, but if the beads aren’t fused well you’ll get some pull-out of beads.

Thank you all!!


It cannot be the blades as the hitachi is a brand new machine and blades are new 

I focused on slowing down and that helped a lot. I think it’s a combination of going to fast and the way the xps cells are fused. 




Slow but not too slow fast but not too fast…Listen to the foam…Look at the board…

…if you work only with PS, you need the drum kit to get rid of that problem at normal speed.

reverb is right, grit drums were invented just for this reason.

But I have a hard time advising anyone to use grit drums because they put a lot of heat into the tool. Heat is the enemy of your planer’s bearings.

With XPS the key is to go slow. You can get really smooth cuts if you go slow.

…hello Mike, you are right but for a non production guy that may be only could shape few boards per year, I do not see any problem.

Speaking of grit drums, I have an extra skil 100 that I’d love to put a grit drum in.  Is there anyplace I can get one these days?

It’s all about chip load

Decrease chip load by increasing revs, moving the bit slower across the piece, take out less material on each pass.

Sharp tools help.

If your not already,

Always cut with the planer on an angle… You’ll find your feel

also to avoid heating and streaching of the belt (hitachi) take the belt cover off, just don’t put your finger in there cause you’ll be fucked :wink:

Little bits of eps create hot rocks, they get under and stretch the belt… or maybe it’s just my shaping style haha