SCMS Cut Procedure

[Mike Goetzke]

I've had a SCMS for many-many-many years. I have seen where you make a scoring cut toward the fence, pull back, and push down/forward to complete the cut. I have noticed on a few DIY shows the operators use the same as described above but they add another step. To complete the cut they don't push the saw all the way forward to complete the cut. They stop short raise the saw, push it in and complete the cut with a chop action.

They are very good at this but what is the advantage of the third step?

 

[luvmytoolz]

I don't get why they'd add the third step, it's just introducing the possibility of altering the down/sideways pressure during the motion which could cause the barest of deflection, but enough to see?

 

[smorgasbord]

It's all about trying to reduce tear-out.

If you think about the "standard" action of cutting a wide board:
1) Pull the blade out as far as you can
2) Plunge into the stock (assuming it's wide enough to require that)
  - Note that as you plunge, the teeth exiting the wood mostly already have a kerf, but a zero-clearance insert can help reduce tear-out on the bottom.
3) Slide towards the fence
  - This is where tear-out on the top could occur, as the leading teeth ("back of the blade") are creating a kerf and can tear-out as they exit

As for the scoring cut, that's prone to tear-out on the top as the leading teeth are exiting unsupported wood. I've sometimes done this as a "climb cut", that is scoring the top while pulling the blade towards you. Have to be very careful not to cut too deep and not to be cutting stock that has stresses in it, and probably should clamp the workpiece down, but the idea is to have the down teeth doe the cutting on the top.

 

[luvmytoolz]

If I'm understanding the 3 steps correctly then isn't doing a chop at the end with the blade raised and pushed all the way back going to give tear-out on the bottom? Or maybe I'm getting something wrong here.

To minimise tear-out and improve dust extraction I always do a scoring cut forward then drop the blade and push back. Always gives me very clean results.