Burn baby burn

**Pappy** · 02-21-2006, 06:38 AM

The stock appears to be cupped, not bowed, althouogh it may be both. The cupping shouldn't cause the burning on a cross cut but could cause problems in ripping. Bowing would by causing uneven pressure on the blade.

I think I see a glue line in the pics and the burning is all on the same piece. Redwood, like cedar is often not dried good and that piece may be wetter than the other one.

Too slow a feed rate would be a factor, too.

**JimD** · 02-21-2006, 02:39 PM

If your crosscut sled pushes the wood into the back of the blade after it is already cut by the front of the blade, it can cause burning like you are experiencing. The wood needs to move in line with the cut to avoid this - could it be moving at a slight angle?

Jim

**LCHIEN** · 02-21-2006, 02:54 PM

Originally posted by JimD

If your crosscut sled pushes the wood into the back of the blade after it is already cut by the front of the blade, it can cause burning like you are experiencing. The wood needs to move in line with the cut to avoid this - could it be moving at a slight angle?

Jim

That's the most likely scenario, I'm guessing that the sled is not moving parallel to the blade.

IF you have a BT3 and IF you used the table top edges this will cause the problem, because the BT3 is not guaranteed to have the blade running parallel to the edges of the table top. All alignment is done with the bladde to the SMT and Fence irregardless of the table top.

Lots of burnpics but no pic of how you constructed your sled.

The issue of nonparallel sides is addressed frequently and also in the FAQ.

**boblon** · 02-21-2006, 05:19 PM

When I was setting up my sled to miter the corners of boxes I had difficulty getting the edges perfectly square to the sides.

I believe this was caused by using a thin kerf blade and the blade flexing some as the stock went through.

I don't know if this could be a contributing factor, but I mention it because it might be possible that this blade movement in combination with the cup in the board might cause issues.

Just a thought.

BobL.

**distilledred** · 02-22-2006, 04:15 PM

Thank you for all the help thus far.

I didn't know there was a difference between bow and cup, good to know, and should make for clearer posts in the future =)

My sled does ride the side of the table. I was aware that the blade is not aligned to be parallel to the table top, but was under the impression that if the base of the sled is cut after the runners are put on, the fence is aligned to be 90 degrees to that cut, and the sled travels the same path, then the table not being parrallel wouldn't be a real issue; is this not the case? There may be some play in my sled that is amplified when I try to go as slow as I was.

The two pieces shown are the two halves of the board I cross-cut. I noted that the burn wasn't as bad when I sped up my pass speed. Perhaps the fast speed of travel for my sled keeps it in a straighter line?

**AlanJ** · 02-22-2006, 04:46 PM

Originally posted by distilledred

Thank you for all the help thus far.

My sled does ride the side of the table. I was aware that the blade is not aligned to be parallel to the table top, but was under the impression that if the base of the sled is cut after the runners are put on, the fence is aligned to be 90 degrees to that cut, and the sled travels the same path, then the table not being parrallel wouldn't be a real issue; is this not the case?

No, this is not true. If you think about it, by aligning the fence 90 degrees to the blade, but not making the runners parallel to the blade, your sled is now out of whack. Because the runners control the movement of the sled, it become the controlling axis - and the forward movement across the blade is not 'true' . The leading edge of the blade will hit the stock at point A, but the trailing edge of the blade will be on a different plane. This is almost certainly the cause of the burn.

**distilledred** · 02-22-2006, 07:05 PM

Originally posted by AlanJ

No, this is not true. If you think about it, by aligning the fence 90 degrees to the blade, but not making the runners parallel to the blade, your sled is now out of whack. Because the runners control the movement of the sled, it become the controlling axis - and the forward movement across the blade is not 'true' . The leading edge of the blade will hit the stock at point A, but the trailing edge of the blade will be on a different plane. This is almost certainly the cause of the burn.

Clearly. I was thinking of the blade as a point and not the plane that it is. I guess I will go look at my sled and see if there is a way to salvage it, I would hate to think I did all that work for nothing, ha. Thanks for setting me straight.

I would like some comments on my usability of the wood question. I am making a mitered box, so the wood needs to be flat for the corners to meet properly (obviously), at what point does a bow, or cup make a piece unmanagable for a given task. Thanks again.

**LCHIEN** · 02-23-2006, 12:58 AM

Originally posted by distilledred

...

. I am making a mitered box, so the wood needs to be flat for the corners to meet properly (obviously), at what point does a bow, or cup make a piece unmanagable for a given task. Thanks again.

no bow = no gap.

Little bow = little gap

Big bow = Big gap

you get out of it what you put into it.
Thta's both the thrilling and maddening thing about woodworking...

**distilledred** · 02-23-2006, 03:55 PM

you get out of it what you put into it.
Thta's both the thrilling and maddening thing about woodworking...

... I don't know about this woodworking stuff, all I have been able to accomplish so far is empty my bank account. haha.

I meant was my assesment of the way getting a piece of wood flat correct. If the cup leaves a 1/8" clearence at its peak, does that translate to having to remove 1/8" of each side, or 1/4" of your total board width in order to arrive at a flat piece? If such is the case then would I my ends be best served looking for a new piece of wood, as I don't think a 1/2" piece will hold a 1/4" dado very soundly... ? Should I be in the market for a jointer, or a new piece of wood? How flat can one find wood from a lumber yard? Thanks.

**LCHIEN** · 02-23-2006, 04:38 PM

Originally posted by distilledred

... I don't know about this woodworking stuff, all I have been able to accomplish so far is empty my bank account. haha.

I meant was my assesment of the way getting a piece of wood flat correct. If the cup leaves a 1/8" clearence at its peak, does that translate to having to remove 1/8" of each side, or 1/4" of your total board width in order to arrive at a flat piece? If such is the case then would I my ends be best served looking for a new piece of wood, as I don't think a 1/2" piece will hold a 1/4" dado... ? Thanks.

Yes.
And Maybe - 1/4" dado in 1/2" is Not too bad, depends on what loads it has to bear.

**cobob** · 02-23-2006, 10:01 PM

easy check

Try tapeing a nail to the sled so it is an index card away from the front of the blade. Then slide the sled. If the nail hits the blade ... or is more than an index card away at the back of the blade ... the sleds not 'true'

Burn baby burn

Burn baby burn

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