Baltic Birch cutting - pockets of sap? in the core

[Barry Figgins]

Hi there! Moderate-time reader, first-time poster. Sawmill Creek has been a great source of tips and inspiration.

Anyway, I do laser cutting and engraving, and like many others I've ended up with baltic birch as my material of choice. My laser cuts through it like butter, except that I'm having a problem that I haven't seen mentioned anywhere in the discussion of this material.

It seems like the inner ply is pocked with something resistant...little pockets of sap, maybe. The laser hits these and fails to cut through them. I cut 50-60 pieces from a pieces of 30"x"30" birch, and maybe six of them refuse to come out cleanly. I'm finding that I either need to do multiple passes (slow), use high power (musses up the backside) or just touch up those spots with a razor blade (not always possible, ex. curved cuts).

Has anyone else run into this issue? I doubt there's a workaround, unless this batch of birch is suspect, so I'm just looking to commiserate.

[walter hofmann]

you got a bad quality of Baltic birch.
greetings
waltfl

[Michael Hunter]

Annoying isn't it!
Not too much of a problem if you are doing lots of small things (just add a few spares), but a pain if it happens in a large piece.

I did some architectural model work recently involving 10 20x32" sheets which needed to be cut perfectly (or start over).
I bumped the power right up to makes sure that even the duff bits would cut through - meant that the cut edges were blacker than I would have liked, but at least I didn't waste time and material.

[Ernest Martin]

I don't know where you get your Baltic Birch from, but you might try a cabinet maker in your area they can probably order you some higher quality stuff than your Home Depot, the downside is you might have to wait a week or so to get it.

[Guy Hilliard]

It's not pockets of sap but knots. The knots in the center plies are denser than the surrounding wood so they require a bit more power to burn through. b/bb Baltic Birch plywood (Cabinet grade) has one clean face, one face that may have football patches to replace areas in the veneer that had knots, and the center ply(s) may have knots.

[Barry Figgins]

I don't go through Home Depot, but a smaller lumber yard. What can I tell them in order to ensure they get the right stuff next time? I don't think they're trying to be cheap, just offering whatever their supplier can provide. Maybe I'll get the contact info for their supplier and talk to them directly.

This stuff is marked BB 14-3. I had a previous batch that I liked better, but unfortunately I don't have any of that around to check the markings.

[Joe Pelonio]

Look for a specialty hardwood/woodworking store. I use Rockler, which is close by in Seattle, but they are not in the UK.

[Bill Stearns]

Barry -
I'm not sure if this applies in your case, with your specific issue, (probably not) - but I'll pass along this info anyways. I laser engrave photographs into oval natural bark-trimmed plaques; believe it to be either birch or basswood. Very tiny little spots in the wood surface - believe to be sap - burn dark 'n enlarge upon engraving! (ruining photos.) You mentioned using a razor blade in some way? I use a Q-tip soaked in Clorox - to dampen the burn spot. In most every case, it eliminates the ugly mark. This idea may apply in some way; may not?

Bill

[Barry Figgins]

Barry -
I'm not sure if this applies in your case, with your specific issue, (probably not) - but I'll pass along this info anyways. I laser engrave photographs into oval natural bark-trimmed plaques; believe it to be either birch or basswood. Very tiny little spots in the wood surface - believe to be sap - burn dark 'n enlarge upon engraving! (ruining photos.) You mentioned using a razor blade in some way? I use a Q-tip soaked in Clorox - to dampen the burn spot. In most every case, it eliminates the ugly mark. This idea may apply in some way; may not?

Thanks for the idea! The issue isn't with engraving, but cutting, although these spots do create small dark marks along the side of the cut. So yeah, it's a similar issue.

[Barry Figgins]

Look for a specialty hardwood/woodworking store. I use Rockler, which is close by in Seattle, but they are not in the UK.

Thanks for the advice! Woodcraft is my local specialty store.

[Michael Kowalczyk]

A few years ago they started putting middle sheets with small pin knots. Under the GOST rating system, I was told, it is allowable for 3 B material to have the middle core piece the same as the BB side. So some mills are doing this regularly but it effects only a small amount of the materials. They do not manufacture the standard material to be laser compatible. A saw has no problem cutting through it. There is a manufacturer that does make a laser and die cut specific material but it is VERY expensive compared to regular Baltic Birch Plywood and it is hard to find anything under 18mm in stock anywhere. Most companies that use this specific grade material do not sell to outsiders and I have not found any wholesalers/ distribution centers that stock it in our area.