Wasteboard Burning

[Need4Feed]

For about a year I have been using the same process for new wasteboards and surfacing them.
1. New 5'x8'x3/4" MDF
2. Seal edges with shellac
3. Surface one side
4. Flip and surface other side

I take off .01" for the initial surfacing and resurfacing. I use an Amana RC-2250 at 18,000rpm, 480ipm, .75" stepover. This has worked fine for us without any problems until lately. Two weeks ago I put on a new board we got about 20" into the process when the board started showing signs of burning. We stopped and noticed a build-up of gum on the bit. We cleaned it and continued. Same thing happened. We cleaned it and rotated the inserts and same thing. We tried increasing and decreasing the feed rate and the stepover. Same results. We thought maybe we used too much shellac this time so we replaced the board with one that we didn't shellac and the same thing kept happening. We suspected that the inserts might have lost their temper from the heat so we replaced them. This time we got about 60" in when the burning started again. I felt the board and it was much warmer than it should have been. Now I'm beginning to suspect that the problem is in the MDF. I called my supplier and he assured me that all their MDF comes from one mill.

I can't figure what we're doing wrong. Any suggestions? Has anyone seen anything like this?

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[Jim Dawson]

If nothing else has changed, then as you say, the MDF is highly suspect. Bad cure, too much resin, bad resin mix, or any number of other problems. It could be that your vendor just got a bad batch. Try a piece from a different vendor and see if the problem goes away, at least you stand a pretty good chance of getting a piece from a different batch.

[ger21]

My guess is that MDF is building up under the bottom cutters, and causing the burning.

I'd drop the rpm to 15,000, but a different style tool may help. Like an RC-2255

[Need4Feed]

Jim,
I think it's a bad batch too. This sheet should last for a while. Hopefully they're into a new batch by time it needs replacing.

ger21,
We had varied the rpm as well. When we increased the rpm to 22,000 and 600ipm it was able to go further before the burning started. I had already ordered a RC-2241 before your reply. I'll try it the next time the wasteboard needs surfacing.

Thanks. I'll update this when new results are available.

[ger21]

Increasing the rpm will increase the chance of burning. I run a 3" surfacing bit at 600ipm and 13,000 rpm.

[Need4Feed]

ger21,
Thanks. I'll try that the next time it needs surfacing. Out of curiosity, which surfacing bit do you use?