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I think heat from belt sanding made my glue joint come apart.

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Forum topic by Jimothy posted 07-09-2020 06:16 AM 1182 views 0 times favorited 22 replies Add to Favorites Watch
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Jimothy

56 posts in 1749 days


07-09-2020 06:16 AM

Topic tags/keywords: glue joint failure heat sanding wenge birch

So I glued up some wenge/birch panels together, and I left them for about 2 hours. I know I know I should wait 24 hours, but in my experience it’s always been long enough to at least sand them, I didn’t need to plane them because they were already quite flush. I was using 80 grit on a belt sander and it was producing some heat as per usual, but definitely wasn’t burning the wood, which has happened to me before from putting too much downward pressure. After some time, only one of the glue joints came apart and it seemed like it almost melted the glue or something. It was strange looking, it didn’t look like how uncured glue usually looks.

Is it possible the heat melted the glue joint? Has anyone else had similar experiences? Maybe if it was fully cured it would have been fine, but this has never happened to me before, and I’ve done this a handful of times. Also, it was brand new sandpaper if that makes a difference.


22 replies so far

View LittleBlackDuck's profile

LittleBlackDuck

5001 posts in 1629 days


#1 posted 07-09-2020 07:52 AM

It’s old sandpaper that would tend to buff and therefore heat up (more).

You didn’t mention the glue you used… with Titebond, I’ve often sanded after about 1 hour without issues… Did you put a paper in/on the sander?

You should not put unnecessary pressure on your sander and just let it do it’s job… If you need pressure I thing you should drop a grit or two and work your way up. I think that anything above slightly warm is being overworked.

-- If your first cut is too short... Take the second cut from the longer end... LBD

View PeteStaehling's profile

PeteStaehling

135 posts in 1928 days


#2 posted 07-09-2020 10:05 AM

If you did melt the glue you are probably taking way too heavy of a pass. Multiple lighter passes are the way to go. Speed of feed can be a factor as well. If you are heating up the wood much, I’d recommend rethinking your procedure. You really ought to be able to avoid heating up the wood much at all.

Oh, and yeah I too often run stuff through the sander without waiting long for it to dry. Never had a problem with that.

View Craftsman on the lake's profile

Craftsman on the lake

3397 posts in 4246 days


#3 posted 07-09-2020 11:06 AM

I’ve got two belt sanders. Never had glue come apart but I let it cure a long time. If your piece is fairly large, i.e. it covers the belt, it will generate a lot of heat. The larger the surface the less pressure you can put on it. You must have noticed some slowing down and straining of the unit too. When that happens let up. Takes longr but it has to be.

-- The smell of wood, coffee in the cup, the wife let's me do my thing, the lake is peaceful.

View JackDuren's profile

JackDuren

1260 posts in 1768 days


#4 posted 07-09-2020 01:24 PM

You can pull them from clamps within an hour if clamped correctly. You should be able to work the joint in that time. Just don’t stress the joint.

Why they popped apart u don’t know.

View Rich's profile

Rich

5720 posts in 1398 days


#5 posted 07-09-2020 02:47 PM

I’ve never had that happen. How old was the glue and which one did you use?

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

View splintergroup's profile

splintergroup

3867 posts in 2031 days


#6 posted 07-09-2020 04:14 PM

Same w/me as to sanding after only a few hours (or even less) with a DS.

Heat does soften the glue up somewhat, but I’ve never had issues, even when the surface (cutting boards) gets quite warm to the touch.

Wenge is somewhat oily so lack of surface prep may have had some effect, but still something is amiss.

View trsnider's profile

trsnider

214 posts in 2819 days


#7 posted 07-09-2020 04:27 PM

Klingspor said I had (very) old belts when I sent one in after the glue failed. They said the glue deteriorates over time and won’t hold up against the heat.

View pintodeluxe's profile

pintodeluxe

6181 posts in 3622 days


#8 posted 07-09-2020 04:32 PM

I think the Wenge is part of the issue here. I believe it needed 24 hour cure time.
I don’t think sanding had much to do with the failure, just that it was a somewhat oily exotic wood that was handled too soon. I’ve used Wenge in combination with domestic hardwoods without issue, but as a matter of practice, always let glueups dry overnight.
It’s one of the few legitimate excuses woodworkers have to take a break!

Good luck with it.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View HokieKen's profile

HokieKen

14562 posts in 1947 days


#9 posted 07-09-2020 04:49 PM



I think the Wenge is part of the issue here. I believe it needed 24 hour cure time.
I don t think sanding had much to do with the failure, just that it was a somewhat oily exotic wood that was handled too soon. I ve used Wenge in combination with domestic hardwoods without issue, but as a matter of practice, always let glueups dry overnight.
It s one of the few legitimate excuses woodworkers have to take a break!

Good luck with it.

- pintodeluxe

+1 I suspect your issue is the Wenge. Oily exotics can be hard to glue up effectively.

-- Kenny, SW VA, Go Hokies!!!

View JackDuren's profile

JackDuren

1260 posts in 1768 days


#10 posted 07-09-2020 04:55 PM

Are you talking about the the belt sander belt breaking apart at the glue seam?

I thought you were saying the boards broke apart…

View WoodenDreams's profile

WoodenDreams

1099 posts in 720 days


#11 posted 07-09-2020 05:20 PM

You didn’t mention if the glue joints were ‘end grain to face’ or ‘end grain to edge’ or ‘edge to edge’ or ‘face to face’. Also using 60 grit or 80 grit on a belt sander, shortly after a glue-up, it can grab the wood, and be considered stressing the joint, before glue being cured. Verses using 150 or 180 grit use within a two hour period. Example, I’ve had 80 grit yank the wood out of my hand using my edge sander without a stop block.

I think there’s a lot of woodworking try to take short cuts in time factor after a glue-up. Doesn’t mean it’s not wrong, They’ve been getting by with it. “Knock on wood”. This time stress won.

View LeeRoyMan's profile

LeeRoyMan

1261 posts in 536 days


#12 posted 07-09-2020 05:24 PM

I’m only making an assumption, but it’s my theory that wood breaths,
and Wenge is oily and dense and doesn’t breath as well as others.
Since glue needs air to dry I figure it takes longer for the glue to get it through the dense, oily wood.

I always swipe the joint with acetone or lacquer thinner then glue and clamp and leave it for a longer period of time depending what it is.

Like I say, just an assumption, could be totally wrong, but at any rate more clamp time if nothing else.

-- I only know what I know, nothing less, nothing more -- That doesn't count what I used to know..

View Rich's profile

Rich

5720 posts in 1398 days


#13 posted 07-09-2020 05:35 PM


I m only making an assumption, but it s my theory that wood breaths,

- LeeRoyMan

Tell me about it. My nightstand has COPD and keeps me awake at night with its wheezing.

-- Half of what we read or hear about finishing is right. We just don’t know which half! — Bob Flexner

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LeeRoyMan

1261 posts in 536 days


#14 posted 07-09-2020 06:26 PM


I m only making an assumption, but it s my theory that wood breaths,

- LeeRoyMan

Tell me about it. My nightstand has COPD and keeps me awake at night with its wheezing.

- Rich

Well, if you can’t dazzle them with brilliance, you have to baffle them with bullshit…....

-- I only know what I know, nothing less, nothing more -- That doesn't count what I used to know..

View Sark's profile

Sark

303 posts in 1169 days


#15 posted 07-09-2020 07:50 PM

I also think that Wenge is the most likely culprit. A modest amount of heat with glue that’s not sticking properly and you see the results. What glue should you use? Non-water-based glues, and that would include polyurethanes, epoxies and maybe cyanoacrylates. Also as mentioned, since wenge is an oily wood, the joint needs to be wiped down with a solvent such as acetone or lacquer thinner prior to glue up.

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