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Maple sanding issues

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Forum topic by Dirtyoar posted 05-16-2016 02:31 PM 585 views 0 times favorited 7 replies Add to Favorites Watch
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Dirtyoar

2 posts in 208 days


05-16-2016 02:31 PM

Topic tags/keywords: question finishing sanding sander maple

I’m having nothing but issues with the sanding marks on a maple table top. It’s been run through the planer, then a dual drum sander equipped with 100 and 150 grit abrasive, then hand scraped and random orbit sanded with 150, then finally hand sanded with 150 grit. And it looks terrible. Swirl marks from the sander, lines from the sander path, etc.

The sander is a Bosch RO10 hooked to a Festool CT36 on the lowest suction setting. Abrasives are Klingspor. I’m moving at around 1”/sec.

Any advice would be greatly appreciated. Pictures attached.


7 replies so far

View Ger21's profile

Ger21

1047 posts in 2597 days


#1 posted 05-16-2016 02:49 PM

Could be that you’re too aggressive with the hand scraping?
I’d sand with 220 across the grain, which should remove the marks I’m seeing, then again with the grain.

-- Gerry, http://www.thecncwoodworker.com/index.html http://www.jointcam.com

View BurlyBob's profile

BurlyBob

3695 posts in 1732 days


#2 posted 05-16-2016 02:55 PM

Have you tried swelling the grain. I’ll wet the surface slightly so the imperfections raise and go over it with a fine grain 220 or 320 after it dries. Perhaps that might help you.

View JBrow's profile

JBrow

819 posts in 386 days


#3 posted 05-17-2016 06:31 PM

Dirtyoar,

I am not sure I am qualified to offer advice. However, I describe my experiences and methods for surface preparation, which yield fairly good results, at least to my eye. I have never done a time study, but I would not be surprised if I spent somewhere from 25% to 40% of the total project time preparing the surface for finish.

It appears from the photos that the ridges are more or less regularly spaced and similar in profile down the length of the panel and across its width. This pattern suggests the scalloping is from the drum sander, assuming the ridges and valleys are parallel to the drum. But then the scalloping seems to run parallel to the grain, suggesting these were created after the drum sanding. Nonetheless, checking the manual that came with the drum sander, perhaps in the troubleshooting section, may reveal possible causes.

If the scalloping is parallel to the drum and the panel came off the drum sander scalloped, then my guess is the waviness is attributable to a too slow feed rate through the drum sander. When I first used my Woodmaster single drum sander with a slow feed rate, the surface exhibited similar scalloping. When I increased the feed rate to greater than 80%, running panels through much faster, the scalloping disappeared. The panels came off the drum sander with smooth, flush, and even surfaces ready for final sanding when the feed rate was increased.

If the panel came off the drum sander smooth and flat, then perhaps too much material was removed by the scraper, resulting in scalloping. It seems to me that the more the card scraper is bent during scrapping; the swath of material removed is narrower than when the card scraper is only slight bent. This could produce scalloping. I rarely use the card scraper after drum sanding, fearing that I will create an uneven surface. I stay at the drum sander until the panel is flush across both surfaces. I then tend to go straight to the Random Orbital Sander (ROS), skipping the card scraper.

Like you, I start sanding panels that have just come out of the drum sander with the same grit as is loaded in the drum sander. In my case the drum sander is loaded with 80 grit paper so I start with 80 grit paper on the ROS following the protocol describe below. I sand until the deeper scratches from the drum sander are gone. Strong raking light is helpful, but with 80 grit drum sander paper, the scratches are readily visible. With 150 grit drum sanding paper, these scratches may be more difficult to see without raking light in a dark shop. Once the drum sander scratches are gone, I proceed to the next grit.

My ROS protocol calls for sanding the entire surface a minimum of 4 times at the same grit. The first two times begin and end at the same corner of the panel running the sander perpendicular to the grain down the length of the panel and then back. I advance slowly because I overlap about 80% of the last pass of the sander. The last two surface-sandings begin at one corner running the sander parallel to the grain until the entire surface has been sanded then I return in like manner to the starting corner. I sand without applying downward pressure on the sander. The weight of the sander provides the only downward pressure. The sander is kept flat and in full contact with the panel. I also move at a rate of about 1 foot per 2 to 4 seconds (give or take – sometimes as slow as 6 seconds per foot but rarely any slower) working to keep the rate constant. I try to keep the wood from becoming too warm under the sanding disk. When I am applying a film finish to the project, I stop sanding at 180 grit, otherwise I stop at 220 grit. I suspect stopping at 320 grit yields even better finishing results.

I also keep a close eye on the wear of the sand paper. I change the paper when it appears to lose some of its cutting capability. Refreshing the sand paper with a new disk saves sanding time, yields better results, and prevents burnishing the wood. On occasion I mark the entire or part(s) of the surface to be sanded with pencil marks and continue sanding the surface until all the marks are gone. Pencil marks come in handy when there are high and low spots, for example at joints to be flushed up. The marks in the low spots will only disappear after the high spots have been sanded down. In the case of hard maple, sanding the entire surface more than 4 times could easily be required to remove the scratches from the previous grit.

I stop sanding when swirl marks are no longer visible. When I think I am done sanding, the panel is wetted, which makes any scratches or defects that will show up when finish is applied very apparent. I like to raise the grain with water which also reveals defects, but clean mineral spirits can also be used without raising the grain. If swirl marks or defects are visible, then I go back to sanding at the next smaller grit. I remove the fuzz created from raising the grain with a light hand sanding immediately before applying a finish.

View CharlesNeil's profile

CharlesNeil

1610 posts in 3337 days


#4 posted 05-17-2016 06:41 PM

so what is on the top now ???

Jbrow has some good advice.

One of my lifelong tricks, is what we call “trace coating”. this is where we take a water base dye, or even some food coloring and do a light coat of color, when dry sand it off with some 120, then repeat then sand with some 180 , and your done.

The trace coat acts like a road map, it will show you everything,lightly wet the surface before trace coating to prevent alot of absorption of the dye , between the grain raising of the water (as Jbrow explained) and the trace coat you will be able to see what your doing.
Drum sanders , planers , all of them “Impact” the wood and can cause slight compression, the wetting relaxes it and allows it to swell out and the trace shows the surface as you sand.

Having taught many finishing classes, the trace coat is by far the number one trick folks find to help them sand better and more effectively.

View gargey's profile

gargey

488 posts in 242 days


#5 posted 05-17-2016 06:57 PM

I use 150 grit to dimension lumber. 100 grit is appropriate for building the panama canal. You stop there and wonder why its not super smooth? How about trying 200 grit, 400 grit, etc.

...I mean…

View bondogaposis's profile

bondogaposis

4036 posts in 1817 days


#6 posted 05-17-2016 08:59 PM

I sand maple to 220 grit, 150 grit is too coarse for a maple table top.

-- Bondo Gaposis

View Dirtyoar's profile

Dirtyoar

2 posts in 208 days


#7 posted 06-14-2016 07:17 AM

We’ve recently changed out to a Festool ETS 125 with a soft pad (and a hard pad) to try out different techniques. It’s definitely not scraping or drum sanding that’s causing the issue. We’ve gone straight from the planer to see if that was the case, and it was not. The final grit determined the sanding ‘snail trail’, so we’ve moved to sanding at faster speeds with progressively higher grits, and the finish is noticeably nicer. We typically sand to 220 grit, but with maple, we sand to 320 grit or higher to eliminate swirls.

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