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vacuum chuckers, what is this? and will it go away?

Sam Fleisher

Sam Fleisher

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No one jumped on my what's wrong with waldo bowl (j/k) in the what's on your lathe post so I'll try again.

This bowl I put on my vacuum chuck to remove the tenon and complete the bottom. Up to that I had sanded, put finish on the bowls and then used the vacuum (only 5-6 so far) after cure.

This bowl I decided beforehand I would finish (danish oil) off the lathe so I could remove the tenon quicker without sucking the oil through the wood.

When I took it off the vacuum chuck the inside of the bowl was a lighter shade inside where the chuck was versus outside the chuck. This was not caused by the chuck rubbing because then it would be just a ring. Did the vacuum suck dust through the wood or something? The rough turned bowl was a couple of years old so plenty dry.
There is no mark that can be felt and I went over it with the last grit of sandpaper again to see if it would go away. (400 grit)

In the picture I have put danish oil on at this point to see if that would make it go away. No miracle fix there. Today I left it out in the sun with some more danish oil on it and it helped it darken up a little but is still very apparent.

What is causing this? It's just plain old black walnut and I would think if it sucked the natural oils out of the wood it would be darker not lighter plus it didn't take very long to remove the tenon and sand the spot where it was.

IMG_20230614_181630182.jpgWWWIMG_20230614_181643067.jpg
 
guy laizure said:
what kind of material are you using for a seal on your vacuum chuck
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to me it feels just like the craft foam that everybody else uses except this is formed into what the guy selling them calls an angel wing. The white is just a pvc coupler.

www.odd-not.com

Angel Wing Seals — OddNot

Angel Wing Seals are one of the two magic ingredients that make the ReVaC Vacuum chucking system better than any other vacuum chucking systems on the market today. It’s not often that a seal needs to be replace.
www.odd-not.com www.odd-not.com
 

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The vacuum can suck sawdust thru pores, especially from sanding. It's especially noticeable when you have a porous wood and the vacuum leaks until you start sanding - then it holds great (yay?).

And walnut does seem to like to attract dust in its pores from just normal sanding. And the sanding dust usually looks white sitting in the pores (why? no idea). Sometimes I have to blow out the dust between each grit so it doesn't build up (and I'm talking just normal sanding here, not with vacuum). It's a walnut thing (sometimes).

Probably needed some time with the air compressor and maybe a toothbrush and maybe additional sanding with the last grit(s) to "loosen it up" and even things out.
 
I use a vacuum chuck and think that it can vacuum sawdust out of the wood pores causing a difference in appearance. Before putting any finish on, compressed air might remove the sawdust in surrounding wood pores. Sometimes I'll wipe the piece with mineral spirits or lacquer thinner, to help show any defects before putting on any finish. Now I think you will need to re-sand the bowl to eliminate that mark.
 
Sam, I strongly suspect it is sanding dust. When I am using my vacuum chuck I get a good idea on how porous the wood is by my vacuum gage. If it below 18 in. hg. (larger vacuum chuck) I will put masking tape inside to aid in sealing. it is harder to determine using a smaller vacuum chuck and the leakage could also be from a poor seal.
 
William Rogers said:
Sam, I strongly suspect it is sanding dust. When I am using my vacuum chuck I get a good idea on how porous the wood is by my vacuum gage. If it below 18 in. hg. (larger vacuum chuck) I will put masking tape inside to aid in sealing. it is harder to determine using a smaller vacuum chuck and the leakage could also be from a poor seal.
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Would turning the bowl back around on the vacuum help any or is it probably too late since I've applied the danish oil now?
 
I don’t know, It has been a long time since I had that problem (yes it has happened to me). I don’t remember what I did. Just guessing you might create the same effect on the other side while not fixing the original side.
If you have already applied Danish Oil you will need to sand. The Danish Oil will fill the pours so you should not get the same effect on the other side this time.
 
William Rogers said:
I don’t know, It has been a long time since I had that problem (yes it has happened to me). I don’t remember what I did. Just guessing you might create the same effect on the other side while not fixing the original side.
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At least on the bottom side I could make it look like it's supposed to be there. Probably would just suck through the uncured oil now. I think I'll go down a couple of grits instead of the same as the last like I tried and re-sand the inside again. Maybe use my bigger chuck so it won't be the same size circle. Problem with that is I'll have to turn the pressure down a bit.
 
I would try using the masking tape on the area where the vacuum chuck attaches. Although I doubt you will have porosity since the Danish oil is in place.

Nice bowl.
 
Russ Braun said:
I might suggest trying these fixes on the next bowl; this one looks great the way it is! The great thing about wood is it’s not exactly perfect to begin with!!
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It might not be showing up on your screen as well? The 4 inch circle of lighter colored wood in the center of the inside? It's more pronounced in person though being in the sun yesterday all day seemed to help a little.
 
Doug Freeman said:
You could wet sand with the danish oil, build a bit of a slurry, and then rub that around to equally fill all the pores, wipe/buff off excess.
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good call and a lesson learned. Apply finish, let cure, then remove tenon with a vacuum chuck.

I spent an hour watching netflix while wet sanding with danish oil and 400 then 800 and it is mostly gone. All this for what will probably be a what, $10 dollar bowl at a fall festival in oct. lol
 

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Sam Fleisher said:
I spent an hour watching netflix while wet sanding with danish oil and 400 then 800 and it is mostly gone. All this for what will probably be a what, $10 dollar bowl at a fall festival in oct. lol
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That is not a $10 bowl, it's at least $10.99. 😀 Seriously, even though you're still learning don't sell yourself short. Charge what the market will bear. It might be only $20 or $30 for that bowl or it might be $50, $60, $70 or more. It really depends on the event, your locale and the clientele (sorry for a wishy washy answer). That bowl is worth more than $10. There's lot of post and threads here on pricing.
 
Sam Fleisher said:
What finish would that be? There wasn't a finish on it when I used the vacuum chuck.
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Why are you using a vacuum chuck while sanding? I can only think the rare occasion to do that is for a repair of some sort. I know ... you just want to use your new vac system as much as possible. 😉 A better option would be to use a vacuum plate chuck on any flat-rimmed bowl instead of a drum type chuck. Only the rim touches the seal so there wouldn't be any noticeable ring. This also works well if your finish isn't completely cured ... if any finish pulls out of the pores from the vacuum just wipe it down with a rag or paper towel.
 
Tom Gall said:
Why are you using a vacuum chuck while sanding? I can only think the rare occasion to do that is for a repair of some sort. I know ... you just want to use your new vac system as much as possible. 😉 A better option would be to use a vacuum plate chuck on any flat-rimmed bowl instead of a drum type chuck. Only the rim touches the seal so there wouldn't be any noticeable ring. This also works well if your finish isn't completely cured ... if any finish pulls out of the pores from the vacuum just wipe it down with a rag or paper towel.
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I just left it on the chuck after turning off the tenon and used drill sander where the tenon had been. Then I did finish that with some hand sanding but it was still on the chuck to make it easier to hold. I'm learning that I think I'm sanding more than I need to. I started sanding one at 150 grit instead of 80 where I usually start and go through the grits. I'm not skipping grits other than the ones before where I start at and I'm trying to concentrate more on the scratches and tool marks versus just sanding to be sanding.
 
On the plate chuck idea I see a lot of people use mdf. Is that recommended or can I use some 3/4 ply with a hardwood veneer on both sides. I have some of that laying around. Now that I say that I imagine the mdf is used to be able to true it up better? What about a glue up of say 1.75 inch maple and run it through a planer to get it closer before truing on the lathe?
 
Sam Fleisher said:
On the plate chuck idea I see a lot of people use mdf. Is that recommended or can I use some 3/4 ply with a hardwood veneer on both sides. I have some of that laying around. Now that I say that I imagine the mdf is used to be able to true it up better? What about a glue up of say 1.75 inch maple and run it through a planer to get it closer before truing on the lathe?
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Generally speaking MDF (like a sponge) or any wood should be well sealed. However, there are work arounds if needed. Your bearing set up with the tube (Frugal) is different than what I use so you may be able to skip the sealing ... sort of. Basically the mounting hole and hole (for vacuum) should be well sealed.
MDF is very flat ... so if your faceplate, faceplate ring, chuck, etc., is running true it shouldn't be necessary to true up the MDF surface.
 
I've had the same thing happen that you are describing with walnut. I now am careful to blow out the bowl bottom completely before mounting vacuum chuck never had it occur again.
Also if I have used my vacuum chuck on a bowl before the walnut one if it had anything on the craft foam I wipe it off because I have gotten something on the seal from the previous bowl then it showed up on the next bowl.
 
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