Making a flexible sanding spline... need some input

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cblink.007

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The Sioux body grinder wouldn't be much use for shaping foam. For one thing it takes some muscle to handle it and a lot of practice to learn to control it. It really shines for shaping fiberglass or when you are shaping a part with different hardness materials in it. I never used used foam back in the day. I used wood, fiberglass and bondo. Properly handled, it will cut through all three materials evenly. Probably overkill for foam. I was a husky lad when I was building plugs. I am to old and weak to use the 7" grinder anymore. I use a little Makita 4" grinder now. I still have the touch though!

If you do want to try a grinder, this is the way to do it. You use a sweeping motion - like waving your hand. Start by sweeping the grinder back and forth above the part and gently lower it until it just touches. Keep moving it - don't stop! You want to use the outer part of the disc but not the very edge. The disc will flex and grab when it hits and you have to be sensitive to that. You adjust the pressure you are putting on the tool according to the hardness of the material you are grinding and how much you need to remove. You will have to experiment a bit to get good results, but you can do precise work with it after some practice.

Can you be a little more descript with these grinders, with a picture? Are we talking about orbital sanders? Just trying to be on the same sheet of music on this...and also planning ahead for my full scale build!
 

Marc W

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Here is a picture of my favorite tools. No savvy orbital! The 7" grinder on the left. I just put it on the scale. It weighs 14 lbs. which has the advantage of giving the tool inertia. That is good because it will want to grab and twist when the disc contacts the part. The weight reduces that tendency, but you do have to hold 14 lbs. up to use it. They don't make them anymore but there are other brands. Next is my little Makita peanut grinder. Then my long board hand sander with the 80 grit and 40 grit paper that fits it. Also the rubber sanding block. I also have an air file that uses the long paper around here somewhere. It is to flexible for most shaping but it is handy to level primer and smoothing small lumps. It works well on parts that have the right curvature.

1584924627631.png

The key to using the grinders is to keep them moving. You can stop and park them if you are removing a lot of material but otherwise keep them moving.
 

cblink.007

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Ah, ok... that is what I was starting to envision. Certainly a tad overkill for moldless composite finishing, but good for other more heavy duty applications!

Good stuff...thank you much!!
 

speedracer

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The very best sander I've found for moldless construction (like EZ's - I've built two) is an AFS sanding block. I have two, a 28" and a 36". They're 2 3/4" wide for file board rolls of Sticky back sandpaper. They're medium hard rubber and come with two different dia. steel rods to insert for fine tuning stiffness. Three rods per unit but you can only use one or two for more flex. The bottoms are thin aluminum you glue the sandpaper to. Now...… for the bad news. The person who sold them died and they're not made anymore, the way I understand it. A friend is building a Long EZ and found one at a yard sale so he stopped borrowing mine. eBay? Craigslist? Maybe someone will take up selling them again? Many years ago I saw a Lancair 1V that a guy had faired the wings with a 16" file board. Those wings had more ripples than the Pacific Ocean!
 

Hot Wings

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Now...… for the bad news. The person who sold them died and they're not made anymore, the way I understand it.
Nice tool. Sounds like a project for someone with a 3D printer and a can of urethane?

Edit:
Looks like the Dura-Block is readilly available. Not exactly the same but almost.......
 

cblink.007

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Nice tool. Sounds like a project for someone with a 3D printer and a can of urethane?

Edit:
Looks like the Dura-Block is readilly available. Not exactly the same but almost.......
Looks like I found a good source of sanding tools as well:

 

Kyle Boatright

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Looks like I found a good source of sanding tools as well:

Eastwood. TP Tools. Amazon. Your local body shop supply store. Lots of options
 

berridos

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I am pretty ok with my solution. I have several blocks made out of rectangular plexiglass sheets, cut a bit larger than my hand. Depending on the grit, the plexiglass goes from pretty fine and flexible to less flexible. To each plexiglass plate i have bonded a glove with contact glue.
I stick the sanding paper to the plexiglass with spray photo glue. You can remove the old sandpaper without problem and replace it. This way i have sanded up to micrometer quality surfaces in 2d.
 

speedracer

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I can't imagine anyone doing a good sanding job on a wing using a 16" file board. That person would have to be super talented or spend a huge amount of time. For wings I use a 2"X 2" X 5' long steel square tube with a 2 3/4" plywood bottom for file board roll sandpaper. It weighs 22 pounds. Ain't no ripples in my wings.
 

Geraldc

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I got a roll of 6" wide hook and loop tape and cut off bits and glue them to board or foam and use rolls of hook and loop abrasive with them.
 

Markproa

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Does anyone use the notched trowel method? I notice a lot of micro balloons are used, does anyone use West Z410? It's my filler of choice, very light and easy to sand.
 

Markproa

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This is the notched trowel method for anyone who hasn't seen it before. Cut small notches along the side of a steel trowel then cover your surface with the small beads. They are easy to sand as the paper doesnt clog and surface area is minimal. When you've sanded down to the original surface in places you can the use another un-notched trowel to fill between the notches. I have used this method on many large boat builds for years. Far less waste too.
IMG_20180611_155901.jpgIMG_20180611_155842.jpg
 

Geraldc

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When you've sanded down to the original surface in places you can the use another un-notched trowel to fill between the notches.
Thanks for that tip.I will try it out later today.
Have you weighed your parts before and after? I am worried about
getting a perfect finish at the expense of weight.
 

Markproa

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Thanks for that tip.I will try it out later today.
Have you weighed your parts before and after? I am worried about
getting a perfect finish at the expense of weight.
This method won't weigh any more or less than any other method, the end result is the same. The difference is in how much effort it saves long boarding.
 

speedracer

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Those V-notched trowels are readily available at hardware stores. They're for spreading glue when laying (please don't ask me if she has a sister) linolium. I've used that method on LongEZ wings and it works great, mainly for keeping a constant depth of the micro. The only difference from what Markproa described is that I troweled on the second coat of micro before the first coat had fully cured to ensure bonding. Perhaps not necessary, but, you know...
 

Markproa

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The notched trowels for glue spreading are usually too deep. Either grind them back or make your own in a couple of minutes. Lay a flexible spline over your surface to gauge how deep the grooves need to be. Hopefully you'll only need a mm or two.
 
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