Official Luthiers Forum!

Thinking to use an ROS to cut down on the time.
Just the "normal" interface pads seem a bit soft to just knock off the high spots.
The firmer interface pads don't seem to be available in the UK at all.
But hook and loop directly on the backing pad will have trouble conforming to all the curves involved to sand finish on a guitar.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

You should have it as firm and flat as possible to get the surface level. You might consider doing the first, coarser grit paper by hand using a firm sanding block. Then go to your ROS for the finer grits.

Usually, orange peel is caused by too high of an air pressure from your gun.

Or using a thinner that is too hot.

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"Act your age, not your shoe size" - Prince

What finish are you using?
I spray a lot of nitro
I found this schedule to work for me
A mix a little retarder in your thinner. This is hard to say as I use a 1 oz if retarder in 8 oz of thinner
B Mix some at 50% and some at 30%
C start with stain seal fill seal first coat of finish right away on the last seal coat and other coats 2hr apart for 4 coats
start with the 50% and refill the cup with the 30% mix until you have 4 coat NO SANDING BETWEEN COATS
D after 2 week level sand with 400 grit. use ROS and sanding blocks

do all the touch up and drop ins

spray 3 coats at 50% mix

let set at least 2 to 3 weeks to cure

start wet sanding with 1000 1200 1500 2000 2500 3000
buff and polish

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I'm trying GF High Performance Topcoat, thinned 10% with water.
I've been advised to do preliminary level sanding to around 80% after 2 days, then wait for further curing before final leveling and buffing.
This finish is seriously hard.
I leveled base coats with 3M ScotchBlue P320 2 days after spray 3 coats and I felt it was like trying to get the paper to bite on melamine......
Hence my thinking to try the ROS.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

So I should use my ROS with abrasive on the backing hook and loop pad without the interface pad?
The plan is to use Abranet 1000 initially and go to 800 if I need to.

I thought orange peel was basically lack of atomisation - too high a finish setting, too thick a finish, or insufficient air - ?
Can also be spaying when it's too hot - the finish drying before it has time to flow out and self level.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

when leveling early I would use 400 for the first coat and maybe the 2nd. This coarser paper helps flatten without killing yourself then after that 800 on up and you can use a good hand pad with quality sandpaper. Please don't use something from lowes , if you want to learn good finish technique talk to a car guy. While he may use a different finish he knows how to level and polish

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Nothing wrong using a ROS for this. Stiffer plater better than softer plate. I don’t like super stiff plates. I start at 400 and work up. I do prefer a 3” or so pad for sides. And low speed. I can get a much nicer finish than hand sanding. But, ya gotta learn what works and what doesn’t.

Another thought on this. Any kind of mechanical sander can get away from you. All those edges around the peghead, finger board, binding. Anything below 800 grit, I’m working the ROS like a paint brush. Stiffer pads help from flexing over the edges, smaller pads help with this too. This is one reason you want a good ROS. I use Festool sanders. I used a low profile one (PC 5” DC motor) for years with good results. But there is no comparison with my new sanders.

Orange peel wasn't as bad as it looked at first, settled down a lot in 2 days.
Went fine without an interface pad, 1000 grit Abranet was a bit too fine to start, so went with 800 first, then went up to the 1000 grit.
Didn't touch the edges yet round the guitar, I always leave that to last.
I only did the sound hole and sound port.
In 12 days I'll finish off, 1200/1500/2000 then buff.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Hi Colin,
I make an "interface pad" by gluing a used up hook and loop sanding disc to a scrap of Formica (or other thin hard material) made circular with a large (cheap HF) hole saw . This makes a light weight hard surface that will stick to the ROS and to which I can stick a sanding disc (either self stick or spray glued). I can use this to knock down the orange peel and then quickly change to regular sanding discs.
For sanding sides I like to use a 1/4 sheet pad sander, and for a hard surface pad will glue a piece of Formica to a length of worn out sanding belt that I can use to attach it to the pad sander.
I still sand the last bit of the edges of the back and sides by hand - and when spraying I "band in" the edges to build extra finish on those areas. Sanders and buffers can remove all the finish from the edges in the blink of an eye, and not being a pro finisher I play it safe.

Shilling for HF: https://www.harborfreight.com/34-in-5-i ... 57524.html

The young ospreys have flown the coop!

Same here I tend to ignore the "round over" at the edges until the very last.
It gets basically double everything else when I spray. With the water based I spray sides, wait 20 minutes, back, wait 20, top, wait 20.
The spray curls a bit around the edges.
I did this "rotation" 4 times (with the HP) and this gave me 2.8 thou dry. over about 1 - 1.5 thou base coat after leveling.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Colin North wrote:
" I did this "rotation" 4 times (with the HP) and this gave me 2.8 thou dry. over about 1 - 1.5 thou base coat after leveling"

Since I "pore fill" with epoxy I don't worry too much about finish thickness on the back and sides, as long as I don't think it is so thick it may cause the finish to "check". I do like to keep the finish thin on the soundboard and don't use epoxy or other sealers, just whatever top coat I am using on the rest of the guitar. I've never bothered to measure finish thicknesses, but I probably should. Nitro shrinks back over the first month or so, so I let it cure awhile before sanding and buffing.

P.S. Love the Osprey. Great pic.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Hi Colin,
When I took that picture the young birds were still in the nest, flapping their wings and getting a few feet in the air and coming back down on the nest. I came back a couple of days later and they had all left the nest. This is the second year I have been watching the parent birds. Last year they lost the one chick after a terrible thunderstorm. This year they raised two healthy young. It's nice to see the raptors making a come back. When I was a kid I kept and hunted with a red tailed hawk.

Now back to our regularly scheduled program.....