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Sanding Inside Hollow Forms

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I know this topic has come up before but the last thread I could find on it was eight years old so I thought I would bring it up again. How do you sand the inside of a hollow form? Something with an opening around 1.25 to 1.5" and 8" or more deep.

Maybe a better question would be how to do a good enough finish cut so that sanding is kept to a minimum?
 

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Alan Trout did a demo at SWAT last year and showed his method for making a ball on a dowel and then wrapping sandpaper around it. I don't recall exactly what he did, but my version which I used a few months ago is to wrap 3M Coban self adhesive bandage into a ball on one end of a dowel rod and then apply adhesive backed sandpaper to it. I had my own self adhesive sandpaper by using spray adhesive. I cut star shaped pieces out of the sandpaper sheets and then wrapped them around the ball. Most woodturners do not bother with sanding the interior of hollow forms. Never stick your fingers inside of any turning while it is spinning on the lathe. Just don't ask how I know that this is a bad thing to do. It takes years for finger injuries to heal.
 
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Jay,
When I make my finish cuts inside of a HF, I use a freshly-sharpened scraper tip turned to a 45 degree angle. That eliminates a lot of tear out and sanding. For sanding, I turned several balls of different diameters, drilled a hole and glued either a metal or wood rod into the hole, and glued some Velcro to the surface of the ball. Now, I can stick a hook-and-loop sanding pad to the ball.
 

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Many people do not sand inside hollow forms.

I do a series of southwest forms with large openings.

I don't sand the inside. I do use a teardrop scraper for my final wall thickness.

I do not want any ridges showing from the tools.

Once in a while I don't get the dead center bottom as smooth appearing as I want it.
This I sand to blend in with 2" discs with the sanding mandrel in a drill extender.
The sanding glove sells a really nice drill extender that has a supporting grip.
I use a gloved hand to steady the shaft.
Unsupported the drill extender shaft can wobble and damage the rim.

I've never had a bit of trouble selling my hollow forms or having them accepted into shows

Here are some photos of hollow forms not sanded on the inside.
They are 12 to 14" diameter. Openings are 2-3". The maple burl with the voids I bleached the inside.
Bleaching raises the grain a bit which softens the surface a bit.
I do not think sanding the inside adds anything but busy work.
I'd rather be turning another hollow form.

Al
 

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I agree with Al, the key to hollow form inside finish condition is to ALWAYS use sharp scrapers whether tear drop or not. Develop a light touch when hollowing, start to finish, then the final cuts won't require a lot of fine tuning. I used to sand the interiors of hollow forms but no longer, they do not need to match the outside finish.
 
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Al those hollow forms are fantastic. That is what aspire to be able to do one day. Do you hollow those free hand or with a captive hollowing system of some type?

A few people have mentioned using scrapers, can someone give some specifics on what brand? I'm assuming they are scraper that goes onto a bar of some sort and in order get. I bought the Harrison Simple Hollowing System which I just used for the first time. I was able to achieve a relatively uniform wall thickness but my finish cut was done with a round carbide bit so the surface was a little wavy.
 

hockenbery

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Al those hollow forms are fantastic. That is what aspire to be able to do one day. Do you hollow those free hand or with a captive hollowing system of some type? A few people have mentioned using scrapers, can someone give some specifics on what brand? I'm assuming they are scraper that goes onto a bar of some sort and in order get. I bought the Harrison Simple Hollowing System which I just used for the first time. I was able to achieve a relatively uniform wall thickness but my finish cut was done with a round carbide bit so the surface was a little wavy.

Jay,
I use a Jamieson handle a wooden backrest and a home made laser.

I have a bunch of hollowing bars. Trent Bosch bars that are the ones I use the most along with Stewart bars that hold my scraper bits. These are similar to the ones Trent sells see the picture.
A custom made CA Savoy bar that is 1 1/2" thick with 1/2 diameter tool holders for deeper forms is a pleasure to use too.
I often take this traveling as the one heavy bar is less weight than the 4 bars I would need to do the same job.

My hollowing cutters are high speed steel made from 3/16" square bits or 1/4" diameter round stock.
The scrapers are HSS steel or tantung

I do most of my hollowing through the face grain. So I avoid the carbides as the take so little wood per cut as compared to the 3/16 cutter ground down the leading side.
The carbides work well and probably about as fast on endgrain hollow forms where I take smaller cuts.

I learned hand held hollowing from David Ellsworth and do really small forms by hand but the captive system lets me use the scrapers so much more efficiently, less effort, better posture, and with the laser.
 

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Jay,
I use a Jamieson handle a wooden backrest and a home made laser.

I have a bunch of hollowing bars. Trent Bosch bars that are the ones I use the most along with Stewart bars that hold my scraper bits. These are similar to the ones Trent sells see the picture.
A custom made CA Savoy bar that is 1 1/2" thick with 1/2 diameter tool holders for deeper forms is a pleasure to use too.
I often take this traveling as the one heavy bar is less weight than the 4 bars I would need to do the same job.

My hollowing cutters are high speed steel made from 3/16" square bits or 1/4" diameter round stock.
The scrapers are HSS steel or tantung

I do most of my hollowing through the face grain. So I avoid the carbides as the take so little wood per cut as compared to the 3/16 cutter ground down the leading side.
The carbides work well and probably about as fast on endgrain hollow forms where I take smaller cuts.

I learned hand held hollowing from David Ellsworth and do really small forms by hand but the captive system lets me use the scrapers so much more efficiently, less effort, better posture, and with the laser.


Al, if you don't I'm going derail this thread a little. I looked up the Trent Bosch hollowing tools and I am intrigued by them. The prices of his tools seem exceptionally affordable, and I like the fact they don't use carbide inserts. I do have a few questions that are not real clear on his website.

I am looking at the set of three 5/8 hollowing bars. 1) How deep can you hollow with this set? 2) How are the cutters changed out? He mentions no set screws so are they soldered in? 3) How do you sharpen the bits?
 

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... I am looking at the set of three 5/8 hollowing bars. 1) How deep can you hollow with this set? 2) How are the cutters changed out? He mentions no set screws so are they soldered in? 3) How do you sharpen the bits?

I have Trent Bosch's hollowing tools so I can give my opinion of them. I would say that you could use them to a depth of about 8 inches or maybe slightly more if you are experienced enough, but this is dependent upon the diameter. Diameter is actually more of a critical factor than the depth.

The cutters are just pieces of square HSS bar stock. You sharpen it on a grinder just like you would any other tool. They are glued in place with CA, If you need to replace a cutter, just apply some heat to the glue joint to melt the CA. I have had the tools for a few years and have not needed to replace a cutter yet, but I also do not make a large number of hollow forms.
 

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Al, if you don't I'm going derail this thread a little. I looked up the Trent Bosch hollowing tools and I am intrigued by them. The prices of his tools seem exceptionally affordable, and I like the fact they don't use carbide inserts. I do have a few questions that are not real clear on his website. I am looking at the set of three 5/8 hollowing bars. 1) How deep can you hollow with this set? 2) How are the cutters changed out? He mentions no set screws so are they soldered in? 3) How do you sharpen the bits?

Bill covered your questions except I do something a bit different when I sharpen. I sharpen the tip right at the edged of the wheel and then use the edge of the wheel to sharpen the side of the cutter. When I dress my wheel I dress the corner just a bit too. So the tool shaft does not move much so holing it is not a burden. Just rotate the body a bit and lean forward.

I have never had a CA glued tip come out for me or a student. I did see a CA tip come out during one of our club members demos.
I have has set screws come loose, I've lost set screws, I've stripped the sockets of set screws. I have some hollowing tools that use set screws to hold the tips and I still use them when they are the right tool.

To replace the tip. Heat with a torch it breaks the CA Glue. Often the gas from the glue will pop the worn tip. Otherwise I grab it with vice grips and twist.
Clean out the hole with a drill bit in my hand. I use thick CA on the new tip and a tiny bit in the hole. The new tip has to go as deep,in the hole as it can.
Then be sure to turn the tip so that the top of the cutter is parallel with the top of bar. A slanted cutter only cuts in the direction of the slant and gets a catch going the other way.

The diameter of the bar determines how far over the tool rest you can work.
8" over the tool rest is usually the limit for a 3/4" or 5/8" bar.

Have fun,
Al
 
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Bill Boehme

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... I sharpen the tip right at the edged of the wheel and then use the edge of the wheel to sharpen the side of the cutter...

Thanks for mentioning that bit of information, Al. That is the way that Trent showed me to sharpen the sides of the cutter. The cutter needs to have a rounded nose and be slightly undercut to give the side bevel some clearance from the wood. Sharpening is a delicate operation that only requires just a very quick and feather-light touch to the wheel. Because of its small size, it is very easy to needlessly grind away too much material.

BTW, Trent suggests removing the tool from the handle to make it easier to do a smooth sweeping curve without having to deal with the handle getting in the way.
 
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Unlike some others I do sand as far as a finger will reach in a form. We are talking 7/8ths opening. But if the finger will go in I sand. I will not sand if anything can grab a finger. I use psa paper and only enough that sticks on one surface of the finger. Anymore and I get scared so dont do it. So minimum amount of paper. Nothing to catch the finger and no more than 500 rpm. I do forward and reverse. Every woodturner first thing is they stick a finger in your vessel. But the rest even with big open bark pockets, nothing but tool marks. I can still count to ten. That should be every turners goal at the end of the day. So dont do something if you are not comfortable doing so.
 
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For depth of an inch or two, I wrap sandpaper around plastic tubing, taping the inboard end. I insert a screwdriver shank or wood dowel to stiffen the tubing.

I can also count to ten without removing my shoes.
 
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HI Jay.

Not sure how this fits with your question but when I want the inside of a Hollow Form sanded, which I usually don't pay too much attention to, I try to get as even a finish as I can with my tools then I turn to this cobbled up apparatus.
IMG_3001.jpg
It's driven by a BBQ motor, the Hollow Form has some broken tempered glass in it. I get the glass, which is from a side window of an automobile, from our local glass shop. One small bucket lasts me a very long time.

I usually leave it running for about 5 days so one needs extra chucks but it seems to work pretty well.

It's not my original idea. I read about it on one of these Forums.
 

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HI Jay.

Not sure how this fits with your question but when I want the inside of a Hollow Form sanded, which I usually don't pay too much attention to, I try to get as even a finish as I can with my tools then I turn to this cobbled up apparatus.
View attachment 7442
It's driven by a BBQ motor, the Hollow Form has some broken tempered glass in it. I get the glass, which is from a side window of an automobile, from our local glass shop. One small bucket lasts me a very long time.

I usually leave it running for about 5 days so one needs extra chucks but it seems to work pretty well.

It's not my original idea. I read about it on one of these Forums.

Pete, a few questions If you don't mind?

How smooth is the interior when you stop? And is the glass small chunks or do you crush it or how large would you say the pieces are?
What speed does this run at? Is it a rotisserie type motor?

Many thanks! Mark
 

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.... It's driven by a BBQ motor, the Hollow Form has some broken tempered glass in it. I get the glass, which is from a side window of an automobile, from our local glass shop. One small bucket lasts me a very long time....

Cool idea. I just happened to have a rotisserie motor looking for a purpose. I used to use it on a coil winding fixture for winding transformers back in the good old days when hams built their own rigs. It was packed away in an old box for probably forty years and I unearthed it a couple months ago while digging through stuff cluttering the garage.

One question is what would be the best way to separate all of the wood dust from the glass when you are finished tumbling?

Mark, this sounds very similar to a rock tumbler if you are familiar with the way that they work. I would guess that trying to crush or break up the glass any further than it already is would be a messy job at best. Tempered glass does not break into large pieces like standard glass does -- it tends to break into small pebble size pieces.
 

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Cool idea. I just happened to have a rotisserie motor looking for a purpose. I used to use it on a coil winding fixture for winding transformers back in the good old days when hams built their own rigs. It was packed away in an old box for probably forty years and I unearthed it a couple months ago while digging through stuff cluttering the garage.

One question is what would be the best way to separate all of the wood dust from the glass when you are finished tumbling?

Mark, this sounds very similar to a rock tumbler if you are familiar with the way that they work. I would guess that trying to crush or break up the glass any further than it already is would be a messy job at best. Tempered glass does not break into large pieces like standard glass does -- it tends to break into small pebble size pieces.

Bill,

That's exactly what I was thinking - a rock tumbler. I was wondering about the size of the pieces because I happen to have a friend with an auto glass shop and his shop is literally across the street from me (and endless supply of glass). It seems though that the larger pieces might leave scars don't you think? I have access to a 20 ton forklift and some plate steel. I was considering just driving over a sandwich of glass and plate steel.

Okay, if that sounds ridiculous - and it well might to someone with common sense - please advise me on the folly of this idea.
 

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.... Okay, if that sounds ridiculous - and it well might to someone with common sense - please advise me on the folly of this idea.

You need to get more serious -- a crawler crane is what you need.

I figured that if five days of tumbling were needed then the size of individual particles of glass probably do not have much effect. I would guess that the force is on the order of an ounce -- a rotisserie turns very slowly -- mine takes about 12 seconds to make one revolution so I would guess that after five days the effect of all of the particles averages out to a uniform surface.
 
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actually, tempered glass should only break into a definitive size, that's how they tell if it is tempered to specs or not
(I used to be a glazier in a younger life)
Usually, it's roughly 1/4" sized pieces that meets specs, that, and the smaller you try to make it, will only succeed in crushing it into a powder.
You can pound the center of it until blue in the face and nothing will happen
but a light tap on any outer edge will instantly shatter the whole thing ........

the concept of using it to sand/smooth the inside of a vessel is a novel one, and sounds pretty cool
would be interested in seeing an image of what the end results are.
 
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This "rock tumbler" idea sounds very intriguing. Should be easy enough to experiment with, I think I have an old rotisserie motor laying around as well.

I had a plumber friend once tell me the best way to clean a garbage disposer was to shove a glass coke bottle down it. Never had the guts to try it but I suppose a similar concept just done a whole faster :D
 
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Bill Boehme

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This "rock tumbler" idea sounds very intriguing. Should be easy enough to experiment with, I think I have an old rotisserie motor laying around as well.

I had a plumber friend once tell me the best way to clean a garbage disposer was to shove a glass coke bottle down it. Never had the guts to try it but I suppose a similar concept just done a whole faster :D

Did the plumber have a side business selling garbage disposals? :rolleyes:
 

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You need to get more serious -- a crawler crane is what you need.

I figured that if five days of tumbling were needed then the size of individual particles of glass probably do not have much effect. I would guess that the force is on the order of an ounce -- a rotisserie turns very slowly -- mine takes about 12 seconds to make one revolution so I would guess that after five days the effect of all of the particles averages out to a uniform surface.

Bill, you sound like Tim the Toolman Taylor there :D

I take your point. In fact, probably with such slow revolutions the mass of a larger particle is needed to do the job.
 

Mark Hepburn

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actually, tempered glass should only break into a definitive size, that's how they tell if it is tempered to specs or not
(I used to be a glazier in a younger life)
Usually, it's roughly 1/4" sized pieces that meets specs, that, and the smaller you try to make it, will only succeed in crushing it into a powder.
You can pound the center of it until blue in the face and nothing will happen
but a light tap on any outer edge will instantly shatter the whole thing ........

the concept of using it to sand/smooth the inside of a vessel is a novel one, and sounds pretty cool
would be interested in seeing an image of what the end results are.

Thanks Jerry. You're a man with many hats, aren't you?:)

Okay, so I'm in. Gonna make some sort of rig to try it out. I have an old squirrel cage blower motor (kidding). Well, actually I do have that fan assembly but I'm planning to make a shop exhaust out of it.
 

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:D

I don't have the guts to try it either.

In glass working, you can make frit by feeding chunks of sheet glass through a dedicated garbage disposal into a vessel that also has vacuum to suck out the glass dust. But then the issue is getting out the metal particles before casting. Not so much an issue here, but you could use frit, which is readily available in graded sizes, to use on the inside for this. The frit is made up of glass that isn't safety or tempered, so it would have a more jagged edge. Perhaps a better quality in this case.

As to how to get the wood dust out, a light spray of compressed air would work with the glass in a colander with a little agitation. Too much air and everything is airborne, so lower PSI would be better.
The other option is using ceramic beads like in rock tumbling.
 
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Try the "Toothy Scraper"

Al,
You do great stuff - in response to your comment "I do not want tool ridges to show", you might find the following of interest as will anyone doing larger works:

Before going to the "dark side", I built some custom furniture - anyone doing that type of work is familiar with chisels and, of course, hand planes. I noticed Lie-Nielsen offers "toothed blades" for their bench and block planes - these offer faster stock removal than smooth blades.

When I went to the "dark side" and started doing the large hollow forms, removing tool marks, tool ridges and general high spots was an issue - I needed a tool easy to control (not self feeding), not too aggressive, but able to take shavings. Not being a scraper fan, I:
- took a inch-wide wire stripper blade,
- put a radius on it,
- slotted the back
- cut a 10-degree taper on a long piece of drill-rod
- tapped the middle of the taper with a #10-32 to mount the little wire stripper blade
Nothing special so far - just another angled scraper - no big deal.
- took a dremel with a cut-off cutter and made about a 1/32" deep score about every 1/8" to 1/16" across the radius

I now have the ability to "sand" with an 8-grit sharpenable cutter. The corners of each tooth cuts like crazy as you sweep across while the flats of each tooth keep it reasonably smooth. I have experimented with rolling a burr - jury still out if that is significant.

You can score any scraper blade and try it out - please post the results.
Thanks,
John
 
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Pete, a few questions If you don't mind?

How smooth is the interior when you stop? And is the glass small chunks or do you crush it or how large would you say the pieces are?
What speed does this run at? Is it a rotisserie type motor?

Many thanks! Mark
Hi Mark.
I see this thread has really taken off.
Yes it is a rotisserie motor. It is pretty cool cause it seems to be able to run for days without overheating.
The tempered glass breaks into small pieces about 1/4 to 3/8 chunks that fit easily into most of my medium size or larger vessels.
 

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Hi Mark.
I see this thread has really taken off.
Yes it is a rotisserie motor. It is pretty cool cause it seems to be able to run for days without overheating.
The tempered glass breaks into small pieces about 1/4 to 3/8 chunks that fit easily into most of my medium size or larger vessels.

Hey Pete. Yes it has taken off and for good reason. It's a great idea. I really like the idea of being able to have a smooth interior that is of good quality regardless of opening size. It appeals to me (and apparently, many others) to know the inside is well done, even if no one else can tell.

Thanks again!
 
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sanding hf

I wrap paper around a hemostat. You can get them in several lengths and they fit a small hole nicely. Since they lock the paper stays put.
 
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Tumble sanding

Cool idea. I just happened to have a rotisserie motor looking for a purpose. I used to use it on a coil winding fixture for winding transformers back in the good old days when hams built their own rigs. It was packed away in an old box for probably forty years and I unearthed it a couple months ago while digging through stuff cluttering the garage.

One question is what would be the best way to separate all of the wood dust from the glass when you are finished tumbling?

Mark, this sounds very similar to a rock tumbler if you are familiar with the way that they work. I would guess that trying to crush or break up the glass any further than it already is would be a messy job at best. Tempered glass does not break into large pieces like standard glass does -- it tends to break into small pebble size pieces.
Hi Bill. The glass is so cheap(read free) and I use so little I just toss it all away each time. I also believe that the really sharp edges get tumbled off as the work goes on.
 
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Tumble sanding

actually, tempered glass should only break into a definitive size, that's how they tell if it is tempered to specs or not
(I used to be a glazier in a younger life)
Usually, it's roughly 1/4" sized pieces that meets specs, that, and the smaller you try to make it, will only succeed in crushing it into a powder.
You can pound the center of it until blue in the face and nothing will happen
but a light tap on any outer edge will instantly shatter the whole thing ........

the concept of using it to sand/smooth the inside of a vessel is a novel one, and sounds pretty cool
would be interested in seeing an image of what the end results are.

Hi Jerry. With all the interest today I will embark on an attempt to demonstrate this sanding technique.
I am going to make 4 small hollow forms. Actually they will be square on the outside and holed on the inside. I will try to use identical techniques and sharpen my tools the same for each. I will then cut one in half, and after a week of tumbling cut another and after 2 weeks another then decide if I need to to the fourth at 3 weeks. I'll post the results but as you can see it won't be for a while.
 
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Serrated Cutter

Al,
You do great stuff - in response to your comment "I do not want tool ridges to show", you might find the following of interest as will anyone doing larger works:

Before going to the "dark side", I built some custom furniture - anyone doing that type of work is familiar with chisels and, of course, hand planes. I noticed Lie-Nielsen offers "toothed blades" for their bench and block planes - these offer faster stock removal than smooth blades.

When I went to the "dark side" and started doing the large hollow forms, removing tool marks, tool ridges and general high spots was an issue - I needed a tool easy to control (not self feeding), not too aggressive, but able to take shavings. Not being a scraper fan, I:
- took a inch-wide wire stripper blade,
- put a radius on it,
- slotted the back
- cut a 10-degree taper on a long piece of drill-rod
- tapped the middle of the taper with a #10-32 to mount the little wire stripper blade
Nothing special so far - just another angled scraper - no big deal.
- took a dremel with a cut-off cutter and made about a 1/32" deep score about every 1/8" to 1/16" across the radius

I now have the ability to "sand" with an 8-grit sharpenable cutter. The corners of each tooth cuts like crazy as you sweep across while the flats of each tooth keep it reasonably smooth. I have experimented with rolling a burr - jury still out if that is significant.

You can score any scraper blade and try it out - please post the results.
Thanks,
John
John, any chance you could show us a few photos? I am the sort that needs to see things to be able to actually determine exactly what it is.
 
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Hi Jerry. With all the interest today I will embark on an attempt to demonstrate this sanding technique.
I am going to make 4 small hollow forms. Actually they will be square on the outside and holed on the inside. I will try to use identical techniques and sharpen my tools the same for each. I will then cut one in half, and after a week of tumbling cut another and after 2 weeks another then decide if I need to to the fourth at 3 weeks. I'll post the results but as you can see it won't be for a while.

Pete,

This is great, I can't wait to see the results. I was going to try this myself (and still will at some point), but now that the weather is nice my turning time is very limited so it would likely be fall until I get to experiment with this.

I can't wait to see the results.
 

Bill Boehme

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The serrated cutter discussion reminded me of recently using carving rasps on the inside of a vase. The set that I have is the very cheap kind made in China and not very suitable for use with carving because of their roughness. They have an elongated S shape sort of like this:
I wanted to create the slightly fine ridged look of a hand made pottery vase on the interior and the rasps were just the thing to make the scratch pattern that I wanted. The lathe needs to be running very slowly in case the force pulls the rasp out of your hand. The interior was then finished with stone texture paint. To prevent blow-back, I had the vase open at both ends. Please don't ask how I know about spraying paint into a closed container.
 
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Pete, that is absolutely above and beyond what anyone could ask for, and truly appreciated :)
I wouldn't go to the extreme of cutting 4 in half and wasting all that wood and time, maybe just 1 or 2 at most
I'm just curious as to what the final finish is after the tumbling.........
I know rocks and ball bearings work on other things with this procedure, never thought about glass
And like others, whether anyone else sees or notices, I want to know my insides are as smooth and clean as possible ;)

Hi Jerry. With all the interest today I will embark on an attempt to demonstrate this sanding technique.
I am going to make 4 small hollow forms. Actually they will be square on the outside and holed on the inside. I will try to use identical techniques and sharpen my tools the same for each. I will then cut one in half, and after a week of tumbling cut another and after 2 weeks another then decide if I need to to the fourth at 3 weeks. I'll post the results but as you can see it won't be for a while.
 

Mark Hepburn

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Pete,

Looking forward to the demo! Many thanks,

Mark:)
 
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Pete, that is absolutely above and beyond what anyone could ask for, and truly appreciated :)
I wouldn't go to the extreme of cutting 4 in half and wasting all that wood and time, maybe just 1 or 2 at most
I'm just curious as to what the final finish is after the tumbling.........
I know rocks and ball bearings work on other things with this procedure, never thought about glass
And like others, whether anyone else sees or notices, I want to know my insides are as smooth and clean as possible ;)

James Krenov talks about this in his book "A Woodworker's Notebook" that a true craftsman spends as much time and effort on those parts that are not seen as he does on the parts that are seen. I will never be 10% of the craftsman he was but I do strive to do my best even on those areas that won't be seen or touched.
 
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Quick update.
My small BBQ motor packed it in yesterday. It was making one revolution every 10 seconds which seemed to work really well. I have grabbed the one from my Webber which turns on rev every 20 seconds. When thinking about this I believe the rev time is a more important factor than the actual days it turns. I have started the process on a hollow form but will report on the number of revolutions/day rather than just the days. I know some of you were talking about using a Rock Tumbler which I'm certain has a different speed so I think it may be easier to calculate the required time if you know revolutions instead of days.
The wood I am using is air dried birch. Not as hard as some but should give a pretty good idea. I am also toying with the idea of using one of those cameras that are on the end of a flexible tube so I might be able to see results without actually having to cut, saving me time and material.
 
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Alternative

Personally, I couldn't care much less about the interior "finish" except in very rare instances. I did, however, run into a guy with a nifty system for smoothing the inside walls. He would put several pounds of marbles and carborundum granules, say 100-120 grit, into his vessel, then clamp it into a jig similar to a rock tumbler that ran off a 1/8 hp motor, and just let the thing rotate for a day or two. Inside surface felt like a newborn's butt!

Holes or voids got "sealed" with tape and some shrink-wrap.

I'm sure the "finger-stickers" loved his stuff.
 
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