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Hollowing tools? - jaustin - 02-27-2017

I have been asked to try and make a hollowing tool, with the bent neck.
Trying to get some information on preferred designs since I have never owned or used one.

Are the hollowing tools better on a 3/8 bar or 1/2" bar?
Round or square?


RE: Hollowing tools? - chips ahoy - 02-27-2017

Go to the Lee Valley turning site and look at the Keltons.

Mel


RE: Hollowing tools? - Angus - 02-27-2017

bar size would be based on length of reach. Round or square is personal preference. i prefer round even on a hollower because it gives me the option of shhear scraping. You can do that with a flat bottom tool but it's a lot easier with a round.


RE: Hollowing tools? - MichaelMouse - 02-28-2017

How deep is the first consideration, how aggressive the second.  Either of those wants more stiffness as they increase. 

If you're making it, be a bit clever, and make a couple-three holders to fit into a shank.  That way you can file a flat on the holder for flat or shear scraping.  Round shafts roll, square won't tilt well, so some accommodation is in order.


RE: Hollowing tools? - jaustin - 02-28-2017

Thanks for the input.


RE: Hollowing tools? - MichaelS - 03-01-2017

Depending on what size you envision, what was asked for - you might consider some means by which it could be modular. Meaning, the keltons for ex can be attached to a larger D bar setup for even more impressive hollow vessel turning.

I always liked the approach that allows for a single, high quality tip set to be used in several scenarios.

Also, being able to roll the bar slightly depending on the distance out over the rest helps, so a round bar is my recommendation.

Really, I could have quoted MM w/ a +1
Smile, but figured I'd use some characters. He pretty much nailed it though.

Michael


RE: Hollowing tools? - Arlin Eastman - 03-01-2017

John

They can go from 3/8 to 3/4 depending on how far to the bottom it is.  I know that David Marks goes to 2" thick

I know that for small turnings like bird houses they use 1/4"


RE: Hollowing tools? - iclark - 03-02-2017

(02-27-2017, 09:57 PM)Angus Wrote: bar size would be based on length of reach. Round or square is personal preference. i prefer round even on a hollower because it gives me the option of shhear scraping. You can do that with a flat bottom tool but it's a lot easier with a round.

I have trouble wrapping my mind around shear scraping inside a hollow form.

I agree that the primary consideration for bar size is how far the cutting/scraping edge is beyond the tool rest.

The next consideration is how far the cutting/scraping edge left or right of the support point of the bar on the tool rest. The further the contact between tool and wood being cut is offset from the fulcrum, the more twisting torque there is on the tool bar. The thought of that torque/twisting moment when there is a catch is what has me rather chicken about using my Scorpion hollower. It is why I invested in an articulating arm hollowing system. Of course, I also have a set of the Easy Wood hollowers. I figure the worst that can happen with those is some blisters or skin loss if I get a truly horrendous catch on a big lathe.

So, for a bent neck tool with a square bar, you would prefer that the working part of the tool contact be within the width of the square bar on the tool rest.


RE: Hollowing tools? - Woodshop - 03-02-2017

(03-02-2017, 02:51 AM)iclark Wrote: I have trouble wrapping my mind around shear scraping inside a hollow form.

Segment work is usually all long grain where scraping works great for fine smoothing


RE: Hollowing tools? - iclark - 03-03-2017

(03-02-2017, 09:21 AM)Woodshop Wrote: Segment work is usually all long grain where scraping works great for fine smoothing

I get the scraping part - especially with drop-nose scrapers.

I can't seem to wrap my mind around the "shear" scraping part using a hollowing tool on a concave surface.

How do you get a shearing action by rotating about the long axis on the tool rest?