The Inner Bottom of Deep Vessels - What do you do?

[Matt Hutchinson]

Ok, so as I'm working on my big cherry vase, I started to wonder how in the world I was going to get a reasonably smooth bottom on the inside. Not only will I be working about 3.5 feet beyond the tool rest, but the rpms are at 110. So any suggestions on how to achieve a smooth center with no bump?

Of course, worse case scenario is me with a shop made extension for my sanding pads using ultra course sandpaper, but I want to do as little of that as possible.

Thanks all!

Hutch

 

[n7bsn]

How you could get the following to work, I dono...

What I learned was to bore a hole first. Using a 1-inch speed (spade) bit, ground such that it's a simple smooth curve (probably only is actually cutting with one side). What this really is is a "scraper" that started life as a drill-bit

I do this first, bore down the center of the vessel, to the very bottom (using a mark on the drill shaft).

Then, when I get the hollowing down to the area where the bit finished the bottom, all I do is smooth the transition from the "tool" worked area to the "drill" worked area.

TTFN
Ralph

 

[Charles Henderson]

I don't have experience with anything near that deep, but I would suggest a forstner bit with the point ground off. That's what I use to start all my forms. However, fashioning a 3.5' extension will be a project.

 

[Richard Baker]

Of course, worse case scenario is me with a shop made extension for my sanding pads using ultra course sandpaper.

Make really smooth finish cut and swap tool bit for a sanding disc?

 

[john lucas]

OK I've never done anything that deep. However I love using a Hunter tool to finish off the bottoms on vessels that have a very narrow opening or have a square small bottom. They have a very steep bevel. I turn the cutter so it faces the center and then cut from the outside toward the middle. It's very easy to get the center nub out and it is a cut rather than scrape so you really don't need to do any sanding. It would not be hard to mount a Hunter #1 on the end of one of your bars.

 

[Matt Hutchinson]

Interesting ideas. Hm. Right now I have a round carbide cutter that I played with a little bit today. I could get it to do a reasonable job, except for a dime sized area right in the center, and that was only 16" over the tool rest. Tomorrow I will have to give it a little more concerted effort and see how far I can get.

Hutch

 

[john lucas]

Matt I tilt the tool so it goes from about 11 oclock to 5 oclock with the cutting edge pointed toward the middle. You have to find the sweet spot where it rubs the bevel. You can get buy without rubbing the bevel but you have to take really light cuts. I normally use a #5 or #4 hunter but the number 1 would also work and might be easier to mount on the end of a bar.

 

[MichaelMouse]

Try this mental picture of what you want to do. The Hunter tool and ring/hook tools are really gouges at right angles to the shaft. As John says, support the tool outside the nub and perhaps rotate the top a touch left and cut as if you could get the world's shortest-handled gouge in there.

 

[Matt Hutchinson]

I was out in the shop making some final hollowing cuts on the foot this morning, and the carbide cutter just couldn't get rid of the nipple in the center. It couldn't stay tracking, but I also may not have been exactly at center height. IT was hard to tell at that depth.

Hutch

 

[Barry Elder]

Why not just fill the bottom of the vase? with epoxy until it covers the nub.

 

[Matt Hutchinson]

HA! Nice one....

Actually, it's not like anyone will be able to see it without a flashlight.....

Hutch

 

[john lucas]

Paint the bottom black. Then they for sure won't see it.

 

[Eliot Feldman]

bottom of deep vessel

Here's a method that I believe originates with me and it often works nicely: Use one of those hollowing tools that are curved to the left (e.g. the John Jordon style tool). Now, REVERSE the direction of the lathe ,and cut from right to left into the center nub.

 

[Neil S]

At that depth I'd be scraping to finish with something like a big Oland.

.....

 

[Matt Hutchinson]

Scraping was my initial thought. Unfortunately, every attempt I made at only 14" over the rest didn't work. Again, my technique or tool choice could have played a factor, but at the slow rpms (110 rpms) I could not get it to bite.

I think I will practice different approaches on my other lathe, specifically a smaller radius scraper.....give it a little more bite.

Hutch

 

[glenkey]

Matt,
Here in Tulsa we have a place named Wholesale Tool. You can purchase raw material to make your own borring bars. Get a piece of drill stem in the 1" to 2" diameter and whatever lenght drill it out to accept your tool bit. Add a capture rest and go to work. Doesn't have to be elabrate, just functional.

 

[Matt Hutchinson]

I have actually done just that. I have a couple large boring bars and cutters that I just made, along with a few insertable "cutter heads". I have a 3/16" cobalt cutter that I haven't used for anything yet. That may be my next attempt.

As you can tell, I am flying by the seat of my pants on this one. Never done any deep hollowing, so I have been making a new tool every time I make one that doesn't work quite like I need it to. By the time all is said and done I will have a great selection of hollowing tools that will work for a multitude of hollowing needs.

Hutch

 

[Mr. Don]

deep

If you are going that deep, I would go as stated above, do the best you can do, then dribble in a bit of epoxy to smooth out. It ain't like they are going to put a finger on the bottom, and if they shine a light in, it will be shiny. You do raise some very good questions. This is a learning curve for all of us!!!:cool2:

 

[Neil S]

Scraping was my initial thought. Unfortunately, every attempt I made at only 14" over the rest didn't work. Again, my technique or tool choice could have played a factor, but at the slow rpms (110 rpms) I could not get it to bite.

I'm out of my depth, literally, on this one so please take anything I have said, or will say, with caution as I have only hollowed to about 18".... less than half the depth you are going to.

When scraping at 18" depth I've needed every bit of rigidity and weight provided by a solid 1" diam stainless steel bar. If you are going twice as deep I would be thinking 1.5" to 2". That's going to be a heavy bit of steel. Final cuts are done with top face of cutter at about 1 o'clock and working from centre out (a light shear scrape). I hollow freehand so you may have to adapt for a captured system.

Here is my big Oland (Ripsnorter) and tip. The tip is about 1/2" HSS.





A modification of your drill bit could produce a suitable scraping tip. If you are starting to get catch-ettes, adding a positive rake to the top face of the scraper tip might help get you through the most challenging last bit without a full on catch.

I'd be pre-drilling to the final depth to at least have that advantage.

BTW - there is no rule to say that the thickness of the sides has to be the same all the way down. After about 24" depth (the length of the average arm) you can make up your own rules.....

.....

 

[hughie]

If your going to do a lot of this sort of turning I would suggested custom built tool rest that will reach in and give way less over hang.
They are not hard to build or get built, basically its a long version of a Irons Tool Gate rest.
I have one I made for a few deep vases although not as deep as yours.

 

[Joe Greiner]

+1 for hughie's suggestion. To reach that deep, you need maximum stiffness at minimum overhang.

To get a "handle" on what's going on there, I suggest making some practice cuts on a shallow (or even zero depth) workpiece, with the tool rest far from the working point - easier to see the action. Also, a bowl gouge can work like a spoon bit (old time woodworking) with the cutting edge of the flute at 3 o'clock vertical and sweeping across to 9 o'clock, to slice off the nub. Oland tool the same way.

 

[Matt Hutchinson]

Actually, and extended rest is what I had planned on using. I attached a picture of my hollowing rest. It's quite solid, but the extension arm just doesn't have the rigidity I thought it would. It's "apparently" very rigid, but when I put it to use, it transferred vibration at the cutter VERY easily. I switched over to a regular tool rest, and my problems ceased. SO, I may not be able to shorten the overhang of the boring bar. Rather, I would have to have a new, stronger, shorter extension made. Even than, the boring bar probably would have too much leverage.

In any case, I like the idea of the Oland tool style cutter. The cobalt cutter I mentioned earlier is right in that vein.

Hutch

Photo: The boring bar shown is 6 feet long and 1.375" diam. I have another one that's 1.625" diameter and 10 feet long.

 

[Neil S]

Photo: The boring bar shown is 6 feet long and 1.375" diam. I have another one that's 1.625" diameter and 10 feet long.

That largest boring bar might do it.... if you can lift it....

Reckon I can see from that photo the weak point in your rig. The forward rest (outrigger) is too fragile for what you are asking of it. Looks like it is constructed from square section steel and far too extended for the task.

I'd dispense with that and, as Hughie suggests, build a more substantial support attached to your Banjo which can be positioned right next to the entry point and reach into the piece. A hefty 9" (maybe 12") extension from the tool post might do it. I assume from the size of your lathe you will have a substantial tool post to work off.

The capture end of your rest could still be used with this setup.

As said before, I'm out of my depth on this one Matt and just tossing ideas about for your consideration in case any of them help.

....

 

[hughie]

To get a "handle" on what's going on there, I suggest making some practice cuts on a shallow (or even zero depth) workpiece, with the tool rest far from the working point - easier to see the action. Also, a bowl gouge can work like a spoon bit (old time woodworking) with the cutting edge of the flute at 3 o'clock vertical and sweeping across to 9 o'clock, to slice off the nub. Oland tool the same way.

Now thats a darn good idea, never thought of that A simple way to watch whats going on before you get to the far off bottom.