Wood moves ---> rim problem. Fix?

[Jamie Straw]

Still working on the 10" x 3" Madrone bowl (dry). Went to soften the outer edge of the rim, and things were uneven -- evidently, the wood released some tension and the outside is no longer round. Pics below show position A, then some rotation to position B. Unfortunately, I had already sanded the outside of the bowl to 600. How can I fix, or disguise, this asymmetry? I tried just taking the rim down a bit, not sure it helped. (PS: I suppose there could be a "seating in the chuck" problem? I original mounted it with screw-chuck arrangement in Nova G#, turned the outside and tenon, then mounted in Oneway Talon to do the inside. The shoulder above the tenon is snuggly up to the top of the jaws.)

 

[robo hippy]

Guess that stuff moves a lot even when dry.... Only stable 'dry' madrone I ever worked was dried in a vacuum kiln. For that one, you could use a thin parting tool, and part it off at or near the low spot, using a slow speed on the lathe so when you go through unevenly, the chunks don't bonk you, then sand the rim detail/round over while slowly spinning, or take it as it is and hand sand a round rim on the other half. Slight variation won't show..

robo hippy

 

[Fred Belknap]

Jamie I suspect your problem is the wood. I use the Talon and Stronghold Oneway chucks and when I mount a bowl in the chuck I use the ram on the tailstock to put pressure on the bowl. I was having the problem of a shadow or ghost when I reversed the bowl. I leave a flat for the face of the jaws to rest on, it has pretty much solved my ghost problem.

 

[Jamie Straw]

Jamie I suspect your problem is the wood. I use the Talon and Stronghold Oneway chucks and when I mount a bowl in the chuck I use the ram on the tailstock to put pressure on the bowl. I was having the problem of a shadow or ghost when I reversed the bowl. I leave a flat for the face of the jaws to rest on, it has pretty much solved my ghost problem.

I always leave a flat ("shoulder" in the original post). I was using the tailstock for the first third or so of the hollowing. Seems like wood that resides in the shop tends to settle around 12%-14%, so it well could be the wood.

 

[hockenbery]

Jaime if it is just a 1/16" and the bowl is going to be 3/8" thick, no one but you will notice.

Whenever I plan to do a thin wall. I true the outside of the bowl when it is in the chuck.
If I think there could be tension movement, I hollow a bit before truing the outside.

 

[Jamie Straw]

Jamie (Edited) if it is just a 1/16" and the bowl is going to be 3/8" thick, no one but you will notice.

Whenever I plan to do a thin wall. I true the outside of the bowl when it is in the chuck.
If I think there could be tension movement, I hollow a bit before truing the outside.

The way it sits at this moment, it would be noticeable because the rim is sharp over about 30% of the circumference. I had enough thickness to true the outside when I posted, but I think not the skill to turn while mounted "backwards." After I posted, I turned more of the inside, to get close to final shape and thickness. Will have to do the hand sanding thing.

 

[Bill Boehme]

Nobody besides you will know that you cut the rim down a bit to get it level. Sanding will also work if you do it carefully and keep a crisp edge.

 

[Jamie Straw]

Jaime if it is just a 1/16" and the bowl is going to be 3/8" thick, no one but you will notice.

Whenever I plan to do a thin wall. I true the outside of the bowl when it is in the chuck.
If I think there could be tension movement, I hollow a bit before truing the outside.

Al, I will remember this, even if it's not to be a thin wall! This is the second bowl I've had this happen with, and it really gives me problems with sanding, plus the rim problem if I try to shape the rim. Do you true mostly by using a shear (sheer) cut or scrape? I turn into all thumbs when thinking about cutting the outside of a bowl in that orientation (in the chuck via tenon).

 

[Jamie Straw]

Nobody besides you will know that you cut the rim down a bit to get it level. Sanding will also work if you do it carefully and keep a crisp edge.

I chickened out on cutting it down -- hand-sanded the rim, but to a soft edge, so may not be great. It's all sanded, and ready to finish the foot. Minor problem, that. The bowl is too big for my Cole jaws. Will take it over to Mr. Powermatic's shop this week and finish it. Have no idea why I ordered Mini-jumbo jaws instead of Jumbo back in February. Sheesh. Seasonal affective disorder yielding small expectations? Oh, well.

 

[hockenbery]

Al, I will remember this, even if it's not to be a thin wall! This is the second bowl I've had this happen with, and it really gives me problems with sanding, plus the rim problem if I try to shape the rim. Do you true mostly by using a shear (sheer) cut or scrape? I turn into all thumbs when thinking about cutting the outside of a bowl in that orientation (in the chuck via tenon).

1.With a dry bowl. I begin by jamb chucking it over the Chuck with the tail stock center point in the. Middle of the tenon. I adjust the two high and two low points to be equidistant from the headstock by loose in g the tailstock and shifting where the bowl sit on the Chuck keeping the tail center in place in the tenon. This seems to require 3'hands but it get pretty easy with practice. This gets the warped bowl the most balanced with the waynitnwas when green.

2.I now cut the rim flat. Gouge is level cut direction is parallel to the ways. On some lathe I have my left leg on the outboard side of the legs. I take a series of cuts 3/16 to a 1/4" wide until I have the rim flat. Each cut begins with the bevel edge cutting parallel to the ways the just as it meets the last cut roll into a scrap and pull the gouge across the previous cut area leveling the surface.

3. Once the rim is level, I true the tenon to round. My #2 jaws close to 2" so I turn all my rough out tenons 2.5" diameter. Haven't found any that don't have a 2" diameter dry tenon in them.

4. Then turn the outside if the bowl foot to rim. Light cuts following the curve of the dried bowl. Once round, if It will be a thin walled bowl I put it in the Chuck. If it will be 1/2 wall or more i finish turn the outside. Bevel riding cuts to smooth the curve ( pull cut works real well, bevel riding push cut works too), shear scrape with the gouge, and sand to 220.

5. Put the bowl in the Chuck. I Get the jaws almost tight push the bowl against the Chuck with my hand in the inside bottom. I rotate the bowl a bit back and forth to be sure it is against the tops of the jaws then tighten the Chuck until it just rim against the tenon. Then I run the lathe slowly to check for the bowl running on center. 80-90% of the time they run true and sweet. I use my finger to test for a bounce. If I feel none or a tinny a tiny one I tighten the Chuck.

6. If I'm getting an unwanted bounce I can usually make a bowl run truer by trying a few different things. loosen the chuck and turn the bowl a bit and tighten to firm. Find the high side of the bowl where it come closer to the tool rest and give it wacky with the gouge handle. It might be worth returning the tenon. When I get is good as I can I tighten the Chuck.

7. Truing the outside. I cut from foot ( spot where I can make bevel contact) to rim with a bevel riding push cut or a pull cut. These are light finishing cut with light bevel pressure. "Ride the wave" . I stand close to the headstock often my left foot will be on headstock side of the lathe base. There will be a small area near the foot where you cannot make bevel contact. This can be blended in with shear scrapping, scraping, a spindle forge cutting the wrong way toward the tenon. The advance flut up shear cutting the wrong way. Shear scrap the outside Sand to 220

8. finish turn the rim. I use a light bevel riding push cuts across the top of the rim from outside the bowl to the air inside. This may take 4-5 passes to smooth the rim. I shear scrap the rim but I advise newer turns to skip the shear cut on the rim. A slight miss move and you get a big catch. Once you get good at shear scraping you just start shear scraping the rim. Then same the rim to 220.

9. Hollow the bowl.sand the inside to 220. Then sand the whole bowl with 320

Jamb chukmwithna pad and turn off the bottom.

 

[Hy Tran]

I chickened out on cutting it down -- hand-sanded the rim, but to a soft edge, so may not be great. It's all sanded, and ready to finish the foot. Minor problem, that. The bowl is too big for my Cole jaws. Will take it over to Mr. Powermatic's shop this week and finish it. Have no idea why I ordered Mini-jumbo jaws instead of Jumbo back in February. Sheesh. Seasonal affective disorder yielding small expectations? Oh, well.

Jam chuck to take the foot off. I've done that several times on items that don't quite fit on the cole jaws. Be sure that when you make your foot, you still have a dimple from the tailstock in your foot. Make mushroom-shaped piece that goes into your regular chuck, with the curvature more-or-less matching the inside of the bowl. Use something grippy (jar opening pads, or fine mesh sandpaper) between the mushroom and the bowl, and tailstock into the foot dimple. Adjust by hand to center the bowl as best as you can.

At relatively slow speed, nibble your foot away, using a combination of spindle gouge, bowl gouge, skew, or parting tool. Be aware that skew-as-scraper or parting tool will leave torn grain. Leave about 1/4" diameter of foot.

Use a thin kerf pull saw (or, if you have a dremel or similar, use the dremel) to cut away the remainder of the foot as close to the bottom as you can, then, either sand away the remaining nub, or use a carving tool and carve away the remaining nub. (If you use a thin kerf saw, be careful not to hit any of your nice bowl, DAMHIKT). (If you use a carving tool, be sure to know where your holding hand is at all times).

Hy

 

[John K Jordan]

Whenever I plan to do a thin wall. I true the outside of the bowl when it is in the chuck.
If I think there could be tension movement, I hollow a bit before truing the outside.

On the advice of Raffan, I do something similar when turning lidded boxes, but with an extra step. Even small diameter very dry wood sometimes moves when stress is relieved by hollowing. I mostly shape the outside, mostly hollow, then let the thing set at least overnight. Then finish turning the in and true the out.

This has helped with long-term lid fit. This has also helped to teach me patience.

JKJ

 

[Jamie Straw]

Thanks, Al!

Al, thanks so much for the detailed "how to." I have 8 or 9 green-turned bowls that will be ready for final turning about August, and I'll use the print-out for reference! A couple of questions where I wasn't quite sure what you were describing -- italics indicate where my question lies:

• I now cut the rim flat. [Talking about the upper edge of the rim, right? The top of the bowl, right?] I take a series of cuts 3/16 to a 1/4" wide until I have the rim flat. Each cut begins with the bevel edge cutting parallel to the ways the just as it meets the last cut roll into a scrap and pull the gouge across the previous cut area leveling the surface. [The beginning of this description sounds like a push cut headed toward the head stock. Not sure I follow rolling into a scrap[e] and pulling the gouge.]

The rest I understand, thanks! I think one of the things that presents a challenge to turning the outside from the chuck is the darned speed handle for the Reeves drive -- it sticks out right where I want to cozy up to get a gouge close to the lathe, so I end up trying to figure out how to turn from rim to foot going toward the headstock.

This dry Madrona bowl was just such a different experience than the maple and apple bowls I've turned (most of them green, a couple dry). Living and learning!

 

[Jamie Straw]

Jam chuck to take the foot off. I've done that several times on items that don't quite fit on the cole jaws. Be sure that when you make your foot, you still have a dimple from the tailstock in your foot. Make mushroom-shaped piece that goes into your regular chuck, with the curvature more-or-less matching the inside of the bowl. Use something grippy (jar opening pads, or fine mesh sandpaper) between the mushroom and the bowl, and tailstock into the foot dimple. Adjust by hand to center the bowl as best as you can.

At relatively slow speed, nibble your foot away, using a combination of spindle gouge, bowl gouge, skew, or parting tool. Be aware that skew-as-scraper or parting tool will leave torn grain. Leave about 1/4" diameter of foot.

Use a thin kerf pull saw (or, if you have a dremel or similar, use the dremel) to cut away the remainder of the foot as close to the bottom as you can, then, either sand away the remaining nub, or use a carving tool and carve away the remaining nub. (If you use a thin kerf saw, be careful not to hit any of your nice bowl, DAMHIKT). (If you use a carving tool, be sure to know where your holding hand is at all times).

Hy

Hy, I looked around the shop, thinking to make a jam chuck, but didn't seem to have anything that would work for a 10+" bowl with a fairly wide bottom. I hear ya on the warning about the thin-kerf saw, those things are great, but it's really easy to nick "good wood" with them (or good skin). Have you seen Doc Green's book "Fixtures and Chucks for Woodturning: Everything You Need to Know to Secure Wood on Your Lathe"?? It's a great book for this kind of stuff. A whopping $15 on Amazon. Pulls together stuff that's scattered across the universe and puts it in one well-written and well-illustrated volume.

 

[hockenbery]

Al,
I now cut the rim flat. [Talking about the upper edge of the rim, right? The top of the bowl, right?] I take a series of cuts 3/16 to a 1/4" wide until I have the rim flat. Each cut begins with the bevel edge cutting parallel to the ways the just as it meets the last cut roll into a scrap and pull the gouge across the previous cut area leveling the surface. [The beginning of this description sounds like a push cut headed toward the head stock. Not sure I follow rolling into a scrap[e] and pulling the gouge.]
. Living and learning!

Yes it is the rim at the top of the bowl. It is a series of push cuts.
Using a side ground gouge each cut ends in a little groove because of the curve of the wing.
At the end of the second cut I scrape to the edge of the rim, This flattens ridged left by the nose of the gouge.
If you don't do the scrape the wing might catc

W

 

[Hy Tran]

Hy, I looked around the shop, thinking to make a jam chuck, but didn't seem to have anything that would work for a 10+" bowl with a fairly wide bottom. I hear ya on the warning about the thin-kerf saw, those things are great, but it's really easy to nick "good wood" with them (or good skin). Have you seen Doc Green's book "Fixtures and Chucks for Woodturning: Everything You Need to Know to Secure Wood on Your Lathe"?? It's a great book for this kind of stuff. A whopping $15 on Amazon. Pulls together stuff that's scattered across the universe and puts it in one well-written and well-illustrated volume.

Jamie,

One of my mentors and I made a purpose-built jam chuck for a platter, using just a sheet of MDF. We chucked the sheet of MDF to a chuck, then, turned a groove to hold the rim of the platter. That works fine too. MDF is pretty foul stuff (boy, talk about torn grain on MDF!)

You don't need to match the entire bottom of the bowl--you just need "sufficient" width to grip the bowl and spin it, with sufficient torque to shave wood gently (don't muscle the cuts to remove the foot).

Last weekend, I was working with green silver maple (see my lack-of-technique post, but no photos yet)--about a 10" diameter bowl with a flattish bottom; I had a 3" diameter jam chuck.

No, haven't seen Doc Green's book, will go check it out.

 

[John K Jordan]

...a challenge to turning the outside from the chuck is the darned speed handle for the Reeves drive...

I don't know what this looks like but is there a good way to either make a different (bent?) handle or make a quick disconnect for the existing handle? Someone with metalworking/welding might be able to easily modify it.

JKJ

 

[hockenbery]

Hy, I looked around the shop, thinking to make a jam chuck, but didn't seem to have anything that would work for a 10+" bowl with a fairly wide bottom. I hear ya on the warning about the thin-kerf saw, those things are great, but it's really easy to nick "good wood" with them (or good skin). Have you seen Doc Green's book "Fixtures and Chucks for Woodturning: Everything You Need to Know to Secure Wood on Your Lathe"?? It's a great book for this kind of stuff. A whopping $15 on Amazon. Pulls together stuff that's scattered across the universe and puts it in one well-written and well-illustrated volume.

When I jamb Chuck bowls I use wood about 3" in diameter mounted in a Chuck.
It is hollowed a bit on the end and has rounded edges.
A firm pad is required between the bowl and the Chuck. Folded paper towel works great, piece of leather, thin fun foam.

Tailstock in the center of the tenon ( I leave the point from when the tenon was last trued). brings the bottom of the bowl against the Chuck and pad.
The curved bottom of the bowl almost self centers on the rim of the Chuck.with the pad between the bowl and the Chuck.
This makes a wood sandwich with the pad on two slices of wood. I have never broken a bowl using this approach.

Holding a bowl by the rim or jamming it on the rim only works for bowls with fairly thick walls and fairly flat rims.

The jamb Chuck below is almost universal. It will work for natural edge bowls, thin walled bowls, curve rims.
Before putting the bowl on the jamb Chuck, I measure the bottom thickness with calipers and transfer the measurement to vernier calipers.
The thin metal sticking out of the vernier calipers is the distance from the tailstock center to air inside the bowl.

Once on the Jamb chuck I can turn the tenon away, shape the foot, hollow the foot and use the vernier caliper to judge the thickness of the wood.
I use my bowl gouge, small bowl gouge and spindle gouge
With this method you cannot make a funnel unless you decide you have more wood that the vernier calipers tell you.
I end up with a small cone of wood pressing the bowl to jamb Chuck. This cone gets real weak as the point gets thin.
So no bevel pressure. Turn on the top of the tenon if you let the tool get pulled under the tenon it will break the tenon. Pushing the cut into the point of the tenon will cut it free or break it.
I usually turn the point to about an 1/8" thick turn the lathe off and use the spindle gouge to cut through the cone a 1/8 inch proud if where it joins the bowl at 3rpm.
The 3 rpm is how fast I turn the bowl by hand. This leaves a little button 1/8" tall X 1/8" wide that sands off in seconds.

You can also build a donut Chuck with something like the Jamb Chuck shown (or PVC pipe) mounted in the part of the donut that attaches to the headstock. The the clamping preasure of the donut would damage the rim or break the bowl.

 

[Douglas Ladendorf]

My last two or three bowls were jam-chucked with reject bowls. These I started to turn but found cracks or defects and decided to pass on finishing. They have tenons already and can be shaped as needed. They are still either solid or thick, not final turned. I use a pad of shelf liner, the rubbery checkered kind that dust can fall through. It seems to work fine.