Attaching sacrificial foot

[Mark J]

How do you folks attach a sacrificial foot?  

Some people glue the foot to the sacrificial foot with a piece of heavy paper in between then use a chisel to cleave the two along the paper plane.

Others glue the feet directly and separate with a parting tool.

I took a class and the instructor taught the interposed paper method.  A month later he is telling me to glue directly because he has had numerous failures at the paper plane with the interposed method.

My own experience has been 3 such failures out of the 4 blanks we have done (I was able to reattach two and complete the projects).

So I'm inclined to adopt the direct method which I used on the last bowl.  Unfortunately once parted the foot had a slightly convex surface which made sanding to flat and also parellel to the rim a challenge.  

So ideally I would like to separate the feet easily and have a foot that was flat (or even convex) and therfore easy to sand accurately.

[AndrewPritchard]

20 minutes ago, Mark J said:

How do you folks attach a sacrificial foot?  

Some people glue the foot to the sacrificial foot with a piece of heavy paper in between then use a chisel to cleave the two along the paper plane.

Others glue the feet directly and separate with a parting tool.

I took a class and the instructor taught the interposed paper method.  A month later he is telling me to glue directly because he has had numerous failures at the paper plane with the interposed method.

My own experience has been 3 such failures out of the 4 blanks we have done (I was able to reattach two and complete the projects).

So I'm inclined to adopt the direct method which I used on the last bowl.  Unfortunately once parted the foot had a slightly convex surface which made sanding to flat and also parellel to the rim a challenge.  

So ideally I would like to separate the feet easily and have a foot that was flat (or even convex) and therfore easy to sand accurately.

I've never used the paper method, only ever glued direct to the sacrificial piece. That being said, there's a reason why people buy chucks capable of holding the foot of a workpiece.

Speaking of chucks, I would investigate making a Longworth chuck:

It's a self centering chuck which you can make in your shop to true up the bottom of bowls.

[Mark J]

I'd love to have a chuck, but they are costly so that's not a right now item.

That was a great video.  I have wondered how those things worked.  If he got that built in 7 hours I'm impressed I'd budget 7 days.  But I'd like to give that a try someday.  

Still it wouldn't have solved the problem for this bowl shape.

To use a Longworth I would still need a sacrificial foot.

[Marmotjr]

No, in this case, the longworth would have held the bowl from inside the rim, pushing out, allowing you to finish the foot of the bowl.   The beauty of a LWC is that it can hold from either direction.   Another option would be a Vacuum chuck.  Stephen Oogle (Ogle?) has videos on making both of them, all from parts from a BORG. 

Yet another would be a doughnut chuck.  The problem with doughnut chucks, in my experience, is that the are very project specific.  They are built to have a specific sized opening, and bolts of a specific length placed at a specific radius.  You can easily change out the bolts for different lengths, and you can design the baseplate to have different bolt holes, but the face plate needs to match up pretty well with the bowl you are turning, so that would basically mean fabbing a new face plate each time you turn a bowl, unless you already have a faceplate that matches the bowl.  But eventually you would end up with a selection of sizes so you could easily adjust as needed. 

As for glue blocks, I prefer the paper method.  I use regular newspaper, so the glue can penetrate through and reach both pieces of wood, but still allow for a weak point to pop it off with a chisel.  Of course a paper lined glue line is a weak point that can fail, so use tail stocks, Jam chucks (Tennis balls of various sizes), and very light cuts when using a glue block.

I think another issue you can address is your planning.  Unless you have safe methods for turning the foot of a bowl after the rest has been turned (which would be a longworth, vacuum or doughnut chuck), the foot should be the first thing finished.  In the case of the bowl picture above, I would have used a worm screw to secured the base block to the lathe, true that up, then turn the general outline of the foot, and cut a mortise in the bottom for the chuck to attach to.  Flip that over, then glue on the upper piece and true that up.  This would also give me a chance to start hollowing the base piece a bit before I glued the second block on, allowing me more control over the bottom shape. 

So I have to ask, do you normally use a Tenon or a Mortise on your bowls?  Are you an innie or an outie?

 

[Mark J]

Don't have and have not yet used a chuck.  So I would have to say neither innie nor outie.  For now.

The Longworth is an interesting contraption.  I had not realized it would work in either direction.

Using a faceplate my method is to glue a sacrificial foot to the piece I am going to turn.  The sacrificial foot is then attached to the faceplate with 1 inch wood screws.  

I turn the foot of the bowl first then proceed to shape the remainder.  When I'm finished sanding the bowl the foot and sacrificial foot are separated.

The paper I have used is that heavy brown stuff you can roll out and walk on to protect your wood floors.  It's probably two or three times thicker than a grocery bag.  The glue definitely does not penetrate through the entire thickness.  So maybe it's too thick.  

I like the idea of using the tail stock, but one of the paper failures I had happened with the tail stock in place.  Still it's worth doing.

Another problem I have is that the tail stock does not have a live (rotating) center.  It is just a fixed cup so it definetly leaves a mark.  Not sure how the tennis ball idea would work, either.  I have to experiment.

[Marmotjr]

In my Segmented bowl project thread I did a couple months ago, I demonstrated using a tennis ball and live center to act as a jam chuck to stabilize a bowl while turning the outside.

Live center's are relatively cheap compared to an ER visit.  It's worth investing the $30 or so, and since MT2's are pretty much universal on the size of lathes used for home wood working, it will transfer to any other lathe you may get in the future.  I can't see working without one.  Cone Dead center's are kinda rare, they sell them, but I'd surprised if that's all that came with a lathe.  You might want to check the cone to see if it's actually supposed to be a live center and the bearings have ceased up. 

Chucks are bit costlier, but it will open your eyes to many new opportunities on how to turn things. 

Try using thinner paper, like newspaper, you might have better results.  I also use TB2 as my glue, but that's because it's what I have. 

Here's what I'd try doing until you get a chuck (a live center is a must though).  Forego the paper in your glue up.  Just make a good glue line on your block and piece and bond them together.  When you go to finish the foot after turning the bowl, turn away some of the foot on the workpiece and the block.  Then you can add the desired roundover (or hard edge if you desire).  Shape the area of the bowl that will rest on the table when finished.  You'll be basically cutting a mortise, but with the bulk of the material left inside.  A ring if you will.  Then using a parting tool, cut into the workpiece at an angle, removing from the block as you need for relief, un til the piece comes free.  Then you can use a chisel and sand paper to finish off the bottom. 

Please excuse the very crude drawings:

1) Cut the bottom edge of the bowl, clear out glue block as you need, so the bottom edge of the bottom is as you want.  Sand and apply finish to match the rest of the bowl.

2) Part the bowl from the glue block by cutting into the bowl piece itself, cut relief cuts as needed into the glue block. 

 

[Mark J]

I get your suggestion and the drawing helps.  I was thinking along the same lines.  Use the parting tool to make a flat outer perimeter for the bowl foot.  Then use the parting tool to cut the remainder of the bowl foot a bit concave.  Lastly sand the whole foot flat using the perimeter as the reference surface.

As to the universality of parts for my lathe I have to chuckle a bit.  This is a 1974 Craftsman.  I doubt there are parts for it universal or otherwise.  The "dead" center is indeed fixed and the shape is a sharp edged cup with a center spike.  In fact if you're doing spindle work the tail stock needs periodic snugging up as the wood fibers conpress/wear.

There's a reason nobody makes anything like this lathe design any more.  Someday I will replace it with a real lathe, but I'll work with this for now.

I will look for your project thread.  I'm interested in the tennis ball and segmented bowls.

[thatCharlieDude]

While making my beer tankards I glued a piece of scrap wood to the bottom of my piece with medium CA glue. When I was ready to remove it I chiseled it off with a putty knife. The 6 times I did it the scrap came right off with a little scrap still attached to the bottom of the piece. I put the mug in a jacob's chuck and sanded the bottom clean. The CA is brittle enough that it breaks off very cleanly.